Energy-saving by heat recovery, Priozersk WWTP
The energy-saving project of reconstructing the heat supply system at Priozersk WWTP by using a heat-generating unit based on a heat pump. The introduction of a heat-generating unit is to decrease the cost of electricity consumption for heating the administrative building of the treatment plant.
Solution to which problem
Before the implementation of the project, the heating of the administrative building was carried out by electrode electric boilers, due to the remoteness of the treatment plant site from the centralized heat supply systems of Priozersk city.
The heat energy from the wastewater is transferred to the heat carrier circulating in the geothermal circuit by means of a heat exchanger installed in the aerotanks. Due to the supply of thermal energy (year-round positive temperature of the treated wastewater), the heat carrier is heated and it enters the evaporator of the heat pump. Refrigerant is circulated inside the refrigerant circuit. This refrigerant, in a liquid state and at low temperature and low pressure, enters the evaporator of the heat pump.
The temperature of the refrigerant is lower than the temperature of the heat carrier in the geothermal circuit, therefore, in the evaporator of the heat pump, heat energy is transferred from the heat carrier to the refrigerant. As a result of the supply of thermal energy, the refrigerant boils away and passes from a liquid to a gaseous state.
Then the refrigerant enters the compressor, where it is compressed, leading to an increase in pressure and temperature. Having a high temperature, the refrigerant enters the condenser of the heat pump, through which the heat carrier of the heating system circulates. Since its temperature is lower than the temperature of the coolant, the heat energy from the coolant is transferred to the heating medium of the heating system. Further, the refrigerant from the condenser of the heat pump is supplied to the throttling device, where due to the throttling effect its temperature and pressure are reduced, and then it enters the evaporator of the heat pump. Thus, the cycle of the refrigeration machine operating in the heat pump mode is closed.
Electricity consumption for heating in the heating season of 2017–2018 decreased by 219.825 thousand kWh, which corresponded to a payment decrease by ~12 000 EUR.