Decarbonisation Technology - November 2022

100%

Waste heat sources

Industrial heat demand

75%

Food sector Paper sector

Chemical sector Renery sector

50%

25%

100

140

180

200 20

100

140

180

200

Tw (˚C) Waste heat temperature

Tw (˚C) Process heat temperature

Figure 1 Industrial waste heat sources vs process heat temperature demand per industry sector

Because in many situations there is a disparity between the temperatures used and those actually required, the potential of heat pumps is gaining greater attention. A heat pump functions in a similar way to a normal refrigerator (see Figure 2 ): a liquefiable gas (the refrigerant) is evaporated in a cyclic process at low pressure, compressed in a compressor, and condensed at a higher pressure. A pressure reduction component, such as an expansion valve, closes the cycle, while during evaporation the refrigerant absorbs heat, typically from inside the refrigerator or from a low-temperature environmental or process heat source. The gaseous refrigerant condenses after compression at high pressure and high temperature. In the case of the refrigerator, this heat is released into the ambient air. With a heat pump, this heat is put to practical use,

ranging from process heat to district and domestic heating. The COP and getting the most from the electricity One significant advantage of the heat pump is that it generates much more usable heat from the same amount of electricity compared to other technologies. In fact, no CO₂ is emitted if green electricity from the sun, wind, water, nuclear power, or other sources is used. It works by the heat being loaded into a refrigerant and raised to a higher temperature level using additional energy. The ratio of electricity used to usable heat is referred to as COP (coefficient of performance), and for a heat pump it typically means that 2-4 kWh of heat can be pumped with 1 kWh of electricity. Electric heaters have a COP of 1, and the electrolysis and combustion of hydrogen are typically 0.6, mainly due to losses in electrolysis (see Table 1 ). The long farewell to fossil fuels The first large-scale heat-pump installations were operated in Switzerland, back in 1938, and they provided a solution to minimising dependence on imported coal, which resonates with the current challenge. Heat pumps offer enormous potential to save CO₂, as seen in Scandinavia today, where several large Atlas Copco Gas and Process heat pumps using turbocompressors have operated since the 1980s. The setup works with

Process heat

= COP OUT

W IN

High temperature vapour

High temperature liquid

Condenser

Compressor

Expansion valve

Electricity

Evaporator

Low temperature vapour

Low temperature liquid/vapour

Waste heat

Figure 2 Typical setup of a single-stage heat pump