GB2614525A

GB2614525A - Underground gasification

Info

Publication number: GB2614525A
Application number: GB2116342.3A
Authority: GB
Inventors: Stamp Clive
Original assignee: Rockfuel Innovations Ltd
Current assignee: Rockfuel Innovations Ltd
Priority date: 2021-11-12
Filing date: 2021-11-12
Publication date: 2023-07-12
Anticipated expiration: 2041-11-12
Also published as: GB2614525B; GB202116342D0

Abstract

A method of producing fuel includes burning synthesis gas 14 in a furnace 11, the furnace being used to generate hot gasses 12. At least a portion of the hot gasses is transferred to an underground fossil fuel seam 13 to gasify the fossil fuel to produce synthesis gas. A portion 15 of synthesis gas produced by the gasification process is utilised to power the furnace. Methods of producing carbon-neutral fuel also involve heating limestone (fig. 2, 32) in a limekiln (fig. 2, 28) to produce calcium oxide, which is then used to absorb carbon dioxide from the atmosphere.

Description

Underground Gasification This invention relates to a method for the production of fuel using underground fossil fuel gasification. Furthermore, the invention relates to the production of carbon neutral fuel utilising underground fossil fuel gasification. The invention may be utilised in the formation of carbon neutral fuels for transport, domestic and commercial use, and the formation of useful carbon neutral gases.

The phrase "carbon neutral" is used herein to mean that the amount of carbon dioxide produced during the process is balanced and negated by the subsequent absorption or capture of an equivalent or even greater quantity of carbon dioxide by calcium oxide produced by the process. Carbon neutrality must be distinguished from carbon offsetting; in contrast to carbon neutrality, the process of offsetting requires a reduction in emissions of carbon dioxide to compensate for emissions made elsewhere. Carbon offsetting is subject to the fundamental moral principles of the individuals involved and is fundamentally flawed; there are various investigations and reports that show that even gold and platinum carbon offset schemes are faulty, and in some cases, they are simply scams. Essentially, the financial value of carbon offsets does not cover the sum needed to make processes carbon neutral. In essence, "carbon offset" does not equate to "carbon neutral" or "zero emissions".

The combustion of fossil fuels creates large quantities of greenhouse gases and harmful emissions. The combustion of coal in particular creates an enormous amount of carbon dioxide each year. Throughout the world coal is used as the main energy source for the generation of electricity. With increasing concerns of climate change due to greenhouse gases, there is a need to reduce -2 -the amount of air pollution caused by the combustion of coal and by industrial manufacturing processes. Existing underground gasification processes require external igniting sources to be brought to the fossil fuel bed. The transportation of such inevitably enhances the problem of pollution and increases the cost of the overall process.

In an attempt to reduce pollution caused by the burning of coal, there is an increasing need for a clean carbon neutral coal technology for the production of carbon neutral fuel. Processes for producing fuels using compounds and elements, such as carbon dioxide and hydrogen are well established. Almost inevitably, such methods are not carbon neutral since, for example, obtaining carbon dioxide directly from the atmosphere is not only expensive but is also problematic in that the extraction process can create yet more pollution.

The United Kingdom alone has vast reserves of coal which is inaccessible by conventional mining methods. Such coal can now be accessed by new technology combined with underground gasification but the emissions from standard underground coal gasification are considered too high and are not conducive to a low carbon solution.

To address the foreseeable problems associated with global warming, the process of carbon sequestering is used to capture and supposedly store atmospheric carbon dioxide. Again, this process avoids dealing properly with the issue. Carbon dioxide has been found to leak from sequestration sites. As more carbon dioxide is sequestered, there will be more leakage affecting future generations, which defeats the object of trying to make things better for future generations. -3 -

Several methods have been proposed to deal with atmospheric carbon dioxide, as an alternative to sequestration. One of those proposals is the conversion of carbon dioxide into carbon and oxygen. The process of splitting carbon dioxide is achievable but requires large amounts of energy. Under the principles of thermodynamics, if that energy is supplied by hydrocarbon fuels the net result will be more carbon dioxide than from the outset.

There is an urgent need for us all to take action for the sake of the future of humanity. The general consensus of scientific opinion is that we are in a race against time; the clock is ticking. Innovators and all those involved in the protection of new ideas, to reverse the potentially cataclysmic impact of humankind in this area, have a particularly important part to play in encouraging the development of processes that will make a difference at this critical time. It is a principal aim of the present invention to provide a method for producing fuel, which addresses at least some of the environmental problems 15 created by conventional fuel production methods discussed above.

According to a first aspect of this invention, there is provided a method of producing fuel comprising: burning synthesis gas in a furnace, the furnace being used to generate hot gasses; transferring at least a portion of the hot gasses to an underground fossil fuel seam to gasify the fossil fuel to produce synthesis gas; and utilising a portion of synthesis gas produced by the gasification process to power the furnace. -4 -

Conventional gasification techniques typically require ignition of the underground coal seam and air, pure oxygen and water to be superheated and pumped into the seam. In the present invention, by recirculating a portion of the synthesis gas produced during gasification of the fossil fuel, the process can become largely self-sustainable; there will be no need for external igniting sources to be brought to the coal bed, thus reducing the associated expense. Upon start-up any fuel required to initiate the process can be compensated for by a proportion of the calcium oxide produced by the process, which can be allocated to marine purposes where this will absorb almost twice the carbon dioxide produced in the making of that carbon dioxide.

Preferably the method includes additional steps to facilitate the production of carbon neutral fuel. To achieve this, the method may further comprise the step of: heating limestone in a limekiln having an inlet for the introduction of limestone, a heater for heating limestone and an outlet for the release of carbon dioxide yielded by the heated limestone; wherein calcium oxide produced by the calcination of the limestone is collected from the limekiln and is used to absorb carbon dioxide from the atmosphere. In some instances, the recirculation of synthetic fuel from the gasification 20 process to the furnace, may be secondary to the process of producing a fuel which is carbon neutral. According to a second aspect of this invention, there is provided a method of producing a carbon neutral fuel comprising: burning synthesis gas in a furnace, the furnace being used to generate hot gasses; -transferring at least a portion of the hot gasses to an underground fossil fuel seam to gasify the fossil fuel to produce synthesis gas; and - heating limestone in a limekiln having an inlet for the introduction of limestone, a heater for heating limestone and an outlet for the release of carbon dioxide yielded by the heated limestone; wherein calcium oxide produced by the calcination of the limestone is collected from the limekiln and is used to absorb carbon dioxide from the atmosphere.

In this second aspect, a portion of synthesis gas produced by the gasification process may be used to power the furnace.

In the present invention, the gasification process may be carried out in the absence of oxygen (pyrolysis), as distinct from the standard gasification process where oxygen (or oxygen in air) is injected into the coal seam after or contemporaneously with ignition.

Standard gasification processes involve the ignition of the fossil fuel seam.

In the present invention it is the synthesis fuel in the furnace which is ignited. The distinction is important. Standard gasification of a coal seam uses air, oxygen and/or steam and the coal is consumed, usually by partial combustion, to produce a calorific gas. Complete combustion can alternatively be achieved by using more air to produce gas containing carbon monoxide and hydrogen. In either case, combustion is integral to the process. In contrast, the present invention can involve destructive distillation of the fuel seam by carbon dioxide, with or without combustion.

Preferably, the furnace is being used to generate hot gasses comprising carbon dioxide. It will be appreciated however that the term "hot gases" as used -6 -herein, in relation to the furnace, may be interpreted as including water vapour, air and other phases such as steam. In the case of a coal seam, the reaction would be as shown in Table 1 below:

Table 1

Since coal is primarily a mix of carbon and hydrogen, the carbon dioxide will react therewith to produce additional fuel.

Calcination of limestone by heating releases carbon dioxide and produces calcium oxide (referred to hereinafter as quicklime), as shown in Table 2, below: Limekiln CaCO3 > CaO + CO2 Calcium Carbonate > Calcium Oxide + Carbon Dioxide Table 2 The combustion of synthetic fuel produced by the gasification process of the present invention, for example by the operation of vehicles, will inevitably create carbon dioxide emissions. The reactions are illustrated in Table 3 below: Combustion of Fuel Products 2C0 + 02 > 2CO2 Carbon Monoxide + Oxygen > Carbon Dioxide 2H2 + 02 > 2H20 Hydrogen + Oxygen > Water Gasification C + CO2 >2C0 Carbon + Carbon Dioxide > Carbon Monoxide

Table 3 -7 -

In the present invention, quicklime produced by the heating of limestone is collected from the limekiln and is then used to absorb carbon dioxide from the atmosphere, as shown in Table 4 below: Recovery of Carbon Dioxide by Calcium Oxide CaO + CO2 > CaCO3 Calcium Oxide + Carbon Dioxide > Calcium Carbonate

Table 4

Such quicklime could be used in vehicle exhaust filters or along motorways or other areas of high carbon dioxide pollution in order to absorb the carbon dioxide. Additionally, or alternatively, the quicklime could be made into mortar-like slabs which could be utilised in sea defences, new quays and the like.

Quicklime is particularly good at absorbing carbon dioxide when placed in water and this could be especially beneficial in coastal projects. In fact, quicklime is able to absorb nearly twice the carbon dioxide produced in its formation when it is placed in water; thus, quicklime could be used in the sea and coastal works or sewage schemes, to counter any excess carbon dioxide resulting from the process. The resultant synthetic fuel can be considered carbon neutral because the carbon dioxide produced in the later combustion of these fuels, for example in an internal combustion engine of a vehicle, will be countered by the quicklime produced by the kiln.

Preferably, the underground fossil fuel seam is an underground coal seam.

In this way, the considerable reserves of coal in the UK can be utilised without causing adverse effects due to emissions. As an alternative, the underground -8 -fossil fuel seam could be an underground crude oil field. In this way, the present invention can be used to turn a carbon polluting fuel and/or a carbon polluting process, into a carbon neutral fuel/process.

Preferably in the present invention air will be inserted into the furnace and 5 the synfuel burnt, thereby causing combustion and hot gasses. The chemical reactions are shown in Table 5 below: Furnace 2C0 + 02 > 2CO2 Carbon Monoxide + Oxygen > Carbon Dioxide 2H2 + 02 > 2H20 Hydrogen + Oxygen > Water Table 5 The heat produced by the furnace will ideally be over 500°C The hot 10 gasses will be mainly carbon dioxide. The furnace is used directly and/or indirectly to generate hot gasses which may comprise carbon dioxide.

The furnace may be used directly by passing the hot gases from the furnace to the fuel seam, where the gasification may take place. In practice the hot gases may be directed through pipes to the fuel seam.

Alternatively, or additionally, the furnace may be used indirectly either by way of the limekiln or by way of a boiler, as discussed in more detail below. When the furnace is used indirectly by way of the limekiln, hot gasses may be passed from the furnace to the heater of the limekiln to heat the limestone within the limekiln. The resultant carbon dioxide hot gases, yielded by the heated limestone, may be transferred to the underground fossil fuel seam to facilitate -9 -gasification thereof or may be processed in other ways, as discussed in more detail below.

Carbon dioxide produced by the limekiln is pure and is quantifiable. This carbon dioxide may be passed to the fossil fuel seam to pyrolyse the coal (in the 5 absence of air) to form a carbon monoxide based synthetic fuel.

When the furnace is used indirectly by way of a boiler, hot gases may be passed from the furnace to heat water in a boiler. The resultant hot gases, which may comprise air and steam, may be transferred to the underground fossil fuel seam to facilitate gasification thereof. In this arrangement, carbon dioxide from 10 the furnace may be processed in other ways, as discussed in more detail below. In either of these arrangements, excess carbon dioxide from the furnace combustion may be electrolysed, sequestered in a spent fossil fuel seams or additionally used to gasify the fossil fuel seam.

Sequestration, as proposed in the present invention, may be particularly effective because it is so much deeper than other forms of sequestration. This is because the coal seams to be gasified are phenomenally deep structures and are situated far under water tables and other environmental risks. This arrangement also provides a far greater percentage of entrapment for the carbon dioxide. If necessary, more calcium oxide may be allocated to marine projects to cover any minimal leakage over time. In the preferred embodiment a system performing the method includes a boiler for converting water to steam, the boiler having an inlet for the introduction of water and an outlet for steam. At least a portion of heat energy, in the form of hot gases, produced by the furnace may be directed to heat water in a boiler to produce steam. This could be transferred to -10 -the fossil fuel seam, as discussed above. Alternatively, or additionally the heater of the limekiln may be in communication with the boiler outlet so that steam from the boiler is supplied directly to the heater to facilitate the heating of limestone within the limekiln.

The term "system" is used herein to mean an arrangement of apparatus and, while some of the component parts of the apparatus are conventional and/or known per se, the particular assemblage is novel and wholly inventive.

In another arrangement the heater of the limekiln may be in communication with the boiler outlet indirectly by way of other apparatus so that /0 energy from the steam is supplied to the heater to facilitate the heating of limestone within the limekiln. In this way a portion of the steam output from the boiler may be used to generate electricity. The heater of the limekiln may be an electrical resistance heating element powered by electricity.

A system performing the method may comprise a turbine-driven generator set connected to the boiler and means to direct steam from the boiler to the turbine of the generator set for the production of electricity. Preferably, in this arrangement, where an electrical resistance heating element is provided, the heater of the limekiln is electrically powered by the turbine-driven generator set. If the steam produced by the boiler is less than 900°C, this arrangement is particularly advantageous as it allows the limekiln to be supplied with sufficient heat for the calcination of limestone.

Both of the above discussed arrangements may be used together such that the heater of the limekiln is capable of receiving steam directly from the boiler (or hot gasses from the furnace) and also comprises an electrical heating element -11 -to provide additional heat within the limekiln. In such an arrangement, if the steam produced by the boiler is less than 900°C, a portion of the steam produced by the boiler may be supplied directly to the heater to facilitate the heating of limestone within the limekiln with the remainder of the steam being directed to the turbine for the production of electricity to power the electrical heating element further to heat the limestone within the limekiln and to power the limekiln. Following gasification, the resultant gas would consist largely of carbon monoxide and hydrogen, thereby forming synthesis gas. The carbon monoxide produced could either be sold as a valuable calorific gas or utilised in further reactions (such as a water gas shift reaction) for the production of fuels for vehicles.

A portion of the synthesis gas may be recirculated to fuel the furnace and the remainder may be collected from the fossil fuel seam in any conventional manner. The synthesis gas could be sold as produced, for example to the gas grid. Alternatively, or additionally, Synthetic fuel (synfuel) may be obtained from the resultant synthesis gas using common methods, as will be appreciated by those skilled in the art. For example, a portion of synthesis gas produced by the gasification process may be converted into synthesis fuel using the Fischer Tropsch process, for use in motor vehicles and aircraft for example.

Any balance of carbon dioxide produced by the process may be directed elsewhere for further processing. To achieve further processing of the carbon dioxide, a system performing the method of the present invention may further comprise an electrolysis plant arranged to receive excess carbon dioxide -12 -produced by the system and to convert the carbon dioxide into carbon and oxygen by electrolysis, as shown in Table 4:

Table 4

The splitting of carbon dioxide into carbon and oxygen is energy intensive, but by utilising energy derived from elsewhere in the system, the process may become viable.

The system may additionally or alternatively further comprise a chemical processing unit arranged to receive excess carbon dioxide produced by the method and to convert the carbon dioxide and water to oxygen or hydrogen. This may require the use of a catalyst. Under normal circumstances, the high energy requirements for converting carbon dioxide and water into oxygen or hydrogen makes the process generally unfeasible, but this may be addressed by exploiting energy which has been produced by the combustion of synthesis gas in the furnace.

The electrolysis plant and/or chemical processing unit may be operatively connected to the limekiln to receive excess carbon dioxide and/or heat produced by the calcination of limestone. The electrolysis plant and/or chemical processing unit may alternatively or additionally be connected to the furnace to receive excess carbon dioxide and/or heat therefrom; this may be of particular use in an arrangement where the fossil fuel seam is gasified solely by carbon dioxide from the kiln. Heat reclamation from the limekiln and the furnace can therefore be Electrolysis CO2 > C + 02 Carbon Dioxide > Carbon + Oxygen -13 -used to assist the conversion process in the electrolysis plant and/or the chemical processing unit. The electrolysis plant and/or chemical processing unit may be powered by electricity produced by the method. The electrolysis plant and/or chemical processing unit may be operatively connected to the turbine-driven generator set and/or the boiler to receive electricity or steam produced thereby to facilitate the conversion process Advantageously, excess carbon dioxide produced by a system performing the method may be sequestered in spent coal seams and/or the geologic formation formerly gasified, such as the spent oil reservoir.

In an alternative arrangement or in addition to some or all of the methods hereinbefore described in relation to the processing of excess carbon dioxide, the system of the present invention may include means for the processing of excess carbon dioxide into useful carbon dioxide-based products. Electricity, excess heat and/or excess steam produced by the method can be utilised for this purpose.

There are known processes for the processing of carbon dioxide into carbon neutral products.

Catalysts effectively to convert carbon dioxide into carbon monoxide and oxygen or hydrogen have been identified. Such catalysts have been shown to provide highly effective results, but the process requires large amounts of energy, making such conversion inefficient in practice.

An important aspect of the present invention is that carbon dioxide produced by the methods is pure and is not atmospheric carbon dioxide. This pure carbon dioxide can be quantified and collected and utilised in a variety of ways. Excess carbon dioxide may be sequestrated or used in making fuels or -14 -other processes on the basis that a proportional amount of calcium oxide produced by the process can be used in marine projects where nearly twice the amount of carbon dioxide can be absorbed than the carbon dioxide produced by the systems of the present invention. Preferably, this excess carbon dioxide is processed further such that the whole process is inherently whole cycle carbon neutral.

By way of example only, an embodiment of this invention will now be described in detail, reference being made to the accompanying drawings in which:-Figure 1 is a simplified diagram of a process of producing fuel, which operates in accordance with a first aspect of this invention; Figure 2 is a simplified diagram of a process of producing a carbon neutral fuel, which operates in accordance with a second aspect of this invention; Figure 3 is a simplified diagram of a process of producing a carbon neutral 15 fuel, which operates in accordance with the first and second aspects of figures 1 and 2 of this invention; and Figure 4 is a simplified diagram of an alternative process of producing a carbon neutral fuel, which operates in accordance with the first and second aspects of figures 1 and 2 of this invention.

Referring initially to Figures 1 and 3, there is shown a system 10 performing the method of the present invention. The system 10 includes a furnace 11 which comprises burners (not shown) for combusting synthesis gas. The furnace 11 will receive air and synthesis gas is burned therein to produce hot exhaust gases 12 in excess of 500°C. The hot exhaust gases 12 mainly comprise -15 -carbon dioxide and these are directed through pipes to an underground fossil fuel 13. The fossil fuel 13 may be a coal seam or may be a crude oil or oil-shale seam. Passing of the hot carbon dioxide rich exhaust gases 12 over the fossil fuel seam 13 will result in predominately carbon monoxide and hydrogen. This is because the fossil fuel seams 13 are carbon intensive. The resultant carbon monoxide and hydrogen together form a synthesis gas 14.

A portion of the synthesis gas 15 produced by the gasification process is recirculated to fuel the furnace 11. In this way, the process is self-fuelling.

The remaining synthesis gas 16 produced by the gasification process can be collected by conventional methods, as known by those skilled in the art.

The synthesis gas 16 could be sold as produced, for example to the gas grid. Alternatively, or additionally, Synthetic fuel (synfuel) may be obtained from the resultant synthesis gas 16 using common methods, as will be appreciated by those skilled in the art. For example, a portion of synthesis gas 16 produced by the gasification process may be converted into synthesis fuel 18 using the Fischer Tropsch process 17, for use in motor vehicles and aircraft 19 for example.

The burning of synthesis gas and/or synthetic fuel will of course cause carbon dioxide pollution. However, such carbon dioxide 20 may be compensated for by the process of the present invention, as discussed in more detail later.

Referring now to Figures 2 and 3, a process for producing a fuel which is inherently carbon neutral is shown.

The burning of synthesis gas in the furnace 11 produces vast amounts of heat 23 which can be utilised further. To facilitate this, a system 10 performing a method of the present invention includes a boiler 24. The boiler 24 receives heat 23 from the furnace 11 to convert water into steam. A turbine-driven generator set 25 is arranged to receive steam from the boiler 24 and is configured to generate electricity for supply elsewhere in the system 10.

A limekiln 28 is provided for the production of carbon dioxide from limestone. Calcination of limestone by heating releases carbon dioxide 29 and produces calcium oxide 30 (referred to hereinafter as quicklime). The limekiln 28 is connected to the turbine generator set 25 to receive power 31 therefrom, as discussed in more detail below. The limekiln 28 is provided with an inlet for the introduction of limestone 32, a heater (not shown) for heating the limestone 32, an outlet for the release of carbon dioxide 29 and an outlet for the release of quicklime 30. Quicklime 30 produced by the heating of limestone 32 may be collected from the limekiln 28 and used to absorb carbon dioxide from the atmosphere 20. The calcining of limestone 32 produces carbon dioxide 29. The limekiln outlet is configured to direct the carbon dioxide 29 away for further processing, as discussed in more detail below.

Excess carbon dioxide 29 produced by the method of the present invention can be processed in various ways. As shown, a system 10 performing the method may include an electrolysis plant 33 arranged to receive excess carbon dioxide 29 produced by the limekiln 28 and to convert the carbon dioxide 29 into 20 carbon 34 and oxygen 35 by electrolysis. Such processes are known by those skilled in the art and are thus not discussed in detail herein. The electrolysis plant 33 is powered by electricity 31 produced by the turbine-driven generator set 25. Carbon dioxide 29 produced by the limekiln 28 is pure and can be sold to industry 36 and carbon dioxide 29 generated by such industrial use, can be -17 -absorbed by quicklime 30 expelled from the limekiln 28. Alternatively or additionally, excess carbon dioxide 29 produced by the limekiln 28 can be sequestered 37 in spent fossil fuel seams.

An alternative arrangement is illustrated in Figure 4. Here, carbon dioxide 29 produced by the limekiln 28 may be transferred directly to the coal seam to gasify the seam in addition to or as an alternative to the gasification of the seam by the carbon dioxide rich exhaust gases 12 from the furnace. Where this arrangement is an alternative, the carbon dioxide rich exhaust gasses 12 from the furnace 11 can be sequestered in spent fossil fuel seams and/or conveyed to the electrolysis plant 33 for processing.

Instead of, or in addition to, the electrolysis plant, other processes may be utilised for the negation of excess carbon dioxide, that can use the heat,steam and/or electricity produced by the system 10 for this purpose but which do not form part of this application. The system may also include a chemical processing unit (not shown) arranged to receive excess carbon dioxide produced by the limekiln 28 and/or furnace 11 and to convert the carbon dioxide and steam in to oxygen or hydrogen. Such processes are known by those skilled in the art and are thus not discussed in detail herein. The chemical processing unit may be powered by electricity 31 produced by the turbine-driven generator set 25.

Excess carbon dioxide is processed further such that the whole process is inherently whole cycle carbon neutral. As such, synfuel 14 produced by the process can be considered carbon neutral.

Claims

-18 -CLAIMS 1. A method of producing fuel comprising: - burning synthesis gas in a furnace, the furnace being used to generate hot gasses; transferring at least a portion of the hot gasses to an underground fossil fuel seam to gasify the fossil fuel to produce synthesis gas; and utilising a portion of synthesis gas produced by the gasification process to power the furnace.
2. A method as claimed in claim 1, further comprising the step of: - heating limestone in a limekiln having an inlet for the introduction of limestone, a heater for heating limestone and an outlet for the release of carbon dioxide yielded by the heated limestone; wherein calcium oxide produced by the calcination of the limestone is collected 15 from the limekiln and is used to absorb carbon dioxide from the atmosphere.
3. A method of producing carbon neutral fuel comprising: burning synthesis gas in a furnace, the furnace being used to generate hot gasses; transferring at least a portion of the hot gasses to an underground fossil fuel seam to gasify the fossil fuel to produce synthesis gas; and - heating limestone in a limekiln having an inlet for the introduction of limestone, a heater for heating limestone and an outlet for the release of carbon dioxide yielded by the heated limestone, -1 9 -wherein calcium oxide produced by the calcination of the limestone is collected from the limekiln and is used to absorb carbon dioxide from the atmosphere.
4. A method as claimed in claim 3, wherein a portion of synthesis gas 5 produced by the gasification process is used to power the furnace.
5. A method as claimed in any of claims 2 to 4, wherein heat is passed from the furnace to the heater of the limekiln to heat the limestone within the limekiln.
6. A method as claimed in claim 5, wherein the hot gasses transferred to the underground fossil fuel seam comprise carbon dioxide produced by the limekiln.
7 A method as claimed in any of the preceding claims, wherein a portion of heat energy produced by the furnace is directed to heat water in a boiler to 15 produce steam.
8. A method as claimed in claim 7, wherein the steam from the boiler is directed to a turbine of a turbine-driven generator set for the production of electricity.
9 A method as claimed in claim 8 when dependent upon any of claims 2 to 8, wherein the heater of the limekiln is electrically powered by the turbine-driven generator set.
10. A method as claimed in any of the claims 2 to 9, wherein excess carbon dioxide yielded by heated limestone is passed to an electrolysis plant and is therein converted to carbon and oxygen by electrolysis.
11. A method as claimed in claim 10, when dependent upon claim 8 or claim 9, wherein the electrolysis plant is powered by the turbine-driven generator set.
12 A method as claimed in any of the preceding claims, wherein excess carbon dioxide generated by the furnace is passed to an electrolysis plant and is therein converted to carbon and oxygen by electrolysis.
13. A method as claimed in any of the preceding claims wherein a portion of synthesis gas produced by the gasification process is converted into synthesis fuel using the Fischer Tropsch process.
14 A method as claimed in any of the preceding claims, wherein excess carbon dioxide produced by a system performing the method is sequestered in spent coal seams.
15. A method as claimed in any of the preceding claims, wherein the underground fossil fuel seam is an underground coal seam.
16. A method as claimed in any of claims 1 to 14, wherein the underground fossil fuel seam is an underground crude oil field.