Bag dust collector anti-corrosion measures and structural improvement
The kiln tail dust collector of a cement plant is usually equipped with equipment such as humidification tower and waste heat boiler in front, and its inlet exhaust gas temperature is usually in the range of 90 to 200 ℃, with a dew point temperature of about 47 ℃. Acidic components in the exhaust gas and low temperature condensation are the main causes of corrosion inside the kiln tail bag dust collector.
In recent years, most cement plants have added SNCR denitrification units and cement kiln co-processing facilities to their process systems. The addition of these two process facilities has brought corrosive gases to the system and increased humidity, exacerbating the corrosion inside the kiln tail precipitator and affecting the stable use of the system.
In short, air leakage and condensation in the body, ammonia escape from SNCR denitrification and cement kiln co-processing solid waste are the main causes of corrosion inside the kiln tail precipitator.
Air inlet.
The part of the duct near the inlet of the bag dust collector is mainly large particles, and the part after entering the bag dust collector is mainly impact abrasion, as the flow rate is faster this time, there is no condensation corrosion, the flue needs to be checked and repaired.
Middle box Filter area.
The middle box of the bag dust collector with insulation layer outside, after the flue gas enters the middle box, the pipe diameter further increases, the flow rate of flue gas further decreases, some of the relatively larger particle size of the dust also falls under the action of gravity, at this time the flue gas abrasion degree of the equipment surface decreases.
If the insulation layer is intact and meets the insulation requirements, the internal temperature remains above the dew point of the flue gas and no condensate is generated at this time, so there is almost no acid-base corrosion.
If the insulation layer here is destroyed, water, or the use of longer insulation effect decreases and can not meet the insulation design requirements, the internal temperature in the flue gas dew point below, then there will be condensate, there will be local corrosion, the larger the area of the failed insulation layer, the more condensate, the more serious the corrosion situation. Here the corrosion can be started from two aspects: the external insulation layer of the box and internal corrosion layer.
Upper box clean air chamber.
With the flue gas filtered by the bag into the clean air chamber, the dust content in the flue gas is greatly reduced, and the cement kiln tail bag dust collector usually adopts a pulse type backflush gas cleaning device, which is timed or fixed differential pressure to pass into the room temperature compressed air backflush bag to shake off the accumulated dust on the bag, and then realize continuous work.
It is due to the regular or fixed pressure difference into the room temperature air, and the net gas room flue gas heat exchange, will make the net gas room flue gas temperature overall lower, especially the backflush tube surface, back flush tube and dust collector connection temperature will be greatly reduced, the formation of condensate, condensate absorption of cement dust to produce alkali, absorption of sulfide in the flue gas to produce acid, will occur acid-base corrosion. This acid-base corrosion is a serious part of the whole dust collector.
Therefore, the upper box net gas chamber mainly prevents acid and alkali corrosion of condensate, and must meet long-term and simultaneous acid and alkali corrosion resistance, excellent resistance to permeability, and certain wear resistance.
According to the specific situation, the effective use of appropriate anti-corrosion coating is also a good solution.
Reasonable anti-corrosion coating can not only isolate the direct contact between air and water and the inner surface of the steel dust collector at the end of the kiln, but also resist the erosion of corrosive gases such as ammonia water and ammonia compounds.
Suitable anticorrosive coating materials available on the market are: lightweight glass ceramic anticorrosive materials, epoxy phosphoric acid paint, modified epoxy coal asphalt FRP paint, glass scale, etc., silicone coatings, they can all form a dense protective film on the steel surface, blocking the key link in corrosion. Conditional enterprises, porous plate, blowing tube, pulse blowing elbow, maintenance door cover, clean room side plate can be used stainless steel.
At the same time in the dust collector structure to further optimize, sealing type of good or bad mainly depends on the shell, to make the shell to maintain a good seal, must ensure its manufacturing and installation quality. All connections of the shell should be welded continuously, and the welds should be checked by kerosene penetration method.
The top of the dust collector is the concentrated part of gas accumulation and condensation, and is also the most serious area of corrosion. In view of the problem that the access door on the top of the structure of low net gas chamber is easy to leak air, resulting in cold and hot condensation, we put forward two solutions.
1. Structure of upper and lower door covers: double layer insulation access door is used for dust collector at the end of kiln, and the access door is made of upper and lower layers. Heat-resistant silicone rubber should be used for sealing around the door frame.
This scheme combined with the structural characteristics of waste incineration high corrosion flue gas precipitator, the original equipment flue structure does not need to be changed, the equipment changes less, maintenance is safer, at the same time because of the heavy door cover, can be set on the top of the simple car for door cover replacement.
2. High clean air chamber structure: the top clean room is raised to 4 meters as a whole, and each room at the top is provided with an access door. The replacement of the dust filter bag is completed in the clean air chamber.
This scheme costs more and needs to replace the entire top structure. At the same time, safety needs to be considered because the maintenance belongs to a confined space.
At the same time, due to the exchange of hot and cold air, it is extremely easy to cause condensation. It is generally recommended that the elbow be replaced with stainless steel material, and the flower plate can be replaced with 316L stainless steel material if possible.
Conclusion
Due to the improvement of cement process, the dust collector at the end of cement kiln has corrosive smoke, so the original dust collector needs to be designed and manufactured with anti-corrosion, and the structure should be optimized and improved with low air leakage to ensure the long-term stable operation of the equipment.