A process for the conversion of carbon dioxide to carbon monoxide using modified high capacity by-product coke ovens

Technical Field

The present invention relates to an efficient process for conversion of carbon dioxide to carbon monoxide. The invention also relates to an apparatus that may be used to carry out the process.

Background of the Invention

There are two major problems that currently confront world populations. One problem is the declining reserves of crude petroleum, leading inevitably to a progressive reduction in the availability of liquid fuels and many other petroleum-based products and an escalation in price of these essential commodities. The other major problem is the continuing increase in the concentration of greenhouse gases in the atmosphere, particularly carbon dioxide generated from burning liquid fuels in transport vehicles, aircraft and ships, coal or oil in fixed plants and gas, whether LPG or LNG, in both conveyances and fixed plants.

The current view of climatologists, oceanographers and environmentalists is that the growing concentrations of carbon dioxide in the atmosphere are accelerating global warming. Vast sums of money are now being devoted world wide to action and research aimed at mitigating carbon dioxide emissions by reducing fossil fuel combustion, developing various forms of renewable energy and capturing carbon dioxide with the intention of sequestering it deep underground.

Solutions to the problem such as sequestering carbon dioxide underground represent major engineering challenges in relation to infrastructure that would likely cost billions of dollars. As such, there remains a need for an economical process whereby carbon dioxide emissions into the atmosphere can be largely minimised wherever possible.

The present inventor has developed a sustainable economical process whereby carbon dioxide can be converted to carbon monoxide, from which syngas may be prepared.

The process is more economic than current processes for production of syngas from coal as it provides twice as much carbon and all of the oxygen for production of carbon monoxide per tonne of coking coal. By providing waste emissions gas free of charge for conversion to syngas, industries are able to avoid costly carbon trading penalties.

Summary of the Invention

In a first aspect, the present invention provides a process for converting carbon dioxide to carbon monoxide, said process comprising:

(i) providing carbon obtained from pyro lysis of carbonaceous solids; (ii) allowing carbon dioxide to react with the carbon to produce carbon monoxide,

(iii) combusting a fuel gas which generates a flue gas that provides heat energy to drive reaction of carbon dioxide with carbon.

The process may further comprise pyrolysis of the carbonaceous solids to give carbon and volatile matter and separating the volatile matter from the carbon.

The pyrolysis of the carbonaceous solids may be performed without the addition of water.

The reaction of carbon dioxide with carbon may be performed in an environment consisting essentially of carbon dioxide. The carbonaceous solids may be coal.

The concentration of the carbon dioxide of step (ii) may be greater than about 85%. The concentration of the carbon dioxide of step (ii) may be greater than about 90%. At least a portion of the carbon dioxide produced from combusting the fuel gas may be captured. At least a portion of the captured carbon dioxide may form a portion of the carbon dioxide used in step (ii).

Substantially all of the captured carbon dioxide may form a portion of the carbon dioxide used in step (iϊ).

No other gases may be added to the carbon dioxide prior to reaction with carbon. The other gases may comprise carbon monoxide and/or oxygen.

No carbon monoxide produced in step (iii) may be recycled through the reaction of carbon dioxide with carbon.

The concentration of the carbon monoxide produced in step (ii) may be greater than about 85%. The concentration of the carbon monoxide produced in step (ii) may be greater than about 90%.

At least a portion of the fuel gas may be obtained by refining the volatile matter. The carbon may be prepared and reacted with carbon dioxide in situ.

Following preparation, the carbon may be maintained at about the same temperature at which it was formed when reaction with carbon dioxide commences.

At least a portion of the carbon dioxide of step (ii) may be obtained from one or more fossil fuelled industrial plants. The fossil fuelled industrial plant may be oxy-fuel fired.

The fossil fuelled industrial plant may be air fired and carbon dioxide may be separated from flue gas produced from the fossil fuelled industrial plant prior to use in step

(ϋ).

The carbon monoxide produced in step (iii) may be mixed with hydrogen to produce syngas.

The carbon monoxide produced in step (ii) may not be combusted. Heat energy for pyrolysis of carbonaceous solids may be provided by combusting a fuel gas which generates a flue gas.

The fuel gas may be combusted in the presence of oxygen and carbon dioxide. The fuel gas may be combusted in the presence of a gas mixture consisting essentially of oxygen and carbon dioxide.

The carbon dioxide may be obtained from a fossil fuelled industrial plant which is oxy-fuel fired.

The process may be carried out as a batch process. The process may be carried out in one or more modified coke ovens.

The process may be carried out in a battery of modified coke ovens operating out of phase thereby resulting in continuous production of carbon and carbon monoxide.

In a second aspect, the present invention provides a process for converting carbon dioxide to syngas, said process comprising: (i) pyrolysis of carbonaceous solids to give carbon and volatile matter;

(ii) isolating a fuel gas from the volatile matter;

(iii) allowing carbon dioxide to react with the carbon to produce carbon monoxide;

(iv) combusting the fuel gas which generates a flue gas that provides heat energy to drive reaction of carbon dioxide with carbon, and

(v) mixing the carbon monoxide with hydrogen to provide syngas; At least a portion of the carbon dioxide produced from combusting the fuel gas may be captured.

At least a portion of the captured carbon dioxide may form a portion of the carbon dioxide used in step (iii).

Substantially all of the captured carbon dioxide may form a portion of the carbon dioxide used in step (iii). The carbonaceous solids may be coal.

No other gases may be added to the carbon dioxide prior to reaction with carbon.

The concentration of the carbon dioxide of step (iii) may be greater than about 85%.

The carbon monoxide produced in step (iii) may not be recycled through the reaction of carbon dioxide with carbon. The concentration of the carbon monoxide produced in step (iii) may be greater than about 85%.

The concentration of the carbon monoxide produced in step (iii) may be greater than about 90%.

The fuel gas may be combusted in the presence of oxygen and carbon dioxide. The fuel gas may be combusted in the presence of a gas mixture consisting essentially of oxygen and carbon dioxide.

The carbon dioxide may be obtained from a fossil fuelled industrial plant which is oxy-fuel fired.

Heat energy for pyrolysis of carbonaceous solids may be provided by combusting a fuel gas which generates a flue gas.

The carbon may be prepared and reacted with carbon dioxide in situ.

At least a portion of the carbon dioxide of step (iii) may be obtained from one or more fossil fuelled industrial plants.

The fossil fuelled industrial plant may be oxy-fuel fired. The fossil fuelled industrial plant may be air fired and carbon dioxide may be separated from flue gas produced from the fossil fuelled industrial prior to use in step (iii)

The syngas may be used to produce liquid fuels.

Carbon dioxide produced in the production of the liquid fuels may form at least a portion of the carbon dioxide used in step (iii). The process may be carried out as a batch process such that steps (i) and (ii) are completed prior to commencement of step (iii).

The process may be carried out in one or more modified coke ovens.

The process may be carried out in a battery of modified coke ovens operating out of phase thereby resulting in continuous production of carbon and carbon monoxide.

In a third aspect, the present invention provides a process for converting carbon dioxide to syngas, said process comprising: (i) pyrolysis of carbonaceous solids to give carbon and volatile matter;

(ii) separating the volatile matter from the carbon; (iii) refining the volatile matter to obtain a fuel gas;

(iv) allowing carbon dioxide, at least a portion of which is obtained from an oxy-fuel fired fossil fuelled industrial plant, to react with the carbon to produce carbon monoxide;

(v) combusting the fuel gas to generate a flue gas that provides heat energy to drive reaction of carbon dioxide with carbon and pyrolysis of carbonaceous solids; (vi) capturing at least a portion of the carbon dioxide produced from combusting the fuel gas and using said carbon dioxide as a portion of the carbon dioxide in step (iv); and

(vii) mixing the carbon monoxide with hydrogen to provide syngas. The carbonaceous solids may be coal.

No other gases may be added to the carbon dioxide prior to reaction with carbon. No carbon monoxide produced in step (iv) may be recycled through the reaction of carbon dioxide with carbon.

The fuel gas may be combusted in the presence of oxygen and carbon dioxide. The fuel gas may be combusted in the presence of a gas mixture consisting essentially of oxygen and carbon dioxide.

The carbon dioxide may be obtained from the fossil fuelled industrial plant. The fossil fuelled industrial plant may be a power station.

The syngas may be used to prepare liquid fuels.

Carbon dioxide produced in the production of the liquid fuels may form at least a portion of the carbon dioxide used in step (iv).

Oxygen used in the process for oxy-fuel firing may be obtained from an oxygen generator which also produces nitrogen.

Oxygen necessary for converting carbon dioxide to carbon monoxide is not separately generated as all of the required oxygen used in the reaction is present in the carbon dioxide.

The nitrogen may be used as a condensing agent in the preparation of liquid fuels thereby producing heated and pressurised nitrogen.

The heated and pressurised nitrogen may be used to drive generators so as to provide power for operating the process. In a fourth aspect, the present invention provides an apparatus for pyrolysis of coal and conversion of carbon dioxide to carbon monoxide, said apparatus comprising: a refractory enclosure defining a gastight chamber, one or more coal-charging openings located at the top of the chamber for introducing coal into said chamber, a heat source for providing heat to said chamber, an inlet for introduction of carbon dioxide into said chamber, a first outlet for removal of volatiles produced from the pyrolysis of coal from said chamber, a second outlet for removal of carbon monoxide from said chamber, and a third outlet for removal of ash from said chamber.

The inlet for introduction of carbon dioxide may be located above the second outlet for removal of carbon monoxide. The inlet for introduction of carbon dioxide may be located at the top of the chamber, and the second outlet for removal of carbon monoxide may be located at the bottom of the chamber.

The inlet for introduction of carbon dioxide may comprise a pipe connecting the chamber to a main pipeline, said pipe including a gas tight valve for regulating the flow of carbon dioxide entering the chamber.

The heat source may be indirect heat transfer from a heat source such as a combustion reaction.

The heat source may be one or more flues in which a combustion reaction occurs.

The combustion reaction may be combustion of a fuel gas in the presence of a gas mixture consisting essentially of oxygen and carbon dioxide.

The apparatus may comprise means for carrying out oxy-fuel firing.

The second outlet for removal of carbon monoxide may be in communication with a gastight enclosure, said enclosure being in communication with a gastight valve which, when open, permits the flow of a stream of carbon monoxide out of the enclosure and into a pipe.

The pipe may include a gas sampler and analyser to detect carbon dioxide present in the stream of carbon monoxide such that when a predetermined amount of carbon dioxide is detected, the gastight valve is at least partially closed.

The analyser may also detect other gases which are impurities in the stream of carbon monoxide such as nitrogen, nitrogen oxides and sulphur oxides.

The enclosure may further comprise a gastight door valve located at the opposite end of the enclosure to the second outlet such that when the door valve, second outlet and third outlet are open, a pusher ram may move though a lower portion of the chamber to remove ash from the chamber.

The second outlet and the third outlet may be gastight door valves that may further be aligned.

The height of the aligned gastight door valves may be less than about 60%, or less than about 50%, or less then about 40%, or less than about 30% of the height of the chamber.

The height of the aligned gastight door valves may be between about 20% and about 40% of the height of the chamber.

The process of the first aspect, or a part of the process of the second or third aspects may be performed, or partly performed in the apparatus of the fourth aspect.

Brief Description of the Figures

Figure 1 shows a transverse cross section of an apparatus that may be used to perform the process of the invention.

Figure 2 shows a flow diagram of an embodiment of the invention wherein carbon dioxide is converted to carbon monoxide.

Figure 3 shows a flow diagram of an embodiment of the invention wherein carbon dioxide captured from a power station is converted to liquid fuels.

Figure 3 A shows a. stage of the process of Figure 3, the production, capture and conversion of carbon dioxide to carbon monoxide. Figure 3B shows a stage of the process of Figure 3, the separation of by-products from the volatiles emitted and the refinement of fuel gas.

Figure 3 C shows a stage of the process of Figure 3, production of hydrogen, its combination with carbon monoxide as syngas for production of liquid fuels, the use of nitrogen as a condensing agent and as a medium for generation of electrical power. Figure 4 graphically illustrates the theoretical effects of temperature and pressure on equilibrium yield of carbon monoxide, as calculated by standard thermodynamic methods assuming ideal behaviour and ignoring side reactions (reproduced from US patent 4,190,636).

Figure 5 shows a longitudinal cross section of a modified coke ovens battery, illustrating the arrangement of ovens, combustion flues and exhaust flues and the reversible firing system employing a mixture of carbon dioxide, oxygen and fuel gas.

Definitions

5 Li the context of this specification, the terms "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

In the context of this specification, the term "comprising" means "including principally, but not necessarily solely". Furthermore, variations of the word "comprising",o such as "comprise" and "comprises", have correspondingly varied meanings.

In the context of this specification, the term "syngas" is understood to mean a gas mixture that contains varying amounts of carbon monoxide and hydrogen.

In the context of this specification, the term "batch process" is understood to mean that one cycle of the process is completed prior to commencement of the next cycle. Fors example, pyrolysis of carbonaceous solids to give carbon and separation of volatile matter may be completed prior to commencement of the reaction of the carbon with carbon dioxide.

In the context of this specification, the terms "oxy-fuel fired" and "oxy-fuel firing" may be used interchangeably and are understood to mean a process whereby heating is0 achieved by burning a gas mixture comprising or consisting essentially of fuel and oxygen, and optionally carbon dioxide, wherein the amount of nitrogen present in the gas mixture is less than about 7%, or less than about 6%, or less than about 5%, or less than about 4%, or less than about 3%, or less than about 2%, or less than about 1%, or less then about 0.5%.

In the context of this specification, the term "modified coke oven" is understood toS mean a coke oven that has been modified in such a way that it is capable of performing the step of preparing carbon from carbonaceous solids, and subsequently performing the step of reacting the carbon with carbon dioxide to form carbon monoxide.

Detailed Description of the Invention

In one aspect, the present invention provides a process for converting carbon dioxide0 to carbon monoxide, said process comprising: providing carbon obtained from pyrolysis of carbonaceous solids; allowing carbon dioxide to react with the carbon to produce carbon monoxide, combusting a fuel gas which generates a flue gas that provides heat energy to drive reaction of carbon dioxide with carbon.

The carbonaceous solids may be coal, and the carbon may be coke. In one embodiment, the process may further comprise pyrolysis of the carbonaceous solids to give carbon and volatile matter, and separating the volatile matter from the carbon. In this embodiment, the process may comprise preparation of carbon and reaction with carbon

5 dioxide in situ. The process may be run so as to provide a continuous stream of highly concentrated carbon monoxide by supplying coal and carbon dioxide. The process may be performed in the apparatus described in the fourth aspect.

The process may form part of a larger process whereby carbon dioxide is captured from one or more sources (for example power stations, oil refineries, cemento manufacturing plants, coke ovens, furnaces, alumina plants or aluminium refineries), converted to carbon monoxide, which is then converted to liquid fuels and other petrochemicals via syngas. As such, in one embodiment, the present invention may be used to convert waste carbon dioxide to syngas, liquid fuels and other desirable petrochemical products. The present invention is therefore able to prevent a problematic5 greenhouse gas from entering the atmosphere, whilst at the same time converting this gas to highly useful petrochemical products.

The carbon dioxide used in the process may be substantially pure, and comprise minimal or no nitrogen. The carbon dioxide may also be free, or substantially free of carbon monoxide and/or oxygen. The concentration of carbon dioxide used in the processQ may be between about 60% and about 99%, or between about 65% and about 99%, or between about 70% and about 99%, or between about 75% and about 99%, or between about 75% and about 98%, or between about 75% and about 97%, or between about 80% and about 98%, or between about 80% and about 95%, or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or ₅ 99%. In an alternative embodiment, the concentration of carbon dioxide may be greater than about 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%.

Other gases such as carbon monoxide may not be added to the carbon dioxide stream ₀ that is reacted with the carbon. Other gases such as carbon monoxide and oxygen may not be introduced into the reaction of carbon dioxide and carbon. Such additions may limit the carbon dioxide reaction capacity and impact on the overall efficiency of the process.

The carbon dioxide may be obtained from any suitable source, for example fossil fuelled industrial plants such as power stations, oil refineries, cement manufacturing plants coke ovens, furnaces, alumina plants or aluminium refineries. Where the carbon dioxide to be used in the process is contaminated with other gases such as nitrogen, the carbon dioxide may be separated from the other gases prior to being reacted with the carbon. Carbon dioxide may be separated from flue gas by adsorption onto zeolites and other solids, by adsorption in solvent liquids such as monoethanolamine (MEA), cryogenic separation or by the use of membrane technology.

Where MEA is used to separate carbon dioxide from flue gas, this compound may be prepared from ammonia, which is generated during refining of the fuel gas, and ethanol which is prepared from syngas in accordance with an embodiment of the invention. MEA may therefore be prepared using products of the process of the present invention at an otherwise lower cost than if it was to be purchased.

A portion of the carbon dioxide used in the process may be received from a source in concentrated form. For example, the carbon dioxide may be obtained from a fossil fuelled industrial plant (for example a power station) which is oxy-fuel fired. The flue gas produced from such a plant comprises greater than about 90% carbon dioxide as compared to an air fired equivalent which results in a flue gas having between about 85% to 90% nitrogen, and only 7% to 10% carbon dioxide. In one embodiment, no other gases (for example carbon monoxide) are added to the carbon dioxide stream that is obtained from the fossil fuelled industrial plant. Rather, the carbon dioxide stream is simply used in the process as it is received. Where the carbon dioxide used in the process is of a high concentration (for example greater than 80%), carbon monoxide of a correspondingly high concentration (for example greater than 80%) is obtained without the need for additional purification. The concentration of the carbon monoxide obtained from the process may be between about 60% and about 99%, or between about 65% and about 99%, or between about 70% and about 99%, or between about 75% and about 99%, or between about 75% and about 98%, or between about 75% and about 97%, or between about 80% and about 98%, or between about 80% and about 95%, or about 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%. In an alternative embodiment, the concentration of carbon monoxide obtained from the process may be greater than about

70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%

All or a portion of the fuel gas used in the process may be obtained by refining the volatile matter liberated following pyrolysis of the carbonaceous solids. Portions of the volatile matter may therefore be used to provide energy to drive pyrolysis of the carbonaceous solids and/or the reaction of carbon dioxide with carbon.

All or a portion of the carbon dioxide that is produced from combustion of the fuel gas may be captured. All or a portion of the captured carbon dioxide may be recycled through the process and allowed to react with the carbon. In one embodiment, the fuel gas is combusted in the presence of substantially pure oxygen and carbon dioxide thereby producing a flue gas comprising about 84% or more carbon dioxide and about 14% or less water, present as superheated steam. The carbon dioxide may or may not be separated from the water prior to being allowed to react with the carbon, hi one embodiment of the first aspect, the carbon dioxide stream of step (ii) may comprise flue gas from step (iii) and carbon dioxide obtained from a fossil fuelled industrial plant, hi this embodiment, all carbon dioxide generated during the operation of the fossil fuelled industrial plant and the process of the invention is converted to carbon monoxide with no atmospheric emission of carbon dioxide occurring. Where the fuel gas is combusted in the presence of air, carbon dioxide present in the flue gas may be separated from other gases as described above prior to being reacted with the carbon.

The process in accordance with one embodiment of the invention may be run as a batch process wherein one cycle of the process is completed prior to commencement of the next cycle. For example, pyrolysis of carbonaceous solids to give carbon and separation of volatile matter may be completed prior to commencement of the reaction of the carbon with carbon dioxide.

Where the carbonaceous solids used are coal, the coal may be bituminous, agglomerating coal that has an ash content of below about 12%, or below about 10%, or below about 8%, or below about 6%. Coals having a higher ash content may however also be used. The coal used in the process preferably possesses characteristics which enable it to form a stable and reactive coke, however the coke does not require rigid strength characteristics as it is not subject to pressure, crushing, impact or abrasion.

Cokes with high Coke Strength after Reaction (CSR more than 50) tend to have lower reactivities, while cokes with lower CSRs are more reactive. Therefore, a different set of criteria is required for selection of coking coal for the process of converting carbon dioxide to carbon monoxide as opposed to blast furnace coking coals. The reactivity of coke is measured by weight loss during reaction with carbon dioxide and is termed the Coke Reactivity Index (CRT). It is determined by the Nippon Steel Corporation (NSC) Coke Reactivity and Strength Test, in which a 200 g crushed and screened coke sample is reacted with carbon dioxide for 2 hours at HOO ⁰ C.

CRI = (Amount of change in mass x 100) / Mass of sample The selected coals preferably have medium to high volatile content, mean maximum reflectance of vitrinite between 0.5 and 1.0, adequate concentration of reactive vitrinites, together with exinites and resmites, which are the main coke- forming macerals. The latter two form vacuoles in the coke creating the porous structure.

The reactivity of the coke may be increased by employing one or more catalysts, for example iron oxide and/or ferronickel. Lime may also be added to improve the basicity of the ash and reactivity of the coal. The catalysts may be recovered with, for example, rare earth magnetic separators. Recovered catalysts may be recycled.

Other preferred characteristics of the coking coal include sulfur content less than 0.8% ad, total moisture less than 10% as sampled, CSN 5-9, Hardgrove Grindability Index (HGI) higher than 40. In addition, a deformation temperature of ash greater than 125O ⁰ C and flow temperature greater than 1500 ⁰ C ensures that the hot ash may be easily handled.

The process of the invention may be conveniently carried out in a commercial coke oven that has been modified in such a way that it is capable of performing the step of preparing carbon from carbonaceous solids, and subsequently performing the step of reacting the carbon with carbon dioxide to form carbon monoxide. An example of a coke oven that may be modified in this manner is found in the ThyssenKrupp-Uhde (TKU) Schwelgern Coke Ovens Plant, which includes the world's largest coke ovens (see http://www.uhde.bizbin/bvteserver.pl/archive/upload/uhde brochures pdf en_ 17.00.pdf). However, any commercial coke oven design may be modified so as to facilitate the step of reacting carbon with carbon dioxide as described herein.

Tables 1 and 2 below summarise the modifications that may be made to a typical commercial coke oven so as to permit reaction of carbon dioxide with coke formed therein.

Table 1 lists components of conventional coke ovens that may be omitted, whilst Table 2 lists components that may be added.

Table 1

* The numerals in the above table refer to Figures 1 and 5

Figure 1 depicts a modified coke oven that may be used to perform the process of the invention. Whilst only a single oven is shown, the process may be performed with a battery of ovens or more than one battery of ovens. In one embodiment, the process is not a continuous process, but rather a batch process that may be performed in a battery of modified coke ovens. For example, an oven is charged with a batch of coal, air is excluded and the coal is pyrolysed to give coke and volatile matter, the latter being removed from the oven. Carbon dioxide is then reacted with the coke thereby producing carbon monoxide and ash. The process is stopped and the ash is removed, where after the oven is refilled with a new charge of coal, and the process commences again. The entire process may take about 36 hours.

Where the process is performed in a battery of modified coke ovens comprising, for example, 72 to 76 ovens, continuity is achieved artificially by staggering the 36 hour cycles of all of the ovens 30 minutes apart from each other. As such, two thirds of the ovens are undergoing progressive stages of pyrolysis, while one third of the ovens are performing reduction of carbon dioxide to carbon monoxide. Operating under such

conditions, the modified coke ovens are able to produce a constant stream of carbon monoxide gas.

Modified coke ovens that may be used in the present invention may be air-fuel fired or oxy-fuel fired. In one embodiment, carbon dioxide present in flue gas produced from 5 the firing of the modified coke oven may be recycled through the process of the invention. In this embodiment, large quantities of carbon dioxide are able to be efficiently converted to carbon monoxide in a process that does not in itself lead to any emission of carbon dioxide to the atmosphere. Where the modified coke oven is air-fuel fired, the flue gas produced comprises carbon dioxide that is contaminated with large amounts of other gaseso (primarily nitrogen), and therefore separation of the carbon dioxide from the other gases may be performed prior to the carbon dioxide being introduced into the modified coke oven for reaction. Where the modified coke oven is oxy-fuel fired, such separation is not necessary as the flue gas, after dewatering, is likely to comprise about 90% to 96% carbon dioxide. Flue gas obtained from oxy-fuel fired modified coke ovens may therefore bes introduced into the modified coke oven for reaction without any separation from other gases, or alternatively after separation from water only.

Turning to Figure 1, the modified coke oven shown comprises rail mounted charging car 2 adapted to deliver ground coal into a refractory enclosure defining a gastight chamber 1, which may be about 20 metres long, about 8 metres high and about 50 centimetres wide,Q via charging holes 3. Lid handling mechanisms mounted on the charging car 2 are modified to slightly rotate the lids 25 on the charging holes, which engage keepers to maintain the seals and prevent the lids from lifting during operation. The charging holes 3 are sealed in a gas tight manner by oven lids 25. If any leakage of gas should occur due to an imperfect charging hole lid seal, the leaked gas will be harmless carbon dioxide rather5 than the more toxic carbon monoxide. In communication with chamber 1 is levelling bar door 17 which facilitates entry into chamber 1 of coal levelling bar 18, which levels the coal introduced into chamber 1 prior to pyrolysis thereof. The levelling bar 18 may have rakes attached along its underside and may be located on a movable machine 24 which is adapted to move between each constituent oven in a modified coke ovens battery. Located ₀ underneath levelling bar 18 is ash pusher ram 10 which is adapted to remove ash from chamber 1 via door valve Vl (which may be in the form of a gas tight door valve) to movable ash extractor 12 which empties into ash conveyor 13. Ash conveyor 13 may be a plate conveyor with ceramic coated overlapping plates, designed to transport red hot ash.

At the end of the battery, ash conveyor 13 is housed in a tunnel (not shown) in which the ash is dry quenched with super cooled nitrogen gas. Ash extractor 12 may be located on a rail track such that it is able to move between constituent ovens of a battery.

Ash pusher ram 10 gains access to chamber 1 via door valve V2 (which may be in the form of a gas tight door valve) and door valve V3 (which may be in the form of a gas tight door valve). Ash pusher ram 10 may be located on movable machine 24 which may be located on a rail track such that it is able to move between constituent ovens of a battery.

Carbon dioxide is delivered to chamber 1 from carbon dioxide main pipeline 14 via descension pipe valve V5. Main pipeline 14 may draw carbon dioxide from a gas holder (not shown).

Chamber 1 is also in communication with fuel gas ascension pipe 4 (which may be fire brick lined), that directs gases and volatiles formed during the pyrolysis process through shut off valve V6. Fuel gas ascension pipe 4 also incorporates emergency gas flare bleeder 6, which may be used to vent and bum gases generated in chamber 1 if necessary, hi communication with fuel gas ascension pipe 4 is raw fuel gas collector main 5. Located between raw fuel gas collector main 5 and shut off valve V6 is downcomer pipe 20 which is in communication with cooling liquor pipe and valve 19. Recirculated ammoniacal flushing liquor may be introduced into downcomer pipe 20 via cooling liquor pipe and valve 19, the ammoniacal flushing liquor flowing to fixed-cup valve 21. Also located in the downcomer pipe 20 is a pneumatic cylinder 22 which positions a plug valve so as to regulate the water level in the fixed-cup valve 21. Fixed cup valve 21 and pneumatic cylinder/controller 22 may comprise the operating apparatus of the ThyssenKrupp-Uhde patented PROven® controller (see page 17, "The Schwelgern Story", Uhde GmbH www.ulide.biz).

Also in communication with chamber 1 via door valve V2 is carbon monoxide exhaust box 11 which may be refractory lined. Exhaust box 11 is connected to carbon monoxide main pipeline 16 (which maybe ceramic lined) via carbon monoxide descension pipe 15 (which may also be ceramic lined), which incorporates gas sampler and analyser 23. Exhaust box 11 and carbon monoxide descension pipe 15 are separated by control valve V4.

The exhaust box and door valves assembly 11, V2 and V3 may be attached to the oven door frame, valve V4 and hydraulic pipes by quick release connections, which do not

employ bolts or nuts. This permits rapid disassembly while the chamber 1 is hot followed by removal and replacement by a spare assembly within minutes, using a jib crane mounted on the movable machine 24. No interruption occurs to operation of the coke ovens. The assembly that has been removed may be refurbished in a workshop and assigned as a spare unit.

The oven walls located above door valves Vl and V2 may be of a solid refractory brick construction. Alternatively, the oven wall above door valve V2 may be replaced by a conventional shorter coke oven door secured by latch bars. Such doors may be removed by a conventional door extractor mechanism mounted on the movable machine 24. In a similar manner, the oven wall above door valve Vl may be replaced by a conventional shorter coke oven door. A door extractor machine may be incorporated into the ash extractor machine 12, which runs on a rail track. Two ash extractor machines incorporating door extractor machines may be parked at each end of the battery. Regardless of the position of the ash extractor 12, one or other of the door extractor machines can service any oven. The door extractor machines may be fitted with equipment to remove both door valve Vl and the upper door if fitted. Both doors are furnished with quick release mechanisms.

Any of the doors of the coke oven may be removed if repairs to oven refractory walls or floor become necessary. However, because coke is never pushed, there is no risk of abrasive damage to oven walls or floors. All of the ash remaining in the chamber 1 is not necessarily removed prior to recharging with coal. A layer of ash may be left on the floor of the chamber 1 so that ash pusher ram 10 has clearance from the oven floor and also from the walls. If, for any reason, all ash must be cleared from the floor, ash pusher ram 10 may be temporarily fitted with a shoe and side bars for this purpose. At the lower level, below the regenerator system 125 are located carbon dioxide main pipeline 7, oxygen main pipeline 8, and fuel gas main pipeline 9, all of which may be ceramic lined. Also located at the lower levels are flue gas main pipeline 120 and carbon monoxide main pipeline 16. The fuel gas, carbon dioxide, flue gas, oxygen and carbon monoxide all flow at controlled rates, either under suction or pressure, propelled by exhausters or fans installed at appropriate gas preparation or treatment stages.

The process of the invention may be performed using the apparatus of Figure 1 as follows.

Charging the modified coke oven with coal

When chamber 1 is empty and ready for charging, the charging car 2 with the four canisters full of coal is parked above it. Charging car 2 automatically removes the lids 25 located above the four charging holes 3, telescopic chutes descend to seal around the holes and charging commences. Charging is completed in a few minutes, after which time the lids 25 are firmly replaced to ensure gas tight seals.

Because chamber 1 is typically at operating temperature when the coal is added, shut off valve V6 is open during the charging cycle so as to allow the initially formed gases, water vapour and volatile matter to flow via fuel gas ascension pipe 4 to raw fuel gas collector main 5. Door valves Vl and V2 and descension pipe valves V4 and V5 are all closed during this time.

Once charging is complete, movable machine 24 is positioned in front of the modified coke oven, levelling bar door 17 is opened and coal levelling bar 18, which may be fitted with rakes, passes through the entire length of chamber 1, after which it is withdrawn and levelling bar door 17 is closed. Following operation of the coal levelling bar 18, the top of the coal bed in chamber 1 is levelled and space is created above the coal charge for passage of raw coke oven gas during pyrolysis and flow of carbon dioxide during the subsequent reaction with the coke.

As the gases move through downcomer pipe 20, they are sprayed and cooled with recirculated ammoniacal flushing liquor via cooling liquor pipe and valve 19 and flow to the fixed cup-valve 21. A pressure sensor in the downcomer pipe 20 relays a signal to a controller which operates the pneumatic cylinder 22. Pneumatic cylinder 22 positions a plug valve to regulate the water level in the fixed cup-valve 21, thus controlling the negative pressure in the system. Pyrolysis (coking) process

The oven walls of chamber 1 in contact with the coal may be heated to a temperature of between about 800 ⁰ C and about 1300 ⁰ C, or between about 85O ⁰ C and about 1200 ⁰ C, or between about 900 ⁰ C and about 115O ⁰ C, or between about 95O ⁰ C and about HOO ⁰ C.

Evolution of gas from the coal is accompanied by formation of hollow pores, which are small, relatively even sized and have thick cell walls. Initially, the coal contracts slightly but then swells substantially at a temperature of about 400 ⁰ C to 45O ⁰ C. As heating progresses the mass resolidifies. Two peaks are observed, the first at about 500 ⁰ C soon after resolidification, and the second at around 73O ⁰ C. These changes, taking place in a

mass with significant temperature gradients, create differential strains which result in the formation of fissures in the coke. Porosity is created via hollow pores and fissures with the volatiles escaping through these apertures. The porous structure of the coke persists after solidification, in fact the stack height may increase above 700 ⁰ C improving porosity. As the pyrolysis process proceeds, gases and volatile matter are drawn from the top of chamber 1, at a temperature of about HOO ⁰ C through fuel gas ascension pipe 4 to raw fuel gas collector main 5 via a remote exhauster fan. The gases and volatile matter are sprayed and cooled to about 95 ⁰ C with ammoniacal flushing liquor as described above, after which they are fed to a primary nitrogen cooled cooler, where water, tar and naphthalene condense out. The gas proceeds to an electrostatic tar precipitator tower, which removes the fine tar particles. Pyrolysis is allowed to continue for a time period between about 12 hours and about 24 hours during which time gases and volatile matter are continually removed from the chamber 1 to raw fuel gas collector main 5.

The tar and ammoniacal liquor may be recovered by removal through a seal tank to a decanter, where the tar sinks to the bottom and the ammoniacal liquor overflows. The tar may be pumped to a tar distillation plant, or alternatively is transferred to tanker trucks for transport to an off-site processing plant. Ammonia gas may be removed by scrubbing the gas with water and then recovered by distillation of the liquor. Flushing liquor, also containing ammonia, may be cooled by cold nitrogen in heat exchangers then recirculated to the gas collector main 5.

The gas may then pass through a series of packed scrubbing towers where it is sprayed with a de-benzolised oil (DBO). The light oil vapours, benzol, toluol, xylol and naphthalene are absorbed by the DBO converting it to benzolised oil (BO). The BO is preheated and distilled to separate light fractions, the recovered DBO being recirculated to the scrubbing towers. Alternatively, the condensate can be purified by acid and alkali washing then separated into each of the liquid products, benzene, toluene and xylene, by fractional distillation, condensed, stored in separate tanks and transferred to tanker transporters or pumped to the liquid fuels refinery for blending with synthesised fuels. Following purification, the resultant gas is directed to a gas holder, and from there by fuel gas main pipeline 9 where it is used to fire the modified coke ovens. Approximately 60% of the fuel gas produced is sufficient to fuel the modified coke ovens, the remaining 40% being available for use in other process applications, for example supplementing coal firing of power station boilers.

Reaction of coke with carbon dioxide

Following extraction of all of the volatile matter and completion of the pyrolysis process, the temperature of the chamber 1 is maintained between about 800 ⁰ C and about 1300 ⁰ C, or alternatively at about the same temperature at which the pyrolysis process was performed. As such, the coke remains at approximately the same temperature at which it was formed when the reaction with carbon monoxide begins. Due to the swelling and solidification of the coke, the height and width of the coke mass is almost the same as that of the initial coal charge. The next stage of the process involves introduction of carbon dioxide into chamber 1. Once the pyrolysis process is complete, shut off valve V6 closes, door valve V2 opens, after which descension pipe valve V5 and control valve V4 open. Preheated carbon dioxide gas is conducted under pressure to chamber 1 via carbon dioxide main pipeline 14 and descension pipe valve V5. The relatively low pressure in carbon dioxide main pipeline 14 is that which is sufficient to force the carbon dioxide downwards through the fissures and vacuoles in the coke consistent with the reaction rate, whilst not being at a level so as to force unreacted carbon dioxide into exhaust box 11 and descension pipe 15. Prior to introduction into chamber 1, the carbon dioxide may be heated in the shell sides of heat exchangers in which freshly produced hot carbon monoxide is cooled by passing through the tube sides. The carbon dioxide flows into the horizontal space above the coke and downwards through the pores and fissures, reacting with the coke to form carbon monoxide gas. The mass of coke is progressively reduced as the reaction proceeds, continuously exposing new, reactive surfaces for the continuation of the conversion of carbon dioxide to carbon monoxide. The single product reaction is simple and efficient and the only by-product is ash. The reaction is run for a period of between about 8 and 24 hours, or until all of the coke is consumed. Hot carbon monoxide gas is removed from chamber 1 under vacuum via door valve V2 to exhaust box 11. The hot carbon monoxide gas then travels through control valve V4 into carbon monoxide descension pipe 15, and then to carbon monoxide main pipeline 16. A computer operated instrumental control system may be employed for regulating carbon monoxide gas quality. A key parameter is the concentration of the carbon monoxide product. Gas sampler and analyser 23 responds to set point concentrations of carbon monoxide and carbon dioxide in the product gas flowing through control valve V4.

If carbon monoxide concentration falls below a set point, for example 95%, a signal from the gas sampler and analyser 23 dampens control valve V4 to reduce gas flow rate until the carbon monoxide concentration is restored to a level above 95%. Simultaneously, descension pipe valve V5 is also dampened to stem carbon dioxide flow and prevent an

5 increase in pressure above the coke bed. Carbon dioxide concentration in the product gas may also be regulated by activation of the flow controls if a set point, for example 2% is exceeded. Other gases, for example nitrogen, hydrogen, nitrogen oxides and sulfur oxides may also be monitored by the gas sampler and analyser 23. An alarm may be relayed to an operator's computer if gas concentrations exceed set levels, thereby causing concentrationo of carbon monoxide to fall below the set point, for example 95%.

Initially, descension pipe valve V5 is virtually fully open and carbon dioxide pressure in the top of the chamber 1 is similar to the pressure in pipeline 14. As the reaction of carbon dioxide proceeds, coke is consumed and the level of coke in the chamber 1 continually subsides. Thus, resistance to gas flow is reduced and the carbons dioxide flow rate tends to increase beyond the rate of reaction. The control system described above then acts to prevent gas flow rate exceeding the rate of reaction.

There is a gradient in gas pressure varying from positive to negative from top to bottom of the coke bed. Figure 4 illustrates that the lower the gas pressure, the lower the reaction temperature. Hence if carbon dioxide pressure rises, the consumption and costs ofQ fuel gas and oxygen would increase. The ideal operating pressure is therefore about one atmosphere, however carbon dioxide pressure above the coke bed is initially higher than one atmosphere and falls as the coke bed level subsides. The carbon monoxide is evacuated by vacuum and the negative pressure in the exhaust box 11 will be lowest during the early stage of the reaction. However, it will rise, though remaining negative, until the ₅ reaction is complete. The differential between inlet positive pressure and outlet negative pressure may remain reasonably constant and may be about 1 atmosphere. At a reaction temperature of at least 1080 ⁰ C, conversion of carbon dioxide to carbon monoxide is essentially complete.

The reaction CO ₂ + C _(S) <-»2CO is reversible and the reverse reaction can occur at0 reduced initiating temperature, although it is exothermic. The carbon monoxide flowing rapidly from exhaust box 11 to main pipeline 14 entrains fine particles of ash and carbon. It is preferred that as much as possible of this material is removed while the gas is still at

an elevated temperature so as to prevent partial conversion of carbon monoxide back to carbon dioxide.

Tar deposits may build up on the sliding gates of door valves Vl, V2 and V3. These valves may therefore be fitted with horizontal, stationary tungsten carbide tipped scraper bars positioned inside the exhaust box 11 below the valve bonnets. The scraper bars remove the tar from the sliding gates into the exhaust box and the scrapings are removed by ash pusher ram 10, along with the accumulated ash material at the completion of the carbon dioxide to carbon monoxide reaction.

Carbon monoxide handling The carbon monoxide main pipeline 16 may feed a bank of ceramic lined dry cyclones (not shown) which remove most of the solids to a sealed bin fitted with a lock hopper below. The hopper may be periodically locked off by a timed valve. After the valve closes, a discharge valve at the bottom of the hopper opens to deliver the grit to the ash conveyor 13. The two valves then reverse to allow the lock hopper to refill. A high level control on the hopper may override the timer mechanism and operate the valves to discharge the hopper if it fills prematurely. The level controller also maintains a minimum level of dust in the hopper to improve the seal when it is receiving cyclone underflow.

An overflow pipeline from the cyclones conducts all of the carbon monoxide gas and some entrained ultra-fine dust through heat exchangers. The cooled carbon monoxide gas is then piped to bag filters for final cleaning. The clean carbon monoxide may then be stored in a gas holder from which it may be delivered to a refinery for preparation of syngas and liquid fuels.

Ash handling

When all the coke in the chamber 1 is consumed, an ash residue is all that remains. Control valve V4 and descension pipe valve V5 are closed, and door valves Vl, V2 and V3 are all opened. Ash pusher ram 10 then moves along the floor of chamber 1 thereby pushing the ash through ash extractor 12 into ash conveyor 13. When ash pusher ram 10 retracts, door valves Vl, V2 and V3 close, control valve V4 and descension pipe valve V5 remain closed, and shut off valve V6 is opened. The chamber 1 is then recharged with coal in readiness for the next pyrolysis cycle.

In situations where problems are encountered limiting the carbon dioxide contamination in the carbon monoxide product as a result of all of the coke in the chamber 1 being consumed, it may be necessary to maintain a minimum level of coke in the

chamber 1. Residual coke, in addition to ash, may therefore remain in the chamber 1 when it is recharged with additional coal. It is therefore advantageous that a clean coal having an ash content of about 6% to 8% be utilised to maximise coke yield and minimise ash residue. Multiple recharges without pushing ash reduces the time each chamber is isolated between charges and also reduces the cycle time for pyrolysis. When these few process cycles are completed, it is necessary to push the ash and residual coke.

The ash conveyor 13 feeds an inclined, vibrating screen (not shown), fitted with a perforated plate deck with apertures in the range 15 mm to 25 mm. Most of the ash passes through the screen and is then disposed of. The coke, being lumpier than the ash, overflows the screen, is blended with coal feed to the grinding plant and is recycled with the ground coal to the modified coke ovens.

Firing of the modified coke ovens

The modified coke oven depicted in Figure 1 is adapted for oxy-fuel firing. As such, the system of firing used by TKU may be employed, but with injection of oxygen rather than air. The firing system is illustrated in Figure 5, which shows a part of a longitudinal cross section of a typical coke oven battery. Referring to Figure 5, the carbon dioxide, oxygen and fuel gas main pipelines 117, 118 and 119 correspond to the main pipelines 7, 8 and 9 in Figure 1. Five coke ovens are shown, of which one oven is designated 111, corresponding to 1 in Figure 1. The ovens are typically only 50 cm wide, but 8.4 m high. The narrowness is necessary because coal is a very poor conductor of heat. Uniform heating of the coal charge and expulsion of all of the volatiles typically takes about 24 hours. The ovens and flues are supported and surrounded by the battery refractory structure 113.

The heating flue 112 on each side of oven 111 burns a gas mixture at about 1300 ⁰ C to produce about an HOO ⁰ C temperature in the oven 111. There may be at least 20 parallel flues in each wall of oven 111. The heating flue 112 crosses the oven 111 at the top and hot flue gas continues to heat the oven 111 as it descends down the opposite side. Each half hour (or thereabouts, depending on how the firing is regulated), the firing reverses burning up the right hand side of the heating flue 112 and down the left hand side. The arrows on the conduits leading to the burners indicate the direction of flow for one firing mode. The left hand conduit from flue 121 conducts carbon dioxide, the narrow vertical conduit from flue 123 conducts fuel gas and the right hand conduit from flue 122 conducts oxygen.

The conduits may be of a firebrick or ceramic composition, as metal pipes would soften and deform at the temperatures employed. The conduits are fed from horizontal, rectangular section flues, each of which is divided by a central, vertical diaphragm. Flue 121 carries carbon dioxide, flue 122 carries oxygen and flue 123 carries fuel gas. The three conduits connect separately to the corresponding horizontal flues 121, 122 and 123. Two of the horizontal flues, the oxygen 122 and fuel gas 123, are fed from the corresponding main pipelines 118 and 119. A flow control and isolating valve, V19 feeds oxygen from main pipeline 118 to one side of the diaphragm in flue 122, and valve V17 feeds fuel gas to one side of the diaphragm in flue 123. Simultaneously, cool carbon dioxide flue gas is fed to lower split flue 124 by valve V13. Lower split flue 124 feeds the regenerators 125, which may be constructed of firebricks arranged in cribiform pattern to permit the free flow of gas around the preheated bricks. The heated carbon dioxide flows from the regenerators 125 into one compartment of flue 121, and from there by conduit to the combustion flue 112. The carbon dioxide is mixed with the oxygen and fuel gas in an approximate ratio of 70%:22%:8% so as to ensure complete combustion. The fuel gas mixture burns at a temperature of about 1300 ⁰ C, maintaining the temperature within the oven 111 at approximately HOO ⁰ C. The reaction of carbon dioxide with carbon is highly endothermic and maintenance of oven temperature at a minimum of 1080 ⁰ C is preferred to achieve efficient and compete conversion to carbon monoxide. Whilst heating proceeds, the corresponding valves V18, V20 and V14, which feed the opposite compartments of the horizontal flues 123, 122 and 124 are closed. After a nominal period, which may be about 30 minutes, the direction of firing reverses. Valves V17, V19 and V13 close and valves V18, V20 and V14 open. Half of the regenerators 125 are heated by hot flue gas passing out of the system, while the other half of the regenerators 125 heat carbon dioxide entering the system. Therefore, the regenerators 125 from each oven are also arranged in two parallel rows, corresponding to the divided flues 121 and 124. The fuel mixture gases then pass through the flues 121, 122 and 123 on the opposite side of the diaphragms which were previously conducting flue gas.

Most coke ovens batteries do not employ combustion in all vertical flues in one wall, but operate a system of "inner" and "outer" flues, wherein half the flues in the wall are burning fuel and the other half are conducting hot flue gas. However, the coke ovens flue gas flows to only one horizontal flue, on one side of flue 124, through either valve V15 or V16 to coke ovens flue gas main pipeline 120. The closed valves on the fuel gas

pipeline 119 and oxygen pipeline 118 prevent coke ovens flue gas from entering the fuel and oxygen gas systems. AU of the valves in the firing system have integrated or separate in-line non return valves to prevent back flow.

The simplified flow diagram of Figure 2 illustrates an embodiment of the process of the invention wherein carbon dioxide is converted to carbon monoxide. Catalyst 26, which may for example be hematite and/or ferronickel, is added to finely ground coking coal 27, and the mixture is transferred to coke ovens 28, where it will be converted to coke that is suitable for reaction with carbon dioxide to produce carbon monoxide. Fuel gas holder 29 supplies fuel gas 30 to the combustion flues of coke ovens 28. Oxygen/nitrogen generator 32 supplies cool oxygen 33 to heat exchanger 34, where heating of the oxygen takes place prior to delivery to the combustion flues of the coke ovens 28. Carbon dioxide from carbon dioxide gas holder 39 is preheated in the regenerators of the coke ovens 28 before being mixed with fuel gas 30 and heated oxygen 31 at fuel gas burners of the coke ovens 28. Nitrogen obtained from the oxygen/nitrogen generator 32 may be used as a condensing agent and/or in heat exchangers where desired.

When the coke ovens 28 are operating, flue gas 35 is produced from the combustion of the fuel gas/oxygen mixture. Flue gas 35, which has a temperature of approximately 1300 ⁰ C, typically comprises about 47% carbon dioxide, 49% water (which is present as super heated steam) and 4% nitrogen. Flue gas 35 is partially cooled in heat exchanger 34 and is then conducted by pipeline 53 to condenser plant 54, which separates water from the carbon dioxide. Dewatered carbon dioxide, having a concentration of about 95%, is delivered from condenser plant 54 by pipeline 55 to carbon dioxide gas holder 39. Condensed water is further treated at condenser plant 54 and then conducted by pipeline 56 to recycle water tank 57. Gases 36 that are produced from the pyrolysis process are contacted with ammoniacal liquor and then cooled and purified to remove water, tar, BTX (benzene, toluene and xylene) and ammonia. The resulting purified fuel gas 37 is recycled to fuel gas holder 29 for use in firing the coke ovens 28.

Carbon dioxide, which may be obtained as a flue gas from an oxy-fuel fired industrial plant 38, is transferred to carbon dioxide gas holder 39. This carbon dioxide is mixed with flue gas 35 which has been cooled and dewatered as described above. Once the pyrolysis process is complete, the coke ovens 28 contain only reactive coke. Cool carbon dioxide gas 40 from gas holder 39 travels through heat exchanger 41, where heating

of the carbon dioxide takes place. The hot carbon dioxide 43 is introduced into reactor 44, where reaction of the coke with carbon dioxide occurs to produce carbon monoxide. In this embodiment, reactor 44 is the same apparatus as coke ovens 28, such that coke ovens 28 are adapted to perform pyro lysis of coal to form coke and also facilitate reaction of the coke with carbon dioxide. Because the flue gas produced by operation of the coke ovens 28 and reactor 44 is captured, no carbon dioxide is emitted to the atmosphere as a result of the process.

Once formed, carbon monoxide 45 is transferred from reactor 44 to dry cyclones 46, which are adapted to remove entrained ash and particulate matter from the carbon monoxide gas stream, which is transferred to ash bin 51. From the dry cyclones 46, the hot carbon monoxide 47 travels through heat exchanger 41, thereby providing cooled carbon monoxide 42. The cooled carbon monoxide 42 is then conducted to gas filters 48 where ultrafme dust is removed, thereafter carbon monoxide 49 is stored in carbon monoxide gas holder 50. The catalyst 26 which is present in ash bin 51 may be recovered (52) and recycled through the process. From gas holder 50, the carbon monoxide may be transferred to a liquid fuels refinery.

The entire process from receipt of the coking coal and handling through to production and delivery of carbon monoxide may be automatically controlled from a central computer system, for example a modified version of the COKEMASTER ^® automation system developed by TKU.

Reference is now made to Figure 3, which depicts an example of a complete process for operating a fossil fuelled industrial plant and converting carbon dioxide generated from such a plant to liquid fuels via syngas. The plant is described in three stages, wherein Figure 3 is divided into Figures 3 A, 3B and 3C. The flow rates of solids, liquids and gases are expressed in tonnes per hour (t/h). The fossil fuelled industrial plant is an oxy-fuel and coal fired power station of 2640 MW output, equivalent to the largest in Australia. It consists of four parallel 660 MW boilers and electricity generating units. The coke ovens battery selected for modification to permit reaction of carbon dioxide with coke is the ThyssenKrupp En Coke-Uhde large coke oven type, as built at Schwelgern in Germany. The first number above each line in Figure 3 refers to the flow rate based on output of carbon dioxide from one 660 MW boiler and generating unit. The second number, following the forward slash above the flow line, or alternatively appearing below the flow line, is the flow rate based on carbon dioxide emitted from four parallel 660 MW units.

The modified coke ovens plant and ancillary coal handling, chemical by-products and carbon monoxide handling plants are based on one coke ovens battery per 660 MW power generating unit. Each of the four batteries comprises 72 to 76 coke ovens. In all, the four batteries house 296 to 304 coke ovens. For clarity, the following description is based on 5 one 660 MW unit only.

Referring to Figure 3A, fuel coal for fuelling the power station is stored in fuel coal stockpile 58 and may be reclaimed at about 300 t/h by a series of reciprocating or vibratory feeders in a tunnel below fuel coal stockpile 58, or by a travelling scraper or bucket wheel- type reclaimer above ground. In either case, the fuel coal is reclaimed onto a belt conveyoro and elevated to fuel coal bunker 59. A vibratory feeder may deliver fuel coal at about 147 t/h from the fuel coal bunker 59 to a conveyor, which delivers the fuel coal to pulverisers 60. The pulverisers 60 may be either ball mills or vertical shaft gas-swept ring roller mills, which pulverise the coal to an extremely fine powder, approximately 80% to 90% passing a 75 micron sieve. s In conventional operation of the power station, the vertical shaft mills are normally swept with hot air, which is termed the "primary air". Further air referred to as "secondary air" is introduced directly into the wind box. The velocity of the primary air is adjusted so as to remove the ultra fine coal, but leave the coarser particles in the mill for further grinding. Q To facilitate efficient operation, it is preferable to employ oxy-fuel firing of the power station boilers instead of using primary and secondary air. Where air is used, the flue gas from the power station comprises about 86-89% nitrogen and only 7-10% carbon dioxide, plus small quantities of water vapour, NOx and SOx. In such a case, purification of the flue gas is required so as to enrich the amount of carbon dioxide. As noted above,5 oxy-fuel firing produces a flue gas having about 95% carbon dioxide and only an infinitesimal amount of nitrogen. The primary and secondary combustion gas may be a mixture of substantially pure oxygen and recycled hot flue gas obtained from the boiler windbox 61, such that only traces of nitrogen are present.

Oxygen is produced in oxygen/nitrogen generator 63, (also called an Air Separation0 Unit (ASU)), which may produce 31,000 tonnes per day of super-cooled oxygen gas, sufficient for firing all four power station boilers and the four batteries of coke ovens. Both gases may be stored in pressurised storage tanks 64 and 65 from which outflow quantities, velocities and pressure rates are automatically regulated to match process

requirements. Oxygen, at a temperature of approximately -200 ⁰ C, may flow from the gas holder 64 at about 278 t/h, and pass through the tubes of a bank of heat exchangers associated with flue gas cooler 62, while hot flue gas from the boiler windbox 61 passes through the shell sides of the heat exchangers, thus heating the oxygen, while cooling the flue gas. Piping and valving is included to split the oxygen into a primary stream of approximately 107 t/h and secondary stream of approximately 171 t/h.

The primary stream of oxygen may be combined with approximately 285 t/h of flue gas, comprising about 95% carbon dioxide. The secondary stream of oxygen may be transferred to the boiler windbox 61 for direct combustion with pulverised coal, flue gas and fuel gas, the latter obtained from fuel gas holder 85. The velocity and pressure of the flue gas/primary oxygen stream mixture is regulated and it sweeps through the pulverisers 60 entraining about 147 t/h of ultra fine coal and conveying it at high velocity to burner nozzles of the boiler windbox 61. The coal and oxygen mixture burns rapidly, with the heat generating high pressure steam in the boiler tubes above the boiler windbox 61. The flue gas exits the boiler windbox 61 and its temperature is reduced to approximately 15O ⁰ C in flue gas cooler 62. The flue gas stream, which may have a flow rate of about 1275 t/h, is cleaned by flue dust filters 66, or by electrostatic precipitators, and passes to a three way flue gas splitter vessel 67. Waste dust from the flue dust filters 66 is dumped in bin 107. The flue gas may be split into three streams exiting the splitter vessel 67. The larger flow of 930 t/h may be further split again into primary and secondary streams, the primary stream returning to the pulverisers 60 at about 285 t/h, whilst the secondary stream may flow at 645 t/h and is combined with 171 t/h of oxygen for direct combustion in the boiler windbox 61. The second stream of carbon dioxide may flow at 143 t/h to regenerators below the coke ovens 75, where heating takes place prior to distribution as hot inert gas to the combustion flues, where it is mixed with oxygen and fuel gas to form the combustion mixture in the heating flues of the coke ovens 75.

The third stream of flue gas from splitter vessel 67 may flow at 203 t/h to the carbon dioxide gas holder 78. Gas holder 78 therefore comprises carbon dioxide returned from the condensers 77 (see Figure 3C), flue gas from the power station and may further comprise carbon dioxide that is generated from the preparation of liquid fuels (for example carbon dioxide generated during fractional distillation (see 99 and 103 in Figure 3C). The capture of all carbon dioxide emissions from the process and recycling to the reactors 89

for conversion to carbon monoxide ensures that no greenhouse gases are emitted to atmosphere.

Coking coal, which may be sized minus 50 mm is stockpiled (68) near the coke ovens plant and may be reclaimed at about 300 t/h, in a similar manner to that described for reclamation and handling of the fuel coal feed to the power station. The coking coal is conveyed to a bunker 69, then fed at about 300 t/h to a coal mill 72. It is then crashed in hammer mills or rod mills. Unlike the fuel coal, the grind of the coking coal is fairly coarse, approximately 95% passing 3 mm. A catalyst such as iron oxide (fine hematite ore) and/or ferronickel alloy may be drawn from a bin 70 by feeder 71, and fed to the hammer mills or rod mills at about 9 t/h of hematite and 0.5 t/h of ferronickel for admixture with the coking coal. The catalyst enhances the reactivity of the coke and therefore increases the rate of conversion of carbon dioxide to carbon monoxide. Oil may also be added to raise the bulk density of the coal, thereby increasing the tonnage capacity of the coke ovens 75. Another possible additive is lime which improves the basicity of the coal ash, as an ash low in acidity assists reactivity.

The ground coking coal may be conveyed at about 300 t/h from the coal mill 72 to a fine coal bunker 73, having a capacity of about 1000 tonnes. The coke ovens 75 may be divided into two sub-batteries of 36 to 38 ovens each and the fine coal bunker 73 may be positioned above the space between them. Below the oven top level in this central section are the switch room, control room, offices, workers' amenities and access ways.

The bottom of the fine coal bunker 73 may be fitted with four or more rows of four remotely controlled discharge gates and set at an elevation which accommodates a charging car 74 below it. The washed coking coal has a solid density of 1.25 to 1.40, but the ground coke ovens feed has a bulk density of approximately 0.9 t/m due to the fine average particle size and voids between the particles. This factor is taken into account in the design of bunker 73 and the charging car canisters. Since the pyrolysis and carbon monoxide gasification interval for an individual oven is up to 36 hours, the period between charging ovens for a 72 to 76 ovens battery may be about 28 to 30 minutes. This allows ample time between charges for one car to serve both sub-batteries of 36 to 38 ovens each. Charging car 74 supplies coal to coke ovens 75. Oxygen is drawn from oxygen gas holder 64 at about 44 t/h and preheated by passing through the shell sides of heat exchanger 76. The pre-heated oxygen from heat exchanger 76 and the fuel gas from gas holder 85 are conveyed by separate pipelines to the respective horizontal flues below the

ovens and distributed to rows of burners feeding the vertical combustion flues. The gases are mixed at the burners with hot carbon dioxide from a set of regenerators in the ratio of about 70:22:8 (carbon dioxide:oxygen:fuel gas). The gases burn in the upward flowing vertical flues at about 1300 ⁰ C and hot flue gas passing down the reverse vertical flues is used to pre-heat the second set of regenerators before being discharged to the flue gas main pipeline (See Figure 5 and the description of the firing system above).

Hot flue gas discharged from the coke ovens is piped to the tube sides of heat exchanger 76, while cold oxygen enters the shell side. Flue gas exiting the heat exchanger 76 is transferred to condenser and water treatment plant 77 (see Figure 3C), where the water in the gas stream is condensed and decanted. The cooled, dewatered flue gas comprising about 97% carbon dioxide is then transferred to gas holder 78, while the decanted water is further cooled prior to removal of condensed organic liquids.

Referring to Figure 3B, as the pyrolysis of coal process proceeds, volatile compounds are liberated from the coke ovens 75. Separation of the heavier volatiles into condensible products provides a fuel gas for heating the coke ovens 75 and the reactors 89. On exiting the coke ovens 75, the volatiles are sprayed with ammoniacal flushing liquor, cooled and fed to primary gas coolers 79, where water, tar and naphthalene condense out. The tar and ammoniacal liquor are recovered by removal through a seal tank to a decanter, where the tar sinks to the bottom and the ammoniacal liquor overflows. The flushing liquor passes through coolers 81 and may be recycled to the coke ovens 75. The gas emitted from the primary gas coolers 79 flows to electrostatic tar precipitator towers 80 which remove fine aerosol tar prior to the gas moving to the exhausters 83. The exhausters 83 are large fans which induce volatiles to flow from the coke ovens 75 and through the primary gas coolers 79 and tar precipitators 80 under vacuum. The gas discharged from the exhausters 83 is propelled through the remainder of the gas train under pressure. The exhausters may be variable speed machines which regulate negative and positive gas pressures throughout the gas purification train.

The tar is pumped to a tar distillation plant or is transferred to tanker trucks 82 for transport to an off-site processing plant. The principal refined product from tar is carbon electrodes for metal smelting furnaces. Coal tar is also a vital raw material for production of carbon black for the leather and ink production industries, fuel tar oils, road tars, naphthalene and pitch.

Following tar extraction, what is now raw fuel gas is pumped under pressure through a series of packed scrubbing and stripping towers 84, where it is sprayed with DBO, which is converted to BO as described above. The separated BTX may be further processed if desired (90). Ammonia gas which passes on with the fuel gas flow is extracted in an ammonia absorber plant 86. hi this plant, the gas passes up a multi-level tower into which weak acid is sprayed. Dilute ammonium sulfate or nitrate solution passes to a vacuum evaporator where it is concentrated. Ammonium sulfate or ammonium nitrate crystallises out (87) and may be marketed as fertiliser. Ammonium nitrate is also used as an ANFO blasting agent in mining. The clean fuel gas obtained from the volatiles-produced from the coke ovens 75 is then stored in fuel gas holder 85. A portion of the fuel gas may be used to fire the coke ovens 75, and the reactors 89, whilst another portion may be conducted to the boiler windbox 61 as described above in Figure 3 A.

Referring to Figure 3 C, carbon dioxide gas drawn from the carbon dioxide gas holder 78 is pre-heated in the shell sides of heat exchanger 91, in which the freshly produced hot carbon monoxide is cooled by passing through the tube sides. The heated carbon dioxide may be conducted under pressure at about 373 t/h into reactors 89, wherein reaction with coke takes place. The coke ovens 75 (see Figure 3A) and the reactors 89 may be the same apparatus, for example a modified coke oven or ovens as depicted in Figures 1 and 5. The carbon monoxide produced in reactors 89 feeds ceramic lined dry cyclones 110 at 474 t/h which remove solids at 19 t/h to a sealed bin fitted with a lock hopper. An overflow pipeline from the cyclones 110 conducts all of the carbon monoxide gas and some entrained ultra-fine dust through heat exchanger 91. The cooled carbon monoxide is then piped to gas filters 92, where final cleaning takes place. Waste material from the final cleaning is dumped in bin 109. The carbon monoxide is then temporarily stored in a gas holder 93, from which it is delivered to the liquid fuels refinery at 474 t/h. On completion of the reaction of the coke with carbon dioxide, an ash residue remains in reactors 89, which is transferred to bin 108.

Carbon monoxide obtained from the reactors 89 may be used to prepare liquid fuels as follows. Hydrogen gas from hydrogen generator 95 is stored in hydrogen gas holder 96. Once drawn from hydrogen gas holder 96, the hydrogen is pre-heated in a heater/compressor 97 by for example using fuel gas or distillate from the liquid fuels conversion process and oxygen. Because compression raises the gas temperature, little

additional sensible heat is applied. Carbon monoxide from gas holder 93 is preheated in a heater/compressor 94. Surplus fuel gas refined from the volatile matter liberated from the pyrolysis of coal may be used for other heating purposes in the process, such as the carbon monoxide pre-heater 94, hydrogen pre-heater 97, the fractional distillation columns 99 and 103 or even for supplementing coal fuel to the power station boilers. Emission gases from these heating processes may be captured and pumped back to the reactors 89 for conversion of contained carbon dioxide to carbon monoxide.

The heated carbon monoxide and hydrogen, mixed in correct proportions, enter a reactor, for example a High Temperature Fischer Tropsch (HTFT) plant 98 at 45O ⁰ C and 170 bar pressure in the presence of a nano-scale iron based catalyst dispersed in a slurry. A mixture of hydrocarbons is produced and each is separated by fractional distillation 99, separately condensed into components of liquid fuels in condenser 100 and stored in individual tanks 101. The oxygen and nitrogen generator 63 produces 100,000 t/d of super cooled nitrogen gas, which may be stored in gas holder 65 and subsequently used for cooling and condensing in condensors 100 and 104 in addition to other heat exchangers, condensors and dry quenching of hot ash, as described above. This use of nitrogen as a condensing agent results in the temperature, pressure and pipeline velocity of the nitrogen being greatly increased and it may therefore be utilised to drive generators 106, which may supply power to all stages of the process, and potentially feed power to an electricity grid. Water condensed from the process may be treated (77) and recycled (88).

For production of ethanol and other alcohols, hydrogen drawn from hydrogen gas holder 96 undergoes an increase in temperature and pressure in heater/compressor 97. Carbon monoxide from gas holder 93 also undergoes an increase in temperature and pressure in heater/compressor 94. Both gases flow to alcohol reactor 102 at a pressure of about 20MPa and 300 ⁰ C, and are mixed at a ratio of 1.5 to 2 moles of hydrogen per mole of carbon monoxide, to maximise the proportion of ethanol in the product. The alcohol reactor 102 may be a packed tower with a catalyst such as zinc chromite plus small amounts of alkali metal or iron salts packed between perforated shelves. Blended carbon monoxide and hydrogen are piped into the base of the packed tower and are forced through the packed tower by the gas pressure. The catalytic reaction between the carbon monoxide and hydrogen forms various alcohols. Where fractionation is necessary to separate the constituent alcohols, the gaseous vapour is sent directly to a fractionation still 103, and on to condensers 104. Fractions ranging from methanol and ethanol to heavier alcohols such

as n-propanol, isopropanol and isobutyl alcohol may be separated and stored (105). These alcohols have many uses. Ethanol in particular is now used in quantities of up to 10% in pump unleaded gasoline in Australia, and up to 80% in other countries such as Brazil.

It should be noted that the preparation of syngas, a mixture of carbon monoxide and hydrogen, gives rise to the possibility of synthesising a very large range of liquid fuels, such as is performed at plants operated by SASOL Limited in South Africa.

The entire process depicted in Figures 3, 3A, 3B and 3C has a number of significant advantages. First, it eliminates carbon dioxide emissions to the atmosphere from a coal- fired power station. Second, it allows conversion of a problematic greenhouse gas to useful liquid fuels, such as petrol, diesel, aviation fuel and ethanol. Third, the process results in minimal waste products and is sustainable with a continued supply of coal and carbon dioxide. The volatile materials produced in the pyrolysis stage are fractionated and reused in the process (for example fuel gas and liquid fuel blending components benzene, toluene and xylene) or in other industries (for example coal tar is vital for the production of road tar and carbon electrodes).

Another important advantage is that the process relieves the fossil fuel industries, particularly coal and natural gas, of censure for being major contributors to atmospheric pollution and global warming.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications.