In the desulfurization system, why can't the skin bear it?
The old iron who runs the desulfurization site knows that there is a problem with the skin-air leakage, slurry leakage, shutdown for maintenance, which is a lot of trouble. Why is desulfurization flue gas pipeline so expensive? To put it bluntly, the working conditions are too bad.
Although the desulfurized flue gas temperature has dropped, generally 80-150℃, it contains a large amount of SO₂, SO₃ and chloride ions. After condensation, dilute sulfuric acid and hydrochloric acid are formed, and the pH value can be as low as 2. Coupled with the flue gas being washed by water and solid particles, this environment is more ruthless than the flue at the tail of the boiler. Many factories try to save money and change their skin with ordinary rubber compensators. As a result, they are brittle and cracked in three months-I just met a customer two days ago, and that is the case.
The skin is not a layer of cloth, but layers of composite materials stacked together. This site'sNon-metallic expansion joint (fabric fiber expansion joint)AndDesulfurization flue gas baffle doorIs specifically designed to deal with this kind of scenario. Usually including fluororubber layer, polytetrafluoroethylene film, fiberglass cloth, aluminum silicate wool, etc., each layer does each layer of work.
How does the skin carry corrosion? The core lies in the material combination
The core of corrosion lies in the middle layer of fluororubber and PTFE (polytetrafluoroethylene). Take what we always sayPTFE compensatorSpeaking, PTFE hardly reacts with any acid and base, and its temperature resistance can reach 260℃ for a short time, but 200℃ for a long time. The temperature of desulfurization flue gas fluctuates greatly, so the skin design has to leave a margin. Usually, fluororubber + PTFE composite layer is selected, and then high silicon oxide cloth or ceramic fiber is used as heat insulation layer.
Why can't the skin changed from ordinary rubber work? Ordinary rubber cannot withstand acid, so you have to use fluororubber (FKM) or perfluoroether rubber. The cost is a little higher, but it can last five years once, so it is cost-effective to calculate the general ledger. For example, the rectangular flue at the outlet of the desulfurization absorption tower of a power plant usesRectangular non-metallic expansion jointThe original skin bulges for two years. When disassembled, it was found that the outer fiberglass cloth was seeped in by slurry, and the thermal insulation cotton in the middle absorbed water and swelled-this was actually the wrong choice of material and failed to withstand the combined attack of acid and water.
Type selection not only depends on material, but also depends on pressure and displacement
In addition to corrosion resistance, pressure rating and displacement capacity should also be kept an eye on. Desulfurization flue is usually low pressure, generally within 0.1MPa, but the rectangular section is mostly, and the lateral displacement caused by thermal expansion and contraction of pipeline is too large. At this timeRectangular non-metallic expansion jointMore suitable than circular-it absorbs multidimensional displacement, especially angular displacement.
Enough compensation space should be left in the four directions up, down, left and right. Don't stretch the skin too tightly, otherwise the stress will be concentrated, and the weld will have to be fully welded in sections. contrastNational standard for non-metallic expansion joints(JB/T 12235-2015), the withstand pressure test shall be at least 1.5 times the design pressure. In some sites, the skin and desulfurization flue gas baffle door are installed together, and the expansion joint begins to leak before the baffle door is closed tightly. Why? The baffle door itself has dead corners to accumulate dust, and the ash accumulates to stick the edge of the skin. The solution is to add a sealed air interface between the skin flange and the baffle door, purge it with high-pressure air, or chooseDouble-sealed single-axis circular baffle doorReduces dust accumulation.
Installation details determine life, don't ignore it
Skin replacement cycle andService life of expansion jointThat FAQ says something similar-3-5 years under normal working conditions. If you start and stop frequently and the temperature changes drastically, the life will be shortened by half. It is recommended that the temperature difference on the skin surface be scanned with an infrared thermometer every six months. If it exceeds 30℃, it means that the insulation layer has failed, and it has to be replaced quickly.
The rectangular flue at the outlet of the desulfurization absorption tower of a power plant is covered with rectangular non-metallic expansion joint, which is partially bulged after two years of operation. When disassembled, it was found that the outer fiberglass cloth was infiltrated by slurry, and the middle insulation cotton swelled after absorbing water. The solution is to change the skin structure to three layers of fluororubber and two layers of PTFE, and add a stainless steel wire mesh to prevent wear on the outer layer. It has been almost a year since it was changed. The pressure test is about 0.15MPa, and the displacement is ±50mm. There is no problem at all. In the final analysis, material combination is more important than thickness, and installation is more important than type selection. Don't just try to be cheap, but talk to manufacturers more-such as ours for many yearsDesulfurization flue gas baffle doorAndNon-metallic expansion jointExperience-explain the working condition data clearly, so as to save the trouble later.