1. Find out how "dirty" your desulfurization flue is first-find out the temperature, pressure and corrosive components
Don't rush through the selection manual. The first step is always to find out the "details" of your flue. The flue gas after desulfurization is not a good thing-the temperature is low but the humidity is high, and the residual SO₂, SO₃ and HCl are strong acids when they meet water vapor. Coupled with gypsum slurry and dust particles, it corrodes ordinary steel in minutes. You have to ask yourself at least three questions:
- Temperature Range:What degree is the inlet desulfurization raw flue gas? What is the exit net smoke degree? Are there any quenching or heating conditions? For example, the wet desulfurization outlet is usually 45~55℃, but GGH leakage or accident conditions may soar above 90℃.
- Pressure fluctuations:What is the pressure between the induced draft fan and the booster fan? Positive or negative pressure? Usually the desulfurization flue pressure is within ±3000Pa, but the desulfurization tower inlet may be higher.
- Corrosive media:In addition to the condensed acid below the acid dew point, it also depends on the chloride ion concentration and dust hardness (whether it will wear).
Write down these data in a small notebook, and the next step of material selection can be targeted. Otherwise, if you buy the wrong expansion joint, it will leak every end in three days. The cost of replacing it once is enough for you to buy several new equipment.
2. Take your seat: metal corrugated expansion joint or non-metal expansion joint? Don't choose the wrong material
After figuring out the working conditions, the next step is the classic problem of "choose one". There are two most commonly used in desulfurization flue:Metal corrugated expansion jointAndNon-metallic expansion joints (fabric fiber expansion joints)。 How to choose? Look at three points:
Low temperature, high pressure, large amount of compensation required?-Preference is given to non-metallic expansion joints. For example, this site'sNon-metallic expansion joint (fabric fiber expansion joint)The main body is silicone glass fiber cloth or fluororubber coating, and the temperature resistance can reach more than 200℃. The key is that it can absorb multi-directional displacement, and it is light in weight and easy to install. Desulfurization flue, a large-area rectangular pipe, is the most cost-effective with non-metal models.
High temperature, clean media, limited space?-Upper metal corrugated expansion joint. For example, this site'sCorrugated expansion joint for power station industryOrHigh temperature axial expansion jointWith stainless steel 304L or 316L, it can withstand the high temperature above 500℃. However, the metal parts in the desulfurization flue should pay attention to anti-corrosion, usually lined with PTFE or sprayed with anti-corrosion coating. If the acidic condensate in your pipes is particularly aggressive, you might even considerPTFE-lined hoseOrPTFE compensator— But these are more used in small-diameter pipes.
Almost all rectangular desulfurization flues (such as a large section of 3m ×4m) use non-metallic expansion joints, because metal rectangular expansion joints are expensive and difficult to form. If you don't believe me, go to the desulfurization area of the power plant and go around, and you can see the exposed orange-red fabric expansion joint.
3. Teach you to calculate the compensation amount step by step: lateral, axial and angular displacement, none of which can be missed
Type selection is most afraid of missing the displacement. Many people only count the axial displacement of thermal expansion and contraction of the pipeline. As a result, as soon as the machine is turned on, the expansion joint is twisted into a twist. Remember that the desulfurization flue will be displaced in three directions due to the settlement of the support foundation, wind load, and equipment vibration:
- Axial displacement:Changes in length due to temperature differences. The formula Δ L = α × L × Δ T. α is generally 0.012 mm/ (m·℃), that is, a change of 0.012 mm per meter per degree Celsius. For example, a section of 10-meter flue, the temperature difference is 80℃, and the axial displacement is 9.6mm, which is rounded by 10mm.
- Lateral displacement:Pipe thermal expansion offset or seismic displacement. Usually between ±5mm and ±20mm, don't pat your head, but according to the direction of the pipeline and the layout of supports and hangers.
- Angular displacement:The amount of rotation at the corner of the pipe. If the distance between two adjacent expansion joints is close, the angular displacement is easy to ignore, but it is actually fatal-the angular displacement will cause the bellows to stretch on one side and squeeze on the other side, and soon fatigue crack.
How to calculate? Get a simple way: draw the pipeline layout diagram, mark all the fixed points (such as the outlet of desulfurization tower and the inlet of induced draft fan), and use software simulation (CAESAR II or AutoPIPE) to be the most accurate. No software? Then calculate by hand: divide each section of pipe into sections, and each expansion joint bears the displacement of the middle position. Don't forget to putPre-biasWrite in the contract-pre-stretched or pre-compressed half when installed to extend life.
If the displacement exceeds the capacity of a single expansion joint (e.g. more than 50mm in the axial direction), useCompound hinge transverse expansion jointOrStraight pipe pressure balanced expansion jointTo share. These are all available in the product line of this site, so don't push it yourself.
4. Three things must be done before installation: direction of guide tube, pre-tightening of tie rod, and joint adjustment of baffle door
When you buy something, don't rush to weld it. Do three things first, and then install them after finishing:
First, check the direction of the guide tube.The guide tube (also called liner tube) inside the expansion joint is directional, and the arrow mark must be consistent with the direction of flue gas flow. If it is reversed, the smoke directly washes the bellows, and it will perforate in a few days. You can refer to the article "Specific Function of Expansion Joint Guide Tube" in the question and answer of this site, which has a schematic diagram.
Second, adjust the tie rod nut.Metal expansion joints usually have a tie rod (to control the amount of tension). Before installation, the nut on the tie rod should be loosened to the factory marked position and cannot be locked. After the pipeline welding is completed and the pressure test is completed, the pre-deformation amount is adjusted according to the design requirements. How exactly to adjust? See the answer of "How to adjust the tie rod nut of the expansion joint" on this site-to put it bluntly: measure the actual clearance, compare it with a gauge, and twist the nut for a circle to correspond to about 2mm displacement.
Third, joint debugging with the baffle door.There must be in the desulfurization flueDesulfurization flue gas baffle door(For example, double-seal single-axis circular baffle door or electric plug-in insulation door), the expansion joint is upstream and downstream of the baffle door. Before installation, confirm the opening and closing position of the baffle door to avoid the expansion joint being squeezed and deformed when closing the door. It's best to simulate the full-stroke action-you don't want to wait for the system to run before discovering that the expansion joint is stuck in the baffle door, do you?
Use a torque wrench when putting on the bolts, and don't use wind cannons to hit them indiscriminately. Torque reference: M16 bolt approximately 80Nm, M20 approximately 150Nm. If tight, it will crush the flange, if loose, it will leak air.
5. Record of routine maintenance pit stepping: Don't wait for it to leak before repairing it. Look at these checkpoints once a week
Many bosses complain that the life of expansion joints is short, but in fact, 90% of them are not maintained in place. In the acidic environment in the desulfurization flue, people can't go in every day, but you can set several "inspection points":
- Appearance inspection:Are there any bulges, cracks and blisters on the surface of non-metallic expansion joints? Does the metal expansion joint bellows have corrosion spots and peeling paint? Take a picture with your phone and compare it with the last record.
- Displacement Check:Use a ruler to measure the current displacement of the expansion joint. If it is found that the compensation amount is close to the limit (for example, the axial direction is set to ±20mm, but it has actually reached 18mm), it means that there is a problem with the pipeline support, hanger or foundation, so check it quickly.
- Leak Inspection:Spray with soapy water or blowing agent on the flange connection, if there are bubbles, it is leaking. Don't use an open flame-there may be residual CO in the desulfurization flue. Who's responsible for the explosion?
- Tie rod nut status:See if the nut is loose. Some nuts will come with their own anti-loosening spacers, but over time the spacers fail and you have to relock them and apply anti-loosening glue.
In addition, be sure to open the manhole and check the inside of the expansion joint during an annual overhaul. The fiber material in the non-metallic expansion joint will adsorb the gypsum slurry and form hard lumps. Just shovel it off gently with a wooden shovel. Don't use a metal scraper-it will be wasted if the coating is scratched. Metal expansion joint to see if there are cracks at the weld, you can use colored penetration detection, which is very cheap.
6. One-sentence summary: four-step formula for selection of desulfurization flue expansion joint
Can't remember the first five steps? It doesn't matter. I'll give you four formulas and post them on the wall of the workstation:
Look at temperature, pressure and corrosion, and choose metal or fabric;
Third, calculate the axial transverse plus rotation angle, and fourth, the guide tube tie rod baffle should be considered.
One last nag-don't be cheap. The special expansion joint for desulfurization flue has a very important reputation in the industry. If it leaks once, the environmental fine is enough for you to buy a hundred sets. If you choose the right one, it will be fine to use it for three or five years; If you choose the wrong choice, you have to change it in three months. You taste, you taste.