GB2468483A

GB2468483A - Synthesising carbon-based fuels from carbon dioxide

Info

Publication number: GB2468483A
Application number: GB0903964A
Authority: GB
Inventors: David Leslie Mcneight
Original assignee: STRATOS FUELS Ltd
Current assignee: STRATOS FUELS Ltd
Priority date: 2009-03-09
Filing date: 2009-03-09
Publication date: 2010-09-15
Also published as: GB0903964D0

Abstract

A method for making hydrocarbon fuels from atmospheric carbon dioxide comprising the steps of:generating electricity from solar energy by the use of a solar tower arrangement 12 in which solar heated air is drawn up a tower and drives turbine generating equipment 13;extracting carbon dioxide from air using extraction equipment 16;and combining said carbon dioxide with hydrogen in a reaction to synthesise hydrocarbon fuels; characterised in that:the carbon dioxide is extracted from air in the vicinity of the turbine generating equipment. Apparatus for carrying out the method is also described.

Description

Synthesising Carbon-based Fuels This invention relates to synthesising carbon-based fuels such, for example, as hydrocarbons such as diesel and kerosene.

With the exception of a small fraction of biofuels, carbon-based fuels in current use are derived from fossil sources, either as coal, oil or natural gas. Burning them loads the atmosphere with carbon dioxide, a greenhouse gas, widely blamed for global warming.

Fossil fuels are a wasting asset, and reserves are increasingly difficult to access, which naturally affects the cost of mining or drilling. Reserves are also not distributed fairly among the nations of the world, which gives rise to international disputes and suggestions that military intervention is primarily occasioned by a need to protect or gain access to fuel supplies. Reserves yet to be accessed are located in polar regions, which are likely to be seriously disturbed by drilling operations, leading to loss of global albedo and enhanced global warming as a result.

It has on numerous occasions been suggested that carbon-based fuels can be derived from non-fossil sources, and, indeed, quantities of diesel fuel, or diesel-like fuel, are already derived from vegetable sources such as oil palm and oil seed rape. A problem with these bio-fuels is that they require quantities of agricultural land, which could, and, many argue, should preferably be used for food crops, and which, by increasing the monetary yield of an area of land, push up the price of food, especially in regions where food is already barely affordable to many of the population. Marine algae have also been investigated as a source of fuel, but require encouragement in the form of added nutrients to large oceanic regions, and it is hard to see how nutrient may be provided in the quantities required or without serious risk of affecting the marine environment in unpredictable ways -the appearance of algal growths is usually accompanied by a ban on consumption of seafood that might be affected thereby.

It has also been proposed, in order to combat global warming, to extract from the atmosphere the carbon dioxide produced by burning fossil fuels and sequester it underground, possibly as calcium carbonate. There is obviously a cost to that, which usually means that governments would have to do it at substantial cost to the taxpayer, or that those responsible for the emissions are penalised, which puts up the cost of goods or services, particularly power, or are otherwise encouraged to do it, which, again, results in a cost to the eventual consumer.

It has also been proposed to extract carbon dioxide from the atmosphere and use it to produce carbon-based fuels. The Fischer-Tropfsch reaction, devised in the 1920s, reacts carbon monoxide with hydrogen to produce aliphatic hydrocarbons, and is, in fact, used to produce liquid fuels, starting, however, from existing fossil fuels such as coal and natural gas, though there is more recently a move to use the reaction with biomass as a starting material. There is little point in any of this, of course, from the point of view of overburdening the atmosphere with greenhouse gases, if energy to power the procedure is itself derived from fossil fuels.

There have also been proposals to use carbon dioxide derived from the atmosphere to manufacture liquid hydrocarbon fuels, using non-fossil power sources. This is a completely carbon-neutral procedure, but it does nothing to stop the build up of carbon dioxide from burning fossil fuel or to reduce the carbon dioxide level. The only way conversion of atmospheric carbon dioxide into fuel could be useful in controlling greenhouse gas emissions is if it substantially completely replaced fuel production from fossil sources.

This is unlikely to happen, at least until global warming has done a substantial amount of damage that can no longer be overlooked, and it is equally unlikely to happen so long as the vested interests if oil producing countries and international corporations require the continued production of fossil fuel.

The oni)' basis, meanwhile, on which fossil fuels can be replaced by carbon-neutral fuels made from atmospheric carbon dioxide is by the latter being substantially less expensive to produce.

The Fischer-Tropfsch reaction is carried out in large-scale plants. A minimum commercial size yields some 500 barrels of hydrocarbon per day, and larger plants can produce up to 2000 barrels per day. Supplying fossil-based raw materials, or biomass, to such plants is not problematic. However, to gear such plants to the production of hydrocarbons from atmospheric carbon dioxide poses substantial problems. Recovering carbon dioxide from the atmosphere and producing hydrogen from water both require electricity. As the object is to replace fossil fuels, the electricity must be produced from a renewable source. A solar power station generating enough power for a 500-barrel per day Fischer Tropfsch plant will cover an area on about one square kilometre. On the scale envisaged, the only reasonable power source is the sun, and this suggests tropical locations, to maximise insolation, and deserts where there is ample space for solar power collection.

This, in turn poses problems in supplying the plant with water and carbon dioxide.

The present invention provides means by which fuels may be synthesised from atmospheric carbon dioxide which are, or are equivalent to, hydrocarbon fuels ordinarily produced from fossil sources, at a cost competitive with fossil fuels.

The invention comprises a method for making hydrocarbon fuels from atmospheric carbon dioxide comprising the steps of: generating electricity from solar energy by the use of a solar tower arrangement in which solar heated air is drawn up a tower and drives turbine generating equipment; extracting carbon dioxide from air; and combining said carbon dioxide with hydrogen in a reaction to synthesise hydrocarbon fuels; characterised in that: the carbon dioxide is extracted from the in the vicinity of the turbine generating equipment.

A solar tower arrangement is a structure comprising a translucent canopy over a solar radiation absorbing arrangement whereby solar energy heats up air under the canopy.

The heated air is drawn, through turbines, up a tower, which may be 250m, 500m or even 1000m and more in height.

The air from which the carbon dioxide is extracted may be the same air that drives the turbine generating equipment.

The carbon dioxide may be reformed to carbon monoxide prior to reaction with hydrogen.

The reaction with hydrogen may be a Fischer Tropfsch reaction. The reaction may, however, be a microwave plasma reaction, which may proceed directly from carbon dioxide and water without the need to reform the carbon dioxide to carbon monoxide, and without the need to electrolyse the water into hydrogen and oxygen.

The carbon dioxide may be recovered from the atmosphere by an extraction process powered by electricity generated by the solar tower arrangement. The extraction process may be cryogenic, in which the air is cooled to a temperature at which the carbon dioxide precipitates. The extraction process may, however, be chemical, in which atmospheric carbon dioxide reacts to form a carbon compound, which can be further processed to release carbon dioxide to a synthesis reaction. The extraction process can be an absorption process, in which carbon dioxide is absorbed into a material, for example a plastic sheet material, from which it can be released in to the synthesis process.

In addition to the carbon dioxide, water may also be extracted from the air and used as a source of hydrogen for the synthesis. The amount of water vapour in atmospheric air, even in dry, desert conditions that are ideal for solar power generation, is more than enough to react with the carbon dioxide that is present.

The electricity generation may be based on an airflow that contains at least as much extractable carbon dioxide as is consumed in the reaction, on a continuing basis.

The invention also comprises apparatus for making hydrocarbon fuels from atmospheric carbon dioxide comprising: a solar tower arrangement in which a turbine arrangement generates electricity from air drawn up through the tower by solar heating; extraction means extracting carbon dioxide from air; reactor means reacting the extracted carbon dioxide with hydrogen to synthesise hydrocarbon fuels; characterised in that: the extraction means extracts carbon dioxide from air in the vicinity of the turbine arrangement.

The extraction means may extract carbon dioxide from the air that drives the turbine arrangement.

The extraction means may also extract water from the air.

The extraction means may comprise a cryogenic arrangement in which the air is cooled to a temperature at which carbon dioxide precipitates, or may comprise a chemical extraction arrangement or an absorptive extraction arrangement.

The invention also comprises hydrocarbon fuel made by a method or using apparatus according to the invention. Hydrocarbon fuel made by the method or using the apparatus may be characterised by substantial freedom from sulphur.

Methods and apparatus according to the invention for making hydrocarbon fuels from atmospheric carbon dioxide will now be described with reference to the accompanying drawings, in which: Figure 1 is an aerial view of a solar tower; Figure 2 is a vertical section through the tower; Figure 3 is a plan view of a sector of the tower; Figure 4 is a block diagram of a first fuel synthesis method; and Figure 5 is a block diagram of a second fuel synthesis method.

The drawings illustrate a method and apparatus in which atmospheric carbon dioxide is reacted with hydrogen to make hydrocarbon fuels, particularly paraffins such as octane, nonane and decane, comprising the steps of: generating electricity from solar energy by the use of a solar tower arrangement 11 in which solar heated air is drawn up a tower 12 of the arrangement 11 and drives turbine generating equipment 13; extracting carbon dioxide from air; and combining said carbon dioxide with hydrogen in a reaction to synthesise hydrocarbon fuels; characterised in that: the carbon dioxide is extracted from the air in the vicinity of the turbine generating equipment 13.

The solar tower arrangement 11 is a structure comprising a translucent canopy 14 over a solar radiation absorbing arrangement 15 whereby solar energy heats up air under the canopy 13. The solar radiation absorbing arrangement may comprise a good solar radiation absorbing substrate, such as a matt black floor. The heated air is drawn, through turbines of the generating equipment 13, up the tower 12, which may be 250m, 500m or even l000m and more in height. The taller the tower 12, generally speaking, the more efficient the arrangement, as it is driven to some extent by the temperature differential between the top and the bottom. Atmospheric temperature falls by 1°C for every lOOm elevation.

The translucent canopy 14 may be of any material such as glass, polycarbonate or other synthetic material. The generating capacity of the arrangement will be improved if special glass is used that has an enhanced greenhouse effect -trapping solar energy beneath it. The canopy may have a substantial area -the more area, the more solar energy is captured and the more electrical power can be generated. A solar collector area of 1 square kilometre would, were it situated on the equator, receive 1000MW of solar energy at midday. The insolation is less at latitudes north and south of the equator, and rises from zero at dawn through peak insolation at noon falling back to zero again at dusk, and, of course, there is no energy input during the ours of darkness. And the efficiency of conversion of solar to electrical energy is another factor. Taking all these into consideration, there is nevertheless a considerable amount of power generated, in the region of 1500 megawatt hours per day, in suitable locations.

In one realisation of this invention, the carbon dioxide is reformed to carbon monoxide prior to reaction with hydrogen. The reforming process comprises reacting the carbon dioxide with hydrogen under heat and pressure in the presence of a catalyst.

The reaction with hydrogen can then be a Fischer Tropfsch reaction, in which the carbon monoxide is further reacted with hydrogen, a mixture known as synthesis gas, or syngas, again in the presence of a catalyst such as iron or cobalt. The product of this reaction is a mix of aliphatic hydrocarbons. The mix is determined by the composition of the syngas and the reaction conditions, but can be a mixture of liquid hydrocarbons and some wax.

This will need fractionation into the various blends required for conventional motor, furnace or aviation fuels.

Hydrogen for the Fischer Tropfsch reaction may be produced by electrolysis of water using electricity from the solar tower. Water may, of course, be piped in from a source such as a neighbouring lake, river or ocean, but it may also be recovered from the atmosphere. Electrolysis of water yields 1 cubic metre of hydrogen per 4kWh. Some 1500 Megawatt hours will therefore produce 1500 x 1000/4 cubic metres, or 375,000 cubic metres. One cubic metre of hydrogen weighs 90 grams. Daily production could therefore be therefore about 44 tonnes, if all the electricity were devoted to producing hydrogen. However, a smaller fraction of the output of the turbine arrangement would be used for this purpose, the rest going to power carbon dioxide recovery, the synthesis reaction and general running of the plant.

The reaction may, however, be a microwave plasma reaction, which may proceed directly from carbon dioxide and water without the need to reform the carbon dioxide to carbon monoxide, and without the need to electrolyse the water into hydrogen and oxygen.

The carbon dioxide may be recovered from the atmosphere by an extraction process in extraction equipment 16 powered by electricity generated by the solar tower arrangement.

The extraction process may be cryogenic, in which the air is cooled to a temperature at which the carbon dioxide precipitates. The extraction process may, however, be chemical, in which atmospheric carbon dioxide reacts to form a carbon compound, which can be further processed to release carbon dioxide to a synthesis reaction. The extraction process can be an absorption process, in which carbon dioxide is absorbed into a material, for example a plastics material, from which it can be released in to the synthesis process.

These different processed use different amounts of energy. The chemical route uses less than 1 OOkWh per tonne of carbon dioxide recovered.

Particularly when cryogenics are used to extract the carbon dioxide, the extraction may be carried out in the equipment 16 located around the perimeter of the canopy 14. To make 20 tonnes of carbon dioxide per day requires about 600,000 tonnes of air, which is about 500 million cubic metres.

If we assume an airflow at 10km/h, which is 240 km/day, we need a treatment intake area of 600,000,000/240,000 square metres, or about 2,S00square metres. The perimeter of a circular canopy of area 1 square kilometre is about 3,500 metres, and a canopy height at the periphery would need to be about 0.7 metres.

In addition to the carbon dioxide, water may also be extracted from the air and used as a source of hydrogen for the synthesis. The amount of water vapour in atmospheric air is, even in dry, desert conditions ideal for solar power generation, more than enough to react with the carbon dioxide that is present. Water may be extracted by condensation, and may be a first step in cryogenically extracting carbon dioxide.

Other means for extracting carbon dioxide may be less suitable for use on air that drives the turbine arrangement, as they may not be capable of operating at air speeds commensurate with driving turbines, but they may still be deployed in the vicinity of the tower and use electricity generated by the tower and involve minimal transportation costs.

Synthesis of hydrocarbon fuel is carried out in a plant 17 adjacent the solar tower arrangement 11, which can also house the electrolysis plant 18 if water is electrolysed to make hydrogen. A cracking plant 23 can also be situated adjacent the tower arrangement 11 to produce required mixtures of hydrocarbons, and a tank store 19 can hold production pending delivery by tanker or pipeline.

Figure 4 illustrates a Fischer Tropfsch synthesis process in which water is fed to an electrolysis plant 18 supplied with electricity from the tower arrangement 11. Hydrogen is fed to a reformer 21 also supplied with carbon dioxide from the extraction equipment 16. Oxygen, also produced by the electrolysis, may be collected for use elsewhere or simply released to atmosphere. From the reformer 21, syngas is supplied to the Fischer Tropfsch reactor 22, which in turn supplies a mixture of liquid hydrocarbons, together with some that are waxes at ordinary temperatures. The liquid is sent for fractionation to a distillation plant 23, thence to the tank store 19.

Figure 5 illustrates a microwave plasma operation, in which carbon dioxide and water are fed to a microwave plasma reactor 51, which generates a liquid hydrocarbon mixture, which is then passed to the distillation plant 23 and thence to store 19.

The methods for making hydrocarbon fuels described above involve minimal running costs. There will be substantial capital costs for the installation of the solar tower, the carbon dioxide and water recovery plant and the synthesis reactor, but after that, the only substantial costs will be overhead costs for plant supervision and maintenance -the power is free, the carbon dioxide and water are free. The cost of producing a barrel of fuel, neglecting the overheads, will therefore be the plant amortization per barrel. For a SOObbl/day output, a barrel of hydrocarbon would cost $5.5 each $20,000,000 of capital cost, assuming amortization over a twenty year period.

This is clearly commensurate with costs of fossil fuels, and very much less expensive when costs of dealing with global warming problems associated with fossil fuels are taken into account.

Claims

Claims: 1 A method for making hydrocarbon fuels from atmospheric carbon dioxide comprising the steps of: generating electricity from solar energy by the use of a solar tower arrangement in which solar heated air is drawn up a tower and drives turbine generating equipment; extracting carbon dioxide from air; and combining said carbon dioxide with hydrogen in a reaction to synthesise hydrocarbon fuels; characterised in that: the carbon dioxide is extracted from the air in the vicinity of the turbine generating equipment.
2 A method according to claim 1, in which the carbon dioxide is extracted from the same air that drives the turbine generating equipment.
3 A method according to claim 1 or claim 2, in which the carbon dioxide is reformed to carbon monoxide prior to reaction with hydrogen.
4 A method according to any one of claims 1 to 3, in which the reaction with hydrogen comprises a Fischer Tropfsch reaction.
A method according to any one of claims 1 to 3, in which the reaction comprises a microwave plasma reaction.
6 A method according to claim 5, in which the reaction proceeds directly from carbon dioxide and water without the need to reform the carbon dioxide to carbon monoxide, and without the need to electrolyse the water into hydrogen and oxygen.
7 A method according to any one of claims 1 to 6, in which the carbon dioxide is recovered from the atmosphere by an extraction process powered by electricity generated by the solar tower arrangement.
8 A method according to claim 7, in which the extraction process is cryogenic, in which the air is cooled to a temperature at which the carbon dioxide precipitates.
9 A method according to any one of claims 1 to 8, in which water is recovered from the atmosphere during the carbon dioxide extraction.
A method according to any one of claims 1 to 7, in which the extraction process is a chemical process, in which atmospheric carbon dioxide reacts to form a carbon compound, which can be further processed to release carbon dioxide to a synthesis reaction.
11 A method according to any one of claims 1 to 7, in which the extraction process comprises an absorption process, in which carbon dioxide is absorbed into a material from which it can be released to the synthesis process.
12 A method according to claim 11, in which the material comprises a plastic sheet material.
13 A method according to any one of claims I to 12, in which he electricity generation is based on an airflow that contains at least as much extractable carbon dioxide as is consumed in the reaction, on a continuing basis.
14 Apparatus for making hydrocarbon fuels from atmospheric carbon dioxide comprising: a solar tower arrangement in which a turbine arrangement generates electricity from air drawn up through the tower by solar heating; extraction means extracting carbon dioxide from air; reactor means reacting the extracted carbon dioxide with hydrogen to synthesise hydrocarbon fuels; characterised in that: the extraction means extracts carbon dioxide from the air in the vicinity of the turbine arrangement.
Apparatus according to claim 14, in which the extraction means extracts carbon dioxide from the same air that drives the turbine arrangement.
16 Apparatus according to claim 14 or claim 15, in which the extraction means may also extract water from the air.
17 Apparatus according to any one of claims 14 to 16, in which the extraction means comprise a cryogenic arrangement in which the air is cooled to a temperature at which carbon dioxide precipitates.
18 Apparatus according to claim 14, in which the extraction means comprise a chemical extraction arrangement.
19 Apparatus according to claim 14, in which the extraction means comprise an absorptive extraction arrangement.
Apparatus according to any one of claims 14 to 9, in which the tower arrangement comprises a translucent canopy surrounding a tower, said canopy housing the extraction means.
21 Apparatus according to claim 20, in which the extraction means are located around the periphery of the canopy.
22 Apparatus according to claim 20 or claim 21, in which the canopy covers an area of the order of 1 square kilometre, 23 Apparatus according to any one of claims 20 to 22, in which the canopy overlies a substrate of good radiation absorbing material.24 Hydrocarbon fuel made by a method according to any one of claims 1 to 13 or using apparatus according to any one of' claims 14 to
23.