Introduction to Stainless Steel Tubular Membranes

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Introduction to Stainless Steel Tubular Membranes 1.1 Overview and Working Principle of Stainless Steel Tubular Membranes Stainless steel tubular membranes can be widely used for the clarification of various types of fermentation broths. It can effectively remove suspended solids in the system (such as silica, kaolin, and metal precipitates like calcium and magnesium), bacteria, yeast, most oils and fats, glucose sludge, colloids, and solid proteins. It can replace traditional separation methods such as plate and frame filters and centrifuges to clarify fermentation broth. For example: the clarification of fermentation broths such as antibiotics, organic acids, amino acids, glucose, etc. Stainless steel tubular membranes – utilizing a counter-current flow pattern – have proven to be the most effective, reliable, and cost-efficient membrane separation method. The cross-flow method prevents clogging during dead-end filtration. The feed stream flows over the surface of the membrane; under pressure, the liquid passes through the membrane, while solid particles and suspended matter are retained. The feed stream has a sufficient flow rate to remove the solid particles trapped by the membrane from its surface. This continuous removal prevents the accumulation of solid particles on the membrane, thus minimizing membrane fouling. This makes the filtering process an extremely simple task, enabling a high degree of automatic control in the production process. The cross-flow process also avoids the need to rely on a filter cake layer for filtration during dead-end filtration processes (such as plate and frame filter presses or drum vacuum filters); separation occurs on the surface of the membrane rather than within the filter cake layer, thereby ensuring that the quality of the filtrate remains uniform and stable throughout the process. The quality of the filtrate depends on the membrane itself, keeping the production process under complete effective control. 1. Structure of the stainless steel tubular membrane: The porous stainless steel tube forms the basis of the counterflow system; it is produced by compressing granular 316L stainless steel powder and then sintering it at extremely high temperatures and under reduced pressure. No binders or other materials that may cause contamination are used in the preparation process. The sintered tube is not quenched; it is an austenitic stainless steel with an extremely low carbon content and is non-magnetic. During the manufacturing process of the membrane tube, a patented technology is used to permanently apply a titanium dioxide layer to the inner surface of the stainless steel tube. The titanium dioxide layer is formed by titanium dioxide particles that are bonded to the stainless steel tube through firing. It is an FDA-approved material. The effective pore size of the titanium dioxide layer is 0.05–0.1 um, resulting in an asymmetric membrane structure. Stainless steel membrane modules are similar to tubular heat exchangers in terms of structure and operational characteristics. The diameter of the membrane module can reach 1.27M, and its length can reach 6.1M. The components are manufactured in accordance with ASME (American Society of Mechanical Engineers) standards. The maximum filtration area per membrane module can reach 801 M2. Standard specifications: Nominal diameter (in): 0.75; Standard inner diameter (in): 0.72; Standard outer diameter (in): 0.85; Standard wall thickness (mm): 1.5; Recommended operating temperature (°C): 10–90. Advantages of stainless steel tubular membranes: Traditional membrane materials and membrane module designs, in many applications, suffer from reduced membrane lifespan, longer downtime for cleaning, and high operating costs due to limitations related to operating temperature, pressure, pH, and cleaning methods, as well as narrow feed channels. And stainless steel membranes solve these problems. The stainless steel membrane system combines robust stainless steel tubes with patented coating technology to provide a membrane separation system that achieves excellent separation performance under harsh process conditions, as well as reliable operation over many years. Cross-flow technology and an inert stainless steel structure make the membrane separation system an essentially flawless system. The system can handle a wide variety of difficult-to-filter liquid systems under extremely broad ranges of chemical conditions, pressure, and temperature. For applications under certain extremely harsh conditions, no other membrane equipment can fulfill the requirements. The stainless steel membrane separation system has proven to be particularly effective, especially for systems with high solid contents or high viscosities, or for processes that must be carried out at elevated temperatures and/or pressures, or at extremely high or low pH levels. Main advantages of stainless steel membranes: Ø Long service life – The stainless steel material and special manufacturing process confer a long service life to the stainless steel tubular membranes. Ø High separation precision: A separation aperture of 0.1um enables 100% removal of mycelium, colloids, and solid proteins. It can also remove many metal ions, and effectively eliminate the soluble proteins that precipitate from the fermentation broth. Ø Pollution resistance: Thanks to a special manufacturing process, the surface of the metal membrane is made of an inorganic material with extremely high smoothness; as a result, no proteins adhere to the membrane surface, making it resistant to pollution. Throughout the operation, the flux remains relatively stable, which ensures high clarification efficiency and simplifies process control. Ø High-pressure resistance: Stainless steel membranes possess high mechanical strength and toughness, enabling them to withstand pressures of up to 10 kg/cm2, as well as various vibrations and shocks that are inevitable during system operation. Ø High-temperature resistance: Thanks to the material of the membrane and the sealing method used in welding, the membrane module can withstand high temperatures, eliminating the risk of leakage or damage to the filter membrane due to excessive temperatures or temperature fluctuations. Ø Wide channels: In the later stages of the process, the bacterial concentration is very high; the membranes in narrow channels are prone to clogging, resulting in high pressure losses, and under such conditions the membranes are likely to get damaged. Stainless steel tubular membranes have wide channels with an inner diameter of 19 millimeters, making them suitable for applications with high cell contents in the feed solution. Ø No leakage: The membrane components are welded together as a whole, eliminating the need for polymer seals; thus, leakage is impossible. Ø It is easy to clean. It can withstand high temperatures and pressures, as well as a wide range of pH values; therefore, the cleaning conditions for this membrane are very flexible. Moreover, its smooth and dense surface makes the cleaning process extremely simple. Ø The system process is simple and requires minimal space. It features a filter membrane system with the fewest possible pipelines, valves, instruments, and controls, making it simple and compact. With only a small number of components, faults are easy to resolve, the system operates stably, and its utilization rate is high. The processing capacity of the membrane depends only on the diameter of the component, not on the number of components, thus minimizing the floor space required. Wide applicability – it can be used for the treatment of various types of fermentation broths, and the system can serve multiple products simultaneously. 1. Application areas of stainless steel tubular membranes: Over the years, stainless steel tubular microfiltration systems have been successfully applied in a wide range of fields, including the treatment of fermentation broths and culture media, the clarification of sugars, the concentration of proteins, and the recovery of products from waste streams. For many fields, stainless steel membrane separation systems are the only option. This is because no other membrane technologies can meet the requirements. In other applications, the reliability of the membrane and its long service life make it an obvious and cost-effective choice. Fermentation and Biotechnology: Clarification of antibiotic fermentation broths and cell recovery; Clarification of amino acid and organic acid fermentation broths; Protein separation or recovery; Recovery of yeast; Recovery of enzyme preparations; Continuous enzyme conversion systems; Clarification of solutions treated with activated carbon; Sugars, sweeteners, flavorings, and food products: Clarification of glucose, fructose, and oligosaccharide syrups; Removal of sugar sludge; Separation of modified starch; Separation of medium-starch; Separation of extracts; Clarification and filtration of vinegar and soy sauce; Recovery of rice starch from wastewater; Papermaking: Concentration of washing wastewater; Concentration of pigment/decolorization wash liquids; Separation and recovery of black liquor; Concentration and recovery of sulfite wastewater; Recovery of white water; Sludge dewatering; Chemical/Petrochemical industries: Recovery of catalysts; Recovery of monomers; Recovery of used oil; Oil/water separation; Separation of dyes; Textile industry: Recovery of dyes; Recovery of PVA; Recovery of alkalis; Concentration of textile polishing agents; Beverage processing: Clarification of fruit juices; Clarification of alcoholic beverages; Clarification of tea products; Surface treatment: Concentration and recovery of electroplating wastewater; Recovery of alkaline degreasing solutions; Environmental protection: Concentration of hazardous wastewater; Recycling of hot water/wastewater in electroplating processes; Nuclear industry: Recovery of enriched oil; Concentration of low-radioactivity waste. 1.5 Characteristics of the liquid to be treated – Fermentation broths: Fermentation broths or culture media are complex multiphase systems that contain cells, metabolic products, and unused culture medium. The solid and colloidal substances dispersed within it are compressible, have a density similar to that of liquids, and exhibit high viscosity; they are non-Newtonian fluids, which makes it difficult to separate the solids from the fermentation broth. Finding an effective method for treating the fermentation broth can significantly improve the overall efficiency of the post-extraction process. Fermentation broths or culture media are usually processed in batches, and there is significant biological variability as well as differences between batches; this requires that the processing methods be flexible, especially when dealing with batches that are contaminated by bacteria. To facilitate the separation of the fermentation broth, a conventional approach is to add various filter aids and flocculants to improve its properties. However, this method introduces new impurities into the system to be treated, increases the workload of subsequent processing steps, and may damage some of the products. It increases the extraction cost and reduces the extraction yield. Furthermore, the fermentation broth generation process produces large amounts of wastewater and waste residue, with high BOD and COD levels, which must be treated before they can be discharged. The cost of waste disposal has a significant impact on production costs. Therefore, it is crucial to find a direct treatment method for the fermentation broth. Appendix: Cell conditions of several common fermentation broths: Bacterial species in the fermentation broth, cell diameter (um), cell content (dry weight %), and pH of the system. Glutamic acid bacillus: 0.7–1.0, 1–26.5, 7.5–7.5; Lysine bacillus: 0.7–1.0, 1–26, 7; Citric acid Aspergillus: 5–10, 8–10, 1.0–2.0; Amylase bacillus: 0.74, 7.2; Glycosidase Aspergillus: 51, 54.0; Yeast: 55, 5.0; Riboflavin bacillus: 0.74, 7.2; Pyridoxine bacillus: 0.74, 7.2; Penicillin Penicillium: 5–10, 11–14, 6–7; Streptomycin Streptomyces: 0.58–10, 6–7; Gentamicin Micromonospora: 0.3–0.6, 8–10, 6–7; Erythromycin Rhodococcus: 0.5–0.8, 8–12, 6–7