Small-scale pellet combustion for heating applications has made great inroads in markets in countries such as Sweden, Austria, and Germany and to a lesser extent in Finland and France. Technology development has led to the application of strongly improved heating systems, which are for example automated and have catalytic gas cleaning equipment. Such systems reduce significantly the emissions from fireplaces and older systems while at the same time they improve significantly the efficiency.
Modern pellet stoves are nowadays efficient home heating appliances. While a conventional fireplace is less than 10% efficient at delivering heat to a home, an average modern pellet stove achieves 80%-90% efficiency.
Modern pellet stoves: aesthetic design and profile
Today, many of the small boilers available on the market use two stage combustion systems equipped with ceramic refractory lining and are combined with a suitable hot water tank for heat recovery. In this configuration, the boiler can then be operated at optimal load with sufficient air and high process temperatures independently from the heating demand. This leads to relatively low emissions of all products of incomplete combustion. With this, over the last ten years, boilers thermal efficiencies have improved from an average of 60 to 80-90%, while the emissions of VOC and tars have been reduced 100 fold. For a single family house, a pellet boiler of 8 kW will burn 3,200 kg of pellets to cover the heat needs over the year. This amount requires a storage space of approximately 5 cubic meters. Bigger boilers are used in district heating systems.
Profile of a pellet boiler
One common low-cost solution when changing from heating oil to pellets in small houses is retrofitting the old oil-fired furnace with a new burner designed for pellets. Several pellet burners convenient for substitution for oil burners are already available on the market. These are relatively simple but functional devices that in general give lower emissions than the best firewood boilers.
Profile of a pellet burner alone (left) and in replacement of an oil burner on a boiler (right)
Source: Ecotec (left), PellX (right)