Tham khảo tài liệu 'what went wrong part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | storage Tanks 123 The source of ignition was never found but a report 19 on the explosion lists six possible causes thus confirming the view well known to everyone except those who designed and operated the plant that sources of ignition are so numerous that we can never be sure they will not turn up even though we do what we can to remove known sources. Flammable mixtures should not be deliberately allowed to form except under rigidly defined circumstances where the chance of an occasional ignition is accepted. This is particularly true where hydrogen is handled as it is more easily ignited than most other gases or vapors. The plant was restarted after 23 days. Most of the tanks are now blanketed with nitrogen but a few which were difficult to blanket are fitted with an air sparge system designed to keep the hydrogen concentration well below 25 of the lower flammable limit. f Paper mills use large quantities of water and the water is usually recycled. Buffer storage is needed and at one paper mill it took the form of a 740-m3 tank. Experience showed that this was insufficient and another tank of the same size was installed alongside. To simplify installation it was not connected in parallel with the original tank but on balance with it as shown in Figure 5-13. A week after the new tank was brought into use welders were completing the handrails on the roof when an explosion occurred in the tank. Two welders were killed and the tank was blown 20 m into the air landing on a nearby building. Figure 5-13. Extra buffer storage for water was provided by installing a second tank on balance with the first one. Lack of aeration allowed hydrogen-forming bacteria to grow and an explosion occurred. Reproduced with permission of the American Institute of Chemical Engineers. Copyright 1995 AIChE. All rights reserved. 124 What Went Wrong Investigation showed that the explosion was due to hydrogen formed by anaerobic bacteria. In the original tank the splashing of the inlet liquor
