Evaluation of the Combustion Process of Pellets from Herbaceous Biomass with the Addition of Kaolin and Urea Solution in Low-Power Boilers

In this study, an analysis was carried out of the combustion of pellets made from chamomile and English ryegrass biomass, including those with the addition of kaolin and urea, in terms of their physical and chemical properties. During combustion tests with synchronized timing, the concentrations of CO2, CO, NO, and SO2 in the flue gases were measured, along with the temperatures of the supplied air and the flue gases. The addition of kaolin improved combustion parameters, reduced CO emissions, and stabilized the combustion process, despite the deterioration of the mechanical durability of the pellets. Combustion in the drop-in burner (type B tests) showed higher energy efficiency (CEI) and lower flue gas toxicity (TI) than in the grate system (type A tests). The SiO2 content in the chamomile ash explained its higher resistance to slagging, confirmed by characteristic ash temperatures. Comparison with other biofuels (straw, hay, sawdust) showed similarities or advantages in terms of reducing CO, NO, and SO2 emissions. NO emissions were lower for pellets with urea and kaolin added, although in the case of biomass with high nitrogen content these relationships require further improvement. The research results indicate the potential of herbaceous biomass as a fuel in local heating systems. However, modification of such fuels is also associated with the need for further research on reducing emissions during unstabilized combustion phases, with particular emphasis on the ignition phase.