Research On Drying And Burning Characteristics Of Biomass Fuel

Renewable energy has received more attention along with the exhaustion of fossil energy and environmental problems caused by combustion of fossil fuel. Biomass energy is an important renewable source for cleaning and zero CO2emission. Wastes from agriculture, forestry and municipal refuse could be used for power generation through direct combustion or gasification methods.The range of moisture changed in biomass is wide. Initial moisture content of crop straws can be higher than30wt%, and longtime storage would cause straw deterioration. Biomass grate boiler direct combustion technology got general attention for its preferable fuel adaptability and no need for pretreatment. Unfortunately, grate boiler still has some operation problems such as high carbon content in fly ash, low combustion efficiency and high pollutant discharge, although it has been operated and debugged for many years in our country. Besides, combustion system could be readily deposited and corroded due to the element characteristics in biomass fuel. Consequently, understanding of the drying and combustion properties of biomass boiler possesses a great significance.Influence of moisture content, pyrolysis and volatile removal properties of biomass fuel to boiler combustion efficiency and operation stability was investigated in this paper. Cornstalk and rice husk were selected as raw materials to research the drying property with various drying temperature, initial moisture content and material layer thickness. The optimum drying temperature interval was obtained through the analysis of drying curve. Furthermore, drying characteristics of core stalk was studied under coupling effect of drying conditions and material layer thickness. Drying characteristics with diverse material layer thickness, drying conditions and air moisture was investigated with core stalk, sorghum straw and rice husk. Devolatilization experiments were conducted under multiple factors with corn stalk in air atmosphere, and influence of temperature, initial moisture of fuel and material layer thickness to devolatilization was investigated. On the basis of drying and devolatilization curves, regenerative drying scheme was proposed, and the experimental results could provide necessary data base for the design and optimization of biomass direct combustion boiler.Considering the deficiencies of the existed biomass boiler dust removal equipment in China, on the basis of a deep understanding the existing problems of the48t/h biomass boiler, a new type of equipment for dust removal in furnace was put forward. The equipment makes use of the inertia separation principle for large particle separation, and it is arranged in the turning of pass, being composed of three groups of vertical and inclined baffle. The device can not only remove dust in furnace, but also correct the flue gas flow direction, relieving the severe airflow deviation of the biomass boiler. Double grates modification scheme was proposed according to the operation status of a48t/h biomass boiler in Bio Energy Group. Biomass fuel could be fully burned through changing the proportion between primary air, secondary air, ignite air and secondary air rate in front and rear wall using double grates combustion method. Besides, residence time of biomass fuel in furnace could increase through such a scheme, and combustion efficiency could hence be promoted. Combustion characteristic parameters would be obtained by conducting numerical simulation, cold-state and thermal state experiments. Feasibility of reforming scheme can be tested and then reference data for the operation of biomass power plant boilers can be provided.