Copenhagen HOFOR Sets The Example

HOFOR, Greater Copenhagen Utility, is the metropolitan area’s utility company. HOFOR is municipally owned, where the ownership of the water and wastewater services are shared between 8 municipalities.
Already in the 1980s Copenhagen community realized that something should be done about the air quality in the town and the avoidance of waste heat. The whole town was ploughed up to install district heating piping, that was getting its energy from a waste incinerating plant and the production of electricity at other plants just outside town.
At first the electricity was produced from natural gas and coal in different plants. First the natural gas plant was redesigned to burn wood pellets and finally a few years ago the big decision was taken to replace the coal fired station with a top of the line wet wood chips burning combined heat and power plant.
In 2019 the plant started production, annually using up to 1.2 million tonnes of wet wood chip (at least 45% moisture content). At the end of the commissioning period, finally this year January the plant reached 100% utilization, meaning that it produced 150 MW electricity and 370 MW of heat simultaneously.
The efficiency of the plant as expressed on the lower heating value of the fuel is well above 100%. This very high number can be achieved due to the fact that the plant uses the low temperature returning district heating water to cool the flue gasses. Once the flue gasses come below 65 degrees C, the evaporated water from the fuel condenses and releases the energy that was used to evaporate it. Not only the water that was evaporated will condense, but also the water that was generated by burning the wood. Wood is a carbohydrate and will form CO2 and water as the main constituents of the fuel gasses. The energy is transferred to the district heating water prior to be run through the boiler to be brought up to the normal running temperature.
Fortunately, the CHP plant is situated at a deep-water port, which makes it possible for even large ships to dock at the plant and transfer their chips directly into production. At the present rate of consumption a ship with between 4000 and 5000 tonnes of fuel is needed every day to keep the plant running. The storage capacity on site is limited to a few days of operation. A little bit of leeway can be obtained by receiving some roundwood (as deck cargo) which can be chipped on site in times of need.