From power stations to cement lines, where exactly are rectangular non-metallic high temperature expansion joints used?
When talking about flue gas pipelines, we can't avoid a reality: the temperature difference and displacement are always there. From the boiler outlet of the power plant to the desulfurization tower, the flue gas temperature ranges from 150℃ to 400℃, and the pipeline is tens of meters long at every turn. How to calculate the account of thermal expansion and contraction? Hard carry? The pipe collapses directly for you to see. So we have to rely onRectangular non-metallic high temperature expansion joint compensatorTo eat these displacements. We always have corrugated expansion joints for power stations, but when it comes to large-section and low-pressure flues, non-metals are more reliable than metals. Cement kiln tail, steel sintering machine, chemical catalytic cracking unit-which line has high-temperature flue gas, there is this thing. You asked how to eliminate the vibration at the fan outlet? It can also isolate vibration and be used for two purposes.
Compared with metal rectangular expansion joint, what are the flaws and advantages of non-metal?
Don't listen to non-metal and think it's "rubber skin".Rectangular non-metallic high temperature expansion joint compensatorThe fabric layer is usually fluororubber and silicone rubber composite glass fiber cloth, and the temperature resistance can be above 600 DEG C. However, the metal rectangular expansion joint depends on the bellows to bear pressure. Although the pressure level is high, the compensation displacement mainly depends on the transverse deformation, and the multi-directional displacement ability is weak-it can eat the axial expansion, transverse offset and angular displacement of the pipeline, while the non-metal depends on the flexibility of the fabric to absorb it almost in all directions. What about the hard flaw? The pressure capacity is poor, usually tens of kPa, and it is afraid of sharp objects scratching. When selecting the model, don't just compare the price, the temperature resistance grade and compensation amount are the life gate. For example, the medium contains acidic gas, and the fabric layer has to choose corrosion-resistant coating; If the temperature exceeds 350℃, thermal insulation has to be added.
The three parameters that are easiest to ignore when selecting the model: temperature, medium corrosiveness, and should the guide tube be be added?
Many people only ask "how much is the length and width, and how much is the resistance" when placing an order. As a result, the fabric layer aged and cracked after three months of installation. Follow JB/T 12235-2015, don't feel it.First, the temperature should leave a margin.The design temperature is 400℃, but it may actually run to 450℃ due to the fluctuation of working conditions. The fabric layer is selected according to the resistance of 450℃ or above. Second, media corrosiveness. Sulfur dioxide and nitrogen oxides in flue gas are acids when they meet condensed water, and the fabric layer must be coated with fluororubber resistant to acid and alkali. Third, should we add the guide tube? The flue gas flow rate of large section flue is high, and the fabric layer can be directly washed, so the service life is greatly reduced. Add a metal guide tube to guide the airflow to the center and also protect the inner wall. But note: the deflector itself is also a consumable-the case in the cement plant later will teach you the lesson.
The installation thing: pull rod, screw rod, arrow direction, really not just screw it on and finish it
When I received the goods, I saw that the tie rod nut was tightened and the direction of the arrow was reversed. Loosen the adjustment nut on the tie rod before installation, so that the expansion joint is in a free state-this is the experience of referring to the correct installation method of large tie rod expansion joint. The direction of the arrow indicates the flow direction of the medium, and when the guide tube is installed backwards, it has the opposite effect: the air flow impacts the back of the fabric layer, which is equivalent to white. In addition, the function of the screw is to pre-stretch or pre-compress: calculate the compensation amount according to the ambient temperature at the time of installation, and adjust the screw so that the initial displacement is in a reasonable range. Dismantle or not? Remember to remove the limit screw after installation in place, otherwise once the pipeline expands, the screw is pressed, and the compensator is equal to display. When we install the desulfurization flue gas baffle door, the construction team often ignores this step, so we have to keep an eye on it.
When used with flue gas baffle door and desulfurization baffle door, how can the expansion joint reserve a position?
Flue gas baffle doors (including manual plug-in insulation doors, electric plug-in insulation doors) are responsible for cutting off the flue gas, while the expansion joint is responsible for absorbing the heat displacement. The two are dressed next to each other, and the thermal expansion and contraction are not synchronized. The baffle door is a metal shell, and the expansion joint is a non-metal flexible body. When the temperature rises, the metal extends more and the non-metal extends less, and the joint is prone to stress concentration and air leakage. How to deal with it? Leave a short pipe between the baffle door and the expansion joint (the length shall be 0.5~1 times the diameter of the pipe), and leave at least 200mm straight pipe sections on both sides of the expansion joint. In addition, the metal hose or rubber PTFE compensator can be used to transition between the expansion joint and the baffle door, depending on the medium temperature. We have encountered users who welded the expansion joint directly to the flange of the baffle door, and as a result, the flange was deformed and sealed not tightly-that was a headache.
A real case: After three years of use in a cement plant, the fabric layer of rectangular non-metallic expansion joint was intact, but the metal guide tube was burned through
In a cement rotary kiln project two years ago, the flue temperature at the outlet of the high-temperature fan at the kiln tail was around 380℃ for a long time. Picked oursRectangular non-metallic high temperature expansion joint compensatorThe fabric layer is a silicone rubber coated fiberglass cloth with a metal guide tube. After three years of disassembly and inspection, the fabric layer is intact, but two holes have been burned through the guide tube near the smoke inlet side. What reason? The guide tube is made of 304 stainless steel, which runs for a long time at 380℃, and the strength decreases due to grain boundary corrosion. In addition, the flue gas flow rate is fast, and the erosion is aggravated. What's the lesson? The material of the guide tube should be upgraded: heat-resistant steel (such as 1Cr18Ni9Ti or higher grade) should be used when the temperature exceeds 350℃, or a layer of ceramic fiber insulation lining should be added. In addition, the installation direction of the guide tube must be consistent with the air flow, and a certain gap must be kept with the fabric layer to avoid heat conduction burning the fabric. Later, in this case, we changed to the 316L + insulation scheme, and there was no problem again. What about you, have you ever encountered a similar situation?