【Identify hidden dangers around you】Flame detectors ‘blinded’ by dust

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【Identify hidden dangers around us】Flame detectors blinded by dust. There are various types of heating furnaces in chemical enterprises. To effectively monitor the combustion of flames within these furnaces and prevent flash explosions caused by the accumulation of flammable gases in case of sudden flame out, installing flame detectors is a common monitoring method. Recently, however, while inspecting a company, the author saw a flame detector that had been \"blinded\" by dust. The author and other experts found that there were two alarms related to flame detection in the pre-hydrogenation heater of one of the company’s production units that were not addressed in a timely manner; the DCS indicated that these flame detectors were in a red alarm state, indicating an abnormal condition. Upon inquiry, the operator said, “These flame detectors were added after maintenance and are still in the testing phase. They have been giving abnormal alarms frequently lately; we suspect there is a problem with the instruments. The furnace should be functioning normally, and our operators have carried out regular inspections without finding any abnormalities with the flames.” ”But the operator’s explanation did not completely dispel our doubts, so we said to the manager beside us, “Let’s go to the site together to check it out.” ”Upon arriving at the site and looking through the viewing window of one of the heating furnaces, it was seen that there was almost no flame coming from the burners inside; everyone present was terrified. Experts emphasized, \"If this burner goes completely out and the fuel gas valve is suddenly opened wide during operation, causing a large accumulation of fuel gas, it is very likely to lead to a flash explosion. Fortunately, it was detected in time; otherwise, the consequences would have been disastrous!\" ” Meanwhile, the operator checking the other furnace reported that all burners in the other furnace were burning normally; he concluded that there was a problem with the flame detector. But the instrument engineer said, “There’s nothing wrong with the instrument itself. We’ve been working on this issue lately; every time we removed the flame detector probe, there was a thick layer of dust on its lens. It’s likely this dust is the reason why the flame couldn’t be detected, which in turn triggered the alarm.” ” Experts say, “During the production process, we must promptly verify all instrument alarms and eliminate the causes of instrument failures; we cannot ignore them.” In the event that the story of ‘The Boy Who Cried Wolf’ actually comes to pass one day, ignoring it could lead to serious explosion accidents. ” Basis for potential hazards: A flame detector is a device used to measure the intensity of the flame in a combustion chamber or burner. It consists mainly of a probe and a signal processor, and it outputs an analog signal indicating the flame intensity, a digital signal indicating whether there is a flame or not, and/or a video signal representing the flame intensity. A visible light flame detector uses a photodiode as the sensing element, and is composed of components such as a probe, a housing, and cooling equipment. The visible light in the furnace flame passes through the lens at the end of the probe, is transmitted via optical fibers to a photodiode, which detects the visible light signal. In the above example, it was precisely because the lens of the detector was covered with dust that no light signal could be detected, resulting in the flame detector issuing a false alarm. Therefore, under normal circumstances, after installation, this type of detector should be tilted at 30 to 45 degrees downward, allowing it to look both downward and forward while reducing the likelihood of mirror contamination. There are also some detectors that come with a purge air line from the factory, which can promptly remove dust from their surfaces. Article 7 of Item 2, which deals with the elimination of outdated equipment listed in the \"Catalogue of Outdated Safety Production Processes, Technologies and Equipment for Hazardous Chemicals (First Batch)\) issued by the General Office of the Ministry of Emergency Management: Gas heating furnaces and heat transfer oil furnaces without flame monitoring and flameout protection systems are prone to cause explosions in the furnace chamber, and it is required that these furnaces be upgraded within one year. However, many chemical companies have still not completed the required rectifications to date. Even those that have completed the rectifications have failed to put their safety facilities into use for various reasons. Safety facilities exist only in name, with no progress made in addressing potential hazards. Are the company’s executives aware of such risks? Are the employees aware that they are in danger? Are there any issues of formalism in safety supervision, inspections, and hazard identification? Are these procedures being carried out merely as a formality? Therefore, strictly implementing the requirements for hazard rectification and ensuring the normal operation of safety facilities are fundamental guarantees and necessary conditions for enhancing an enterprise’s inherent safety level and preventing major safety accidents involving hazardous chemicals.