1. What exactly is the expansion joint carrying at the entrance? — — The working condition determines the selection direction
The expansion joint at the entrance of the horizontal flue of the absorption tower looks inconspicuous, but it is actually one of the most gas-receiving positions in the whole desulfurization system. Think about it, the temperature of the original flue gas from the inlet flue followed by the boiler is high and low, and the desulfurization tower is an acidic wet environment. The expansion joint should not only absorb the displacement caused by the sinking of the tower body, but also bear the thrust of thermal expansion and contraction of the horizontal flue. If you choose the wrong choice, you can leak air and slurry, or crack the tower wall. Don't ask me how I know. I've seen too many at the maintenance site.
Therefore, the first step is not to turn over the samples, but to list the working conditions clearly: What is the flue gas temperature? How high is the sulfur content? Is there a possibility of backward flow of slurry? What is the approximate settlement of the tower body? Is pipeline design pressure positive or negative? There is a point that is easy to overlook here-the inlet of the desulfurization tower is generally negative pressure, but positive pressure impact may occur at the instant of starting and stopping the furnace. If this is not considered when selecting the expansion joint, the ripples will be reversely damaged.
Second, metal or non-metal? Don't pat your head, look at the temperature and the medium
"Do you have a metal rectangular expansion joint?" I usually ask back: Is the temperature of your inlet flue above 200℃? Is there any condensation of corrosive media? Non-metallic expansion joints (fabric fiber expansion joints) tend to be more suitable if the perennial operating temperature is below 120°C and there is a risk of sulfuric acid dew point corrosion. It is not afraid of acid and alkali, has a large amount of displacement compensation, and can reduce vibration and noise. On the other hand, if the temperature exceeds 250℃, or the particulate matter in the flue gas is seriously eroded, metal rectangular expansion joints or stainless steel corrugated structures are necessary.
Both structures have their own destinies. The fabric layer of non-metallic compensator is a consumable, which generally needs to be replaced in three or five years, but the price is cheap and easy to replace; Metal can withstand high-temperature abrasion, but once chloride ions exceed the standard, pitting corrosion will be worn. It is not that metal must be advanced, it depends on whether there is a large amount of halogen in the flue gas component. The flue gas at the inlet of the desulfurization tower is not so clean.
3. Displacement, pressure and caliber-all three parameters are indispensable
When selecting, many people only quote one diameter size, such as "2m ×3m rectangular flue", and then wait for a quotation. That's not gonna work. If one of the three core parameters is less, the supplier can only give you an estimate. In the end, it can't be installed on site.
The first is the amount of displacement. The settlement of the tower body generally gives the vertical displacement, the thermal expansion of the horizontal flue gives the axial displacement, and the lateral swing caused by wind load. You have to give the axial, transverse and angular displacement requirements respectively, such as "±30mm axial and ±15mm transverse". Without this number, how to determine the number of layers of non-metallic expansion joints? How to calculate the wave number of metal ripples?
The second is stress. Don't just say "negative pressure 3000Pa", but tell the designer what the maximum positive pressure is. Under negative pressure conditions, the expansion joint is easy to be deflated, so it is necessary to add an internal support skeleton; The pressure bearing capacity of the corrugation is tested when the positive pressure impact is carried out. Therefore, the pressure parameters must be written in full: negative pressure in normal operation, positive pressure in abnormal working conditions, and full pressure of fan.
The third one is caliber – it's easiest to step on pits here. Rectangular flue is not only width and height, but also inner diameter or outer diameter, flange connection or insertion welding. You only gave a "4 meters long and 3 meters wide", and they did it according to the outer diameter. When they went to the scene, they found that it was larger than the flue, and they had to cut it on the spot. Is it troublesome?
4. The easiest pits to step on in the installation and maintenance links
Everything will be fine when the expansion joint is installed? Thinking too much. I have seen this scene several times: when hoisting, the wire rope is directly strangled on the bellows, and the corrugated pressure is deformed and unknown; Or forget to remove the transportation protection tie rod when installing, and the expansion joint is locked tightly, so no displacement can be made up. Therefore, the first thing when you arrive, check whether the transportation bracket has been disassembled, and don't take a "tightening curse" to work.
In addition, the direction of the guide tube must be opposed to the direction of the medium flow. Install backwards, the smoke directly washes the root of the corrugation, and it will leak soon. There is also a pit in the non-metallic expansion joint-the insulation cotton is damp. During installation, if the surrounding welding operation is not blocked, the welding slag falls into the fabric layer, or rainwater pours back into it, the insulation layer fails, and the outer skin will quickly burn through. The same is true during maintenance. Before changing the non-metallic ring belt, be sure to clean the old bolts and polish the sealing surface smoothly, otherwise it will leak no matter how tight it is.
Another point, try not to install other supports and hangers near the expansion joint. The constant force hanger of the horizontal flue should be arranged on the other side of the expansion joint, otherwise the compensation amount will be eaten by the support hanger. Isn't it installed for nothing? If you want to understand these questions, then go to the manufacturer to talk about the selection, and the reported scheme is reliable. After all, the selection of the expansion joint at the inlet of the horizontal flue of the absorption tower is never to copy the operation according to the model, but to chew the working conditions and feed them to the designer, so that he can hand over qualified parts to you.