How "ruthless" is it in the original flue? — — High temperature, corrosion and negative pressure are many
The brothers who run the power plant know that the original flue is not for people. The temperature of flue gas that has not been desulfurized always rushes above 150℃. It is not unusual for the instantaneous temperature to reach 200℃ when the coal type changes or the unit load fluctuates. What is even more headache is that the smoke contains sulfur and chlorine, and dew condenses directly below the acid dew point. Diluted sulfuric acid is pasted on the expansion joint, and the corrosion rate is visible to the naked eye. In addition, the induced draft fan is pumping air, and negative pressure is maintained in the pipeline all the year round. If the seal is a little lax, air leaks, and the efficiency drops severely.
Therefore, the first thing to do when selecting the original flue expansion joint of a power plant is to recognize three words: heat, corrosion and pressure. If you can't handle any of these three conditions, there will be trouble behind.
Metal bellows or fabric compensator? How to choose between two mainstream schemes
One is a metal corrugated expansion joint, like the one in our stationCorrugated expansion joint for power plant industryOrHigh temperature axial type expansion joint; The other isNon-metallic expansion joints (fabric fiber expansion joints), also called fabric compensator. Which one to choose? Depends on the specific working conditions.
Let's start with metal bellows. It has high pressure resistance and good fatigue resistance, especially suitable for high-pressure pipelines or places that need to bear large axial displacement. However, the corrosive gas in the original flue is a test for metal materials, and corrosion-resistant alloys (such as 316L and 254SMO) must be selected, and the cost will go up at once. In addition, once the metal bellows is corroded and perforated, the air leaks quickly, and it can't be repaired online, so it has to be stopped for replacement.
Let's talk about the fabric compensator. It uses multi-layer composite materials, the inner layer is temperature-resistant and corrosion-resistant, and the outer layer is sealed with glass fiber or silicone cloth. It has the advantages of corrosion resistance, noise reduction, convenient installation and multi-dimensional displacement compensation. Disadvantages-the pressure resistance is limited, and it is easy to deflate when the negative pressure is too large. In addition, the life is generally shorter than that of metal.
Then how to pick? My suggestion: If the original flue temperature is well controlled (below 250℃ all year round) and the negative pressure is not extreme, it is preferredNon-metallic expansion jointLow cost and quick replacement. If the temperature fluctuates greatly, the pressure is high, or the pipe diameter is particularly large (more than 3 meters), then you have to goMetal rectangular expansion jointEspecially the one with a deflector.
The points that are most prone to rollover during installation, don't make mistakes with the guide tube and the tie rod
I met a customer two days ago, saying that the expansion joint leaked after one year of use. I asked him to send pictures to see, and guess what? The deflector is backwards installed!Function of Expansion Joint Guide TubeIt is to guide the airflow and protect the bellows from being washed, and the direction of the arrow must point to the flow direction of the medium. Once installed backwards, the flue gas blows directly into the inner wall of the bellows, and it will wear out in less than half a year. Alas, this low-level mistake is really wronged.
Another rollover point is the tie rod. In order to save trouble at many sites, the transportation tie rod is not disassembled after installation. As a result, once the pipe expands thermally, the tie rod is stuck, and the expansion joint can't compensate at all. The correct use of the tie rod is: adjust the length before installation, fix the position of the compensator, and loosen the tie rod nut after the pipeline connection is completed and the system is preheated. As forHow to adjust the tie rod nut of expansion jointWe have a detailed question and answer before, and the core is to ensure the free movement of both ends while preventing over-stretching.
The thickness and material of the guide tube. The original flue has a large dust content, and the guide tube is too thin and will be worn through in two or three years. It is recommended to choose wear-resistant materials, or add a ceramic coating to the inner wall, which can run one more overhaul cycle.
Don't wait for it to leak before replacing it. Daily inspection to see where and what the life is affected
Many people find it troublesome to inspect this matter, but they really wait until it leaks before replacing it. The downtime loss is enough to buy several sets of expansion joints. The daily inspection mainly looks at three places:
- Corrugated surface: Are there any cracks and corrosion spots in metal bellows? Does the fabric compensator bulge and peel?
- guide tube outlet: Look at the depth of wear marks. If it exceeds one third of the original thickness, it should be replaced.
- Flange sealing surface: Are there any signs of air leak? Are the bolts loose?
Service life of expansion jointAffected by what? Number one is the combined effect of temperature and corrosion. Metal corrosion rate doubles for every 20℃ increase in temperature; Fabric fibers also age at an accelerated rate in acid mist. The second is the installation quality-the guide tube is installed crooked, the tie rod is not adjusted properly, and the life is directly discounted. The third is the pipeline stress: if the pipe system design is unreasonable, the expansion joint bears the extra displacement outside the design, and the fatigue damage will be advanced.
Expansion joints andFlue gas baffle doorThe cooperation of. The original flue outlet often needs to be fitted withDesulfurization flue gas baffle doorOr double-sealed baffle doors to insulate air leaks. If the baffle door is not tightly sealed, cold air flows back into the original flue, and the temperature drops suddenly, resulting in acid dew point corrosion, and the expansion joint also suffers. Therefore, when selecting the model, don't just stare at the expansion joint itself, but the balance of the whole smoke and air system has to be seen.
In fact, the core is one sentence: the original flue is not an ordinary pipe, and the choice of expansion joint can't be cheap, let alone patting your head based on experience. Find out the working conditions thoroughly, keep an eye on the installation details, and then cooperate with regular inspections. The money is worth it. If you are unsure, you can send me the parameters and we will help you calculate the useMetal rectangular expansion jointStillNon-metallic expansion joint— You don't charge anyway, do you?