PROCESS AND SYSTEM FOR REMOVING IMPURITIES FROM A GAS
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[01] This invention was made with government support under United States
Department of Energy - National Energy Technology Laboratory (NETL) Contract
DE-AC26-99FT40675 awarded by the Department of Energy. The United States
Government has certain rights in the invention.
BACKGROUND OF THE INVENTION
Field of the Invention
[02] The present invention relates to novel processes and systems for the
removal of impurities, such as sulfur compounds, hydrogen chloride, arsenic,
selenium, hydrogen cyanide, ammonia, and combinations thereof, from a gas stream
by a solid sorbent stream which is simultaneously regenerated to remove the
impurities.
Description of Related Art
[03] Removal of impurities from gas streams is desirable in numerous
instances to address various process, environmental, chemical, and/or other
industrial considerations as will be apparent to the skilled artisan. For example,
"synthesis gas" or "syngas" produced by the gasification of fossil fuels such as coal,
or other carbonaceous materials is becoming increasingly important as a viable
alternative energy source and as an important raw material source for the industrial
synthesis of various organic chemicals. However, syngas often contains various
impurities, such as sulfur, arsenic, and selenium compounds, which are desirably
removed in whole or part to facilitate subsequent processing and/or use of the gas.
In particular, the gasification of coal, heavy oil fractions, and some types of
carbonaceous waste, typically produces a syngas containing gaseous impurities
such as hydrogen sulfide, carbonyl sulfide, hydrogen selenide, arsine, and the like.
These impurities can be corrosive or toxic in some cases, and/or can act as catalyst
poisons and/or environmental pollutants. There is a need, therefore, for methods to

remove these compounds from synthesis gas streams in chemical processes to
prevent damage to catalyst systems and to meet environmental standards.
[04] Current commercially available processes for removing sulfur species
from reducing gas streams, such as syngas, typically employ one of two methods: A)
liquid phase absorption, either physical or chemical; or B) adsorption onto solid
sorbents in fixed beds.
[05] Syngas, such as that from the gasification of coal or other carbonaceous
materials, generally exits a gasifier as a high temperature gas stream, typically at a
temperature higher than about 900 °F (482 °C). Current liquid phase absorption
methods for impurity removal are generally inefficient in the case of such high
temperature gas streams because they typically operate at temperatures of about
100°F (38 °C) or less. Therefore, large scale cooling and related heat recovery
processing are necessary in the case of gasification syngas streams to allow
removal of impurities at the lower temperatures required by liquid phase absorption
processes. Such cooling, heat recovery and related processing steps result in
thermal inefficiencies and substantial equipment cost as will be apparent.
[06] Typically, solid sorbent, hot gas adsorption processes involve contacting
a solid sorbent comprising an active metal oxide with hot gas to convert the active
metal oxide into a metal compound comprising the impurity or a derivative thereof.
The impurities may include, but are not limited to, sulfur, hydrogen chloride, arsenic,
selenium, hydrogen cyanide, and/or ammonia. Desirable active metal oxide
containing sorbent compositions and processes for sulfur removal are disclosed in
US Patent No. 6,951,635 B2 issued October 4, 2005 to Gangwal et al; US Patent
No. 6,306,793 B1 issued October 23, 2001 to Turk et al; US Patent No. 5,972,835
issued October 26, 1999 to Gupta; US Patent No. 5,914,288 issued June 22, 1999 to
Turk et al; and US Patent No. 5,714,431 issued Feb. 3, 1988 to Gupta et al; which
are each hereby incorporated herein by reference in their entireties.
[07] Following the adsorption reaction and depending on the impurity, the
impurity loaded sorbent is regenerated at high temperature. In other cases, the
impurity loaded sorbent is discarded. If the sorbent is regenerated, hot gases
containing impurities are typically produced during the regeneration step. In these
cases the impurities can be typically separated from the regenerator off-gas for

disposal or downstream processing. For example, in the case where syngas
contains a sulfur impurity, regeneration of the sulfur loaded sorbent with an oxidizing
gas stream, typically oxygen or an oxygen containing gas, produces sulfur dioxide
which can be absorbed and/or converted to sulfuric acid, elemental sulfur or the like.
In particular, the regeneration reaction converts the metallic sulfide back to metallic
oxide via the following reaction:
MS + 3/2 02 -> MO + S02 (I)
wherein M is the active metal present in the sorbent, for instance Zn; MO represents
a metal oxide; and MS represents a metal sulfide. The skilled artisan will understand
that although oxidation is a preferred means of regenerating active metal oxide
sorbents, other methods, such as thermal regeneration, also may be possible,
particularly in the case of different solid sorbent compositions.
[08] Fluidized bed adsorption and absorption/regeneration processes are
known in the art and are disclosed for example in the previously identified US Patent
publications of Gangwal et al, Gupta et al, and Turk et al. Coupled fluidized bed
reactor/regeneration systems are also known and used in the processing of
hydrocarbons, for example in Fluid Catalytic Cracking (FCC) processes.
[09] Dual loop fluidized bed absorption/regeneration processes for removing
sulfur contaminants from hydrocarbon gases such as syngas, are disclosed in US
Patent Nos. 5,447,702 and 5,578,093, issued Sept. 5, 1995 and Nov. 26, 1996,
respectively, to Campbell et al, which are hereby incorporated herein by reference.
In such dual loop processes, absorption and sorbent regeneration are
simultaneously conducted in coupled fluidized beds. In these dual loop processes,
the solids flow rate of the sorbent through the absorber can be different than the
solids flow rate of the sorbent through the regenerator. In particular, the sorbent
stream exiting the absorber can be separated into two streams, a recycle stream
which is recycled to the absorber, and a regeneration stream which is passed to the
regeneration zone for removal of absorbed sulfur. The regenerated sorbent stream
exiting the regenerator is returned to the absorber where it is mixed with the recycled
sorbent. However, in order to achieve steady state operation and establish

equilibrium between absorption and regeneration in such dual loop processes, the
quantity of sulfur removed from the sorbent in the regenerator must match the
quantity of sulfur removed from the feed gas in the absorber. In turn, since the
quantity, i.e., flow rate, of sorbent solids passing through the absorber exceeds the
quantity of sorbent solids passing through the regenerator, the sulfur pick-up in the
absorber, as a percentage of sorbent weight, must be lower than the sulfur removal
rate in the regenerator, based on sorbent weight.
[010] In practice, long term, steady state operation of the dual loop
absorber/regenerator fluidized bed reactor systems disclosed in Campbell et al. can
present problems since process changes in either loop must be accompanied by
corresponding changes in the other loop in order to maintain stable continuous
operation. For example, variations in the composition, feed rate, temperature,
pressure, etc., of the feed gas fed to the absorber can cause long term and short
term variations in the rate of sulfur removal from the feed gas in the absorber (with a
corresponding change in weight percent sulfur pick-up by the sorbent, based on
sorbent weight), requiring corresponding process and/or sorbent flow rate variations
in the regenerator for the maintenance of stable continuous operation. Moreover,
conventional mechanical valves such as the solids plug valves disclosed by
Campbell et al. as a means for varying the flow rates of sorbent solids to the
absorber and/or regenerator, are subject to erosion, plugging and other problems
due to the high temperature, high pressure, and corrosive and abrasive conditions
inherent in the desulfurization processes disclosed by Campbell et al.
SUMMARY OF THE INVENTION
[011] The present invention comprises, in one embodiment, a process and
apparatus for removing impurities from a gas by treating the gas with a solid sorbent
while simultaneously achieving continuous sorbent regeneration under controlled
conditions and controlled solid flow rates. In advantageous embodiments of the
invention, dual-loop and multi-loop, fluidized bed, absorber/regenerator processes
are provided having enhanced long term stability. In particular, advantageous
embodiments of the invention can provide enhanced control of solids flow rates
between loops of multi-loop fluidized absorber/regenerator processes to

accommodate a variety of process designs and operational process variations,
and/or can provide self correcting action in response to changing process conditions,
flow rate variations and the like, between the loops; without reliance on mechanical
valves which are subject to problems and potential failure at high temperature, high
pressure, corrosive and/or abrasive conditions. Additional advantageous
embodiments of the invention provide enhanced process control for balancing
impurity removal in the regenerator with impurity removal in the absorber despite
process variations in the absorber and regenerator loops. In other aspects, the
present invention can provide control of the solids flow in a multi-loop fluidized
reactor system between a holding vessel and a fluidized zone of a fluidized reactor
system without the use of mechanical valves.
[012] In one embodiment of the invention, separate loops of multi-loop
fluidized absorber and regenerator processes are fluidly connected to allow
continuous solids flow between the loops while providing a gas seal between the two
loops to prevent mixing of the feed and regeneration gases. An impurity containing
feed gas stream is contacted with a solid sorbent stream in a fluidized absorber zone
under conditions sufficient to reduce the impurity content of the gas stream and
increase the impurity loading of the solid sorbent stream. An impurity loaded solid
sorbent stream is removed from the absorber zone and at least a portion of the
impurity loaded solid sorbent stream is passed to a first non-mechanical gas seal
forming solids transfer zone which is fluidly connected to a fluidized solids
regenerator zone and adapted to transfer solids into the regenerator zone. The first
non-mechanical gas seal forming solids transfer zone is constructed for operation in
the "valve mode" wherein solids are passed through the transfer zone at a
controllable flow rate. In particular, non-mechanical gas seal forming solids transfer
zones operating in the valve mode are capable of varying the flow rate of solid
streams through the zone in response to variations in the feed rate of an "aeration
gas" fed to the solids transfer zone as discussed in greater detail subsequently. The
impurity loaded solid sorbent stream exiting the solids transfer zone is admitted into
the regenerator zone and contacted with a regeneration feed gas to provide a
regenerated sorbent stream having a reduced impurity content. The regenerated
sorbent stream exiting the regenerator zone is passed to a second non-mechanical

gas seal forming solids transfer zone which is fluidly connected to the absorber zone
and adapted to transfer the regenerated sorbent stream to the absorber zone. The
second non-mechanical gas seal forming solids transfer zone is constructed for
operation in the "automatic mode" wherein solids are passed through the transfer
zone at the same flow rate as the feed rate of solids into the zone. Thus the second
non-mechanical transfer zone transfers the regenerated sorbent stream to the
absorber at the flow rate of the regenerated sorbent stream exiting the regenerator
and also maintains a pressure seal between the regenerator and absorber zones.
[013] The use of non-mechanical solids transfer devices, or zones, to control
and accomplish the solids transfer in the multi-loop absorber-regenerator system
minimizes or avoids the capital cost and potential system upsets associated with
maintenance and mechanical failures of mechanical valves. The combination and
arrangement of valve mode and automatic mode non-mechanical solids transfer
devices in accordance with this aspect of the invention can allow relatively consistent
solids flow rates between and through the absorber and regenerator while
maintaining stable pressure seals to prevent mixing of absorber and regenerator
feed and/or effluent gases. Nevertheless, the arrangement of valve mode and
automatic mode non-mechanical solids transfer devices in accordance with this
aspect of the invention can also accommodate variations in gas feed rates and
reaction conditions in the regenerator and/or the absorber as may be desirable for
various purposes, for example, to maintain balance between impurity removal in the
absorber and sorbent regeneration, and/or to accommodate variations in feed rate
and/or impurity content of the feed gas treated in the absorber.
[014] Numerous gas seal forming, non-mechanical, solids transfer devices of
various constructions and arrangements are known to the skilled artisan, and are
described, for example, in Wen-Chen Yang, "HANDBOOK of FLUIDIZATION and
FLUID-PARTICLE SYSTEMS", Marcel Dekker, Inc, 2003, Chapter 21, pages 521-
597, which is hereby incorporated herein by reference. In general, such solid flow
devices use an aeration gas in conjunction with a predetermined geometrical shape
to cause particulate solids to flow through the device. The solid flow devices can be
constructed for operation in a "valve mode", in which the flow rate of solids through
the device is controlled by aeration gas flow rate, or in an "automatic mode" in which

the flow rate of solids through the device is controlled by the flow rate of solids into
the device. Such solids transfer devices also provide a gas seal of a predetermined
pressure value to prevent the flow of process gases, i.e., absorber or regenerator
process gases, through the device. The capability of the gas seal to withstand
predetermined pressures can be adjusted by variations in the geometrical shapes
and sizes of the devices as will be apparent to the skilled artisan. Advantageously, a
"J-Leg" solid flow device adapted for operation in the valve mode, (also called a "J-
Valve"), is used to transfer the impurity loaded solid sorbent stream removed from
the absorber zone to the regeneration zone. A "Loop Seal" solid flow device,
operating in the automatic mode, is advantageously used to transfer the regenerated
solid sorbent stream recovered from the regenerator zone, to the absorber zone at
the same flow rate as the regenerated sorbent stream is fed out of the regenerator
zone.
[015] Thus the absorber loop and the regenerator loop are fluidly connected
allowing sorbent streams to be continuously passed between the two loops even
though the absorber and regenerator process gas streams in the two loops are
maintained separate from each other. Because of the non-mechanical construction
of the solids transfer devices, various problems associated with mechanical valves,
such as wear, corrosion, and seizure of the moving parts, plugging of valve orifices,
etc., can be avoided. Nevertheless, significant gas pressure upsets that could result
in failure of the gas seal capabilities of the solids transfer zones are eliminated or
minimized by the combination and arrangement of valve mode and automatic mode
solids transfer devices, thus allowing self-regulating flow of a solid material between
the two fluidized reactor loops. Moreover the invention can also alleviate or minimize
the difficulties associated with dual loop absorber and regenerator processes
wherein the sorbent solids flow rates can vary between the loops.
[016] In advantageous embodiments, the invention provides for removal of at
least one sulfur impurity from a hot hydrocarbon or hydrocarbon-derived feed gas
such as syngas. The sorbent advantageously comprises an active metal oxide, such
as iron oxide, zinc oxide, zinc ferrite, copper ferrite, copper oxide, vanadium oxide, or
mixtures thereof. In one embodiment, the sorbent has an average particle diameter
from 50 to 140 microns.

[017] The active metal oxide in the sorbent reacts with sulfur impurities in the
feed gas resulting in a sulfur loaded sorbent, as represented by the following
reactions:
H2S + MO -> H20 + MS (II)
COS + MO -> C02 + MS (III)
wherein M is the metal present in the sorbent, for instance Zn; MO represents a
metal oxide; and MS represents a metal sulfide.
[018] In advantageous embodiments of the invention, the fluidized absorber
zone is maintained at a temperature in the range of between about 600°F and about
1200°F (about 316 °C and about 649 °C) and a pressure of between about
atmospheric pressure and about 1200 psig (8274 kPa), and the regenerating zone is
maintained at a temperature in the range of between about 900F to about 1450°F
(about 482 °C to about 788 °C) and about the same pressure as the absorber. In yet
further advantageous embodiments of the invention, the fluidized absorber zone is
maintained at a temperature in the range of between about 700°F and about 1000°F
(about 371 °C and about 538 °C) and a pressure of between about 200 psig and
about 1000 psig (about 1379 kPa and about 6895 kPa), and the regenerating zone is
maintained at a temperature in the range of between about 1200°F and about
1450°F (about 649 °C and about 788 °C) and about the same pressure as the
absorber. The pressure of the impurity-containing feed gas typically ranges from
100 to 1200 psig.
[019] In yet another aspect, the present invention provides a process control
for controlling the flow of solid sorbent streams between separate loops of a multi-
loop fluidized absorber and regenerator process. According to this aspect of the
invention, the pressures of the absorber and regenerator zones are measured
periodically or continuously and the pressure in at least one of the zones is adjusted
as necessary to maintain a predetermined pressure difference between the
pressures of the two zones. In one advantageous embodiment, the predetermined
pressure difference is a pressure difference in the range of between about 1 psi and

about 20 psi (about 7 kPa and about 138 kPa). In another advantageous
embodiment, the predetermined pressure difference is a pressure difference in the
range of between about 2 psi and about 10 psi (about 14 kPa and about 69 kPa).
Advantageously, the pressure difference between the zones is maintained by
adjusting the pressure of the regenerator zone. This allows the pressure in the
absorber zone to change in response to changes in the pressure of an incoming
impurity-containing feed gas. Advantageously, the pressure difference between the
zones is maintained by adjusting the pressure of impurity laden gases exiting the
regenerator zone.
[020] In yet another aspect, the present invention provides a process control
for enhancing stability of a multi-loop fluidized absorber and regenerator process
wherein impurities are removed from a gaseous feed stream by contact with a solid
sorbent stream in the absorber zone and at least a portion of the sorbent stream is
continuously regenerated by contact with a regeneration gas in the regenerator
zone. In particular, enhanced process control according to this aspect of the
invention comprises a feed forward process control wherein the quantitative impurity
removal rate in the absorber is monitored and if the impurity removal rate changes
beyond a predetermined control value, the rate of the regenerator feed gas is
adjusted as necessary to provide a stoichiometrically calculated change in the
quantitative impurity removal rate in the regenerator zone. In one advantageous
embodiment, the quantitative impurity removal rate in the regenerator is also
monitored and compared to the quantitative impurity removal rate in the absorber. In
the event that the difference between the removal rates exceeds a predetermined
value, the feed rate of the regenerator feed gas is adjusted as necessary to provide
a stoichiometrically calculated change in the quantitative impurity removal rate in the
regenerator. In another embodiment, the impurity loading of the impurity loaded
sorbent removed from the absorber is monitored and if the impurity loading differs
from a predetermined loading range, the feed rate of the regenerator feed gas is
adjusted to bring the impurity loading of the sorbent to a value within the
predetermined loading range. In yet another embodiment, changes to the feed rate
of the regenerator feed gas are determined in response to both the value of the

impurity loading of the impurity loaded sorbent, and the value of the quantitative
impurity removal rate in the absorber.
[021] In one embodiment, the invention provides a process for removing
impurities (e.g., sulfur compounds, arsenic and compounds thereof, and selenium
and compounds thereof) from a gas, comprising:
[022] (a) contacting an impurity containing feed gas stream with a solid
sorbent stream in a fluidized absorber zone under conditions sufficient to reduce an
impurity content of the feed gas stream and increase impurity loading of the solid
sorbent stream (e.g., with a residence time in the absorber zone of about 3 to about
25 seconds or about 3 to about 10 seconds);
[023] (b) removing an impurity loaded solid sorbent stream from the absorber
zone and transporting at least a portion of the impurity loaded solid sorbent stream to
a first non-mechanical gas seal forming solids transfer zone (e.g., a J-Leg), the first
solids transfer zone being fluidly connected to a fluidized solids regenerator zone
and adapted to transfer solids to the fluidized regenerator zone at a controllable flow
rate in response to the flow of an aeration gas through the transfer zone;
[024] (c) transferring the impurity loaded solid sorbent stream from the first
solids transfer zone to the fluidized solids regenerator zone and contacting the
impurity loaded solid sorbent stream with a regenerator feed gas (e.g., oxygen or a
mixture of oxygen and at least one inert gas) in the fluidized solids regenerator zone
to thereby reduce the impurity content of the impurity loaded solid sorbent stream
(e.g., with a residence time in the regenerator zone of about 3 to about 25 seconds);
[025] (d) transferring the solid sorbent stream of reduced impurity content
from the fluidized regenerator zone to a second non-mechanical gas seal forming
solids transfer zone (e.g., a loop seal), the second solids transfer zone being fluidly
connected to the regenerator and absorber zones and adapted to transfer the solid
sorbent stream of reduced impurity content to the absorber zone at the same flow
rate as the flow rate of the solid sorbent stream of reduced impurity into the second
solids transfer zone; and
[026] (e) recovering a purified gas stream from the absorber zone using, for
example, a cyclone separator to separate the impurity loaded sorbent stream from

the purified gas. Optionally, the impurity loaded sorbent stream leaving the cyclone
separator can pass through a gas stripper.
[027] The impurity loaded sorbent exiting the absorber zone can be
characterized by impurity content. In one embodiment, the impurity content of the
impurity loaded sorbent exiting the absorber zone ranges from 10% to 90% of the
impurity adsorption capacity of the sorbent (e.g., from 30% to 75% of the impurity
adsorption capacity of the sorbent). In certain embodiments, the arsenic content of
the impurity loaded sorbent exiting the absorber zone ranges from 0 to 3000 ppm.
[028] The purified gas stream recovered from the absorber zone can also be
characterized by impurity content. For example, the purified gas stream recovered
from the fluidized absorber zone in certain embodiments has a sulfur level of less
than or equal to 50 ppm, or less than or equal to 20 ppm, or less than or equal to 10
ppm.
[029] The process may further include transporting at least a portion of the
impurity loaded solid sorbent stream removed from the fluidized absorber zone to a
third non-mechanical gas seal forming solids transfer zone (e.g., a J-Leg), the third
solids transfer zone being fluidly connected for receiving a solids stream from a
downstream portion of the fluidized absorber zone and for delivering a solids stream
to an upstream portion of the fluidized absorber zone, the third solids transfer zone
being adapted to transfer solids to the fluidized absorber zone at a controllable flow
rate in response to the flow of an aeration gas through the transfer zone; and
transferring the impurity loaded solid sorbent stream from the third solids transfer
zone to the upstream portion of the fluidized absorber zone for contact with the
impurity containing feed gas stream.
[030] The process of the invention can also include measuring the pressures
of the absorber and regenerator zones; determining the pressure difference between
the zones; comparing the pressure difference to at least one predetermined pressure
difference value; and adjusting the pressure in at least one of the absorber and
regeneration zones in response to the measuring step, such as by adjusting the
pressure of impurity laden gases exiting the regenerator zone. The predetermined
pressure difference value can be, for example, a pressure difference in the range of
between about 1 psig and about 20 psig or between about 2 psig and about 10 psig.

[031] In one embodiment, the process includes the steps of determining a
quantitative impurity removal rate in the absorber zone; comparing the impurity
removal rate to a predetermined control value; and adjusting the flow rate of the
regenerator feed gas fed to the regenerator zone in response to the comparing step.
[032] In yet another embodiment, the process includes determining a
quantitative impurity removal rate in the absorber zone; determining a quantitative
impurity removal rate in the regenerator zone; comparing the impurity removal rates
to a predetermined control value; and adjusting the flow rate of the regenerator feed
gas fed to the regenerator zone in response to the comparing step.
[033] In still another embodiment, the process includes determining impurity
loading of a sample of the impurity loaded sorbent stream removed from the
absorber zone; comparing the impurity loading to a predetermined control value; and
adjusting the flow rate of a regenerator feed gas fed to the regenerator zone in
response to the comparing step.
[034] When needed, heat can be provided to the fluidized regenerator zone
(and the material therein) by any of a variety of methods including: 1) adding a
pyrophoric additive; 2) adding a supplementary fuel; and 3) using a dry gas
preheating system.
[035] An exemplary J-Leg structure for use in the first solids transfer zone
can include:
[036] (a) a descending pipe in fluid communication with a holding vessel; and
[037] (b) a transfer pipe in fluid communication with the descending pipe to
transfer the impurity loaded sorbent from the descending pipe to the fluidized
regenerator zone;
[038] and wherein the angle between the descending pipe and the transfer
pipe is less than or equal to 90°. The diameter of the transfer pipe is typically less
than the diameter of the holding vessel and the descending pipe optionally includes
a flow restrictor. The aeration gas can be introduced into one or more of the holding
vessel, the descending pipe, and the transfer pipe.
[039] An exemplary J-Leg structure for the third solids transfer zone can
include:
[040] (a) a descending pipe in fluid communication with a holding vessel; and

[041] (b) a transfer pipe in fluid communication with the descending pipe to
transfer the separated impurity loaded sorbent from the descending pipe to the
fluidized absorber zone;
[042] and wherein the angle between the descending pipe and the transfer
pipe is less than or equal to 90°. As noted above, the diameter of the transfer pipe is
typically less than the diameter of the holding vessel and the descending pipe
optionally includes a flow restrictor. The aeration gas is typically introduced into one
or more of the holding vessel, the descending pipe, and the transfer pipe.
[043] In yet another aspect of the invention, a fluidized reactor system for
removing impurities from a gas, the system including:
[044| (a) a fluidized absorber adapted for contacting an impurity containing
feed gas stream with a solid sorbent stream zone under conditions sufficient to
reduce the impurity content of the feed gas stream and increase the impurity loading
of the solid sorbent stream;
[045] (b) a fluidized solids regenerator adapted for contacting an impurity
loaded solid sorbent stream with a regeneration gas under conditions sufficient to
reduce the impurity content of the impurity loaded solid sorbent stream;
[046] (c) a first non-mechanical gas seal forming solids transfer device in
fluid communication with the fluidized absorber, the fluidized solids regenerator, and
a supply of aeration gas, the first non-mechanical gas seal forming solids transfer
device being adapted and arranged to receive an impurity loaded solid sorbent
stream from the absorber and to transport the impurity loaded solid sorbent stream
to the fluidized regenerator at a controllable flow rate in response to the aeration gas;
and
[047] (d) a second non-mechanical gas seal forming solids transfer device
fluidly connected to the fluidized regenerator and the fluidized absorber, and being
adapted to receive a solid sorbent stream of reduced impurity content from the
fluidized regenerator and to transfer the solid sorbent stream of reduced impurity
content to the fluidized absorber without changing the flow rate of the solid sorbent
stream of reduced impurity content.
[048] The system can also include a third non-mechanical gas seal forming
solids transfer device fluidly connected to a downstream portion of the fluidized

absorber, an upstream portion of the fluidized absorber, and a supply of aeration
gas, and being adapted and arranged to receive a solids stream from the
downstream portion of the fluidized absorber and transfer solids to the upstream
portion of the fluidized absorber at a controllable flow rate in response to the aeration
gas. Both the first and third non-mechanical gas seal forming solids transfer devices
can include a J-Leg as disclosed herein.
[049] The system may optionally further include one or more sensors
adapted and arranged to measure the pressure of an effluent gas of the absorber
and an effluent gas of the regenerator or to measure the pressure differential
between the two effluent gases; and a controller connected to the one or more
sensors, the controller configured to receive pressure or pressure differential input
measurements from the one or more sensors and to compare the pressure
difference between the two effluent gases to a predetermined pressure difference
value, the controller also being connected to a controllable valve adapted and
arranged to adjust pressure of the effluent gas of the regenerator based on
instructions received from the controller.
[050] Still further, the system can optionally include a controller configured to
receive inputs enabling determination of a quantitative impurity removal rate in the
absorber and configured to compare the impurity removal rate to a predetermined
control value, the controller being connected to a controllable valve adapted and
arranged to adjust the flow rate of the regeneration gas fed to the regenerator based
on instructions received from the controller.
BRIEF DESCRIPTION OF THE DRAWINGS
[051] In the drawings which form a portion of the original disclosure of the
invention;
[052] Figure 1 is a schematic diagram of a representative J-Leg solids flow
device positioned before the fluidized absorber and/or the fluidized regenerator zone
and which is capable of providing a controllable solids flow rate to the connected
fluidized zone;
[053] Figure 2 is a schematic diagram of a representative loop seal solid flow
device for forming a gas pressure seal between the regenerator zone and the

absorber zone and for transferring the sorbent stream from the regenerator zone to
the absorber zone at a solids flow rate determined by the solids flow rate of the
regenerated sorbent stream;
[054] Figure 3 is a schematic diagram of one embodiment of a dual loop
process and apparatus for removing impurities from a gas according to the invention
wherein a portion of the impurity laden solid sorbent stream recovered from the
absorber is recycled to the absorber, and another portion of the impurity laden solid
sorbent stream is passed to a regenerator zone, and illustrates the use of holding
zones, in the form of standpipes, in each of the absorber and regenerator loops or
zones, to assist distribution and flow of particulate solid sorbent through and
between the loops;
[055] Figure 4 is a schematic diagram of another embodiment of a dual loop
process and apparatus for removing impurities from a gas according to the invention
wherein a single, shared standpipe is used to feed impurity loaded sorbent to both
the fluidized absorber zone and the fluidized regenerator zone;
[056] Figure 5 is a schematic diagram of another embodiment of a system
and process for removing impurities from a gas where impurity loaded sorbent is not
recycled to the fluidized absorber zone;
[057] Figure 6 is a schematic diagram of the dual loop process and
apparatus used in Example 1; and
[058] Figure 7 graphically illustrates the ability of the feed forward control
scheme described in Example 2 to maintain relatively constant sorbent sulfur loading
even during significant changes in the sulfur absorption rate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[059] In the following detailed description, preferred embodiments of the
invention are described to enable practice of the invention. Although specific terms
are used to describe and illustrate the preferred embodiments, such terms are not
intended as limitations on practice of the invention. Moreover although the invention
is described with reference to preferred embodiments, numerous variations and
modifications of the invention will be apparent to those of skill in the art upon
consideration of the foregoing together with the following detailed description.

[060] The following definitions of some terms used herein are set forth for
clarity; it being understood that such definitions are included solely for purposes of
the present application and are to be applied solely to the present application.
[061] As used herein, the term "impurity containing feed gas" is understood
to mean a gas comprising one or more impurities including for example, sulfur
compounds, hydrogen chloride, arsenic, selenium, hydrogen cyanide, mercury,
and/or ammonia. In advantageous embodiments, the feed gas is a reducing gas
such as syngas and the impurity comprises at least one sulfur compound. In one
advantageous aspect, the feed gas is a reducing gas such as syngas and includes
H2S and/or COS, typically both sulfur impurities in the reduced form.
[062] As used herein, the term "sorbent" is understood to mean solid
particulate materials of a fluidizable size which are capable of removing impurities
from a feed gas through the mechanism of absorption, adsorption, and/or chemical
reaction. It will be apparent that "sorbents" can include mixtures of particulate solids
including different sorbents, other additives and the like.
[063] As used herein, the term "fluidized absorber zone" is understood to
mean a region of the process stream in which an active sorbent is fluidized or
suspended in a feed gas stream containing impurities under conditions sufficient that
the sorbent absorbs, adsorbs, or reacts with at least one impurity from the feed gas
stream so that the sorbent exits the absorber zone with an increased impurity
content and treated feed gas exits the absorber zone with a decreased impurity
content.
[064] As used herein, the term "fluidized" or "fluidization" is understood to
mean an operating condition in which particulate solids are suspended in a moving
gas.
[065] As used herein, the term "fluidized regenerator zone" is understood to
mean a region of the process stream in which an impurity-laden sorbent is partially
or fully regenerated by contact with a regenerating gas under fluidization conditions
sufficient to achieve partial or substantially complete removal of at least one impurity
from the sorbent so that a sorbent exiting the fluidized regenerator zone has a
reduced impurity content compared to the fluidized absorber zone. The term
"regenerated sorbent" is used herein to mean sorbent, e.g., a sorbent stream,

treated in the fluidized regenerator and having a reduced impurity content. The
regenerating gas can comprise, for example, an oxidizing gas such as oxygen.
Examples of oxidizing regenerating gases include substantially pure oxygen, and
gases such as air, containing oxygen mixed with other gaseous components.
[066] As used herein, the terms "impurity loaded sorbent" and "impurity laden
sorbent" are understood to mean sorbent having an increased impurity content as a
result of contact of the sorbent with a gas stream including at least one impurity
selected from sulfur compounds, hydrogen chloride, arsenic and compounds thereof,
selenium and compounds thereof, hydrogen cyanide and organic cyanides, and/or
ammonia or derivatives thereof.
[067] As used herein, the term "impurity content" as applied to sorbents is
understood to mean the content of the sorbent derived from contact with the
impurity, as it is retained by the sorbent. Typically "impurity content" as applied to
sorbents refers to a chemical moiety or component derived from the impurity.
Quantitative expressions of "impurity content" of sorbents and sorbent streams,
unless indicated otherwise, are set forth in weight percent based on the weight of the
fresh sorbent, wherein the weight of the fresh sorbent can be a calculated weight as
will be apparent to the skilled artisan. For example in the case of active metal oxide
sorbents used to remove H2S and COS according to the reactions:
H2S + MO → H20 + MS (II)
COS + MO → C02 + MS (III)
wherein M is the metal present in the sorbent, for instance Zn; MO represents a
metal oxide; and MS represents a metal sulfide and sorbent weight can be
calculated based on the weight of MO and the MO content of the sorbent, and
impurity content can be calculated based on the weight of S (not H2S and/or COS).
[068] As used herein, the term "solids separator" is understood to mean a
device for removing solids from a fluid. An example of a solids separator may be a
cyclone separator, which uses centrifugal force to remove solids from a fluid stream.

Other examples include electrostatic precipitators, filters, and gravity settling
chambers.
[069] As used herein, the term "gas stripper" is understood to mean a device
for displacing a gas or gas mixture from solid particles using a different gas or gas
mixture. For example, a gas stripper can be used for displacing syngas from the
sorbent particles using dry nitrogen, carbon dioxide or any other suitable inert gas.
[070] As used herein, the term "bulk density" as applied to the particulate
sorbent is understood to mean the mass of unfluidized sorbent divided by its volume.
The volume, as will be apparent to those skilled in the art, includes the space
between particulate solids as well as the space inside the pores of individual
particles.
[071] As used herein, the term "fluidized density" is understood to mean the
instantaneous combined density of a mixture of fluidized solid particles and the gas
used to fluidize the particles.
[072] As used herein, the term "fluid" is understood to mean a fluid stream
such as a liquid stream, a gas stream, or a gas stream comprising particulate solids
such as a sorbent, wherein the particulate solids are mixed with the gas stream to
enhance the flow properties of the solids particulate stream.
[073] As used herein, the terms "impurity capacity" as applied to sorbents,
and "sorbent impurity capacity" are understood to mean the maximum amount of
"impurity content" that can be retained by the sorbent, expressed as a weight percent
based on fresh sorbent weight (or the calculated weight of the fresh sorbent).
[074] As used herein, the term "average particle diameter" means the volume
weighted, mean particle size of a liquid dispersion of sorbent particles. The average
particle diameter of the sorbent particles may be measured by laser diffraction
techniques using instrumentation such as, for example, a Malvern Mastersizer
2000™, and procedures well known in the art.
[075] As used herein, the term "holding vessel" can be, for example, a
standpipe or any other vessel that is positioned and adapted to accumulate or store
a portion of a particulate solids stream, and to transfer same to a zone of higher
pressure as compared to the holding zone pressure.

[076] As used herein the term "aeration gas" refers to a gas added to a
particulate solids stream to modify the flow properties thereof.
[077] The terms "packed bed flow", "packed bed region", "packed bed flow
region" and "moving packed bed flow" are used interchangeably herein in
accordance with the definition set forth in Wen-Chen Yang, "HANDBOOK of
FLUIDIZATION and FLUID-PARTICLE SYSTEMS", Marcel Dekker, Inc, 2003,
Chapter 21, pages 571-573. In particular, in the packed bed flow region, the relative
gas-solids velocity (vr) is less than the interstitial fluidization velocity (vmf) of the
particulate stream. More particularly, relative gas-solids velocity (vr) is calculated
based on the solids velocity (vs) and the interstitial gas velocity (vg) of the solids/gas
stream according to the equation:
vr = | vs - vg |
and Vmf is defined as the vr at which the pressure drop, ∆P, of the gas moving
through the solids stream equals the pressure drop per unit length (∆P/Lg) of the
particulate solids stream. Reference can be made to the aforementioned
"HANDBOOK of FLUIDIZATION and FLUID-PARTICLE SYSTEMS" for a more
detailed explanation.
[078] Other than in the operating examples, or where otherwise indicated, all
numbers expressing quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being modified in all
instances by the term "about." Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and attached claims are
approximations that may vary depending upon the desired properties sought to be
obtained by the present invention. At the very least, and not as an attempt to limit the
application of the doctrine of equivalents to the scope of the claims, each numerical
parameter should be construed in light of the number of significant digits and
ordinary rounding approaches.
[079] Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the numerical values set
forth in the specific examples are reported as precisely as possible. Any numerical
value, however, inherently contains certain errors necessarily resulting from the
standard deviation found in their respective testing measurements.

[080] Turning now to the drawings, Figure 1 is a schematic diagram
illustrating a non-mechanical gas seal forming solids transfer device, or zone,
adapted for operation in the valve mode to transfer solids at a controllable flow rate.
In particular, Figure 1 illustrates a J-Leg solids transfer device, 10, adapted for
operation in a valve mode, fluidly connected to and positioned upstream of a
fluidized zone 12, which can be the fluidized absorber and/or the fluidized
regenerator zone as discussed in greater detail subsequently.
[081] The J-Leg 10 comprises a descending feed pipe 20 containing a
fluidized stream of particulate solids 22, moving through the pipe 20 in moving
packed bed flow. The feed pipe 20 is fluidly connected to a standpipe 24 which
functions as an accumulator or holding vessel and delivers the stream of particulate
solids 22 to feed pipe 20 via a conical restriction 21. The feed pipe 20 is fluidly
connected to and discharges into an upwardly directed transfer pipe 28. The stream
of particulate solids 22, moves through the transfer pipe 28 in moving packed bed
flow and is delivered to the fluidized zone 12 at the discharge end of transfer pipe 28.
The feed pipe 20 connects to the transfer pipe at an angle 30 of less than about 90
degrees thereby forming the characteristic J-Leg shape.
[082] Aeration gas is added at a controllable rate to the particulate solids
stream 22 moving through the feed and transfer pipes 20 and 28, respectively, of the
J-Leg, at one or a plurality of locations 32a, 32b, 32c, 32d, and 32e. The aeration
gas can be any of various inert gases, such as nitrogen or the like, or can be a gas
having the same chemical composition as the process gas used or treated in the
fluidized zone 12. The flow rate of the particulate solids stream 22 through the J-Leg
can be controlled by varying the flow rate of aeration gas at one or more of the
locations 32a-e. In particular, the flow of aeration gas produces a drag force on the
particulates that pulls the particulate stream through the bend, i.e., angle 30, of the J-
Leg. Because the drag force in the direction of solids flow increases as the flow of
aeration gas increases, increasing the flow rate of the aeration gas increases the
flow rate of the particulate stream 22.
[083] The solid flow rate of particulate stream 22 can also change in
response to variations in the relative pressure difference between the dense phase
holding vessel or standpipe, 24, and the fluidized zone 12. An increase in the relative

pressure difference between the dense phase standpipe 24 (higher pressure) and
the fluidized zone 12 can result in an increase in the solids flow rate. A decrease in
the relative pressure difference can result in a decrease in the solids flow rate.
Nevertheless, the design and construction of the J-Leg valve mode device illustrated
in Figure 1 generally provides a relatively constant solids flow, at a flow rate
determined primarily by the aeration gas flow despite minor variations in such
pressure differences and the like, so long as such variations fall within
predetermined parameters determined by the particular geometry, sizing, and
arrangement of parts, of the J-Leg valve mode device, as will be appreciated by the
skilled artisan.
[084] The height 34 of sorbent in the holding vessel should preferably be
maintained at a level sufficient to provide enough pressure head to force sorbent into
the fluidized zones. The holding vessel can be sized to hold a sufficient inventory of
sorbent to adequately deal with system upsets including changes in the impurity feed
concentration and regenerator upsets.
[085] Other suitable non-mechanical gas seal forming solids transfer device,
or zones, adapted for operation in the valve mode to transfer solids at a controllable
flow rate can also be employed in the invention (e.g., L-Leg structures and other J-
Leg structures including for example, curved pipes, additional horizontal pipe
elements, and the like), so long as the functions of controlling the flow of solids into
the fluidized reactor system, preventing reverse flow of gases from one system to
another, and controlled flow of solids leaving the system are all achieved. Examples
of such other devices are set forth and discussed in the aforementioned
"HANDBOOK of FLUIDIZATION and FLUID-PARTICLE SYSTEMS". In general,
such devices are characterized by a reservoir or hopper feeding a downwardly
directed feed pipe containing a stream of particulate solids moving through the feed
pipe in moving packed bed flow; a fluidly connected horizontal or upwardly directed
transfer pipe; and one or more aeration gas supply lines fluidly connected and
arranged to move the particulate solids stream at a controllable flow rate through the
feed and transfer pipes by applying a frictional drag force in the direction of flow of
the particulate stream, to at least a portion of the particulate stream.

[086] Figure 2 is a schematic diagram of a non-mechanical gas seal forming
solids transfer zone constructed for operation in the "automatic mode" wherein solids
are passed through the transfer zone at the same flow rate as the feed rate of solids
into the zone. In particular, Figure 2 illustrates a loop seal device 40 comprising a
vertical downflow leg 42 fluidly connected to a vertical upflow leg 44 via a lower
horizontal leg 46. A dense phase particulate solids stream admitted into the
downflow leg 42 flows through the lower horizontal leg 46 and upwardly through the
upflow leg 44, and is discharged via dip leg 48 into fluidized zone 12, which is
advantageously the absorber zone as discussed hereinafter. The dip leg 48
connects to the vertical upflow leg 44 at an angle alpha of less than about 90
degrees. Aeration gas is admitted into the loop seal device 40 at one or more
locations 50a and 50b adjacent the lower end portion of the upflow and/or downflow
legs 42 and 44, respectively. The aeration gas is admitted at a constant flow rate
sufficient to support a smooth and steady flow of solids through the device. The flow
rate of aeration gas sufficient to achieve smooth and steady flow of solids through
the loop seal can be determined by the skilled artisan according to design and test
criteria known in the art and discussed, for example, in the aforementioned
"HANDBOOK of FLUIDIZATION and FLUID-PARTICLE SYSTEMS". For example, in
the case of Geldart Group B solids, the aeration gas flow rate must be sufficient to
fluidize the upflow section 44 of the loop seal in order to establish smooth and steady
flow, while little or no fluidization gas may be required to be added to the upflow leg
in the case of Geldart Group A solids.
[087] The height h1 of the upflow leg 44 is fixed by the location of the dip leg
48 and angle alpha. The height of the solids stream flowing into the downflow leg 42
will automatically adjust to balance the pressure required to move solids upwardly
through the height h1 of the upflow leg 44. The height of the vertical flow of solids
through the legs of the loop seal, in combination with the fluid characteristics of the
particulate solids provides a pressure seal capable of insulating operation of the loop
seal from minor fluctuations in pressures across the loop seal 40, and also prevents
large pressure variations from blowing the pressure seal established by the vertical
legs 42 and 44 of the loop seal 40. The design of the loop seal 40, and particularly
the height h1 can be selected by the skilled artisan to accomplish seals of

predetermined pressures according to design and test criteria known in the art and
discussed, for example, in the aforementioned "HANDBOOK of FLUIDIZATION and
FLUID-PARTICLE SYSTEMS".
[088] As indicated previously, the design and construction of the loop seal
solids transfer device 40 provides an "automatic mode" solids transfer in that the flow
rate of solids through the loop seal automatically adjusts so that solids are passed
through the loop seal 40 at the same flow rate as the feed rate of solids into the
zone. In particular, the height of the solids stream flowing into the downflow leg 42
will automatically adjust to balance the pressure required to move solids upwardly
through the height h1 of the vertical upflow leg 44. Thus the flow rate of the solids
stream flowing into the vertical downflow leg 42 automatically establishes the same
flow rate of solids through the vertical upflow leg 44 so that a balance in pressure is
maintained between the two vertical legs.
[089] Various different types and constructions of non-mechanical gas seal
forming solids transfer zones are known to the skilled artisan and can be substituted
for the loops seal device 40 illustrated in Figure 2. Such devices include seal-pot, N-
Valve, V-Valve, L-Valve constructions, and the like, discussed for example in the
aforementioned "HANDBOOK of FLUIDIZATION and FLUID-PARTICLE SYSTEMS".
[090] Figure 3 is a schematic diagram of one embodiment of a dual loop
process and apparatus for removing impurities from a gas according to the invention.
An impurity containing feed gas is admitted into a fluidized absorber 100 via feed gas
line 102. The feed gas is contacted in the absorber 100 with a stream of recycled
sorbent admitted to the absorber 100 via J-Leg 105 and with a stream of
regenerated sorbent which is admitted to the absorber 100 via a dip leg line 106
which, in turn, is fluidly connected to a upstream loop seal device 110. The feed gas
is treated in the absorber 100 and a fluidized stream comprising treated feed gas
and impurity loaded sorbent is recovered from the absorber via line 112 which is fed
to solids separator 120. Treated feed gas having reduced impurity content is
recovered from the solids separator 120 via line 121.
[091] Impurity loaded solid sorbent is recovered from the solids separator
120 and a portion thereof is passed to standpipe 122, while another portion is
passed via a dip leg 124 to a second standpipe 130. Fresh sorbent can be added to

the recycle standpipe 122 via a supply line 123. The impurity loaded sorbent in
standpipe 122 is recycled via J-Leg 105 to the absorber 100, while impurity loaded
sorbent in standpipe 130 is fed via a second J-Leg 135 to the fluidized regenerator
zone 140. The J-Leg solids transfer devices 105 and 135 are fluidly connected to
controllable aeration gas supply lines, 144 and 146, respectively, which control the
feed rate of solids through the J-Leg transfer devices 105 and 135. Control of the
aeration gas supplied to each of the J-Leg solids transfer devices can be conducted
by any of various control devices, 147, which are connected to controllable valves
148 and 149 associated with the aeration gas feed lines 144 and 146, respectively.
The J-Leg transfer devices 105 and 135 are thus operated in the valve mode as
discussed in connection with Figure 1 previously.
[092] The impurity loaded sorbent which is fed via J-Leg 135 to the
regenerator zone 140 is contacted in the regenerator zone 140 with regenerator feed
gas admitted to the regenerator zone via line 150. A fluidized effluent stream is
recovered from the regenerator zone 140 and passed to a solids separator 155 for
separation into a regenerator off gas which is recovered via line 156 and passed to
an appropriate downstream cleanup zone (not shown). A regenerated solid sorbent
stream is recovered from the solids separator 155 and is passed into the downflow
leg 158 of loop seal solids transfer device 110, which in turn, transfers the
regenerated sorbent to the absorber 100 via dip leg 106 as indicated previously. An
aeration gas supply line 160 is fluidly connected to a lower portion of loop seal solids
transfer device 110 to aid in establishing a smooth flow of solids through the loop
seal as discussed in connection with Figure 2, previously.
[093] One advantageous process control 170 for controlling the flow of solid
sorbent streams in and between the absorber and regenerator loops is illustrated in
Figure 3. Control 170 is connected via control input 171 to a differential pressure
sensor 172 which in turn is connected via sample gas lines 173 and 174, to the
respective effluent gas lines 121 of the absorber 100 and 156 of the regenerator 140.
In addition, control 170 is operatively connected via a control output 176, with a
controllable valve 178 which is operatively connected to regenerator off gas line 156.
The differential pressure sensor 172 outputs to control 170, a control input (171)
representative of the pressure difference between the absorber and regenerator

pressures. Control 170 compares the pressure differential information received from
the differential pressure sensor 172 with a control set point representative of a
predetermined pressure difference in-range value for stable system operation. If the
actual pressure difference value differs from the control set point, control 170 sends
instructions to controllable valve 178 via a control output 176, for adjustment of the
valve to thereby change the pressure in the regenerator 140, and in turn, the
pressure difference between the absorber and regenerator with the specific objective
of achieving the desired pressure differential in-range value between the absorber
and regenerator.
[094] In an alternative embodiment (not shown), a first pressure sensor
operatively associated with the absorber effluent line 121 and a second pressure
sensor operatively associated with the regenerator effluent gas line 156 are used to
collect data representative of the gas pressures within the effluent gas lines 121 and
156, of the absorber 100 and the regenerator 140, respectively. Signals
representative of the pressures in the absorber 100 and the regenerator 140 are sent
from the first and second pressure sensors to the control 170, which then compares
these signals to determine a calculated pressure difference value representative of
the pressure difference between the absorber 100 and the regenerator 140. In the
same manner as discussed above, the calculated pressure difference is then
compared to a set point representative of a predetermined pressure difference in-
range value for stable system operation. If the calculated pressure difference value
differs from the control set point, control 170 sends instructions to controllable valve
178 via a control output 176, for adjustment of the valve to thereby change the
pressure in the regenerator 140, and in turn, the pressure difference between the
absorber and regenerator with the specific objective of establishing the desired
pressure differential set point between the absorber and regenerator.
[095] In one advantageous embodiment, the predetermined pressure
difference in-range value comprises a pressure difference in the range of between
about 1 psig and about 20 psig. In another advantageous embodiment, the
predetermined pressure difference in-range value comprises a pressure difference in
the range of between about 2 psig and about 10 psig. The pressure difference in-
range control value can be a single value, a range of values, or a control algorithm

for sending different instructions to the controllable valve 178 depending on factors
such as the quantitative difference between the calculated pressure difference and
one or more predetermined pressure difference set points, the temperature in the
absorber and/or regenerator, the rate at which the calculated pressure difference is
moving towards or away from one or more predetermined pressure difference set
points, and the like, as will be apparent to those of ordinary skill in the art.
[096] It will also be apparent to the skilled artisan that pressure adjustments
to maintain the pressure difference between the absorber and the regenerator within
a predetermined pressure difference in-range value can be effected by adjusting the
pressure of the absorber instead of the regenerator pressure, or by adjusting the
pressure of both, and that pressure adjustments can be made to the absorber and/or
regenerator gas influent lines if desired.
[097] The control of the pressure difference between the absorber and the
regenerator as discussed in connection with control 170, is particularly effective for
controlling the sorbent solids flow rates between and through the absorber and
regenerator when used in combination with valve mode and automatic mode non-
mechanical solids transfer devices as illustrated in Figure 3. Nevertheless, the
control process can alternatively be used with substantial benefits and advantages
with controllable mechanical valves, as will be apparent to the skilled artisan.
Moreover, the use of a valve mode non-mechanical solids transfer device arranged
to feed the regenerator 140, such as J-Leg 135, in combination with an automatic
mode non-mechanical solids transfer device arranged to receive regenerated
sorbent from the regenerator and feed same to the absorber 100, such as loop seal
110, can provide significant benefits and advantages with or without use of the valve
mode non-mechanical solids transfer device arranged to feed recycled sorbent to the
absorber 100, i.e., J-Leg 105 illustrated in Figure 3.
[098] One advantageous process control 180 for maintaining a balance
between the impurity removal rate in the absorber and the impurity removal rate in
the regenerator is also illustrated in Figure 3. Control 180 is connected via control
inputs 182 and 184, to impurity analyzers (not shown) associated with the absorber
influent feed gas, and effluent treated gas lines, 102 and 121, respectively. In
addition, control 180 is operatively connected, via control inputs/output 186, with a

controllable valve 188 which is operatively connected to regenerator feed gas line
150. Enhanced process control according to this aspect of the invention comprises a
feed forward process control wherein the impurity removal rate in the absorber is
calculated by comparing the impurity content values fed to control 180 from the
impurity analyzer inputs 182 and 184. The impurity removal rate in the absorber is
then compared to the impurity removal rate in the regenerator which may be
calculated from input received via control input/output 186. Alternatively the
calculated impurity removal rate in the regenerator can be calculated from
measurements representative of impurity content of the regenerator off gas, obtained
via sensors and control connections not shown.
[099] If the calculated impurity removal rates in the absorber and regenerator
differ from a predetermined in-range stoichiometric control value, the control 180
sends instructions to controllable valve 188 via a control output 186, for adjustment
of the valve 188 to thereby change the feed rate of active regenerator feed gas to the
regenerator which in turn changes the impurity removal rate in the regenerator 140.
[0100] The term "active regenerator feed gas" refers to the content of the
regenerator feed gas which is capable of interacting (typically by chemical reaction)
with the sorbent under conditions present in the regenerator to reduce the impurity
loading of the sorbent. It is to be noted that the content of the active regenerator feed
gas in the regenerator feed gas can be changed. Changing the content of the active
regenerator feed gas in regenerator feed gas will affect the rate and amount of
regeneration accomplished. For example when regeneration of the sorbent is
accomplished by contact with an oxidation regeneration gas, the regenerator feed
gas can be air with a fixed oxygen content, air and inert gas mixtures or oxygen and
inert gas mixtures.
[0101] In those cases, in which the regenerator feed gas contains a fixed
content of active regenerator feed gas (i.e., air with 21 mole % oxygen) and is
admitted to the regenerator 140 via line 150, the adjustment of controllable valve 188
according to the instructions sent by control 180 will result in a change of the flow
rate of the regenerator feed gas in line 150. On the other hand, in those cases where
the content of the active regenerator feed gas can be changed in the regenerator
feed gas (i.e., air and inert mixtures or oxygen and inert mixtures) is admitted to the

regenerator 140 via line 150, valve 180 can effect a change in the feed rate of active
regenerator feed gas fed to the regenerator 140 by changing the relative content
(i.e., % content, mol% content, etc.) of active regeneration gas in the regeneration
feed gas admitted to line 150 without changing the overall flow rate of the
regenerator feed gas in line 150. Alternatively, valve 180 can effect a change in the
feed rate of active regenerator feed gas fed to the regenerator 140 by changing the
overall flow rate of the regenerator feed gas in line 150 when no change is made in
the relative content of active regeneration gas in the regeneration feed gas. In
summary, the feed rate of active regenerator feed gas to the regenerator can be
changed by changing the content of active regenerator feed gas present in the
regenerator feed gas, or by increasing or decreasing the flow rate of the regenerator
feed gas without changing its content, or by changing both the composition and the
overall flow rate of the regenerator feed gas admitted to the regenerator zone via line
150.
[0102] The predetermined in-range stoichiometric control value is based at
least in part on the material balance between the impurity removal rate in the
absorber and the impurity removal rate in the regenerator. In some cases the
predetermined in-range stoichiometric control value will be calculated to maintain an
even material balance between the impurity removal in the absorber and
regenerator. However, in additional advantageous embodiments of the invention, the
predetermined in-range stoichiometric control value is calculated to provide less
than, or greater than, an even material balance between the impurity removal in the
absorber and regenerator in order to achieve various desirable process functions
such as, for example, decreasing, or increasing, the average impurity loading of the
sorbent.
[0103] In particular, control 180 can be programmed to receive at least one
impurity loading input signal 190 containing information directly or indirectly
representative of the impurity loading of the impurity loaded sorbent removed from
the absorber via line 112. The impurity loading input signal 190 is compared to a
predetermined in-range sorbent impurity loading value to determine whether the
predetermined in-range stoichiometric control value, discussed above, should be
adjusted to provide less than, or greater than, an even material balance between the

impurity removal in the absorber and in the regenerator in order to decrease, or
increase, the average impurity loading of the sorbent. For example, if the impurity
loading input signal 190 indicates that the sorbent has less than a desired minimal
average impurity loading, the predetermined in-range stoichiometric control value
can be adjusted to increase the impurity loading of the sorbent. If the impurity
loading input signal 190 indicates that the sorbent has greater than a desired
maximum average impurity loading, the predetermined in-range stoichiometric
control value can be adjusted to decrease the impurity loading of the sorbent.
Similarly, if the impurity loading input signal 190 indicates that the average impurity
loading of the sorbent is within a predetermined desirable range, but is increasing or
decreasing, the predetermined in-range stoichiometric control value can be adjusted
as necessary to maintain a relatively constant average impurity loading of the
sorbent.
[0104] Information directly representative of the impurity loading of the sorbent
can comprise analytical information obtained by analysis of at least one impurity
loaded sorbent grab sample recovered from the absorber, or obtained by in-line
analysis of all or a portion of the impurity loaded sorbent stream removed from the
absorber. Alternatively, information directly representative of the impurity loading of
the sorbent can be obtained by exposing batch or side stream samples of impurity
loaded sorbent to a concentrated or essentially pure impurity gas stream under
absorption conditions ensuring saturation of the sorbent's remaining impurity
removal capacity whereby the quantity of impurity removed from the impurity gas
stream can allow calculation of the remaining impurity removal capacity of the
sorbent. Information indirectly representative of the impurity loading of the sorbent
can comprise on-line measurements of variations in the reaction conditions in the
absorber and/or regenerator which, in combination with the .impurity removal rate
information calculated from impurity analyzer inputs 182 and 184, can be used to
determine if the impurity removal capacity of the sorbent is at, or close to, full
capacity. Measurements of impurity content of the regenerator off gas and/or
measurements of variations of the reaction conditions in the regenerator can also be
used to provide information indirectly representative of the impurity loading of the
sorbent.

[0105] Figure 4 is a schematic diagram of another embodiment of a system
and process for removing impurities from a gas where a single, shared standpipe
200 is used to feed impurity loaded sorbent to both the fluidized absorber zone and
the fluidized regenerator zone. The various controls, valves and the like discussed in
connection with Figure 3 are advantageously included in the system and process of
Figure 4, but are not specifically shown.
[0106] Figure 5 is a schematic diagram of another embodiment of a system
and process for removing impurities from a gas similar to the processes and systems
of Figures 3 and 4, where impurity loaded sorbent recovered from the absorber is not
recycled to the fluidized absorber zone. Instead, as shown in Figure 5, all of the
impurity loaded sorbent recovered from the absorber is passed to a single standpipe
300 and is then transferred to the fluidized regenerator 140 via J-Leg 135. The
various controls, valves and the like discussed in connection with Figure 3 are
advantageously included in the system and process of Figure 4, but are not
specifically shown.
[0107] As indicated previously, in various advantageous embodiments, the
processes, systems and apparatus of the invention can be used for removal of any
of various impurities from a feed gas including sulfur compounds, hydrogen chloride,
arsenic, selenium, hydrogen cyanide, and/or ammonia. Nevertheless, the invention
is currently believed to be particularly advantageous when used for reducing the
content of at least one sulfur impurity in a reducing gas. Desirably, the invention can
be employed for the reduction of at least one sulfur impurity comprising H2S and/or
COS from a reducing gas of carbonaceous origin.
[0108] The invention is applicable to a wide variety of feed gases, including a
wide variety of syngas compositions having sulfur impurity levels ranging from about
100 to about 40,000 ppmv, advantageously from about 1000 to about 15,000 ppmv,
or in alternative advantageous embodiments, sulfur impurity levels ranging from
about 5000 to about 10,000 ppmv. The processes and apparatus of the invention
can be applied to various sulfur contaminated feed gas streams to achieve sulfur
impurity levels of 100 ppmv or less, advantageously 50 ppmv or less in the purified
treated gas stream exiting the absorber. Where desirable, the invention can be used

to reduce sulfur impurity content from an initial level exceeding 5000 ppmv to a final
level of about 30 ppmv or less, e.g., about 20 ppmv or less, or 10 ppmv or less.
[0109] In advantageous embodiments of the invention, the fluidized absorber
zone is maintained at a temperature in the range of between about 600°F and about
1200°F and a pressure of between about atmospheric pressure and about 1200
psig, and the regenerating zone is maintained at a temperature in the range of
between about 900°F to about 1450°F and about the same pressure as the
absorber. In yet further advantageous embodiments of the invention, the fluidized
absorber zone is maintained at a temperature in the range of between about 700°F
and about 1000°F and a pressure of between about 100 psig and about 1200 psig
(e.g., between about 200 psig and about 1000 psig), and the regenerating zone is
maintained at a temperature in the range of between about 1200°F and about
1450°F and a pressure which is the same or about the same as the absorber
pressure.
[0110] In one embodiment, impurity containing feed gas is introduced into the
base of a fluidized absorber zone, as shown in Figures 3-5, where it is mixed with a
sorbent. The superficial velocity of the impurity containing feed gas stream may be
maintained above the minimum fluidization point (dependant on operating pressure
and temperature) and, generally, within a range from 2 to 5 ft/sec (0.6 to 1.5 m/sec),
though other suitable velocities may be chosen.
[0111] In one embodiment of the present invention, impurity-containing feed
gas may be mixed with an active metal oxide sorbent. The sorbent contacted with
the impurity containing feed gas in the fluidized absorber zone may comprise one or
more active metal oxides chosen from iron oxide, zinc oxide, zinc ferrite, zinc
tJtanate, copper ferrite, copper oxide, vanadium oxide, and mixtures thereof.
Desirable active metal oxide containing sorbent compositions and processes for
sulfur removal are disclosed in US Patent No. 6,951,635 B2 issued October 4, 2005
to Gangwal et al; US Patent No. 6,306,793 B1 issued October 23, 2001 to Turk et al;
US Patent No. 5,972,835 issued October 26, 1999 to Gupta; US Patent No.
5,914,288 issued June 22, 1999 to Turk et al; and US Patent No. 5,714,431 issued
Feb. 3,1988 to Gupta et al.

[0112] In another embodiment, before contacting the sorbent with the impurity
containing feed gas in the fluidized absorber zone, the bulk density of the sorbent
can range from 60 to 110 lb/ft3 (0.96 to 1.76 g/cm3) and can have an average particle
diameter from 50 to 140 microns.
[0113] In still another embodiment, and depending on other process
parameters, for instance, the inlet impurity concentration and the temperature of the
fluidized absorber zone, the fluidized absorber zone may optionally have a back-
mixed zone to increase the total gas-solid contact time. If long contact times are not
desired, the fluidized absorber zone may be entrained flow. Regenerated sorbent is
returned from the regenerator system to the fluidized absorber zone where it assists
in removing impurities from the gas and transfers heat from the sorbent to the
purified gas, thus improving the thermal efficiency of the integrated system. A
suitable residence time in the fluidized absorber zone ranges from 3 to 25 seconds,
and in another embodiment from 3 to 10 seconds.
[0114] In one embodiment of the present invention, at steady state conditions,
the average impurity content of the impurity loaded sorbent exiting the absorber
ranges from 10% to 90% of the sorbent impurity capacity, for example from 30 to
75% of the sorbent impurity capacity.
[0115] When the feed gas stream comprises arsenic, the arsenic content of
the loaded sorbent increases at a rate proportional to the amount of gas that has
contacted the sorbent. The arsenic content, for example, of the arsenic loaded
sorbent may be at least 0-3000 ppm as it exits the fluidized absorber zone.
[0116] When the feed gas stream comprises selenium, the selenium content
of the loaded sorbent increases at a rate proportional to the amount of gas that has
contacted the sorbent. The selenium content, for example, of the selenium loaded
sorbent may be at least 0-500 ppm as it exits the fluidized absorber zone.
[0117] The impurity loaded sorbent recovered from the absorber can be
treated to enhance removal of retained feed gas prior to recycling of the sorbent,
and/or prior to treatment of the sorbent in the regenerator. Thus, for example,
sorbent recovered from solids separator 120 in Figure 3, in one embodiment of the
invention, can be passed through a gas stripper. The gas stripper uses an inert gas,
such as nitrogen, steam, carbon dioxide, or the like, flowing countercurrent to the

sorbent flow to displace synthesis gas from the void spaces between sorbent
particles, thus minimizing gas losses to the fluidized regenerator zone.
[0118] In at least one embodiment of the present invention, the absorber
system comprises an optional holding vessel, for instance a standpipe (e.g.,
standpipes 122 and 130 in Figure 3), which serves as the primary holder of sorbent
inventory and will normally operate in a dense phase mode. For instance, the
effective density of the separated impurity loaded sorbent in the holding vessel is
greater than or equal to 50 lb/ft3 (0.80 g/cm3). The majority of the separated impurity
loaded sorbent, for example the partially metal sulfided sorbent, continues to the
bottom of the optional holding vessel where it is returned to the fluidized absorber
zone.
[0119] In one embodiment, the treated feed gas (absorber off-gas) having a
reduced impurity content exits the top of the absorber via a solids separator, for
example, a cyclone separator. After exiting the solids separator, the absorber off-gas
may also be passed through a filter to remove any fine solid particles not captured by
the solids separator. Acceptable filter media must be capable of withstanding the
high temperature and potentially corrosive nature of the absorber off-gas.
Specifically, Dynalloy™ D215-160 was shown to be an acceptable fitter media for the
absorber off-gas derived from syngas comprising sulfur and arsenic impurities. The
acceptable filter media may be different for different feed gas and off-gas streams
and can be identified by various testing regimes, such as, for example, by exposing
samples (or coupons) of various filter media to simulated off-gas compositions at
temperatures and pressures simulating use, or long term use, of the filter media
under actual process conditions, followed by testing to identify any resultant changes
in the physical properties, composition and/or crystalline structure, etc., of the
sample.
[0120] The solids captured by the filter are transferred to a separate pressure
vessel (lockhopper) that can be isolated from the filter without affecting filter
operation or gas flow. Once isolated, the lockhopper pressure is reduced to a safe
level and the solids are discharged. Once the discharge is complete, the lockhopper
is sealed and pressurized with gas (inert or process gas) and then opened back up
to the filter.

[0121] The impurity-containing feed gas may or may not contain water vapor.
By use of a feed gas heat exchanger, the temperature of the fluidized absorber zone
may be controlled between 600 and 1200 °F, for instance ranging from 700 to 1000
*F. The pressure of the impurity containing feed gas can be controlled between
atmospheric pressure and 1200 psig by using, for instance, a throttling control valve
located in the effluent gas flow path, usually downstream of the filter or scrubber.
The effective sorbent density in the fluidized absorber zone can range from 5 to 50
lb/ft3 (0.08 to 0.80 g/cm3) by adjusting the sorbent flow from the optional holding
vessel and/or the process gas flow.
[0122] A suitable density to achieve impurity removal can depend on 1) the
inlet gas impurity concentration; 2) the impurity concentration on the sorbent, for
instance the metallic oxide sorbent; 3) temperature of the fluidized absorber zone;
and 4) water vapor content. Inert gas, such as nitrogen, steam, or carbon dioxide,
may be used to aid in achieving the velocity required for solids transport and/or to aid
in partially fluidizing the sorbent in the holding vessels, for example standpipes.
[0123] The average impurity content of the sorbent may be controlled by
diverting a portion of impurity loaded sorbent, or alternatively all the impurity loaded
sorbent, from the absorber system to the regenerator system where the metal oxide
is recovered. Impurity loaded sorbent transported to the fluidized regenerator zone
may enter an optional holding vessel before being regenerated. If that occurs, the
impurity loaded sorbent may be maintained in dense phase mode in the holding
vessel. The density of the transported impurity loaded sorbent in the holding vessel
is greater than or equal to 50 lb/ft3. The impurity loaded sorbent is then fed into the
fluidized regenerator zone.
[0124] As disclosed herein, the descending pipe of the J-Leg shown in Figure
1, which is positioned before the fluidized absorber zone and/or the fluidized
regenerator zone, may comprise, for instance, a flow restrictor chosen from a conical
or eccentric reducer and a flat plate or disk with at least one fixed orifice. Other
suitable J-Leg structures can be utilized. Such J-Leg structures should control the
flow rate of fluid material transferred from, for example, a dense-phase holding
vessel into a dilute-phase fluidized zone.

[0125] The transfer pipe of the J-Leg, such as shown in Figure 1, may be
positioned before the fluidized absorber zone and/or the fluidized regenerator zone.
The diameter of the transfer pipe is equal to or less than the diameter of the holding
vessel. The transfer pipe transfers the material from the descending pipe to the gas-
solid fluidized zone. The transfer pipe may employ, for example, a change in flow
direction of more than 90° such that a seal or trap of solid material is formed to
prevent reverse flow of gas through the J-Leg. The elevation gained by the transfer
pipe may be, for instance, designed based on the material density and the relative
pressure of two sides of the system such that it is sufficient to withstand any process
upsets without emptying of solids.
[0126] The transported impurity loaded sorbent is contacted with regenerator
gas in the fluidized regenerator zone. When oxidative regeneration is required, air
can be fed into the fluidized regenerator zone to provide oxygen for the regeneration
reaction and to provide adequate fluidization velocity over a nominal range of
operating conditions. To provide for a greater operating range, it is possible to blend
an inert gas (comprising, for example, nitrogen, steam, and carbon dioxide) and
oxygen to create oxygen mixtures from 2 % to 50%. The amount of oxygen can be
controlled such that the rate of impurity removal from the sorbent in the fluidized
regenerator zone equals the rate of impurities deposited on the sorbent in the
fluidized absorber zone. The concentration of oxygen in the regenerator off-gas is
preferably maintained at very low levels and can be periodically or continuously
measured and compared to a predetermined set point to provide a process control
indicator of proper stoichiometry.
[0127] Fluidization conditions in the fluidized regenerator zone may, for
example, be maintained to provide adequate back-mixing of the hot sorbent with the
cooler sorbent entering the fluidized regenerator zone to sustain the temperature in
the fluidized zone from 900 °F to 1450°F, for instance from 1200 to 1450°F. These
operating temperature windows ensure that operating conditions minimize formation
of sulfate during oxidative regeneration according to the following reactions:
MO + S02 + 0.5 02 ↔ MS04 (IV)

MS + 2O2 ↔ MS04 (V)
wherein M is the metal present in the sorbent, for instance Zn; MO represents a
metal oxide; MS represents a metal sulfide, and MSO4 represents a metal sulfate.
[0128] The regenerator temperature may be maintained by a combination of
any of the following: 1) adjusting the feed of cooler sorbent from the second holding
vessel to mix with the hotter sorbent in the fluidized regenerator zone; 2) adjusting
the temperature of the sorbent via heaters prior to entering the fluidized regenerator
zone; 3) the co-combustion of a supplementary fuel such as syngas, natural gas,
propane, diesel, or other flammable material whose flow can be adequately
controlled and will combust under normal regenerator conditions; and 4) adjusting
the temperature of the oxidant gas prior to entering the fluidized regenerator zone.
[0129] To aid in maintaining the appropriate reaction temperature in the
regenerator, the impurity loaded sorbent density in the fluidized regenerator zone
can be adjusted to a density in the range of from 5 to 60 lb/ft3, such as from 10 to 40
lb/ft3 (0.16 to 0.64 g/cm3), and the reactor portion of the regenerator can be designed
to achieve operation in a back-mixed mode. An acceptable residence time in the
fluidized regenerator zone can range from 3 to 25 seconds, such as from 3 to 10
seconds.
[0130] Upon leaving the regenerator back-mixed zone, the superficial velocity
of the regenerated sorbent stream can be increased by reducing the cross-sectional
area of the riser and/or by the addition of an inert gas to the sorbent stream. The
increased gas velocity transports the regenerated sorbent, for instance regenerated
metallic oxide sorbent, up the fluidized regenerator zone toward a solids separator.
Prior to entering the solids separator, the gas velocity may be again be altered in
order to provide improve separation in the solids separator. For example, the gas
velocity may be further increased to effect better separation in a cyclone separator.
[0131] In one embodiment of the present invention, the solids separator may
be a cyclone separator wherein a majority of the regenerated sorbent is separated
from the regenerator off-gas. For instance, 90 to 99% of the regenerated sorbent
may be separated from the regenerator off-gas.

[0132] The regenerator off-gas exits the top of the solids separator, for
example, a cyclone separator. After exiting the cyclone separator, the regenerator
off-gas may also pass through a filter to remove any fine solid particles not captured
by the cyclone separator. Acceptable filter media must be capable of withstanding
the high temperature and potentially corrosive nature of the regenerator off-gas.
Specifically, Alloy 59 (also know as Alloy HR or DIN No. 2.4605) or Dynalloy™
D215-160 were shown to be suitable filter media for embodiments of the invention
described in the working examples set forth hereinafter. As with the acceptable filter
media that can be used downstream of the absorber for solids separation, discussed
previously, acceptable filter media may be different depending on the sorbent
composition, impurity composition, impurity loading, regeneration gas composition
and/or the specific temperature and pressure conditions in, or following the
regenerator zone. Acceptable filter media can be identified by various testing
regimes discussed previously in connection with filter media used downstream of the
absorber.
[0133] The solids captured by the filter are transferred to a separate pressure
vessel (lockhopper) that can be isolated from the filter without affecting filter
operation or gas flow. Once isolated, the lockhopper pressure is reduced to a safe
level and the solids are discharged. Once the discharge is complete, the lockhopper
is sealed and pressurized with gas (inert or process gas) and then opened back up
to the filter.
[0134] The pressure of the regenerator system may be controlled by use of a
throttling valve in the regenerator off-gas flow path downstream of the particulate
filter. Sulfur dioxide levels in the regenerator off-gas stream range from 1 to 33%
volume depending on oxygen feed concentration.
[0135] The regenerated sorbent leaves the bottom of the solids separator and
passes optionally through a gas stripper. The gas stripper uses an inert gas, for
instance, nitrogen, steam, and carbon dioxide, flowing countercurrent to the sorbent
flow to displace regenerator off-gas from sorbent particles, thus minimizing transfer
of sulfur dioxide to the absorber.
[0136] In the event that the feed gas comprises solid particles, the particle
size distribution within the invention may be effectively maintained by passing the

feed gas through solids separators with similar efficiency to that used in the absorber
and regenerator systems. Particulate matter present in the feed gas will either be
removed by the pretreatment separator or passed through the system without
accumulation.
[0137] On paths that have infrequent, intermittent sorbent flow, for instance
sample lines and charging lines, if steam is allowed to condense around stagnant
sorbent, plugs will form. These plugs can be prevented by a combination of
adequate heat tracing, insulation, and/or dry gas purges, such as for example inert
gases or dry syngas to prevent water condensation.
[0138] Adequate provision may be incorporated, for instance, into the design
to allow for charging and discharging of sorbent while at operating conditions, similar
to Fluid Catalytic Cracker (FCC) systems. These systems can be designed to
operate at pressures in excess of 1200 psig in accordance with the disclosures
made herein.
[0139] Prior to charging sorbent, the system may be, for example, purged of
condensable gas with a dry inert gas. After establishing appropriate aeration and
transport gas flows, sorbent is charged to the system and circulated. Solids
circulation helps ensure uniform heat distribution. The system then can be heated to
a temperature greater than the dew point of the process gas prior to its introduction.
Preheating the system also minimizes the potential for equipment damage due to
thermal shock or dew point corrosion. At least one method of achieving this objective
incorporates the use of a startup heater, a recirculation compressor and a dry, inert
gas, for example nitrogen. Use of a single such system will allow the absorber and
regenerator to be simultaneously pre-heated.
[0140] Once the system is pre-heated, the impurity containing gas is
introduced to the absorber. Circulation is maintained in the regenerator using the dry
inert gas system described previously until sufficient amount of impurities have has
been loaded on the sorbent to initiate the regeneration reaction.
[0141] The initial minimum regeneration reaction temperature of 1000 °F in
the fluidized regenerator zone may be obtained by at least one of the following
methods: 1) addition of a pyrophoric additive, such as iron sulfide or similar material,
that will spontaneously combust when exposed to oxygen and have sufficient heat of

combustion to raise the temperature of the fluidized regeneration zone high enough
to support regeneration reaction; 2) addition of a supplementary fuel, such as
syngas, natural gas, propane, diesel, or other flammable material, whose flow can be
adequately controlled and will combust under normal regenerator conditions; and 3)
continued application of the dry gas preheating system with an adequately designed
startup heater. Where supplementary fuel is utilized, the fuel may be added directly
to the fluidized regeneration zone or it may be mixed with the oxygen and combusted
prior to entering the fluidized regenerator zone. In either case, the hot combustion
gases are used to raise the temperature of the fluidized regenerator zone to the
minimum temperature required for the regeneration reaction. Once this temperature
is reached, the flow of supplementary fuel may be stopped or scaled back as needed
to assist in maintaining the fluidized regenerator reaction zone above the minimum
reaction temperature. Persons skilled in the art would understand other methods and
techniques to achieve the minimum reaction temperature in the fluidized
regeneration zone.
[0142] To minimize the potential for sorbent agglomeration, condensable
vapors can be purged from the system with dry inert gas. This purging may be
performed while the system is cooling down. The above mentioned startup
circulation system is also designed to allow controlled cooling of the system while
purging condensables.
[0143] The following examples are intended to illustrate the invention in a
non-limiting manner. The term "standard" is used throughout these examples to
provide reference conditions of 70 °F (21 °C) and atmospheric pressure to establish
gas volumes and gas volumetric flow rates.
EXAMPLES
Example 1
SULFUR REMOVAL
[0144] A dual loop desulfurization pilot plant system schematically illustrated
in Figure 6 was utilized for this experiment. A zinc oxide based sorbent was used in
the absorber. Specific dimensions of the different components in the dual loop pilot
plant system are provided in Table 1. The experiments conducted with the dual loop

apparatus are summarized in Table 2. These data are the average values for each
experiment. The system was successful in increasing the ability to match the
regeneration reaction rate to the absorption reaction rate and thus maintain a
consistent sulfur concentration on the zinc oxide based sorbent and lower sulfur
levels in the desulfurized syngas leaving the absorber cyclone.

[01451 Experiments summarized in Table 2 were used to vary process
conditions (e.g. temperature, pressure, residence time, etc.) for the absorber reactor
loop in order to learn the relationship between absorber performance, as measured
by sulfur removal, and the process variable.

VOLATILE METAL REMOVAL
[0146] Special sampling was conducted to determine the fate of volatile
metals, specifically arsenic (As), cadmium (Cd), mercury (Hg), and selenium (Se),
that are often present in coal-derived syngas. For these experiments slip streams of
the feed syngas and the desulfurized syngas were metered into a series of "traps"
designed to remove the volatile metals from the syngas. The "traps" were then
analyzed off-site for metal content. Three different capture methods (traps) were
used as described below:
Charcoal Adsorption Method
[0147] The sample train consisted of three (3) sorbent sampling tubes, each
containing 1.0 gram of acid-washed, coconut-shell charcoal, placed in series. Gas
from each location was fed to the sample tubes at a rate of 0.5 standard liters per
minute over a 2-hour period for a total sample volume of 60 standard liters.
Iodine Monochloride Impinqer Method
[0148] The sample train consisted of three (3) impingers, each containing
100 ml of a 16% iodine Monochloride solution prepared in glacial acetic acid. Gas
from each location was fed to the sample tubes at a rate of 14.2 standard liters per

minute (0.5 scfm) over a 2-hour period for a total sample volume of 852 standard
liters (60 scf).
Potassium Permanganate Impinger Method
[0149] The sample train consisted of initial impingers containing 20% sodium
hydroxide solution to remove H2S followed by impingers containing 100 ml of 4%
potassium permanganate in 10 % sulfuric acid solutions to capture mercury. The
feed syngas was sampled at a rate of 8.5 standard liters per minute (0,3 scfm) for
90 minutes for a total sample volume of 765 standard liters (27 scf). The
desulfurized syngas was sampled for 2 hours at a rate of 14.2 standard liters per
minute (0.5 scfm) for a total sample volume of 1,704 standard liters (60 scf).
[0150] The above sampling was conducted a total of 5 times over a 3 day
period. The results of the testing are summarized in Table 3. Process conditions
were held relatively constant for the five sampling periods and were as follows:
Absorber Temperature: 8950F
Absorber Pressure: 450 psig
Syngas Feed Rate, Sample 1: 7,160 scfh
Samples 2-5: 4,993 scfh
Regenerator Temperature: 1,303 °F
[0151] As can be seen from these data, the apparatus shown in Figure 6
also removed about 92 % of the arsenic and over 97% of the selenium present in
the syngas. The mercury data were inconclusive for both the charcoal and
permanganate methods.


[0152] In addition to the above gas analysis, samples of the ZnO sorbent
were periodically removed from the dual loop reactor system. These samples were
analyzed for arsenic and selenium content. These data are presented in Table 4. As
can be seen in the data, the arsenic and selenium content increases as the total
amount of operating time increases.

[0153] After 1,500 hours of operation, ZnO sorbent samples removed from
the reactor system were also analyzed for sulfate. The unexposed sorbent sample
was found to have < 0.1% sulfur as sulfate. The sample taken after 1,500 hours of
operation was found to also have < 0.1 % sulfur as sulfate. Thus, the sulfate
concentration after 1,500 hours of operation was essentially identical to the
unexposed sorbent sample indicating that sulfate formation had not occurred.

Example 2
[0154] This example illustrates a process control where in the sulfur
absorption rate was used to predict the amount of air needed to maintain a
balanced removal of sulfur in the absorber and regenerate zones in a system
essentially as illustrated in Figure 3. The following equation was programmed into
the control system:
Air required = alpha X Absorption rate (pounds of sulfur per hour)
where
Alpha = a1 X a2 X a3 X a4
a1 = stoichiometric oxygen required per mole of sulfur in reaction I (1.5 moles of
oxygen per mole of sulfur);
a2 = molar volume of ideal gas at standard conditions (359 cubic feet/lbmole);
a2 = molar weight of sulfur (32 Ib/lbmole); and
a4 = concentration of oxygen in air (0.21 moles of oxygen/ mole of air).
[0155] The calculated air requirement was then used as a remote set point
for the air flow controller. The operators were then allowed to add a bias between -
100 and +100 scfh to allow for any measurement inaccuracies. Figure 7 provides an
example of how well the feed forward control scheme was able to maintain relatively
constant sorbent sulfur loading even during significant changes in the sulfur
absorption rate caused by intentional changes to the syngas feed rate. In Figure 7,
"Sulfur Absorbed" refers to the calculated amount of sulfur removed from the
syngas and loaded onto the sorbent in the absorber. "ROG Sulfur" refers to the
calculated amount of sulfur released from the sorbent during regeneration and
removed in the regeneration off-gas. "Abs-Load" refers to the sulfur loading on the
sorbent determined by samples removed from the absorber standpipe. "Reg-Load"
refers to the sulfur loading on the sorbent determined by samples removed from the
regenerator standpipe. "Sulfur in Clean SynGas" refers to the total (H2S and COS)
present in the effluent syngas from the absorber.

WHAT IS CLAIMED IS:
1. A process for removing impurities from a gas, comprising:
(a) contacting an impurity containing feed gas stream with a solid sorbent
stream in a fluidized absorber zone under conditions sufficient to reduce an impurity
content of the feed gas stream and increase impurity loading of the solid sorbent
stream;
(b) removing an impurity loaded solid sorbent stream from the absorber zone
and transporting at least a portion of the impurity loaded solid sorbent stream to a
first non-mechanical gas seal forming solids transfer zone, the first solids transfer
zone being fluidly connected to a fluidized solids regenerator zone and adapted to
transfer solids to the fluidized regenerator zone at a controllable flow rate in
response to the flow of an aeration gas through the transfer zone;
(c) transferring the impurity loaded solid sorbent stream from the first solids
transfer zone to the fluidized solids regenerator zone and contacting the impurity
loaded solid sorbent stream with a regenerator feed gas in the fluidized solids
regenerator zone to thereby reduce the impurity content of the impurity loaded solid
sorbent stream;
(d) transferring the solid sorbent stream of reduced impurity content from the
fluidized regenerator zone to a second non-mechanical gas seal forming solids
transfer zone, the second solids transfer zone being fluidly connected to the
regenerator and absorber zones and adapted to transfer the solid sorbent stream of
reduced impurity content to the absorber zone at the same flow rate as the flow rate
of the solid sorbent stream of reduced impurity into the second solids transfer zone;
and
(e) recovering a purified gas stream from the absorber zone.
2. The process according to claim 1, additionally comprising:
transporting at least a portion of the impurity loaded solid sorbent stream
removed from the fluidized absorber zone to a third non-mechanical gas seal forming
solids transfer zone, the third solids transfer zone being fluidly connected for
receiving a solids stream from a downstream portion of the fluidized absorber zone

and for delivering a solids stream to an upstream portion of the fluidized absorber
zone, the third solids transfer zone being adapted to transfer solids to the fluidized
absorber zone at a controllable flow rate in response to the flow of an aeration gas
through the transfer zone; and
transferring the impurity loaded solid sorbent stream from the third solids
transfer zone to the upstream portion of the fluidized absorber zone for contact with
the impurity containing feed gas stream.
3. The process according to claim 1, additionally comprising:
measuring the pressures of the absorber and regenerator zones;
determining the pressure difference between said zones;
comparing said pressure difference to at least one predetermined pressure
difference value; and
adjusting the pressure in at least one of said absorber and regeneration zones
in response to said measuring step.
4. The process according to claim 2, additionally comprising:
measuring the pressures of the absorber and regenerator zones;
determining the pressure difference between said zones;
comparing said pressure difference to at least one predetermined pressure
difference value; and
adjusting the pressure in at least one of said absorber and regeneration zones
in response to said measuring step.
5. The process according to claim 3 or claim 4, wherein said predetermined
pressure difference value comprises a pressure difference in the range of between
about 1 psig and about 20 psig.
6. The process according to claim 5, wherein said predetermined pressure
difference value comprises a pressure difference in the range of between about 2
psig and about 10 psig.

7. The process according to claim 3 or claim 4, wherein said adjusting step
comprises adjusting the pressure of the regenerator zone.
8. The process according to claim 3 or claim 4, wherein said adjusting step
comprises adjusting the pressure of impurity laden gases exiting the regenerator
zone.
9. The process according to any one of claims 1 to 4, additionally comprising:
determining a quantitative impurity removal rate in the absorber zone;
comparing said impurity removal rate to a predetermined control value; and
adjusting the flow rate of the regenerator feed gas fed to said regenerator
zone in response to said comparing step.
10. The process according to any one of claims 1 to 4, additionally
comprising:
determining a quantitative impurity removal rate in the absorber zone;
determining a quantitative impurity removal rate in the regenerator zone;
comparing said impurity removal rates to a predetermined control value; and
adjusting the flow rate of the regenerator feed gas fed to said regenerator
zone in response to said comparing step.
11. The process according to any one of claims 1 to 4, additionally
comprising:
determining impurity loading of a sample of the impurity loaded sorbent
stream removed from the absorber zone;
comparing said impurity loading to a predetermined control value; and
adjusting the flow rate of a regenerator feed gas fed to said regenerator zone
in response to said comparing step.
12. The process according to any one of claims 1 to 4, wherein said first
solids transfer zone comprises a J-Leg.

13. The process according to any one of claims 1 to 4, wherein said second
solids transfer zone comprises a loop seal.
14. The process according to any one of claims 1 to 4, wherein said impurity
loaded sorbent stream is contacted with oxygen in the fluidized regenerator zone.
15. The process according to claim 14, wherein said impurity loaded sorbent
stream is contacted with a mixture of oxygen and at least one inert gas in the
fluidized regenerator zone.
16. The process according to any one of claims 1 to 4, wherein a cyclone
separator separates said impurity loaded sorbent stream and said purified gas
removed from the absorber zone.
17. The process according to claim 16, wherein said impurity loaded sorbent
stream leaving the cyclone separator passes through a gas stripper.
18. The process according to any one of claims 1 to 4, wherein the
temperature of the fluidized absorber zone ranges from 600 to 1200°F.

19. The process according to claim 18, wherein the temperature of the
fluidized absorber zone ranges from 700 to 10000F.
20. The process according to any one of claims 1 to 4, wherein the pressure
of the impurity-containing feed gas ranges from 100 to 1200 psig.

21. A process according to any one of claims 1 to 4, wherein the impurity
comprises at least one material selected from the group consisting of sulfur
compounds, arsenic and compounds thereof, and selenium and compounds thereof.
22. The process according to any one of claims 1 to 4, wherein the solid
sorbent stream comprises at least one active metal oxide selected from the group

consisting of iron oxide, zinc oxide, zinc ferrite, copper ferrite, copper oxide,
vanadium oxide, or mixtures thereof.
23. The process according to any one of claims 1 to 4, wherein the solid
sorbent stream has an average particle diameter from 50 to 140 microns.
24. The process according to any one of claims 1 to 4, wherein said impurity
containing feed gas stream is contacted with said solid sorbent stream in said
fluidized absorber zone for a residence time of about 3 to about 25 seconds.
25. The process according to claim 24, wherein the residence time in the
fluidized absorber zone ranges from 3 to 10 seconds.
26. The process according to any one of claims 1 to 4, wherein said impurity
loaded solid sorbent stream is contacted with said regenerator feed gas in said
fluidized solids regenerator zone for a residence time of from about 3 to about 25
seconds.
27. The process according to any one of claims 1 to 4, wherein the impurity
content of the impurity loaded sorbent exiting the absorber zone ranges from 10% to
90% of the impurity adsorption capacity of the sorbent.

28. The process according to claim 27, wherein the impurity content ranges
from 30% to 75% of the impurity adsorption capacity of the sorbent.
29. The process according to any one of claims 1 to 4, wherein the arsenic
content of the impurity loaded sorbent exiting the absorber zone ranges from 0 to
3000 ppm.
30. The process according to any one of claims 1 to 4, wherein the purified
gas stream recovered from the fluidized absorber zone has a sulfur level of less than
or equal to 50 ppm.

31. The process according to claim 30, wherein the purified gas stream has a
sulfur level of less than or equal to 20 ppm.
32. The process according to claim 31, wherein the purified gas stream has a
sulfur level of less than or equal to 10 ppm.
33. The process according to any one of claims 1 to 4, wherein the
temperature of the fluidized regenerator zone ranges from 900 to 14500F.
34. The process according to claim 33, wherein the temperature of the
fluidized regenerator zone ranges from 1200 to 1450°F.
35. The process according to any one of claims 1 to 4, further comprising
heating the fluidized regenerator zone by at least one of the following: 1) adding a
pyrophoric additive; 2) adding a supplementary fuel; and 3) using a dry gas
preheating system.
36. The process according to any one of claims 1 to 4, wherein said first
solids transfer zone comprises a J-Leg.
37. The process according to claim 36, wherein the said first solids transfer
zone comprises:
(a) a descending pipe in fluid communication with a holding vessel; and
(b) a transfer pipe in fluid communication with the descending pipe to transfer
the impurity loaded sorbent from the descending pipe to the fluidized regenerator
zone;
and wherein the angle between the descending pipe and the transfer pipe is
less than or equal to 90°.
38. The process according to claim 37, wherein the diameter of the transfer
pipe is less than the diameter of the holding vessel.

39. The process according to claim 38, where in the descending pipe
comprises a flow restrictor.
40. The process according to claim 37, wherein aeration gas is introduced
into one or more of the holding vessel, the descending pipe, and the transfer pipe.
41. The process according to claim 2 or claim 4, wherein said third solids
transfer zone comprises a J-Leg.
42. The process according to claim 41, wherein the said third solids transfer
zone comprises:

(a) a descending pipe in fluid communication with a holding vessel; and
(b) a transfer pipe in fluid communication with the descending pipe to transfer
the separated impurity loaded sorbent from the descending pipe to the fluidized
absorber zone;
and wherein the angle between the descending pipe and the transfer pipe is
less than or equal to 90°.
43. The process according to claim 42, wherein the diameter of the transfer
pipe is less than the diameter of the holding vessel.
44. The process according to claim 43, where in the descending pipe
comprises a flow restrictor.
45. The process according to claim 42, wherein aeration gas is introduced
into one or more of the holding vessel, the descending pipe, and the transfer pipe.
46. A fluidized reactor system for removing impurities from a gas, comprising:
(a) a fluidized absorber adapted for contacting an impurity containing feed gas
stream with a solid sorbent stream zone under conditions sufficient to reduce the

impurity content of said feed gas stream and increase the impurity loading of the
solid sorbent stream;
(b) a fluidized solids regenerator adapted for contacting an impurity loaded
solid sorbent stream with a regeneration gas under conditions sufficient to reduce
the impurity content of said impurity loaded solid sorbent stream;
(c) a first non-mechanical gas seal forming solids transfer device in fluid
communication with said fluidized absorber, said fluidized solids regenerator, and a
supply of aeration gas, said first non-mechanical gas seal forming solids transfer
device being adapted and arranged to receive an impurity loaded solid sorbent
stream from said absorber and to transport said impurity loaded solid sorbent stream
to said fluidized regenerator at a controllable flow rate in response to said aeration
gas; and
(d) a second non-mechanical gas seal forming solids transfer device fluidly
connected to said fluidized regenerator and said fluidized absorber, and being
adapted to receive a solid sorbent stream of reduced impurity content from said
fluidized regenerator and to transfer said solid sorbent stream of reduced impurity
content to said fluidized absorber without changing the flow rate of said solid sorbent
stream of reduced impurity content.
47. The system according to claim 46, additionally comprising:
a third non-mechanical gas seal forming solids transfer device fluidly
connected to a downstream portion of said fluidized absorber, an upstream portion of
said fluidized absorber, and a supply of aeration gas, and being adapted and
arranged to receive a solids stream from the downstream portion of the fluidized
absorber and transfer solids to the upstream portion of said fluidized absorber at a
controllable flow rate in response to said aeration gas.
48. The system according to claim 47, wherein said third non-mechanical gas
seal forming solids transfer device comprises a J-Leg.
49. The system according to claim 48, wherein said third non-mechanical gas
seal forming solids transfer device comprises:

(a) a descending pipe in fluid communication with a holding vessel; and
(b) a transfer pipe in fluid communication with the descending pipe to transfer
the impurity loaded sorbent from the descending pipe to the fluidized absorber;
and wherein the angle between the descending pipe and the transfer pipe is
less than or equal to 90°.
50. The system according to claim 46, wherein said first non-mechanical gas
seal forming solids transfer device comprises a J-Leg.
51. The system according to claim 50, wherein said first non-mechanical gas
seal forming solids transfer device comprises:

(a) a descending pipe in fluid communication with a holding vessel; and
(b) a transfer pipe in fluid communication with the descending pipe to transfer
the impurity loaded sorbent from the descending pipe to the fluidized regenerator;
and wherein the angle between the descending pipe and the transfer pipe is
less than or equal to 90°.
52. The system according to claim 49 or claim 51, wherein the diameter of the
transfer pipe is less than the diameter of the holding vessel.
53. The system according to claim 52, wherein the descending pipe
comprises a flow restrictor.

54. The system according to claim 49 or claim 51, wherein at least one of the
holding vessel, the descending pipe, and the transfer pipe is configured to receive
the aeration gas.
55. The system according to claim 46, wherein said second non-mechanical
gas seal forming solids transfer device comprises loop seal.
56. The system according to claim 46, additionally comprising:

one or more sensors adapted and arranged to measure the pressure of an
effluent gas of the absorber and an effluent gas of the regenerator or to measure the
pressure differential between the two effluent gases;
a controller connected to said one or more sensors, the controller configured
to receive pressure or pressure differential input measurements from said one or
more sensors and to compare the pressure difference between the two effluent
gases to a predetermined pressure difference value, said controller also being
connected to a controllable valve adapted and arranged to adjust pressure of the
effluent gas of the regenerator based on instructions received from the controller.
57. The system according to claim 46, additionally comprising:
a controller configured to receive inputs enabling determination of a
quantitative impurity removal rate in the absorber and configured to compare the
impurity removal rate to a predetermined control value, said controller being
connected to a controllable valve adapted and arranged to adjust the flow rate of the
regeneration gas fed to said regenerator based on instructions received from the
controller.
58. The system according to claim 46, further comprising a cyclone separator
adapted and arranged to separate an effluent from the absorber into an impurity
loaded sorbent stream and a purified gas.
59. The system according to claim 58, further comprising a gas stripper
adapted and arranged to receive the impurity loaded sorbent stream leaving the
cyclone separator.

ABSTRACT
A fluidized reactor system for removing
impurities from a gas and an associated process are provided. The system includes a fluidized absorber for contacting a feed gas with a sorbent stream to reduce the impurity content of the feed gas; a fluidized solids regenerator for contacting an impurity loaded sorbent stream with a
regeneration gas to reduce the impurity content of the sorbent stream; a first non-mechanical gas seal forming solids
transfer device adapted to receive an impurity loaded sorbent stream from the absorber and transport the impurity
loaded sorbent stream to the regenerator at a controllable
flow rate in response to an aeration gas; and a second non-mechanical gas seal forming solids transfer device adapted
to receive a sorbent stream of reduced impurity content
from the regenerator and transfer the sorbent stream of reduced impurity content to the absorber without changing
the flow rate of the sorbent stream.