Enhancing thermal efficiency of wood pellet boilers by improving inlet air characteristics

Abstract

The characteristics of air supplied to a wood pellet boiler during operation affects combustion efficiency and therefore, the thermal efficiency of the wood pellet boiler. Inlet air flow and quality can be improved to enhance thermal efficiency. To improve the inlet air flow, a ‘nozzle-type burner pin’ and ‘vortex generator’ were applied to the primary and the secondary air inlets, respectively. The former supplies inlet air directly into accumulated pellets, improving combustion conditions. The latter introduces vortexed air, improving mixing between pellet volatiles and inlet air thereby increasing the heat transfer rate from the combustion gas to the heating water. A system was designed to dehumidify and reheat inlet air by reaction with a lithium bromide solution to improve combustion conditions. Finally, three experimental groups and an integrated experimental group applying all the improvements were designed. The thermal efficiency of the experimental groups was compared and analyzed with the conventional wood pellet boiler through experiments. In each group, the thermal efficiency was improved from a minimum of 2.81% to a maximum of 5.78%, compared to conventional wood pellet boilers. The thermal performance of the wood pellet boiler was enhanced and the improvement and significance of thermal efficiency was validated.