Water Recovery Performance Research Articles

Efficient water recovery and power generation system based on air-cooled fuel cell with semi-closed cathode circulation mode

Air-cooled proton exchange membrane hydrogen fuel cell with on-line hydrogen production by hydrolysis has potential for portable applications due to its high volumetric power density and self-humidification. However, plenty of reserve water significantly reduces the power density of fuel cell system. Moreover, water recovery from fuel cell tail gas is difficult, because the tail gas humidity is very low due to excess cathode air as coolant. In this work, the dead-ended anode and semi-closed cathode proton exchange membrane fuel cell is proposed to achieve efficient water recovery and energy conversion via semi-closed cathode circulation mode. In this mode, cathode O2-poor tail gas is recycled as coolant instead of fresh air, which helps to enlarge the tail gas humidity by reducing the stoichiometric ratio of cathode to anode gas. The system lumped model with detailed component description is developed for optimization. >96% water production can be recycled under atmosphere temperature. The demand of fresh air is greatly reduced from 56 to 2 times of the consumption. Besides, the multi-objective optimization between water recovery and electrochemical performance shows high-efficiency water recovery of 94.70% and high energy conversion efficiency of 54.82%.

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.

Solvent-free polyamide TFC membrane fabrication based on TMC vaporization for saline water recovery

While thin film composite (TFC) membranes have dominated the global desalination process, using large amounts of organic solvent during membrane manufacturing remains a major concern. Thus, a greener approach to prepare TFC membranes based on solvent-free trimesoyl chloride monomer vaporization is presented in this work. This study fabricated the solvent-free membranes by varying relevant parameters during the vapor interfacial polymerization (VIP) process and studied their impacts on the membrane properties. Evidently, the VIP membranes exhibited thinner polyamide layers than conventionally prepared membrane following the slow polymerization rate. This resulted in higher pure water permeability (2.93 L/m2.h.bar) than the conventional membrane (2.53 L/m2.h.bar) when both membranes were tested at 8 bar. Despite demonstrating slight decrease in salt rejection, the saline water recovery performance of VIP membrane was unaffected, as high salt rejection was unnecessary. Under the best synthesis conditions, a VIP membrane with lower salt rejection could rival the conventional membrane with a >98 % dye rejection while attaining substantially higher NaCl/dye selectivity (up to 330) than the conventional ones (68.75). Pertinently, the study findings demonstrated the potential of the solvent-free IP-fabricated TFC membrane for saline water recovery.

Performance analysis of a novel combined open absorption heat pump and FlashME seawater desalination system for flue gas heat and water recovery

Thermal desalination processes generally consume a huge amount of thermal energy and industries release a large amount of latent waste heat in flue gas exhausts into the environment. In order to efficiently utilize this waste heat and to improve the energy efficiency of desalination process, this paper presents a novel combined system based on the open cycle absorption heat pump and low-grade thermal energy driven FlashME desalination. The proposed combined system is designed to recover the latent waste heat from flue gas exhausts in a parallel double stage open absorption heat pump which is driven by multiple energy sources and efficiently utilizes the recovered low temperature heat in FlashME for freshwater production. The validated process model of the combined system is developed in Aspen Plus and a parametric assessment is carried out to analyze its energy performance with the impact of various independent operational parameters by using HCOOK-H2O as an absorbent solution. The simulation results of the parametric study show that the combined system is capable of recovering the waste heat with an efficiency of 89.42 % by operating at a thermal performance coefficient of 2.21 and utilizes this heat in the form of hot seawater at 70 °C to drive FlashME desalination process for freshwater production at the performance ratio of 3.05. The critical analysis of the results highlights that the heat recovery performance of the absorption cycle is strongly dependent on the inlet parameters of flue gas and spray solution. In contrast, the water recovery performance of FlashME is dependent on regeneration pressure such that the water recovery rate varies from 9.19 % to 37.17 % with a pressure variation between 23.23 and 51.39 kPa which raises the seawater temperature 60–79 °C before the flashing stage. Furthermore, the system is flexible enough to operate with two heat sources of different temperature levels by adjusting the regeneration load in separate regenerators.

Insufficient desorption of ions in constant-current membrane capacitive deionization (MCDI): Problems and solutions

Membrane capacitive deionization (MCDI) is a water desalination technology that involves the removal of charged ions from water under an electric field. While constant-current MCDI coupled with stopped-flow during ion discharge is expected to exhibit high water recovery and good performance stability, previous studies have typically been undertaken using NaCl solutions only with limited investigation of MCDI performance using multi-electrolyte solutions. In the present work, the desalination performance of MCDI was evaluated using feed solutions with different levels of hardness. The increase of hardness resulted in the degradation of desalination performance with the desalination time (Δtd), total removed charge, water recovery (WR) and productivity decreasing by 20.5%, 21.8%, 3.8% and 3.2%, respectively. A more serious degradation of WR and productivity would be caused if Δtd decreases further. Analysis of the voltage profiles and effluent ion concentrations reveal that the insufficient desorption of divalent ions at constant-current discharge to 0 V was the principal reason for the degradation of performance. The Δtd and WR can be improved by discharging the cell using a lower current but the productivity decreased by 15.7% on decreasing the discharging current from 161 to 107 mA. Discharging the cell to a negative potential was shown to be a better option with the Δtd, total removed charge, WR and productivity increasing by 27.4%, 23.9%, 3.6% and 5.3%, respectively, when the cell was discharged to a minimum voltage of – 0.3 V. Use of such a method should be feasible for operation of full scale MCDI plants and would be expected to lead to better regeneration of the electrode, improved desalination performance and, potentially, a significant reduction in the need for use of clean-in-place procedures.

Analytical investigation of the dew point water recovery system with potential application for drinking water production

The article presents the analytical investigation of the Dew Point Water Recovery (DPWR) system with potential application for drinking water production. Four different configurations of the DPWR system were proposed, differing in the number and type of dew point cooling exchangers used, and their operation was described using a validated convective heat transfer coefficient mathematical model. It was found that the three stage configuration of the DPWR system with a regenerative exchanger has the best water recovery performance, while the three stage configuration with a counter-flow exchanger has the best ratio of energy supplied to the system in relation to the amount of water produced. It was also found that the DPWR system can operate in a wide range of operating conditions with a specific electric energy consumption reaching below 0.9 kWh/m3 and GOR in the range of 0.36–2.16. What distinguishes the DPWR system from other methods of drinking water production is the ability to work without an additional source of thermal energy apart from the energy of the air supplied to the system. Thanks to this property, the system has the potential to fill the technological gap of a low-energy and easily accessible method of drinking water production.

Chromium-containing wastewater reclamation via forward osmosis with sewage sludge ash temperature-sensitive hydrogel as draw agent

A temperature-sensitive hydrogel modified with sewage sludge ash (SSA) was used as an advanced draw agent for forward osmosis (FO) application in treating chromium-containing wastewater. The performance of the modified hydrogel (SSA-TSH) was measured in terms of the swelling and deswelling properties, as well as adsorption and desorption effects on Cr(VI), chemical oxygen demand (COD), total phosphorous (TP) and ammonium (NH4+-N) in chromium-containing wastewater. Furthermore, the efficiencies of wastewater treatment, water flux, and the reusability of the SSA-TSH as draw agent in the FO process (FO-SSA-TSH) using a commercially available thin-film composite membrane (Sterlitech) were also investigated. The results indicated that FO-SSA-TSH achieved high removal rates of pollutants (Cr(VI): 96.9 %–97.4 %, COD: 97.1 %–97.4 %, TP: 97.7 %–99.6 %, and NH4+-N: 76.8 %–77.9 %) in various Cr(VI) concentrations (0– 40 mg/L) due to the high rejection rate of FO membrane and notable adsorption capacity of the hydrogel. Moreover, the average water flux of FO-SSA-TSH (1.95– 2.02 LMH) was nearly twice as much as that of the FO with pure temperature-sensitive hydrogel as draw agent (FO-TSH, 1.33– 1.42 LMH) in 24 h chromium-containing wastewater treatment. In addition, SSA-TSH with excellent deswelling property exhibited high water recovery performance and good reusability in low cost and energy consumption after the FO permeation process for wastewater treatment.

Novel sandwich-like membrane with hydrophilic-omniphobic-hydrophilic structure for sustainable water recovery in membrane distillation

Membrane distillation (MD) is attractive for water recovery from surfactant-stabilized oil-in-water emulsion due to its unique characteristics. To address the membrane fouling and wetting issues, a novel hydrophilic-omniphobic-hydrophilic sandwich-like membrane (PFZP) was firstly developed. Top PDA skin layer induced the hydration shell facing feed, which endowed membrane with high energy barriers (0.12 kT) to limit free hexadecane deposition. Omniphobic substrate (FZP) effectively avoided the deposition of free sodium dodecyl sulfate (SDS) and hexadecane-SDS aggregate. Bottom PDA skin layer was beneficial to maintain transmembrane temperature difference and driving force. Besides, both PDA layers (∼4.1 μm) partly intruded into FZP substrate to shorten water vapor transmembrane transfer path. Compared with pristine membrane, PFZP membrane displayed greatly improved anti-fouling, anti-wetting and water recovery performance with stable water flux (18.0 LMH) and high salt rejection (99.99%). Obtained findings further improved the understanding of robust MD membrane design, its anti-fouling, mass and heat transfer mechanism.

Simulation study of an open compression absorption heat pump in water and heat recovery of low-temperature and high-humidity flue gas

Realizing the recovery of latent heat and moisture from low-temperature and high-humidity flue gas (LHFG) can effectively improve energy efficiency and reduce carbon emissions. A novel open compression absorption heat pump (OCAHP) is proposed to fulfill the demand for flue gas water and heat recovery. In this paper, Aspen Plus is used to establish a model, and the coefficient of performance (COP), water and heat recovery rate are evaluated to investigate the effects of the gas inlet temperature, compression ratio, liquid-to-gas ratio, and absorber inlet solution temperature parameters on water and heat recovery performance for OCAHP. The parameters are optimized, and exergy analysis is carried out. The simulation results show that wet flue gas with successive adiabatic compression and CaCl2/H2O solution absorption has significant water and heat recovery performance. The results also prove that the water recovery efficiency of the OCAHP system is 82.4% at a compression ratio of 1.4, which is approximately 12.3% higher than that of the conventional open absorption heat pump (OAHP) system, and it is suitable for wet flue gas with a higher saturation temperature. Furthermore, exergy analysis shows that the exergy efficiency of the OCAHP system is higher than that of the conventional OAHP system, while the exergy loss is mainly concentrated in the regenerator heating process and the solution-water heat exchanger.

Performance study of transport membrane condenser using condensate water to recover water and heat from flue gas

Transport membrane condenser (TMC) is an effective equipment for water and heat recovery from flue gas exhausted by coal-fired power plants. Characteristic of cooling water source for TMC is crucial to design and performance of the device. Due to the high water quality and relatively large water flow rate, the condensate water from the unit condenser is a suitable water source. However, the water flow rate in related research exceeds the range of condensate water flow rate, and the results cannot be applied in this condition. Thus, we established a numerical model for performance study of TMC. The condensate water from the condenser of a 600 MW coal-fired power unit is adopted. The effects of structural and operating parameters on the performance of TMC are investigated, and the technical and economic analysis is conducted. Results show that series connection of membrane modules is more suitable than parallel connection for engineering applications. Moreover, the number of transverse rows should be larger than 60 by comprehensively considering heat and water recovery performance and flow resistance. Due to the high benefit of recovered heat, the maximum payback period is 1.68 years. This study provides theoretical support for the engineering application of TMC using condensate water as the cooling water source.

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.

ECTFE Membrane Fabrication Using Green Binary Diluents TEGDA/TOTM and Its Performance in Membrane Condenser.

Poly(ethylene-chlorotrifluoroethylene) (ECTFE) membrane is a hydrophobic membrane material that can be used to recover water from high-humidity gases in the membrane condenser (MC) process. In this study, ECTFE membranes were prepared by the thermally induced phase separation (TIPS) method using the green binary diluents triglyceride diacetate (TEGDA) and trioctyl trimellitate (TOTM). Thermodynamic phase diagrams of the ECTFE/TEGDA: TOTM system were made. The effects of the diluent composition and cooling rate on the structure and properties of the ECTFE membranes were investigated by characterizing the SEM, contact angle, mechanical properties, pore size and porosity. The results showed that ECTFE membranes with cellular structure were successfully prepared and exhibit good mechanical properties. Moreover, increasing the TOTM content in the binary diluents and decreasing the cooling rate could effectively improve the mean pore size of the ECTFE membranes, but the increase in TOTM content reduced the mechanical properties. During the MC process, the water recovery performance of ECTFE membranes increased with the increase in the mean pore size of the membranes, and the condensation flow and water recovery of membrane prepared at 20% TOTM were 1.71 kg·m−2·h−1 and 54.84%, respectively, which were better than the performance of commercial hydrophobic PVDF membranes in the MC. These results indicated that there is good potential for the application of ECTFE membranes during the MC process.

Design and multi-objective optimization of low-temperature proton exchange membrane fuel cells with efficient water recovery and high electrochemical performance

Water generated by electrochemical reaction in the proton exchange membrane fuel cell (PEMFC) could be used as an important resource. Several studies have been carried out to recycle the water from PEMFC emissions, which verifies the feasibility of water recovery. However, the quantitative description of the water recovery mechanism inside PEMFC is not clear and the water recovery performance could be further improved from the perspective of internal mass transfer. In this paper, a two-dimensional model is developed to present the fluid flow and mass transfer inside a PEMFC. Also, a detailed investigation into the effects of operating parameters, including pressure, temperature, and relative humidity, on both the electrochemical performance and the water recovery performance is conducted. Besides, a multi-objective optimization is carried out for the performance optimization of PEMFC. The results show that the expanded water recovery efficiency (EWRE) of PEMFC is more sensitive to pressure and relative humidity than temperature. The optimum solution at 1 atm shows that EWRE reaches 141 % with the current density of 0.7163 A·cm−2. The operation strategy of decreasing the humidification temperature and increasing the relative humidity at the cathode inlet, and maintaining PEMFC working at a moderate temperature is proposed to keep the balance between the electrochemical and water recovery performance. This work contributes to the operation optimization of water recovery and to the application extension of PEMFC.

Wire-wrapped and helically-finned tubular ceramic membranes for enhancing water and waste heat recovery from wet flue gas

Recycling water and waste heat from wet flue gas is crucial for sustainable energy-water-environment nexus in industrial processes. Herein, we report the use of wire-wrapped and helically-finned tubular ceramic membranes to construct membrane condensers for simultaneous water and heat recovery. Compared with conventional plain tubular ceramic membrane (PTCM), wire-wrapped tubular ceramic membrane (WTCM) and helically-finned tubular ceramic membrane (FTCM) both exhibit superior water and heat recovery performance, indicating a non-negligible effect of chaotic fluid mixing on heat and mass transfer enhancement. FTCM shows better condensate capture performance than WTCM. Moreover, improved condensing heat transfer performances are observed on FTCMs provided with large fin height and pitch. FTCM provides higher heat transfer coefficients than PTCM at around 7.4% to 59.3% depending on different fin structures. Effects of operation parameters on membrane condensation process using FTCM are also investigated. Gas-side parameters have significant effects on water/heat recovery performance than water-side parameters. This study can serve as a basis for process intensification of membrane-based condensation used for flue gas dehumidification.

Recycle coal fly ash for preparing tubular ceramic membranes applied in transport membrane condenser

Water recovery from flue gas with transport membrane condenser (TMC) has gained much attention in recent years. It has great potential in water conservation and air pollution control. However, effects of porosity and pore size variation of macroporous membranes on TMC application have not been revealed. Coal fly ash (CFA) is used as main raw material to prepare various tubular macroporous ceramic membranes for TMC application. The extrusion method is adopted. Characterization of membranes are conducted for structural parameters evaluation. Prepared membranes were used for TMC application to experimentally study the water and heat recovery performance. Influences of temperatures and flowrates of flue gas and cooling water on recovery performance have been investigated. Increasing cooling water flowrate and flue gas temperature, as well as decreasing cooling water temperature can promote water and heat recovery performance of TMC. The highest water recovery efficiency is 79.21%. Although membrane pore size increasing improves water and recovery, the average pore size should be less than 2 μm to avoid transmembrane gas permeation. Results indicate that CFA membrane is suitable for TMC application and provides investment reduction.

Non-evaporative solvent extraction technology applied to water and heat recovery from low-temperature flue gas: Parametric analysis and feasibility evaluation

The performance of solution absorption systems is significantly influenced by the energy consumed during the solution regeneration process when it is applied for water and heat recovery from low-temperature flue gas. Solvent extraction is a non-evaporative technology without phase change that features water solubility sensitive to temperature, which has advantages in energy consumption. In this paper, the high-concentration CaCl2 solution is selected as the liquid desiccant and the feasibility of three amines used for water extraction is explored. The results show that diisopropylamine has the highest water recovery efficiency of 4.1% and that N,N-dimethylcyclohexylamine has the highest salt removal efficiency of >99%. The influence of the stirring intensity and volume ratio on the water recovery performance is also researched with diisopropylamine as the solvent. Simulation results show that compared with the evaporative regeneration method, the energy consumption of the solvent extraction method is reduced by 22.7–51.6%. A coefficient of performance (COP) of 1.71 is achieved in the novel solution absorption system, which utilizes solvent extraction for solution regeneration.

Performance analysis of ceramic membrane tube modules for water and heat recovery in coal-fired power plants

Ceramic membrane separation technology is a promising method for water and heat recovery from exhaust flue gas in thermal power plants. Matching among function, load and structure of membrane modules is critical to design and operation of such recovery processes. In this paper, an analytical model based on membrane separation mechanism is proposed to evaluate the water and heat recovery performance in a ceramic membrane module. A series of calculation considering both structural parameters and load conditions in a power plant is conducted. Results show that under the conditions of different flue gas temperature and water vapor volume fraction, the membrane module has three working modes corresponding to different condensation processes. For flue gas with high temperature and low humidity, the temperature rise of cooling water can reach up to 40 °C when the mass flow rate ratio of cooling water to flue gas is less than 50%. For flue gas with low temperature and high humidity, low cooling water temperature could promote water recovery process. Keeping the mass flow rate ratio higher than 200% can maintain the water recovery rate not less than 60%. The optimal water and heat recovery rate is obtained by optimizing the size and structure of the membrane module within limited volume. This study provides a basis for structure optimization and operation regulation of ceramic membrane modules for water and heat recovery purpose.

Improving heat transfer and water recovery performance in high‐moisture flue gas condensation using silicon carbide membranes

Desulfurated flue gas in coal-fired power plants contains profuse water vapor and latent heat, the recovery of which is crucial. Herein, a novel use of silicon carbide (SiC) membranes to construct a transport membrane condenser (TMC) for simultaneous water and waste heat recovery from high-moisture flue gas is reported. The performances of water and heat recovery were systematically compared between typical dense heat exchange materials (304 stainless steel and perfluoroalkoxy [PFA]) and porous ceramic membranes (Al2O3 membrane and SiC membrane). Porous ceramic membranes showed higher heat transfer performance than dense materials, suggesting a non-negligible mass transfer effect on heat transfer. Compared with the Al2O3 membrane, the SiC membrane exhibited better water and heat recovery performance because of its superior thermal conductivity. Using the SiC membrane as the heat exchange material, a water flux of 11.3-44.4 kg·m−2·h−1 and a water recovery efficiency of 46.5%-76.9% were achieved. The thermal resistance from the gas boundary layer dominated the heat transfer process in SiC membrane condensers as the thermal resistances from the membrane and condensate film were markedly reduced. This study forms a basis for future investigations on heat transfer enhancement of membrane condensers used for industrial moisture recovery.

Macroporous ceramic membrane condenser for water and heat recovery from flue gas

In this work, we experimentally study a macroporous ceramic membrane condenser (MCMC) with an average pore size of 3 µm for water and heat recovery from flue gas. Firstly, the heat and mass transfer mechanisms of MCMC are analyzed. The membrane surface is only wetted and no condensate accumulation, suggesting that the condensation rate is the key factor affecting the water recovery performance. Moreover, the thermal resistance in MCMC is concentrated at gas side, and the conductive resistance of the membrane occupies only about 1% of total resistance. The results also show that the experimental Sherwood numbers are larger than the correlated Sherwood numbers obtained by heat and mass transfer analogy. It may be caused by the hydrophilic properties of the membrane surface. Finally, the effects of operating conditions on water and heat recovery performance are investigated. The CMCM shows excellent performance in recovering water and heat, and the gas flow rate and gas/cooling water temperature have significant effect on recovered water/heat flux. In the future, we will further explore the coupled heat and mass transfer process and clear up the cause of the mass transfer enhancement.

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.