District heating systems that use industrial waste are increasingly common, which helps the transition to a circular economy.
There is no such thing as a perfect energy efficient process. The second law of thermodynamics states that all energy generating processes produce heat as a by-product. This so-called waste heat is often released into the atmosphere as hot air or water.
According to a study by the US department of energy, 20-50 % of industrial energy is lost as waste heat. It has a small contribution to global warming but is literally a huge waste of energy. By using it for heating purposes, it can replace other CO2 emitting processes and thus be an effective alternative for reducing greenhouse gas emissions.
Power plants – whatever their energy source – that do recover their waste heat are cogeneration plants called ‘combined heat and power’ (CHP) plants. In the industrial sector these plants are abundant, and the waste heat is already routinely used for internal processes, either for space heating/cooling or to increase the efficiency of procedures that require heat.
However, the waste heat recovered by CHP plants is enormous and often after using it for internal purposes, some energy still goes lost. Therefore, why not use the waste heat outside of the industrial sector?
Waste heat recovery for so-called district heating (DH) purposes became widely popular during the global energy crisis in the 70’s and 80’s and has been experiencing a comeback since 2007 with the beginning of global warming concerns.
A district heating system supplies heat from a centralised location for either space or heating water in homes. In combination with modern thermal home insulation, this reduces residents' energy consumption and directly leads to lower energy bills. It has an impact on an underestimated problem in cities where people still heat up their buildings with old wood or coal stoves.
In the Turkish town of Soma, where 70% of people still use this old heating method, the Municipality together with the European smart city project CITyFiED have adapted the concept of district heating by using waste heat energy from a thermal power plant.
“The energy comes from pressurised, hot steam, but a considerable amount of the waste heat is lost in the final stage,” explains Mustafa Soyoral, supervising director of the Soma thermal power plant. “Now a significant part of the waste heat is turned into a useful resource.”
Although the final step, a distribution line, to link a demo site area of the project with the district heating system couldn´t be completed for administrative reasons, 4,000 buildings outside of the demo site have been already connected to the waste heat system. And the numbers are growing.
Just as in Turkey, “district heating is becoming more common with great potential,” says Ulrika Jardfelt of E.On Energy Systems in Sweden. Now one of the issues faced by distributors is to improve their knowledge about the exact amount of energy the customer needs. “In this context, digitalisation is a great chance for new systems to soon supply the right amount of high quality energy, there is a transformation of energy supply underway,” she concludes.