Study Of Heat And Moisture Transfer Characteristics Of Negative Pressure Membrane Distillation Based On Porous Ceramic Membrane

The depletion of freshwater sources,coupled with the lack of adequate wastewater treatment and mature desalination technologies,exacerbates the challenge of meeting global water needs for drinking water,agriculture and industry.The efficient treatment and utilization of desulfurization wastewater can not only reduce environmental pollution,but also reduce water consumption,which is of great significance to the clean and sustainable development of thermal power generation.The traditional desulfurization wastewater treatment method is mainly chemical precipitation method,but because it can not meet the dechlorination and other often do not meet the emission standards,so the desulfurization wastewater"zero"discharge technology is generated,mainly including pretreatment,concentration reduction and crystallization solidification three,membrane distillation because of its good recovery water quality,high efficiency is a commonly used fresh water recovery process.Ceramic membrane,one of the process membranes,has excellent mechanical properties,better chemical and heat resistance,higher thermal conductivity,lower fouling,longer service life and lower maintenance costs,and has become one of the important materials for membrane research.At present,there have been many studies on the technology of membrane distillation using porous ceramic membranes,but due to the hydrophilic characteristics of the membrane itself,hydrophobic modification is required before use,which increases the process and cost,and the hydrophobicity gradually weakens with the use process.Therefore,this paper proposes a negative pressure membrane distillation method for desulfurization wastewater based on porous ceramic membrane,which directly adopts hydrophilic porous ceramic membrane to form negative pressure of the solution in the membrane through the suction action of the pump to prevent the solution from seeping out of the membrane.In order to explore the heat and mass transfer mechanism of negative pressure membrane distillation,the transfer characteristics of affinity and hydrophobic porous ceramic membranes under different working conditions were compared experimentally.In order to obtain the better experimental parameters of the hydrophilic and hydrophobic ceramic membrane,the reverse flow model of air and wastewater was established by using the lumped parameter model,and the experimental verification was carried out,which effectively reduced the energy consumption.The experimental results show that the negative pressure value in the membrane is less than the capillary force of the solution in the membrane pores,and the solution transport and water vapor transport in the membrane pores of the affinity and hydrophobic porous ceramic membrane are respectively.When the air flow rate was 22 L·min^-1,and the wastewater temperature and flow rate were 50°C and 11L·h^-1,respectively,the permeation flux of hydrophilic membrane was between 1.9～3.9kg·m^-2·h^-1,while the permeation flux of hydrophobic membrane was only 0.13～0.25 kg·m^-2·h^-1.The thermal efficiency of hydrophilic and hydrophobic porous ceramic membranes was about 92%and 55%,respectively,indicating that the permeation flux and thermal efficiency of hydrophilic membranes were significantly higher than those of hydrophobic membranes.With the increase of air flow from 12 L·min^-1to 22L·min^-1,the permeation flux of hydrophilic membranes increased from 1.5 kg·m^-2·h^-1 to2.3 kg·m^-2·h^-1.When the wastewater inlet temperature increased from 50°C to 70°C,the permeation flux of hydrophilic membrane increased from 1.9 kg·m^-2·h^-1 to 2.9 kg·m^-2·h^-1,indicating that with the increase of air flow or wastewater temperature,the membrane permeable flux increased.The numerical simulation results show that the numerical simulation of affinity and hydrophobicity shows that the simulation results are in good agreement with the experimental results,and the two models are successfully verified,and the deviations are within the range of 1～10%.The heat and mass transfer process of the two models was compared and illustrated,and the thermal efficiency simulation results of the hydrophilic film were above 98%,indicating that its transport performance could make full use of its high thermal conductivity to improve the transport efficiency.The mass transfer performance under higher operating parameters of the experiment was explored,and the better experimental parameters were obtained,the wastewater flow rate was 0.25 m·s^-1,the air flow rate was 0.8 m·s^-1,and the wastewater temperature should improve the membrane transfer performance at 90°C.