| Chemical industry production process（such as printing and dyeing,papermaking,etc.）produce waste liquid which may contain low concentration of Na OH solution.Discharging this type of waste solution directly into the external environment will cause water and land pollution and raw materials waste,obeyed the concept of energy conservation and environmental protection.Therefore,it is necessary to condense and regenerate industrial waste solution efficiently to obtain high concentration of Na OH solution and utilize it.Heat pump is widely used in industrial production because of its high coefficient of performance.It will achieve better energy-saving effect when the heat pump is matched in evaporation system.Domestic and overseas Scholars have done some analysis and research on the Na OH solution evaporation system based on the heat pump cycle,but they have not studied the performance change of the Na OH solution evaporation heat pump system at low temperature from the perspective of the change of Na OH solution evaporation pressure.In this paper,theoretical analysis and simulation research are carried out on two kinds of Na OH solution evaporative heat pump systems:single-effect low-temperature evaporative heat pump system and double-effect low-temperature evaporative heat pump system.The single-effect low-temperature evaporative heat pump system combines the heat pump cycle with the Na OH solution evaporation process,and heats the Na OH solution with condensing heat of refrigerant.At the same time,the secondary steam is generated by the cooling capacity from the refrigerant evaporates,and the heat energy is recovered consequently.However,in the actual operation,we found that the compressor pressure ratio matched with the single-effect system heat pump cycle was too low.If the common refrigeration compressor were matched with the single-effect system heat pump cycle,the compressor would be in the operating state with a low compression ratio and could not perform its maximum benefits.The secondary steam generated in the Na OH solution evaporation process was directly fed into the refrigerant evaporator for condensation.The thermal energy of the secondary steam was not fully utilized,and the thermal energy of system could be further recovered during the Na OH solution process.The multi-effect lye evaporation technology raises the temperature of the secondary steam generated during the previous effect of lye evaporation and condenses it to evaporate the next effect of Na OH solution.If the evaporation technique is applied to one effect of low temperature multiple effect caustic Na OH solution evaporation heat pump system,it not only condensing heat recycling,and because of secondary steam condensing temperatures make heat pump circulation compressor exhaust pressure,thus increasing the compressor pressure ratio,make existing compressors for air conditioning system can match the Na OH solution evaporation heat pump cycle,but also improves the heat recycling Na OH solution evaporation system utilization.Based on the single-effect system,the secondary steam generated in the evaporation process of the first-effect Na OH solution is used as the heat source in the evaporation process of the second effect lye solution in the the double-effect system,in order to improve the Specific Moisture Extraction Rate（SMER）and compressor pressure ratio of heat pump cycle of the system.The initial conditions of dilute Na OH solution for the double-effect evaporation system established in this paper are:mass concentration of dilute Na OH x=5%,mass flow F=2t/h,concentration target:concentrated Na OH solution with mass concentration x=25%.On the basis of the physical model of single-effect and double-effect system flow and lye evaporation,the mathematical model of single-effect and double-effect system was established through the thermodynamic calculation of the system,which laied a foundation for the simulation calculation.Through the study,under the same Na OH solution treatment condition,the double effect low temperature Na OH solution evaporation heat pump system compared with the single effect low temperature Na OH solution evaporation heat pump system,the SMER is 10.98kg/h·k W,higher than the latter SMER（7.14kg/k W·h）,at the same time,the former of the heat pump cycle compressor pressure ratio 2.31,higher than the latter in the heat pump cycle compressor pressure ratio（1.75）,so the double low temperature Na OH solution evaporation heat pump system is superior to the single effect of low temperature alkali liquor evaporation heat pump system.In addition,based on the Na OH solution evaporation pressure p1,p2as decision variables,it is concluded that when the first effect evaporation pressure p1is 4.7 k Pa and the second effective evaporation pressure p2is 3.3 k Pa,the double effect low temperature Na OH solution evaporation heat pump SMER obtain maximum（11.47kg/k W·h）,by constructing the SMER optimization as the objective function of the system.At the same time,according to the characteristics of the lye evaporation process and the simulation results of the double-effect system,a control scheme of the double-effect system is designed to ensure the safety and efficiency of the double-effect system in the actual operation. |
