Can H2S be destroyed in the firebox?

[essenwood]

Hi all,
We have a DOE spec of <5 ppmv of H2S from our furnace stacks.
Typical Fuel gas composition contains about 100 ppmv H2S ex the amine scrubbers.
Recently we have problems in one of our process units and the this producer of Fuel gas is sending about 3000 ppm of H2S (after their amine absorber) to our fuel gas drum mix drum; resulting in approx 500 ppm H2S fuel gas quality after being mixed with other producers.


Our furnaces are run at a typical 4-5% excess O2. Is there a chance that the H2S are not fully destroyed at these ppm levels of H2S? Our fire boxes temperatures are normal.
Looking back at why they have Claus and Super Claus; made me ask this question; can H2S be fully destroyed to SO2 in normal fire boxes?


Thanks

 

[Montemayor]

essenwood:

As a Chemical Engineer you know you can't "fully destroy" any chemical compound - especially to SO2! What you can do is convert it to another chemical compound -like SO2 - under the proper process conditions and/or catalyst(s). The term "destroy" as it relates to compounds is hardly -if ever- used in chemical or chemical engineering practice.

I'm not nit-picking your use of the English language; I'm wondering if you understand the basis under which chemical reactions take place in order to address your concern. In my experience, in a properly designed furnace and with proper burners, most or all sulfur compounds will be combusted (thermally oxidized) to the basic sulfur oxides: SO2 and SO3.

No one outside of the people who designed and built your furnace and burner(s) can predict if the H2S present in your fuel gas will be totally oxidized to the SO2 and/or SO3 levels. For this type of specific combustion question regarding existing equipment you should refer to your supplier(s). They hold the information and answers to specific performance levels of your equipment. It is next to impossible for anyone on the Forum to accurately identify precisely just what equipment and combustion efficiencies you can or are achieving. There are just too many design and operating variables involved and you have only furnished generalities like "normal fire box temperatures" - whatever normal means. The chances are, if you are operating with sufficient excess air and efficient burners, that you are converting all the H2S to SO2. However, this is only speculation at best.


Art Montemayor
Spring, TX

 

[owg]

I have seen quite a few furnaces in this type of service. You get about 50% H2S destruction and about 50% furnace destruction.

HAZOP at

http://www.curryhydrocarbons.ca

 

[Samiran]

It will indeed be very difficult to convert all the H2S - you would need a very high flame temp (> 1200 C) and adequate residence time.

However, another thing to watch out is that whether your furnace tubes are properly designed to handle this acid gases. You could be seeing cold end corrosion very easily. Confirm your tube mettallurgy.

 

[25362]

Looking at the subject from another angle. Isn't 500 ppmv higher than the ~160 ppmv allowed by EPA as a maximum H[sub]2[/sub]S concentration in a fuel gas ?

If higher values are forbidden you'll be obliged to reduce the concentration either by absorption, chemical treatment, or by changing the proportion of the dilution components.

 

[essenwood]

Thanks all for replies.
Art, it is always intimidating to ask a stupid question when you are around!

Yes, we have routed the high H2S fuel gas from the troubled unit to the flare to comply with the law. That's why the question was asked; we expected to see < 5 ppm at the furnace stacks coz we thought with the excess O2 (confirmed no leaks) we would have burnt all the H2S to NOx.
Since that was not the case, we had to flare.
Thanks

 

[essenwood]

Meant to say SOx not NOx; before I get into trouble with Art!