Selection of pipe materials around ion-exchange membrane caustic soda electrolyzers
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This post was last edited by sunjl1981 on 2013-1-7 00:06. Regarding the material of the pipes surrounding the ion membrane electrolyzers, if they are purchased domestically (which is generally the case), I would like to know what materials are used in the electrolyzers operated by various companies – which manufacturers use what materials? How is it after using it? Regarding the tanks used in chlorine processing, from what I understand: 1. For the feed brine (typically 300–310 g/l NaCl), Ti tubes are recommended; in some projects, steel lined with rubber or steel lined with PTFE is used. I would like to know how effective these materials are in practice I’m not sure if there are any projects that use CPVC-L (low calcium and magnesium) + FRP (Regarding pipes made of certain plastics, many foreign ones can meet the process requirements, while domestic ones may not be able to do so – it’s a bit sad.) 2. Circulating brine (usually 200–210 g/l NaCl): Ti pipes are recommended; steel-lined PTFE pipes are also used. Plastic pipes are generally not recommended, especially in the outlet pipes of pumps, where there is several kilograms of pressure and higher requirements are placed on the pipes. Regarding steel-lined PTFE, I would like to ask whether free chlorine in saltwater can cause erosion of the PTFE. 3. Wet chlorine gas (pressure generally within 400 mmH2O, temperature generally not exceeding 90°C): Ti tubes are recommended; it is unknown what the performance would be for systems using C-PVC+FRP or PVC+FRP. 4. Circulating alkaline solution (about 30%, temperature of 80–90°C). In China, steel-lined PTFE is generally used; it is not clear whether there are any projects that use PP+FRP. 5. Hydrogen has relatively low requirements for pipelines. This post was last edited by yzhms on 2008-3-2 01:25 ] # hcbbs
If you have money, use titanium tubes; if not, use UPVC to cover fiberglass
Do not use PP+FRP for circulating alkaline solutions; it is not heat-resistant and prone to deformation. The anode is preferably titanium.
1. Feed brine: Our factory uses steel lined with rubber, and after more than 2 years of use it still performs well; the outlet pressure of the brine pump is 0.55 MPa. The biggest concern here is the rubber lining coming off, allowing iron ions to enter the electrolytic cell. 2. Circulating brine: titanium tubes are used. The temperature of the brine coming out of the tank is high, and coupled with the pressure of 0.3 MPa at the pump’s outlet, it cannot be used. 3. Circulating alkali solution: 310S stainless steel is used. This post was last edited by yzhms on 2009-2-27 13:20]
The outlet on the anode side is made of FRP or FRP+CPVC, the inlet is made of FRP+CPVC, and PPH can be used when brackish water is not recycled. The outlet on the cathode side is made of PPH or FRP+CPVC, while the inlet is made of FRP+CPVC or PPH. This post was last edited by yzhms on 2009-2-27 13:21]
Do not use steel-lined rubber for circulating brine, as this can lead to localized cracking of the rubber lining, allowing iron ions to enter the brine. Moreover, free chlorine is corrosive to tetrafluoroethylene, as fluorine is more reactive than chlorine!
For circulating alkaline solutions, PPH or steel-lined PTFE is a good choice, as it offers good durability and a high safety factor!
Alkaline SUS310L, Ni% >= 20% Last edited by yzhms on 2009-2-27 13:25]
Another option is to use fluoroplastic pipes with an added FRPR layer. This post was last edited by yzhms on 2009-2-27 13:28]
The material used for filtering saltwater is titanium, while the secondary saltwater uses PPH. The finished alkali is made of 316L; the parts related to the circulating alkali are made of nickel, while the material used for the circulating alkali itself is PPH. Wet chlorine gas is made of FRP, dry chlorine gas is made of carbon steel, and hydrogen gas is also made of carbon steel. This post was last edited by yzhms on 2009-2-27 at 13:27
Generally, in the anode solution circulation section, that is, around the electrolyzer, titanium tubes are used, while SUS310S pipes are employed for the cathode. In the case of Asahi Kasei/Kita Kikai’s electrolyzers, some manufacturers use PPH pipes instead of metal pipes. Wood’s electrolyzers typically use plastic pipes – PPH pipes
Titanium tubes; if there’s no money, use UPVC to cover the fiberglass. Some of our clients have used this approach
CPVC is used for the feed brine, titanium tubes are used for the circulating brine, and stainless steel tubes are generally used for alkalis
Feed brine: steel-lined CPVC with low calcium and magnesium content; Ti material can also be used. It is somewhat wasteful; Ti is required for circulating fresh brine. Rubber-lined pipes cannot withstand high temperatures, and long periods of shutdown or shutdown in winter make it difficult for the rubber lining to adhere properly. For alkaline solutions, 310S stainless steel is used
Regarding the tanks used in chlorine processing, as far as I know: 1. For the feed brine (typically 300–310 g/l NaCl), TI is the best choice; those designed with FRP have always encountered problems, and it’s possible to use CS+PTFE during major repairs. Replacing TI is too expensive. 2. Circulating brine (typically 200–210 g/l NaCl): The same as above; no erosion of PTFE has been observed so far. Moreover, it is also used in other areas where there is free chlorine, so there should be no problem. 3. Wet chlorine gas (pressure generally within 400 mmH2O, temperature generally not exceeding 90): C-PVC+FRP is used. Both pressure and temperature are within acceptable ranges, so there’s no problem; however, attention should be paid to the corrosion issue of the expansion joints. 4. The circulating alkaline solution (about 30%, at a temperature of 80–90°C) initially used PP+FRP materials, but later SS materials were used instead
The part that connects the feed pipe and the discharge pipe is made of polytetrafluoroethylene; it allows visibility of the fluid, while the rest is made of titanium. The gas-liquid separator is made of PVC
Never use ordinary stainless steel! Otherwise, at 90°C and with 32% alkali, iron ions can easily precipitate and contaminate the membrane. Last edited by yzhms on 2009-2-27 13:20.]
12# caijie1231 May I ask which manufacturer you represent?
Let’s talk about our situation: 1. For the feed brine, we use a steel-lined PO layer before it enters the system; after passing through the chelating resin tower, CPVC is used, and titanium tubes are employed after heating. So far, no problems have occurred with this setup. CPVC-L (low calcium and magnesium) + FRP is recommended for use in applications with low pressure and temperature. 2. Circulating brine (typically 200–210 g/l NaCl): Uses Ti tubes to meet the pressure requirements of the pump’s outlet pipeline. 3. Wet chlorine gas (pressure generally within 400 mmH2O, temperature generally not exceeding 90): Ti tubes are recommended. However, to control costs at that time, we opted for FRP pipes, taking the following points into consideration: A/ A large temperature difference between the inside and outside can have an impact on the FRP pipes themselves; B/ There is the issue of pipe expansion, which is addressed by using fixed supports in combination with guide supports. Generally, the spacing between fixed supports is 90 meters, and π-shaped expansion joints can be installed in between, or the pipeline can be routed in such a way as to relieve expansion stresses. It can be determined based on the specific conditions of the project route. C. For corrosion resistance, D470 resin can be used for the lining and structural layers. Wet chlorine is a highly corrosive and dangerous medium, so material selection should prioritize safety considerations. It is recommended to set the lining thickness at 5mm. 4. Circulating alkaline solution (about 30%, temperature of 80–90 degrees). 316L stainless steel is used; initially, PPH+FRP was considered, but its linear expansion coefficient is too high – it exceeds 150 mm/10M at a working temperature of 90 degrees – and the welding quality cannot be guaranteed, which poses potential risks.
Regarding CPVC-L (low calcium and magnesium content), I searched for information on this topic but found nothing relevant. In many chlor-alkali projects, CPVC pipes are used directly, as the calcium and magnesium content in them is already very low. I wonder if the original poster has learned anything more about the suppliers or use cases later on?