Experimental Investigation of an 18-kW-Wood-Log-Fired GasificationBoiler

Abstract

Compared with other solid biofuels, fuelwood as the oldest biomass fuel source, requires lessprocessing, which results is smaller processing and transportation emissions. Oppositely, the air pollutantemissions are larger due to inefficient combustion control influenced by an uneven size distribution anddifferent moisture content. The previous facts explain why biomass gasification boilers are mainly usedfor steady-state combustion. In this kind of operation, the majority of air pollutant emissions are emittedduring the start-up and stoking processes. In the paper, experimental investigations of an 18-kW-wood-log-gasification boiler are presented. The boiler uses proven technology: two dampers for the control ofgasifying and combustion air, an extractive fan and downdraft gasification. Even this, proven technologycould be substantially improved regarding the efficiency and emission by the use of small modifications.The most creative modifications could be made by the use of: (i) refractory insets in the combustion zoneand (ii) different turbulators and small wings in the convective part of the boiler. The first are used topromote complete combustion and radiant heat transfer whereas the second are used to support convectiveheat transfer and to reduce particulate matter emissions. The examined boiler implemented thesemodifications and fulfilled the most stringent annexes of the standard EN 303-5:2012 regarding theefficiency and pollutant emissions.