Applications of Absorption Heat Transformers in Desalination, Cogeneration and the Use of Alternative Working Pairs

In recent years considerable attention has been given to reduce the use of fossil fuels for heating and cooling applications. Large amounts of thermal energy at low temperatures from the process industries are released into the atmosphere, which causes thermal pollution. The Absorption Heat Transformer (AHT), being principally heat operated, is a useful tool to upgrade this low temperature rejected heat to the required heat energy at higher temperatures for useful applications. The desalination of seawater is one of such applications, which requires heat input at higher temperatures. Therefore, integrating the AHT and the desalination system for the aim of seawater desalination can significantly contribute to improve energy utilization and also the energy conservation. This thesis presents theoretical investigations on AHT based desalination systems. Alternative configurations of AHT systems using LiBr/H2O as the working fluid and integrated with a water purification system are analyzed and optimized thermodynamically. First, the waste heat from a textile factory is utilized to run the AHT systems and the generated high temperature heat is employed for the purpose of desalination. A computer program is developed in the EES (Engineering Equation Solver) to investigate the effects of different parameters on four different configurations of AHT and the desalination system. It is shown that applying different modifications can increase the coefficient of performance (COP) of the AHT and consequently the productivity of the desalination system. The maximum flow rate of the distilled pure water reaches 0.2435 kg/s when waste heat from the condenser is utilized by the evaporator. The risk of crystallization of LiBr is lowered in the modified configurations. In the subsequent section of the study the waste heat from a novel cogeneration cycle based on the recompression supercritical carbon dioxide (S-CO2) Brayton cycle is utilized to produce power through a transcritical CO2 power cycle and pure water by means of distillation process. Alternative configurations of AHT systems are employed to upgrade the lower temperature waste heat in order to run desalination system. It was found that in the best configuration, both the energy and exergy efficiencies are about 5.5–26% and 9.97-10.2% higher. The thermodynamic performance of the absorption chiller using (H2O+LiCl) as the working pair was simulated and compared with the absorption chiller using (H2O+LiBr). The effects of evaporation temperature on the performance coefficient, COP, generation temperature, concentration of strong solution and flow rate ratio were also analyzed. The results showed that the coefficient of performance of the absorption chiller, using (H2O+LiBr) at the optimum conditions, was around 1.5–2% higher than that of (H2O + LiCl). Keywords: Absorption Heat transformer, absorption chiller, Alternative configurations, Desalination, LiBr+H20, crystallization