Chemical Heat Pumps for Efficient Heat Exchange

By using organic liquid-gas, chemical heat pumps designed to operate by transferring heat between the source and sinks of a system. During a waste heat recovery or to design a heating and cooling network chemical heat pumps now can be used to manage the heat balance and control the heat loss from the heat network system.

A reversible chemical reaction which can be described as a reactant reacts to form a product at particular state or condition and if a change in those conditions takes place than the product so formed till than will react and generate the reactant back to its state of existence. By using this concept if there are two possible states, for example, let a flue gas from the furnace has high temperature this energy is used by chemical heat pumps to absorb a heat energy from other location in the system say a control room of the plant which is to be maintained at lower than room temperature.

We have to choose an organic liquid-gas mixture so that when we supply heat at low temperature to the organic chemical liquid-gas mixture a forward reaction can take place by means of the endothermic property of the reaction, and have exothermic reaction condition during backward reaction while releasing the heat in the sink with the high-temperature condition. These endothermic reactions and exothermic reaction of the organic chemical will determine the temperature of the system on which a chemical heat pump can work, by sucking the heat from the low-temperature source and release heat at the high-temperature sink.

We can consider a waste heat obtained from a control room or an office room cooler coil where temperature will be less than ambient temperature, the heat from the room is used by the organic liquid-gas mixture to carry endothermic reaction and form a product these products are sent to sink source (heat exchanger) where the backward reaction takes place by means of exothermic reaction of the system. Of course, a catalyst will make the reaction favourable to each stage. The best organic liquid-gas mixture would be isopropanol, acetone and hydrogen.

The chemical reaction carried out in the chemical heat pumps system will be:

  • Isopropanol (liquid)  → acetone + hydrogen [forward reaction with endothermic reaction]
  • Acetone + hydrogen  → Isopropanol (vapor) [backward reaction with exothermic reaction]

Phase change:

  • Isopropanol (vapor)—-> Isopropanol (liquid) [release latent heat]

The above systems forward reaction takes place at temperature 353K and 0.1 MPa(exothermic reaction), the backward reaction at temperature 473K and 0.1MPa (exothermic reaction). This system can handle 100.4 kJ per mole.

Water source and geothermal heat pumping systems are well designed to obtain enough energy by using organic liquid-gas chemical heat pumps and in near future, this would be the best heat pump.