Dry desulfurization brothers, nine out of ten have been tormented by expansion joint leaks. Get a new one up, and it can't last three months to start dripping slurry again. The inspection fills in the maintenance sheet every day, and the leader stares at you and asks, "Can you do it at once?"
In fact, the problem is not the expansion joint itself-the one you bought may not be bad, but the root of the leak was not dug out at all. Let's play one by one.
Why is the desulfurization flue easy to leak? How is it different from ordinary flue
The ordinary flue takes high-temperature flue gas, which is high in temperature but clean. What about the desulfurization flue? The temperature is not high, but it is full of "hard work"-high humidity, low pH, and particle gypsum slurry. And guess what? After the flue gas is washed once in the wet desulfurization tower, the humidity is directly saturated, and the acid mist with liquid droplets comes out. The expansion joint is most afraid of this kind of working condition: the metal part is corroded by condensate acid, and the non-metallic fabric layer is permeated by slurry, which rotts from the inside out.
What's worse is that the pressure of desulfurization flue fluctuates greatly. When the fan is started or shut down, the pressure difference between the inside and outside of the expansion joint changes instantly, and the seal is blown open without being careful. Therefore, when the expansion joint used in ordinary flue is taken to the desulfurization section, it is a consumable.
Waterproofing not only depends on the expansion joint itself, but also the guide tube and baffle door must be well matched
Two days ago, I met a customer, and the large-diameter thick-walled expansion joint used at home was changed twice and still leaked. I asked if the deflector was installed? The other party was stunned. "What is that?"
The guide tube is the key component inside the expansion joint. There is an article on Baidu specifically talking about "the specific function of the guide tube of the expansion joint"-to put it bluntly, the function of the guide tube is to guide the flow of smoke and avoid the airflow from directly washing the bellows or fabric layer. More importantly, it can channel condensate and slurry away from accumulating at the root of the corrugation of the expansion joint. If the guide tube is not installed, or the length of the guide tube is not enough, the liquid is directly soaked in the expansion joint, so it is strange that it is not rotten.
And smoke baffle doors. For the convenience of maintenance, many sites have installed double-sealed single-axis circular baffle doors or desulfurization flue gas baffle doors. However, the sealing sheets of many baffle doors age quickly and are not closed tightly. When the machine is shut down, rainwater flows back into the flue along the gap, and the expansion joint is directly soaked in water. The sealing surface of the baffle door must be inspected regularly, and it must be replaced when it is necessary.
Selection doorway: Which is more suitable for desulfurization environment, non-metallic expansion joint or metal?
The matter of selection depends on the scoring position. The working conditions of the inlet and outlet of the desulfurization tower are quite different.
The inlet temperature of the desulfurization tower is high (raw flue gas), but the humidity is low, so metal rectangular expansion joint or universal corrugated expansion joint can be used. But be sure to pull the deflector on to prevent corrosion-not prevent corrosion? Ha, welds rotten first.
The temperature of the outlet (net flue gas) of the desulfurization tower is 40~60℃, the humidity is close to 100%, and there is also gypsum slurry. At this time, the metal bellows is easy to show timidity: pitting corrosion, stress corrosion cracking, which is impossible to prevent. The more reliable option isNon-metallic expansion joint (fabric fiber expansion joint)。 It is not afraid of acid and alkali corrosion, and has good elasticity, which can absorb multi-dimensional displacement. The disadvantage is that it is not wear-resistant, and the fabric layer will become brittle and cracked when the slurry accumulates for a long time. Therefore, you have to cooperate with the drain outlet and the guide tube, and don't let the slurry "soak" in the expansion joint.
In addition, the rubber compensator can also be used on the evacuation pipe in the low-pressure section, which is cheap and easy to change, but don't use it in the main flue, which can't bear the negative pressure.
The easiest detail to overlook during installation-should the tie rod nut be removed? Did you leave the drain?
The tie rod nut is not correctly adjusted.
Some masters think that the tie rod is used as a lifting lug, and it is welded to death directly. Look carefully at the "How to adjust the tie rod nut of the expansion joint" written by our colleague. That thing is a transportation protective part, and it has to be loosened to the designated position after installation, otherwise the expansion joint can't expand or contract by heat. Some people are completely dismantled, but it can't work-tie rod tie rod, its main function is to limit excessive displacement and prevent the expansion joint from being broken. The correct way is to loosen the nut after installation and reserve space for pipe displacement.
Drain outlet. At the bottom of the expansion joint of the desulfurization flue, a drain port or a drain valve must be reserved. Otherwise, the condensate and slurry are all accumulated inside, the fabric layer at the bottom of the non-metallic expansion joint will be soaked, and the corrugated root of the metal expansion joint will be corroded by water accumulation. If you think about it, the drain outlet is not left, and any model of expansion joint will not work-it is equivalent to letting it work in the water tank.
Routine maintenance Don't just stare at the leakage point, first check whether the fabric layer has been corroded by the slurry
Many people's maintenance habit is to "make up where there is a leak", put some glass glue, add a hoop, and fool it. Hey, it's leaking next to it in two days.
Touch the surface of non-metallic expansion joint fabric layer, is there any stiffness, peeling, local discoloration? That's the chloride ions corroding the fiberglass cloth after the slurry penetrated. If detected early, it can also be repaired locally; When there is a perforation and the insulation cotton inside is full of slurry, it will have to be replaced as a whole.
Another is to pay attention to the state of the guide tube. The guide tube is worn out and deformed, which will cause the smoke gas to rush directly into the inner wall of the expansion joint, accelerating the damage. During maintenance, open the manhole and illuminate the inner wall of the guide tube with a flashlight to see if there is any obvious thinning.
316L or even duplex stainless steel is commonly used in desulfurization system, but if pickling passivation is not done during installation or welding, the surface passivation film will be damaged, and it will still pitting. This thing doesn't look good to the naked eye, but it shows up with the blue dot method.
Therefore, the desulfurization flue expansion joint is waterproof, not just change the expensive one. Deflectors, baffle doors, tie rod nuts, drain outlets, fabric layer corrosion-any link is not stuck, and water leakage is a matter of time. Let's fill these holes so we can have a peaceful sleep.