Highly Efficient Heat Recovery from Biomass Combustion by Applying a Quench/packed Bed Condenser Coupled with a Compression Heat Pump

A flue gas condenser based on a combined quench/packed bed approach and directly coupled to a compression heat pump has been developed within the EU Horizon Europe project CBE4I to maximize sensible and latent heat recovery from biomass combustion. This paper presents a modelling approach for predicting condenser performance and supporting reactor design. An existing one-dimensional heat exchanger model has been modified to represent packed-bed operation by mapping the gas-side free flow area to the packed bed porosity, matching effective transfer area to the packed bed specific surface and numerically suppressing wall conduction resistance to emulate direct gas–liquid contact. A testing plant based on the reactor design according to the model has been built and test runs have been performed. Model parameters have been fitted based on a dedicated validation test and subsequently the model has been applied under varying operating conditions. The adapted model reproduced measured flue gas exit temperatures with good agreement, demonstrating suitability for design studies and sensitivity analyses. Furthermore, the new quench/packed bed condenser directly coupled with a compression heat pump confirmed ultra-low temperature spreads between flue gas outlet and water inlet (<1 °C), thereby maximizing condensation efficiencies.