Effect of particle size and secondary air for particulate biomass combustion in a bubbling fluidized bed reactor

Abstract

Biomass combustion is used as basic technology to generate heat by humans for millennia. With the incremental needs of modern man, biomass combustion still plays a major role in heat and power generation. In Sri Lankan context, biomass combustion is extensively used in manufacturing industries for boilers, furnaces, dryers, etc. Even though biomass is abundantly available as an energy source in Sri Lanka, industrial biomass combustion systems are operating under very low efficiencies. Operating these industrial combustion systems in an optimum manner will help in numerous ways to industries, environment and society. In this study, particulate biomass combustion in a bubbling fluidized bed combustor model is used to evaluate optimum secondary air flow rate rates and particle sizes. First Proximity of particulate biomass (saw dust) was conducted to find out moisture and volatile content, then sieve analysis was conducted to segregate and name the particle sizes. Different particle sizes were fluidized using measured primary air flow and combusted under varied secondary air flow rates and obtained maximum temperature achievement in three distinct locations (top, middle and bottom) in the fluidized bed reactor by using installed temperature transducers. Secondary air flow rates and temperature results were tabulated for each particle sizes to analyze temperature variation. Matlab CFTool feature was used to generate surface fits for all three location (top, middle and bottom) temperature variation against particle size and secondary air flow rates. After evaluation results and surface fits, Optimum operating secondary air flow rates and particles sizes were identified for used lab scale bubbling fluidized bed combustor. Recommendations were suggested for industrial scale particulate biomass combustion systems such as boilers, furnaces, etc. for optimum operation based on lab scale system results.