WO2013088116A1

WO2013088116A1 - A water-gas -shift process

Info

Publication number: WO2013088116A1
Application number: PCT/GB2012/052896
Authority: WO
Inventors: Peter Edward James Abbott; Gary Bevan COMBES
Original assignee: Johnson Matthey Public Limited Company
Priority date: 2011-12-15
Filing date: 2012-11-22
Publication date: 2013-06-20
Also published as: GB201408984D0; GB2512758A; CN104066821A; GB201121566D0

Abstract

A process for increasing the hydrogen content of a synthesis gas containing one or more sulphur compounds is described, comprising the steps of (i) heating the synthesis gas and (ii) passing at least part of the heated synthesis gas and steam through a reactor containing a sour shift catalyst, wherein the synthesis gas is heated by passing it through a plurality of tubes disposed within said catalyst in a direction counter-current to the flow of said synthesis gas through the catalyst. The resulting synthesis gas may be passed to one or more additional reactors containing sour shift catalyst to maximise the yield of hydrogen production, or used for methanol production, for the Fischer-Tropsch synthesis of liquid hydrocarbons or for the production of synthetic natural gas.

Description

A WATER - GAS - SHIFT PROCES S

This invention relates to a process for increasing the hydrogen content of a synthesis gas, in particular increasing the hydrogen content of a synthesis gas generated from a carbonaceous feedstock.

Synthesis gas, also termed syngas, comprising hydrogen and carbon oxides (CO and C0₂) may be generated by gasification of carbonaceous feedstocks such as coal, petroleum coke or other carbon-rich feedstocks using oxygen or air and steam at elevated temperature and pressure. Generally, the resulting synthesis gas is hydrogen deficient and to maximise the yield of hydrogen, it is necessary to subject the raw synthesis gas to the water-gas-shift reaction by passing it, in the presence of steam, over a suitable water-gas shift catalyst at elevated temperature and pressure. The C0₂ that is formed is then removed in a downstream gas washing unit to give the desired hydrogen rich product gas. The synthesis gas generally contains one or more sulphur compounds and so must be processed using sulphur-tolerant catalysts, known as "sour shift" catalysts. The reaction may be depicted as follows;

H₂0 + CO → H₂ + C0₂

This reaction is exothermic, and conventionally it has been allowed to run adiabatically, with control of the exit temperature governed by feed gas inlet temperature and composition.

Furthermore, where it is required that only fractional shift conversion is needed to achieve a target gas composition, this is conventionally achieved by by-passing some of the synthesis gas around the reactor. Side reactions can occur, particularly methanation, which is usually undesirable. To avoid this, the shift reaction requires considerable amounts of steam to be added to ensure the desired synthesis gas composition is obtained with minimum formation of additional methane. The cost of generating steam can be considerable and therefore there is a desire to reduce the steam addition where possible.

WO2010/013026 discloses a process for increasing the hydrogen content of a synthesis gas containing one or more sulphur compounds, comprising the steps of (i) heating the synthesis gas and (ii) passing at least part of the heated synthesis gas and steam through a reactor containing a sour shift catalyst, wherein the synthesis gas is heated by passing it through a plurality of tubes disposed within said catalyst in a direction co-current to the flow of said synthesis gas through the catalyst. The resulting synthesis gas may be passed to one or more additional reactors containing sour shift catalyst to maximise the yield of hydrogen production, or used for methanol production, for the Fischer-Tropsch synthesis of liquid hydrocarbons or for the production of synthetic natural gas. While effective, we have found that it is possible to reduce the cost of provision of heat transfer by reducing the required heat transfer area.

Accordingly, the invention provides a process for increasing the hydrogen content of a synthesis gas comprising hydrogen, carbon monoxide, carbon dioxide and steam and containing one or more sulphur compounds, comprising the steps of:

(i) heating the raw synthesis gas and

(ii) passing at least part of the heated raw synthesis gas through a reactor containing a sour shift catalyst to form a shifted gas stream,

wherein the raw synthesis gas is heated by passing it through a plurality of tubes disposed within said catalyst in a direction counter-current to the flow of said synthesis gas through the catalyst.

In the present invention the synthesis gas comprising hydrogen and carbon oxides and containing one or more sulphur compounds may be produced by any method although it is particularly suited to synthesis gas produced by gasification of a carbonaceous feedstock at elevated temperature and pressure. Any known gasification technology may be used. The carbonaceous feedstock may be coal, petroleum coke or another carbon-rich feedstock, such as biomass. Preferably the carbonaceous feedstock is a coal. In coal gasification, a coal powder or aqueous slurry may be partially combusted in a gasifier in a non-catalytic process using oxygen or air and in the presence of steam at pressures up to about 85 bar abs and exit temperatures up to about 1450°C, preferably up to about 1400°C, to generate a raw synthesis gas comprising hydrogen and carbon oxides (carbon monoxide and carbon dioxide) and containing one or more sulphur compounds such as hydrogen sulphide and carbonyl sulphide.

The R ratio, defined as R = ([H₂] - [C0₂])/([CO] + [C0₂]), in the synthesis gas feed may be < 0.6 and preferably is in the range 0.1 to 0.6, more preferably 0.2 to 0.6. R may be readily calculated form the molar concentration of the components in the synthesis gas. Before the synthesis gas is subjected to the water-gas shift reaction, the gas is preferably cooled, optionally filtered and then washed to remove particulates such as coal ash.

The synthesis gas comprises one or more sulphur compounds, such as hydrogen sulphide. In order that the water-gas shift catalysts remain suitably sulphided, the sulphur content of the synthesis gas fed to the water-gas shift catalyst is desirably >250ppm.

If the synthesis gas does not contain enough steam, steam may be added to the synthesis gas, for example by live steam addition or saturation or a combination of these. Steam may be added to the synthesis gas before or after heating. The steam to carbon monoxide ratio of the synthesis gas mixture fed to the first water-gas catalyst is preferably < 1 .8, more preferably 0.2 to 1 .8, most preferably 0.7 to 1 .8. In some embodiments, it may be desirable to operate in the range 0.95 to 1 .8.

The shift catalyst may be any suitably stable and active sulphur-tolerant water-gas shift catalyst. The synthesis gas contains one or more sulphur compounds and so the water-gas shift catalyst should remain effective in the presence of these compounds. In particular so- called "sour shift" catalysts may be used, in which the active components are metal sulphides. Preferably the water-gas shift catalyst comprises a supported cobalt- molybdenum catalyst that forms molybdenum sulphide in-situ by reaction with hydrogen sulphide present in the synthesis gas stream. The Co content is preferably 2-8% wt and the Mo content preferably 5-20% wt. Alkali metal promoters may also be present at 1 -10% wt. Suitable supports comprise one or more of alumina, magnesia, magnesium aluminate spinel and titania. The catalysts may be supplied in oxidic form, in which case they require a sulphiding step, or they may be supplied in a pre-sulphided form. Particularly preferred sour shift catalysts are supported cobalt-molybdate catalysts such as KATALCO K8-1 1 available from Johnson Matthey PLC, which comprises about 3% wt. CoO and about 10% wt. Mo0₃ supported on a particulate support containing magnesia and alumina. It is desirable to adjust the temperature of the synthesis gas so that the temperature is maintained within suitable operating conditions. For instance, after the synthesis gas is washed, thereby significantly cooling it, it may be advantageous to preheat the synthesis gas passing to the tubes. A suitable heat exchanger can be placed on the feed synthesis gas stream. According to the particular details of the process, suitable media for heat exchange with the inlet gas may be, for example, another gas stream at a different temperature, steam or water. Furthermore, using such a heat exchanger, with a bypass provided around it, gives the ability to control the inlet temperature to the tubes, independently of variation in other parameters. In one embodiment, the synthesis gas is pre-heated by using it to cool reacting gases in a water-gas shift reactor fed with a shifted gas stream downstream of the counter- current cooled reactor. In this downstream reactor, the synthesis gas being preheated may flow co-current or counter-current to reacting gas. By cooling the reacting gas in this way it may be possible to enhance the amount of CO conversion in this downstream reactor.

In the present invention, at least part of the temperature adjustment of the synthesis gas before it is fed to the water-gas shift catalyst includes heating it by passing the synthesis gas through a plurality of tubes disposed within the catalyst bed. The synthesis gas is at a lower temperature than the reacting gas stream and accordingly the synthesis gas acts as a cooling medium thereby removing heat from the catalyst bed. A preferred temperature for the synthesis gas fed to the tubes within the catalyst bed is in the range 150 to 250°C. The synthesis gas is heated as it passes through the tubes. The heated synthesis gas recovered from the tubes may be further heated or cooled to provide the desired inlet temperature for the shift catalyst. In one embodiment of the invention, the heated synthesis gas leaving the tubes is cooled before it passes to the catalyst in counter-current flow. In this way significant shift conversion of CO can be accomplished without excessive peak temperatures in the catalyst bed. Such cooling can be by another gas stream, or by heating, or boiling, water.

If desired, the synthesis gas may be divided into first and second streams prior to the water-gas shift stage, with the first stream fed to the shift reactor where it is heated in the tubes and at least a portion passed over the sour shift catalyst, and the second stream, which may be termed the reactor by-pass stream, fed to the shifted gas stream or separately to downstream processes. The reactor by-pass stream may be in the range 0 - 50% vol of the raw synthesis gas, preferably 0 - 30 % vol, more preferably 0 - 20% vol, particularly <10% vol. It is believed that generally the design of the reactor is enhanced by maximising the cooling capability, i.e. by maximising the gas flow through the tubes and not having such a by-pass.

The synthesis gas that does not by-pass the water-gas shift reactor is firstly fed to a plurality of tubes disposed in a bed of sour shift catalyst disposed within the shift reactor. The size of the reactor and the number of tubes is dependent upon the scale and composition of the raw synthesis gas and the required exit composition and may be determined using normal chemical engineering practices. The reactor and tubes should be arranged such that the catalyst may be readily loaded into the reactor and removed from the reactor. The feed to the tubes should be arranged such that the raw synthesis gas, once it has passed through the tubes is fed to the catalyst such that it passes in the opposite direction through the catalyst, i.e. that the flow through the catalyst is counter-current to the flow through the tubes. In this way the temperature profile through the bed may be controlled to minimise steam consumption without excessive by-product methane formation, while minimising the heat transfer area required. Preferably, the reactor comprises a cylindrical shell fitted with a synthesis gas inlet and outlet and containing a bed of a particulate sour shift catalyst arranged so that the heated synthesis gas can flow along a vertical axis through the reactor and catalyst, with a plurality of tubes through which the synthesis gas may flow arranged vertically and co-axially through the catalyst and connected at one end by a suitable header arrangement to a source of synthesis and at the other end by a suitable collector arrangement to the line returning at least a portion of the heated synthesis gas containing steam to the catalyst. The size, pitch and number of tubes may be determined knowing raw synthesis gas composition and temperature and the desired amount of shift and catalyst volume, using normal engineering practices.

The synthesis gas passes through the tubes and is heated thereby cooling the catalyst and reacting gases. The synthesis gas therefore acts as the coolant for the reactor. The heated synthesis gas containing steam is fed to the catalyst. In one embodiment, the heated synthesis gas is divided into first and second streams, with the first stream, optionally combined with steam and passed over the shift catalyst, and the second stream, which may be termed a catalyst bypass stream, fed to the shifted gas stream or downstream processes. This provides a means to control the overall conversion of CO. Where it is required to control the R ratio of the product gas (before or after gas washing downstream to remove C02), 0-50%, of the heated raw synthesis gas may by-pass the catalyst. Where it is desirable to maximise conversion to hydrogen, it is preferred to have minimal (e.g. <10% vol) or no catalyst bypass stream or reactor bypass stream. The synthesis gas and steam mixture is passed at elevated temperature and pressure, preferably temperatures in the range 190 to 420°C more preferably 200 to 400°C, and pressure up to about 85 bar abs, over the first bed of water-gas shift catalyst. The flow-rate of synthesis gas and steam mixture may be such that the gas hourly space velocity (GHSV) through the bed of sulphur-tolerant water-gas shift catalyst in the reactor is > 6000hour^"1 ,

Where there is a bypass of raw synthesis gas around the water-gas shift reactor (reactor bypass), or heated raw synthesis gas around the catalyst (catalyst bypass), it may be desirable to combine them before they are combined with the shifted gas stream or used in downstream processes.

The reactor by-pass stream, catalyst by-pass stream or combined by-pass stream may be subjected to a carbonyl sulphide (COS) hydrolysis step by passing the combined stream over a COS hydrolysis catalyst, such as a particulate alumina or titania based catalyst, disposed in a suitable vessel. In this step, the COS in the by-pass streams is hydrolysed by steam to form H₂S, which may be easier to remove in downstream processes. In such a COS hydrolysis step, essentially no water-gas shift reaction takes place.

Where the objective of the process is to maximise hydrogen yield, the product synthesis gas from the reactor may be fed to one or more additional water-gas shift reactor stages. These may be conventional adiabatic sour shift stages or sour shift performed according to the present invention.

The resulting shifted gas stream may be used in downstream processes for the production of methanol, DME, Fischer-Tropsch liquids or synthetic natural gas (SNG). Where a higher degree of water-gas shift is required, for example when making hydrogen or a low carbon content fuel for combustion in a gas turbine, additional water-gas shift steps may be performed. In such cases, one or more further water-gas shift stages, which may be uncooled or cooled and operated in series or parallel, may be used. Preferably one or two further stages of adiabatic water-gas shift are used in series, with optional cooling before each stage, to maximise CO conversion in the shifted gas stream.

In order to generate a hydrogen-rich synthesis gas the process preferably further comprises the steps of:

(i) cooling a shifted gas stream or a mixture of the shifted gas stream and a bypass stream, to below the dew point to condense water,

(ii) separating the resulting condensate therefrom to form a dry gas stream,

(iii) feeding the dry gas stream to a gas-washing unit operating by means of counter- current solvent flow, to produce a product synthesis gas and

(iv) collecting the product synthesis gas from the washing unit.

The shifted gas stream may be subjected to these steps alone to form a dry shifted gas stream, or as a mixture with a bypass stream. Alternatively, a bypass stream may be separately subjected to these steps to form a dry un-shifted by-pass stream, which is fed to the same or a separate gas washing unit. Where the dry un-shifted gas is fed to the same gas washing unit, preferably this un-shifted stream is fed to the gas washing unit such that the solvent flowing through said unit contacts first with the dry un-shifted synthesis gas and then the dry shifted gas stream.

The cooling step may be performed by heat exchange, e.g. with cold water, to cool the gases to below the dew point at which steam condenses. The resulting condensate, which comprises water and some contaminants, is separated. The gases may be further cooled and dried, e.g. by means of chilled solvent, and then fed to a gas-washing unit operating by means of counter-current solvent flow. In the gas-washing unit, also known as an acid-gas removal (AGR) unit, a solvent suitable for the dissolution/absorption of carbon dioxide flows counter-current to gas flowing through the unit and dissolves/absorbs carbon dioxide present in the gas stream. A small quantity of other gas components in the gas stream, particularly carbon monoxide, will also be co-absorbed. Contaminants present in the gas stream that may poison downstream catalysts, e.g. sulphur compounds such as H₂S & COS, may also be removed to differing extents. Using AGR, C0₂ levels may be reduced to below 5 mole%, on a dry gas basis.

Suitable solvents for absorbing C0₂ are physical solvents, including methanol, other alcohol or glycol products, such as glycols or polyethylene glycol ethers, and propylene carbonate, and chemical solvents, such as activated alkanolamines. Methanol is the preferred solvent where a downstream catalyst is being used. Methanol may be used at temperatures in the range -30 to -70°C and at elevated pressures up to about 75 bar abs. A gas-washing unit may comprise, for example, a column having a solvent inlet near the top and a solvent outlet near the bottom, down which a solvent suitable for the

dissolution/absorption of carbon dioxide flows over one or more perforate trays or packing. The gases passing up through the column contact the solvent and carbon dioxide is

dissolved/absorbed. The gases may leave the column near the top via a synthesis gas outlet. The synthesis gas is cold and may be used to cool the feed gases to the gas-washing unit using suitable heat exchange means such as a spiral wound heat exchanger. In one embodiment, the dry by-pass synthesis gas mixture and dry shifted gas stream are fed separately to the unit, with the separate feeds arranged such that that the solvent contacts first with the dry by-pass synthesis gas mixture and then the dry shifted gas stream. This is in contrast to previous processes, where a synthesis gas mixture is fed to a gas-washing unit so that the solvent contacts the gas mixture in one stage. We have found that by separately feeding the two different gas streams to the unit such that that the solvent contacts first with the dry gas mixture and then the dry shifted gas stream, the efficiency of the process is improved, which offers the potential for reduced CO co-absorption and an increased potential for methanol or liquid hydrocarbon production from a given quantity of synthesis gas.

The process is operated such that the synthesis gas collected from the gas-washing unit has an R ratio suited to the downstream use, such as methanol or DME production, FT hydrocarbon production or SNG production. For the production of methanol or hydrocarbons, the desired stoichiometry ratio, R, of the product synthesis gas is preferably in the range 1 .4 to 2.5. For generating synthetic natural gas (SNG) the range is preferably in the range 2.8 to 3.3.

Alternatively, the sour shift reactor, additional downstream sour shift stage or stages, and gas- washing stage may be operated such that the synthesis gas collected from the gas-washing unit is hydrogen rich, with minimal CO and C0₂ content, where this is desirable. Such hydrogen- rich gas streams may be used in ammonia synthesis, for hydrogenation purposes, for chemicals synthesis or power generation by combustion in a gas turbine with or without additional hydrocarbon fuels. The invention is further illustrated by reference to the accompanying drawings in which;

Figure 1 is a depiction of one embodiment according to the present invention in which a synthesis gas mixture is heated in tubes disposed within a bed of sour shift catalyst, cooled and then passed through the catalyst in a counter-current arrangement, and

Figure 2 is a depiction of a further embodiment according to the present invention in which the synthesis gas mixture is pre-heated in tubes disposed within a second bed of sour shift catalyst, further heated in tubes disposed within a first bed of sour shift catalyst, then passed through the first bed of sour shift catalyst in a counter-current arrangement and then passed through the second bed of sour shift catalyst in a co-current arrangement. In Figure 1 , a synthesis gas 10 containing one or more sulphur compounds is fed to a distributor arrangement 12 disposed within a cylindrical sour shift reactor 14. The distributor arrangement 12 is connected to a plurality of tubes 16 that pass vertically through a bed of particulate Co/Mo sour shift catalyst 18. The synthesis gas is able to pass from the distributor arrangement 12 vertically through the tubes 16 where it is heated thereby cooling the catalyst reactant gases in the catalyst bed 18. The tubes are connected to a receiver arrangement 20 at the other end that collects heated synthesis gas. The heated synthesis gas in line 22 is optionally mixed with steam 24 and the resulting mixture fed to heat exchanger 26 where it is cooled to the desired inlet temperature before being fed via line 28 to the catalyst bed 18. The feed arrangement is such that the synthesis gas and steam mixture passes through the bed of sour shift catalyst 18 vertically in substantially the opposite direction to the gas passing through the tubes 16, i.e. the coolant and reactant gases are flowing counter-currently through the reactor 14. The water-gas shift reaction takes place. The hot shifted synthesis gas recovered from the reactor 14 via line 30 is cooled in heat exchanger 32 (used e.g. for generating steam) then is passed via line 34 to two further heat exchangers 36 and 38 in series. The resulting product synthesis gas 40 may be used in methanol production or sent to one or more water- gas shift stages. A reactor vessel by-pass stream 42 (shown by a dotted line) runs from line 10 to line 34 to allow some of the raw synthesis gas to by-pass the shift reactor. In addition a catalyst by-pass stream 44 (also shown by a dotted line) runs from line 22 to line 30 to allow some of the heated raw synthesis gas to by-pass the shift catalyst.

In Figure 2, heat exchangers 36 and 38 are replaced by a second gas-cooled shift reactor in which the synthesis gas 10 is pre-heated and in which the shifted synthesis gas from the first shift reactor 14 is further reacted. Thus a synthesis gas 10 containing one or more sulphur compounds is fed to a distributor arrangement 50 disposed within a cylindrical sour shift reactor 52. The distributor arrangement 52 is connected to a plurality of tubes 54 that pass vertically through a bed of particulate Co/Mo sour shift catalyst 56. The synthesis gas is able to pass from the distributor arrangement vertically through the tubes where it is pre-heated thereby cooling the catalyst reactant gases in the catalyst bed 56. The tubes are connected to a receiver arrangement 58 at the other end that collects heated synthesis gas. The pre-heated synthesis gas in line 60 is fed to a distributor arrangement 12 disposed within a cylindrical sour shift reactor 14. The distributor arrangement 12 is connected to a plurality of tubes 16 that pass vertically through a bed of particulate Co/Mo sour shift catalyst 18. The pre-heated synthesis gas is able to pass from the distributor arrangement 12 vertically through the tubes 16 where it is heated thereby cooling the catalyst reactant gases in the catalyst bed 18. The tubes are connected to a receiver arrangement 20 at the other end that collects heated synthesis gas. The heated synthesis gas in line 22 is optionally mixed with steam 24 and the resulting mixture fed to heat exchanger 26 where its temperature is adjusted to the desired inlet temperature before being fed via line 28 to the catalyst bed 18. The feed arrangement is such that the synthesis gas and steam mixture passes through the bed of sour shift catalyst 18 vertically in substantially the opposite direction to the pre-heated synthesis gas passing through the tubes 16, i.e. the coolant and reactant gases are flowing counter-currently through the reactor 14. The water-gas shift reaction takes place. The hot shifted synthesis gas recovered from the reactor 14 via line 30 is cooled in heat exchanger 32 (used e.g. for generating steam ) then is passed via line 34 to the shift vessel 52 containing the catalyst bed 56. The feed arrangement is such that the shifted synthesis gas passes through the bed of sour shift catalyst 56 vertically in substantially the same direction to the gas passing through the tubes 54, i.e. the coolant and reactant gases are flowing co-currently through the reactor 52. The water-gas shift reaction takes place. The hot shifted synthesis gas recovered from the reactor 52 via line 62 is cooled in heat exchanger 64 to produce a shifted gas mixture 66. The resulting product synthesis gas 66 may be used in methanol production or sent to one or more further water-gas shift stages. A reactor vessel by-pass stream 42 (shown by a dotted line) runs from line 10 to line 62 to allow some of the raw synthesis gas to by-pass the shift reactors. In addition a catalyst by-pass stream 44 (also shown by a dotted line) runs from line 22 to line 30 to allow some of the heated synthesis gas to by-pass the shift reactor 14.

The invention is further illustrated by reference to the following calculated Examples.

In the following Examples, each example is related to the same synthesis gas composition and molar flow rate. The synthesis gas is a scrubbed gas from a coal-gasifier having a steam:CO ratio about 1 .36.

Example 1 (Comparative)

In this case, the water-gas shift reaction is carried out in one adiabatic fixed bed reactor operated at a gas-hourly space velocity of about 6500IY .

In Out

Mol fraction

H20 0.38685 0.19883

CO 0.28383 0.09503

C02 0.08589 0.27468

COS 0.00015 0.00006

H2S 0.00545 0.00555

Argon 0.00583 0.00583

N2 0.00665 0.00665

NH3 0.00127 0.00127

CH4 0.00075 0.001 14

H2 0.22333 0.41095 In Out

Flow (kgmols/hr) 31849.7 31825.0

T (deg C) 238 439

P (bar abs). 63.8 63

Peak T (deg C) 439

The results show that the CO conversion is about 67% and the peak temperature, at the bottom of the bed is about 440°C. Example 2 (Comparative^')

In this case, the water-gas shift reaction is performed according to WO2010/013026. The gas is heated up in the tubes from 220°C to 381 °C, and then the temperature is adjusted to 350°C, before entering the sour shift catalyst to pass at a space velocity of about 9000IY¹ in co-current flow relative to the cooling gas flow in the tubes.

In catalyst Out catalyst In tubes Out tubes

Mol fraction

H20 0.38685 0.18978 0.38685 0.38685

CO 0.28383 0.08643 0.28383 0.28383

C02 0.08589 0.28335 0.08589 0.08589

COS 0.00015 0.00005 0.00015 0.00015

H2S 0.00545 0.00556 0.00545 0.00545

Argon 0.00583 0.00583 0.00583 0.00583

N2 0.00665 0.00665 0.00665 0.00665

NH3 0.00127 0.00127 0.00127 0.00127

CH4 0.00075 0.00094 0.00075 0.00075

H2 0.22333 0.42014 0.22333 0.22333

Flow (kgmols/hr) 31849.7 31837.0 31849.7 31849.7

T (deg C) 350 399 220 381

P (bar abs). 63.5 62.5 63.9 63.8

Peak T (deg C) 400

Average ΔΤ 46

Relative heat transfer area 1 .98 The peak temperature, near the bottom of the bed is about 400°C. Despite having a significantly higher space velocity than Example 1 , the CO conversion is slightly higher (about 70%). Example 3

In this example according to the invention depicted in Figure 1 , the synthesis gas is heated up in the tubes 16 from 220°C to 303°C and then, without steam addition, cooled to 250°C in exchanger 26, before passing to the sour shift catalyst at a space velocity about 6750IY¹ in counter-current flow relative to the cooling gas flow in the tubes.

The peak temperature, about 2/3 of the way down the bed is about 400°C, as in Example 2, and the CO conversion is also about 70%. This example shows that the current invention is able to achieve the same reduction in peak temperature as that of WO2010/013026, when compared to using an adiabatic fixed bed reactor. However, due to the flow being counter- current, rather than co-current, the average temperature difference (ΔΤ) between the reacting and cooling gas is around 40% higher, reducing the heat transfer area required by almost 50%.

Claims

SYN 70058 WO 2013/088116 PCT/GB2012/052896 12 Claims.

1 . A process for increasing the hydrogen content of a raw synthesis gas comprising

hydrogen and carbon oxides and containing one or more sulphur compounds, comprising the steps of:

(i) heating the raw synthesis gas and

(ii) passing at least part of the heated raw synthesis gas and steam through a reactor containing a sour shift catalyst to form a shifted gas stream,

wherein the synthesis gas is heated by passing it through a plurality of tubes disposed within said catalyst in a direction counter-current to the flow of said synthesis gas through the catalyst.

2. A process according to claim 1 wherein the synthesis gas containing one or more

sulphur compounds is formed by gasification of a carbonaceous feedstock at elevated temperature and pressure, followed by cooling, optionally filtering, and washing the resulting gas stream to remove particulate material.

3. A process according to claim 2 wherein the gasification is performed on a coal powder or aqueous slurry in a gasifier using oxygen or air and in the presence of steam at a pressure up to about 85 bar abs and an exit temperature up to about 1450°C.

4. A process according to claim 2 or claim 3 wherein the steam to carbon monoxide ratio in the synthesis gas is in the range 0.2 to 1 .8, preferably 0.7 to 1 .8.

5. A process according to any one of claims 2 to 4 wherein the R ratio, defined as R = ([H₂]-[C0₂])/([CO]+[C0₂]), in the synthesis gas feed is < 0.6, preferably 0.1 to 0.6, more preferably 0.2 to 0.6.

6. A process according to any one of claims 1 to 5 wherein the synthesis gas is pre-heated by using it to cool reacting gases in a water-gas shift reactor downstream of the counter- current cooled reactor.

7. A process according to any one of claims 1 to 6 wherein the heated synthesis gas is cooled before passing it to the catalyst.

8. A process according to any one of claims 1 to 7 wherein the inlet temperature for the water-gas shift catalyst is in the range 190 to 350°C.

9. A process according to any one of claims 1 to 8 wherein the heated raw synthesis gas is divided into first and second streams, with the first stream passed over the shift catalyst SYN 70058

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and the second stream by-passing the shift catalyst, thereby forming a catalyst by-pass stream.

10. A process according to any one of claims 1 to 9 wherein upstream of the shift stage, the raw synthesis gas containing one or more sulphur compounds is divided into first and second streams, with the first stream fed to the shift reactor where it is heated and at least a portion passed over the sour shift catalyst, and the second stream by-passing the shift reactor, thereby forming a reactor by-pass stream.

1 1 . A process according to claim 9 and claim 10 wherein the catalyst by-pass stream is combined with the reactor by-pass stream, thereby forming a combined by-pass stream.

12. A process according to any one of claims 9 to 1 1 wherein the catalyst by-pass stream and reactor by-pass stream are each < 10 %vol of the raw synthesis gas stream.

13. A process according to any one of claims 9 to 12 wherein the by-pass stream is subjected to a carbonyl sulphide (COS) hydrolysis step by passing the stream over a COS hydrolysis catalyst prior to further downstream processing.

14. A process according to any one of claims 9 to 13 wherein the by-pass stream is mixed with the shifted gas stream.

15. A process according to claim 14 wherein the mixed by-pass and shifted gas stream is subjected to one or more water-gas shift stages to further increase the hydrogen content of the synthesis gas.

16. A process according to any one of claims 1 to 13 further comprising the steps of:

(i) cooling the shifted gas stream, to below the dew point to condense water,

(ii) separating the resulting condensate therefrom to form a dry shifted gas stream,

(iii) feeding the dry shifted gas stream to a gas-washing unit operating by means of counter-current solvent flow, to produce a product synthesis gas and

(iv) collecting the product synthesis gas from the washing unit.

17. A process according to claim 14 or claim 15 further comprising the steps of

(i) combining the shifted gas stream and a by-pass stream selected from the catalyst by-pass stream, the reactor by pass stream, or the combined by-pass stream,

(ii) optionally performing one or more shift stages on the resulting mixture to

increase the hydrogen content thereof, SYN 70058

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(iii) cooling the resulting mixture, to below the dew point to condense water,

(iv) separating the resulting condensates therefrom to form a dry gas mixture,

(v) feeding the dry gas mixture to a gas-washing unit operating by means of

counter-current solvent flow, to produce a product synthesis gas and

(vi) collecting the product synthesis gas from the washing unit.

A process according to claim 1 1 wherein the combined by-pass stream is subjected to steps of

(i) cooling to below the dew point to condense water,

(ii) separation of the resulting condensate to form a dry un-shifted gas mixture,

(iii) feeding the dry un-shifted gas to a gas-washing unit operating by means of counter-current solvent flow, to produce a product synthesis gas and

(iv) collecting the product synthesis gas from the washing unit.

A process according to claim 18 wherein the dry un-shifted gas mixture is fed to a gas washing unit along with a dry shifted gas stream formed according to claim 15 or claim 16, such that the solvent flowing through said unit contacts first with the dry un-shifted gas and then a dry shifted gas stream.

A process according to any one of claims 16 to 19 wherein the shift, by-pass and gas washing stages are operated such that the product synthesis gas has a stoichiometry ratio, R = ([H₂]-[C0₂])/([CO]+[C0₂]), in the range 1 .4 to 3.3.

21 A process according to claim 20 wherein the stoichiometry ratio is in the range 1 .4 to 2.5.