The old problem of container classification
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The design pressure is 1.78 MPa at 100 degrees Celsius; the volume is 7 cubic meters. The fluids handled are hydrogen sulfide, ethanolamine, and thiol. It is a liquid separation tank. The drawings classify it as category 3, but I think it should be category 2. Let’s discuss this.
The reason is simply whether the equipment is a storage vessel or a separation vessel. Judging from the name, it’s better to separate them.
The toxicity levels of hydrogen sulfide, ethanolamine, and thiols can be found in available sources.
After checking, thiol is quite potent: Acute toxicity: LD50 682 mg/kg (oral, in rats)； LC50: 11227 mg/m3, 4 hours (rat inhalation). Hazardous property: Its vapors can form explosive mixtures with air. It is highly flammable and explosive in the presence of open flames or high temperatures. It reacts violently upon contact with oxidizers. Contact with acids and acid mist produces toxic gases. Reacts with water and water vapor to release toxic or flammable gases. It reacts violently with calcium hypochlorite and calcium hydroxide. Its vapor is heavier than air, allowing it to spread over considerable distances at lower levels; it can ignite and cause backdraft when exposed to an open flame. In the event of high temperatures, the pressure inside the container increases, posing a risk of cracking and explosion. It seems this is considered a highly hazardous medium, which means it falls under category three containers.
It belongs to category 3; hydrogen sulfide, ethanolamine, and thiol are all non-corrosive substances. A pressure of 170 kilograms falls within the range of medium pressure
Category three: the toxicity and hazard of the medium are too high
Three types of containers! Reasons for classification: 1. Article 6-1.2 of the Code: “Medium-pressure vessels (only for media with extremely high or high toxicity levels)”. 2. Design pressure of 1.78 MPa – classified as medium pressure; the medium is hydrogen sulfide, which is considered a highly hazardous medium, in accordance with GB5044 “Classification of Hazards from Occupational Exposure to Toxic Substances”
Hydrogen sulfide is classified as a medium-toxicity medium in HG20660.
Both ethanolamine and hydrogen sulfide are of moderate hazard; no information is available for thiols, so it is estimated that they also have a moderate or higher hazard level, which makes it a bit difficult to be certain. This jar isn’t a storage container; the key lies in the thiol, right?
I have also looked into the properties of thiol compounds; effects occur only when their concentrations are high, as indicated by LD and LC values. Compared to the LC value of hydrogen sulfide, it shouldn’t be considered highly hazardous. If it’s a separate container, I personally prefer Type 2. It should be clear why the original design classified it as category three; the toxicity of the medium and its flammability and explosiveness should be indicated on the drawing
Medium-pressure vessels with a PV product that meets the requirements are classified as Category III vessels.