Development of thermally-driven hybrid LiBr-water absorption system for simultaneously supplying steam and refrigeration effect

Abstract

• A hybrid LiBr-water absorption system for producing steam and refrigeration effect. • System characteristics with respect to part-load conditions. • The overall COP of the proposed hybrid absorption system of 0.463. • Experimental thermodynamic states concerning several operating modes. • Pay-back analysis of the proposed system compared to the existing business cases. Waste heat is a form of renewable energy discarded into the atmosphere. Waste heat-driven absorption systems (i.e., heat pumps and refrigeration systems) have attracted attention as district heating and cooling systems. This study proposes a waste heat-driven hybrid lithium bromide-water absorption system for the simultaneous generation of available steam and refrigeration effects. The proposed system is a form of the combined closed thermal cycle between the sub-heat pump and the sub-refrigeration system. It shares a generator and condenser, which allows the system to be more compact and flexible. We first present a description of the proposed system, designed for a cooling capacity of 350 kW with a steam generation rate of 200 kg/h. Our preliminary study proposed a pilot-scale system to clarify the flexible and simultaneous control means of the heating and cooling capacities by partially distributing the flow rate of the LiBr solution entering each sub-cycle. In addition to the results from the preliminary study, the present work examined the effect of part-load conditions on the operating parameters of the hybrid absorption system. The results showed that the coefficient of performances of sub-refrigeration and sub-heat pump cycle were approximately 0.787 and 0.658, respectively, and as a result, the total coefficient of performance of 0.463 was achieved. The theoretical model was validated by the experimental data, and the payback analysis was suggested to assure the economic validity of the proposed system. It was noted that the proposed hybrid absorption system demanded high initial facility cost than the comparison groups, but a payback of 2.79 and 2.36 years was evaluated because of the use of low-grade energy.