Active condensation in hot and superheated water boilers

Abstract

Return temperatures in hot and superheated water boilers are frequently higher than the corresponding flue gas dew point temperature. To utilize the fuel’s higher heating value in such boilers, active condensation (AC) systems must be employed. However, these systems require additional energy to transfer heat from below the dew point to above the return water temperature. This paper analyzes three AC systems in three case studies: (i) a compressor heat pump (HP) in a boiler room supplying a hot water district heating (DH) system; (ii) a superheated water DH system fueled by natural gas, using a flue gas condenser coupled with a compressor HP-based AC system; and (iii) the same system as (ii) but with an absorption HP. The case studies are based on experimental investigations of DH systems in Loznica (i) and Kraljevo (ii and iii). Numerical models were developed using experimental data and findings from other researchers, combined with material and energy balances. The results address the following key questions: (i) When is AC implementation economically feasible? (ii) What type of HP should be used, and under what conditions? (iii) What HP design specifications are required? (iv) What is the optimal flue gas temperature for AC systems? (v) Under what circumstances is coupling flue gas condensation with AC viable? (vi) When is an absorption HP economically justified?