Frøstrup Fjernvarmeværk A.m.b.a, Frøstrup District Heating Plant

The district heating plant in Frøstrup is a modern wood chip fired plant supplying heat to 257 consumers in the village of Frøstrup. Frøstrup District Heating Plant is a user owned company established in 1991 as a decentralized energy producing unit located in close vicinity to the users in Frøstrup.
The plant takes advantage of its proximity to the neighbouring staircase manufacturer Dolle A/S by purchasing surplus heat from the industrial processes in the factory.

Frøstrup Fjernvarmeværk A.m.b.a., Håndværkervej 11,
7741 Frøstrup.
Phone: +45 97 99 18 28

Frøstrup District Heating Plant has many visitors who come to learn about and experience the operations of a modern district heating plant. Foreign visitors who often represent communities in the process of establishing district heating, are very interested in seeing a plant in operation.

  • Guided tours: Yes
  • Open: By appointment
  • Booking: 2 work days prior to visit
  • Participants: By appointment
  • Admittance fee: None
  • Parking: Yes
  • Public transportation: Busstop 200 meters from the plant
  • Toilet: Yes
  • Language: English / Danish.


frøstrup-fjernvarme_20130218-DSC_4884-Editat Frøstrup District Heating Plant is primarily fueled by wood chips and the plant receives around 2500 tonnes of wood chips from state owned forests each year. Usually the wood chips are produced locally but can be delivered from other areas as well depending on availability and prizes. Occasionally willow grown for biofuel by a local farmer is used. In 2009 the plant invested in a new wood chip fired boiler intended for wet wood chips containing between 40 and 50% water. The new boiler produces 30-40% more energy than the previous one, and is built to accommodate wet solid fuel and not dry solid fuel like wood pellets. The wet wood chips take a long time incinerating and in that process they develop a large amount of damp flue gasses that are used in reheating the return water in the district heating system.
In the storage room an automated process crane continuously supplies the boiler with wood chips. The crane is installed with a safety device ensuring operations only at the back of the storage room whenever the door to the room is opened. This way there can never be unintended contact between personnel and machine.

Industrial Surplus Heat

Heat recovery from industrial surplus heat is a cheap alternative to other fuels utilizing heat that would otherwise have gone to waste. Being the neighbour to a staircase manufacturer, Dolle A/S, Frøstrup District Heating Plant buys surplus heat from the industrial processes at Dolle, thereby saving money on the wood chip account. All summer the boiler at the plant is put out of operation and the hot water for the consumers in Frøstrup comes from Dolle.


frøstrup-fjernvarme_20130218-DSC_4853-Edit The district heating plant in Frøstrup has three operational boilers but only one of them is operating on a daily basis. The other two are for emergency backup. The oil boiler is fired once in awhile to make sure it is operational but only around 2000 liters of oil is used per year. The original 1.1 MW wood fired boiler is fully operational, but it lasts around 24 hours from startup till the water is hot enough for circulation. The new 2.0 MW wood chip fired boiler with 0.5 MW flue gas scrubber has increased production at Frøstrup District Heating Plant with 67%.

Cleaning the Flue Gas

Incineration of the wet wood chips generates large quantities of flue gasses containing particles that are harmful to the health. In order to reduce the emission of harmful substances like nitrogen oxide (NO) and nitrogen dioxide (NO2) into the atmosphere, the flue gas is cleaned in a flue gas scrubber before it is released through the chimney. Before the flue gas reaches the atmosphere it is run through a cyclone cylinder where the gas swirls around forcing the particles to the cyclone wall from where they fall to the bottom, while the cleaned gas exits through the top of the cyclone. From here it is directed into the actual flue gas cleaner where the 180 degrees hot flue gas is showered with water several times. The water from this process is led to containers with wood shavings, filtering the water and letting the cleaned water sift into the sewer through a pump pit. The emitted water is routinely tested twice a year. The wood shavings are changed once a month and the used material is taken to the municipal incineration plant in Thisted. Each weak measurements of the amount of NOx remaining in the excess steam is made and Frøstrup District Heating Plant is 50% below the allowed amount.
But the flue gas cleaner not only cleans the flue gas. The system also uses the heat from the flue gas to heat up the cooled return water that runs back to the plant from the consumers. This process increases the output of the district heating system, which is evident from the fact that the steam emitted from the chimney is only 40 degrees as opposed to the 180 degrees that went into the flue gas cleaner.

Water Quality

The water in district heating systems circulates in a closed circuit between the plant and the consumers. The quality of the water is paramount to production efficiency and is constantly monitored. If the oxygen level in the water is too high it will cause the pipes to corrode. Likewise the pH value in the water is monitored in order to maintain the ideal pH value of between 9 and 10.

Additional Levies Result in Rising Prices

District heating plants and CHP’s are taxed by the state for the emission of nitrogen oxide (NO) and nitrogen dioxide (NO2) into the atmosphere. In 2012 the so called NOx levey rose from  DKK  5.20 per kg NOx to  DKK  25.50 per kg NOx. The purpose of the levy is to decrease the amount of harmful particles emitted into the atmosphere which is a constant concern of district heating plants. And even though plants are constantly working on bringing down NOx emissions the increase in levies will affect heating prices. In addition, 2014 will see the introduction of yet another levy, the supply security levy, which is a tax on all types of space heating. The size of the upcoming levy has not yet been announced but it will be fully applied in 2020 generating a total of  DKK 2.8 billion for the Danish state to invest in wind energy and the production of electricity from biogas.
At Frøstrup District Heating Plant there is an ongoing effort to supply heating at competitive prices which is achieved by thorough attention to maintaining the facility and the grid.


frøstrup-fjernvarme_20130218-DSC_4868-Edit Each year district heating plants in Denmark submit their price lists to the Danish Energy Regulatory Authority. According to the price list of December 2012, district heating from Frøstrup District Heating costs  DKK 579 per MWh VAT included. This means an annual cost of  DKK 13.588 for heating in a standard flat of 75 m2 consuming 15 MWh per year, and an annual cost of  DKK 16.688 for heating in a standard single-family house consuming 18.1 MWh per year.
The above mentioned prices are standard prices and in order to calculate the actual price for heating it is necessary to consider the actual heat consumption of a given family and the fixed costs of for example subscription.
For more Danish district heating prices see

Production Data

  • Established in 1991
  • 2009 new Weiss boiler in new building. Construction costs:  DKK 9 million
  • 2.0 MW oil fired boiler, Danstoker, emergency backup
  • 1.1 MW wood chip fired boiler, Weiss, with 0.4 MW flue gas scrubber
  • 2.0 MW wood chip fired boiler, Weiss, with 0.5 MW flue gas scrubber
  • Demag 1200 kg automated process crane.