Effects of Flue Gas Recirculation on Emissions from a Small Scale Wood Chip Fired Boiler

This paper aims to investigate major pollutant formation and emissions from a typical biomass fired boiler. Emission tests were conducted on a 500 kW, wet wood chip fired district heating system under two operational conditions: (1) with flue gas recirculation (FGR) and (2) without FGR. Mathematical modelling work using FLIC (FLuid dynamic Incinerator Code) and FLUENT codes was carried out for both cases to simulate the overall performance of the boiler. Results show CO emissions in the case with FGR were higher than those in the case without FGR. FGR reduced both the average NOx and PM emissions from the wood chip fired boiler. The mathematical modelling shows that the introduction of FGR reduces the whole temperature level in the furnace. This helps to prevent slagging in the combustion chamber and the formation of thermal NOx. The distribution of the primary and secondary air jets must also be optimised in order to reduce the fuel-NOx formation.