Pain Points of Sulfur Conditions: Why Can't Ordinary Skins Hold?
The skin of the newly installed non-metallic compensator cracked in less than half a year, and the scene was in a mess. Such things are too common in power plants and chemical plants. There are not only SO₂ and SO₃ in sulfur-containing flue gas, but also high-temperature water vapor, which becomes dilute sulfuric acid when it meets condensed water, and the pH value can be as low as 1~2. Ordinary rubber skin or ordinary fiber cloth in this environment is just like paper paste-first bulging, then corroding and perforating, and finally the whole layer falls off. The reason is simple: the inner material of conventional skin usually only considers temperature resistance, but not strong acid resistance. When it encounters acid dew point corrosion, its life is directly discounted in half. Therefore, the skin of non-metallic compensator with high sulfur content must be selected separately, and you can't just make do with a general model.
Skin Structure Disassembly: Which Layer Is Helping You Carry Sulfur Corrosion?
The skin of a non-metallic compensator (also called a fabric fiber expansion joint), which looks like a piece of cloth, is actually a multi-layer composite structure. Let's count from the outside to the inside: the outermost layer is silicone rubber coated glass fiber cloth, which is responsible for weather resistance and UV resistance; In the middle is an insulation layer, usually ceramic fiber felt or aluminum silicate wool, to insulate heat; The innermost layer is in direct contact with flue gas, called corrosion isolation layer, which is the key to sulfur resistance.
What is used for corrosion barrier? The mainstream options are polytetrafluoroethylene (PTFE) films or F46 (tetrafluoroethylene-perfluoroalkoxyvinyl ether copolymer). PTFE can withstand almost all strong acids, including concentrated sulfuric acid, but the disadvantage is that it is low in strength and easy to tear, so it is necessary to add a layer of reinforced skeleton, such as stainless steel wire mesh or glass fiber cloth. Some manufacturers combine PTFE with fluororubber, which not only improves flexibility, but also retains corrosion resistance. To put it bluntly, the core of the non-metallic compensator skin with high sulfur content is the inner anti-corrosion film-if the film is broken, the whole skin will be wasted.
Actual selection: How to match the desulfurization flue gas baffle door and the high temperature zone?
There is a big gap in working conditions in different positions, so the selection cannot be one-size-fits-all. Let's first look at the desulfurization flue gas baffle door-that is, the "desulfurization flue gas baffle door" in the product information of this site. It is usually installed at the inlet or outlet of the absorption tower. The flue gas temperature is 80~150℃, with high sulfur content, high humidity and slurry splashing. In this position, it is recommended to use a double-layer PTFE-lined skin, add a layer of PTFE film in the middle as an airtight layer, and cover it with chlorinated polyethylene (CPE) or neoprene on the outside. The price is moderate and the life can reach 3~5 years.
But if you are facing a high-temperature zone, such as the original flue gas side (without passing through the desulfurization tower, the temperature is 200~300℃), ordinary PTFE can't bear it-the upper limit of the long-term working temperature of PTFE is 260℃, and it will degrade if it exceeds it. At this time, you have to change to F46, which has a temperature resistance grade of 280℃, or use polyimide film (PI), which is expensive but more reliable. By the way, this station also has "circular baffle door (double seal)" and "double seal single axis circular baffle door". The compensators matched with these valves have to be matched according to the high temperature and sulfur working conditions, so don't save that little material money.
Installation and maintenance: Don't let good materials be ruined in details
If you choose the right skin, it will be useless if you mess up the installation. The worst case I have ever seen: the customer bought the inner skin of imported F46, and the screws were tightened too tightly during installation, which crushed the PTFE film. After air leakage, the acid corroded the whole circle of metal frame along the break, and it was scrapped in two months. Therefore, the first point of installation: the torque of the strip bolt should be uniform. It is recommended to use a torque wrench, which is controlled at 20~30N·m. Don't try to save trouble and beat it with a wind cannon.
Deflector tube. The "specific function of the expansion joint guide tube" in this station's product has been made very clear-the guide tube can guide the high-temperature flue gas away from the skin, avoid direct erosion and reduce the surface temperature of the skin. For sulfur-containing flue gas, the guide tube can also reduce the condensation of acid liquid on the skin, killing two birds with one stone. If the site space does not allow the addition of a deflector, at least a layer of acid-proof coating, such as fluorocarbon paint, should be applied to the inner surface of the skin.
Don't use a wire brush to clean up the dust on the skin during maintenance. Wire brushes will scratch the PTFE membrane and become a starting point for corrosion. Rinse with a high-pressure water gun or gently sweep with a soft bristle brush, just clean it. Another reminder: The maintenance cycle is clearly written in the product manual of "Non-metallic Expansion Joint (Fabric Fiber Expansion Joint)" on this site. Check the appearance once a quarter. If you find bulging or discoloration, replace it immediately. Don't wait until it leaks.
How long does a skin last? The measured data tells you the answer
According to the plan I said, how many years can it last? We reviewed the actual replacement records of three power plants: the desulfurization inlet baffle door of a 330MW unit was covered with ordinary silicone cloth, and it leaked for 8 months; After replacing with PTFE + F46 composite skin, it only appeared slight aging after continuous operation for 3 years, and it was replaced in the fourth year. The high-temperature raw flue gas side (design temperature 280℃) of another 600MW unit is covered with PI inner layer + ceramic fiber felt, which is still in use for 5 years. During this period, it was shut down and inspected once, and the inner layer is intact.
But don't be too happy, life is also related to fluctuations in smoke conditions. If the load changes frequently, the acid dew point will be higher and lower, and the condensed acid will erode repeatedly, and the life will be shortened by 30% ~50%. Therefore, it is best to leave a margin when selecting the model, such as raising the design temperature by 30℃ and increasing the thickness of the inner layer from 0.5mm to 0.8mm. Do this step, and the non-metallic compensator skin with high sulfur content can make you worry-free.
Oh, by the way, if you have a project that is being remodeled, or are not sure which plan to use, please call us directly. We have been making non-metallic compensators for more than ten years, and we are familiar with the complete set of supporting equipment from "rectangular non-metallic expansion joint" to "desulfurization flue gas baffle door", which will help you avoid the cost of trial and error.