Recover Water Flux Research Articles

Efficient and economic water and heat recovery from flue gas by novel hydrophilic polymeric membrane condenser

The membrane technology for water and heat recovery from flue gas possesses the advantages of a simple structure and high water quality. In this study, we propose a novel hydrophilic polymeric membrane condenser (HPMC) to efficiently recover water and heat from flue gas. Compared to current hydrophilic ceramic membrane condenser (HCMC), HPMC offers the benefits of cost-effectiveness and high packing density. An experimental investigation is conducted to explore the fluid flow characteristics as well as the water and heat recovery performance of HPMC. The maximum recovered water flux reaches 6.7 kg/(m2·h), while the maximum recovered heat flux amounts to 18.6 MJ/(m2·h). Enhancing gas/water flow rates or increasing heat transfer temperature difference can significantly improve both recovered water and heat fluxes. Notably, it is found that thermal resistance primarily stems from the polymeric membrane, emphasizing the importance of enhancing the membrane's thermal conductivity to improve HPMC performance. The overall heat transfer coefficient can be enhanced by increasing the gas/water flow rate, while the influence of gas/water temperature on the overall heat transfer coefficient is relatively insignificant. Furthermore, by fitting experimental data, a correlation formula for friction factor is obtained, which greatly enhances accuracy in pressure drop calculations under practical operating conditions. Based on the technical and economic analysis, the payback period for HPMC is merely 0.3 years, significantly shorter than that for HCMC, thereby indicating a substantial potential for commercial application of HPMC. This study demonstrates that the HPMC is an excellent candidate for recovering water and heat from flue gas, and the fundamental data provides valuable foundational insights for future enhancement of HPMC.

Efficient purification of high-salt rural groundwater in the areas along the Yellow River in Henan Province, China, by hollow fiber membrane distillation process

The vast rural drinking water sources along the Yellow River basin in Henan Province mainly come from the local high-salinity groundwater, which cannot be directly drunk. Zeolitic imidazolate framework-71/polyvinylidene fluoride hollow fiber composite membrane was applied to treat rural groundwater through membrane distillation technology. The variations of water quality parameters from 12 different rural regions after membrane distillation treatment were well analyzed and compared. Membrane separation performance for water samples from different regions during the membrane distillation process was investigated, including water flux and salt rejection. During a continuous 24-h membrane distillation process for the treatment of these water samples, hollow fiber membrane exhibits high solute retention rates (>99%) for salt ions, suspended solids and total dissolved solids, which are within the limits of national standards (GB 5749-2006), meanwhile membrane permeation water flux can remain stable. After the acid-cleaning for 180 min, all hollow fiber membranes can recover water flux well with a flux recovery rate above 98%. Even if the concentration ratio continued to increase, the water production rate of membrane distillation was basically maintained between 50% and 60%, which was obviously higher than the 30% of the reverse osmosis process. The economic analysis confirmed that the water production cost varied between US$0.45 and US$0.29/m3. With the extension of membrane service life, the specific membrane cost decreased rapidly in the first 6 years and then leveled off. The proposed vacuum membrane distillation process proved to be a promising water purification method for treating rural high-salinity groundwater.

Acid mine drainage treatment by fertilizer drawn forward osmosis for irrigation

This work utilized fertilizer driven forward osmosis (FDFO) to extract fresh water from acid mine drainage (AMD) wastewater for irrigation, and investigated the effects of draw solutes on membrane fouling behaviours. The carbon nanotubes (CNTs) and polydopamine (PDA) were coated on the thin film nanofibrous composite (TFNC) membrane #FO-0 as anti-fouling modification. When 1 M NH4H2PO4 (MAP) and 500 mg/L copper AMD wastewater (pH=3.0) used as draw and feed solutions, #FO-0 and PDA-coated TFNC membrane (#FO-PDA) exhibited rapid declines of water fluxes due to the dense fouling layer. In contrast, the CNT-coated membrane #FO-CNT exhibited the lowest flux decline of 26.0% attributed to better hydrophilicity, the lowest roughness and neutral surface charge. All the TFNC membranes exhibited insignificant membrane fouling when (NH4)2SO4 (SOA) was used as draw solute. Additionally, the osmotic backwashing could effectively recover water flux. The discharged draw solution promoted plant growth without posed potential health threat.

Enhancing water recovery performance of transport membrane condenser by different coolants

Transport membrane condenser (TMC) has been proven an effective device for reclaiming water in flue gas. Ameliorations in device parameters and structure, operation conditions, and membrane properties have been trialed to augment water recovery performance. But research on improving the performance by adopting different coolants is still absent. In this paper, water in simulated gas was captured by a combination of traditional TMC and liquid desiccant. Three types of ceramic membranes with different pore sizes were adopted. The water and heat recovery performances with pure water or LiCl solution as cooling media were compared. The experimental results show that by adopting LiCl solution as coolant, water recovery rates were increased under different experimental conditions, confirming the potency of liquid desiccant for enhancing water recovery performance of TMC. The recovered water flux increased by 26.7% while water recovery rate increased by 17.5 percent points with LiCl solution in high concentration. On the contrary, heat flux recovered by LiCl solution is lower than that recovered by water. Heat transfer driving force and resistances are analyzed to explain the variation in heat flux. The analysis can be a guidance for coolant selection.

Conjugated microporous polymer Janus membrane for dye rejection from water

Forward osmosis (FO) is a process that uses the osmotic pressure of a high-concentration draw solution to separate solutes, e.g., ions and molecules, from solvents. We prepared a conjugated microporous polymer (CMP) Janus membrane with very thin hydrophilic and hydrophobic surfaces at both sides, respectively, for FO measurement, in which the asymmetric membrane architecture results in water diode phenomenon, namely, the transport of water in one direction is accelerated while the salt diffusion in the reverse direction is depressed. The asymmetric transport effect of the TTB-CMP Janus membrane on water and salt was thoroughly investigated by using various salt solutions with different hydrated radius as draw solution, e.g., NaCl, KCl, MgCl2, K3[Fe(CN)6], etc. Thanks to the asymmetric transport of water and salts, the Janus membrane shows a high recovered water flux (Jw) of 10.6 L m-2 h-1, with reverse salt flux (Js) as low as 1.39 g m-2 h-1 when 0.1 M NaCl is used as the draw solution. When further used for recovering water from dye solutions, the recovered water flux maintains up to 9.4 L m2 h-1, with molecular weight cut-off (MWCO) of 680 g mol-1, exhibiting obvious molecular sieving effect originated from the pore size of CMP. This study provides fundamental insight and guidance into the potential application of porous Janus membrane for removing dyes from water.

Influence of dextrin content and sintering temperature on the properties of coal fly ash-based tubular ceramic membrane for flue gas moisture recovery

In this paper, in order to reduce the preparation cost of high-performance ceramic membrane, coal fly ash-based tubular ceramic membrane for flue gas moisture recovery was prepared, and its properties were optimized from two aspects: pore-forming agent (dextrin) content and sintering temperature. The results show that the ceramic membrane with dextrin content of 3 wt.% and sintering temperature of 1150 ℃ has the best performance. Through characterization, the ceramic membrane exhibits an open porosity of 42.0 %, mechanical strength of 26.6 MPa, average pore size of 0.49 μm, pure water flux of 5616 L/(m2 barh). And, it has excellent corrosion resistance in acid and alkali. In addition, the flue gas moisture recovery performance of coal fly ash-based tubular ceramic membrane was studied experimentally. The highest water recovery ratio and the highest recovered water flux is 87.7 % and 6.01 kg/(m2 h, respectively.

Study on the Preparation and Properties of Talcum-Fly Ash Based Ceramic Membrane Supports.

Ceramic membrane method for moisture recovery from flue gas of thermal power plants is of considerable interest due to its excellent selection performance and corrosion resistance. However, manufacturing costs of commercial ceramic membranes are still relatively expensive, which promotes the development of new methods for preparing low-cost ceramic membranes. In this study, a method for the preparation of porous ceramic membrane supports is proposed. Low-cost fly ash from power plants is the main material of the membrane supports, and talcum is the additive. The fabrication process of the ceramic membrane supports is described in detail. The properties of the supports were fully characterized, including surface morphology, phase composition, pore diameter distribution, and porosity. The mechanical strength of the supports was measured. The obtained ceramic membrane supports displays a pore size of about 5 μm and porosity of 37.8%. Furthermore, the water recovery performance of the supports under different operating conditions was experimentally studied. The experimental results show that the recovered water flux varies with operating conditions. In the study, the maximum recovered water flux reaches 5.22 kg/(m2·h). The findings provide a guidance for the ceramic membrane supports application of water recovery from flue gas.

Application of transport membrane condenser for recovering water in a coal-fired power plant: A pilot study

Transport membrane condenser is considered as promising equipment for recovering water and heat in the thermal power plants. However, most of the studies on transport membrane condenser are either at laboratory scale or theoretical research level. In this study, a pilot scale testing platform is established for investigating the feasibility of transport membrane condenser application in engineering. The importance of this pilot study is to find the fundamental factors affecting the transport membrane condenser and make comprehensive technical and economic analysis of the engineering application. These are the factors which previous laboratory scale did not investigate. Various transport membrane condensers are manufactured for the two-stage experiments in a coal-fired power plant, and some innovative optimization measures are proposed for improving the performance of transport membrane condenser. In this study, the modified transport membrane condenser performs much better than that in other studies. Furthermore, the relationship between recovered water flux, condensation and permeation resistances is analyzed. Condensation resistance is found as the most fundamental factor affecting the recovered water flux. Finally, taking a 330 MW coal-fired unit as an example for technical and economic analysis, transport membrane condenser exhibits a good economic application prospect in engineering.

Fouling mitigation of a graphene hydrogel membrane electrode by electrical repulsion and in situ self-cleaning in an electro-membrane reactor

Abstract The conductive membrane can improve water flux and selectivity when it is employed as a membrane electrode. However, stability of the membrane structure during electro-filtration is still a challenge. In this study, a conductive graphene hydrogel membrane (GHM) was fabricated by compaction of a graphene hydrogel under external pressure. The pore size of GHM was stable at ~100 nm under anodic oxidation and cathodic reduction state, which was beneficial for long term electro-control of membrane fouling. When the GHM was negatively charged, membrane fouling was mainly reduced by electrical repulsion, and in situ electro-oxidation played a primary role in the self-cleaning to recover water flux. The water flux of the GHM electrode with a bias of −1 V was 10% higher than that of the GHM without applied bias. After fouled by bovine serum albumin (BSA), the flux recovery ratio of GHM electrode could maximally achieve 99.0 ± 1.4% by the self-cleaning, indicating that almost all the foulants were removed from the GHM. Lower foulant concentration, higher electrolyte concentration, and longer self-cleaning time were beneficial to recover the flux. These findings provide a foundation for the development and application of the electro-membrane reactor (EMR) system using conductive membranes.

Experimental research on the heat transfer and water recovery performance of transport membrane condenser

Transport membrane condenser (TMC) is a device for extracting moisture and heat from the exhaust. This paper designs a TMC which contains 46 ceramic membrane tubes to treat the exhaust from a gas-fired boiler. The trends of the recovered water flux, the convective heat transfer coefficient, and latent and sensible heat under different experimental conditions are investigated. The experimental results show that the heat transfer and water recovery performance of the TMC can be increased by increasing the flowrate of flue gas and cooling water, and increasing the temperature difference between flue gas and cooling water. Compared with other studies, the novelty of this paper is reflected in two aspects. Firstly, using TMC consisting of ceramic membranes with the pore size of 1 μm can recover more water than traditional TMC. Secondly, the convective heat transfer coefficient, latent heat and sensible heat released by flue gas are calculated quantitatively under different working conditions. The maximum recovered water flux is 15.77 kg/(m2 h), and the latent heat released by condensation accounts for more than 75% of the total heat released by the flue gas.

Moisture recovery from gas-fired boiler exhaust using membrane module array

Abstract: Many studies on the moisture recovery of flue gas by the membrane method use a single ceramic membrane tube to recover the simulated flue gas. In this paper, a membrane module array containing 46 ceramic membrane tubes was constructed to recover moisture and heat in real flue gas produced by a gas-fired boiler. The maximum recovered water flux was 15.77 kg/(m2·h), and the maximum heat flux was 14.83 MJ/(m2·h). Based on the experimental results, applying membrane module array in the thermal power plants could recover a considerable amount of water and heat. Recovering moisture could solve the water shortage problem of some thermal power plants, and decrease overall humidity in the lower atmosphere, which is conducive to the spread of pollutants in the lower atmosphere. Furthermore, the optimal boundary conditions of the experiments are discussed for guiding the actual production in the future. According to the results, the optimal operation temperatures of flue gas and cooling water are about 50 °C and 25 °C, respectively.

Enhanced filtration performance and anti-biofouling properties of antibacterial polyethersulfone membrane for fermentation broth concentration

The anti-biofouling performance of silver nanoparticles (Ag NPs) modified polyethersulfone (PES) membrane was evaluated during the concentration of fermentation broth. The Ag NPs containing membrane did not exhibit biofouling mitigation performance during the first filtration cycle, but could help to recover water flux upon physical cleaning. After three filtration-clean cycles, the Ag NPs containing membranes presented higher water flux and slower flux decline than the control membranes without Ag NPs. Ag NPs on the membrane surface facilitated the effective removal of cake layer. Moreover, the Ag NPs-containing membrane had no negative effects on the activities of bacteria in fermentation broth.

A pilot study on pressure retarded osmosis operation and effective cleaning strategies

A SWRO-PRO pilot was built to systematically investigate the osmotic power generation from state-of-the-art thin-film composite (TFC) hollow fiber membrane modules. For performance benchmarking, three feed pairs were examined. They were (1) synthetic brine and tap water, (2) real seawater reverse osmosis brine (referred to as SWBr) and tap water, and (3) real SWBr and wastewater retentate (referred to as WWBr) feed pairs. All feed pairs had the capabilities to produce power densities ranging from 5W/m2 to 5.7W/m2, which were obtained based on draw solution pressure and NaCl concentration of 15bar and 0.8M, respectively. These results were equal or more than the required power density of 5W/m2 proposed by Stafkraft. Various cleaning strategies at pilot level were adopted and proven to be effective and feasible to sustain module performance. Online cleaning approaches; namely, backwash, clean-in-place (CIP) and maintenance cleaning (MC) were performed to evaluate the cleaning efficiencies of the fouled membrane modules. The effectiveness of various cleaning agents was also evaluated using (1) tap water, (2) 200ppm HCl solutions at pH2.3 and (3) 200ppm NaOCl solutions at pH10.5. The results showed that for the case of SWBr and WWBr feed pair, acid maintenance cleaning was able to fully recover the water flux or power density, whereas caustic cleaning was only able to recover the water flux up to 80%. Chemical-free cleanings by backwash and CIP could only recover water flux from 42% to 51%. The introduction of intermittent CIP cleanings at a fixed interval was found to be effective in slowing down the water flux decline, thereby prolonging the operational duration.

Assessing the removal of organic micro-pollutants from anaerobic membrane bioreactor effluent by fertilizer-drawn forward osmosis

In this study, the behavior of organic micro-pollutants (OMPs) transport including membrane fouling was assessed in fertilizer-drawn forward osmosis (FDFO) during treatment of the anaerobic membrane bioreactor (AnMBR) effluent. The flux decline was negligible when the FO membrane was oriented with active layer facing feed solution (AL-FS) while severe flux decline was observed with active layer facing draw solution (AL-DS) with di-ammonium phosphate (DAP) fertilizer as DS due to struvite scaling inside the membrane support layer. DAP DS however exhibited the lowest OMPs forward flux or higher OMPs rejection rate compared to other two fertilizers (i.e., mono-ammonium phosphate (MAP) and KCl). MAP and KCl fertilizer DS had higher water fluxes that induced higher external concentration polarization (ECP) and enhanced OMPs flux through the FO membrane. Under the AL-DS mode of membrane orientation, OMPs transport was further increased with MAP and KCl as DS due to enhanced concentrative internal concentration polarization while with DAP the internal scaling enhanced mass transfer resistance thereby lowering OMPs flux. Physical or hydraulic cleaning could successfully recover water flux for FO membranes operated under the AL-FS mode but only partial flux recovery was observed for membranes operated under AL-DS mode because of internal scaling and fouling in the support layer. Osmotic backwashing could however significantly improve the cleaning efficiency.

Permeability recovery and changes in fouling layer characteristics of PTFE membrane by enhanced backwash cleaning using NaOCl during coagulation and microfiltration

Polytetrafluoroethylene (PTFE) membrane has high resistance to chlorine, which is a great advantages in chemical cleaning to recover water flux during membrane processes in drinking water systems. A humic kaolin water with approximately 4 mg/L of DOC and 10 NTU of turbidity was prepared as a feed water. Coagulation pretreatment with or without settling was applied. The coagulation with settling showed the greatest water production. The reduced flux was effectively recovered by NaOCl cleaning, i.e., 21% recovery by 50 mg/L of NaOCl cleaning and 49% recovery by 500 mg/L NaOCl cleaning. The images of SEM and AFM analyses were corresponded to the water flux variation. However, when the floc was accumulated on the membrane surfaces, the efficiency of NaOCl cleaning was substantially limited. In addition, dynamic contact angle became greater after cleaning, which indicates changes in characteristics of fouling layer such as surface hydrophobicity. Proper cleaning technologies during enhanced backwash using NaOCl would expand application of PTFE membranes in drinking water systems.

Fouling phenomena in microporous membranes. Flux decline kinetics and structural modifications

The fouling mechanisms in microfiltration are analyzed with two symmetric and one asymmetric membranes. Fouling kinetics when microfiltering bovine serum albumin solutions (BSA) are studied for both the consecutive processes of surface blocking and cake formation. Influence of shear stresses and aggregates is analyzed. Permeate flux is recovered by cleaning with different agents and temperatures, thus with different removal and cake coagulation performances. Finally, modifications of the structure of the porous matrix due to the appearance of a cake on the retentate layer of the membrane are studied by air permeation porometry. The flux decay and recovery characteristics as well as the structural modifications obtained agree with the two consecutive steps in the fouling mechanism leading to a solute accumulation on the pore entrances whose consequences are analyzed here. This model predicts asymmetries in the recovered water flux after cleaning which are effectively found.

Application of ceramic membrane as a pretreatment in anaerobic digestion of alcohol-distillery wastes

Pretreatment of alcohol-distillery wastes with ceramic membranes was performed prior to anaerobic digestion. Ceramic membranes with 0.05 μm pore size were chosen based on the particle size distribution in raw wastes. In this pretreatment, chemical oxygen demand (COD) was reduced from 36,000 to 18,000 mg/l and suspended solids were almost completely removed. The permeates from the ceramic membrane were further separated by ultrafiltration, but further COD reduction by using the PM30 and PM10 membranes was not achieved. Mixed stillages exhibited higher fouling tendency than pure naked barley stillage. Several cleaning methods were attempted to recover water flux. Although lumen flushing was effective, hydrogen peroxide proved to be the most effective cleaning agent. The negative flux recovery after nitric acid cleaning could be explained by the ligand exchange theory. The performance of digester was greatly improved with membrane pretreatment, specially in the ease of naked barley based stillage.