10 replies to this topic

[arun261085]

In refinery SRU units incineator is hept at the tail end of the SRU unit to convert unconvertable H2S into SO2 before venting to atmosphere. TLV Data suggest SO2 is more toxic and heavier than H2S.Then why refineries convert less toxic materials H2S to more Toxic SO2??? Waiting for calrifications....

[SUPRIYAPRA]

Simple Arun, It is a colorless, very poisonous, flammable gas. Even at 5 ppm inhallation by body, you can imagine the result. SO2 is not poisonous gas.

[Fr3dd]

As DHIREN said, H2S is not only toxic, but deadly at really low concentrations. Please double check your toxicity data sources, bear in mind that it is "Hydrogen Sulphide" (H2S) and not sulphuric acid or other sulphur-related substances.

As a process engineer working in the oil industry, you should always be aware of the presence of this substance in your designs. It requires a lot of safety measures and a good material selection.

Regards,

[Dacs]

SO2 is lesser of two evils, in comparison in what H2S can do to a person (affects one's nervous system, knocking you down when inhaled in enough quantities).

[breizh]

Take some time to read MSDS .

Breizh

[arun261085]

I have attached the MSDS of H2S and S02 which shows TLV of S02 as 2 PPM and that of H2S as 10 PPM, which clearly implies that SO2 is more toxic than H2S.Dont know how you peoples are saying H2S as more toxic than SO2??????

Attached Files

•  Sulfur Dioxide.pdf   84.65KB   69 downloads
•  h2s copy.pdf   21.32KB   62 downloads

[Dacs]

Yes, SO2 is more toxic than H2S per molecule basis, but SO2 does not incapacitate you (which means you can run away from any source of leakage), while H2S surely does (you're dead if you get knocked out).

At least that's my understanding of things.

[Fr3dd]

Dear arun261085

Taking a look at the MSDS you attached, I understand why you may be confused. Bear in mind that you're comparing threshold limits of exposure. This means that a worker could be exposed to this concentration of the substance day after day without adverse health effects. In this case, a regular exposure to 2ppm of SO2 will be harmful, meanwhile, the maximun concentration at which you can have regular exposure to H2S is 10ppm.

Both gases are dangerous but, as Dacs says, the health effects are more severe and can happen a lot quicker when exposed to H2S than to SO2. For example, a prolonged exposure to 400ppm of SO2 affects the lungs and could lead to death. The exposure to 400ppm of H2S will produce unconciousness and breathing stop in a short time. Also, H2S attacks the sense of smell making it harder to detect at higher concentrations.

However, this incinerators are suposed to burn a small quantity of this gases (most of the sulphur is recovered as elemental sulphur), and the resultant SO2 is dispersed after venting. If by mistake you release a high concentration of SO2 for a few minutes, some people may have irritations and minor health issues; if you do the same mistake with H2S, people may die.

Regards,

[Pronab]

H2S is combustible, while SO2 is not. that is why before venting to atmosphere, need to convert H2S to SO2 to avoid any accumulation whichwill finally cause of explosion.

[Ali_gholamalian]

Dear Arun

In fact Sulfur Recovery Plant(Unit) has made to recover sulfur from H2S gas (from LPG treating units eg MEROX unit). SRU feed is H2S and the product is solid sulfur. Main process in SRU unit is a catalytic process which named Claus Process.
The overall reaction in Claus (with activated aluminum) is:
2(H2S) + (SO2)* <--> 3S + 2(H2O)

* Required SO2 for is produced by H2S combustion.

[Padmakar Katre]

In refinery SRU units incineator is hept at the tail end of the SRU unit to convert unconvertable H2S into SO2 before venting to atmosphere. TLV Data suggest SO2 is more toxic and heavier than H2S.Then why refineries convert less toxic materials H2S to more Toxic SO2??? Waiting for calrifications....

Hi,
Please understand the SRU process and answer will be with you. What do you mean by venting to atmosphere? Please go through the reaction steps to understand this. I hope it explains your issue.