District heating from a crematory in Aalborg, Denmark

This case study is part of a project catalogue produced by ReUseHeat to inspire how to utilize excess heat from urban sources for heating and cooling purposes. The catalogue contains 25 existing or planned projects, 12 of which are Danish and 13 from other European countries.

Description

In connection to the installation of a new filtration system at the municipally owned crematory in Aalborg, it was agreed, that a system utilizing energy from combustion should be installed. Hereby, the local district heating company, Aalborg Fjernvarmeforsyning, can receive excess heat from the crematory.

The project has been enabled due to extra regulations on flue gas cleansing from crematory ovens. The regulation demands a filtration system to remove mercury. To do so, the flue gasses must be cooled. Instead of emitting heat to the surrounding ambient air, it is possible to use the excess heat in the district heating network. Hereby, excess heat is extracted, benefiting the district heating consumers. The heat from the crematory can annually heat approximately 20 to 25 regular Danish households in the order of 120 and 140 m2.

To enhance the lifetime of the filtration system, the flue gasses are cooled from approximately 800 degrees Celsius to approximately 120-140 degrees Celsius. This cooling process contains potential excess energy. In Aalborg, the crematory is expected to produce approximately 585,000 kWh annually based on 2340 cremations. The average amount of energy produced for each cremation is approximately 250 kWh. About 55,000 kWh of the energy produced from flue gas cooling is used internally, while the remaining is delivered to the district heating network. Additional energy is added to the crematory ovens to reach high operation temperatures, often above 800 degrees Cels.

Cremation is a well-established funeral excerpt in Denmark and is more frequent than casket funerals. The issue of using heat from cremation in district heating has created moral discussions in Denmark and other European countries. The Danish Council of Ethics have processed district heating from crematoriums and concluded that there are no acts of indecency when using crematory heat for district heating. On the contrary, council members have found great environmental benefits from using crematory heat instead of disposing of it in the surroundings.

As the main purpose of crematoriums is not to produce heat, the excess heat can be seen as a by-product of the cremation. Most heat comes from the energy used to reach operation temperatures in the crematory ovens. Expensive and energy-demanding cooling towers are avoided by using excess heat with a direct heat exchanger for the district heating network. However, potential gains from heat sales to district heating companies must be used internally to lower process operation costs, according to the Danish Council of Ethics. Here, the exploitation of crematory excess heat does not have a commercial purpose.

Throughout Denmark, multiple crematoriums have begun utilising excess heat to produce district heating. The crematoriums are often located in urban areas and close to existing district heating networks. Other Danish cities that use excess heat from crematoriums are Ringsted, Holstebro, Randers, Hillerød, Svendborg, Hjørring and Glostrup. The potential is present in other European countries as well. A single crematorium is not capable of supplying district heating on its own, however, they can assist both Danish and European cities in their district heating production.

Aalborg, Denmark

ReUseHeat

Finished in 2010

IVL Swedish Environmental Research Institute

External links:

1. Danske Krematoriers Landsforening
2. Aalborg crematory
3. Aalborg Fjernvarmeforsyning
4. The Danish Council of Ethics
5. Handbook - 25 cases of urban waste heat recovery