An important part of asphalt production involves heating and drying aggregates, and it was essential to investigate at what temperature this takes place, whether it is possible to operate at lower temperatures, and how this can be supplied by district heating. SINTEF is working extensively on new concepts for high-temperature heat pumps, and it was interesting to investigate whether this could be a suitable area of application.
Some of the most important questions were:
- Can asphalt production make use of the energy supplied by the district heating network?
- How much emission reduction can be achieved?
- How efficient will a new system be?
- Does mature technology exist?
- Is it economically feasible to change the heating method?
Results
The project showed that about half of the energy supplied in the current solution (the gas burner) goes to heating and evaporating water in the aggregates, while just under half goes to heating the stone. To save energy, the project wanted to look at more efficient methods for evaporating water in asphalt production.
During the project, temperature and humidity were measured in the stack at the plant. Since much of the energy goes to evaporating water, and all of the evaporated water leaves through the stack at high temperatures, there is also a lot to gain by finding ways to use the waste heat here.
For all the concepts assessed, large reductions in CO2 emissions of between 5 and 35% were found. The challenge in realising this potential is that there is no equipment for drying aggregates for asphalt production at low enough temperatures. There is equipment with the potential to be developed further to dry at lower temperatures, which would also make it possible to use waste heat from other industries in the asphalt process.
Partners:
The project is partly funded by the Regional Research Fund (RFF)