Ammonia Absorption Refrigeration, Multi-Effect Desalination, Kalina Cycle, Combined Power Cooling and Desalination
Contemporary facilities experience growing demand of energy-intensive products like cooling, power and fresh water, which turn in results in energy and environmental concerns. The separate production of these intensive products potentially consumes more primary energy compared with combined production (polygeneration). We therefore seek the most sustainable and suitable polygeneration technology. The driving energy source for the polygeneration system is assumed to be low-grade heat available from solar thermal, geothermal, industrial waste heat, etc. The natural refrigerant based ammonia-water absorption system has the potential for more exploration in the field of polygeneration. In the past decades, ammonia-water based Combined Cooling and Power (CCP) systems were experimentally proven with different configurations. It is of great interest to integrate fresh water generation with an existing CCP system; hence, increasing the system output degrees of freedom with higher system potential performance. So far, the majority of existing desalination plants are Multi Stage Flash (MSF) desalination type, while Multi Effect Distillation (MED) technology has prominent advantages relative to MSF with high thermal efficiency, lower number of effects, low pumping power, high heat transfer coefficient, and tube do not contaminate the distillate water. According to the literature review, none of the published research works has investigated the ammonia absorption system for simultaneous cooling, power and fresh water. In this work, a thermodynamic study was conducted for natural refrigerant polygeneration system operated by low-grade heat sources to produce power and cooling output through generated ammonia vapour, with the rejected heat effectively utilized for desalination of salt water though MED with single flash technology. The combined system is the result of integration of absorption refrigeration, Kalina power and MED with single-stage flash desalination cycles. The low-grade heat source energy generates the refrigerant vapour in the generator, which is divided into two parts for power and cooling. The split ratio is used to vary the power and cooling output, based on demand variation. The total heat rejection from the absorber by heat of absorption and condensation heat from the condenser are effectively utilized for desalination through the MED system. The thermodynamic performance of the system is evaluated at the typical operating conditions of heat source, sink and evaporator temperatures of 250°C, 60°C and -10°C respectively for unit mass flow rate of weak solution. The system generates 170 kWth of cooling, 25 kWe of power generation and 950 kWth of rejected heat available for MED flash desalination. The system performance is evaluated through the effective exergy of the combined system, MED flash system performance ratio and power-to-cooling ratio.