Combustion behavior in a dual-staging vortex rice husk combustor with snail entry

The combustion characteristics of rice husk fuel in a dual-staging vortex-combustor (DSVC) are experimentally investigated. In the present work, the vortex flow is created by using a snail entrance mounted at the bottom of the combustor. The temperature distributions at selected locations inside the combustor, the flue gas emissions (CO, CO2, O-2, NOx) and the combustion/thermal efficiency are monitored. Measurements are made at a constant rice husk feed rate of 0.25 kg/min with various excess airs (37%, 56%, 74% and 92%) and different secondary air injection fractions (lambda=0.0, 0.15 and 0.2), respectively. The combustion chamber is 1800 mm high and 300 mm in diameter (D) with a centered exhausted pipe while the middle chamber of the combustor is set to 0.5D. The smaller section at the middle chamber is introduced to split the chamber to be dual-staging chamber where a large central toroidal recirculation zone induced by swirl flow through the small section is generated in the top chamber. The experimental results reveal that the highest temperature inside the combustor is about 1000 degrees C whereas both the thermal and the combustion efficiency are 41.6% and 99.8% for 74% excess air without the secondary air injection (lambda = 0.0). In addition, the emissions are CO2=8.1%, O-2=9.3%, CO=352 ppm, NOx=294 ppm and small amount of fly ash. Therefore, the DSVC shows an excellent performance, low emissions, high stabilization and ease of operation in firing the rice husk. (C) 2008 Elsevier Ltd. All rights reserved.