陶瓷膜冷凝器用于烟气脱白烟过程的中试研究

将平均孔径5、20和50 nm的管式陶瓷外膜制成膜冷凝器，并搭建膜面积0.3 m²的膜冷凝中试实验装置，开展陶瓷膜冷凝器在烟气水、余热资源回收及脱白烟领域的中试研究。对比采用不同排布方式的两级陶瓷膜冷凝器的水、热回收效果，考察进气相对湿度、进气温度、进气线速度等操作条件和不同孔径陶瓷膜的排布方式对膜冷凝器水通量及水回收率的影响。研究表明，在两级膜冷凝器中，烟气、冷却水均为串联流动时，可得到更高的水、热通量及回收率。过程水通量随进气相对湿度、进气温度、进气线速度的增加而增加；水回收率随进气相对湿度、进气温度的增加而增加，随着进气线速度的增加而降低。在三级膜冷凝器中，采用每级均填充平均孔径50 nm的管式陶瓷外膜的排布方式时，可获得最佳的水、热回收效果；不同孔径陶瓷膜的排布方式对膜冷凝器水回收效果影响明显，对热回收效果影响不大。在各实验工况下，三级膜冷凝器水通量及水回收率最高分别可达38.5 kg·m^–2·h^–1和50.6%。与传统换热器相比，陶瓷膜冷凝器不仅可实现水、余热的同时回收，且其总传热系数为415 W·m^–2·℃^–1，换热效果更佳，并能明显缓解“白色烟羽”等视觉污染。基于陶瓷膜的膜冷凝技术在中试实验阶段展现出良好的回收效果，在资源回收及脱白烟过程有广阔的应用前景。     

基于空冷的疏水陶瓷膜冷凝器用于烟气脱湿过程强化的实验研究

以环境空气为冷源,采用硅烷接枝的疏水Al₂O₃陶瓷膜构建膜冷凝器开展烟气脱湿实验。对比了疏水陶瓷膜与传统疏水钢管的冷凝性能;系统考察了烟气流量、烟气温度、吹扫因子、吹扫气温度、跨膜压差等过程参数对疏水陶瓷膜水回收性能的影响;比较了疏水陶瓷膜冷凝器(空冷)与亲水陶瓷膜冷凝器(水冷)的冷凝性能。结果表明,相同水接触角下(120°),多孔陶瓷膜的烟气温降是致密304钢管的1.3~2.5倍,疏水陶瓷膜能有效强化冷凝传热。疏水陶瓷膜的过程水通量随烟气流量、烟气温度、吹扫因子的增加而上升,随跨膜压差、吹扫气温度的增加而降低。过程水回收率随烟气流量、跨膜压差、吹扫气温度的增加而降低,随吹扫因子的增加而增加,随烟气温度的增加先上升,然后趋于稳定,而后下降。实验工况下,疏水陶瓷膜实现了0.6~5.2 kg·m^-2·h^-1的水通量和7.6%~57.4%的水回收率。低冷却介质流量下,基于水冷的亲水陶瓷膜的烟气冷凝性能更优异;随着冷却介质流量的上升,疏水陶瓷膜的冷凝性能迅速提升,并达到亲水陶瓷膜的性能。疏水陶瓷膜冷凝器在气体脱湿和水分回收领域有广阔的应用前景,将为改善工业过程的“能源-水资源-环境”关系助力。     

High-flux whisker layer ceramic membrane prepared by gel spin-coating method for low-pressure oil/water emulsion filtration

Insufficient permeability and membrane fouling significantly influence the efficiency of ceramic microfiltration (MF) membranes in oil/water emulsion treatment. In this study, a high-flux whisker layer ceramic MF membrane with super-hydrophilicity was successfully fabricated through gel-spin coating method and a low-temperature oxidation method, which was used to separate oil/water emulsion. The effects of the whisker layer and surface wettability were systematically investigated, and the mechanism of in-situ gelling and pore size distribution was proposed. The super-hydrophilic ceramic MF membrane with an average pore size of 250 nm exhibited a high gas flux of 934 m³/(m²·h·bar) and excellent pure water flux of 9754 L/(m² h bar). Even after a long-term circulating filtration process, the super-hydrophilic ceramic MF membrane still maintained a high water flux of over 50 L/(m²·h) at a transmembrane pressure of 5 KPa during the treatment of oil-in-water emulsion with a concentration of 1000 mg/L. Overall, the developed ceramic MF membrane demonstrated high permeability and excellent anti-fouling performance, making it a promising candidate for oil/water emulsion wastewater treatment.     

Preparation of a new ceramic microfiltration membrane from mineral coal fly ash: Application to the treatment of the textile dying effluents

New microfiltration membranes from mineral coal fly-ash material are obtained using ceramic method. Paste from mineral coal fly ash (obtained by calcinations at 800 °C of non-grinded mineral coal) is extruded to elaborate a porous tubular configuration used as supports. The support heated at 1125 °C, shows an average pore diameter and porosity of about 4.5 μm and 51%, respectively. The properties in terms of mechanical and corrosion resistances are very interesting. The elaboration of the layer based on fly-ash powder (obtained by sintering at 700 °C of a finely grinded mineral coal) is performed by slip-casting method. The heating treatment at 800 °C leads to an average pore size of 0.25 μm. The water permeability determined of this membrane is 475 L/h m² bar. This membrane can be used for crossflow microfiltration. The application to the treatment of the dying effluents generated by the washing baths in the textile industry shows an important decrease of turbidity (inferior to 1 NTU), of chemical oxygen demand (COD) values (retention rate of about 75%) and a total color removal. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 L h⁻¹ m⁻²). So, it seems that the prepared membrane is suitable for such wastewater treatment.     

Zirconia ultrafiltration membranes on silicon carbide substrate: microstructure and water flux

This study reported the preparation of ZrO₂/SiC ceramic membrane with silicon carbide as the substrate and intermediate layers and zirconia as the selective layer. The substrate and intermediate layers were sintered by evaporation-condensation process at 2200 and 1900 ℃, respectively. After sintering, the intermediate layer presented layer thickness of 50 μm, pore size of 0.87 μm and pure water permeability of 2140 L/(m²·h). The selective lay was deposited on the silicon carbide substrate by dip-coating method and then sintered in the temperature range from 800 to 1000 ℃. For the membrane coated by one dip-coating cycle and sintered at 800 ℃, it presented average pores of 82 nm and water flux of 850 L/(m²·h). Due to the exclusion of low-melting oxides during sintering, the ZrO₂/SiC ceramic membrane can satisfy the separation and purification of chemical corrosion and high temperature wastewater.     

多孔陶瓷膜烟气水分回收理论与模型研究

化石燃料燃烧烟气中含有大量水分和潜热,高湿度烟气的直接排放造成极大的资源浪费和环境问题。多孔陶瓷膜是目前烟气水热回收最有前景的技术之一,其水分回收热力学和动力学的定量描述是该技术发展和装置设计的关键所在。分析了水分在多孔陶瓷膜表面及内部传质机理,基于Kelvin理论建立了水分在陶瓷膜内毛细凝聚热力学模型,并选取典型烟气温/湿度条件,得出不同工况下陶瓷膜发生毛细凝聚的临界孔径、凝聚水量及工作孔体积占比;进而基于毛细凝聚的表面传质和孔道输运Hagen-Poiseuille方程建立了陶瓷膜水分传质动力学模型,对典型温/湿度工况下回收水通量进行了计算,结果表明,多孔陶瓷膜的毛细凝聚效应对烟气水分回收的优越性十分明显,其表面回水通量远远大于冷凝法的水通量,孔径越小,表面水通量越高,但及时将孔道内的液态水输运到陶瓷膜另一侧需要的压差也越大,本文计算条件下,膜孔径为20.0 nm的陶瓷膜较为适宜。     

Multifunctional fly ash-based GO/geopolymer composite membrane for efficient oil-water separation and dye degradation

Membrane fouling and separation materials with low cost and high efficiency are challenges for membrane separation technology in wastewater treatment. Superhydrophilic and underwater superoleophobic membranes show broad application prospects in oily wastewater treatment because of their high permeability, selectivity, and antifouling performance; however, they are generally ineffective for organic pollutant molecules. In this study, a novel graphene oxide (GO)/geopolymer composite membrane with superhydrophilic and underwater superoleophobic characteristics was prepared by dipping a mixed slurry of GO and fly ash-based geopolymer onto a stainless steel mesh via a facile self-assembly process. The results show that GO could adjust the hydrophilicity and water flux of composite membranes. The composite membrane containing 0.4 wt% GO (4GO/GCM) had the best hydrophilic, water flux of 1363 kg/(m²·h), and high separation efficiencies (≥98.2%) for oil-water mixtures and oil-in-water emulsions under gravity-driven. In addition, the 4GO/GCM sample exhibited excellent stability under harsh conditions, including hot water and strong acid, alkali, and salt solutions. Importantly, the sample derived from fly ash exhibited unique photocatalytic degradation performance for organic dye molecules under simulated solar-light irradiation. Thus, it is believed to this strategy has substantial potential for high-value utilization of fly ash and the sustainable treatment of oily and dye wastewater.     

多孔陶瓷膜烟气水分回收理论与模型研究

化石燃料燃烧烟气中含有大量水分和潜热,高湿度烟气的直接排放造成极大的资源浪费和环境问题。多孔陶瓷膜是目前烟气水热回收最有前景的技术之一,其水分回收热力学和动力学的定量描述是该技术发展和装置设计的关键所在。分析了水分在多孔陶瓷膜表面及内部传质机理,基于Kelvin理论建立了水分在陶瓷膜内毛细凝聚热力学模型,并选取典型烟气温/湿度条件,得出不同工况下陶瓷膜发生毛细凝聚的临界孔径、凝聚水量及工作孔体积占比;进而基于毛细凝聚的表面传质和孔道输运Hagen-Poiseuille方程建立了陶瓷膜水分传质动力学模型,对典型温/湿度工况下回收水通量进行了计算,结果表明,多孔陶瓷膜的毛细凝聚效应对烟气水分回收的优越性十分明显,其表面回水通量远远大于冷凝法的水通量,孔径越小,表面水通量越高,但及时将孔道内的液态水输运到陶瓷膜另一侧需要的压差也越大,本文计算条件下,膜孔径为20.0 nm的陶瓷膜较为适宜。     

Ceramic tiles derived from coal fly ash: Preparation and mechanical characterization

Coal fly ash (CFA) accounts for a large fraction of the solid waste produced in China. Hence, there is an urgent need for the effective utilization of CFA, for example, as a raw material for ceramics production. In this study, clay- and feldspar-like materials fabricated by alkali activation pre-treatment of CFA were mixed with untreated CFA (regarded as a quartz-like material) and sintered to prepare fully ash-based ceramic tiles. The obtained tiles exhibited excellent sintering properties, e.g., low firing temperature and a wide sintering range; further, they showed better green strength (due to hydrogen bonding) and post-sintering performance (due to fluxing and mullite skeleton effects) than ceramic tiles produced exclusively from untreated CFA. The fully ash-based ceramic tiles sintered at 1100 °C exhibited optimal post-sintering properties (bulk density, 2.5 g/cm³; rupture modulus, 50.1 MPa; and water absorption, 0%). Thus, the proposed method is well suited for preparing a novel kind of ceramic tiles completely derived from CFA, highlighting its importance in the field of fly ash ceramics.     

Influencing factors on the performance of tubular ceramic membrane supports prepared by extrusion

Inorganic ceramic membrane has the advantages of excellent thermal stability, mechanical strength, chemical resistance and fouling resistance. And it has been widely studied and applied in flue gas moisture recovery, gas purification and wastewater treatment. The support is the basis of preparation and application of inorganic ceramic membrane, and its performance determines the performance of the ceramic membrane to a certain extent. At present, extrusion is a common method used in the ceramic industry to prepare supports, which has the advantages of high production efficiency and good product uniformity. In this paper, the processes of preparing support by extrusion including mixing, vacuum pugging, aging, extruding and sintering are introduced in detail. In preparing support by extrusion, the product performance is easily affected by many factors, including the type of raw materials, raw material particles, extrusion parameters, pore-forming agents, sintering temperature, and sintering aids. Therefore, this paper also conducts a comparative and comprehensive study on the process parameters and influencing factors in the process of preparing ceramic membrane support by extrusion to obtain the support with the best performance. The main influencing factors that this paper focuses on are the types of raw materials, powder particles, water content, pore-forming agents, binders, sintering temperature, and sintering aids. The trends and mechanisms of these factors affecting the performance of the support are analyzed in detail.     

Elaboration and characterisation of low cost ceramic support membrane

Abstract

A porous tubular ceramic membrane was prepared from low cost Tunisian clay. The characterisation of the raw material and the effect of the sintering temperature on the morphology, pores size distribution and the mechanical properties of the ceramic membrane were studied. A ceramic membrane fired at 1000°C for 1?h presented a mean pore diameter of ～1·04?μm. The porosity was equal to 38?vol.-%. The filtration of a 0·5?g?L^?1 bovine serum albumin solution indicated that the limiting flux of permeate was 245?L?h^?1?m^?2?bar^?1, which corresponded to a retention rate of about 13%.     

Covalent crosslinked assembly of tubular ceramic‐based multilayer nanofiltration membranes for dye desalination

A tubular ceramic‐based multilayer composite nanofiltration membrane has been developed for dye desalination. Poly(acrylic acid)(PAA)/poly(vinyl alcohol)(PVA)/glutaraldehyde(GA) was dynamically assembled on to the inner surfaces of tubular ceramic microporous substrates which had been pretreated using dynasylan ameo silane coupling agents. Subsequently, the composite membranes were thermally crosslinked to form covalent ester bonds. Experimental results proved that the composite membrane had good nanofiltration performance for dye desalination. The (GA/PVA/PAA)₃/ceramic multilayer membrane shows over 96% retention of Congo red and less than 3% NaCl retention using a permeate flux of about 25 L/(m²·h). An investigation of membrane performance as a function of operating conditions suggested that the covalent crosslinking multilayer membrane possessed much higher stability compared to other, electrostatically assembled, multilayer membranes. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3834–3842, 2013     

Enhancement of super-hydrophilic/underwater super-oleophobic performance of ceramic membrane with TiO2 nanowire array prepared via low temperature oxidation

A gradient porous ceramic membrane with surface super-hydrophilic and underwater super-oleophobic performance was prepared by combining hydrogel directional freezing method and low temperature oxidation process. The effects of solid contents and sintering temperature on the ceramic membrane matrix were examined. The reaction time and synthesis temperature on the TiO₂ nanowire array were also evaluated. In addition, the related effects on pore size distribution, permeation flux, contact angle, and oil-in-water emulsion separation were systematically investigated. The ceramic membrane matrix pore size changed from 0.5 μm to 25 μm gradually, indicating the gradient structure controlled by the growth of ice. The super-hydrophilic and underwater super-oleophobic performance of ceramic membrane surface was obtained with surface modification by TiO₂ nanowire array, and the surface water contact angle and underwater oil contact angle were less than 5° and over 158°, respectively. The bonding strength between TiO₂ nanowire and ceramic membrane matrix was high enough to withstand ultrasonic waves. The ceramic membrane modified with TiO₂ nanowire array was used for 1000 ppm diesel oil-in-water emulsion separation, and the stable separation efficiency and flux were about 97% and 100–200 L/(m² h bar) even after 10 filtration cycles.     

Preparation of novel (MgCoNiCuZn)O high-entropy ceramic membrane and its dye separation

(MgCoNiCuZn)O high entropy ceramic (HEC) membrane was prepared successfully by phase inversion and calcination, and was used to remove Congo red. Raman spectra and XRD measurements showed complete transformation to single rock salt phase, and EDS exhibited uniform distribution of five metals. The hydrophilicity of HEC membrane became weak due to low free energy which was attributed to the high configuration entropy. The porosity of HEC membrane decreased and densification took place as the temperature enhanced, yielding the increase of bending strength. When the HEC membrane was calcined at 1040 ℃, the pure water flux and Congo red rejection reached 881.5 L/(m²·h) and 99.35%, respectively. The HEC membrane exhibited good long-term stability. When continuous filtration was performed for 10 h, the pure water flux ranged from 857.5 to 879 L/(m²·h), while Congo red rejection changed from 98.85% to 99.32%. The HEC membrane showed good chemical stability under weakly acidic and strong alkaline conditions.     

Sintering behaviour and characterisation of low-cost ceramic foams from coal gangue and waste quartz sand

New ceramic foams have been successfully synthesised with coal gangue and waste quartz sand, which supply a feasible way to recycle these hazardous solid wastes. An objective of this research was to investigate the sintering behaviour and effects of sintering conditions on the crystalline phase change, microstructure and main properties of final ceramic foams. Good correlations among porosity, thermal conductivity, water absorption, bulk density, mechanical properties were studied. Results indicated that increasing sintering temperature or time had similar effects on the physical–mechanical properties. Samples sintering at 1140°C for 1 hour exhibited the highest porosity (87.5%), lowest bulk density (0.39?×?10^?3?kg?m^?3), lowest thermal conductivity (0.085?W·(m?K)^?1), moderate water absorption (9.38%) and adequate flexible strength (2.4?MPa). Combined with excellent properties and low-cost characteristics, the new development for ceramic foams preparation will be widely used in building insulation materials for no-load bearing walls.     

Tuning microstructures and separation behaviors of pure silicon carbide membranes

This study reports the preparation of silicon carbide ceramic membranes with pure silicon carbide particles without sintering aids. The effects of sintering temperature on the microstructure, mechanical and filtration properties were investigated. The porosity of the substrate layer increased from 37% to 41% when the sintering temperature ranged from 2150 to 2300 °C, whereas the flexural strength increased from 14.5 to 18.2 MPa. The separation layer was coated on the substrate layer using a spray process. When sintered at 1850 °C, a smooth and defect-free layer was formed with an average pore size and layer thickness of 1.2 and 60 μm, respectively. With the increase of average pore size, the filtration flux increased from 2650 to 2800 L/(m² h bar). Such ceramic membranes can be used to separate corrosive wastewater and high-temperature wastewaters owing to the exclusion of sintering aids, unlike the conventional ceramic membranes.     

CRITICAL FLUX DETERMINATION IN ULTRAFILTRATION OF WASTEWATER FROM A FOOD INDUSTRY BY OPTIMIZATION METHOD

Two ultrafiltration membranes with different geometries (spiral polymeric and tubular ceramic) but similar cutoffs were used to treat wastewater from a food industry. Hydrodynamic conditions were optimized by statistical methods as a strategy to get more accurate values of the critical parameters and then to produce higher water flux and minimization of membrane fouling. The validation of the optimization method was obtained by experimental critical flux determination at critical parameters. Membrane fluxes revealed significant differences during filtration. The polymeric membrane showed an optimal flux of 45.60 Lh^?1 m^?2 at 3.21 bar while operating at a stable time of 11.61 h, whereas optimal flux of the ceramic membrane was 32.43 Lh^?1 m^?2 at 3.98 bar for 16.03 h. Experimental critical flux values were only slightly lower than optimal fluxes for both membranes, showing the validity of the statistics models applied. Negligible osmotic pressure was found on the two membranes at critical flux parameters, indicating irreversible fouling for both cases. The polymeric membrane revealed strong fouling behavior and the ceramic membrane showed a weak form; the flux decline occurred first in the polymeric membrane, whereas the ceramic membrane exhibited high stability during the filtration operations. A high degree of purification of wastewater was obtained by this membrane at critical flux conditions.     

单通道陶瓷膜管低压透水性能实验分析

无机陶瓷膜作为多孔介质具有分离效率高、耐酸、耐碱等优点,被视为在海水淡化、废水处理、气体分离等领域的研究热点。采用Al₂O₃管式单通道陶瓷膜材料构建膜组件,以燃煤电厂自来水、烟气冷凝水、脱硫废水三种不同水质为例,开展低跨膜压差下的膜组件透水性能实验,研究了膜参数、跨膜压差及水体温度等因素对渗透通量、渗透水质的影响,并对引发膜污染的机理过程进行了探讨分析。实验结果表明：陶瓷膜管的结构参数是关键因素,如孔隙率、孔径及厚度等;低跨膜压差下的渗透通量随压力增大呈线性提高,并未发现浓差极化现象,水体温度变化通过改变黏度进而影响渗透通量,同时水质较差时会导致渗透通量降低;陶瓷膜管的孔径是影响渗透水质的核心要素,微滤与纳滤膜对改善悬浮物含量、浊度及色度效果明显,不同孔径对盐度、电导率影响不同;从SEM图可以看出,污染物在膜表面或膜内部发生的沉积、架桥等现象导致严重的膜污染。充分认识影响陶瓷膜管渗透特性的关键因素及污染物的作用机理,对提高无机陶瓷膜的应用前景具有重要意义。     

Development of high strength,porous mullite ceramic hollow fiber membrane for treatment of oily wastewater

Ceramic hollow fiber membranes (CHFMs) are known for their excellent characteristics including high surface area, compact design, and good chemical, thermal, and mechanical stabilities. Despite these interesting attributes, CHFMs are also prone to certain limitations, such as brittleness and high cost that hinder them from being commercialized. To mitigate this drawback, we have developed a high strength, porous ceramic hollow fiber membrane, derived from mullite–kaolinite powder, for efficient oil–wastewater separation. The superhydrophilic, low-cost mullite-based (CHFM) was successfully fabricated through combined phase inversion and sintering techniques. Prior to the fabrication, the as-received mullite–kaolinite was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analyses. Subsequently, operational parameters such as the effect of mullite content, sintering temperature, and air gap were optimized during the fabrication of mullite ceramic hollow fiber membrane. The resulting membranes were systematically characterized and evaluated in terms of morphology, porosity, mechanical strength, water flux, and oil–water separation. Increasing the mullite content, air gap, and sintering temperature enhanced the formation of microvoid structure. It is interesting to note that the mechanical strength of 86 MPa was obtained for the membrane containing 60 wt % of mullite sintered at 1450 °C and an air gap of 5 cm. The membrane induced a stable permeate water flux and oil rejection of mullite CHFM of 182 L/m²?h and 97.1%, respectively. As compared to kaolin ceramic counterparts, this porous mullite ceramic hollow fiber membrane can be used in various water treatment applications, including for the separation of oily wastewater due to its mechanical strength and water flux.     

Robust super-hydrophobic inorganic nanoparticles modified layered structure Si2N2O membrane for membrane distillation

Robust super-hydrophobic ceramic membranes consisting of layered structure Si₂N₂O grains and organosilane-derived inorganic nanoparticles were successfully fabricated and employed for membrane distillation. First, phase inversion and sintering method were used to prepare porous Si₂N₂O membranes. The slurry composition and sintering temperature were optimized to obtain a pure phase Si₂N₂O membrane with high bending strength, tailored average pore size, and high permeability. Then, the Si₂N₂O membranes were modified with organosilane-derived inorganic nanoparticles through ammonolysis and pyrolysis reactions. Due to the micro and nano-hierarchical rough structures and the presence of -Si-CH₃ groups, the membranes showed super-hydrophobicity with a water contact angle of 152 ± 1°. Finally, the membranes were applied to desalinate seawater by sweeping gas membrane distillation. A stable water flux of 76 ± 0.9 L/(m² day) with a salt rejection of > 99% was recorded during 30 h distillation test at 75 °C, demonstrating the stability and durability of the membranes.