dcsimg We cracked it! Waste-to-Energy heat pumps. - Ramboll Group

We cracked it!

Until now, no waste-to-energy plant in Denmark has used heat pumps to boost flue gas condensation and recover heat. No one believed it could be done cost-effectively. However, the design team at Ramboll Energy had other ideas.


December 2015

“We thought that if we could minimise the energy that drives the heat pump while also maximising energy output from the process, it would pay off,” explains Tore Hulgaard, Technical Manager at Ramboll Energy.

Traditionally, the flue gas condensation process at waste-to-energy plants involves three steps, during which a so-called wet scrubber removes pollutants from the gas. In the third step the scrubber can recover heat by using a heat exchanger to create direct condensation from water that is approximately 50 degrees Celsius– the temperature of the water when it returns from the district heating system.

Recovering heat when the scrubbing temperature is below the district heating temperature requires a heat pump, which recovers the heat by means of a cold circuit – the reverse of a refrigerator. This process, the fourth step, is usually highly energy-intensive and thus results in considerable electricity loss.

But Tore Hulgaard and his colleagues figured that if you built the turbine system to extract the steam from the middle of it, where the temperature is still just enough to drive the heat pump, less electricity would be lost.

They also discovered that the heat pump could cool the flue gas down to 25 degrees Celsius. That produces 5-6 kWh of heat for every kWh of power put into the system.

“These optimisation techniques boost energy production by around 20%, which probably makes the system the most energy efficient of its kind in the world. At the same time, this fourth step removes even more pollution from the gas,” Tore Hulgaard points out.

These facts and figures convinced the owners of Amager Bakke, a waste-to-energy plant currently under construction in Copenhagen. They installed Ramboll’s system earlier this year, and other waste-to-energy plants are following suit.

“It’s good not only for the plant owners but also for society as a whole: You could argue that the system is resource efficient and carbon neutral, because no additional fuel is used to recover the heat from the flue gas condensation,” Tore Hulgaard says.

Amager waste-to-energy-plant by BIG

Related articles, projects and services

Avedøre power plant
Greening energy plants
Heat and power plants are being converted from coal to biomass, especially in Northern Europe. President Obama’s Clean Power Plan will probably enhance the transition process in the USA. However, going green also poses its challenges.
District heating is getting cooler
Cogenerating heat and electricity lowers costs and carbon emissions. One pioneering project will use the waste heat from the London Underground to produce district heating.


Installing pipes for district heating
Our waste-to-energy services
In a world with an increasing consumption there is a pressing need to use resources in the best possible way. This involves reducing the generation of waste, and use of the residual waste for efficient and clean energy generation. Read more about our services in waste-to-energy here.
Iconic Copenhill delivers high-efficient energy from waste, recycling and recovery with a recreational touch
The multi-functional Copenhill waste-to-energy facility in Copenhagen raises the bar for resource optimisation with an energy efficiency of 107% and high potential for recycling and recovery.


Tore Hulgaard
Senior Chief Consultant
T+45 5161 8628