喷气增焓型单级MVR蒸发结晶系统性能分析

Performance analysis of single-effect MVR evaporative crystallization system using vapor injected compressor

针对工业废水蒸发结晶过程中含盐浓度增大、从而导致沸点升和增压比偏高等问题,提出了喷气增焓型单级机械式蒸汽再压缩(MVR)蒸发结晶系统。基于EES软件建立了喷气增焓型单级MVR蒸发结晶系统数值模型,并研究了闪蒸压力P_(flash)、物料入口浓度c_0、物料循环倍率CR、换热温差?T_(preh)和?T_(mhex)以及补气压比指数n和补气率β_v对系统热效率COP、单位闪蒸量的压缩机耗功w_(comp)、压缩机出口蒸汽过热度?t_(suph)和换热器UA值等参数的影响。结论如下:喷气增焓型MVR系统相比无喷气过程的单级MVR蒸发结晶系统具有更高的COP、更低的w_(comp)以及更小的?t_(suph);随CR增大,压缩机增压比降低了32.8%,COP提高了54.8%;随P_(flash)增大,COP呈先降后升趋势,在30~35kPa时存在最低值;换热系统中,主换热器温差?T_(mhex)对MVR系统性能影响更为显著,?T_(mhex)每增大1K,COP平均降低4.0%、w_(comp)平均升高4.9%、UA_(mhex)平均增加8.9%。

Considering the industrial waste is always characterized with high salinity in the evaporative crystallization process,a single-effect mechanical vapor recompression(MVR)system with vapor injected compressor was proposed to deal with the issues like high boiling temperature lift,high-pressure ratio and high compressor superheat.A mathematical model has been developed using the engineering equation solver(EES).The effects of the flashing pressure(Pflash),the feeding waste water salinity(c0),the preheater and main heat exchanger temperature differences(ΔTpreh andΔTmhex),the vapor injection pressure ratio index(n)and the waste water circulation ratio(CR)on the coefficient of performance(COP),compression work for unit flashed vapor(wcomp),compressor outlet superheat(Δtsuph)and heat exchanger design parameters(UAmhex and UApreh)were studied in detail.The results showed that the vapor injected MVR system obtains higher COP,lower wcomp and lessΔtsuph.With the increase of the CR,the pressure ratio decreased 32.8%and the COP increased 54.8%.There exists a lowest COP with the increase of Pflash,and it appears among 30-35kPa.Comparing toΔTpreh,the influences of theΔTmhex are more prominent,and the COP decreases by 4.0%,the wcomp and UAmhex increase by 4.9%and 8.9%,respectively,per unit raise inΔTmhex.