The Simulation Analysis And Revamp Of Two-stage Ammonia-water Absorption Refrigeration System

Energy-saving and ejection-decreasing are the main thesis of the modern industry. For energy conservation and environment protection, the absorption chillers have been widely used. A two-stage ammonia-water absorption refrigeration system uses raw gas from shift conversion process as heat resource. The temperature of the gas from shift conversion process is about 180 celsiur scale, which should be cooled down before entering the low temperature methanol washing unit(Rectisol), and the liquid ammonia provides energy for the Rectisol. In this task, using Aspen Plus software, based on ammonia-water thermodynamic data from paper and reference books, with the improved PSRK state equation, and appropriate transport models to compute transport properties are adopted, and the simulation of unit operations such as heat exchangers, high and low pressure distillation columns, evaporators, high and low pressure absorbers have been performed. Finally, the whole process simulation of the system is finished, and the simulation results with the design condition match very well and the thermodynamic models could describe the process of thermodynamic behavior exactly. The model calculated a series of capability properties of the system to get the relationship between the properties and various temperatures(such as regeneration temperature, condensation temperature, evaporation temperature). The impact of the content of water in the liquid ammonia on the system stability and performance coefficient are also analyzed. Methods of improved absorption effect are suggested. The relationship between circular ratio and ammonia content have been analyzed. Optimization of the system has been performed, and got the maximum COP of design case.The evaporation temperature differences between design condition and practice condition have been analyzed. The calculation of practice case have been done, and the solution is suggested.A feasible and reasonable revamp scheme is proposed based on this kind of model which focus on the Rectisol change. The equipment simulations have been done for design and revamp case including the high and low pressure distillation tower hydraulics simulation and heat exchangers checking based on process simulation. The size of the low pressure distillation tower and heater exchangers have been changed for the new case, and a new ammonia cooler is added for the Rectisol unit change. The low pressure distillation tower replacing of the high pressure distillation tower is suggested for the new case, and the cost of revamping is reduced. It provides theoretical reference for plant revamping.