Why is desulfurization and denitrification system inseparable from non-metallic compensator? — — Working conditions where the metal parts can't be handled
Buddies who have worked in desulfurization and denitrification projects all know that the gas in the flue is clearly a "chemical weapon". High temperature, acidic corrosion, dusty particles, several pieces are put together, and the metal corrugated expansion joint will be perforated in less than half a year. Tsk, it's not that we look down on metal parts. Do you let stainless steel soak in the low-temperature and high-humidity flue gas after wet desulfurization? Once chloride and sulfate crystallize, stress corrosion cracking can't escape.
So at this time,Non-metallic compensator for desulfurization and denitrificationWell, we have to play. It is not as afraid of acid and alkali as metal, and it can absorb three-dimensional displacement-it can be eaten in axial, transverse and angular directions, and it can withstand the thermal expansion and contraction of the pipe no matter how fierce it is. Two days ago, a friend from a power plant complained to me, saying that their original metal expansion joint began to leak after two months of installation, and they changed the non-metallic one for two years. Do you think this thing is just needed?
Structural disassembly: fabric fiber, rubber, PTFE, what exactly is each layer of material carrying?
The non-metal compensator looks like a large spring wrapped in cloth, but in fact it is a "sandwich cookie" structure. From the inside out, let's smooth it out: the innermost one with the media attached isPTFE compensatorThe commonly used tetrafluorine layer (PTFE), this thing has first-class corrosion resistance, and hydrochloric acid and hydrofluoric acid are casually greeted; There is a rubber layer sandwiched in the middle, usually EPDM or neoprene, which mainly plays the role of sealing and vibration damping; The outermost layer is fabric fibers – such as fiberglass cloth, ceramic fiber cloth, which is responsible for tensile resistance and insulation.
In some working conditions, the temperature soars above 600℃, and the outer layer has to be replaced with high-temperature resistant aluminum silicate fiber felt.Non-metallic expansion joint (fabric fiber expansion joint)The multi-layer design can hold it. Each layer has a division of labor: the inner layer is impermeable, the middle layer is cushioned, and the outer layer is fire-resistant. One layer less won't do, just like when you wear a down jacket and forget to zip it, the wind will cool your heart.
And metal expansion joints hard? Where Nonmetallic Compensators Win and Lose
Metal expansion joints are cheap, why do you have to use non-metal? Let's be honest, non-metallic compensators beat metal in three dimensions: first, displacement compensation ability-non-metals can be rectangular or circular in any shape, with a large displacement (± 50mm is easy to handle), and metal bellows have to pile up many waves; Second, corrosion resistance-metal, let alone acid, can't hold up in a humid environment, and the non-metallic PTFE layer directly ignores it; Third, vibration and noise reduction-the flexible structure naturally absorbs vibration, and the pipeline noise can be reduced by 5-10 decibels.
But non-metals also have shortcomings. The pressure bearing capacity is weak, and the general design pressure does not exceed 0.1MPa. If you install it hard on the high-pressure steam pipe, it is purely uncomfortable. In addition, although the upper limit of temperature resistance is high, it is afraid of direct burning by open flame. Therefore, you must look at the working condition parameters when selecting the model, and don't use non-metals as universal glues.
Three-step selection: temperature, pressure and medium concentration. If a parameter is wrong, it is useless
chooseNon-metallic compensator for desulfurization and denitrificationYou have to be as accurate as glasses. The first step is to look at the temperature: if the flue gas temperature is lower than 250℃, just use neoprene or EPDM lining; 250-400 DEG C to replace fluorine rubber or silicone rubber; Over 400℃, the ceramic fiber composite structure is directly applied. The second step is to look at the pressure: the positive pressure pipeline should pay attention to the tensile strength of the flange sealing surface, and the negative pressure pipeline (such as the outlet of the induced draft fan) should be lined with stainless steel wire mesh or skeleton ring to prevent deflation.
The third step is also the easiest place to roll over – the media composition. The flue gas at the inlet of the desulfurization tower contains high SO₂ concentration, and the outlet carries a large amount of gypsum slurry. At this time, there must be wear-resistant lining inside the compensator, such asRubber PTFE compensatorThat composite structure, both acid and erosion resistant. Don't just look at the "general type" written on the sample. When the pH value is 2.5 at the scene, ordinary rubber will rot in half a month. I have seen a chemical plant that ignored the chloride ion concentration when selecting the model. As a result, the compensator was brittle and cracked in three months, and I lost 200,000 yuan. Parameters are almost a world of difference.
Installation and maintenance: taboos that manufacturers will not explicitly state (with real cases)
The arrow on the non-metallic compensator indicates the flow direction of the medium. Don't install it backwards, otherwise the airflow directly impacts the fabric layer, and the life will be discounted in half. Also, the tie rod nut for transportation must be loosened during installation-don't laugh, someone really forgot to dismantle it, and the pipeline expansion directly tore the compensator apart after turning on. Refer to the question and answer on this site "Does the screw of the expansion joint need to be disassembled?" This problem is recruited every year.
Let's talk about maintaining taboos. Many operation and maintenance personnel saw dust on the surface of the compensator, so they rushed with high-pressure water guns. Tsk, with a dozen water pressure, the edge of the PTFE layer cocks up, the medium infiltrates the interlayer, and the internal corrosion accelerates. The right thing to do is dry sweep with a soft brush, or low pressure nitrogen purge. There was a cement factory last year,Rectangular non-metallic expansion jointIt leaked after two years of use. When I took it apart, the inner layer was full of scale-it was the fault of rinsing. Usually, the inspection focuses on whether the flange bolts are loose and whether the fabric surface is bulging. If any abnormality is found, the furnace will be stopped immediately. Don't wait for the smoke to remember to change it, when the pipes are all deformed.
In the final analysis, it is not a problem to use a non-metallic compensator for five or six years if you choose, install and maintain the right one. If you have a desulfurization and denitrification project in your hand, you might as well go through the above ones. If you are not sure, you can step on a few fewer pits.