沸点温升影响下机械蒸汽再压缩系统性能研究
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摘要
以低质量分数氯化镁溶液的蒸发浓缩为例,建立了以竖管降膜蒸发器和离心式压缩机为主要部件的单效机械蒸汽再压缩(MVR)系统数学模型。以对数平均温差来计算传热面积,以蒸发器内的蒸发压力、名义传热温差以及蒸发器出口物料的质量分数为变化参量,研究物料在蒸发器内蒸发时因质量分数增大导致物料沸点温升升高较大的情况下,变化参量对供热系数(COP)、年总费用这2个主要的系统经济、性能指标的影响规律。结果表明:在名义传热温差一定时,COP随蒸发压力的升高而降低,随物料出口质量分数的增加而降低;在蒸发压力一定时,COP随名义传热温差的增大而降低。名义传热温差在2—6℃时,年总费用随蒸发压力的升高而增大;名义传热温差超过6℃时,年总费用随蒸发压力的升高而减小。在蒸发压力一定时,年总费用随名义传热温差的升高而增大;在名义传热温差一定时,年总费用会随物料出口质量分数的增加而增大。
Taking the evaporation and concentration of MgCl2 at low mass fraction as an example,a mathematical model of single-effect mechanical vapor re-compression system with vertical tube falling film evaporator and centrifugal compressor as the main components was established. The heat transfer area was calculated by logarithmic average temperature difference. The evaporation pressure,nominal heat transfer temperature difference and mass fraction of the material of the evaporator outlet were regarded as parameters. The influences of the parameters on heating coefficient COP and annual total cost were studied,when the material boiling point increased with the increase of mass fraction in evaporating of the evaporator. The results show COP decreases with the increase of evaporation pressure and mass fraction of material at the outlet when the nominal heat transfer temperature difference is constant. COP decreases with the increase of the nominal heat transfer temperature difference when the evaporation pressure is constant. The annual total cost increases with the increase of evaporation pressure when the nominal heat transfer temperature difference is 2-6 ℃. While the total annual cost decreases as the evaporation pressure increases when the nominal heat transfer temperature difference exceeds 6 ℃.When the evaporating pressure is constant,the annual total cost increases with the increase of the nominal heat transfer temperature difference. And when the nominal heat transfer temperature difference is constant,the annual total cost increases with the increase of the mass fraction of the material at the outlet.
Taking the evaporation and concentration of MgCl2 at low mass fraction as an example,a mathematical model of single-effect mechanical vapor re-compression system with vertical tube falling film evaporator and centrifugal compressor as the main components was established. The heat transfer area was calculated by logarithmic average temperature difference. The evaporation pressure,nominal heat transfer temperature difference and mass fraction of the material of the evaporator outlet were regarded as parameters. The influences of the parameters on heating coefficient COP and annual total cost were studied,when the material boiling point increased with the increase of mass fraction in evaporating of the evaporator. The results show COP decreases with the increase of evaporation pressure and mass fraction of material at the outlet when the nominal heat transfer temperature difference is constant. COP decreases with the increase of the nominal heat transfer temperature difference when the evaporation pressure is constant. The annual total cost increases with the increase of evaporation pressure when the nominal heat transfer temperature difference is 2-6 ℃. While the total annual cost decreases as the evaporation pressure increases when the nominal heat transfer temperature difference exceeds 6 ℃.When the evaporating pressure is constant,the annual total cost increases with the increase of the nominal heat transfer temperature difference. And when the nominal heat transfer temperature difference is constant,the annual total cost increases with the increase of the mass fraction of the material at the outlet.
引文
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[4]梁林.处理高浓度含盐废水的机械蒸汽再压缩系统设计及性能研究[D].南京:南京航空航天大学,2013:19-21.
[5] HISHAM E. Design of single-effect mechanical vapor compression[J]. Desalination,2006,190(2006):1-15.
[6] RIVERA-ORTEGA P,PICON-NU'NEZ M,TORRES-REYESA E. Thermal integration of heat pumping system in distillation columns[J]. Applied Thermal Engineering,1999,19(8):819-829.
[7]鞠婉兰.用于丝光工艺碱回收的机械蒸汽再压缩蒸发系统热力性能研究[D].上海:东华大学,2015:1-87.
[8]张武,李新宏,惠明.高性能MVR水蒸气压缩机技术及应用[J].设备节能,2016(3):35-39.