Seek advice on the implementation of fluid diversion facilities for chemical plant cofferdams

Cannot the drainage ditch of the device cofferdam exceed 30 meters? What are the standards there?

Yes, GB50160-2008, 7.3.2； 7.3.37.3.2 The discharge of production wastewater shall be carried out through concealed pipes or concealed ditches with a soil cover thickness of not less than 200 mm. If open-channel drainage must be used inside the facility, it should be arranged in sections, with each section having a length not exceeding 30 m; the distance between adjacent sections should not be less than 2 m. 7.3.3 Water seals shall be installed at the following locations of the production wastewater pipelines, with a height of not less than 250 mm: 1. The drainage outlets of the enclosures around towers, heating furnaces, pumps, heat exchangers, etc., within the process units ； 2. Drainage outlets for process units, tank groups, or other facilities, as well as buildings, structures, pipe trenches, etc ； 3. On the branch pipes at the intersections of branch pipes and main pipes throughout the plant ； 4. For plant-wide branch and main pipes, sections of the main pipes that are longer than 300 m should be separated using water seal wells. Explanation of the provision: 7.3.2 Ditches or trenches that have only covers but no soil covering (where the covers are often removed and thus prone to damage) are susceptible to external influences that can lead to contact with sources of fire. There is a high likelihood of fires breaking out, and when fires do occur, they spread rapidly and cause significant damage. It is difficult to extinguish such fires, and explosions resulting from them can cause the covers to break away, leading to further damage. During maintenance work in the distillation section of a refinery, channel steel was cut at a distance of 3 meters from a drainage ditch; sparks fell into the ditch and ignited the gas there, causing fires to spread along 960 meters of the drainage ditch. The covers on 600 meters of that ditch were damaged to varying degrees, and the fire lasted for 4 hours. During maintenance at a refinery, sparks fell into a drainage ditch, igniting the oil and gas there; the fire spread to the sludge tank and burned for 2 hours. During the draining of a reforming feed tank at a refinery belonging to a petrochemical company, the oil and gas released ended up in the drainage ditch, where it was set alight by workers carrying out work downstream. 200m of drainage ditches caught fire one after another. The above examples all illustrate that discharging process wastewater through open ditches or trenches with covers but without soil cover poses a high fire risk. A concealed ditch refers to a trench covered with soil; it has good sealing properties, which prevent flammable gases from escaping. It also ensures that the cover plate does not get moved or damaged, thereby reducing the impact of external factors. Inside the facility, open ditches are often required in certain areas; in the event of a fire caused by a material leak, it could lead to the spread of the fire along these ditches. To control the spread of the fire, it is required that the length of each section not exceed 30 m, with each section being connected to the production wastewater pipeline separately. 7.3.3 This clause specifies the requirement for a water seal in production wastewater pipes. 1 Water seal height: In China, 250 mm was used in the past, while countries such as the United States, France, and Germany use 150 mm. Taking construction errors into account, this value remains set at 250 mm, as it increases safety without adding much to the workload. 2 Fire accidents in the production wastewater pipelines have occurred many times in various factories; in some cases, the fire spread for hundreds of meters or even thousands of meters along the sewer systems, several manhole covers were blown off, and it was difficult to extinguish the fire. Therefore, strict requirements are placed on the installation of water seals. In the past, less important areas such as ducts or ordinary buildings were often neglected; several accidents have occurred due to the absence of water seals at sewer outlets. For example, a refinery was carrying out pipe repair welding in a process valve chamber; the drainage pipe in that chamber lacked a water seal, allowing sparks to enter the sewer system through it. As a result, more than 400 meters of pipes caught fire, and several manhole covers were blown off. Another example is situations in which multiple petrochemical plants have experienced explosions due to wastewater from toilets being discharged into the production wastewater pipelines; since no water seal was installed at the outlets, flammable gases from external sewers entered the toilets, and when someone smoked there, an explosion occurred. 3 The drainage pipes are separated from one another by water seals, ensuring that in the event of a fire or explosion in the drainage pipes of one area, it will not spread to another area. I learned about it after reading the post, but many devices these days don’t do this

Open ditches within the cofferdam, equipped with grates, serve as diversion facilities; when discharging sewage and initial rainfall, the water flows into the sewage system, while when discharging normal rainfall, it goes into the flood drainage facilities. Equipment that requires wastewater discharge must be connected directly to the sewage system