Subject of the contract: Feasibility study aimed at identifying solutions for recovering heat dissipated from wastewater at a treatment plant and using it to supply part of a district heating network
Project Objective: Evaluation of possible layout configurations for the recovery of heat that would otherwise be lost from the wastewater treatment plant, and preliminary sizing of the main components and necessary utility rooms
Key information
Client Name: A leading company in the design and implementation of heat generation and distribution systems
Project Name: Feasibility Study for Heat Recovery from a Wastewater Treatment Plant
Project Period: March 2022
Total cost of the work: The estimated total cost of the proposed projects ranges from €10,860,000 to €11,385,000, depending on the solution
Buildings involved: Wastewater treatment plant in northern Italy
Description of activities:
In preparing the feasibility study in question and the related technical documents, a careful analysis of the documentation provided (architectural floor plans, flow rate data for the water treatment lines, electricity and heat consumption, and biogas production) was conducted, and targeted site inspections were carried out.
According to estimates, the thermal capacity that the district heating line can receive—located approximately 600 meters from the boundaries of the wastewater treatment plant—is around 20 MW, assuming a temperature difference of 40°C (60–100°C).
In order to recover the excess thermal energy produced during the wastewater treatment cycle, the plan calls for the use of a heat pump, a cogenerator, and a high-efficiency boiler as a heat recovery unit. The heat pump would extract heat from the treatment plant’s effluent through the evaporator, while the condenser would transfer the thermal energy to the district heating network with a temperature difference of 20°C (60°C–80°C). The natural gas-fired cogeneration unit would be used to power the heat pump and, at the same time, to raise the temperature of the water leaving the heat pump from 80°C to 87°C. Finally, to raise the water temperature to 100°C (the district heating network’s supply temperature during the coldest periods), the use of a fire-tube boiler—also fueled by natural gas—is proposed.
Four solutions have been identified that differ in the size and type of the cogeneration unit used to recover heat from graywater.
Once the general layouts were defined, the main components of the system and the technical center were preliminarily sized, and the costs of all the identified configurations were estimated.
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