Analysis Of The Influence Factors Of Ammonia Distillation Purity And Effects On The Performance Of Ammonia-water Absorption Refrigeration System

As the energy and environmentproblem becoming more and more serious,the pursuit of higher energy utilization efficiency and greater use of resource utilization types become the focus of today's scientific research.The ammonia absorption refrigeration system which using heat and natural refrigerant ammonia is brought to the attention of the researchers once again.But because the difference between the ammonia and water with the standard boiling point only 133.4?,the generator inevitably produce water vapor while producing ammonia at the same time.It makes the ammonia liquid pouring into the evaporator is not pure,producing adverse influence on the performance of the refrigeration system,so the rectifying tower is introduced to improve the ammonia distillation purity.The result of the ammonia distillation purity in the rectifying column is affected by many factors,such as plate number,cooling water temperature and so on.These factors will indirectly affect the refrigeration system coefficient of performance(COP).To improve the performance of the ammonia absorption refrigeration system and enlarge its application scope,researches on the various factors influencing the ammonia distillation purity and the effects on the performance of the refrigeration system become the priority.In this paper,under the guidance of this idea and using relevant software,the specific contents and conclusions are as follows:(1)State equation is derived using Schulz equations of state for the system ammonia-water,resulting the balanced equation of ammonia solution and the relationship between temperature,pressure,enthalpy,gas liquid phase mole fraction and so on.Matlab software is used to program the above equations,and the program calculation results are compared with the literature data to complete the verification.The software calculating program provides support for subsequent internal rectification process in distillation tower.(2)The advantages and disadvantages of the equilibrium stage model and non-equilibrium stage model of the rectification tower are analyzed.Based on the consideration of various influence factors of distillation process,the non-equilibrium stage model of the rectifying column is established,and its accuracy is verified.The model is used to study the effects of a total of six factors on the ammonia distillation purity,such as the cooling water temperature,reflux ratio,rectifying and stripping section plate number,feed flow rate and concentration.Research shows that the ammonia distillation purity increases with the decrease of cooling water temperature and the feed flow rate,and the increase of the column plate number and the feed concentration,and there is an optimal reflux ratio making the system COP the largest.The analysis of these factors provides a reference for the optimization of aqua-ammonia absorption refrigeration system.(3)Following the previous chapters,the simulation of the whole ammonia absorption refrigeration system is made to explore the effects of the ammonia distillation purity on evaporation pressure of the system,absorbing solution concentration,the generator heat load and the COP using EES software.Results show that under certain conditions,with the decrease of the ammonia distillation purity,the evaporation pressure and the absorption pressure reduce,the absorption solution concentration and the deflated range decrease,and the system circulation ratio increase,eventually leading to the generator heat load increased and the system COP reduced.The results can illustrate the importance of the high ammonia distillation purity for the performance of the refrigeration system.(4)From the perspective of reflux ratio,a modified ammonia absorption refrigeration cycle is studied.It employs evaporator liquid blowdown to provide reflux for the distillation column.Aspen Plus is used to simulate the conventional and the improved circulations,comparing the generator heat load and COP under different evaporation temperature,-12??4?.The results show that under the same refrigeration capacity,the modified cycle can reduce the ammonia flow rate from the distillation column,thus reducing the generator heat load,especially applicable to lower evaporation temperature.Compared to the conventional cycle,the modified cycle with heat recovery can make the COP improved about 5% under-12? evaporation temperature.The above results show that the modified cycle has certain advantages.