Performance Study On Integrated System Of Ammonia-Water Kalina-Rankine Cycle And Dual-Pressure Evaporation Kalina Cycle

An integrated system of ammonia-water Kalina-Rankine cycle (AWKRC) for cogeneration of power and heating water and a dual-pressure evaporation Kalina cycle for further improving the Kalina cycle efficiency in reclaiming mid temperature waste heat resource were studied in this thesis.The Kalina cycle has large temperature difference during evaporation and small one during condensation therefore with high thermal efficiency for power generation, while the ammonia-water Rankine cycle has large temperature difference during condensation as well as evaporation, thus the later can be adopted to generate heating water as a by-product in winter. So called the integrated system of ammonia-water Kalina and Rankine cycle (AWKRC) is based on the Kalina cycle and can be converted to the Rankine cycle by adding three pairs of three-way valves or three sets of four-way valves, to make certain equipment out of the service. The AWKRC system operates respectively on the Rankine cycle in the heating season for heating demand in northern areas and on the Kalina cycle in non-heating seasons for better thermal efficiency.The theoretical calculation of the integrated system was conducted with the engineering calculation software EES. Firstly the calculation models were built of the system and the each equipment with mass and energy conservation equations, and then the evaluation indexes of the thermal efficiency, waste heat absorbing ratio and power recovery efficiency were adopted. At the predetermined initial conditions, the performance of the system changing with the different basic solution and work solution was studied, and the optimum values of basic concentration with the work concentration were obtained. Under the external conditions of inlet temperatures of heat source is 300℃, and the inlet temperatures of cooling water are respectively 25℃ for Kalina cycle and 15℃ for Rankine cycle, the temperatures of heating water and back water are respectively 90℃ and 40℃, and the concentrations of both work solution and basic solution of the Kalina cycle are taken respectively the optimum values of 0.5 and 0.314. Also the concentration of work solution of the Rankine cycle is taken 0.5. At the above conditions, the state parameters and the performance of the two cycles were calculated. When the concentrations of the basic solution and the work solution are taken the optimum values, the thermal efficiency and power recovery efficiency of the Kalina and Rankine cycle are 20.9%,17.4% and 17.0%,13.0 respectively; and when the heating recovery efficiency is added the composite power recovery efficiency of the Rankine cycle can reach 19.2%.The exergy analysis of the integrated system was also studied and the impact of superheat of the work solution in the evaporator was investigated. The results show that the superheat of the work solution at the outlet of evaporator has an optimum value to make the performance reach the best status when the inlet temperature of the heat resource and cold resource are determined, and the optimum value of the superheat is changing with the concentration of work solution. Thus, the trends of the optimum superheat varying with the change of inlet temperature of heat resource are presented with different concentration of work solution. The exergy analysis not only on the system but also on the main components and the exergy efficiency and exergy loss of component equipment in the system are presented under the conditions of optimum superheat of work solution and optimum concentrations of both basic and work solutions. When the external conditions of inlet temperatures of heat source and cooling water are respectively set as the above mentioned values and the internal conditions are optimized, the power recovery efficiency and exergy efficiency of the Kalina cycle are respectively 18.2% and 41.1%; while the power recovery efficiency and exergy efficiency of the Rankine cycle are 14.6% and 33.1% and when the heating section is added, the composite power efficiency and composite exergy efficiency of the Rankine cycle can reach 19.6% and 46.5%. The results of the exergy analysis of equipment show that the exergy loss of exhaust gas is more than 30% and the exergy loss of either evaporator or turbine is more than 40%.A dual-pressure vaporization Kalina cycle (DPV-KC) for cascade utilization of mid grade heat resource was also studied. The DPV-KC is designed by adding the second evaporator behind the evaporator of the Kalina cycle; and the second evaporator is used for reclaiming exhaust heat of the heat resource from the first evaporator to increase the export work. Through the calculation it can be known that it exist also an optimal relationship between the concentration of basic solution and work solution of the DPV-KC, and when the work concentration is taken 0.3,0.35, 0.4 or 0.45, the corresponding optimum match of basic concentration is 0.177,0.206,0.244 or 0.272 respectively. Under the conditions of inlet temperatures of both heat source and cooling water are respectively 400℃ and 25℃, the trends of performances of the DPV-KC system changing with the dew point temperature of evaporation with different work concentrations were investigated and the optimal dew point temperatures were obtained in different work concentration. The optimal concentrations of work solution and basic solution are 0.45 and 0.272 respectively; the optimal dew point temperature is 310℃; and the corresponding the power recovery efficiency of the DPV-KC is 28.4% which is more than 16.9% higher than that of the Kalina cycle. The exegy analysis shows that the exergy loss of exhaust gas of the DPV-KC is decreased by more than 60.2% comparing with that of the Kalina cycle.