Bio4Energy

Bio4Energy Researchers Tackle Soot Agglomeration in Entrained-flow Gasification of Biomass

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Source: Bio4Energy

Researchers in Bio4Energy may be close to delivering one of the final 'missing link' pieces of scientific knowledge on gasification of biomass from woody residue at high temperatures. Doing so would pave the way for industry to start attempting a technology scale up for the purpose of making biofuel on a commercial level, according to the project leader.

The technology is known as entrained-flow gasification and, when applied to woody biomass residue or black liquor in the way it has been in Bio4Energy, has the advantage of producing a synthetic gas which is virtually free of impurities. This so-called syngas, in a second step, may be turned into biofuels (or energy carriers) such as methane, methanol, diesel or dimethyl ether.

A 2013 report on the potential of biofuels, part of a Swedish government investigation on a fossil-free transport fleet in Sweden, indicated that this type of biofuel production technology 'can be competitive to fossil fuels [if] reasonable environmental policies' were put in place, such as a tax on emissions of carbon dioxide, the greenhouse reference gas.

However, whereas the high temperatures used in entrained-flow gasification ensure that tar formation is kept to a minimum during the conversion process, soot production inside the biomass reactor—the gasification chamber in which the syngas is made—is a remaining impediment to the smooth functioning of the technology, Bio4Energy scientists have said.

'Reducing the formation of soot is one the biggest issues because it affects the economic feasibility of the overall biofuel production system through both investment and operating cost… and reliability of the plant', said Kentaro Umeki, researcher in Bio4Energy at the Luleå University of Technology (LTU) and head of Bio4Gasification, one of three research nodes in the Swedish Centre for Biomass Gasification.

Remaining issues: Soot formation, ash deposition and material handling

After years of dedicated work, researchers on the Bio4Energy Thermochemical Platform have not only succeeded in making a substantial contribution to laying down the basic science on entrained-flow gasification of woody biomass, but because they have had access to state-of-the-art pilot and demonstration facilities for testing the method they have also been able to map what issues still have to be solved before definite technology directions and scale up may take place.

Soot formation and ash deposition inside the biomass reactor, as well as material handling and availability, were the largest knots yet to be untied, according to Magnus Marklund, CEO of the SP Energy Technology Centre at Piteå, Sweden, whose organisation provides the role of intermediary in Bio4Energy between the basic research and the development activities run by industrial actors.

'Anything that will improve the process parameters will be of value. [Reducing soot formation in the reactor] is definitely very important, not only to make the technology function smoothly, but also in terms of efficiency. We do not want the chemical energy to end up in the soot, but rather in the synthesis gas', Marklund said. He added that the soot might be 'interesting' in its own right as a residual product from which to extract chemicals, but that this was another matter.

For his part, postdoctoral research fellow Umeki was more bullish about the possible implications of delivering a new method for preventing soot agglomeration inside biomass reactors used in entrained-flow gasification fueled by residue from forestry operations.

'If we can solve the issue of soot, then it is just a financial issue before scale up' of the technology by industry, according to Umeki, who was recruited into Bio4Energy in 2011 to work on thermal conversion of biomass to fuels and chemicals.

Fresh funds to help combat soot agglomeration

In the final days of 2014, the Research Council of Norrbotten (Norrbottens forskningsråd) acknowledged the Japan-born researcher's work by awarding him SEK3 million (€319,000) to work out the soot issue over three years. The Council expected the research to 'make a contribution to the [economic] development of Norrbotten', it said in its grant application criteria.

Without wanting to reveal too much, Umeki said he and LTU colleagues Rikard Gebart and Burak Göktepe had been working on a new method for lessening the concentrations of soot and which was designed to give the biomass particles an even spread inside the reactor. He predicted that the new method would be incorporated in future biomass reactor designs intended for use in entrained-flow gasification.

'I like this new method because it doesn't have to affect other parts of the process, like efficiency.

'We researchers should demonstrate to people that we have enough' knowledge about entrained-flow gasification to make it a method of choice for industry or technology owners, he added.

How much longer will it be before the remaining technology hurdles have been solved and the technology is ready for scale up to commercial levels?

For Marklund at the SP ETC the answer had everything to do with industrial investments and political goodwill, and less with getting to grips with specific process parameters.

'It depends what resources there are. The process has to be driven by the market. Whether it will take one, three or ten years entirely depends on this. If we have the resources we can do it much more quickly. [As for the remaining technology hurdles,] I am convinced we will solve the problems that need to be solved', Marklund said.

He added that several other industrial actors had stakes in the Sweden-based technology development, including Bio Green, Sveaskog and Smurfit Kappa. The Swedish Energy Agency and LTU were also heavily vested in the development process. The monetary investment needed could be in the range between SEK10 million and 100 million (€1.07-10.7 million): 'The more resources we have, the quicker it will be done'. Marklund repeated.

Could Bio4Energy seek help from other entities world-wide to speed up the development of scientific knowledge?

'Yes', Umeki said, collaboration would hopefully be initiated with the one other major entity developing entrained-flow gasification of biomass: the Karlsruhe Institute of Technology in Germany.

'We have a joint meeting in April with Karlsruhe and Bio4Gasification.

'Apart from that, there are many small groups who work on entrained-flow gasification on a very small scale. What is unique for us in northern Sweden is that we have [research and development] going hand in hand. We have [laboratory-based] pilots and demonstration units and plants that are in between pilot and demo' in size, Umeki said.

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