Sampling of Fly Ash and Fine Particles (PM10) in Two Full-Scale Boilers Firing Pulverized Wood with Coal Fly Ash Addition
In order to increase the share of renewables in future energy systems, biomass can be used to replace coal in medium- to large-scale Combined Heat and Power (CHP) plants. The European H2020 project “Biofficiency” is dealing with the enhancement of biomass-fired CHP plants by handling ash-related problems. Especially the composition and concentration of fine particulate matter and fly ash particles in the flue gas, influence the deposit build-up and consequently the efficiency and availability of the power station. Therefore, fine particles and fly ash were sampled in the reheater section of two wood fired full-scale power plant boilers, namely at the tangentially-fired 800 MWth boiler Avedøre Power Station Unit 2 (AVV2) and at the boxer-fired 900 MWth Studstrup Power Station Unit 3 (SVV3). Low-NOx swirl burners are used in both power stations. Coal fly ash is inserted in both boilers to act as an alkali capture additive. Fine particle concentrations (PM10) and size distributions were measured by an electrical low-pressure impactor (ELPI). Fly ash particles > 10 μm were separated by a cyclone before the sample flow entered the ELPI system. Fine particles were analyzed for their composition in an electron microscope by energy dispersive X-ray spectroscopy (SEM/EDX). Additionally, the composition of the sampled fly ash was evaluated by X-ray fluorescence spectroscopy (XRF).
A comparison of particle concentrations of both power stations with additive insertion revealed a higher amount of particles < 1 μm (PM1) in the tangentially fired system (approx. 44 mg/Nm³) compared to the boxer-fired system (approx. 27 mg/Nm³). The coal fly ash insertion was reduced to 50 % of the base value in Studstrup Power Station, which caused an increase of PM1 matter from approx. 27 mg/Nm³ to approx. 42 mg/Nm³.