Co-firing of biomass with gas fuel in low–power boilers

Combustion is a complex process. It consists of many physical and chemical processes of thermal decomposition and fuel combustion taking place in a specific space and time. This paper examines the evaluation of the process of combustion pellets and briquettes made from oat straw in a low-power grate boiler 10 kW, which was carried out in two variants: without modification of the combustion chamber and with its modification. In the boiler processing, an element limiting the combustion chamber was used; it was made of steel strips with dimensions (length × width × thickness) of 100×3×1 mm attached radially at one end to a steel core 50 mm long, under which, using a mixture of butane and propane in a 70:30 ratio, a secondary combustion zone was created. Combustion of pellets without modification of the combustion chamber was characterized by increased dynamics, which was indicated by higher combustion rate, higher flue gas temperature and lower air excess. At the same time, modification of the combustion chamber applied in the scope of these parameters contributed to reduction of the combustion rate and flue gas temperature, while reducing the air excess that was absorbed by combustion of the gaseous fuel. Emission of pollutants with combustion of pellets and briquettes without modification of the combustion chamber was characterized by similar values in the CO and NO range, only for briquettes, the SO2 emission was more than twice as high. However, by modifying the combustion chamber along with the use of additional gaseous fuel, a reduction of CO by 15 % was achieved. Higher NO and SO2 emissions were observed. It would be expedient to conduct research to a greater extent related to optimization of CO, NO and SO2 emissions using other types of herbaceous biomass