The effect of the District Heating Return Temperature Reduction on Flue Gas Condenser Efficiency

Abstract

The use of flue gas condensers proved to be effective in increasing boiler efficiency and achieving primary energy savings. The transition to the 4th generation district heating will lead to temperature reduction in district heating networks. The aim of this study is to determine the effects of the reduction in the district heating return temperature on flue gas condenser efficiency. Different DH return temperatures and fuel moisture contents were examined, and a calculation model was created. The results show that a reduction in district heating return temperature can lead to an increase in heat recovery through the flue gas condenser. Primary energy savings were estimated based on the amount of heat recovered.

Valorisation of Waste Heat in Existing and Future District Heating Systems

“…Nevertheless, it is more useful to use a flue gas condenser for heat recovery in boiler houses and CHPs, especially when the used fuel has a high moisture content, for example, woodchips and biomass. In the case of biomass combustion, a flue gas condenser can increase the boiler efficiency by up to 20% (relating to the lowest heating value) depending on the biomass parameters, design of the boiler, and operating conditions [19].…”

“…The estimations of waste heat factors are described further in this section. The waste heat factor for the heat recovery from flue gases in boiler houses and CHP in this study assumes that 20% of heat could be recovered by integrating flue gas condensers in biomass-based facilities [19]. An additional 5% of heat could be recovered in the case of a low-temperature DH system using additional deep cooling of flue gases by integrating a heat pump.…”

Method of linear approximation of COP for heat pumps and chillers based on thermodynamic modelling and off-design operation

“…The DH system is constantly undergoing improvements and changes. A new biomass CHP plant has been built, bringing the non-fossil fuel capacity to 220 MW in 2019 [60]. Furthermore, old DH pipes are being replaced with pre-insulated pipes [61].…”