What are the characteristics of carbon sintered tube filters?

I want to know that too; could that brother give an answer?

1 The significance of carbon tube filters in ion membrane electrolysis: The chelating resin column in the secondary purification system can only remove Ca2+ and Mg2+ from brine, but not SS. If suspended particles enter the chelating resin system, they will clog the micropores of the resin, thereby significantly reducing the performance of the chelating resin system. By using carbon tube filters during the secondary purification process, it is ensured that the chelating resin can perform its functions optimally; as a result, its regeneration cycle is extended by 3 to 5 times compared to when no carbon tube filters are used. This reduces the amount of ion exchange membrane alkali and high-purity hydrochloric acid required for regeneration, and in particular prevents impurities from entering the ion exchange membrane electrolyzer. 　　Our factory uses DuPont’s NE966TX perfluorosulfonic acid/carboxylic acid composite membrane; excessive SS will precipitate as crystals on the membrane, causing irreversible physical damage to it. At the same time, organic impurities can cause the membrane to swell, thereby leading to an increase in cell voltage and a decrease in current efficiency. Carbon tube filters can not only remove SS from the primary purified brine but also prevent the degradation of the chelating resin properties, thereby extending the service life of the ion exchange membrane. 2 　Overview and operating principle of carbon tube filters 2.1 　Overview of carbon tube filters 　In 1961, the German company Schleicher & Schnell was the first to develop carbon tube filters (Tubular Modules). Their excellent performance enabled them to be used for filtering various liquid substances, and they feature long operational life, high efficiency, as well as good corrosion resistance. The filtering element is a carbon sintered tube (cylindrical, with an outer diameter of 120 mm, an inner diameter of 70 mm, and a length of 500 mm). The two filters in our plant (with a surface area of S = 12 m2, 64 carbon tubes per filter, and specifications of Φ 1,100 × 4,700) have containers and components made of steel lined with low-calcium magnesium glue; they operate alternately, one in use and the other as a backup. 2.2 Properties of carbon sintered tubes Carbon sintered tubes are formed by sintering a porous carbon material that is created by molding pure carbon along with petroleum coke (whose main component is C). It has good chemical resistance to corrosion; aside from being unsuitable for use with strong oxidizing agents, it can be used in acidic and alkaline solutions at temperatures up to 200 ℃. 2.3 Filtration aids – α-cellulose and its use 2.3.1 α-Cellulose α-Cellulose is obtained by hydrolyzing refined cotton; its molecular formula is: N, where N = 170–200. Our factory uses α-cellulose produced by the Salt Chemicals Plant of Sinopec Jianghan Oilfield Branch. The particle size distribution is as follows: the proportions of α-cellulose with particle sizes of 250 μm, 200–250 μm, 150–200 μm, 100–150 μm, and 50–100 μm are 30%, 17%, 26%, 26%, and 1.0% respectively. The particle size distribution of α-cellulose is related to the pore size of the carbon tube (average 110 μm). If the fibers are too fine, they can easily clog the capillaries, increasing the filtering resistance; if the fibers are too coarse, their adhesion is weak and they tend to fall off, resulting in an increased use of alpha-cellulose and poor filtering performance as well. Therefore, the particles of cellulose need to be coarse and uniform. 2. 3. 2 Use of α-cellulose 　　 The use of α-cellulose involves the pre-coating method and the slurry addition method. The pre-coating method is used to prevent the clogging of the micropores in carbon tubes and to improve filtration accuracy. Before filtration, the filtering aid α-cellulose (12 kg per batch) is first dispersed in saline to prepare a pre-coating solution, which is then used for cyclic filtration in the filtration tank. Through cyclic filtration, a pre-coating layer with a thickness of 2–3 mm can be formed on the surface of the carbon tube. 　　The slurry addition method involves pre-adding a filter aid to the refined brine at the beginning. The added filter aid acts as a nucleating agent in the saltwater, promoting the crystallization of soluble calcium carbonate present in it; it also helps to coagulate tiny particles of SS, thereby improving the precision of filtration. This filtration method can delay the increase in filtration resistance, extend the filtration cycle, and reduce the amount of filter aid required per unit volume of brine. 2.4 Working process of carbon sintered tubes: During filtration, brine passes through the pre-coating and enters the filter chamber, causing the residues to be retained on the outer surface of the element. After use for a certain period of time, when the filtration speed decreases, the filtration pressure difference exceeds 0.2 MPa, or the SS content in the filtered saline is high, the filter should be replaced after every 48 hours of operation. It should then be cleaned repeatedly 4 times using pure water (instead of the cleaning saline) and compressed air at 0.45 MPa. During washing, the flow direction of the material is opposite to that during filtering; the washing liquid exits the filter chamber and passes through the filter elements to remove the residues attached to their outer surfaces. After cleaning, fill the filter with filtered saline and set it aside for use. 3 　Discussion on the filtration mechanism of carbon sintered tubes 　The entire filtration process involves filter cake filtration and deep filtration. Firstly, there is surface adsorption and mechanical interception between the filtered particles and the filtering medium, but the filtration process is primarily confined to the surface layer of the filtering medium, rather than its deeper layers. As surface filtration progresses, pore bridging occurs at the surface capillaries, and eventually the filtration process shifts from the pore openings to outside the surface of the filtering medium, resulting in thin-layer filter cake filtration. 3.1 Filter cake filtration: During filtration, brine passes through the pre-coating and enters the filter chamber, causing the residues to be retained on the outer surface of the sintered tube, thus forming a filter cake. Assuming that the solid particles in the filter cake layer are stationary, and that the porosity as well as the average flow velocity of the fluid through the filter cake layer remain constant, it can be considered as pressure-controlled filtration. That is, during the process the filtration pressure remains constant; the filter cake continues to thicken, the filtration resistance keeps increasing, and the filtration rate decreases continuously. The basic equation for its constant-pressure filtration process is: t = a1·V²/2·S²·ΔP + b1·V/S·ΔP. (1) In the formula: V is the volume of the filtrate, in m3; t is the filtration time, in seconds; ΔP is the pressure difference during filtration, in Pa; S is the filtration area, in m2; a1 is a constant related to the properties of the feed suspension; b1 are constants related to the filter cloth and the filtrate. 　　With all parameters known, the relationship between the volume of the filtrate and the required filtration time is determined by Equation (1). 3.2 Deep filtration The deep filtration process takes place within the filtering medium, with a filtration speed of generally 5–15 m/h. Its filtration mechanism is relatively complex: under the combined action of factors such as gravity sedimentation, diffusion, and hydraulic effects, solid particles are transported to the surface of the pores in the filtering medium, where they are adsorbed by electrostatic or molecular forces (see Figure 3). 4 　Effect of free chlorine on carbon tubes: The free chlorine content in the brine used for primary purification is relatively high (primarily in the form of hypochlorite ions). Free chlorine reacts chemically with the carbon present in the carbon tubes, as well as with petroleum coke, which serves a bonding role. The reaction equation is as follows: C + 2ClO- → 2Cl- + CO2 ↑. (2) This reaction increases the size of the pores in the carbon tubes; a small amount of α-cellulose and S.S. enter the interior of these tubes, causing the micro-pores to become blocked. As a result, backwashing is not effective, which leads to an increase in filtration resistance. In severe cases, this can cause the carbon tubes to rupture. Such situations have occurred both in our factory and in a chlor-alkali plant in the southwest. 　 This post was last edited by yzhms on 2009-3-12 13:40]

Carbon sintered tube filter: The housing of the carbon sintered tube filter is made of a steel substrate with a rubber anti-corrosion coating. Inside, multiple sets of carbon-based tubes are evenly fixed on a frame; its structure is shown in Figure 6-2. The filtration area of carbon tube filters depends on the production capacity; generally, for a plant with an annual production capacity of 10,000 tons, the filtration area is around 7–8 m2, and the service life is 8–10 years. The carbon-silicon sintered tube is made by sintering pure condensed material; it has an outer diameter of 120 mm, an inner diameter of 70 mm, and a length of 500 mm, and is a cylindrical component. The properties of the formed cut-rope sintered tubes are shown in Table 6–1. The characteristic of carbon-sintered tube filters is that they can be regenerated and reused after being used for a certain period of time. The filtration principle of carbon sintered tubes is shown in Figure 6-3. Once, the refined brine flows from the outside of the cylinder into its interior for filtration. Suspended particles are trapped outside the carbon tubes. To maintain the highest filtration accuracy, a pre-coating of filter aid is first applied outside the carbon tube; the thickness of this pre-coating is approximately 2–3 mm. The filter aid is added in such a way that a fixed amount of it is mixed with the initially purified saline before being fed into the filter for filtration. The initial resistance during filtration is 0.02 MPa, and as suspended particles accumulate in the saline, this resistance gradually increases. When it reaches 0.15–0.20 MPa, the filter should be stopped from use and cleaned for regeneration. However, if the concentration of suspended particles in the saline is low, the filter can continue to be used for up to 48 hours even if the pressure does not reach 0.15–0.20 MPa ； In that case, it too needs to be stopped for cleaning and regeneration in order to maintain long-term stable operation. Name, Nature, Chemical Composition, Chemical Resistance, Particle Size, Pore Size, Average, Maximum, Porosity, Flexural Strength, Density, Specific Heat Capacity, Thermal Conductivity, Coefficient of Thermal Expansion, Dimensions: Carbon-free pure carbon, 99.93%. Suitable for acidic, neutral, and alkaline solutions from low temperatures up to 200°C, with the exception of strong oxidizing agents. 40#: 100, 180, 42%; 35.2×106 Pa (36 kgf/cm2); 1.1 kg/m3; 1.163 W/(m·K)°C; 5.0×106/°C. Outer diameter: 120 mm ； Inner diameter 70mm ； With a length of 500 mm, Table 6-1 shows the properties of carbon tubes. The cleaning and regeneration of carbon tubes involves backwashing the cleaning solution from inside the tube to the outside, while simultaneously introducing compressed air at 0.45 MPa. When the special drain valve is quickly opened, the brine, under the pressure of the compressed air, flows rapidly from the inside of the tube to the outside, thereby removing the pre-coating on the outside of the carbon tube as well as any suspended particles that have accumulated there. After going through these cleaning steps, the tubes can regain their original properties and be reused. This post was last edited by haining on 2009-3-12 13:29]

Are they referring to graphite filters?

Where can I buy carbon sintered tubes?