| There are abundant waste heat resources in our country,and the Kalina cycle(KC)which uses ammonia-water as working medium is an efficient power system that as the alternate of the traditional steam Rankine cycle(SRC)to reclaim waste heat and provide electricity.The KC is of great significance for energy saving and emission reduction,cascade recovery of waste heat and development of distributed energy system,since it has the characteristics of adjustable working fluid concentration,diverse schematic structures,high waste heat recovery ratio,superior thermal performance and so on.At present,the research hot spots on the KC system are no longer limited to the power generation but extended to the power/refrigeration/heating cogeneration.Based on the combination of theoretical analysis and numerical simulation,indepth research on the KC systems and the cogeneration cycles based on KC are carried out in this dissertation,which are specified as the followings:According to the operating principles and characteristics of the dual and triple pressure KC systems,the mathematical models for the thermal processes of the systems were established,and the EES(Engineering Equation Solver)physical programming software was applied to calculate and analyze these thermal cycles.By analyzing the parameters such as working fluid concentration and pressure,two arrangement configurations of the separator in the dual pressure KC system were discussed.The investigation results indicate that the dual pressure KC is mainly suitable for the case where the temperature grade of heat source is relatively low,and the internal energy recuperation is more sufficient but the applicable range of heat source temperature or high pressure is relatively narrow in the cycle with separator located before the heat exchanger with heat source(KC-34R).When the inlet temperature of flue gas is 200?,the waste heat recovery ratio ?wh and the power recovery efficiency ?0 of the KC-34R are 9.14%and 32.9%respectively higher than those of the dual pressure cycle KC-34 with the separator located behind the heat exchanger with heat source.Therefore,the performance of the KC-34R is much better than the KC-34 under the same heat source condition.The triple pressure Kalina cycle(TP-KC)suitable for reclaiming power from medium and high temperature heat sources was investigated,and the main parameters affecting cycle performance were analyzed and optimized.The analysis results indicate that the optimization of the parameters such as working fluid concentration can make the TP-KC more excellent thermal performance under the premise of good matching with heat source.With the flue gas inlet temperature of 350?,the power recovery efficiency ?0 of TP-KC is 12.2%higher than that of SRC.In addition,by analyzing the TP-KC under the condition that the flue gas inlet temperature range is 250?400?,the waste heat recovery ratio ?wh is about 85?88%,which means that the exhaust waste heat source still has value to be further reclaimed.Therefore,an improvement ideal was proposed to further explore the potentiality of the TP-KC with cogeneration of power/refrigeration.By summarizing many problems that need to be solved in the existing power/refrigeration cogeneration cycles,a parallel power/refrigeration Kalina cycle(PPR-KC)based on the TP-KC was proposed and analyzed.The work solution at the outlet of the mid-pressure absorber in the PPR-KC is split to two streams,and one of which is introduced to the absorption refrigeration sub-cycle with rectification process.The vapor refrigerant is eventually led to the low-pressure absorber,thus the refrigeration evaporation pressure corresponds to the turbine back pressure,and the provided refrigeration temperature is low,which can be used for many refrigeration applications such as ice energy storage.The refrigeration sub-cycle can further utilize the exhaust heat source already reclaimed by the boiler in the power main cycle,thus the waste heat source can be fully recovered by the PPR-KC.Besides,the parallel structure of PPR-KC can realize the independent adjustment of the power or refrigeration capacity.The analysis results showed that the PPR-KC can obtain different amounts of power and refrigeration capacity by adjusting the power split fraction i.e.the mass flow fraction of working fluid in the boiler.When the other conditions are fixed,the minimum value of the power split fraction corresponds to the optimal performance of the cycle with the heat source fully reclaimed and producing the maximum refrigeration capacity(converted to electricity by the average COP of compression refrigeration cycle under the same refrigeration temperature).By comparing the optimized PPR-KC and TP-KC,it is found that the refrigeration sub-cycle of PPR-KC can increase the comprehensive power recovery efficiency of TP-KC by 19.8%,and the exhaust flue gas can be further utilized with its exhaust temperature declined from 141.8? to 93.5? and additional refrigeration capacity provided.To meet the chilling demand for air-conditioning in the summer is a vital task for the distributed energy supply system,thus the power/refrigeration cogeneration system with adjustable refrigeration temperature zone was further modified.The vapor refrigerant in the modified cycle can be switched into two destinations.When it connected to the low-pressure absorber,the cycle is exactly the PPR-KC,providing refrigeration energy in freezing temperature zone;when it connected to the mid-pressure absorber,the refrigeration capacity in air conditioning temperature zone can be provide,and it is then called PPRA-KC,in which"A" represents air-conditioning.Based on the first and second laws of thermodynamics,the mathematical model of PPRA-KC is established and analyzed.In the calculation and analysis,the refrigeration load was taken as the prior consideration in heat source utilization,that is,the minimum pinch temperature between working fluid and the heat source in the sub-cycle is kept as the limited value of 20 K.When the heat source(flue gas)inlet temperature is 450?,the optimal dew point temperature at boiler pressure of each work concentrations xw in the cycle is the highest value it can reach,and the minimum pinch temperature difference in the boiler is the lowest limit value of 20 K.For a given cooling water condition,the refrigeration temperature is only determined by the work concentration xw,with the constrains of the lowest limit of the heat source exhaust temperature th5 of 90? and the turbine exhaust vapor dryness limit of 0.88.The variable range of xw is 0.4542-0.5374 with corresponding refrigeration temperature range of 0.5-12?.When PPR-KC and PPRA-KC are both in the optimal state,the refrigeration capacities of these two cycles are very close,even though the refrigeration temperatures are different that the average evaporation temperatures of the PPR-KC and the PPRA-KC are respectively about-20? and 7?.Although the net power of the PPR-KC is lower than that of the PPRA-KC,its exergy of the refrigeration capacity is greater than that of the PPRA-KC,and the exergy efficiencies of these two cycles are almost the same,respectively 56.22%and 56.12%.Two refrigeration temperature adjusting schemes of the power/refrigeration cogeneration cycle were proposed,and their thermal performances were compared and analyzed.A pressure-regulating absorber is added to the original cycle and all the refrigerant is introduced into the new absorber been absorbed by either the dilute solution(scheme a)or part of the basic solution(scheme b),and then variable refrigeration pressure(and refrigeration temperature it determines)between the low and mid pressures can be obtained.The analysis results indicate that the refrigeration temperature of the two schemes can be independently and flexibly adjusted without affecting the adjustment or production of power and refrigeration energies.With the same refrigeration temperature,the performance of scheme b is relatively better;while for scheme a,there is a smaller effect on the power consumption of the working fluid pump when the refrigeration temperature is adjusted in a larger range.To meet the heating demand in winter,this dissertation introduced the separate heat pipe heat exchangers into the parallel power/refrigeration cogeneration cycle.The separate heat pipe heat exchangers are used to replace the generator in the refrigeration sub-cycle,with one heat exchanger(evaporation section)for flue gas and one for ammonia-water solution(condensation section 1)and one for heating water(condensation section 2).Thus the cogeneration of power and refrigeration or heating supply by season could be achieved.During heating season in winter,the entire refrigeration sub-cycle does not work,and the flue gas from the boiler is utilized to heat the heating water in the heat pipe heat exchangers of evaporation section and condensation section 2,and the regulation of heating capacity can be achieved by bypassing some flue gas with a valve.When the flue gas is used to the lowest discharge temperature and the waste heat recovery ratio ?wh reaches 100%,the flow rate of heating water and heating load reach their maximum values,and the cycle performance is the optimal.Additionally,the ammonia water Kalina-Rankine combined cycle system is also applicable with the power/refrigeration cogeneration cycle to provide users with refrigeration and heating in different seasons beside the power.In the non-heating season,it runs in the Kalina cogeneration cycle mode to provide users with either pure power or the power/refrigeration cogeneration outputs.In winter,it operates in the ammonia-water Rankine cycle mode,and the heating purpose is achieved by recovering the heat released by the ammonia-water with large temperature slope in the condenser. |
PDF Full Text Request