FIELD OF THE INVENTION
The present disclosure relates to a system and process for purification of Syngas from high
ash Indian coal meeting specification of methanol production and recovering high purity CO2
from the syngas. In particular, the present disclosure relates to a low-pressure system and a
process for recovering high purity CO2 from syngas.
BACKGROUND AND PRIOR ART
Generally, the Syngas generated from high ash Indian coal through gasification process
contains typical gas compositions of H2S, CO2, H2, CO, H2O, N2 and NH3. The specifications
of syngas required for methanol production is very stringent where CO2 content is <2%, H2S in
ppb level and NH3 content is nil. Conventionally Syngas is treated in Quench column 1 to
remove any dirt or soluble impurities. The cleaned syngas is then heated to a temperature of
water gas shift reaction in shift reactor. This reaction is exothermic in nature. The hot syngas is
then routed to quench column 2, where any further dirt and soluble impurities are trapped and
removed from the Quench column 2.
Syngas is now free of Ammonia and any other water-soluble impurities is treated in
absorber column where typically Methyl diethanolamine (MDEA) flows counter currently.
The cleaned syngas still contains substantial amount of undesired H2S and CO2 other than
desired H2 & CO. Hence, there is a need for proper adsorbent solution. The rich amine leaving
from the absorber bottom is routed to regenerator, where acid gas (typical compositions of
H2S, CO2 and water vapors) is getting separated.
The acid gases are treated in liquid redox process-based Sulphur Recovery Unit (SRU)
to recover sulphur from H2S and flue gases are leaving to atmosphere in the form of CO2.
Carbon emissions contribute majorly to climate change and it leads to global warming by
increasing the temperature in the atmosphere. Also, which can have serious consequences to
humans and their environment.
Therefore, there is a need in the art to develop a system and a process for recovering
high purity CO2 from Syngas.
The present disclosure discloses a system and a process for purification of Syngas from
high ash Indian coal and separating pure CO2. The process/system disclosed below is devoid
of above limitations.
SUMMARY
The present disclosure relates to a system and process for purification of syngas which meets
the specification of syngas required for methanol production and also provides recovery of
3
high purity CO2 from the syngas in an integrated manner in a low-pressure system reducing
the carbon emissions to the atmosphere.
BREIF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1. is an illustration of a system for purification of syngas for methanol production
along with recovery of pure CO2 according to an embodiment of the present disclosure.
Figure 2. is a detailed illustration of a system for purification of syngas for methanol
production along with recovery of pure CO2 according to an embodiment of the present
disclosure
DETAILED DESCRIPTION
While the invention is susceptible to various modifications and alternative forms, specific
aspect thereof has been shown by way of example 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.
4
The Applicants would like to mention that the examples are mentioned to show only those
specific details that are pertinent to understanding the aspects 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”, or any other variations thereof, are intended to cover a
non-exclusive inclusion, such that a process that comprises a list of components does not
include only those components but may include other components not expressly listed or
inherent to such process. In other words, one or more elements in a system or process
proceeded by “comprises… a” does not, without more constraints, preclude the existence of
other elements or additional elements in the system or process.
Accordingly, the present disclosure relates to system and process for the purification of
syngas from high ash Indian coal for methanol production and recovery of high purity CO2.
The system and process is carried on an integrated manner in a low-pressure system reducing
the carbon emissions to the atmosphere.
The system comprises of one or more quench columns, shift reactor, heater, absorber column,
compressor, cooler, one or more separators, pumps, adsorbent bed and lean amine circuit
contains combinations of Methyl diethanolamine (MDEA) and Piperazine (PZ). An
exemplary system for purification of syngas has been illustrated in the figure 1 and figure 2.
Syngas coming from gasifier battery limit is entering to quench column 1. The syngas enters
from the bottom section of quench column and raises to the top and water is entering from top
of quench column. Quench column provides the contact surface for the syngas and cooling
water. This results in cooling of syngas and condensation of water. The quench water leaves
from the bottom section is going to ETP/closed blow down. The cleaned syngas is heated up
to 240-270 oC in Quench column 1 overhead heater and then enters to shift reactor for water
gas shift reaction.
The syngas entering to shift reactor undergoes the following two major reactions on the
catalyst bed. The water gas shift reaction and hydrolysis reactions occur in the shift reactor.
These reactions are exothermic in nature. The unconverted Carbonyl sulphide is converted to
Hydrogen sulphide and Carbon dioxide.
The water gas shift reaction is:
CO + H2O → CO2 + H2 + Heat (1)
5
The Hydrolysis reaction is:
COS + H2O → H2S + CO2 (2)
The syngas leaving from the shift reactor enters to quench column 2, after the valuable heat is
recovered from the water gas shift reaction. The syngas in quench column 2 leaves from top
of the column to the absorber column.
The absorption column comprises a first inlet, preferably located at the bottom part of the
absorption column, through which syngas stream may be introduced, and a second inlet,
preferably located at the top part of the absorption column, through which the lean amine
(combination of MDEA and PZ) stream to be introduced. The absorption column defines a
volume wherein said syngas stream (stream F) contacts the said lean amine stream. The
absorption column further comprises a first outlet, preferably located at the top part of the said
absorption column, through which a purified syngas stream (Stream G) containing high in
CO, H2 and less in CO2 compared to the syngas stream that was introduced into the said
absorption column, may leave; and a second outlet, preferably located at the bottom part of
the said absorption column to discharge a liquid solution of amine, rich in H2S and CO2 to a
Amine regeneration unit (ARU) and Sulphur Recovery Unit (SRU). The absorption column
may have low pressure drop internals to minimize the pressure drop resulting from the
contacting of lean amine and syngas and to maximize the available contact area between the
said two phases (lean amine and syngas). To maximize available contact area between the two
phases, packaging materials made from either of ceramics, metals or plastics are used. Any
number of packing materials with various size, shape and performance can be utilized. The
packing materials may be dumped or random packing materials, structured packing materials,
grid packing materials. Lean amine can be a combination of MDEA and PZ with varying
concentration to get the desired syngas compositions for methanol production.
The acid gas is treated in SRU to recover sulphur from H2S and flue gases leaving the SRU
can be treated in adsorbent bed via compressor. The outlet of SRU is connected to compressor
and due to increase in compressor discharge pressure, temperature raises and cooled in cooler
and any water vapor is getting condensed in separator. The gas leaving the separator is routed
to adsorbent bed, where H2S getting adsorbed and it contains typically less than 10 PPMV.
The regenerated H2S is then reacted with O2/Air on the adsorbent bed and adsorbed H2S is
routed to SRU, H2S concentration at the inlet of <100 PPMV. The recovered gas from
6
adsorbent bed is going to pressure swing adsorption for separation of CO2 and N2. The high
purity CO2 is then recovered from pressure swing adsorption (PSA) section.
Accordingly, one aspect of the present invention relates to a process for the purification of
syngas which meets the specifications of methanol production along with recovery of high
purity CO2.
In one of the embodiments, the process for the purification of syngas has the following steps:
a) introducing the raw syngas (stream A) to raw syngas cleaning section to attain a
purified raw syngas (1);
b) passing the purified raw syngas (1) through a cleaned syngas conditioning section to
achieve the purified raw syngas (2),
c) passing the purified raw syngas (2) through an acid gas removal section (AGR)
wherein syngas is treated with circulating amine solution to provide the impurity free
syngas and to provide an amine solution rich in CO2 and H2S for producing acid gases
rich in CO2 and H2S;
d) passing the acid gases rich in CO2 and H2S through Sulfur recovery unit (SRU) for
H2S removal and to provide CO2 rich gas;
e) passing the CO2 rich gas through CO2 recovery section for removing H2S impurity
followed by routing the CO2 rich gases (Stream J) to Pressure Swing Adsorption
(PSA) section to achieve 99.9V% or more purified CO2.
In one of the embodiments, the process is an integrated process and carried in a low-pressure
system.
In one of the embodiments, circulating amine solution is a mixture of MDEA, Piperazine and
water.
In yet another embodiment, the circulating amine solution comprises MDEA in the range of
35-40 Wt % and Piperazine in the range of 3-8 Wt %.
In one of the embodiments, the acid gas removal section (AGR) comprises an absorber
column having structure packing with a surface area of 125 to 350 m2
per m3
of packing. This
kind of packing offers a very low pressure drop and high contact area.
7
In one of the embodiments, the process provides syngas which has ratio of H2/CO in syngas
leaving the acid gas removal section (AGR) at around 2.0.
In one of the embodiments, the treatment of acid gas stream in SRU is carried on a liquid
redox process wherein the catalyst is a circulating liquid of iron chelate to provide the CO2
rich gases.
In one of the embodiments, the CO2 rich gases are compressed in CO2 recovery section
preferably to increase the pressure up to 6 Kg/cm2
g and passed through an adsorbent bed
having as adsorbent an oxide of trivalent metal from elements of group VIII in periodic table
to trap H2S.
In one of the embodiments, the process for the purification of syngas has the following steps:
a) introducing the raw syngas (stream A) produced by oxy-blown gasification process in
Quench column-1 wherein it is cooled and contacted with fresh water (Stream B) to
produce purified raw syngas (1),
b) purified raw syngas (1) which is free of impurities like particulate matter, metals, metal
carbonyls of raw syngas (Stream A) leaves the Quench column-1 (as Stream-C) and enters
hydrolysis and shift reactor section where COS is hydrolysed to H2S and ratio of H2 / CO
is increased to the desired level of downstream units,
c) steam is added (as Stream D) to hydrolysis and shift reactor section in order to facilitate
the reactions in this section to achieve the purified raw syngas (2) leaves this section (as
Stream E) is cooled and routed to Quench column-2 is further contacted with circulating
cooling water to cool the gas and excess water is condensed and routed to ETP,
d) the syngas is recovered from Quench column-2 (as Stream F) is routed to Acid gas
removal section consisting of Amine Absorption and Regeneration unit (ARU) and
Sulphur Recovery unit (SRU), wherein syngas is treated with circulating amine solution
having a predefined mixture of MDEA and Piperazine in water to provide the impurity
free syngas (Stream G) which is routed to Methanol production unit and an amine solution
rich in CO2 and H2S which are routed to regeneration column in order to produce acid
gases (Stream H) rich in CO2 and H2S,
e) the acid gases (Stream H) are routed to SRU for H2S removal and provide CO2 rich gas
stream, by circulating liquid catalyst by means of redox reactions to provide CO2 rich gas
stream having H2S < 100 ppmw, leaving SRU (as Stream I), are routed to H2S adsorption
section,
8
f) the CO2 rich gas streams (Stream I) are compressed in H2S adsorption section to a
sufficient pressure in order to meet downstream hydraulic requirement by compressor to
provide pressurized CO2 rich gases followed by cooling in a cooler,
g) the pressurized CO2 rich gases are routed to H2S guard bed, where H2S impurity is
reduced <10 ppmw followed by routing the CO2 rich gases (Stream J) to Pressure Swing
Adsorption (PSA) section,
h) in PSA section, impurities in CO2 rich gases (Stream J) like CH4, H2S and water vapor are
further removed to provide high purity CO2 rich stream (Stream K) as the product.
In one of the embodiments, the process relates to the purification of syngas from high ash
Indian coal.
In one of the embodiments, the process for the purification of syngas from high ash Indian
coal provides syngas purification to meet the inlet specification of methanol production.
In one of the embodiments, the process according to present disclosure provides syngas and
high purity CO2 gas in an integrated manner with significantly reduced CO2 emissions.
In one of the embodiments, the process for the purification of syngas from high ash Indian
coal provides high purity CO2, preferably the purity of CO2 is equal to or greater than 99.9
V%.
In yet another embodiment, the process for the purification of syngas from high ash Indian
coal provides high purity CO2 due to amine solution/solvent having a predefined mixture of
MDEA and Piperazine in water.
In one of the embodiments, amine solvent is a mixture of MDEA in the range of 35-40 Wt %,
Piperazine in the range of 3-8 Wt % and water. In a preferable embodiment, the amine solvent
enters the absorber column of the ARU at 40 oC.
In one of the embodiments, the absorber column or ARU uses structure packing having a
surface area of 125 to 350 m2
per m3
of packing. This kind of packing offers a very low
pressure drop and high contact area.
9
In one of the embodiments, the process according to present disclosure provides syngas
containing H2S (which is poison to Methanol reactor catalyst) in much reduced level,
preferably in ppb level.
In one of the embodiments, the process according to present disclosure provides syngas which
has ratio of H2/ CO in syngas leaving the absorber at around 2.0.
In one of the embodiments, according to the process present disclosure acid gas stream
coming from the top of regenerator column contains CO2 in the range of 85 to 95%V, H2S in
the range of 1 to 0.5%V and H2O is routed to Sulphur recovery unit (SRU).
In one of the embodiments, the treatment of acid gas stream in SRU is carried on a liquid
redox process wherein the catalyst is a circulating liquid of iron chelate to provide the CO2
rich gases.
In one of the embodiments, the CO2 rich gases are compressed in CO2 recovery section
preferably to increase the pressure up to 6 Kg/cm2
g and passed through an adsorbent bed
having as adsorbent an oxide of trivalent metal from elements of group VIII in periodic table
to trap H2S.
In one of the embodiments, the CO2 rich gases leaving the adsorbent bed of CO2 recovery
section are further treated in a Pressure swing adsorber (PSA), where purity of CO2 is
increased to 99.9V% or more.
Another aspect of the present invention relates to a system for the purification of syngas from
high ash Indian coal which meets the specifications of methanol production along with
recovery of high purity CO2.
In one of the embodiments, the present invention relates to a system for the purification of
syngas from high ash Indian coal which meets the specifications of methanol production along
with recovery of high purity CO2 in an integrated manner in a low-pressure system reducing
the carbon emissions to the atmosphere.
In one of the embodiments, the system for the purification of syngas from high ash Indian coal
comprises an absorption column, one or more coolers, one or more separators, pumps,
10
compressors, adsorbent beds, amine circuit, circulating liquid catalyst and wash water flow
circuit.
In one of the embodiments, the system according to present disclosure has multiple sections
linked with each other as described below:
• raw syngas cleaning section,
• cleaned syngas conditioning section,
• acid gas removal (AGR) section,
• Sulfur recovery unit (SRU), and
• CO2 recovery section.
In one of the embodiments, the multiple sections of the disclosed system are linked with each
other and operate in an integrated manner.
In one of the embodiments, the raw syngas cleaning section comprises a quench column
having a fresh-water inlet at top and an inlet for raw syngas from gasification unit at the
bottom.
In one of the embodiments, the cleaned syngas conditioning section comprises a heater, a
hydrolysis and shift reactor, a cooler and an inlet for steam. In a preferred embodiment, the
heater is placed at the inlet of the hydrolysis and shift reactor and the cooler is placed at the
outlet.
In one of the embodiments, the syngas leaving the conditioning section is routed through a
quench column before entering the acid gas removal (AGR) section.
In one of the embodiments, the acid gas removal (AGR) section comprises amine absorption
and regeneration unit (ARU) having an amine absorber column and an amine regeneration
column.
In one of the embodiments, the absorber column of ARU has an inlet for raw syngas at the
bottom and an inlet for amine solution at the top. The absorber column of ARU also has an
outlet for the purified syngas which is routed for methanol synthesis and an outlet for the
amine solution to route to the amine regeneration column.
11
In one of the embodiments, the absorber column of ARU uses structure packing having a
surface area of 125 to 350 m2
per m3
of packing. This kind of packing offers a very low
pressure drop and high contact area.
In one of the embodiments, the amine solvent utilized in the absorber column of ARU is a
mixture of MDEA in the range of 35-40 Wt %, Piperazine in the range of 3-8 Wt % and
water. In a preferable embodiment, the amine solvent enters the absorber column of the ARU
at 40 oC.
In one of the embodiments, the Sulfur recovery unit (SRU) is based on a two-reactor
configuration.
In one of the embodiments, the Sulfur recovery unit (SRU) comprises a first reactor wherein
H2S is removed and a second reactor wherein liquid catalyst is regenerated by contacting with
atmospheric air.
In one of the embodiments, comprises a compressor, cooler, separator, adsorbent bed and
Pressure swing adsorber (PSA).
In one of the embodiments, the CO2 recovery section comprises an adsorber column having an
adsorbent column bed for H2S adsorption. In a preferable embodiment, the adsorbent column
bed having oxide of trivalent metal from elements of group VIII in periodic table as
adsorbent.
In one of the embodiments, the CO2 recovery section comprises an adsorber column having an
adsorption capacity of the adsorbent column bed from 0.2 to 1.0 Kg of H2S per 100 Kg of
adsorbent.
In one of the embodiments, the Pressure swing adsorber (PSA) comprises a layered bed of
solid adsorbents, preferably selected from molecular sieve and activated alumina.
In one of the embodiments, the Pressure swing adsorber (PSA) is useful for removing CH4,
CO and H2O in order to improve the purity of CO2 to 99.9V% or more.
Further salient features of the present invention are discussed in the examples provided below.
12
EXAMPLES
The following examples are given to illustrate the present invention and should not be
construed to limit the scope of the present invention.
Receipt of Raw Syngas: For the current case study, gasifier having an Indian coal processing
capacity of 1700 TPD is being considered. Raw syngas is generated from oxy-blown
Gasification unit which process high ash Indian coal as feed. The total flow rate of the Raw
syngas is 136500 Kg/h and it has the following composition.
VOLUMETRIC % Range
H2O 35-60
H2 0.5-6
CO2 14-34
CO 25-35
CH4 0.4-2
N2 1-5
Ar 0.3-1.5
Particulate Matter, g/nm3 10-100
H2S, ppmv 400-6500
COS, ppmV 50-1100
NH3, ppmv 800-5500
HCN, ppmv 100-600
Cl, ppmw 0.5-11
F, ppmw 3-22
Hg, ppbw 1-3
Ca, ppmw 0.5 - 10
Mg, ppmw 0.5 - 10
Na+K, ppmw 0.5 - 10
Pb, ppmw 0.01 - 0.5
V, ppmw 0.01 - 0.5
Ni & Fe Carbonyls, ppmw 1 - 10
Inlet Raw syngas temperature 350 ± 50 oC
13
The syngas cannot be used directly as it has lot of impurities like H2S, NH3, HCN, COS,
Alkali metals, metal carbonyls and particulate matter. These impurities create many issues in
downstream units i.e. particulate matter causes choking, H2S/COS/NH3 causes acid corrosion
& are poisonous to catalyst, metal & metal carbonyls are poisonous to downstream catalyst.
Hence, the above-mentioned impurities are removed in raw syngas cleaning section.
Raw syngas cleaning section: In this section, the temperature of the raw syngas is cooled
from 350 oC to 40 oC in a series of exchangers and followed by water quench. Water quench
is carried in a quench tower, where hot gas at 180 oC will come into contact with fresh water
at 40 oC. This tower has structured packing of 125 to 350 m2
of surface area /m3
of packing
which offers very low pressure drop. In this tower, Excess water, NH3, particulate matter,
metal and metal halides are completely removed. Further, HCN and H2S are partly removed.
Sour water leaving from the tower bottom is routed to Effluent treatment plant (ETP). The gas
which leaves from the top of the column is at 40 oC. The composition of this gas is further
adjusted to meet the downstream process requirement like ration of H2/CO for Fischer
Tropsch synthesis and Methanol synthesis in cleaned syngas conditioning section.
Cleaned syngas conditioning section: This section consists of heat exchangers, reactors,
coolers and water removal tower. Cleaned syngas is heated up to 240-270 oC from 40 oC in a
heat exchanger by using High Pressure steam. The hot syngas is routed to hydrolysis reactor
and shift reactor.
In hydrolysis reactor following reactions will occur:
COS + H2O →H2S + CO2 + Heat
HCN + H2O→ NH3 + CO + Heat
In shift reactor following reactions will occur:
CO + H2O →CO2 + H2 + Heat
Depending on the ratio of H2/CO the syngas is bypassed around shift reactor. As the
hydrolysis and shift reactions need lot of water in gas phase, steam is added to the syngas.
Amount of steam added depends on required product specifications like H2/CO ratio, typically
for every kg of syngas 0.5 to 0.8 Kg of steam is added. Any relevant commercial catalyst can
be used in hydrolysis and shift reactors.
14
Inlet / outlet conditions of hydrolysis reactor and shift reactor are 234 oC / 236 oC and 270 oC /
445 oC, respectively. The syngas at 445 oC is cooled up to 180 oC in a heat exchanger were
High pressure steam is produced. The syngas is further cooled up to 40 oC in water removal
tower, were, it is contacted with circulating water. Here, water molecule produced in above
reactions and excess steam supplied are condensed. In this process, H2S and NH3 are absorbed
from the syngas into the circulating wash water. The gas leaving the water removal tower will
have predominantly CO – 25 to 35 Wt%; H2 - 3 to 5 Wt%; CO2 - 55 to 65 Wt%; H2S – 0.1 to
1Wt%; H2O – 0.1 to 2 Wt% and CH4 – 1 to 4 Wt%.
The contaminants in this syngas are H2S and CO2 and these are removed in downstream Acid
gas removal (AGR) section.
Acid gas removal (AGR) section: In this section, syngas is contacted with circulating amine
solution which removes both H2S and CO2 to an acceptable level. This section predominantly
consists of an amine absorber and regenerator with associated equipment’s like heat
exchangers, pumps, filter, surge vessels and amine storage system.
The amine solvent is a mixture of MDEA (35-40 Wt %), Piperazine (3-8 Wt %) and water.
Amine enters from top of the absorber column at 40 oC. The absorber column uses structure
packing having a surface area of 125 to 350 m2
per m3
of packing. This kind of packing offers
a very low pressure drop and high contact area. In Syngas H2S and CO2 content are reduced to
100 to 200 ppmv and 1.5-2.5 %V, respectively. The ratio of H2/CO in syngas leaving the
absorber is around 2.0. Syngas leaves the acid gas removal section at 40 oC and meets the
specifications of methanol production and ready for entering methanol production section.
The amine rich in H2S and CO2 leaves the bottom of the absorber and enters amine
regeneration section, where, H2S and CO2 are stripped-off from the amine in a Regenerator
column using steam. From the top of Regenerator column acid gas stream containing CO2 –
85 to 95%V, H2S – 1 to 0.5%V and H2O at saturation leaves for Sulphur recovery unit (SRU).
From the bottom of Regenerator column, amine lean in CO2 and H2S at 125-130 oC leaves and
re-enters the absorber at 40 oC after getting cooled in a series of heat exchangers.
Sulphur recovery unit (SRU): In SRU, from the acid gases rich in CO2 and H2S, H2S from
the acid gases is removed and CO2 is recovered and sent for further product purification. The
SRU is based on a liquid redox process, in which the catalyst is a circulating liquid of iron
15
chelate. It has a two-reactor configuration, wherein, in first reactor H2S is removed as per
below reaction.
H2S (g) → H2S (l)
H2S → H + +HSHS- → H+ + S2-
S
2- + 2 Fe3+ → S + 2Fe2+
The gases leaving the first reactor are rich in product CO2 & saturated with water vapor and it
is at atmospheric pressure and 40 oC. The H2S impurity in the CO2 rich gas is reduced below
100 ppmv. The system is inert to CO2.
In the second reactor, liquid catalyst is regenerated by contacting with atmospheric air. The
following reaction occurs during the catalyst regeneration phase.
O2 (g) → O2 (l)
2Fe2++
0.5 O2 (l) + H2O → 2 Fe3++
2OH
-
The regenerated liquid catalyst is again routed back to the first reactor. From the top of this
reactor excess air leaves at atmospheric pressure and 40 oC. The sulphur is removed from the
liquid catalyst by filtration.
The product CO2 rich gases leaving the SRU are further treated to increase the product CO2
purity. This is done in CO2 recovery section.
CO2 recovery section: This section consists of compressor, cooler, separator, adsorbent bed
and Pressure swing adsorber (PSA).
In this section, CO2 rich gases are compressed to increase the pressure up to 6 Kg/cm2
g. This
increases the gas temperature above 40 oC. As the H2S adsorption can happen at 40 oC, the
compressed gas is cooled to 40 oC and water condensed is removed in a Separator. Gases
leaving the top of Separator are routed to an adsorbent bed having adsorbent as oxide of
trivalent metal from elements of group VIII in periodic table. H2S is adsorbed on to the
adsorbent material and CO2 pass through the bed as an inert. The CO2 rich gas leaving the
Adsorber will have H2S < 10 ppmw. Adsorbtion capacity of the bed is 0.2 – 1.0 Kg of H2S per
100 Kg of Adsorbent.
16
The adsorbed H2S can be regenerated by air, wherein, a part of H2S is converted to Sulphur
and remaining is desorbed as H2S.
The gases leaving the adsorbent bed are treated in a Pressure swing adsorber (PSA) over a
layered bed of solid adsorbents (Molecular sieve and activated alumina), where CH4, CO and
H2O are removed and purity of CO2 is increased to more than 99.9V%.
Figure 1 and Figure 2 describe in detail the process and system of the present invention.
Further, the concentrations of various syngas streams and CO2 gas streams A to J have been
provided in Table 1 below:
Table 1: Stream composition
Stream Description Stream Number
Components Units A B C D E F G H I J K
H2S Wt% 0.3 0.4 0.33 0.48 400
ppmw
0.5 <100
ppmw
<10
ppmw
0
CO2 Wt% 24.5 40.5 42.8 63 6.8 95 95 95 99.99
CH4 Wt% 1.4 2.3 1.4 1.7 1 1 1 1 0
H2 Wt% 1.7 2.9 2.5 3.8 10 0 0 0 0
CO Wt% 29.7 49 18 26.3 69 0 0 0 0
H2O Wt% 39.1 100 0.1 100 32 0.29 1.6 3.4 4 4 0
O2 Wt% 0 0 0 0 0 0 0 0 0
N2 Wt% 2.7 4.5 2.5 4 10.7 0 0 0 0
COS Wt% 0.1 0.2 0 0 0 0 0 0 0
NH3+HCN Wt% 0.08 0 0 0 0 0 0 0 0
Metals +
Metal
carbonyls
ppmw 50 0 0 0 0 0 0 0 0
Particulate
matter
g/nm3 50 0 0 0 0 0 0 0 0
Temp. degC 350 40 240 180 40 60 90 50 40 40
As evident form the above table 1, the process and system according to present invention
provide the specification of syngas (Stream G) required for methanol production and at the
same time recovering high purity CO2 having the purity of CO2 to 99.9V% or more.
17
The system and process of the present disclosure is carried in an integrated manner in a lowpressure system reducing the carbon emissions to the atmosphere and cost of operation.
The advantages of the disclosed invention are thus attained in an economical, practical and
facile manner. While preferred embodiments and example have been shown and described, it
is to be understood that various further modifications and additional configurations will be
apparent to those skilled in the art. It is intended that the specific embodiments herein
disclosed are illustrative of the preferred and best modes for practicing the invention and
should not be interpreted as limitations on the scope of the invention

WE CLAIM:
1. A process for the purification of syngas and production of high purity carbon dioxide
(CO2) having the following steps:
a) introducing a raw syngas (stream A) to raw syngas cleaning section to attain a purified
raw syngas (1);
b) passing the purified raw syngas (1) through a cleaned syngas conditioning section to
achieve the purified raw syngas (2),
c) passing the purified raw syngas (2) through an acid gas removal section (AGR)
wherein syngas is treated with circulating amine solution to provide the impurity free
syngas and to provide acid gases rich in CO2 and H2S;
d) passing the acid gases rich in CO2 and H2S through Sulfur recovery unit (SRU) for
H2S removal and to provide CO2 rich gas;
e) passing the CO2 rich gas through CO2 recovery section for further removal of H2S
impurity followed by routing the CO2 rich gases (Stream J) to Pressure Swing
Adsorption (PSA) section in order to achieve 99.9V% or more purified CO2.
2. The process as claimed in claim 1, wherein the process is an integrated process and carried
in a low-pressure system.
3. The process as claimed in claim 1, wherein the raw syngas is obtained from high ash
Indian coal.
4. The process as claimed in claim 1, wherein the impurity free syngas meets the requirement
of methanol production.
5. The process as claimed in claim 1, wherein the circulating amine solution is a mixture of
Methyl diethanolamine, Piperazine and water.
6. The process as claimed in claim 1, wherein the circulating amine solution comprises
Methyl diethanolamine in the range of 35 to 40 Wt % and Piperazine in the range of 3 to 8
Wt %.
7. The process as claimed in claim 1, wherein the acid gas removal section (AGR) comprises
an absorber column having structure packing with a surface area of 125 to 350 m2
per m3
of packing.
8. The process as claimed in claim 1, wherein impurity free syngas has ratio of H2/CO at
around 2.0.
9. The process as claimed in claim 1, wherein the treatment of acid gas stream in SRU is
carried on a liquid redox process wherein the catalyst is a circulating liquid of iron chelate.
10. The process as claimed in claim 1, wherein the CO2 rich gases are compressed in CO2
recovery section up to a pressure of 6 Kg/cm2
g and then passed through an adsorbent bed
19
having as adsorbent an oxide of trivalent metal from elements of group VIII in periodic
table to trap H2S.
11. A system for the purification of syngas having the following sections:
• raw syngas cleaning section,
• cleaned syngas conditioning section,
• acid gas removal (AGR) section,
• Sulfur recovery unit (SRU), and
• CO2 recovery section,
wherein the sections are linked with each other in the order specified and operate in an
integrated manner.
12. The system as claimed in claim 9, wherein the raw syngas cleaning section comprises a
quench column having a fresh-water inlet at top and an inlet for raw syngas from
gasification unit at the bottom.
13. The system as claimed in claim 9, the cleaned syngas conditioning section comprises a
heater, a hydrolysis and shift reactor, a cooler and an inlet for steam.
14. The system as claimed in claim 11, wherein the heater is placed at the inlet of the
hydrolysis and shift reactor and the cooler is placed at the outlet.
15. The system as claimed in claim 9, comprising a quench column before the acid gas
removal (AGR) section.
16. The system as claimed in claim 9, wherein the acid gas removal (AGR) section comprises
amine absorption and regeneration unit (ARU) having an amine absorber column and an
amine regeneration column.
17. The system as claimed in claim 9, the absorber column of ARU has structure packing
having a surface area of 125 to 350 m2
per m3
of packing.
18. The system as claimed in claim 9, wherein the Sulfur recovery unit (SRU) is based on a
two-reactor configuration.
19. The system as claimed in claim 18, wherein the Sulfur recovery unit (SRU) comprises a
first reactor wherein H2S is removed and a second reactor wherein liquid catalyst is
regenerated by contacting with atmospheric air.
20. The system as claimed in claim 9, wherein the CO2 recovery section comprises a
compressor, cooler, separator, adsorbent column bed and Pressure swing adsorber (PSA).
21. The system as claimed in claim 18, wherein the adsorbent bed having oxide of trivalent
metal from elements of group VIII in periodic table as adsorbent.
22. The system as claimed in claim 18, wherein adsorption capacity of the adsorbent column
bed is from 0.2 to 1.0 Kg of H2S per 100 Kg of adsorbent.
20
23. The system as claimed in claim 18, wherein the Pressure swing adsorber (PSA) comprises
a layered bed of solid adsorbents, preferably selected from molecular sieve and activated
alumina.