Roasting biomass to produce more energy
According to engineers at the University of Leeds, UK, it is possible to use torrefaction, a process usually associated with coffee production, to increase the energy content of some of some crops by up to 20 per cent. Not only torrefaction would lead to an increase of the energy extracted from some of these crops, it would lead to solid products, easier to store and transport than raw biomass. The engineers have used reed canary grass, wheat straw and willow for their study. And they've found that willow was the most efficient. But read more...
This study was sponsored by the Supergen Bioenergy Consortium, an initiative created by the Engineering and Physical Sciences Research Council (EPSRC) in the UK.
It was led by Jenny Jones, Professor in Sustainable Energy at the University of Leeds. She's worked in the Energy & Resources Research Institute (ERRI) with Toby Bridgeman, a PhD student (you'll find what he does near the top of this page.
Here is what writes Bridgeman. "Torrefaction is a mild temperature pyrolysis process that removes moisture, causes partial endothermic decomposition of cell wall composites and alters the chemical structure of wood polymers causing biomass to develop more favourable fuel properties. Work as part of this PhD will utilise a bench scale reactor and laboratory scale apparatus to study various parameters of a low temperature pyrolysis heat treatment of wood and energy crops to gather data to help optimise a process based on the improvements in the physical, chemical and thermal fuel properties of solid biomass."
In the University of Leeds news release, Jenny Jones adds some more details. "'Raw biomass takes up a lot of space and has a low energy density which makes it costly -- environmentally and economically -- to transport. Plus you need more of it than say, coal, to produce energy efficiently,' says Professor Jenny Jones who worked on this study with PhD student Toby Bridgeman. 'Torrefaction is not currently used in the UK in either the agricultural or the energy sectors,' says Bridgeman. 'But our paper shows that it has a lot of benefits, besides those to do with fuel handling, so we feel it's definitely something we'd like to explore further.'"
This technical paper has been published in Fuel, an Elsevier journal, under the title "Torrefaction of reed canary grass, wheat straw and willow to enhance solid fuel qualities and combustion properties" (Volume 87, Issue 6, Pages 844-856, May 2008).
Here is the beginning of the abstract. "Torrefaction is a treatment which serves to improve the properties of biomass in relation to thermochemical processing techniques for energy generation; for example, combustion, co-combustion with coal or gasification. The topic has gathered interest in the past two decades but further understanding is required for optimisation of the process thus enhancing economic efficiency, which is crucial to the success of the treatment commercially and within industry. In particular there is a noticeable gap in current literature regarding the combustion properties of torrefied biomass."
Campuspr, a public relations company which promotes university research, sent me a copy of the full paper. Here is one excerpt of the conclusions. "Observations of combustion behaviour revealed a number of differences between torrefied biomass and raw fuels. For all fuels, volatile combustion was modified and occurred over a shorter temperature range and the herbaceous crops produced heats of combustion that were between 10–65% higher, depending on the treatment temperature and crop. The higher fixed carbon content also meant that torrefied biomass produced greater heats of combustion during char burnout. All these observed behavioural changes were more pronounced for the products of higher torrefaction temperatures. From DTA and the analysis of high speed videos of the combustion of untreated and torrefied willow particles it was observed that the ignition times of both combustible volatiles and char were reduced as a result of torrefaction. These changes in properties are expected to be beneficial during combustion applications."
The engineers don't say when their technology could be ready to increase the amount of energy picked from crops. The paper ends with this somewhat ambiguous sentence. "It is suggested that future work investigates the change in nature of the composition of volatile component of torrefied fuels and should seek to identify any potential benefits for other thermochemical conversion processes."
Sources: University of Leeds news release, May 20, 2008; and various websites
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