Mixed dehydration, sewage discharge, and fire

1. Close the sewage valve; if the fire still isn’t out, use a fire extinguisher to put it out. 2. Check whether the pipelines and valves at the site of the fire are damaged; if so, consider whether it is possible to replace them without shutting down the system first. If not, stop the vehicle. 3. Find the cause of the fire. Analyze whether the sulfur and phosphorus levels in acetylene are within acceptable limits. Analyze whether hydrogen chloride contains free chlorine. 4. Conduct an accident summary analysis in accordance with the principle of \"four must-nots\" to prevent similar accidents from occurring again.

The fire that occurs during discharge due to mixed dehydration is most likely caused by an excessively high purity of hydrogen chloride, which results in the formation of free chlorine; the high external temperatures during discharge also contribute to the occurrence of fires. The solution should lie in controlling the purity of hydrogen chloride and preventing the formation of free chlorine.

Explosions and fires can only occur under specific conditions, and they are related to factors such as temperature and concentration, that is, the degree of perchlorination. The temperature within the mixing and separation system is very low, below zero degrees, which helps to prevent explosions to some extent. Therefore, not all forms of perchlorination will lead to explosions and fires in the system; however, when waste is discharged and the external temperature rises to the ignition point, fires and explosions may occur. I saw this phenomenon many years ago.

The reaction between chlorine and acetylene is a highly exothermic reaction. Since starting work, I have been involved in several mixture explosion incidents. An emergency shutdown is triggered due to an excessive chlorine-to-hydrogen ratio, which also helps prevent accidents. However, accidents are difficult to avoid due to leaks in the synthesis furnace or failures in the hydrogen system. Many years ago, while the chlor-alkali plant was running, the PVC plant was shut down separately; nitrogen was used to displace air at the acetylene sand seal in the acetylene supply line leading to the synthesis process, and sampling analysis showed that the acetylene content was 0.001%. There is a dehydrator on the external acetylene pipeline, and dead zones exist within it where displacement does not take place. This is due to loose chlorine valves in the hydrogen chloride system, loose hydrogen chloride valves in the synthesis system, and a loose main acetylene valve. One hour after nitrogen was shut off following the successful purging of the acetylene system, the acetylene dehydration tank exploded. The explosion caused by perchlorate does not change due to external temperatures (0–minus 30 degrees). When the outdoor temperature in winter drops to nearly minus 40 degrees, accidents still happen anyway.

Chloroacetylene formed through perchlorination explodes under high temperature and shaking conditions. It’s not clear whether one molecule of chloroacetylene is produced or two; if two are produced, I’ve checked that the flash point of 1,2-dichloroethylene is 6℃