Boiler
The biomass boiler uses fluidized-bed technology. Inside the boiler, at the base, 120 tonnes of sand are fluidized, or put into suspension, by 2,000 blowers that inject air. With the boiler temperature at 850°C, the chips are instantly transformed into charcoal. This charcoal then burns more slowly to produce steam at 540°C and 98 bar.
3D film showing the biomass boiler
Biomass boiler
Video interview of Attila Pèterfy, Head of the plant, on the boiler operation:
Two conveyor belts feed biomass to the boiler, either from the storage area or directly from the chipper. The wood chips are deposited in two buffer hoppers that can hold a five-hour supply and then fed into the boiler through four openings by means of a screw conveyor. The amount of biomass entering the furnace must be carefully controlled. The boiler requires 54 tonnes per hour. Its design is based on Finnish technology known as a bubbling fluidized bed process. The furnace is equipped with nearly 2,000 air nozzles that fluidize the sand. The internal furnace temperature is 850°C. When the chips are fed into the boiler, they come in contact with the sand stream, which enhances combustion. The air required for combustion enters the boiler via the blowers and through two other combustion air intakes. This air acts as an oxidant, a chemical compound that promotes combustion of a fuel. The principal oxidant is dioxygen. The fluidized sand, air and temperature combine to ensure high boiler efficiency. Ash is produced when the chips are burned. This ash is in turn fluidized and burns in the boiler. The goal is to eliminate as much unburned residue as possible from the flue gases exiting the boiler. Non-combustible material such as grit and gravel is mixed with the chips fed into the boiler. Any such material passes through the fluidized sand bed and out the bottom of the boiler, since it is important to keep the bed free of contaminants. Fluidized-bed technology helps us to comply with regulations governing emissions. The boiler generates high-pressure, high-temperature steam that is supplied to the production unit’s turbine. The turbine produces electricity via the generator, as well as a small amount of heat, which is sent to the district heating network.
Attila Pèterfy, Head of the plant
During periods when heating is not needed, the unit supplies the city of Pécs with domestic hot water. The flue gas released by the boiler is filtered by an electrostatic precipitator that traps solids, in this case ash from the chips. The ash is bagged and sold as fertilizer to farms.
Boiler furnace
Burner used to activate the boiler
Suspended sand fluidized bed
Air intake nozzles
One of the boiler's two 250-cubic-meter supply tanks
The steam generated by the biomass boiler is channelled to a condensing turbine, where it expands to power a generator that produces electricity.
Steam turbine
Generator