| In recent years,with the acceleration of industrialization,the pressure on ecological environment has become increasingly serious,among which the most typical examples are the sharp reduction in the quantity of available fresh water resources and the serious pollution of living water.As an important seawater desalination,pure water preparation and sewage treatment method,membrane distillation?MD?has made some achievement in theoretical and laboratory application research after decades of development.The technology application on large-scale industrialization has been hindered due to its shortcomings,involving low water production efficiency,poor anti-pollution resistance and low long-term operational stability.In order to improve tubular membrane distillation flux and optimize the anti-pollution ability of membrane modules,this thesis mainly carried out the following aspects of work and reached corresponding conclusions.1.Structural design on tubular membrane module:Firstly,theoretical analysis has been done on membrane module structural parameters,which will affect the mass transfer process in the membrane distillation system.Then two types of air gap layer?2 mm air gap/membrane contact?,three forms condensation tube with different materials?copper,stainless steel,PE?,three groups different ratio S?/S??1:1.77,1:1.46,1:1.24?,two modes inlet and export methods?intermediate,tangential?were designed to investigate the influence of module structural parameters on the membrane flux.Finally,the optimal solution for high flux membrane modules is determined as follows:stainless steel condenser,S?/S?=1:1.24,and tangential membrane contact type.The results indicate that under the same operating conditions,the water-producing flux of the new membrane module is 2.1 times higher than AGMD and the producing water efficiency is equivalent to DCMD.2.Comparative study on different types of membrane module in cycle concentration procession:New module?called membrane Contact Membrane Distillation M-AGMD?,AGMD and Direct Contact?DCMD?Membrane module were compared.1 mol·L-1 KCl was prepared as a simulated solution in this work.Then,three membrane modules were used to concentrate the same amount of liquid at the same membrane distillation system for comparing their producing water efficiency,operational stability and anti-pollution ability.The results show that the flux of produced water is DCMD>M-AGMD>AGMD.Besides,membrane fouling and wettability are DCMD>AGMD>M-AGMD in the concentration process.M-AGMD shows the smallest decline in membrane surface contact angle.On the whole,M-AGMD has the best comprehensive performance.3.Application study on actual waste acid treatment by membrane distillation:Firstly,the feasibility of concentrating waste acid was explored.Then the differences between dilute sulfuric acid and waste acid in concentration process were investigated.Furthermore,the research focused on the recovery of sulfuric acid,the removal of As,F,Cl,and the product in the concentration and crystallization process.Besides the performance of the membrane material and condenser tube also been discussed in this work.Complying with the basic principles of "reduction,harmlessness,and resource utilization",this study adopted three steps to treat waste acid.First is concentration.At this step,reusable water is produced from waste acid and the valuable resources?H2SO4,valuable metals,etc.?are enriched at the same time.in addition,this process reduced the volume of waste acid liquid?only 1/4 time of the initial volume after concentration,the water production rate is 75%?.Second is crystallization.The concentrated waste acid is cooled under low temperature for crystallizing out the heavy metal ions and other harmful impurity elements.The recovered quality of the sulfuric acid in the concentrated liquid also can be improved at this step.Third is filtration and separation.The crystalline product in the concentrate liquid is separated by filtration and finally recovered as a crystalline powder.The results reflects that H+ and SO42- in the waste acid are synchronously enriched in the membrane distillation concentration process.Meanwhile,the mass recovery rate of sulfuric acid reaches 88.06%.The concentration-crystallization process has excellent removal rate of As,while cooling crystallization process has rarely removal rate on Cl-.Finally,the roughness of the membrane hot side surface has decreased.However,the membrane material mechanical properties did not become worse.In addition some corrosion pits appeared in the stainless steel condenser. |
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