Producer Gas Composition and NOx Emissions from a Pilot-Scale Biomass Gasification and Combustion System Using Feedstock with Controlled Nitrogen Content

Abstract

This study is focused on the effects of nitrogen content in biomass feedstock on the producer gas composition and the flue gas NOx emissions from a pilot-scale gasification and combustion system. Biomass gasification has the potential to produce carbon neutral energy by using renewable resources. When the biomass-derived gas is burned, NOx emissions are a critical factor that can limit the use of the system. In this study, tests were conducted in a pilot-scale fluidized-bed gasifier using biomass feedstock with different nitrogen contents varying from 0.14 to 1.75 wt %. The producer gas from the gasifier undergoes a gas cleaning phase before its combustion in a burner. The producer gas and the exhaust flue gas were analyzed. Results show that there is a direct and proportional relationship between nitrogen in biomass, ammonia in the producer gas, and NOx emissions in the flue gas. Additionally, NOx emissions do not vary noticeably with the overall equivalence ratio in the burner but vary significantly with increased heat rate. It was also found that thermal NOx is less significant than fuel NOx, which constitutes a majority of the total NOx emissions when biomass-derived producer gas is used.