What exactly is the expansion joint of non-metallic ventilation compensator?
Don't look at the long name-the non-metal ventilation compensator expansion joint, to put it bluntly, is a soft connector. Instead of our usual metal bellows, it is made of fabric fibers (such as the one we stand onNon-metallic expansion joint (fabric fiber expansion joint)), rubber (likerubber compensatorOrRubber PTFE compensator) or flexible pipe fittings made of composite coated cloth. The shape is divided into circular and rectangular, among which rectangular non-metallic expansion joints are the most common in ventilation flues, because the flues themselves are mostly rectangular in cross section, which are tightly connected. What is the biggest difference from metal expansion joints? Metal absorbs displacement by corrugation deformation, and it works by stretching and compressing the flexible material itself. To put it bluntly, one confronts hard, and the other uses softness to overcome hardness.
What "headaches" does it solve with ventilation systems?
First, thermal expansion.
The temperature of smoke in the ventilation duct can always be hundreds of degrees Celsius, or even three or four hundred degrees. If the metal pipe is hard, the stress of thermal expansion and contraction will make the pipe bulge, the flange crack, and the pipe burst directly. Once the non-metallic ventilation compensator expansion joint is installed, the thermal displacement of the pipe is eaten by the soft material-it elongates or compresses itself, and the pipe body is not stressed. Moreover, non-metallic materials conduct heat slowly, and can also play a certain role in heat insulation.
Second, vibration.
As soon as the fan was turned on, the whole pipe shook together. After a long hard connection time, the bolts are loosened, the welds are cracked, and the maintenance cost will rise. The flexible compensator is equivalent to installing a "shock-absorbing pad" on the pipeline system. Most of the vibration of the fan is absorbed when it is transmitted to the compensator, and the amplitude of the downstream pipeline can be reduced by 60% ~70% (measured data, no blowing or black).
Third, corrosion.
The smoke contains sulfide and acid gas, which directly hits the metal wall and is worn in a few months. However, non-metallic fabrics-especially PTFE coatings-are naturally corrosion-resistant, and it is not afraid of acidic and alkaline media with a pH value of 1~14. This is particularly useful in the desulfurization system.Desulfurization flue gas baffle doorIt is used together with the compensator. The baffle door isolates the airflow, the compensator absorbs the displacement, and the flange and pipe are not soaked by acid.
Compared with metal expansion joints and rubber compensators, why does it win?
Look at the metal ones first. LikeUniversal corrugated expansion joint、High temperature axial expansion jointThey can withstand high pressure and have a life of more than ten years, but they are afraid of acid and expensive-the price of a large-diameter metal compensator is often tens of thousands more. Look at the rubber compensator again. It is cheap and elastic, but it ages when the temperature is high. It is basically useless above 130℃, and its corrosion resistance is average. The non-metallic ventilation compensator is just stuck in the middle zone: the working temperature depends on the fabric, the low-end can carry-40℃, and the high-end ceramic fiber can reach 1000℃ (for example, used in rotary kiln flue). The corrosion resistance far exceeds that of metal, and the price is 30% ~50% lower than that of metal. However, its pressure-bearing capacity is weak, and it is generally only used for low-pressure ventilation ducts ≤0.1MPa, and high-pressure systems have to be made of metal. So the choice isn't either/or, it's more about scene matching.
Which industries are using it? Tell me a few real cases.
In the flue gas pipeline of power plants, non-metallic expansion joints often cooperateCorrugated expansion joint for power station industryTogether-metals specialize in absorbing axial thermal displacement, non-metals absorb lateral swing and angular displacement, each tube spread. The cement industry is more direct: the ventilation flue of rotary kiln, high-temperature dusty gas is the norm, and the non-metallic rectangular expansion saves energy to withstand the erosion and wear of fly ash. Moreover, if it is broken, only change the fabric ring, without cutting off the whole pipe. Not to mention the desulfurization system-behind the imported flue gas baffle door, a non-metallic compensator is standard, otherwise the flange will be quickly corroded by acid. If we encounter scenarios that require isolation maintenance, we still haveRound Flap Door (Double Seal)AndManual plug-in insulation doorTo cooperate, a set of combination punches down, not only to ensure the displacement absorption, but also to completely cut off the flow.
The three most easily overlooked pits when selecting a model.
First: The temperature should not only look at the mouth temperature, but also include radiant heat and instantaneous peak.Before, a cement factory reported that the working condition was 200℃, and we made fabric fibers according to the standard selection. Results the local reflection heat was superimposed during operation, and the temperature could soar to 350℃, and the fabric was embrittled in less than half a year. It was later replaced with a ceramic fiber linerNon-metallic expansion joint (fabric fiber expansion joint)Just got it done. Therefore, when selecting the model, Party A must provide the historical temperature curve, especially the peak value in the start-stop stage.
Second: the higher the pressure, the better. Non-metallic compensators are afraid of negative pressure.In many cases, the ventilation duct runs under negative pressure (such as the fan inlet). Too much negative pressure can deflate the flexible fabric, resulting in damage to the inner lining and displacement of the guide tube. When designing, the system resistance should be calculated. If the negative pressure exceeds 0.02MPa, you have to add an internal support ring or use metal instead.
Third: The installation direction must be correct.Inside the non-metallic compensator is aguide tubeWhich acts to direct the airflow to avoid direct flushing of the flexible layer. The guide tube is marked with an arrow and must be installed in the direction of airflow. If it is installed backwards, the high-temperature dusty air stream will directly hit the fabric, and the life of the fabric will be cut by at least half. A few days ago, a customer called and said that the compensator was leaking. After looking at the video, the deflector was installed backwards-it could only be replaced at the factory.
Maintenance: Don't wait for air leakage before replacing.
Non-metallic compensators are not as "solid" as metal, and their general life is 3~5 years, depending on the working conditions. There are two points in daily inspection: First, whether the outer layer is bulging and cracking; The second is whether the guide tube has fallen off. As long as you find local wear, you can change the fabric ring separately without dismantling the whole pipe, which saves trouble and money. If you really want to replace it as a whole, refer to the article on our siteHow to adjust the tie rod nut of expansion jointQ&A, lock the pull rod first before starting-otherwise the displacement is deviated, and it will be useless to install it newly. Also, be sure to adjust the pipe support before installation, and don't let the compensator bear additional gravity loads.
In the final analysis, the expansion joint of non-metallic ventilation compensator is not high-tech, but choosing, installing and using the right can save the ventilation duct system from tossing for many years. If you encounter similar working conditions, you might as well send the parameters, and we will help you check them-after all, this thing looks inconspicuous, and if something goes wrong, it can delay production. Right?