Upgrading of waste heat to process heat

If one can upgrade the waste heat that is released to the environment to usable process heat at the same location, energy can be saved. To this end, a heat pump is necessary that can operate at the temperature levels of the waste heat and the process heat. In addition, the heat pump has to deliver the required temperature lift. The previous page showed that the temperature level of the waste heat varies between 50ºC and 200ºC. Likewise, the temperature level of the required process heat covers a wide area but will always be much higher that the waste heat temperature. If the temperature level of the waste heat is upgraded to a process heat level of 180 - 230ºC less fuel is required for this process heat.

The heat pump which has to meet this requirements has to operate in a temperature window of 100 to 250ºC. The required temperature lift should be in the order of 50-100ºC. The heat pumps that are available nowadays are not able to fulfill both requirements.

ECN is working on two innovative heat pump concepts that are in principle able to deliver the performance in the wanted temperature range. These two heat pump concepts are:

Thermochemical heat pump

A heat pump that uses reversible absorption and desorption reaction of a vapour (water, alcohol, ammonia, hydrogen) with a solid (salt, ceramic, metal).

Thermoacoustic heat pump

A  heat pump that is based on the physical phenomena that a sound wave is able to create a temperature difference in interaction with a porous medium.