Effects of air staging on emission characteristics in a conical fluidized-bed combustor firing with sunflower shells

This paper presents experimental results investigated from combustion of sunflower shells in a conical fluidized-bed combustor at feed rate 45 kg/h. Effects of operating parameters, such as excess air (EA) and secondary air to total air ratio (S/T) on combustion performance and emission characteristics of CO, CxHy and NO as well as combustion efficiency (ηc) were studied. Temperature and gas concentrations were measured along the combustor and at the outlet. The secondary air was tangential injected to the combustor at 0.5 m above the fuel feeding system and it was supplied at S/T = 0-0.4 for EA of 20-80%. The high combustion rates were found into two different zones of the combustor; in the bed region with the primary air and in freeboard region which were evidenced by two peaks of CxHy and CO concentrations. According to Thailand emission standard, the optimum operating condition to control CO and NO emissions at the quite high combustion efficiency (∼99%) seems to be EA at 40-60% and S/T = 0.3. Compared with conventional combustion, air staged combustion can reduced the NO emission by 27% when the combustor was operated at EA = 40% and S/T = 0.3. However, CO and CxHy emissions were apparently high.