FIELD OF INVENTION
The present disclosure relates to a low-pressure process for recovering hydrogen sulphide (H2S)
from a Claus tail gas and a system thereof for absorbing H2S.
BACKGROUND
Increase in crude oil consumption leads to a manifold increase in the air pollution. Crude oil
products contain various types of pollutant which are sufficient enough to deteriorate the
environment if released untreated. A typical off gas stream leaving from crude processing units
comprises of impurities like SOX, NOX, CO and other volatile organic materials.
The quantity of SOX released depends on the nature of the crude being processed, efficiency of
different units, and recovery of sulphur bearing species by the sulphur recovery units (SRU).
Sulfur recovery process removes H2S present in acid gas coming from Amine Regeneration Unit
(ARU) and from Sour Water Stripping Unit (SWSU). Claus process is a well-known process for
removal of sulphur species as elemental sulfur. The Claus based Sulfur Recovery Units (SRU) are
considered to meet the desired sulfur recovery. The three Claus reactor configuration of SRU gives
96%-97% sulfur recovery. Some configurations comprise of reactors that are operated at low
temperature, where sulfur is deposited on the catalyst itself, has sulphur recovery of 99%. To meet
the environmental norms (sulphur recovery of >99.9%) especially for operation of high capacity
sulfur plants, the Claus based SRU is integrated with Tail Gas Treating Unit (TGTU). The Claus
tail gas coming from two Claus reactors of SRU consists of H2S, SO2, COS, CS2, H2O, N2, H2,
CO2, CO, SX etc. and the overall sulfur recovery is 96% (max.). Un-reacted sulfur species i.e. SO2,
COS, CS2 and SX are treated in Tail Gas Treating Unit (TGTU).
A typical TGTU operates at pressure closer to the atmospheric conditions. The tail gas from the
Claus based SRU is the feed to TGTU. The unreacted sulfur containing species are hydrogenated
in a hydrogenator at high temperature using a Co-Mo catalyst. A tail gas waste heat boiler and a
quench column are provided to reduce the temperature of the hydrogenated Claus tail gas and to
remove water vapor. The purpose of this quench column is to create favorable temperature for
successful operation of amine absorber. The amine absorber is a typical absorption column for
selective absorption of H2S in aqueous solution of amine. The treated gas is finally incinerated and
3
the amine solution enriched with H2S is regenerated using low pressure steam. The H2S rich gas
stream leaving the regenerator is recycled to SRU to recover sulfur.
Although, the process available like Shell Claus Offgas Treatment (LTSCOT®), etc. are capable
of recovering 99.9% of H2S from the feed stream, they need high pressure of the Claus tail gas. It
is observed that the Claus tail gases are available at sufficiently low pressures but it is required to
be treated for higher sulphur recovery. In these situations, the above mentioned process does not
work.
US 3752877 discloses a tail gas treating process, in which the tail gas is enriched with H2 to ensure
completion of reactions, cooling reactor effluent to remove water and further treating to recover
H2S by absorption with alkaline solution and/or alkaline salt solution. Rare earth catalyst used
contains Co, Mo, Fe, Cr, V etc. Operating temperature is in the range of 260oC to 430oC. The
disclosure also discloses a reducing gas generator to produce reducing gas mixture which reduces
the oxides of sulphur compounds to H2S.
US 4426369 discloses a low temperature Claus process with upstream water removal. In this
process the sulphur species in gas stream are reduced to H2S or oxidized to SO2, followed by water
removed in quench section to less than 10%(v) in the gas stream. The H2S or SO2 rich stream is
mixed with equivalent amount of SO2 or H2S, respectively, to ensure a 2:1 ration of H2S:SO2
before feeding to a Cold Bed Adsorption (CBA) reactor. SO2 required for mixing is obtained by
bypassing 1/3rd of H2S rich stream downstream of reducing reactor and combusting with oxygen.
H2S required for mixing is obtained by mixing with stoichiometric amount of acid gas containing
H2S. In CBA reactor, by Claus reaction, elemental Sulphur is formed.
US 6506349 discloses a process in which H2S can be selectively absorbed in presence of CO2. The
claim states that by partially recycling regenerated H2S to the inlet of absorber and mixing with
inlet gas stream, the partial pressure of H2S increases in gas stream and selective absorption of H2S
in presence of CO2 will increase. The claim also recommends use of H2S selective amines. Process
is claimed for systems containing H2S, CO2, COS & CS2 or natural gas & CO2. In the former,
where CO2 is rejected, organic solvent is used and in latter, where natural gas is rejected, physical
solvent is used.
4
US 7147691discloses a process in which H2S can be selectively absorbed in presence of CO2. The
absorption process has two absorbers in series. Acid gas or process gas i.e., downstream of tail gas
reactor, containing H2S and CO2, is contacted in first absorber in series. In the first absorber H2S
is absorbed preferentially along with CO2. The treated gas is vented to atmosphere. The rich amine
from the first absorber is routed to the bottom section of second absorber and counter currently
meets H2S rich acid gas from regenerator. Due to high partial pressure of H2S at bottom of
absorber, more amount of H2S is absorbed. The CO2 rich stream leaving the bottom section is
counter currently contacted with regenerated lean amine entering the top of the absorber. CO2 rich
stream leaves the top of second absorber. The acid gas generated from the regenerator will be
relatively rich in the H2S when compared with traditional tail gas regenerator operation.
US 2011/0171115A1 discloses a method and a consolidated apparatus for recovery of sulphur
from acid gases. In this method, the typical configuration of Claus section is adopted like thermal
section followed by catalytic section followed by tail gas section. However, the method claims that
acid gas can be partially bypassed to front end of catalytic section with reheating by process gas
bypass from waste heat boiler. Equipment like Claus converter and Hydrogenation reactor are
clubbed in single shell and quench column and absorber are stacked together. Regenerated acid
gas can be routed to front end of thermal section and or to front end of catalytic section. Acid gas
enrichment is adopted as described in above patents.
Therefore, in order to overcome the above limitations and drawbacks of the prior art, the present
invention discloses a low pressure process for recovering H2S from Claus tail gas and a system for
absorbing H2S.
OBJECTIVE
The primary objective of the present disclosure is to provide a process of recovery of H2S by
processing a Claus tail gas at a low pressure or vacuum.
Yet another objective of the present disclosure is to recover and recycle all the Sulphur compounds
present in the Claus tail gas.
5
Yet another aim of the present disclosure is to provide a system for absorbing the H2S recovered
from the Claus tail gas.
SUMMARY OF THE INVENTION
The present disclosure provides a process for removing and recovering all sulphur species in the
form of hydrogen sulphide (H2S) from low pressure Claus tail gas. The process involves the
conversion of all sulphur species like Sulphur dioxide (SO2), elementary sulphur (Sx), carbonyl
sulphide (COS), and carbon disulfide (CS2) present in the Claus tail gas into hydrogen sulphide
(H2S). The present process requires minimum pressure drop and a blower to pull the process gases
through the system. The recovered H2S from the amine regenerator is recycled back to front end
of Claus section. The present invention also provides a system for recovering the H2Sfrom the low
pressure Claus tail gas.
BRIEF DESCRIPTION OF FIGURE
Further aspects and advantages of the present disclosure will be readily understood from the
following detailed description with reference to the accompanying figures of the drawings. The
figures together with a detailed description below, are incorporated in and form part of the
specification, and serve to further illustrate the embodiments and explain various principles and
advantages but not limiting the scope of the invention.
Figure 1 shows a typical tail gas treating unit (TGTU).
Figure 2 shows the low pressure process for recovering H2S employing additionally a booster
blower and a knock out drum.
Figure 3 shows a flow diagram for “low pressure process for recovery of H2S” employing tail gas
blower, process gas cooler and knock out drum in tail gas treating unit.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
While the invention is susceptible to various modifications and alternative forms, specific
6
embodiment thereof has been shown by way of example in the figures and will be described in
detail below. It should be understood, however that it is not intended to limit the invention to the
particular forms disclosed, but on the contrary, the invention is to cover all modifications,
equivalents, and alternative falling within the spirit and the scope of the invention as defined by
the appended claims.
Before describing in detail the various embodiments of the present invention it may be observed
that the novelty and inventive step that are in accordance with the present invention resides in the
low pressure process for recovering hydrogen sulphide from Claus tail gas and a system for
absorbing the hydrogen sulphide. It is to be noted that a person skilled in the art can be motivated
from the present invention and modify the various steps of the current process and/ or constructions
of current system. However, such modification should be construed within the scope and spirit of
the invention.
Accordingly, the drawing is showing only those specific details that are pertinent to understanding
the embodiments of the present invention so as not to obscure the disclosure with details that will
be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The terms “comprises”, “comprising”, “including” or any other variations thereof, are intended to
cover a non-exclusive inclusion, such that a process or a system that comprises a list of steps or
components does not include only those steps or components but may include other steps or
components not expressly listed or inherent to such process or system, mechanism or setup. In
other words, one or more elements/ parts in the current process or system proceeded by
“comprises” does not, without more constraints, preclude the existence of other steps or elements
or additional elements in the system or mechanism. The following paragraphs explain present
invention and the same may be deduced accordingly.
The Tail gas treating unit (TGTU) of the prior art needs sufficient Claus tail gas pressure to flow
through the unit. But low pressure of the tail gas gives operating problem due to pressure drop
across each equipment. The present invention overcomes the above limitation and discloses a low
pressure process for recovering H2S from Claus tail gas. The process of this invention operates at
pressure values very close to vacuum and incurs very low pressure drop.
7
In the present invention, the low pressure Claus tail gas is heated in a preheater and the temperature
is increased to a value sufficient for operating the hydrogenation reactor. The tail gas exiting the
exchanger is at slight vacuum pressure and undergoes hydrogenation and hydrolysis reactions to
convert the unreacted sulfur containing species i.e. Sulphur dioxide (SO2), elementary sulphur (Sx),
carbonyl sulphide (COS), and carbon disulfide (CS2) of the Claus tail gas to H2S and water. The
gases exiting the hydrogenation reactor are at very high temperature, which need to be brought
down for successful operation of downstream systems. This is done using a waste heat boiler,
which utilizes the excess heat of the hydrogenation reactor exit stream to produce steam. The
quench column separates the water from the gas stream, leaving the waste heat boiler, and further
cools the stream at vacuum pressure.
The gas stream leaving the quench column enters the system for absorbing H2S. The system
comprises a knock out drum for removing mist from the process gas, a blower for increasing the
process gas pressure adiabatically, a process gas cooler, knock out drum for removing any leftover
mist in the process gas and amine section (absorber and regenerator). In order for a successful
operation of the absorber column (in amine section), the desirable stream pressure is kept high and
the temperature low. Since the gas stream is currently at vacuum pressure, it is necessary to
increase the pressure of the stream adiabatically. In order to achieve this, a blower is installed,
which increases the pressure of the stream to values desirable for the successful operation of the
column. The exit from the blower is connected to process gas cooler to reduce the temperature to
a desirable value. One knock out drum is installed before the blower, while another knock out
drum is placed immediately after the process gas cooler, for removal of water mist present in the
process gas before amine section (absorber column).
The absorption column is a typical amine absorber, employing an amine solution for absorption of
H2S from the process gas stream. The absorber for amine absorption is a packed column
comprising a structured packing for efficient mass transfer. The structured packing used in the
present invention has surface area in the range of 125m2/m3 to 350m2/m3. Such packing not only
reduces the pressure drop, but also improves mass transfer efficiency. Moreover, the structured
packing also resists any blockage caused by sulphur during malfunction of quench column. An
8
additional advantage of using this structured packing is in terms of reduction in column size and
hence capital cost.
The amine for H2S absorption is chosen from a group comprising of primary amines, secondary
amines, tertiary amines, sterically hindered amines, physical solvents and a combination of these
amines. The process gas enters the absorber column from the bottom end and meets counter
currently with the amine solution over the packed bed. This results better absorption. The H2S free
gas exits from the top of the column and is incinerated. The rich amine stream comprising amine
enriched with H2S is sent to an amine regenerator.
For successful operation of the blower, a part of the gas stream exiting the absorber column is
recycled to the blower. This is done to maintain the required flow to the blower. In case, this stream
is avoided, during low flow rate of the incipient gas stream, the blower does not develop the
required pressure to the gas stream for better absorption of H2S in the absorber column.
The rich amine solution leaving the absorber column is fed to the amine regenerator column, where
H2S is boiled off by heating the solution by low pressure steam. The gaseous stream exiting the
amine regenerator top is H2S saturated with water vapor, which is sent to the Claus based SRU for
removal of elemental sulfur. The regenerated amine solution is recycled to the amine absorber
column. H2S recovery of more than 99.9% is obtained using Claus based SRU integrated with low
pressure tail gas treating unit.
Accordingly, the present invention provides a process for recovering hydrogen sulphide (H2S)
from Claus tail gas comprising the steps of:
(i) introducing a Claus tail gas at a low pressure to the heat exchanger resulting in an
increase in a temperature of the gas enough for a hydrogenation and hydrolysis of
Sulphur compounds present in the claus tail gas;
(ii) converting the sulphur compounds present in the gas by passing the high temperature
Claus tail gas of the step (i) through the hydrogen reactor consisting of sulphide catalyst
Co-Mo at pressure less than 0.01 kg/cm2g or at vacuum and obtaining a stream
comprising H2S;
9
(iii)introducing the stream as obtained in step (ii) to the wastewater boiler at a pressure less
than 0.01 kg/cm2g or at vacuum and obtaining a cool stream;
(iv) further cooling the stream of step (iii) by passing said stream through the quench
column and obtaining gas stream at a pressure less than 0.01 kg/cm2g or at vacuum;
(v) allowing the gas stream of step (iv) to pass through a system for absorption of H2S
using aqueous solution of alkanol amine and obtaining H2S free process gas and H2S
rich aqueous alkanol amine solution;
(vi) passing the H2S free process gas through incinerator for converting residual sulphur
species to SO2;
(vii)passing the H2S rich aqueous alkanol amine solution of step (v) through a regenerator
for releasing H2S from the stream by applying low pressure stream in the reboiler and
obtaining H2S free alkanol amine solution;
(viii) recycling the H2S free alkanol amine solution of step (vii) by passing through the
series of heat exchangers followed by absorber for further absorption.
In another embodiment of the present invention, the Sulphur compounds present in the claus tail
gas comprises of Sulphur dioxide (SO2), elemental sulphur (Sx), carbonyl sulphur (COS) and
carbon disuphide (CS2).
In another embodiment of the present invention, the SO2 and Sx is converted into H2S by
hydrogenation and COS and CS2 is converted into H2S by hydrolysis reaction.
In another embodiment of the present invention, the Claus tail gas is at a pressure less than 0.02
kg/cm2g.
Yet another embodiment of the present invention, the system for absorbing the H2S gas comprising
the steps of:
(a) passing the gas stream of step (iv) of claim 1 through a knock out drum to remove
the mist and subsequently through the blower for increasing the gas pressure
adiabatically and obtaining hot process gas;
(b) allowing the hot process gas of step (a) to pass through the cooler for cooling and
obtaining cooled hot process gas;
10
(c) passing the cooled hot process gas of step (b) through another knock out drum for
removing any water mist and obtaining mist free gas;
(d) passing the mist free gas of the step (c) at a pressure 0.02 kg/cm2g through the
absorber and
(e) allowing the mixing of the incoming gas stream and alkanol amine solution by
counter current mechanism and thereby resulting in the absorption of the H2S by
alkanol amine solution.
In another embodiment of the present invention, the absorber is operated at a pressure of
0.02kg/cm2g or above.
In another embodiment of the present invention, the hydrogenation reactor is operated at a
pressure of -0.02kg/cm2g or below to covert SO2, Sx, COS and CS2 to H2S.
In another embodiment of the present invention, the quench column is operated at a pressure of -
0.15 kg/cm2g or below to condense water vapors in process gas and to cool the hot stream in the
range of 35oC to 40oC.
In another embodiment of the present invention, the H2S recovery from Claus tail gas is at least
99.9% when compared with total inlet H2S to front end of Claus section.
In another embodiment of the present invention, the alkanol amine belongs to the family of primary
amines, secondary amines, tertiary amines, sterically hindered amines, physical solvents or
combination thereof.
Yet another embodiment of the present invention is to provide a system for recovering hydrogen
sulphide (H2S) from Claus tail gas comprising:
a heat exchanger (1) for increasing the temperature of the low pressure Claus tail gas;
a hydrogenator (2) for conversion of the sulfur species to hydrogen sulphide and water
followed by water waste boiler (3) to decrease the temperature of the stream;
a quench column (4) for the separation of water from the gas stream and for reducing the
pressure to high vacuum;
11
an absorbing system for generation of the hydrogen sulphide free gas and hydrogen
sulphide rich gas stream comprising:
a series of the knock out drum (5, 8) for the removal of the water mist from the
stream;
a blower (6) and a heat exchanger (7) placed between the knock out drums to
increase the gas pressure adiabatically and to increase in the temperature,
respectively;
an amine absorption column (9) for the separation of hydrogen sulphide free gas
(17) recovered from the top end of the column and a hydrogen sulphide rich gas
stream (18) recovered from the bottom of the column;
an amine regenerator column (12) for the separation of the stream into the pure hydrogen
sulphide, hydrogen sulphide saturated with water vapors and amine solution from the
hydrogen sulphide rich gas stream.
In another embodiment of the present invention, the amine absorption column consists of a
structured packing for bed material which gives efficient mass transfer at a low pressure drop
across the column.
In another embodiment of the present invention, the structured packing provides a surface area in
the range of 125 m2/m3 to 350 m2/m3 for better mass transfer at low pressure drop.
In order to have a better understanding, the present invention is explained by the following
experimental work. The experimental work is given by way of illustrations of the present invention
and therefore should not be construed to limit the scope of the present invention.
EXAMPLE
Two existing Maximum Claus Recovery Concept (MCRC) commercial Claus recovery plants
consisting of two trains each with capacity of 2X45 TPD and 2X80.5 TPD were revamped for
testing the process. Figure -3 depicts the process integrated with existing Claus plants.
12
The tail gas from each trains of the Claus plant was combined separately and fed to the Tail gas
treating unit. The tail gas pressure entering to the Tail gas treating unit was at 0.01 kg/cm2g and
having a temperature in the range of 120oC to 130oC. The total sulphur species in terms of H2S,
SO2, CS2, COS and elemental sulphur (Sx) was maximum 1% of the total H2S entering to the Claus
plants.
The gas stream A at a pressure less than 0.02 kg/cm2 was heated in a preheater (1) to increase the
temperature in the range of 235ºC to 245ºC sufficient for the hydrogenation and hydrolysis of the
various Sulphur species present in the Claus tail gas. The heated gas stream (B) at a pressure less
than -0.01 kg/cm2 was then fed to hydrogenation reactor (2) for the hydrogenation and hydrolysis
of the various Sulphur species present in the Claus tail to convert them into hydrogen sulphide.
Since the gas did not have pressure sufficient to pass through the catalyst bed, a tail gas blower
was provided in the downstream of quench column. The sulphur species were converted to H2S
and due to exothermic reactions the temperature of the gas stream increased to 250oC to 300oC.
The catalyst used in the hydrogenation reactor is Co-Mo catalyst.
The hot gas stream (stream C) comprising hydrogen sulphide and water is cooled in waste heat
boiler (3) to 140oC to 180oC and further cooled (stream D) to 35oC to 40oC in quench column (4).
The heat of the gas stream which was released in quench column was removed by quench water
cooler. Since pressure of the Claus tail gas was less, the gas was pulled by tail gas blower and the
waste heat boiler and the quench column were operated at -0.06 kg/cm2g and -0.15 kg/cm2g
respectively.
The cooled gas (stream E) from quench column top was pulled by the blower (6) to develop
pressure from 0.25 kg/cm2g to 0.3 kg/cm2g which is required for absorption of H2S in the alkanol
amine solution and to overcome tail gas treating unit pressure drop. The blower (6) was operated
in adiabatic condition and the process gas temperature increased to 90oC to 100oC at a pressure of
0.25 kg/cm2g to 0.3 kg/cm2g. The hot gas (stream F) leaving the blower was cooled in process gas
cooler and water mist was removed in the knock out drum (5 and 8) placed before the absorber
(9).
13
The gas (stream G) was fed at the bottom of absorber (9) and alkanol amine solution (DEA) fed at
the top of the absorber. The solution rich in absorbed H2S (stream I) was sent to regenerator (12).
The conventional regenerator plant (12) was used for the process to separate H2S from the solution.
The H2S free amine solution was cooled and sent back to the absorber. The gas stream (stream H)
from absorber overhead consisting of less H2S was sent to the conventional incinerator for
incineration (17). Both the units for Claus tail gas treatment were operated at vacuum till quench
column and at positive pressure in the absorber.
The process data of one of the plant i.e., 2X80.5 TPD is given in Table 1 which shows the stream
summary comprising of component flow, temperature and pressure for example. Columns A to J
in the table 1 presents the composition of the various streams passing through the currently claimed
system. The mole rate of H2S in stream A is 0.852 Kg-moles which is increased to the 1.934 Kgmoles
in stream C due to conversion of various Sulphur compounds into the H2S. The mole rate
of COS, SO2, S and CS2 decreases to zero in stream C when compared to stream A. This decrease
is attributed to the hydrogenation and hydrolysis reactions taking place in the hydrogen reactor (2)
and thereby increasing the mole rate of H2S in subsequent streams. From the results summarized
in the table 1, it is clear that only 0.2 Kg-moles (stream H) of the H2S moves into the incinerator
and maximum portion i.e. 1.734 Kg-moles passes into the regenerator (12), wherein alkanol amine
solution is regenerated and H2S gas is recycled back to the front end of Claus tail section.
14
Table 1: Process data of 2X80.5 TPD plant
Total Stream A B C D E
Rate, Kg-moles/hr 755.23 755.23 754.17 754.17 511.84
Temperature, degC 121.6 240 255 160 40
Pressure, Kg/cm2g 0.01 -0.01 -0.06 -0.1 -0.15
Comp. wt rates, Kg-moles/hr
H2S 0.852 0.852 1.934 1.934 1.934
CO2 4.278 4.278 4.378 4.378 4.378
C1 0 0 0 0 0
C2 0 0 0 0 0
H2 11.432 11.432 9.604 9.604 9.604
CO 0.090 0.090 0 0 0
H2O 286.080 286.080 286.826 286.826 44.5
O2 0 0 0 0 0
N2 451.428 451.428 451.43 451.43 451.428
COS 0.003 0.003 0 0 0
SO2 0.426 0.426 0 0 0
S 0.640 0.640 0 0 0
CS2 0.005 0.005 0 0 0
DEA 0 0 0 0 0
Total 755.234 755.234 754.17 754.17 511.84
15
Total Stream F G H I J
Rate, Kg-moles/hr 511.84 511.84 496.72 2015.14 1999.98
Temperature, degC 96.3 45 40 43.8 40
Pressure, Kg/cm2g 0.29 0.15 0.11 0.15 0.11
Comp. wt rates, Kg-moles/hr
H2S 1.934 1.934 0.2 6.14 4.41
CO2 4.378 4.378 4.186 0.1920 0
C1 0 0 0 0 0
C2 0 0 0 0 0
H2 9.604 9.604 9.604 0 0
CO 0 0 0 0 0
H2O 44.5 44.5 31.3 1931.339 1918.1
O2 0 0 0 0 0
N2 451.428 451.428 451.43 0 0
COS 0 0 0 0 0
SO2 0 0 0 0 0
S 0 0 0 0 0
CS2 0 0 0 0 0
DEA 0 0 0 77.47 77.47
Total 511.84 511.84 496.72 2015.14 1999.98

We Claim:
1. A process for recovering hydrogen sulphide (H2S) from Claus tail gas comprising the steps
of:
(i) introducing a Claus tail gas at a low pressure to the heat exchanger resulting in an
increase in a temperature of the gas enough for a hydrogenation and hydrolysis of
Sulphur compounds present in the claus tail gas;
(ii) converting the sulphur compounds present in the gas by passing the high temperature
Claus tail gas of the step (i) through the hydrogenation reactor consisting of sulphide
Co-Mo catalyst at pressure less than 0.01 kg/cm2g or at vacuum and obtaining a stream
comprising H2S;
(iii) introducing the stream as obtained in step (ii) to the wastewater boiler at a pressure
less than 0.01 kg/cm2g or at vacuum and obtaining a cool stream;
(iv) further cooling the stream of step (iii) by passing said stream through the quench
column and obtaining gas stream at a pressure less than 0.01 kg/cm2g or at vacuum;
(v) allowing the gas stream of step (iv) to pass through a system for absorption of H2S
using aqueous solution of alkanol amine and obtaining H2S free process gas and H2S
rich aqueous alkanol amine solution;
(vi) passing the H2S free process gas through incinerator for converting residual sulphur
species to SO2;
(vii)passing the H2S rich aqueous alkanol amine solution of step (v) through a regenerator
for releasing H2S from the stream by applying low pressure steam in the reboiler and
obtaining H2S free alkanol amine solution;
(viii) recycling the H2S free alkanol amine solution of step (vii) by passing through the
series of heat exchangers followed by absorber for further absorption.
2. The process as claimed in claim 1, wherein the Sulphur compounds present in the claus tail
gas comprises of Sulphur dioxide (SO2), elemental sulphur (Sx), carbonyl sulphur (COS)
and carbon disuphide (CS2).
3. The process as claimed in claim 1, wherein the SO2 and Sx is converted into H2S by
hydrogenation and COS and CS2 is converted into H2S by hydrolysis reactions.
17
4. The process as claimed in the claim 1, wherein the Claus tail gas is at a pressure less than
0.02 kg/cm2g.
5. The process as claimed in claim 1, wherein the system for absorbing the H2S gas
comprising the steps of:
(a) passing the gas stream of step (iv) of claim 1 through a knock out drum to remove
the mist and subsequently through the blower for increasing the gas pressure
adiabatically and obtaining hot process gas;
(b) allowing the hot process gas of step (a) to pass through the cooler for cooling and
obtaining cooled process gas;
(c) passing the process gas of step (b) through another knock out drum for removing
remaining water mist and obtaining mist free gas;
(d) passing the mist free gas of the step (c) at a pressure 0.02 kg/cm2g through the
absorber and;
(e) allowing the mixing of the mist free gas stream of step (d) and alkanol amine
solution by counter current mechanism and thereby resulting in the absorption of
the H2S.
6. The process as claimed in claim 1, wherein the absorber is operated at a pressure of
0.02kg/cm2g or above.
7. The process as claimed in claim 1, wherein the hydrogenation reactor is operated at a
pressure of -0.02kg/cm2g or below for conversion of SO2, Sx, COS and CS2 to H2S.
8. The process as claimed in claim 1, wherein the quench column is operated at a pressure of
-0.15 kg/cm2g or below to condense water vapors in process gas and to cool the hot stream
in the range of 35oC to 40oC.
9. The process as claimed in claim 1, wherein the H2S recovery from Claus tail gas is at least
99.9% when compared with total inlet H2S to front end of Claus section.
10. The process as claimed in claim 1, wherein the alkanol amine belongs to the family of
primary amines, secondary amines, tertiary amines, sterically. hindered amines, physical
solvents or combination thereof.
11. A system for recovering hydrogen sulphide (I-12S) from Claus tail gas comprising:
a heat exchanger (1) for increasing the temperature of the low pressure Claus tail gas;
a hydrogenation reactor (2) for conversion of the sulfur species to hydrogen sulphide and
water followed by water waste boiler (3) to decrease the temperature of the stream;
a quench column (4) for the separation of water from the gas stream and for !( ducing the
pressure to high vacuum;
an absorbing system for generation of the hydrogen sulphide free gas and hydrogen
sulphide rich gas stream comprising:
a series of the knock out drum (5, 8) For the removal of the water mist from the
stream;
a blower (6) and a heat exchanger (7) placed between the knock out drums to
increase the gas pressure adiabatically and to increase in the temperature,
respectively;
an amine absorption column (9) for the separation of hydrogen sulphide free gas
(17) recovered from the top end of the column and a hydrogen sulphide rich gas
stream (18) recovered from the bottom of the column;
an amine regenerator column (12) for the separation of the stream into the pure hydrogen
sulphide, hydrogen sulphide saturated with water vapors and amine solution from the
hydrogen sulphide rich gas stream.
12. The system as claimed in claim 10, wherein the amine absorption column (9) consists of a
structured packing for bed material which gives efficient mass transfer at a low pressure
drop across the column.
13. The system as claimed in claim 11, wherein the structured packing provides a surface area
in the range of 125 m2/m3 to 350 m2//m3 for better mass transfer at low ?.re)ssu re drop.