Combustion and emission characteristics of a swirling fluidized-bed combustor burning moisturized rice husk

Burning of rice husk in a swirling fluidized-bed combustor (SFBC) was the focus of this experimental study. Swirl motion of a fluidized bed in this combustor was induced by an annular spiral distributor of primary air and also promoted by tangential injection of secondary air into the bed splash zone. “As-received” rice husk was moisturized with the aim to control NO emission from the combustor. The SFBC was tested at a constant fuel feed rate (of about 80 kg/h) for six fuel-moisture contents (from 8.4% to 35%). In each test series for the particular fuel quality, excess air was ranged from about 20% to 80%. Radial and axial profiles of temperature and gas concentrations (O2, CO and NO) were plotted for different fuel options and operating conditions with the aim to study pollutants formation and reduction in different regions of the SFBC. With increasing the fuel-moisture content, the emission of NO from the combustor apparently reduced, while the emission of CO was adjusted at a quite low level due to the effects of secondary air. An effective least-cost control of both NO and CO emissions and high (over 99%) combustion efficiency are achievable when firing moisturized rice husk in this SFBC.