| Evaporation and concentration is a common operation technology in chemical,desalination,wastewater treatment and food processing fields.Especially in the wastewater treatment field,it recycles waste of useful resources effectively and realizes the waste water recycling use.The conventional evaporation such as single effect evaporation and multi-effect evaporation system are complicated and need high energy consumption and running cost,which affect the use and spread seriously.This paper introduces the mechanical vapor recompression(MVR)evaporation technology,which is a new high efficiency and energy saving technology and with wide application prospect in the wastewater treatment field.Firstly,this paper puts forward the MVR evaporation technology in Na2S04 including high salinity wastewater treatment process.It evaporates the high salinity wastewater afer pretreatment,then recycles the inorganic salt resources and and distilled water to achieve national standards at the same time.A vapor compressor is introduced in this system to recycle the secondary steam for recompression,which uses the latent heat of secondary steam and saves a large amount of water for cooling the secondary steam.Secondly,for the sake of the thorough analysis and research of MVR evaporation system's performance,according to the MVR wastewater treatment process,established the physicaland mathematical models of the system,and carried on the theoretical analysis and research.In view of the current design of MVR evaporation system,related research work and standard specifications are lacked,so the parameter influencing factors for the MVR system are analysed.For the 20kg/h MVRevaporation system for Na2S04 wastewater,higher feed temperature difference and heat transfer temperature difference will significantly reduce the heat exchange area of the system,but corresponding to a larger energy consumption of the compressor.Therefore,from the perspective of energy saving and economy,the feed temperature difference(?Tf)should be chosen in 2—4? and difference of heat transfer(?T)is in the range of 3-10?.Evaporation temperature(Te)has little effect on the heat exchange area and energy consumption of the compressor,which mainly affected by the compressor suction volume,so the range of evaporating temperature is chosen at 70—90?.Based on the analysis of MVR evaporation system's performance,"The Evaporation and Concentration Experiment Platform of Donghua University" has been constructed.This design evaporation of the experiment system is 20 kg/h,which contains conventional single effect evaporation(SEE)and MVR evaporation these two systems.Then,experiments about the system's concentration control,steam compressor's operation,the operations of MVR and SEE systems are carried out.By the experimental results,in the operating condition of Te=80.1?,?T=5.2,Xf=2%and Xb=10%,the evaporating rate of MVR system can reach 18.6kg/h and the compressor running energy consumption is 1kW,converting to the energy consumption of unit evaporation is 53.7kWh/m.As the increases of ?T,the evaporating rate and energy consumption of the compressor increase.In addition,compared with the conventional SEE system,whose energy consumption of unit evaporation reaches 652.7 kWh/m3 and needs 300kg/h water for cooling the the secondary vapor,the energy consumption of MVR evaporation system is only 8.2%,the energy saving and water saving effects are remarkable.Finally,in order to improve the system's theory analysis and optimization of MVR evaporation experiment system,analysis for the experiment system is conducted.In the operating condition of Xj=2%and Xb= 10%,by the calculating results,the evaporating rates and energy consumption of the compressor increase as the ?T increases.On the other hand,the increase of Te can make the system increases in evaporating rateand reduce the power consumption at the same time.Therefore,under the condition of satisfying system's evaporating rate,selecting a smaller value of ?T and larger Te is more economic. |
PDF Full Text Request