Blower Export Non-Metallic Compensator: Wrong Choice Really Will Happen Big Things
It is not exaggerated to say that the operating condition of the blower outlet is the "purgatory" of the pipeline system. High-temperature smoke rushes out, and the temperature easily soars to 200℃ or even higher; The vibration of the fan itself, the displacement caused by thermal expansion and contraction of the pipeline, plus the pile of acidic corrosive media in the desulfurization and denitrification process... none of them are good. If you install a random compensator in this place, you will have to lie down in less than three months-from a leak to an entire pipeline collapse.
Two days ago, I met a buddy from a power plant, who said that the metal compensator used for their desulfurization fan export was changed twice in three months. The last time, the bellows was torn directly, and hundreds of thousands were lost when it was shut down for emergency repair. Later, it was replaced with a non-metallic expansion joint (that is, what we often call a fabric fiber expansion joint), and the vibration dropped by 60%. It has been almost a year now. Tsk, the difference between choosing the right thing and choosing the wrong thing is so naked.
1. Why do metal compensators often "drop the chain"?
Metal stuff is definitely stronger than "cloth". But the exit of the blower is precisely the most afraid working condition of the metal compensator.
- High temperature fatigue:Under the frequent axial expansion and contraction and high temperature cycle, the stress concentration of metal bellows is easy to produce, which leads to trough cracking. Especially stainless steel, sensitization will occur above 350℃, and the risk of intergranular corrosion will double.
- Vibration resonance:The metal compensator itself has great rigidity, so it is difficult to absorb the high-frequency vibration brought by the fan. When the vibration is transmitted to the bellows, the weld joint and wave crest position become the breakthrough point.
- Corrosion penetration:Acidic gases such as SO₂ and Cl⁻¹ in desulfurization flue gas generate dilute sulfuric acid when they meet water, which can not be held by ordinary stainless steel thin-walled bellows at all, and they will be perforated in one year.
Why is the non-metallic compensator the right answer? The reason is simple: it is flexible, vibration-absorbing and corrosion-resistant. The fabric fiber layer (such as fluororubber + glass fiber + polytetrafluoroethylene film) is superimposed, which can not only withstand the temperature of several hundred degrees, but also eat the vibration energy bit by bit through the multilayer structure. Most importantly – it is not afraid of acids and bases. Think about it, the flue gas after desulfurization has high humidity and strong acidity, and non-metallic materials are naturally anti-corrosion materials.
Second, don't just look at the caliber in the selection: if the temperature, pressure and displacement are wrong, they will be wasted
Many purchasing diagrams save trouble, and when you come up, you ask "Give me a DN600 non-metallic compensator". Dude, this thing isn't as simple as buying a steel pipe.
Let's start with the temperature:The flue gas temperature at the blower outlet fluctuates greatly with the working conditions, which may range from normal temperature to 250℃. The upper temperature resistance limit of fluorine-containing fabrics (such as polytetrafluoroethylene film) commonly used in non-metallic expansion joints is about 260℃, but if you run above 280℃ for a long time, you have to consider the composite structure of aluminum silicate fiber cotton + ceramic fiber cloth. Also note-the temperature must look at the "continuous operating temperature", not the short-term peak. It is fine if the peak exceeds 20℃ for half an hour, but the fiber begins to carbonize after 8 hours.
Let's talk about pressure:The blower outlet generally belongs to a low-pressure system, and 0.05~0.15MPa is common. But don't be careless. There will be a pressure shock wave at the moment the fan starts. The pressure of the non-metallic compensator mainly depends on the metal frame and pressure plate, not the fabric. At this time, the role of the guide tube comes out-it can guide the airflow away and avoid the direct impact of high-pressure gas on the fabric layer.
Displacement Amount:It's a big pit. Many people only choose according to axial expansion and contraction, ignoring lateral and angular displacement. The direction of the blower outlet pipe is often complicated, and thermal expansion can lead to displacement in multiple directions. The advantage of non-metallic compensator is that it can absorb axial, lateral and angular displacements at the same time, but it must provide the manufacturer with accurate "three-way displacement value", otherwise the actual displacement capacity of the designed product is not enough, and it will still crack when hard pulled.
Moreover, the standard basis must be read JB/T 12235-2015. The national standard stipulates various technical indicators and test methods of non-metallic expansion joints. When selecting the model, let the manufacturer provide the test report that meets the standard.
Third, the easiest pit to step on in installation and operation and maintenance: the guide tube, tie rod and bolt should not be careless
If you choose the right product, it will be useless if there is a problem with the installation. I've seen too many on-site installation accidents, to mention a few typical ones.
Install the guide tube in reverse direction:The guide tube of the non-metallic expansion joint is used to guide the flow of media and protect the fabric layer. When installed backwards, the high-temperature smoke directly washes the inside of the fabric and burns through in a few hours. Remember: The bell mouth of the deflector should be facing the direction of the media flow-that is, facing the blower outlet.
The tie rod nut is not adjusted properly:Non-metallic compensators usually come out of the factory with tie rods to limit the installation position and prevent excessive compression. In order to save trouble, some workers directly disassembled or screwed the tie rod to death. As a result, as soon as the pipeline expands, the compensator loses its constraint, the flange sealing surface is misaligned, and air leaks. Correct practice: After installation, adjust the nut position according to the drawing, and keep the initial compression amount specified in the design.
Wrong sequence of bolt tightening:The flange bolts must be tightened step by step in diagonal order and the torque should be uniform. Some scenes were directly hit with wind cannons, and the pressure plate was twisted and deformed, and the sealing surface was uneven and leaked. The flange pressure plate of non-metallic compensator is a thin steel plate, which will warp if the force is uneven, and it is useless to press it later.
The easiest thing to overlook in the operation and maintenance phase is to regularly check the aging of the fabric layer. Non-metallic composite fabrics will age gradually under ultraviolet rays, humidity and acidic environments. Generally, the design life is 3~5 years, but the actual situation depends on the working conditions. It is recommended to check it every six months and look after it with a flashlight for bulging, delamination or hardening and brittleness. Once you find a surface crack, don't hesitate to arrange for a replacement immediately-once this thing bursts, it's no small matter.
IV. Real case: the vibration of desulfurization fan outlet of power plant dropped by 60%
The case of that power plant mentioned earlier is worth detailing. They used to use a single-layer stainless steel corrugated expansion joint. Half an hour after the fan was turned on, the whole outlet pipe began to shake violently, with an amplitude of 8mm, and the anchor bolts were loosened. After replacing the non-metallic expansion joint (fabric fiber expansion joint), the vibration value dropped directly from 8 mm to less than 3 mm. Why is the effect so obvious? Because the nonmetallic multilayer fabric structure itself is a natural damper-each layer of fibers rubs against each other and consumes vibrational energy, just like replacing a steel pipe with a rubber hose.
Of course, non-metallic expansion joints are not a panacea. If it is ultra-high pressure (more than 0.3MPa) or ultra-high temperature (more than 500℃), you still have to use metal (such as high-temperature axial expansion joint). However, as far as the operating conditions of "medium and low temperature, low pressure, strong corrosion and high vibration" at the blower outlet are concerned, the non-metallic expansion joint is definitely the optimal solution at present.
Don't choose low-priced general merchandise just to save hundreds of dollars. The core of the non-metallic compensator lies in the fabric composite process and flange seal design. Regular manufacturers will at least issue calculation sheets, provide type test reports, and produce and inspect in strict accordance with JB/T 12235-2015. It is cheaper to replace this thing if it is broken, but the downtime loss and repair cost are the biggest.
If you have a blower export renovation project at hand, list the four parameters of temperature, pressure, displacement and medium composition clearly, and directly find the manufacturer to customize the non-metallic expansion joint (fabric fiber expansion joint), which basically won't overturn. If you are really unsure, leave me a message and I will help you look at the selection parameters.