Heat Transfer Enhancement Study And Evaporator Design On The Concentration Process Of Molasses Alcohol Wastewater

Molasses alcohol waste liquid is a kind of organic wastewater with high viscosity,high soluble solid content and environmental hazard,which is generated in molasses bioethanol process.Its treatment technology limits the development of molasses alcohol industry.In the treatment process of molasses alcohol waste liquid,multi-effect evaporation incineration is an ideal technical solution,but there are problems such as low heat transfer rate and unsuitable structure of the evaporator for high viscosity waste liquid.In order to solve the above problems,this paper uses a threaded pipe as the evaporator to strengthen the heat exchange tube type,and improves the heat exchange part of the evaporator.A single-tube heat transfer test platform was built,and under the same experimental conditions,the heat transfer effect between the smooth pipe and the threaded pipe and the threaded pipe with different thread pitches were compared.The experimental results show that when the thread pitch is 35 mm,compared with the smooth tube,the total heat transfer coefficient is increased by 20%,which has better heat transfer enhancement effect.Moreover,as the pipe pitch is reduced,the heat transfer enhancement effect of the threaded pipe is gradually enhanced.According to the experimental results,the use of a threaded pipe with a thread pitch of 15 mm facilitates the heat transfer enhancement of the molasses alcohol waste liquid concentration process.In order to further analyze the heat transfer enhancement mechanism of the threaded pipe,this paper uses CFD software to simulate the flow and heat transfer process of molasses alcohol waste liquid in the threaded pipe.Through the simulation of the temperature distribution in the heat transfer tube and the velocity distribution of the fluid in the tube,it can be seen that the degree of turbulence is enhanced at the protrusion in the tube of the threaded tube,and the boundary layer flow of the waste liquid in the tube becomes thin,which is favorable for the wall surface.The heat is conducted to the inside of the fluid,which enhances the heat exchange between the fluid in the tube and the shell-side steam,and enhances the heat transfer effect.In this paper,based on the characteristics of high viscosity and high soluble solid content of molasses alcohol waste liquid,the existing evaporator was improved according to the working conditions of multi-effect evaporation and concentration treatment of existing molasses alcohol waste liquid.The evaporator adopts an externally heated forced circulation structure,the heat exchange element of the heating chamber adopts a threaded pipe,and the circulation pump selects a screw pump suitable for a high viscosity waste liquid.The use of a detachable high-efficiency gas-liquid separation device reduces the increase in COD of condensate due to entrainment of mist.The equipment material is made of S30408(06Cr19Ni10)material with good corrosion resistance.In this paper,the design and calculation of the evaporator are carried out,the structure and various size parameters are calculated,the assembly drawing of the evaporator is drawn,and the feasibility scheme of the evaporator design which can satisfy the treatment waste liquid of 8000kg/h is given.