Influence of burner form and pellet type on domestic pellet boiler performance

Abstract

Abstract. The study presents combustion and emission results obtained using two serial pellet boilers of the same heating capacity 40 kW. These boilers have been designed by producers for domestic conditions of exploitation. The principal difference between boilers was the type of the burner. The study concerns the efficiency and ecological performance difference between burners of circular and rectangular forms. The features of the combustion process in both types of burners were studied when boiler operated with different sorts of pellets. The results suggest that the burner of circular form excels the rectangular form burner. However, there is some difference of NO x emission between circular and rectangular burners. IntroductionAt present day many economical, technical, ecological, as well as political reasons motivate firms and homeowners to use their own autonomous, independent of central heating pipeline and gas pipeline heat energy sources. The causes of such choice usually are striving for independence of the heat supplying organization pricing policy, avoidance of bureaucratic apparatus cooperation with (in questions of tariff agreement, the correspondence heating pipeline and gas pipeline connection standards, payment for extra project documentation necessary for central pipeline connection), unwillingness to bear expenses for the heat energy losses in a long and, sometimes, not of perfect quality heating pipeline from a relatively distant central heating source. A diesel fuel boiler, a wood boiler, a coal boiler, a heat pump may be used as independent heat energy source, when it is technically possible. A boiler with biomass and a boiler with granules can also be used. The use of boilers with fuel manual load with relatively big heat power is complicated by the need of heavy manual work. Diesel fuel heating is appreciably more expensive that all others named above and causes serious air pollution. The heat pump for relatively big heat power requires sufficiently big electrical power; a pellet or ground biomass boiler is the most suitable option for such decision.In the last 15-20 years pellet boilers have gained serious popularity in Russia and the EU countries and the number of sold pellet boilers keeps growing. The high prevalence of such heat energy sources is reached thanks to several certain factors: easiness of automatization of the fuel feeding process owing to the standardized size of pellets; easy ash removal that can be automatic or manual, because the pellets ash content seldom exceeds 4 %. The exception is pellets made of straw with the ash content from 7 to 10 percent; compactness of all equipment as compared with unstandardized solid fuel boilers; accessibility of pellets in the market, reasonable price for domestic use. In all pellet boilers the fuel-bed firing technology is used. However, prevailing burner and feeding systems in the EU countries and Russia are different.