Causes and prevention of fires in anti-corrosion construction of desulfurization towers

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In recent years, with the strengthening of environmental awareness and the improvement of environmental regulations, various companies have increased or improved desulfurization processes. The number of desulfurization tower construction projects has increased year by year. Fire accidents caused by improper construction during the anti-corrosion process of desulfurization towers have been reported from time to time. When searching for the keyword "desulfurization tower fire" on the Internet, the news and pictures are shocking. If anyone is careful to study the causes of these accidents, it is not difficult to find that the vast majority of accidents are caused by: Anticorrosive materials catch fire. In the early days of new desulfurization towers, the desulfurization tower was hoisted and welded after large-area anti-corrosion on the ground was completed. However, due to reasons such as the low temperature resistance of conventional anti-corrosion materials (such as vinyl glass flake cement, etc.) and the resin itself is not flame retardant, many fires occurred during later welding due to local high temperatures or falling welding slag. We had to modify the process to carry out internal anti-corrosion of the tower body after the main body of the tower was successfully constructed and all welding work was completed. Anti-corrosion after the tower body is welded is a restricted space operation. Ventilation, dust removal, lighting, coating drying, etc. will be restricted. The solvents and diluents volatilized by the anti-corrosion coating are more likely to cause explosion risks. It is even more difficult to achieve complete anti-corrosion for the roof and the narrower restricted space in the tower. The overall project duration has also been extended due to process changes, and project costs have increased. How to prevent fire accidents during anti-corrosion construction of desulfurization towers? Most papers or engineering companies give the following advice: 1. Strengthen safety training for management personnel, construction personnel and project-related personnel, and enhance safety and fire prevention awareness ； 2. Prepare appropriate and sufficient fire-fighting tools at the construction site such as: Fire sand, fire extinguishers, etc. ； 3. Check the construction conditions before construction, and construction can only be carried out after the construction conditions are met. ； 4. Strengthen safety management at the construction site. It is strictly prohibited to bring fire into the site and eliminate the use of equipment that can produce electric sparks and polishing sparks. ； 5. Reasonably arrange the construction process to prevent welding, mechanical grinding and other fire-prone processes from intersecting with anti-corrosion projects. ； 6. Other safety measures... It is not difficult to see that most of the above measures are for personnel management and process management, but in the three elements of "people, machines, and materials" in the safety production process, "people" are the most uncontrollable factors. Negligence, indifference, mood, etc. will affect the accuracy and reliability of system implementation. Let’s recall the basic causes of anti-corrosion construction fires in desulfurization towers: source of fire: Welding slag splashing, sparks caused by weak welding ground wire contact, grinding sparks, non-safe explosion-proof power supplies and lighting fixtures, impact sparks caused by tools falling to the ground, man-made fire sources ； burning matter: Paints, thinners, coatings, construction tools such as brush rollers, wires and other debris. In the absence of burning materials, even if there is a fire source, it will not cause a fire. Therefore, preventing fires in desulfurization tower anti-corrosion construction from the perspective of root control, eliminating burning materials or protecting burning materials will be the most fundamental preventive means, that is, controlling from the "material" aspect of the three elements of "people, machines, and materials", and minimizing burning materials through the selection of anti-corrosion coatings, so that most human errors are unlikely to cause fires, thereby increasing the safety of the entire anti-corrosion construction. The commonly used glass flake cement is mainly composed of about 60% 901 vinyl resin, similar curing agents, about 20% glass flakes, 15% talc powder and other fillers, and 2% styrene diluent. In order to make the coating fluid during construction, about 10% benzene needs to be added. Ethylene is used as a diluent. Styrene has a large molecular weight and poor volatility. Under the good anti-seepage and shielding effect of the fish scale structure of the glass flakes, styrene is more difficult to volatilize. Therefore, a large amount of styrene will still exist in the coating for a long time after the construction of the glass flake cement is completed, which increases safety risks. ； The density of styrene vapor is greater than that of air. When styrene evaporates, it will settle to the bottom of the construction area. As time goes by, the concentration of styrene at the bottom will become higher and higher and even reach its explosion limit. The temperature resistance limit of glass flake cement is about 180°C. When encountering high temperatures such as electric welding, the coating is destroyed. The styrene and organic resin enclosed in the coating are fully in contact with the air and have the conditions to burn, such as the temperature resistance range of glass flake cement. If it is not destroyed by a large increase to a short-term high temperature, the coating will prevent or delay combustion because the coating isolates oxygen and does not have the combustion conditions. Unfortunately, the resin used to make the glass flake cement cannot achieve a large increase in temperature resistance due to structural reasons, and the film-forming material itself is a flammable organic matter. If there is a coating that uses inorganic resin, the diluent uses water or an organic small molecule solvent that is easy to volatilize and has a very small amount of addition, and has a high temperature resistance limit, then in this construction environment, the fire hazard can be minimized from the material selection. Of course, this kind of coating must also have the anti-corrosion, wear resistance, and strong adhesion functions of glass flake cement, which is even better than glass flake cement. ZS desulfurization special anti-corrosion coating can meet the above requirements. It can achieve excellent results of direct welding without catching fire 3-4 hours after coating, and the high-temperature corrosion expansion area is less than 1cm. In June 2017, this fire protection performance was well demonstrated in the new construction project of a waste heat power generation boiler desulfurization tower in a coking plant in Lin County, Luliang, Shanxi. After the anti-corrosion of the ZS composite anti-corrosion system had just been completed on the fourth floor of the tower, due to actual production needs, the top plate of the third floor of the tower (the anti-corrosion bottom plate of the fourth floor) needed to be repaired and reinforced (welding temperature ≥1700°C). Conventional coatings, including glass flake cement coatings, pose great fire hazards, and fire operations are absolutely prohibited. After 3 hours of forced ventilation, the installation and welding team successfully completed the 4-hour welding work. When the safety officers and supervisors were conducting fire preparations and safety supervision on the fourth floor, they found that the welding part emitted less light smoke during welding, and a non-diffusing red high-temperature spot appeared locally. The red high-temperature spot disappeared after the welding was passed. Check the coating after welding. The welding area is damaged by high temperature and the corrosion expansion is only 1cm wide. After removing the corrosion expansion layer, repaint the part of the weld to repair it. The treatment method is extremely simple. When adjusting the size of the desulfurized flue at the site when it is connected to the old flue, the flue that has been coated with anti-corrosion coating must be cut at high temperature. During cutting (the cutting process temperature is ≥1000°C), the coating is destroyed and yellow smoke is emitted. After cutting and hanging, we observed and evaluated the cutting surface and the lifting lugs installed during the hoisting.: The coating damage rate at the cutting point is 0. The coating is hard and dense, and it is difficult to damage with a hammer and has almost no change (open high-temperature environment, relatively brief high-temperature contact) ； The high-temperature corrosion of the lifting lug welding joint does not exceed 1cm on one side, and the high-temperature corrosion surface is only loose and slightly bulging. There is no cracking or bulging at the junction of the expanded corrosion surface and the normal coating surface. Facts have once again verified that ZS desulfurization and anti-corrosion materials have excellent high temperature resistance (can work continuously at 750°C for a long time), the coating does not burn and is a Class B fireproof material, and the paint film is hard and dense with strong adhesion. Whether it is anti-corrosion first and then hoisting and welding, or rationally arranging processes to implement cross operations to meet the deadline, ZS-desulfurization anti-corrosion materials are the best choice. Summarize: When fires occur in desulfurization tower anti-corrosion and chimney flue anti-corrosion, the source of fire is mostly anti-corrosion materials. Reasonable selection of high-temperature-resistant non-combustible materials and coatings with good desulfurization and flue gas anti-corrosion will reduce the occurrence of fire accidents from the root cause, increase the safety factor of the anti-corrosion process, ensure the safety of personnel and equipment, and reduce various losses caused by fires to enterprises. P.S.: The newly constructed desulfurization tower in the coking plant mentioned in this article is a new patented technology of an environmental protection technology company in Shanxi. The internal structure of the desulfurization tower is more complex than that of the general desulfurization tower, but the desulfurization efficiency, flue gas treatment capacity, and smoke exhaust power are all stronger than those of the general tower. In early July, the other two desulfurization towers of the coking plant will be transformed one after another. Interested friends are also welcome to contact Zhisheng Weihua Tanggong to conduct on-site inspections.