Type of CHP system: Grate fired boiler

Plant owner: The plant is part of an Amba company (co-operative society) and is thus owned by its 507 connected heat consumers.

Commissioned: 1997

Status of plant: Commercial

Contractor details:

Buildings: Sønderjyllands Maskinfabrik

Boiler: Eurotherm

Turbine: Siemens (Kaluga)

Generator: AVK

SRO-unit: Circuit Electric

Power generation: Steam turbine

The boiler unit contains a pre-combustor coupled as a vaporiser, a steam boiler, a superheater divided into two sections and an economiser for preheating the feed water.

Main fuel: Wood chips

The plant can be fired on wood chips, waste wood, and veneer. In addition, the plant holds a permit  to incinerate scrap products from diaper manufacturing. The maximum water content of the fuels used in this plant is 55%.

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 4,1 MW

Total thermal input, incl. fossil fuels: 4,1 MW

Gross electrical output: 0,6 MWe

Net electrical output: 0,50189497716895 MWe

Heat output: 3 MJ/s

Electrical efficiency, gross: 15 %

Overall efficiency, gross: 88 %

How is plant controlled: The CHP plant is controlled by the heat demand in the DH network.

Heat usage: Heating only

Energy usage: Supply of district heating to 506 heating consumers and one large customer (equivalent to 200 private consumers).

Heat storage size: 1000 m3

Hours of full load that the heat storage can meet: The heat storage can meet 48-hour heating supply during warm weather and a 12-hour supply during winter weather.

Fuel storage:

The fuel storage is 6,000 m3, which means that the plant has the possibility of buying fuel when it is less expensive, and thus is less dependant on seasonal price fluctuations.

Waste water: Waste water is generated from the new gas scrubber. No information on waste water treatment.

Ash discharge: Fly as well as buttom ashes are taken to a controlled disposal facility. Alternative methods of disposing of the ash are being investigated.

Plant description:

The Hjordkær combined heat and power plant is the smallest steam turbine plant in Denmark.

The CHP plant consists of a hydraulic fuel feeding system, a grate fired prefurnace with a superheater, a smoke tube steam boiler, multicyclones followed by a water cooled economiser, a wet scrubber and a drip catcher. These components influence the combustion quality.


The wood chips are pushed into the prefurnace grate, where it normally is combusted only by addition of primary air under the grate. Secondary air can be added through inlets in the walls of the prefurnace. There is just one fan for combustion air and the distribution of primary and secondary air is controlled manually with throttles. The air is typically pre-heated to 75°C. The flue gases from the grate are guided back towards the front of the prefurnace under the ignition arc, which is lined with brick. The flue gas passes through the superheater, which is placed in the prefurnace. The walls of the prefurnace work as a part of the heating surface of the boiler.


The flue gas is then led through a brick lined challel, which connects the prefurnace and the boiler, and into the “combustion chamber” in the traditional smoke tube boiler with three draughts. In the outlet of the boiler the oxygen meter of the plant is placed.

Fuel feeding system: The fuel is fed into the boiler by a piston, which allows a wide range of fuel sizes to be used at the plant, even relatively large wood chips and waste wood.

Boiler: The steam boiler is designed as a canal fire tube boiler, where the flue gas runs in tubes organised in bunches, while water runs on the outside of these tube bunches.

Turbine: The turbine is a Russian made Siemens machine which is normally used for maritime purposes. It is a backpressure turbine with 5 expansion levels and a steam outlet connected to the feed water tank.

Steam data: 28 bar at 380 degrees C.

Flue gas cleaning:

The exhaust gas is cleaned first in a multicyclone and has so far, afterwards been taken through a bag filter. The bag filter is during the fall of 2001 being replaced by an exhaust gas scrubber because there are often many embers and uncombusted particles carried into the filter which can ignite the filter. A scrubber would also increase the heating production by the condensing operation.

Cooling system: Cooling by district heating water

The canal fire tube boiler secures convective heat transfer where heat transfer in the pre-combustor is due to radiation. The pre-combustor and the steam boiler are parallel connected, as the pre-combustor alone can not supply sufficient amounts of steam.

The pressure and temperature of the steam from both pre-combustor and steam boiler are increased in the superheater. The last cooling of the flue gas takes place in the economiser, where water is heated before the evaporation takes place in the pre-combustor/canal fire tube boiler section.

The pre-combustor consists of a step grate and fire proof refractory sheets. The grate, which operates hydraulically, has a bottom frame made of steel. The grate it self is constructed of specially cast iron parts.

Staff: The plant is manned by three people during daytime.

Electricity sale info: The electricity price is time dependent. Three tariffs apply:

Peak load, high load and low load.

Total capital cost: 2039000 Euro

Data collected and quality assured by: FORCE Technology.

Contact person: Anders Evald