Application Of Ammonia-Water- Lithium Bromide Absorption Refrigeration System Combined With Membrane Separation Technic

Absorption refrigeration system,which can be directly driven by low-temperature heat source and not endanger the ozone layer,has been popularized and applied rapidly,and the research on ternary absorption refrigeration system is more and more common in recent years,in which ammonia-water-lithium bromide is universally accepted.However,it is found that the presence of LiBr will change the properties of solution,resulting in poor absorption performance.In order to improve the effect of absorbing ammonia,this paper proposed a new method of separating LiBr from the solution of entering absorber by membrane separation technology,so as to retain it in the generator as much as possible.And establishing a new NH₃-H₂O-LiBr cycle based on membrane separator.In this paper,we study the new absorption cycle experimentally and theoretically.The limit current density model is established to calculate the theoretical separation efficiency of the membrane separator.The influence of membrane parameters and electrical parameters on the separation characteristics of membrane separator is analyzed theoretically.It is concluded that the selective transmittance of membrane has obvious effect on the separation efficiency,and the bigger selective transmittance is,the better membrane separation performance is.And the higher operating current is,the lower separation efficiency is.The greater flow velocity of solution entering membrane separator,the lower the separation efficiency.Based on above theoretical model,the separation efficiency of lithium bromide was 98.47%when the membrane separator was assembled in two stage and 3363/3364 ion exchange membrane was used.In order to verify the theoretical model,the experiment of membrane separation was carried out.The experimental results showed that the separation efficiency of lithium bromide solution with different concentrations was above 97%,and the error did not exceed±5%compared with the theoretical separation efficiency,so the theoretical model were verified mutually.The theoretical model can be used to calculate separation efficiency of the membrane separator with different assembling modes and different types of ionic membranes.Based on the experimental separation efficiency,the Aspen Plus process Simulator was used to establish a complete new cycle based on the membrane separator.And the effect of LiBr content and separation efficiency on the cycle performance was further analyzed.The simulation results show that,for the specific NH₃ and LiBr mass fraction,with the increase of separation efficiency,the COP of the new cycle increases,the maximum is 0.6599,the mass fraction of NH₃ is 60%and LiBr is 30%.The COP increased by 24.18%than the binary cycle with the same NH₃ concentration and 15.25%more than the common ternary cycle.For a given NH₃ mass fraction,the COP of the new cycle increases gradually with the increase of the LiBr mass fraction,and the COP reaches the highest when the LiBr mass fraction is about 30%,then the COP decreases with LiBr mass fraction increasing.Finally,Aspen Plus process Simulator is used to simulate and analyze the new cycle performance under different working conditions.The results show that when the generating temperature ranges in 60℃¹20℃,the circulating gas is gradually increased,and the energy consumption of new cycle is significantly lower than the common cycle.And the COP of cycle decreases slightly after gradually increases.When evaporation temperature ranges in-15℃⁴℃,the cycle COP increases,and the maximum COP increase is 14.63%compared with common ternary cycle,at this time the evaporation temperature is 4℃.When the condensation temperature ranges in 34℃⁴8℃,the cycle COP decreases gradually compared with common ternary cycle,the maximum increase is 15.83%,at this time the condensation temperature is45℃.Analyzed the effects of different working conditions on cycle performance,which has guiding significance for designing new cycle based on membrane separator.