Simulation Analysis And Upgrading Of Multiple-effect Evaporation System For Molasses Alcohol Wastewater

Multi-effect evaporation and incineration treatment technology is one of the ideal technical solutions for the treatment of molasses alcohol wastewater in China and abroad.However,this process consumes a great deal of energy.Saving energy,reducing consumption,and increasing energy utilization are of great significance for the survival and development of this technology.In this study,the multi-effect evaporation process of molasses alcohol wastewater is taken as the research object.The Aspen Plus software is used to establish process model and simulate calculation.Taking the evaporation concentration device’s capacity of 700t/d molasses alcohol wastewater as reference for an alcohol plant in Guangdong Province.The verification results show that the model can accurately reproduce the actual production process and the error is within the acceptable range.According to the first law and the second law of thermodynamics,a four-effect evaporation process is used as a system to establish thermal analysis and exergy analysis models.By calculation,the main heat flow and exergy flow values are obtained.Based on the results of thermal analysis and exergy analysis,we can find out the weakness in the energy use of the evaporation system,and put forward a feasible energy-saving reconstruction program to provide technical support for improving the energy utilization rate of the process.Different energy utilization schemes are designed based on the transformation of the process flow.Combined with the thermal economic analysis method,the energy consumption level and economic efficiency of the system under different evaporation schemes are comprehensively evaluated from the indexes of thermal efficiency,exergy efficiency,raw steam consumption,and annual total cost.The results of the study indicate that the evaporation scheme 6 proposed in this study has the optimum efficiency in improving the economic benefits of the system and reducing energy consumption.Compared with the existing process of the plant,the evaporation scheme 6 increase the thermal efficiency by 9.98 percentage points and the exergy efficiency by 7.12 percentage points.The amount of raw steam can be reduced by 4,791 tons per year,and the energy utilization rate is significantly improved.In addition,the annual total cost of the evaporation scheme can be reduced by 645,000 RMB.A retrofit scheme is proposed for the evaporation equipment,spiral grooved tube is used as heat exchange element instead of the original smooth tube.The evaporator heat transfer coefficient is greatly increased,the required heat transfer temperature difference is reduced,and the process loss due to irreversibility is reduced.Under the premise of maintaining the original steam pressure and the final vacuum degree unchanged,the multi-effect evaporation system can be increased from the original four-effect to the six-effect.In this way,steam consumption will be reduced by approximately 35.1% compared to current usage,and the thermal efficiency is increased by 11.26 percentage points,the exergy efficiency is increased by 8.31 percentage points.The energy saving effect is very obvious.For the evaporation process of molasses alcohol wastewater,the efficiency of the vapor-liquid separation device of the evaporator is low,and the mist entrainment phenomenon are studied.The improvement scheme is proposed.