Sustainable fuels from renewable energies

What we are doing and why it is important

This approach has the potential of solving two severe problems that the world is now facing regarding its economic development:

• De-carbonising of the supply chain for transport fuels, a particularly difficult topic given the apparent lack of alternatives to fossil fuels.
• Large scale development of renewable energy beyond that permitted by the limitations of power transmission and distribution infrastructures, by developing wind, marine and solar products other than power - namely, fuels and chemicals.

The first point regarding the current lack of sizeable alternatives to fossil fuels is illustrated by the current high price of food staples, partly encouraged by the increased production of biofuels. It has been argued that biofuels would not be able to meet a substantial proportion of our needs for transport fuels without causing havoc to our food supplies or our ecosystems. However, alternatives can and must be developed, utilising sustainable sources of carbon (the chemical backbone of liquid fuels) such as CO₂ and Municipal Solid Waste (MSW), and chemically combining this carbon with hydrogen derived from renewable energies such as wind, marine or solar. Both sources of carbon have availability that is much greater than could be hoped for from energy crops. An interesting figure: The energy content of the Municipal Solid Waste generated each year in the UK represents a third of the UK's energy consumption in petrol and diesel.

Regarding the second point, there are two main applications:

• Transmission and bringing to market of renewable energies from remote areas. Given the significance of the remote renewable resource in the UK and other regions of the world (e.g. North America, China, etc), this type of technology could greastly contribute to the proper development of wind, marine and solar energy on a scale of significance for the meeting of energy needs. In the UK, most of the wave, wind and tidal power resource is located North and West of Scotland.
• Another particularly useful application is for grids with a very high penetration of wind power, where production in 'excess' of demand is frequent (e.g., in Western Denmark).

Some of the research results so far

We have conducted feasibility studies in the area of

• Liquid fuel synthesis from CO₂ plus electrolytic hydrogen – this included methanol, mixed alcohols and gasoline [1]
• Methanol synthesis from CO₂ and electrolytic hydrogen over a range of contact time with the catalyst. The need to vary the load of the plant (from 20% to 120% of designed throughput) stems from the variability of the renewable power sources that are used to produce the hydrogen, coupled with the limited capacity of hydrogen storage that would typically be available. We found that in principle such a plant should be operable.
• An evaluation of the energy efficient bulk storage of hydrogen using the sponge iron system, with a fairly extensive comparison with other systems [2]. We found that this approach showed the promise of being more energy efficient than other methods.
• An evaluation of the excess power that is available on the Western Danish grid for fuel synthesis [3], discriminating between that contributed from CHP plant and that from wind power.
• An evaluation of the practicalities of combining gasification and electrolysis for the synthesis of liquid fuels [4]. For convenience, I refer to these fuels as 'hybrid biofuels'. It was confirmed that the conversion of biomass (woodchips) or MSW to methanol could be doubled if combining the synthesis gas from gasification with hydrogen from electrolysis. A high turn down ratio for the hydrogen that was imposed by the variability of wind or wave energies could also be handled by a suitably designed reactor synthesis loop.

We are currently conducting experimental work on

References

[1] Mignard D. and Pritchard C.L., 2006. Processes for the Synthesis of Liquid Fuels from CO₂ and Marine Energy. Chemical Engineering Research and Design, Special Issue: Carbon Capture and Storage, 84(A9), 828-836
[2] Mignard D. and Pritchard C.L., 2007. A review of the sponge iron process for the storage and transmission of remotely generated marine energy, International Journal of Hydrogen Energy, 32(18), 5039-5049
[3] Mignard D., Harrison G.P, and Pritchard C.L, 2007. Contribution of wind power and CHP to exports from western Denmark during 2000 to 2004 . Renewable Energy, 32(15), 2516-2528
[4] Mignard D. and Pritchard C.L., 2008. On the use of electrolytic hydrogen from variable renewable energies for the enhanced conversion of biomass to fuels. Chemical Engineering Research and Design, 86(5), 473-487

Still under construction - D. Mignard, 09/06/2008