Pfaffenhofen, Kraftanlagentechnik München GmbH, Germany

Wood-fired CHP plant

A new CHP plant was built in Pfaffenhofen, a town of approximately 22,000. The plant generates electricity for the grid and heat for a completely new town district heating network. The network supplies hospital, schools, and other public buildings as well as private buildings. Furthermore, the plant delivers process steam for a large biological baby food factory.

In January 2000 the company Kraftanlagen Anlagentechnik München GmbH, which was responsible for the building of the CHP station, signed a contract with us for the delivery and erection of a wood-fired boiler plant with complete combustion equipment.

The boiler plant was completed in July 2001.

The boiler design: High freedom of construction

The supply includes our well-known boiler with natural water circulation, designed as a self-supporting, fully welded structure in which downcomers and corner tubes form the load-bearing columns. This boiler design offers a high degree of freedom of construction because of the small number of downcomers leading from the boiler drum to the lower distributors. This means that the boiler can be adapted to suit almost any purpose. For this particular plant a very low boiler was required in order to comply with the building height laid down in the authority approval.

Fuel feeding

The fuel, which consists mainly of forestry wood chips and sawmill wood waste, is carried from an approximate 12 m3 buffer silo in front of the boiler via three double conveyor worms to three pneumatic throwers which blow the fuel into the furnace. In the furnace a partial drying and gasification takes place while the fuel is still suspended in the air.

The water-cooled vibrating grate

The combustion takes place on a water-cooled vibrating grate which is divided into three air zones in the longitudinal direction. The air zones are connected to the air duct by means of flexible connections and air dampers for control of the desired supply of combustion air.

Secondary combustion air and recycled flue gas are supplied to the furnace combustion zone through air nozzles arranged strategically in the boiler front and rear walls. Slag and ash are carried to a container by a submerged slag conveying system.

Control and monitoring

A PLC containing all software for the control and regulation of the complete boiler plant is built into a panel and connected with the DCS system.

Plant design data

Process parameters Values Units
Load point 100 %
Steam flow 30 t/h
Steam temperature after superheater 452 °C
Steam pressure after superheater 62 bar
Feed water temperature 120 °C
Boiler efficiency 87.2 %
Energy input 26.7 MW
Moisture content in fuel 45 %
Calorific value 9.07 MJ/kg
Local emission limits out of the boiler
Dust 20 mg/Nm3
CO 125 mg/Nm3
NOX 250 mg/Nm3
Organic substances with 11% O2 in dry flue gas 25 mg/Nm3

*According to TA-Luft the above limits are daily mean values.