12.2 RESEARCH

12.2 RESEARCH

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RESEARCH
First steps toward a new clean fuel
from brown coal


By David McManus, Research Investment Manager, BCIA

DME is a non-toxic, non-greenhouse fuel with similar properties to liquefied petroleum gas (LPG). Typically, DME is produced from natural gas, however this is a very energy-inefficient process. Research undertaken at Monash University has shown that the use of a novel catalyst can lead to a significant improvement in the energy efficiency of DME production from brown coal. David McManus explains further.

Professor Sankar Bhattacharya at Monash University has recently announced the successful completion of the BCIA-funded project 'Catalytic steam gasification and assessment of dimethyl ether'.

This project had its roots in a 2009 agreement between the Victorian Government and the Kyushu Electric Power Company (KEPCo) to cooperatively pursue strategic basic research of high-level utilisation technology for Victorian brown coal.

Japan is the largest coal importer in the world, with Australia and Indonesia supplying 80 per cent of all Japan’s imported coal. Japan is also Victoria’s third largest trading partner, and has a strategic interest in the development of technologies for production of clean energy sources from Victorian brown coal.

Professor Bhattacharya’s project investigated the feasibility of producing dimethyl ether (DME) via gasification of Victorian brown coal. DME is a non-toxic, non-greenhouse but highly flammable gas with properties similar to liquefied petroleum gas (LPG), and is regarded as a clean alternative to diesel fuel for internal combustion engines.

Japan is the world leader in the development of DME-fuelled vehicles, with Nissan and Isuzu conducting field tests of new engine prototypes. DME-fuelled engines are also being developed in China, Korea, the USA and Europe. Commercialisation of DME-fuelled engines is not far off, and is expected to create exciting new opportunities for export of DME derived from Victorian brown coal.

The standard method for producing DME involves the catalytic conversion of methanol. The majority of methanol is currently produced from natural gas, but it can also be produced by gasification of coal. Worldwide, approximately 50 million tpa of methanol is produced from gasifier synthesis gas (syngas) using copper-based catalysts. However, this reaction is not energetically favourable, and the process has an efficiency of only approximately 20 per cent.

Professor Bhattacharya investigated the feasibility of producing DME from syngas in a single step, using a bi-functional catalyst incorporating both a copper-based methanol synthesis catalyst and an alumina methanol dehydration catalyst. A single-step reaction improves the energetics of the process, since the methanol is converted as soon as it is formed, and can increase the conversion efficiency to as high as 80 per cent.

The first part of the project involved the development of an ASPEN Plus simulation of the process, including integrated coal drying, gasification and DME synthesis. The simulation was initially used to define realistic operating conditions for the experimental program, which then allowed data to be obtained for the pyrolysis and gasification reactions of Victorian brown coal. Pyrolysis and gasification studies were performed in a thermo-gravimetric analyser and an entrained flow reactor.

Simulations using the ASPEN Plus model showed that gasification of brown coal at 900
oC would produce syngas with the optimum composition for DME synthesis, without the need for further syngas conditioning steps. As such, the unique properties of Victorian brown coal seem to make it a better feedstock for DME synthesis than black coal.

The second part of the project involved detailed analysis of the performance of the bi-functional catalyst during DME synthesis. Experiments were performed in a high pressure fixed-bed reactor, using a synthetic syngas mixture. A variety of catalyst formulations was investigated, using mixtures of commercial catalysts and new catalysts synthesised at Monash University. Both physical mixing and co-precipitation-impregnation methods were used.



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