Coupling an SOFC with a Vapour Absorption Refrigeration and Cooling Unit

Of late there has been increased interest in the development of small scale vapour absorption refrigeration systems (VARS) for applications where residual thermal energy is freely available. High temperature fuel cells such as Molten Carbonate Fuel Cells (MCFCs) or Solid Oxide Fuel Cells (SOFCs) generate high quality heat at temperatures beyond 450°C which are sufficient to drive an absorption refrigeration or air conditioning unit. The ongoing project at the University of Birmingham is looking into the development of a small scale integrated SOFC-VARS unit to supply cooling loads of up to 10 kW at an
evaporation temperature down to -20oC.
The temperature mismatch between the SOFC and the absorption refrigeration system, prevents direct coupling of heat from the former into the latter. The desorber is therefore one of the key components of the VARS and the development of a small scale VARS primarily hinges on the design and performance of the desorber. Plate heat exchangers (PHE) have been identified as one possible solution for small scale VARS applications and extensive modelling studies have been carried out to develop design maps describing the
desorber performance and the coupling with the SOFC under varying conditions.
Based on the modelling results, an experimental brass board system has been
constructed to showcase the concept. The prototype has the following features: ability to simulate cathode exhaust flow rates from SOFC stacks up to 1 kWe power rating which is then thermally coupled to a 300 mm high plate heat exchanger desorber with 10 plates.
This generates enough refrigerant to provide cooling capacities of up to 1 kW at an evaporation temperature of -20 oC. Experimental results show that about 0.73 kW of heat was produced which is about 61% of the required heat input at the desorber with ability of getting up to over 90% if the thermal oil leaving the desorber is cooled down to the initial starting temperature before getting back to the tank. An overall heat transfer of 5.24 kW/m2-K was also achieved on the coupling heat exchanger.