Analysis of heat and mass transfer in vacuum membrane distillation for water desalination using computational fluid dynamics (CFD)

Experimental mass transfer comparison between vacuum and direct contact membrane distillation for the concentration of carbonate solutions

The rising oil prices, as well as the desire to reduce the environmental impact of fossil fuels, increases the interest in fuels from renewable raw materials. Bioethanol production via starch fermentation is state of the art. Right now researchers focus on second generation biofuels from lignocellulose sources for example like wood and straw. Still investigations have to be done concerning fermentation yield and energy efficiency. Due to low product concentration in the fermentation broth latter downstream processing is quiet energy consuming. Many separation processes like Gas stripping, Liquid-Liquid Extraction, pervaporation and membrane distillation are investigated for an in-situ separation during continuous ethanol fermentation. The aim of this work was to compare two membrane distillation configurations for ethanol separation from aqueous solutions. Two different process variations like vacuum membrane distillation (VMD) and sweepgas membrane distillation (SGMD) were examined. The influencing factors on the separation of the process such as feed temperature, feed concentration, permeate pressure at VMD and sweepgas flow at SGMD were investigated. The gained results were compared in order to find the best application and process conditions. The initial feed concentration varied between 0.5 w% and 5 w% ethanol in the mixture and feed temperature was held at 20, 35 and 50 °C. During the VMD configuration the permeate pressure was kept at 25 and 50 mbar. Using the SGMD set up the sweepgas volume flow was varied between 360, 498, 900, 1,302 and 1,500 L/h. Membrane parameters like transmembrane fluxes and selectivity were calculated and discussed. The results of the VMD configuration showed that transmembrane ethanol flux increased with rising feed temperature and lower vacuum pressure. A linear correlation between feed temperature and transmembrane ethanol flux was found. In comparison VMD showed much higher transmembrane fluxes than SGMD. This result corresponds with the theories, in which the driving force during VMD is much higher due to a larger partial pressure difference between feed and permeate side. Comparison of selectivity results showed that VMD has better separation potential than SGMD. At a feed temperature of 50 °C selectivity was the same in both configurations. Feed concentration has a negligible influence on the selectivity in the investigated value range. The result of this work showed that both membrane distillation configurations have the possibility to separate ethanol from aqueous solutions. VMD has a bigger separation potential due the higher driving force, but the applied vacuum makes permeate condensation more difficult. SGMD with selectivities of around 4 and low transmembrane fluxes shows advantages due to easier process configuration and lower energy consumption.

A comparison of vacuum and direct contact membrane distillation for phosphorus and ammonia recovery from wastewater

BackgroundIn this study, membrane absorption and vacuum membrane distillation were integrated to recover ammonia and water, respectively, from saline ammonia‐containing wastewater discharged by metallurgical plants.ResultsAmmonia was removed by membrane absorption with a parallel hollow fiber membrane (HFM) module to decrease the ammonia content to below 5 mg L−1. Then the wastewater was concentrated by vacuum membrane distillation with a cross‐flow HFM module to maximize fresh water recovery, while maintaining higher permeate flux levels. The Taguchi method was used for experiment designs and contributions of operating parameters were determined over the specified parameter ranges through variance analysis. Recovery of ammonia and fresh water reached 99.8% and 80% within 250 min and 160 min, respectively. Membrane fouling in the membrane distillation process could be mitigated at lower concentrate rate in semi‐batch running mode, while permeate flux was maintained at high levels for a longer time. Permeate flux was greatly restored through a cleaning technique consisting of alkaline cleaning, acid picking, EDTA washing and drying. Permeate flux loss due to irreversible membrane fouling was 0.7%.ConclusionThe experimental results demonstrate the potential for resource utilization of saline ammonia‐containing wastewater by combining membrane absorption and vacuum membrane distillation. © 2013 Society of Chemical Industry

Optimization of hollow fiber membrane module for vacuum membrane distillation (VMD) via experimental study

Three-dimensional numerical simulation of aqueous NaCl solution in vacuum membrane distillation process

Gas flow enhanced mass transfer in vacuum membrane distillation

Modeling and analysis of vacuum membrane distillation for the recovery of volatile aroma compounds from black currant juice

Removal of strontium ions from simulated radioactive wastewater by vacuum membrane distillation

Pilot-scale vacuum membrane distillation for decontamination of simulated radioactive wastewater: System design and performance evaluation

CFD simulation of osmotic membrane distillation using hollow fiber membrane contactor: Operating conditions and concentration polarization effects

Effective separation of methylene blue dye from aqueous solutions by integration of micellar enhanced ultrafiltration with vacuum membrane distillation

Numerical modeling and economic evaluation of two multi-effect vacuum membrane distillation (ME-VMD) processes

Superhydrophobic polypropylene membrane with fabricated antifouling interface for vacuum membrane distillation treating high concentration sodium/magnesium saline water

In order to solve the problem of poor regeneration performance of the solar solution dehumidification air conditioning regeneration system under high temperature and high humidity weather conditions. In this paper, a novel vacuum membrane distillation (VMD) solution regeneration method was proposed for a solution desiccant air conditioning system, and a theoretical study of this novel regenerator is performed. Through the analysis of heat and mass transfer, the mathematical model of VMD regeneration is established, and the mathematical model is verified by experiments. The results indicated that VMD regenerator not only could increase the regenerate rate, but also could exhibit higher energy utilization efficiency. At the same concentration, the VMD regenerator has a higher regeneration performance, and the regeneration rate is 1.6-2.4 times that of the internal heat type regenerator,and the 4.5-6 times that of the adiabatic regenerator.