GB2467292A

GB2467292A - Processing waste gas

Info

Publication number: GB2467292A
Application number: GB0821450A
Authority: GB
Inventors: John Andrew Gordon Brown; David John Hanstock
Original assignee: PROGRESSIVE ENERGY Ltd
Current assignee: PROGRESSIVE ENERGY Ltd
Priority date: 2008-11-24
Filing date: 2008-11-24
Publication date: 2010-07-28
Anticipated expiration: 2028-11-24
Also published as: GB2467292B; GB0821450D0

Abstract

Apparatus and method for processing waste gas comprising carbon monoxide, comprises a humidifier 11 for humidifying the waste gas, a water shift reactor 15 arranged to receive the humidified waste gas and to produce a reaction product comprising at least carbon dioxide and hydrogen, a cooler 16 arranged to cool the reaction product and a separator arranged at least partially to separate the carbon dioxide and hydrogen from the cooled reaction product. Preferably a particulate filter 18 such as a cyclone, semi-porous membrane, electrostatic precipitator, fabric filter or ceramic filter is also provided to remove particulate material from waste gas. Advantageously the apparatus is used to process by-product or waste gases exiting carbon-based industrial processes such as a blast furnace used to produce iron and steel.

Description

WASTE GAS PROCESSING

Field of the Invention

The present invention relates to the processing of waste gas and in particular waste gas containing carbon monoxide as well as other constituents.

Background of the Invention

By-product or waste gases exiting some carbon-based industrial processes (one example of which is a blast furnace used in the production of iron and steel) contain, amongst other constituents, carbon monoxide. This carbon monoxide may be burned to release the chemical energy contained therein. The heat produced may be used to generate steam or hot water, which may then be usefully employed. One example of beneficial use could be the production of electricity via a steam expansion turbine.

Other possible routes by which the energy in the carbon monoxide could be recovered are by combustion (typically following some cleaning process) in a gas turbine or in a reciprocating engine.

Burning this carbon monoxide either in a steam-or hot water-boiler or a gas turbine or in a reciprocating engine produces carbon dioxide. This is usually emitted into the atmosphere, where it is deemed to be a contributor toward global warming.

Some of the other gases exiting the industrial processes mentioned above may also contribute to the energy beneficially recovered into the steam or hot water, and possibly electricity. Other constituents of the gases that do not contribute to the beneficial recovery of energy by burning may include particulate material and water vapour.

Restricting the emission of carbon dioxide may be hampered by the presence of these other constituents of the waste gases.

Therefore, there is required a method and apparatus for waste gas processing that overcomes these problems.

Summary of the Invention

In accordance with a first aspect of the present invention there is provided apparatus for processing waste gas comprising carbon monoxide, the apparatus comprising: a humidifier for humidifying the waste gas; a water shift reactor arranged to receive the humidified waste gas and to produce a reaction product comprising at least carbon dioxide and hydrogen; a cooler arranged to cool the reaction product; and a separator arranged at least partially to separate the carbon dioxide and hydrogen from the cooled reaction product. Waste gas may be a by-product from many different types of industrial processing including, for instance, blast furnaces, smelters, petrochemical and other bulk chemical manufacturing. The apparatus may be suitable for processing large quantities of gas containing many different constituents, but at least carbon monoxide in relatively large concentration. Rather than simply burning off the carbon monoxide and attempting to recover a proportion of its chemical energy (but in the process contributing to atmospheric carbon dioxide) the apparatus may provide both a useful fuel (hydrogen) that may be utilised without any carbon dioxide release and a cleaner source of carbon dioxide in a suitable state for convenient collection without a significant proportion of impurities that may otherwise hinder such collection and confinement.

The waste gas described is typically lost or released to the atmosphere as part of an industrial process rather than being deliberately generated. Therefore, town gas or syngas (synthesis gas) may not be considered a waste gas as it is a primary product typically formed from coal, coke, petcoke and/or natural gas, for instance, and required in its own right (e.g. in ammonia production or for power generation) . Deliberately generated high carbon monoxide containing gases of these types typically may have a relatively high pressure (e.g. 10 of bar gauge or above); the generating process may be designed accordingly.

Moreover, waste gas may instead form at relatively low pressures (under 10 bar gauge) and with high concentrations of impurities. Where a gas has historically been released to the atmosphere in an uncontrolled manner (e.g. through chimneys) this may give a further indication of a waste gas.

Smelters and blast furnaces provide examples of such waste gas emission but other industrial processes also generate waste gas of this type. Waste gas may also be considered a problem for disposal rather than a useful product in certain circumstances. Waste gases are often regulated and controlled to some extent.

The apparatus provides an advantageous thermodynamic arrangement to whereby, for instance, heat generated by a water shift reaction may be removed by the cooler or coolers so that subsequent processes carried out by the apparatus may be operated more efficiently. This heat may be recovered in a useable state and may at least partially help to heat the waste gas during an early stage, e.g. pre-shift superheat ing.

The apparatus provides reduced emissions of carbon dioxide into the atmosphere by adding saturation or humidification, water shift, heat recovery and preferably acid gas removal stages. This flow scheme provides improved thermodynamic characteristics compared to prior art methods.

Preferably, where the waste gas further comprises or contains sulphur compounds and the reaction product further comprises or contains hydrogen suiphide, the apparatus may further comprise: an acid gas remover arranged to remove hydrogen sulphide from the cooled reaction product. This stage may be used to remove sulphur containing contaminants that may otherwise hinder carbon dioxide transport and storage. The waste gas and reaction product may contain other compounds as well.

Optionally, the apparatus may further comprise a sulphur extraction reactor for recovering sulphur from the removed hydrogen suiphide. This further adds value to the process by generating useful sulphur for use as a primary feedstock to other processes.

Optionally, the apparatus may further comprise a particulate filter arranged to remove particulate material from the waste gas. This is particularly advantageous for waste gas from industrial process such as blast furnaces or smelters that contain large quantities of solid phase contaminants.

Optionally, the particulate filter is selected from the group consisting of: cyclone separator, fabric filter, baghouse, sintered filter, ceramic filter, semi-porous membrane and electrostatic precipitator. Other particulate filters may also be suitable.

Optionally, the apparatus may further comprise a compressor for compressing the recovered carbon dioxide.

This provides a convenient form for transporting or exporting the carbon dioxide for later use, storage or disposal.

Preferably, the apparatus may further comprise a heater for heating the humidified waste gas. Heat may be required to allow the water shift reaction to be performed more efficiently and/or more quickly with improved yield and/or to extend the life of the catalyst.

Optionally, the apparatus may further comprise a wet scrubber arranged to remove water soluble salts and/or particulate material from the waste gas and further (or at an earlier stage) humidify the waste gas. Again, this may be used depending on the composition of the waste gas.

Optionally, the cooler may be further arranged to recover condensed water. Cooling the product of the water shift reaction may precipitate out liquid water. This may then be re-used upstream.

Optionally, the apparatus may further comprise a wet scrubber arranged to remove water soluble salts and/or particulate material from the waste gas and further humidify the waste gas. The wet scrubber may act as both a filter (either or both solid and dissolved impurities) and partial saturator to increase the water content (vapour or steam) of the waste gas.

Preferably, the apparatus may further comprise a water treatment plant for cleaning the recovered condensed water and supplying the cleaned water to the wet scrubber. The water treatment plant may also be used to clean or process any water precipitated out or otherwise recovered within the apparatus as a whole. Following water treatment the recovered water may be re-used where necessary.

Optionally, the wet scrubber may be a water sprayer or a Venturi scrubber. Other wet scrubbers may be used where

suitable.

Preferably, the humidifier may be a steam injector.

This adds water content necessary for the water shift reaction and may also be used simultaneously to heat the waste gas to a suitable temperature. The use of steam may therefore reduce the requirements of further separate heaters, i.e. saturate and heat in a single step.

Optionally, the apparatus may further comprise a pressuriser arranged to pressurise the waste gas before entering the humidifier. The pressuriser may be a compressor or other means for raising the pressure of the waste gas. Increasing the pressure may increase the potential water saturation level leading to a higher water content when humidified by steam or other means.

Advantageously, the pressuriser may be configured to raise the pressure of the waste gas to above 20 bar gauge.

This particular pressure region increases the efficiently of subsequent stages including the water shift reaction and the acid gas removal, where present. A range of pressures including 10-30 or 15-25 bar gauge may also improve efficiency, for instance.

Optionally, the apparatus may further comprise a heater for heating the humidified waste gas. The heater may be electric driven or by other fuel means or derived from the process that generated the waste gas or utilise some or all of the heat generated in the shift reaction.

Preferably, the heater may be arranged to raise the temperature of the humidified waste gas to around 280°C.

This may also be a relative rise in temperate of 30°C, i.e. starting at around 250°C. A range of temperatures at this stage may be advantageous such as for instance, 270-290°C or 260-300°C.

Optionally, the apparatus may further comprise a filter after the cooler(s) configured to remove vapour-phase contaminants (eg. mercury, arsenic) from the gas. This may be required if the waste gas is expected to contain heavy metals or similar contaminants.

Preferably, the filter may comprise activated carbon.

Preferably, the apparatus may be arranged to receive the waste gas at a temperature in the range 200°C to 400°C.

Alternatively, this may be the typical output temperature of a blast furnace, for instance.

Preferably, the apparatus may be arranged to receive the waste gas at a pressure in the range 2-5 bar gauge.

Alternatively, this may be the typical output pressure of a blast furnace, for instance.

Advantageously, the cooler(s) may be arranged to cool the reaction product to around 40°C, or under 100°C.

Optionally, the cooler(s) may be further arranged to provide the cooled reaction product at a pressure of around bar gauge. This may require a compressor or similar device.

Preferably, the cooler(s) may be further arranged to recover heat from the reaction product. This recovered heat may be utilised elsewhere in the apparatus and optionally to generate steam or pre-heat the waste gas before entry into the water shift reactor.

Optionally, the apparatus may be arranged to pre-heat the humidified waste gas using the recovered heat.

Preferably, the water shift reactor(s) further comprises a catalyst. This improves efficiency and/or yield of the reaction.

Preferably, the water shift reactor(s) may be arranged to generate the reaction product at a temperature of around 480°C. A range of 470-490°C or 450-500°C may also be advantageous, for instance.

Preferably, the water shift reactor is a multi-stage reactor.

In accordance with a second aspect of the present invention there is provided a blast furnace comprising the apparatus of any previous claim. The blast furnace may of the type used in the production of iron or steel or other metals, for instance. The blast furnace may be configured or adapted to provide its waste gas in a way that may be received by the apparatus described above. The blast furnace may otherwise comprise known components of a typical blast furnace. An existing blast furnace may be converted by adding the apparatus described above or may be manufactured from new by incorporating this waste gas processing apparatus, as described. Both may be considered a method of manufacture. The waste gas processing apparatus may be added to other industrial processes.

In accordance with a third aspect of the present invention there is provided a method for processing waste gas comprising carbon monoxide, the method comprising the steps of: humidifying the waste gas with water; reacting the carbon monoxide with the water to form a product containing carbon dioxide and hydrogen; cooling the product; and separating the carbon dioxide and hydrogen in the cooled product.

Optionally, the method may further comprise the step of recovering heat during the cooling step.

Optionally, the method may further comprise the step of using the recovered heat to pre-heat the humidified waste gas.

Preferably, the humidifying step may further comprise applying steam to the waste gas.

Advantageously, the method may further comprise the step of spaying water into the waste gas.

Preferably, the method may further comprise the step of recovering condensed water from the cooled product and using this recovered condensed water in the spraying step.

Advantageously, the method may further comprise the step of separating the carbon dioxide from the hydrogen.

Preferably, the method may further comprise the step of compressing the carbon dioxide.

Optionally, the waste gas may further comprise sulphur compounds and the product further comprises hydrogen sulphide, the method may further comprise the step of: removing the hydrogen sulphide from the cooled reaction product.

Preferably, the method may further comprise the step of recovering sulphur from the hydrogen sulphide.

Advantageously, the method may further comprise the step of compressing the waste gas before the humidifying step.

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Brief description of the Figures

The present invention may be put into practice in a number of ways and embodiments will now be described by way of example only and with reference to the accompanying drawing, in which: FIG. 1 shows a schematic diagram of a waste gas processing apparatus according to one embodiment, given by

way of example only.

It should be noted that this figure is illustrated for simplicity and are not necessarily drawn to scale.

Detailed description of the preferred embodiments

Figure 1 shows a schematic diagram of a waste gas processing apparatus according to a preferred embodiment.

Each component is shown as a simplified representation and the various required connections and valves, etc. are omitted for clarity although such additional components and connections would be immediately apparent to the skilled person.

Industrial process gas 1 may be a waste gas emitted from any of a number of processes or plants. For instance, the waste gas may originate from a blast furnace, petrochemical process or other industry typically generating significant quantities of carbon dioxide.

The industrial process gas 1 or waste gas enters the apparatus at an intermediate pressure (typically around 2 -barg or bar gauge) and a medium temperature (typically in the range 200-400°C. Other pressures and temperatures may be used encountered or utilised.

Particulate material may be removed during a first filtering state 2. This first filtering stage may be a -11 -cyclone separator, a mechanical filter, or an electrostatic precipitator, for instance.

A vertical cyclone separator (or multiple cyclone separators) may remove the majority (typically over 90%) of the particulate material from the industrial process gas in a dry form. Cyclone separator collectors use cyclonic action to separate particulate material from a gas stream.

A dust-laden gas stream enters an upper chamber at a tangential angle and is spun rapidly. The centrifugal force created by the circular flow throws the dust particles toward the wall of the cyclone, and after striking the wall, the particles fall into a hopper 3 located underneath.

Possible filter mechanisms may also include a fabric filter (baghouse) or a sintered or ceramic filter. A semi-porous membrane may also be arranged so that industrial process gas 1 may pass through the membrane whilst the particulate material remains on the outside. Some of the particulate material may fall under gravity into a hopper located underneath; other particulate material may adhere to the outer surface of the membrane. The adhered particles may be removed by reverse pulses of gas or by mechanical action, and fall into the hopper located underneath.

In an electrostatic precipitator electrostatic forces may also be used to separate particulate material from the industrial process gas 1. A number of high-voltage, direct-current electrodes may be placed in a honeycomb of grounded collecting electrodes. The particulate-laden industrial process gas 1 may flow upward through a passage between by the high voltage and collecting electrodes. As the industrial process gas 1 flows past the high voltage electrode, the particulate material receives a negative charge as it passes through the ionized field between the electrodes. These charged particles are then attracted to -12 -the positively charged electrode and adhere to it by electrostatic attraction. They may be subsequently removed by mechanical action, and fall into a hopper 3 located underneath.

The first filtering stage 2 may be omitted especially if the waste gas 1 contains low levels of solid material.

A wet scrubber 4 may receive the industrial process gas 1 from its source.

The wet scrubber has three functions: 1. to provide partial saturation (of water) to the industrial process gas 1; 2. to wash out further particulate material in the industrial process gas 1; and 3. to remove any water-soluble salts from the industrial process gas 1 if these are present.

Absence of the first filtering stage may impose a higher duty on the wet scrubber, which may then have to remove higher levels of particulate material from water washed through the waste gas 1.

Preferably, the wet scrubber 4 would be a spray water quench but may also be or include one or more pieces of wet gas scrubbing apparatus including a Venturi scrubber, for instance.

A spray water quench may rapidly cool the downward-flowing industrial process gas by spraying water into the gas through spray nozzles. The waste gas 1 cools by losing heat by evaporating water from the surface of the droplets sprayed into the waste gas. The water evaporated is dissolved into the cooled gas in full or partial saturation.

Not all of the water sprayed into the quench is evaporated and that water which is not evaporated falls to the base of the vessel, carrying with it some of the particulate material not removed in any upstream processes, i.e. the -13 -first filtering stage 2, if present. The spray of water also dissolves water-soluble species within the industrial process gas stream 1. The surplus water may be processed in a water treatment plant 7 to remove particulate material and soluble salts, and the cleaned water is returned to the spray nozzles 5, together with make-up water 8 to replace that lost through the evaporative stage.

The temperature at this point in the process may be in the range 120 -150°C (saturation temperature for a pressure of 2-5 barg).

A compressor 9 may be used to compress the scrubbed waste gas. The compressor may be used to improve the efficiency of downstream processes (to be discussed in detail in subsequent paragraphs), which typically require pressures greater than the 2 -5 bar at which the industrial process gases entered the apparatus. The compressor 9, which may be of the axial flow or centrifugal or other design, may be located after the particulate removal stages 2, 4 so that the potential for abrasive damage to the compressor components is reduced. The discharge pressure of the compressor may be above 2obarg (bar gauge) . The washed industrial process gas may gain heat as it is compressed, and some of the water dissolved in it will then be precipitated out. This water 10 may be sent to a water treatment plant 7 for re-injection into the spray water quench or other wet gas scrubbing system 4.

Additional water may be required in the warmed gas. A humidifier or saturator stage 11 may be used to increase the humidity (water content) of the waste gas. Water as steam 12 may be added at a pressure slightly above that of the gas and typically above 250°C. The wet scrubber 4 also humidifies the waste gas to some extent.

-14 -It may be necessary to provide a small amount of superheat to the industrial process gas at this stage (typically about 30 degrees) . In order for the next stage to function more efficiently, the gas should be at about 280°C. Therefore a heater 13 may be included to provide this additional heat, if necessary. The source of this heat could be steam, electricity or a gas/gas heat exchanger using heat released in downstream processes (cooling stage), in whole or in part.

At this stage in the process 14 the industrial process gas may comprise mainly carbon monoxide (CO) , carbon dioxide (Ca2) and water (H20), with traces of other gases (which might include H2S, SO2, COS) and volatile heavy metals (for example mercury (Hg)) . It will preferably, be at a temperature above 280°C and above 2obarg pressure. The exact composition will depend on the originating industrial process.

In the next stage of the process the industrial process gas enters a reactor vessel 15. The superheated mixture of industrial process gas and water undergoes the following chemical reaction (known as the "water shift reaction": CO + H20 -CO2 + H2 This may be a single-stage or multi-stage process.

The reactor vessel 15 (or water shift reaction vessel) may contain beds of catalysts and the reactants may be passed over a number of these catalyst beds in order to produce the reaction. The carbon monoxide is oxidised by the water releasing hydrogen gas. A considerable amount of heat may also be liberated and the gas exits the water shift reaction vessel at a temperature typically above 480°C.

The shift reaction also hydrolyses any COS in the industrial process gas to produce more carbon dioxide and additional H2S: -15 -COS + H20 -* CO2 + HS This reaction also releases heat.

The heat from these two processes is recovered in a cooler or coolers 16: much of this may be beneficially used, for instance to pre-heat the industrial process gas before it enters the water shift vessel, or to raise steam or to heat water.

During the cooling of the industrial process gas some of the water that has not taken part in the shift reaction described above, may condense out 17. This water (condensate) may be recovered and pumped to the water treatment plant 7 for re-use.

The industrial process gas is cooled down to about 400C. It is passed through an additional filter or filters 18, often containing granulated activated carbon, but this may be other materials, which remove volatile heavy metals (particularly mercury, but also arsenic) if these are present. Again, the requirement for this filter is dependent on the specific composition of the waste gas 1 and process that generates it.

Under these conditions (high pressure, low temperature and high partial pressures) the resultant industrial process gas may be "cleaned" of both any H2S and the CO2 using one of a number of processes known to the petrochemical, agri-chemical or other chemical process industries. This is generally described as an acid gas removal system 19. The outputs from an acid gas removal system are: 1. H2S 20, which may be subsequently processed and the sulphur extracted 21 during a sulphur extraction stage; 2. CO2 gas which can be captured and exported off site 22; and 3. A combustible gas 23, mostly hydrogen (H2), but also containing nitrogen (N2) small amounts of un-reacted -16 -Ca, and other gases in small amounts. The hydrogen can be separated out from the other gases and used for purposes other than for combustion.

If the intention is to export the Ca2, it may be S necessary to compress it to a suitable pressure using a compressor which may be of multi-shaft geared, axial flow or reciprocating design 24, for instance.

As will be appreciated by the skilled person, details of the above embodiment may be varied without departing from the scope off the present invention, as defined by the appended claims.

For example, different pressures and temperatures from those mentioned above may be used.

The word "contain', used throughout, includes the possibility that other items or components may be included or found but are not mentioned for clarity reasons only.

Many combinations, modifications, or alterations to the features of the above embodiments will be readily apparent to the skilled person and are intended to form part of the invention.

Claims

-17 -CLAIMS: 1. Apparatus for processing waste gas comprising carbon monoxide, the apparatus comprising: a humidifier for humidifying the waste gas; a water shift reactor arranged to receive the humidified waste gas and to produce a reaction product comprising at least carbon dioxide and hydrogen; a cooler arranged to cool the reaction product; and a separator arranged at least partially to separate the carbon dioxide and hydrogen from the cooled reaction product.
2. The apparatus of claim 1, wherein the waste gas further contains sulphur compounds and the reaction product further contains hydrogen suiphide, the apparatus further comprising: an acid gas remover arranged to remove hydrogen suiphide from the cooled reaction product.
3. The apparatus of claim 2 further comprising a sulphur extraction reactor for recovering sulphur from the removed hydrogen suiphide.
4. The apparatus according to any previous claim further comprising a particulate filter arranged to remove particulate material from the waste gas.
5. The apparatus of claim 4, wherein the particulate filter is selected from the group consisting of: cyclone separator, fabric filter, baghouse, sintered filter, ceramic filter, semi-porous membrane and electrostatic precipitator.

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6. The apparatus according to any previous claim further comprising a compressor for compressing the recovered carbon dioxide.
7. The apparatus according to any previous claim further comprising a heater for heating the humidified waste gas.
8. The apparatus according to any previous claim, wherein the cooler is further arranged to recover condensed water.
9. The apparatus according to any previous claim further comprising a wet scrubber arranged to remove water soluble salts and/or particulate material from the waste gas and further humidify the waste gas.
10. The apparatus of claim 9 when dependent on claim 8 further comprising a water treatment plant for cleaning the recovered condensed water and supplying the cleaned water to the wet scrubber.
11. The apparatus of claim 9 or claim 10, wherein the wet scrubber is a water sprayer or a Venturi scrubber.
12. The apparatus according to any previous claim, wherein the humidifier is a steam injector.
13. The apparatus according to any previous claim further comprising a pressuriser arranged to pressurise the waste gas before entering the humidifier.
14. The apparatus of claim 13, wherein the pressuriser is configured to raiser the pressure of the waste gas to above bar gauge.

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15. The apparatus according to any previous claim further comprising a heater for heating the humidified waste gas.
16. The apparatus of claim 15, wherein the heater is arranged to raise the temperature of the humidified waste gas to around 280°C.
17. The apparatus according to any previous claim further comprising a filter after the cooler, the filter being arranged to remove heavy metals.
18. The apparatus of claim 17, wherein the filter arranged to remove heavy metals comprises activated carbon.
19. The apparatus according to any previous claim, arranged to receive the waste gas at a temperature in the range 200°C to 400°C.
20. The apparatus according to any previous claim, arranged to receive the waste gas at a pressure in the range 2-5 bar gauge.
21. The apparatus according to any previous claim, wherein cooler is arranged to cool the reaction product to around 40°C.
22. The apparatus according to any previous claim, wherein the cooler is further arranged to provide the cooled reaction product at a pressure of around 20 bar gauge.

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23. The apparatus according to any previous claim, wherein the cooler is further arranged to recover heat from the reaction product.
24. The apparatus of claim 23, arranged to pre-heat the humidified waste gas using the recovered heat.
25. The apparatus according to any previous claim, wherein water shift reactor further comprises a catalyst.
26. The apparatus according to any previous claim, wherein water shift reactor is arranged to generate the reaction product at a temperature of around 480°C.
27. The apparatus according to any previous claim, wherein water shift reactor is a multi-stage reactor.
28. A blast furnace comprising the apparatus of any previous claim.
29. A method for processing waste gas comprising carbon monoxide, the method comprising the steps of: humidifying the waste gas with water; reacting the carbon monoxide with the water to form a product containing carbon dioxide and hydrogen; cooling the product; and separating the carbon dioxide and hydrogen in the cooled product.
30. The method of claim 29 further comprising the step of recovering heat during the cooling step.

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31. The method of claim 30 further comprising the step of using the recovered heat to pre-heat the humidified waste gas.
32. The method of any of claims 29-31, wherein the humidifying step further comprises applying steam to the waste gas.
33. The method of any of claims 29-32 further comprising the step of spaying water into the waste gas.
34. The method of claim 33 further comprising the step of recovering condensed water from the cooled product and using this recovered condensed water in the spraying step.
35. The method of any of claims 29-34 further comprising the step of separating the carbon dioxide from the hydrogen.
36. The method of claim 35 further comprising the step of compressing the carbon dioxide.
37. The method of any of claims 29-36, wherein the waste gas further comprises sulphur compounds and the product further comprises hydrogen sulphide, the method further comprising the step of: removing the hydrogen suiphide from the cooled reaction product.
38. The method of claim 37 further comprising the step of recovering sulphur from the hydrogen suiphide.

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39. The method of any of claims 29-38 further comprising the step of compressing the waste gas before the humidifying step.
40. Apparatus as described herein with reference to any accompanying figure.
41. A method as described herein with reference to any accompanying figure.