Characteristics Of Combustion And Emissions Of Biomass Granule Fuel

Biomass granule fuel is an ideal alternative fuel for small and medium industrial boilers, which has been characterized as clean energy. Nowadays, lack of technological basis for the production, utilization and supervision, the low combustion efficiency and high pollutions emissions are the most serious trouble for biomass granule fuel. The systematic, standardized specifications and emissions standards of biomass granule fuel should be formed timely. In this paper, the pyrolysis, combustion and flue gas emissions characteristics were investigated for wood and bamboo granule fuel by thermogravimetric analysis and tube furnace combustion experiments, involving its clean and efficient application. The main results are summarized as follows:(1) Pyrolysis process could be divided into four stages, such as drying, preheating, devolatilization and carbonization. Combustion process includes drying, devolatilization and volatile combustion, transition, char burning. Ignition temperature, volatile devolatilization and combustion temperatue corresponding to the higtest rate increased with the raising heating rate. Tube furnace experiments showed that the temperature has am important impact on the combustion process of biomass granule fule, leading to incomplete combustion when below 800℃ or over 1100℃.(2) In order to find out the mechanisms responsible for the combustion of biomass granule fuel under different temperatures, 15 combustion mechanisms were tested using nonisoconversional method. The results of the non-isoconversional method showed that threedimensional diffusion mechanism(G11) is the most effective mechanism for the initial stage(260~280℃) and the transition phase(360~440℃) of wood granule fuel, while there are some differences compared to other regions. However, G11 mechanism was found to be the main mechanism for all regions of bamboo granule fuel. The evaluations of the kinetic constants for these samples were calculated with the application of Coats-Redfern method. The activation energy related to wood samples changed following the rules of increase-down-increase-down as the temperature grown, while declined after reaching a peak for bamboo samples.(3) The tube furnace experimental results showed that CO emission time decreased with increasing temperature during sufficient combustion, indicating that it needed shorter time during devolatilization and char burnout. NO was released to the gas phase in significant amounts at 900℃, while decreased with increasing temperature or reducing atmosphere. A part of NO was transformed to N2 with the reductive gas of CO as the temperature grown. Fuel-N conversion rates of wood and bamboo granule fuel got the minimum values(12.32, 3.90%) and maximum values(41.79, 9.17 %) in 3 L?min-1 air under the combustion temperature of 1200℃ and 5 L? min-1 air under the combustion temperature of 900 ℃,respectively. No SO2 was released to the gas phase during sufficient burning, since sulfur mainly converted to sulfate stored in ashes or discharged with the flue gas at high temperature. On the contrary, part of the S was discharged in the form of SO2 under lean oxygen combustion.(4) An efficient clean burning solution was proposed, in which NO generation could be well controlled and generated SO2 could be clean effectively. In addition, a corresponding industrialization development path was proposed, basing on summarizing the development problems of biomass granule fuel.