1. Core question: Will the expansion joint of desulfurization flue expand and contract? The answer is yes, but the key depends on how you understand "telescoping".
Two days ago, a customer came to me and asked, "Does the expansion joint of desulfurization flue expand and contract?" I asked him back, "What do you understand about expansion and contraction?" He was stunned for a moment and said that it was like a spring to pull and contract. In fact, the working conditions of desulfurization flue are not so simple.
The expansion joint will, of course, "expand and contract", but this "extension" does not necessarily mean axial elongation, and "contraction" does not necessarily mean axial compression. In the desulfurization system, the diameter of the flue is often two or three meters, and the temperature rises from normal temperature to 150℃ or even higher. The thermal expansion of the flue wall is calculated in millimeters, but what is more troublesome is the relative displacement between pipes-angular, lateral and even torsional. So,Does the desulfurization flue expansion joint telescope?The answer is: it must be able to adapt to multi-dimensional displacement, not just a single direction of expansion and contraction.
Look at our product listMetal rectangular expansion joint、High temperature axial expansion joint, andNon-metallic expansion joint (fabric fiber expansion joint)The structure is designed to absorb axial and radial displacements. So don't expect the expansion joint to go straight like a rubber band, it's more like a joint, flexible but not blind.
Second, why do you have to scale? -Those invisible thermal expansion, contraction and vibration displacement in the desulfurization flue
When the desulfurization system is in operation, fluctuation of flue gas temperature is the norm. Although the net flue gas temperature after gypsum slurry washing has dropped, the original flue gas section may be as high as 160℃. The flue is made of steel structure, and the linear expansion coefficient is about 12×10⁻⁶/℃. You calculate: a 30-meter-long flue, when the temperature rises by 100℃, will elongate by 36mm. If this force is held hard, it will take minutes for the weld to crack and the bracket to deform.
In addition to thermal expansion and contraction, there is more covert-fan vibration. When the induced draft fan and the booster fan are started, the vibration frequency is not high but the amplitude is large, and the flue shakes with it. Coupled with the flue self-weight, wind load, seismic load... these displacements are superimposed, and the elasticity of the pipeline itself can't bear it at all.
What about that? Expansion joints are meant to "eat" these displacements. For example, our commonUniversal corrugated expansion jointThe bellows can absorb axial displacement through compression and stretching of the corrugations;Compound hinge transverse expansion joint andCurved tube pressure balance expansion jointThen specifically deal with lateral and angular displacements. To put it bluntly, a flue without expansion joints is like a car chassis without shock absorption.
Third, metal or non-metal? Material Selection and Structural Difference of Expansion Joint in Desulfurization Flue
This question is chosen wrong, and the post-maintenance costs can make you cry. The desulfurization flue is a typical "three highs and one low" environment: high temperature (above 100℃ in some areas), high humidity (close to saturation), high corrosion (SO₂, HCl gas and condensed acid), and low pressure (slightly positive pressure or negative pressure).
Metal expansion joint(e.g.Corrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement Industry) has the advantages of high strength, strong pressure bearing capacity, and can adapt to large displacements. But the downside is also terrible: corrosion. After desulfurization, the net flue gas humidity is high, the pH value of condensed water is low, and pitting corrosion may occur in 316L stainless steel. We generally suggest addingPTFE-lined hoseOr spray an anti-corrosion coating protective layer.
WhileNon-metallic expansion joint(includingrubber compensator、Rubber PTFE compensator、PTFE compensatoras well asNon-metallic expansion joint (fabric fiber expansion joint)) is becoming more and more popular in desulfurization flues. Why? Because non-metallic materials are inherently corrosion resistant and flexible, they can absorb multi-dimensional displacements. Especially like fabric fiber expansion joint, the main body is made of silicone cloth, glass fiber wool, polytetrafluoroethylene film, etc., and the temperature resistance can reach 250℃, and the inner line is a guide tube (refer to our question and answerSpecific Function of Expansion Joint Guide Tube) It also prevents airflow from directly washing the skin. However, the short board of non-metal is low pressure. Fortunately, the desulfurization flue is a low-pressure system, which matches perfectly.
If the temperature exceeds 250°C and the pressure is greater than 0.1 MPa, preference is given to metal expansion joints with anti-corrosion liners; If the temperature is within 200℃ and the pressure is low, non-metals are the king of cost performance. From our stationRectangular non-metallic expansion jointThere are many application cases in desulfurization system of thermal power plant, and the effect is stable.
Fourth, everything will be fine if the expansion joint is installed? Common Failure Modes and Maintenance Points
Many customers think that they can be installed for ten years, but accidents happen in two years. The most failures I encounter are three:
- Corrosion perforation: If the metal bellows is not treated with anti-corrosion treatment, condensed acid will deposit at the bottom of the corrugation and leak quickly. So chooseUniversal corrugated expansion jointAsk about the material and processing process.
- Fatigue cracking: Frequent vibration leads to stress concentration in bellows. Such asLarge tie rod expansion jointIf the tie rod nut is not aligned during installation (see Q&AHow to adjust the tie rod nut of expansion joint), will limit the displacement and instead accelerate fatigue.
- Non-metallic skin tear: The reason is often that the design of the guide tube is unreasonable or the airflow rate is too high. We have a case where a power plant usedNon-metallic expansion jointThe wind speed exceeded 15m/s. As a result, the end of the guide tube was not fixed, and the skin was worn out in three months.
Regular inspection, pay attention to whether there are corrosion marks or abnormal deformation on the surface of the expansion joint; Check that the tie rod is loose (ref.Do you need to remove the screw of the expansion joint, the transport screw after installation and commissioning must be removed); For non-metallic ones, see the skin for bulging or aging cracks. In addition,Service life of expansion jointThe general design is 10-15 years, but the actual depends on the working conditions. Suggested cooperationFlue gas baffle doorAndDesulfurization flue gas baffle doorRealize maintenance and isolation, and facilitate shutdown and replacement.
At the end of the day,Does the expansion joint of the desulfurization flue expand and contract？ It must stretch and shrink, but more importantly, choose the right type, install the right position and take care of it regularly. Understand these points, and select models without stepping on pits.