Why do desulfurization and denitrification systems experience frequent failures?

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1.jpg On June 15, 2016, a fire broke out in a catalytic unit at a petrochemical plant during repairs to the flue stack at the desulfurization tower, resulting in the death of 4 workers who were working inside. Coincidentally, some time ago a petrochemical company in Nanjing experienced corrosion and perforation in the chimneys of its desulfurization and denitrification systems. During attempts to repair them from the outside, the rubber anti-corrosion coating inside the chimneys caught fire. Due to the strong suction force in those chimneys, it was not possible to extinguish the fire from the outside, and the burning rate was extremely fast. Fortunately, no one was injured. Why do safety accidents occur frequently in the desulfurization and denitration systems of facilities? As we all know, December 31, 2014, was the deadline by which petrochemical companies were required to meet emission standards. During this period, various flue gas desulfurization and denitrification process technologies were applied one after another without sufficient validation and without any industrial application experience. After being put into use, the performance has been inconsistent; corrosion problems with the equipment and pipelines have occurred frequently, and most of them are in a state of constant repair and shutdown. The technology is not yet mature, the equipment is substandard, and both maintenance staff and management personnel are only just beginning to understand this system; there are no lessons to be learned, so it’s still in a trial-and-error phase. Unfortunately, a mass death accident occurred at this company. It was learned that the company’s catalytic desulfurization and denitration system was put into operation in March 2015; its process technology was developed by Nanjing Engineering Company. However, the performance of this system after it was put into use was not satisfactory, as it failed to meet the design specifications. In 2016, the designers changed the type of collector, replacing the stainless steel material with PP (polypropylene) – perhaps to reduce costs or to improve corrosion resistance. The use of non-metallic, flammable components inside the tower created a significant risk of accidents. The system was upgraded in March 2016, and its performance after commissioning was fairly satisfactory. However, after one month of operation, corrosion and perforations appeared in the chimney at the top of the tower; upon stopping operations for inspection, it was found that there was localized corrosion in the stainless steel composite layer, prompting the management to decide on repairs. The repair work began in early May; the safety measures consisted of laying asbestos cloth at the bottom of the chimney for isolation, and setting up scaffolding inside the flue to carry out welding operations. I never expected that a fire accident would occur after the assignment lasted for over a month. Perhaps the construction workers were unaware that what lay below was flammable plastic, perhaps the safety personnel failed to recognize this risk, perhaps those responsible for planning lacked experience, or perhaps the person in charge of monitoring the fire did not expect the plastic collectors to catch fire. Perhaps it's all because of a lack of experience. Over the years, based on the experience in the petrochemical industry, as long as the internal air analysis shows satisfactory results, performing welding or other hot work inside a tower is generally considered safe. The creation of barriers in confined spaces is primarily intended to prevent objects from falling. The question is whether the designers provided any warnings regarding the risks of hot work inside the tower after replacing the flammable internal components Can those who have always relied on experience to do their work realize the huge risks? It can be said that no one fully realized this throughout the entire construction process. Whether it’s managers, operators, or even designers. I hope this bloody lesson will draw everyone’s attention; it was paid for with many lives, and I hope no similar accidents will occur in the future.