Abstract
A cogeneration cycle for electric power and refrigeration, using an ammonia-water solution as a working fluid and the geothermal hot water as a heat source, is proposed and investigated. The system is a combination of a modified Kalina cycle (KC) which produces power and an absorption refrigeration cycle (ARC) that generates cooling. Geothermal water is supplied to both the KC boiler and the ARC generator. The system is analyzed from thermodynamic and economic viewpoints, utilizing Engineering Equation Solver (EES) software. In addition, a parametric study is carried out to evaluate the effects of decision parameters on the cycle performance. Furthermore, the system performance is optimized for either maximizing the exergy efficiency (EOD case) or minimizing the total product unit cost (COD case). In the EOD case the exergy efficiency and total product unit cost, respectively, are calculated as 34.7% and 15.8$/GJ. In the COD case the exergy efficiency and total product unit cost are calculated as 29.8% and 15.0$/GJ. In this case, the cooling unit cost, c p , c o o l i n g , and power unit cost, c p , p o w e r , are achieved as 3.9 and 11.1$/GJ. These values are 20.4% and 13.2% less than those obtained when the two products are produced separately by the ARC and KC, respectively. The thermoeconomic analysis identifies the more important components, such as the turbine and absorbers, for modification to improve the cost-effectiveness of the system.
Highlights
In recent decades, rising concerns over fossil fuels shortages and environmental impact have motivated investigators to seek energy conversion methods with high efficiency and low environmental impact
The results indicate that the Kalina turbine, absorber 2, and absorber 1 take on the first three places, which implies that more consideration in terms of optimization and modification should be paid to those components to improve their cost efficiencies
The effects are investigated of three significant parameters, turbine inlet pressure (TIP), evaporator pressure and condenser mass flow split ratio, on the exergy efficiency and total product unit cost of the system
Summary
In recent decades, rising concerns over fossil fuels shortages and environmental impact have motivated investigators to seek energy conversion methods with high efficiency and low environmental impact. Ahmadzade et al [25] conducted thermodynamic and thermoeconomic analyses and optimization of a solar-driven combined Rankine and ejector refrigeration cycles, using an ammonia-water working fluid. Shokati et al [26,27] investigated with exergoeconomics absorption power and cooling cogeneration cycles based on the KC and including an ammonia-water double effect KC/ARC and two configurations of the KC and ARC They concluded that the boiler and low-pressure absorber make the highest contribution to the exergy destruction and capital investment cost rates, implying that these components are the least cost-efficient components in the proposed system. To determine the optimum working condition for the cycle, optimization is carried out by modifying all parameters to attain either the maximum exergy efficiency (EOD case) or the minimum product unit cost (COD case). Sustainability 2020, 12, 484 component to determine the most important components for modification in order to improve the cost-efficiency of the system
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