How to choose the material of desulfurization flue expansion joint? 4-step practical combat tutorial, just follow it
Two days ago, I met an old customer and called to complain: the newly installed expansion joint took less than half a year, and the weld was etched through by acid, resulting in a whole air leakage, and hundreds of thousands of losses were lost when the furnace was shut down for maintenance. Only after asking did he know that he chose ordinary 304 stainless steel cheaply, and didn't consider the pile of "poisonous gas" in the desulfurization flue at all. Alas, the matter of selecting materials really can't be slapped on the head. Today, I will shake out the 4-step method at the bottom of the box. If you follow it, you will take at least three years of detours.
Step 1: Find out what "poisonous gas" you are facing first-analysis of working conditions of desulfurization flue
Don't rush through the product manual. Take a pen and write down these sets of data first:
Temperature: After wet desulfurization, it is generally 50-80℃, but in the dry-wet interface, the flue gas temperature may suddenly soar to 150℃ or even higher. If you ignore it, the non-metallic expansion joints are baked directly into a crispy crust.
pressure: Most of them are slightly positive or negative pressures, but occasionally have instantaneous fluctuations. Not stressed? Wrong! Under negative pressure conditions, the expansion joint is easy to be deflated, so it is necessary to choose one with reinforcing ring.
Media composition: SO₂, SO₃, HF, HCl…plus condensate at pH as low as 1-2, it's a chemistry lab. Ordinary carbon steel won't last three months.
Tips: Stick these data next to the equipment nameplate, and compare them directly for the next purchase, so as to save the need to flip through the drawings.
Step 2: Main material showdown-metal expansion joint vs non-metal expansion joint vs rubber compensator, who is more built?
Desulfurization flue expansion joint materialThere is no "universal model", only "suitable model".
MetalsFor example, in our siteCorrugated expansion joint for power station industryAndHigh temperature axial expansion jointIt is mainly used in high temperature and high pressure sections, such as when the bypass flue occasionally passes through the original flue gas. But you have to choose the right material-316L is the starting point, 2205 duplex steel is reliable, and 254SMO is a high-order game. Regular 304? Alas, when the weld touches acid mist, it becomes a sieve in a few days.
Non-metallic expansion joint(i.e.Fabric fiber expansion joint) andRectangular non-metallic expansion jointIs the main force of desulfurization flue. Why? Corrosion resistant, large amount of compensation, good heat insulation, and cheap. But fear two things: overtemperature and overpressure. If your working temperature exceeds the design value, the fiber layer will leak immediately as soon as it ages. So when buying, stare at the parameters, and don't believe the nonsense of "universal type".
rubber compensatorAndRubber PTFE compensatorIt performs well in low-temperature wet sections, such as the section from the outlet of the absorption tower to the chimney. However, there is a dead hole in rubber-UV rays age quickly. You have to find a way to shade the light, or choose a style with an outer coating of PTFE. AndPTFE-lined hose、PTFE compensatorStrong acid and high cleanliness scenes are the first choice, the disadvantage is that it is expensive, and care should be taken not to scratch the PTFE layer during installation.
And guess what? Last year, a power plant project manager told me that they used the rubber compensator for three years without breaking. The secret is to apply anti-aging agent every year. Tsk, people who work hard can always last two more years.
Step 3: Step-by-step selection-seat by location and function
In this section, let's choose according to the location of the flue, so don't get confused.
① Inlet section of absorption tower: Large temperature fluctuation, high dust content, and unreacted limestone particles in the flue gas. Recommended useNon-metallic expansion jointOrRectangular non-metallic expansion joint, cooperate withDesulfurization flue gas baffle doorUse it together. By the way, ourDouble-sealed single-axis circular baffle doorAndSingle-axis double-flapper doorThe sealing property is particularly good, which can effectively prevent the backward flow of smoke.
② Section from the outlet of the absorption tower to the chimney: Low temperature saturated wet flue gas, more condensate, the strongest corrosion. userubber compensatorOrPTFE-lined hoseThe most stable, don't forget to add a deflector! The function of the guide tube is to prevent scouring, otherwise the condensate directly impacts the bellows, and it will be perforated in half a year. Our article "The Specific Function of Expansion Joint Guide Tube" has detailed instructions, you can flip through it.
③ Bypass flue: Usually shut down, and occasionally open the high-temperature original smoke. Don't save money at this time, come onMetal corrugated expansion jointThe material is at least 316L, and the condition allows direct use of 254SMO. Bypass Flap Door Recommend OurManual plug-in insulation doorOrElectric plug-in insulation door, tightly sealed.
④ When the expansion joint is matched with the baffle doorNote that the interface size should be correct and the seal form should be selected correctly. If it is a circular flue, refer toDouble-sealed single-axis circular baffle door； For rectangular flueRectangular non-metallic expansion jointCooperateDesulfurization flue gas baffle door。
Step 4: Pit Avoidance Guide – 3 Key Actions for Installation and Routine Maintenance
Choose the right material and install the wrong material equals zero. Here are three things you must keep an eye on.
① Confirm the direction of the expansion joint arrow before installation。 Many masters weld directly without reading the instructions. As a result, the direction of the arrow was reversed, and the compensator was holding back its strength, and it cracked in less than a year. How to judge the direction of the arrow? There is a special article in our question and answer "What is the direction of the arrow of the expansion joint". Let me summarize it: the arrow points to the direction of the medium flow or to the side of the fixed bracket. After installation, don't screw the tie rod nut-it should be adjusted after pressure test. For specific steps, refer to "How to Adjust the Tie Rod Nut of Expansion Joint".
② The flange sealing surface is the easiest to leak!A lot of leaks happened here. You gotta get onPTFE gasketOrMetal winding padThe bolt pre-tightening force is not too large, and the gasket will be crushed if it is tightened too tight. Standard practice: Tighten with a torque wrench in three times, each time cross-symmetrically.
③ Check regularly and don't be lazy。 Is the fiber layer of the non-metallic expansion joint broken? Is there any bulge and crack in the rubber compensator? If you find something wrong, change it immediately. Don't wait for the furnace to stop. Let me tell you a real case: a factory found a small bulge in the rubber compensator, and thought it was okay. As a result, it exploded three months later, and the furnace was shut down for maintenance for a week, resulting in heavy losses.
Tips: When the machine is shut down for maintenance every year, by the way, clean up the ash and crystals in the guide tube. This action is effortless, but it will last for an extra year or two.
Okay, if you still don't choose the right four stepsDesulfurization flue expansion joint materialCome to me, and I will help you see the working condition data for free. After all, if you choose the right equipment, you will worry tenfold later.