Techno-economic study of a heat pump enhanced flue gas heat recovery for biomass boilers

• A heat pump was studied to recover both sensible and latent heat of the flue gas.
• The economic analysis shows a decrease in operating costs between 2% and 13%.
• For a 10 MW wood chip boiler a payback time of 2–12 years was estimated.

An active condensation system for the heat recovery of biomass boilers is evaluated. The active condensation system utilizes the flue gas enthalpy exiting the boiler by combining a quench and a compression heat pump. The system is modelled by mass and energy balances. This study evaluates the operating costs, primary energy efficiency and greenhouse gas emissions on an Austrian data basis for four test cases. Two pellet boilers (10 kW and 100 kW) and two wood chip boilers (100 kW and 10 MW) are considered. The economic analysis shows a decrease in operating costs between 2% and 13%. Meanwhile the primary energy efficiency is increased by 3–21%. The greenhouse gas emissions in CO2 equivalents are calculated to 15.3–27.9 kg MWh−1 based on an Austrian electricity mix. The payback time is evaluated on a net present value (NPV) method, showing a payback time of 2–12 years for the 10 MW wood chip test case.