Renewable energy supply and carbon capture: capturing all the carbon dioxide at zero cost

Abstract

Climate change is likely to be (and is) more serious and likely to proceed much more rapidly than was previously thought. This article surveys and evaluates the technology of processing carbon dioxide and hydrogen into sustainable synthetic carbohydrate fuels and the related economics in relation to a particular route, the capture of carbon dioxide from the flue gas stream of gas burning power stations, provided the gaseous fuel is of biogenic origin. Biogenic methane is renewable and can, after combustion into carbon dioxide, via carbon capture be further processed into a range of carbohydrate fuels, or alternatively captured for final storage under carbon capture and store (CCS). It is proposed that the air intake of a power station be replaced by cooled flue gases consisting mainly of carbon dioxide, enriched with oxygen obtained by electrolysis of water. The co-produced hydrogen can then be processed further into more easily transportable and storable forms of fuel. This implies that a gas-fired power station is not so much a means of producing energy, but rather of producing pure carbon dioxide. The capture process as such is the same as the one which arises if the purpose is carbon capture and use or CCS in which case capture of CO₂ from the combustion of methane from biogenic origin amounts to negative emissions. The indirect route of supplying and using energy via the production of carbohydrate fuels requires much more primary energy than the direct use of electricity does. For this reason, use of that indirect route is efficient for aviation, where the direct route of electric power is impractical. For shipping, there also is the alternative of the implicit transport of hydrogen as part of ammonia. It is assumed that the use of biogenic methane followed by processing of the captured carbon dioxide into synthetic hydrocarbon fuels is in combination with volcanic carbon hydroxide, sufficient to meet the demand for hydrocarbon fuels. Capture of carbon dioxide from biogenic methane can also be applied in the context of CCS.

Physics appendix

The critical temperature of a particular substance is the temperature above which it cannot be liquid, irrespective of the pressure. The distinction between a melting/freezing pressure at which the solid and liquid state can be in balance, and the boiling/condensation pressure, does not exist above that temperature; there only is a sublimation pressure at which the solid and gaseous state can be in balance. To evaluate the implications of this sub-field of physics, a tabulation of the critical temperatures and pressures of some relevant substances is useful at this point. This information is summarized in Table of critical pressures (etc.). The figures for the saturation pressures of carbon dioxide as given in this table are from Wikipedia (2018)

Table of critical temperatures and pressures, boiling points and of solubility in water

References for the information in this table listed above references
Substance	Critical Te. degrees C.	Critical Pr. atmospheres	Boiling Pt. at atmospheres	W. Solubility
Water	374	220.5	100	Not applicable
Carbon dioxide	31.0	72.9	− 57	2.7% at 32 °C
Nitrogen dioxide	36.4	72.3	21	Yes
Sulphur dioxide	157.8	78.8	− 10	Highly
Hydrogen sulphide	100	89.37	− 60	Slightly
Oxygen	− 118.6	50.5	− 183	Not relevant
Nitrogen	− 147	34.0	− 196	Not relevant
Ethane	32.2	48.9	− 88	Not relevant
Methane	− 83	46.5	− 162	Not relevant