Effect of Adding Halloysite to Different Solid Biomass Fuels on Combustion Process in a Small-Scale Domestic Retort Boiler

Biomass combustion in small-scale boilers in Eastern Europe has recently become a very popular heating option. Biomass boilers are gradually replacing old, coal-fired installations, especially in the domestic sector. In comparison with coal, biomass contains more phosphorus, chlorine, and potassium, which may cause the corrosion, slagging, and fouling of heating surfaces inside the combustion chamber. Such problems may be reduced by properly controlling the combustion process, as well as adding substances like halloysite to the fuel. This paper presents the results of adding halloysite to wood pellets made of coniferous wood, rape straw, and wood/rape blend in the combustion process of a 25 kW retort boiler. The results demonstrate that adding halloysite to biomass increases the ash sintering temperature, which may, in turn, reduce slagging. The addition of halloysite also reduces the KCl concentration in the ash and the total solid compounds, potentially lowering the risk of corrosion in the boiler. A slight reduction in CO, OGC, and SO2 concentrations was observed for rape straw biomass pellets with the halloysite addition. Moreover, the experimental results indicate that the addition of halloysite to fuel may influence boiler efficiency, especially during the combustion process of agricultural biomass and its blends.