Quality range of ENplus A1 certified wood pellets and their combustion behavior in residential pellet stoves and pellet boilers

Abstract Use of wood pellets is continuously increasing in Europe, and most of them carry the EN plus A1 label. In this research, 28 assortments of such A1-labeled wood pellets were collected from the fuel market and were comprehensively analyzed and combusted in two residential pellet stoves; up to 8 pellet assortments were also combusted in two residential pellet boilers. Correlation analyses have been carried out, including the results from 31 additional pellet assortments from an own pelleting process where specifically tailored pellet characteristics were produced using different wood species. In particular, the effects of pellet length, moisture content, fines content, raw material preparation, additives, and wood species were investigated to identify the dependencies between the investigated fuel parameters and pollutant emissions. The most important parameters influencing pollutant emissions especially from domestic pellet stoves were identified as the potassium content of the fuel, the hardwood content, the carbonate content of the fuel ash, the Si/K molar ratio, and the energy density. Total particulate matter (TPM) emissions ranged from 45 to 246 mg/m 3 for pellet stove 1, whereas for pellet stove 2, TPM emissions from 23 to 58 mg/m 3 have been observed. Not the same pellets performed best or worst in both pellet stoves. Overall, the current state of the art stoves showed a greater response to variations in pellet quality compared with boilers, and improvements in pellet stove technology and control are recommended.