Experimental Investigation On Effects Of Moisture Content And Particle Size On Smoldering Of Biomass

The combustion of biomass exits widely in application of direct combustion of biomass, waste incineration and fires. In these utilization or natural phenomenon, the moisture content of biomass is varied with the source of raw materials, climate and environment. It ranges from0to30%commonly. It can influence heating value, the transfer of heat and mass internal materials, which affect the combustion temperature of material and the last time of combustion, and so on. In applications of biomass, particle size is the important factor on the difficulty and the high cost of crushing biomass. Particle is the most basic parameter which affects the bulk density of the material, internal pore structure of materials, heat and mass transfer, which influence reaction rate, combustion duration time, the combustion temperature of material and the gas yield. Therefore, it is important to investigate effects of moisture content and particle size on combustion internal solid material.Smoldering inside material is similar to combustion inside large-sized fuels. Therefore, using smoldering experiment inside piled biomass powder can be investigated characteristic of combustion inside large-sized material. In this study, effect of moisture content and particle size on combustion inside large-sized material is investigated experimentally using smoldering method of biomass powder, which provides the basis of combustion inside solid fuels and analysis on characteristic of smoldering.To investigate the effect of moisture content and particle size on combustion inside large-sized material, an experimental setup for biomass smoldering has been designed and manufactured. It consists of ignition device, smoldering stove, monitoring system and data acquisition system. The temperature inside the stove, the mass residue of biomass powder and the percentage content and composition of flue gases during the smoldering process could be monitored and recorded online in real time. It includes a cylindrical reactor (inner size φ270mm×220mm) into which stalk powder is filled. The reactor has a high-aluminum aluminum-silicate blanket insulation layer of100mm thickness above the bottom and along the inside wall of the vessel. The fuel bed can be ignited from the furnace using a heater. The heater was removed from the furnace after stalk powder was ignited. During the smoldering process, temperatures inside fuel were measured using K-type thermocouples (φ1mm). Fuel mass determination used the balance under the reactor. Fuel gas was sampled at a height of1cm above the original fuel bed. Gases yield were detected by a gas analyzer after filtration. Sensors for temperature, gas composition and content and mass were connected to a data acquisition module, and data were recorded every100s.Experiments and repeated experiments of corn stalk powder at different moisture content (0%,3.26%,6.05%,10.78%,20.93%and29.77%) have been carried out. Results showed that:1) propagation of smoldering inside cylindrical reactor is quasi-one-dimensional.2) Moisture content affects the ignition and drying of corn stalk powder significantly. While the effects of moisture content on maximum temperature inside fuel bed, char oxidation rate and radial temperature distribution is insignificant.3) The maximum temperature inside fuel bed increases during smoldering of corn stalk powder.Experiments and repeated experiments of corn stalk powder at different particle size (20-40mesh size,40-60mesh size,60-80mesh size and80-100mesh size) have been carried out. Results showed that:1) In cylindrical reactor, the maximum temperature inside fuel bed increases during smoldering of corn stalk powder. The maximum temperature inside fuel bed increased when particle size decreased.2) In the beginning of reaction, gases yield more than other time. Particle size affects the content of H2,CH4,CO2and CO significantly.3) Particle size affects drying of corn stalk powder significantly. While the effects of particle size on char oxidation rate, radial temperature distribution and mass loss is insignificant.The results of the experiments are used as reference for the investigation of the process of smoldering and solid combustion.