Macroporous Ceramic Membrane Research Articles

Simulation and techno-economic analysis of moisture and heat recovery from original flue gas in coal-fired power plants by macroporous ceramic membrane

Macroporous ceramic membrane can be used to recover heat and water vapor from the original flue gas in coal-fired power plants, which is conducive to saving water and improving the economic benefits of power generation. However, the overall mass and heat transfer model for the application of membrane modules has not been established at present, and the impact of various parameters on economic benefits has rarely been studied. Therefore, a heat and mass transfer model for 45,600 membrane tubes in a 330 MW coal-fired power plant was established in this paper. Then EBSILON software was applied to simulate the entire thermal system to analyze the economic benefits under different parameters, including cooling water temperatures, cooling water flowrates, turbine heat acceptance operating conditions, and ceramic membrane areas. Finally, its net present value was calculated. The results indicated that the cost recovery time of the transport membrane condenser was 6.85 years when the cooling water temperature is 25 °C and cooling water flowrate is 1000 t/h, and the coal consumption rate was reduced by 0.521 g/(kW·h), which provided theoretical and empirical support for industrial applications.

Thermal conductivity analysis of ceramic membranes for recovering water from flue gas

Condensation is the common mechanism of water intake from gases. Transport membrane condenser is a newly proposed technology to recover water from flue gas based on the mechanism of condensation. Most of the existing heat transfer research on transport membrane condenser focuses on water vapor phase change or fluid convection heat transfer, and there is a lack of research on the thermal conductivity of ceramic membranes. The significance of studying thermal conductivity is to optimize the overall heat transfer performance. The thermal conductivity of alumina ceramic solid materials is not good enough, which can affect the industrial application performance to a certain extent. There is currently a lack of experimental measurements or theoretical calculations to quantitatively characterize the thermal conductivity of ceramic membranes. This affects the optimization of overall heat transfer performance of transport membrane condenser. In this paper, coal fly ash is used as the raw materials to prepare macroporous ceramic membranes. Coal fly ash is a very cheap material. It can greatly reduce the manufacturing cost of transport membrane condenser using coal fly ash to prepare ceramic membranes. The classical theoretical model of thermal conductivity of porous materials is introduced, the calculation and experimental results are compared, and the validity and limitation of the classical models in analyzing the heat transfer problem of transport membrane condenser are discussed. Finally, based on the composite effective medium theory, combining with the experimental results, a modified model is proposed. The modified model reduces the average theoretical error to 7.20%, and enriches the research on the heat transfer theory of transport membrane condenser.

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.

Simulation study of using macroporous ceramic membrane to recover waste heat and water from flue gas

Transport membrane condenser based on macroporous ceramic membranes can better meet the requirements of power plants for the recovery of waste heat and water from flue gas. This paper proposes a condensation and permeation model for describing the process of waste heat and water recovery from flue gas by macroporous transport membrane condenser. The results obtained from model are compared with the experimental results. According to results of condensation and permeation rate, errors between the calculated and experimental data are less than 10%. According to results of outlet water and flue gas temperatures, errors between the calculated and experimental results are within 0.06%. Therefore, accuracy of the model is verified. Based on the model, effects of the parameters including flue gas temperature and flow velocity, cooling water temperature and flow velocity, flue gas relative humidity, membrane porosity, and local atmospheric pressure are studied in terms of water and heat recovery performances. The research results show that increasing the flow rate of flue gas and cooling water, increasing the relative humidity of flue gas, increasing the local atmospheric pressure, reducing the temperature of flue gas and cooling water can increase the condensation rate of water vapor, thereby enhancing the recovery performance of the ceramic membrane. The increase of the porosity of the ceramic membrane can increase the penetration rate of the condensate, and more condensate can be recycled into the ceramic membrane, so that the overall recovery effect is better.

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.

Numerical investigation on condensation mode of the transport membrane condenser

Transport membrane condenser is a novel device for capturing water vapor from wet flue gas, which is composed of porous ceramic membranes. The capillary condensation is once considered as the water vapor capture mechanism of transport membrane condenser. Recently, a few scholars have discovered that transport membrane condenser composed of macroporous ceramic membranes can capture more water vapor. Since the capillary condensation cannot occur in the pores of the macroporous membrane, water vapor is believed to condense on the surface of the macroporous membrane. However, there is currently no comparative study of the two condensation mechanisms. In this paper, based on the transport membrane condenser pilot scale testing platform built in a coal-fired power plant, a numerical model is established to discuss the effects of different condensation mechanisms on the performance of transport membrane condenser. Furthermore, the model is extended to the application engineering. The results show that water vapor captured by transport membrane condenser is 25–45 t/h in a 330 MW coal-fired power plant, which can reduce the amount of makeup water to some extent. The numerical model also can be used to calculate the number of ceramic membranes for engineering design.

Numerical study on recovering moisture and heat from flue gas by means of a macroporous ceramic membrane module

Abstract The macroporous ceramic membrane module can effectively recover the moisture and heat from flue gas in thermal power plants, which is helpful for energy saving and clean production in thermal power plants. However, most related research stays in the laboratory stage, lacking corresponding theoretical calculation models and engineering application cases. Therefore, this paper establishes the heat and mass transfer model for describing the moisture recovering process, which can be used to predict the moisture and heat recovery performance in the actual engineering situations. The calculation results show that the errors between the calculated and the experimental values of the model are within ±10%. Therefore, this model can be used for engineering calculations. Based on the model, the recovery performance of the macroporous ceramic membrane module in a 330MWe thermal power unit is calculated and analyzed to provide theoretical support for the industrial application.

Ultrarobust and Biomimetic Hierarchically Macroporous Ceramic Membrane for Oil-Water Separation Templated by Emulsion-Assisted Self-Assembly Method.

Reported herein is a novel ultrarobust and biomimetic hierarchically macroporous ceramic membrane that can achieve a high efficiency of up to 99.98% for oil-water separation, while the efficiency remains nearly unchanged even after 10 rounds of use and storage for up to 4 months. The macroporous ceramic membrane is prepared by combining surface hydrophobic coating with an emulsion-assisted template self-assembly of the modified Al2O3 ceramic powder. The as-prepared ceramic membrane is a lightweight material with high strength because the relative density is only ∼1.02 g/cm3; the compressive strength of the as-prepared ceramic membrane is expected to be 15-fold higher than that of the sample prepared using the traditional solid template approach even at a higher porosity due to the principle of self-assembly of Al2O3 particles. It is the mechanism of self-assembly that has broken the traditional principle in ceramic preparation that leads to a perfectly dense packing structure. Moreover, the ceramic membrane maintained excellent oil-water separation efficiency, because of which even after its top layer was damaged by sand impingement, superfine particles could be separated using our macroporous membrane due to the featured interconnected pore structure. We anticipate that this example of the combination of a superwettability theory and a traditional ceramic material can provide an important application direction of advanced oil-water separation techniques.

Experimental Study on Water Recovery from Flue Gas Using Macroporous Ceramic Membrane.

In this work, a ceramic membrane tube with a pore size of 1 μm was used to conduct experimental research on moisture and waste heat recovery from flue gas. The length, inner/outer diameter, and porosity were 800 mm, 8/12 mm, and 27.2%, respectively. In the experiments, the flue gas, which was artificially prepared, flowed on the shell side of membrane module. The water coolant passed through the membrane counter-currently with the gas. The effects of flue gas flow rate, flue gas temperature, water coolant flux, and water coolant temperature on the membrane recovery performance were analyzed. The results indicated that, upon increasing the flue gas flow rate and its temperature, both the amount of recycled water and the recovered heat increased. The amount of recycled water, recycled water rate, recovered heat, and heat recovery rate all decreased as the water coolant temperature increased. When the water coolant temperature exceeded 30 °C, the amount of recycled water dropped sharply. The maximum amounts of recycled water, recovered heat, and total heat transfer coefficient were 2.93 kg/(m2·h), 3.63 kW/m2, and 224.3 W/(m2·K), respectively.

Modification of Ceramic Membranes by Silica Nanoparticles with Thiourea Functions

Sol-gel approach based on hydrolytic copolycondensation of tetraethoxysilane (TEOS) with ethylthiocarbamidepropyl triethoxysilane (ETUS) was used to deposit functional layers with thiourea functions on the surface of macroporous ceramic alumina membrane supports. According to SEM images, such layers are composed of nanoparticles of about 60-70 nm in diameter, while IR spectroscopy data confirmed the presence of functional groups introduced during the synthesis. Such functionalization technique allows combining sorption and membrane technology and could be successfully used to remove trace quantities of copper, cadmium, and silver metal ions from aqueous solutions.

Preparation and properties of tubular macroporous ceramic membrane supports based on natural quartz sand and dolomite

This study describes the fabrication of macroporous ceramic supports for membranes prepared from quartz sand and dolomite mixtures, which are abundant local raw materials; tubular supports are made using the extrusion technique. The structure was analyzed by X-ray diffraction (XRD) and mercury porosimetry techniques; the presence of possible defects in the prepared porous ceramic materials was investigated with scanning electron microscopy (SEM). Possible phase formation and structural evolutions were evaluated by thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA). The influence of dolomite addition and sintering temperature on phase composition, microstructure, porosity, pore size distribution, and chemical and mechanical properties is investigated. Supports properties such as permeability and three-point flexural strength were also measured and found to be related to both processing and microstructure parameters. The obtained supports show an optimum open porosity within a range of 40–45%, good permeability, and good resistance to corrosion. Such materials could be of great interest in the supports fabrication for membrane applications like water filtration.

Design and characterization of macroporous alumina membranes for passive samplers of water contaminants

Macroporous ceramic membranes with hierarchical pore structure were developed and characterized for the time-integrated analysis of water contaminants. The alumina membranes were boosted to allow a suitable diffusion rate for envisaged applications. Sacrificial fugitives as cornstarch and graphite and partial sintering technique were utilized for the control of pore structure and morphology. The present study includes: (i) Development of ceramic membrane preparation methods based on wet forming techniques and partial sintering in order to control of membrane parameters such as porosity, tortuosity factor and thickness; (ii) Microstructural characterization of the ceramic membranes using two complementary techniques: Hg-porosimetry and SEM; (iii) the diffusion tests performed under laboratory conditions by an innovative, easy and accurate method based in the use of methylene blue (C16H18ClN3S) water solutions as test compound to study the characteristics of ceramic membranes. Using slip casting and partial sintering processing three different Al2O3 membrane configurations with high values 34.5, 36.9 and 39.6 vol% of interconnected porosity and 1.75, 1.7 and 1.3mm thickness were prepared. The pore morphology consisted of spherical cavities of 5-10 μm diameter and small pores of 70–200nm. This study also gathers the basis for the calculation of diffusion coefficients, membrane geometrical factor and sampling rates using methylene blue water solutions whose concentration can be accurately determined by optical absorption measurements at 664nm. Diffusion coefficients for methylene blue range from 2.3±0.5E-8 to 3.0±0.5E-8cm2s−1 increasing as connected porosity increases and membrane thickness decreases. The membrane geometrical factors are low, between 0.6 and 1E-02 and Archie’s constants large 4.5–5.5. This has been associated to the bimodal pore structure with coexistence of large and small pores that may increase the tortuosity factors in membranes. The macroporous ceramic membranes herein developed are suitable for the fabrication of passive samplers aimed at preconcentrating organic contaminants in water.

Physico-mechanical and gas permeability characteristics of kaolin based ceramic membranes prepared with a new pore-forming agent

The objective of this study was to prepare low-cost macroporous ceramic membranes using natural kaolin obtained from deposits in Nigeria and Ghana, and powdery high density polyethelene (PHDPE) as porogen agent. The ceramic membranes have been prepared with porogen content wt% between (0 and 20)% by die pressing. Pellets were fired at 1150°C and soaking time of 4h. The raw materials were characterized using TG/DTA, particle size distribution (PSD) and Zeta potential. The membranes cast as circular disks were subjected for characterization studies using XRD and SEM analysis. In a bid to correlate the physico-mechanical properties vis-à-vis pore former content, the effect of the sintering temperature and pore former (PHDPE) content on porosity, density, water absorption and mechanical strength were evaluated. The membrane corrosion resistance was found to be unaltered with experimental conditions. Obtained membranes showed good porosity with maximum at about 62% with a mechanical strength that does not exceed 18MPa. These membranes can be considered as efficient regarding the results shown in the gas permeation tests at different sintering temperatures. A PHDPE percentage of 20% and a sintering temperature of 1150°C were chosen as the optimum for gas permeation based on enlarged pore diameter of sintered membranes.

In situ repairing the large defects of macroporous ceramic membranes by polyelectrolyte-coated nanoparticles

Abstract Large defects have important impact on performance of separation membranes. In this paper, in order to reduce the large defects of the industrial ceramic supports, we prepared a nanohybrid separation membrane with a selective layer and a sub layer on the macroporous substrate with polyelectrolyte-coated nanoparticles. SEM, EDS and pore size analyses suggest that the although ZrO2 nanoparticles can migrate into the large defects to modify the membrane pores, the matching of pore-mouth size and diameter of NPs plays important role in the in situ modification of the substrates. The integrality of the as-prepared nanohybrid multilayer membrane was evaluated in the nanofiltration of dye solutions. The organic-inorganic composite membranes perform high flux and retention for separation. Membranes were prepared to study the separation performance on different substrates and with different building blocks (polyelectrolyte molecule weights and polyelectrolyte molecule structure). We found that the pore-mouth size of substrates and the structure of building blocks mainly affected the structure and the nanofiltration performance of the composite membranes. Such assembly allow us to in situ modify the large defects of inorganic substrates while preparing the selective layer.

Influence of hydrophobization conditions and ceramic membranes pore size on their properties in vacuum membrane distillation of water–organic solvent mixtures

The initially hydrophilic micro- and macroporous ceramic membranes were successfully hydrophobized by grafting with fluoroalkylsilane (FAS) molecules. The influence of diverse parameters (e.g. type of molecule, duration of grafting, concentration of FAS solution, type of solvent) on the resulting hydrophobic surface was investigated. The liquid entry pressure of water (LEPw) was used as a measure of the hydrophobization efficiency. The prepared membranes were subsequently investigated in vacuum membrane distillation (VMD) process using pure water and water–organic solvent solutions as feed mixtures. It was found that permeate flux of pure water is strictly correlated with LEPw value. The selectivity of membranes in contact with water–organic mixtures depends strongly on the pore size of the hydrophobized membrane. Microporous membrane are much less efficient in the separation of organics from water (separation factor of ethyl acetate – EtAc in the range 1.3–30) comparing with macroporous ones (separation factor of EtAc in the range 32–60). The results were also discussed assuming the various mechanism of transports through porous ceramic membranes. These latter results were additionally compared with the results obtained for hydrophobic polymeric membranes (separation factor of EtAc in the range 25–450).

Preparation of macroporous membrane using natural Kaolin and Tunisian lignite as a pore-forming agent

The objective of this study was to prepare low-cost macroporous ceramic membranes using natural kaolin and natural lignite, as porogen agent, both from Tunisia. The characteristics of this membrane have been defined to be used in filtration processes and as a support for multilayer ceramic membranes. This study includes the characterization of the raw materials in order to define optimal processing parameters to obtain the membranes. A study of the effect of lignite content has been carried out. Porosity, density and mechanical strength were the considered parameters to be optimized. A lignite percentage of 20% and a sintering temperature of 1,050°C were chosen. Obtained membranes show good porosity above 43% but with a slightly low mechanical strength that does not exceed 20 MPa. These membranes can be considered as efficient regarding the results shown in the gas permeation tests.

Synthesis and characterization of α-Alumina membrane supports and the binding effect of Poly (Vinyl Alcohol)

Ceramic Ultrafiltration membranes are considered as an alternative for the treatment of both stable water-in-oil and oil-in-water emulsions proved to be more effective in comparison with other conventional techniques. In this study, symmetric macro-porous ceramic membranes are prepared through dry pressing of α-alumina powder and the addition of various binders including Poly (vinyl alcohol). The disk is sintered after the organic material is burned away and the porosity can also be adjusted by the variation of sintering temperature. The results show that the fabrication of compact membrane supports can be done by increasing the sintering temperature which leads to grain size reduction. Moreover, application of different binders and additives result in various supports possessing different pore size and size distributions. Scanning electron Microscope (SEM) micrographs illustrate the surface and grain size distributions caused by various binders. These membranes can be used for microfiltration at elevated temperatures and extreme environmental conditions and also as porous supports for the fabrication of composite-asymmetric nanofiltration membranes.

Preparation, Characterization and Properties of New Low Cost Multi-Channel Ceramic Membrane Tube for Water Treatment

Multi-channel tubular macroporous ceramic membrane supports were successfully prepared via a plastic extrusion method, using α-Al2O3 with a purity of 94wt% and aluminum hydroxide as starting materials, the ash of burned rice hull as the pore-forming agent and a small amount of talc and kaolin as sintering aids. The effects of the kinds of sintering aids, content of aluminum hydroxide and ash of burned rice hull on the porosity, pore size and distribution, compressive strength, acid and alkali corrosion resistance and permeability of the new multi-channel ceramic membrane supports were investigated. The results showed that aluminum hydroxide effectively improved the mechanical strength, and the support sintered at 1450°C for 4h with the aluminum hydroxide content of 20wt% exhibited higher performance: average pore size diameter and porosity were nearly 5μm and 50% respectively, the compressive strength was around 7MPa, the pure water flux was 26m3/m2h at 0.1MPa and changed to nearly 20m3/m2h after the acid and alkali treatment at 90°C for 48h. The support possesses excellent corrosion resistance and can be used in the water treatment process with large range of pH value.

Cost-effective macro-porous mullite-corundum ceramic membrane supports derived from the industrial grade powder

In order to develop cost-effective macro-porous ceramic membrane supports, the porous supports with large pore size were prepared from the coarse industrial mullite-corundum powder (M) with the mixture of kaolin and basic carbonate magnesium (KM) as sintering additive. Crystalline phase transition mechanism of the sintering additive and the supports was studied respectively by TG/DTA and XRD. The results confirm that at 1200–1400 °C α-cordierite formed from the sintering additive, and that above 1400 °C α-cordierite decomposed into mullite and liquid glassy phase. Sintering characteristic of the coarse mullite-corundum compacts was revealed as a function of KM/M mass ratio. The result indicates that the sintering ability of coarse mullite-corundum improved because of the produced liquid silica-rich glassy phase via the decomposition of KM-derived α-cordierite. In addition, the open porosity of the macro-porous mullite-corundum could be effectively tailored by choosing the KM/M mass ratio, the pore-former/M mass ratio and sintering temperature. The fabricated mullite-based macro-porous supports showed an average pore size of 26.21 μm and nitrogen flux of 2.375 × 10 4 m 3/(m 2 h), as well as good mechanical and thermal properties.

Preparation and Sintering of Macroporous Ceramic Membrane Support from Titania Sol‐Coated Alumina Powder

The preparation of ceramic support at relatively low sintering temperature of 1350°–1500°C was investigated with a powder processing route, namely, titania sol coated on coarse alumina powder (median particle size d50, 27.5 μm). The sintering kinetics analysis indicates that the microstructure control of support is closely related to the sol coating and the sintering conditions. The mechanisms of sintering process were discussed in detail with the corresponding kinetics parameter, i.e., activation energy Ea and exponent n as well as the microstructure characterization. The prepared support provides practical applications with tunable pore size and desired mechanical strength.