Numerical Simulation Of Flow And Heat Transfer In Air Film Reactor For Supercritical Water Oxidation And System Economic Analysis

With the rapid development of industry and agriculture,a large number of industrial waste liquid with organics are produced in petrochemical industry,printing and dyeing industry,synthetic fiber industry and other fields.These high-concentration,hard-degrade organic waste liquid has a great harm on human life and the natural environment.The technology of supercritical water oxidation,as one of the most potential organic waste liquid treatment methods,combines the unique advantages of fast reaction rate,complete degradation,no secondary pollution,and huge potential for heat recovery.However the corrosion and salt deposition in the reaction equipment seriously hindered the industrial application of the technology.The proposal of the water film reactor solves these two problems very well,but the water film reactor needs to consume a large amount of deionized water as evaporation water,which increases the operating cost of the system.In some areas where freshwater resources are scarce,this problem will be even more serious.In addition,water film reactor needs to consume a large amount of pure oxygen as the oxidant for the reaction,which will increase the cost of the material greatly.A supercritical water oxidation reactor using air as the protecting film is introduced in this paper.This reactor uses air to replace the traditional water film,which not only provides oxidant for the reaction,but also reduces the operating cost and protects the porous wall.Based on this,this paper mainly developed the following research:Firstly,based on the energy balance,the influences of the operating parameters on the fluid temperature as well as the outlet temperature for the reactor are analyzed during the initializing stage and the reacting stage.The results showed that at the initializing stage,the air flow rate gives the most significant influence on the fluid temperature,but the feed concentration almost does not affect on the fluid temperature.At reacting stage,the fluid temperature increases with the increase of the feed concentration,and the fluid temperature decreases with increasing the air flow rate.The outlet temperature increases along with the increase of the feed concentration but decreases along with the increase in air flow.Secondly,the appropriate parameters were selected to determine the reactor volume.The 2D reactor is simulated,and obtain the flow and heat transfer in reactor.Then the nozzle size（nozzle length,nozzle internal diameter）and reactor height-to-diameter ratio were studied,and found that:as the nozzle length increases,the high temperature region of the reactor moves down,the maximum temperature of the porous inner wall decreases,but the content of CH₃OH,CO basically unchanged,and the trend of change moves right.As the nozzle diameter increases,the reactor temperature gradually reduces and the content of CH₃OH,CO increases.As the ratio of height to diameter of the reactor increases,the temperature on the central axis of the reactor and the porous inner wall increase,but at the middle and lower part and the outlet of the reactor,the content of organics gradually decreases.That is,the higher the ratio of height to diameter of the reactor,the better the organic removal effect of the reactor.Then,a 3D model of the reactor was established,and the effect of air injection method（each branch has one or two air injection inlet）on the uniformity of the air film in the reactor was investigated.It was found that the number of air inlets in each branch of the reactor has a great influence on the stability of the reaction fluid and the temperature of the porous inner wall,etc.In theory,the more the number of the air inlet,the air distribution will be more uniform and make the reaction fluid more stable,meanwhile the better the protection of the reactor,but it will increase the complexity of the structure and the manufacturing cost.Finally,an economic analysis was conducted on the supercritical water oxidation air film reaction system with a waste liquid treatment capacity of 480t/a.The equipment investment cost and equipment operation cost（including power consumption expenses,depreciation expense,workers’wages,material costs and maintenance fee）and the hot water generated in the system were calculated respectively.And the cost for organic waste liquid treatment is 650￥/t.In addition,calculation found that the increase of the waste liquid concentration is beneficial to the reduction of waste liquid treatment cost,but the increase of the total air flow will make the waste liquid treatment costs increase greatly.