Havesting Straw Bio-Oil on the Field
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - IIa: Energy Production (T1-5a)
Keywords: flash pyrolysis, straw, biomass-to-liquid, bio-oil, harvest
Bioenergy in the form of straw represents a significant energy source on a world-wide scale but is today largely unutilized due to a cost disadvantage and increased operational demands on power stations and district heating facilities. Straw is by itself not expensive but the cost associated with especially logistics, increase the price seven fold from field to a regional processing facility. Further, the five to ten percent ash content of straw is a source of solid waste which can form slag and promote corrosion if the straw is burned in conventional boilers. Our efforts to develop the mobile pyrolyzer/harvester may drastically increase the attractiveness of straw as an energy source. Harvesting straw bio-oil on the field will concentrate the energy content in an energy-dense versatile liquid product and directly recycle inorganic nutrients/ash, without the expenses from baling and transportation of bulky straw. The conversion can be accomplished with flash pyrolysis within a fraction of a second by rapidly heating the organic material to 500 to 600 °C. Heat is provided by combusting the small incondensable pyrolysis gas fraction, whereas the ash is concentrated in the char fraction which may be distributed on the field behind the pyrolyzer/harvester. Bio-oil is the principal product which may be transported from the field to power stations or refineries for further upgrading to e.g. transportation fuels. However, in order to incorporate a flash pyrolysis reactor in a moving agricultural implement, it was necessary to develop and refine a suited reactor technology.
This study presents bench scale (1.5 kg straw pr. hour) results from operation of a Pyrolysis Centrifuge Reactor (PCR), a novel ablative flash pyrolysis reactor with a high capacity/volume ration, well suited for operation in a rough environment. The focus of the study is on the yield of products from flash pyrolysis, i.e. liquid, char and gas with changes of the operational parameters. In the PCR, straw particles are forced centrifugally (4,900 to 17,000 times gravity) against the heated (470 to 620 °C) inner wall of a horizontally arranged pipe by introducing a swirling motion to the gas phase through the action of a centrally located rotor. Experimental runs have shown little variation with reactor operational parameters within the specified domain of yield profiles, water content in the liquid product and molecular weight of the incondensable gas. It was established that solid residence time was controlled by straw feed rate and was independent of rotor speed and gas residence time.
The results obtained in the laboratory with the PCR have proven our platform technology to be robust and able to obtain a high yield of bio-oil. Further developments of the PCR to include stationary or semi-stationary applications in the forestry and solid waste industries are foreseen.
Presented Wednesday 19, 15:00 to 15:15, in session Sustainable & Clean Technologies - IIa: Energy Production (T1-5a).
