Burning mercaptans and H2S

[rogered]

Hello everybody

My question relates to using fired heaters to perform incineration tasks:

My current project has a large, 30 MW fired heater burning a lean fuel gas (3000 kg/hr). I have 2 offgas streams that I want to burn along with the fuel gas.

1. Sour water stripper gas, which is basically wet fuel gas containing 2% H2S (800 kg/hr)
2. tank vent gas, mainly Nitrogen containing < 10ppm mercaptans (300 kg/hr)

Fired heater vendors tell me that there's no problem with these additional gas streams - they burn well and the noxious components, ie. the H2S and the mercaptans, will be completely destroyed.

Has anyone any positive or negative experience of something similar, and even more importantly, is there any information in the public domain which covers burning of mercaptans & H2S?

Many thanks

Rogered

 

[orenda1168]

Have you worked out the SO2 concentration issue in the heater's flue gas, as well as potential cold end corrosion from SO3/condensed sulfuric acid?

Orenda

 

[mbeychok]

Hydrogen sulfide and mercaptans will not be completely destroyed. They will be converted to SO2 and some amount of SO3 plus water vapor.

As pointed out by Orenda1168, that will lead to problems with your local air pollution regulatory agency and possibly to corrosion as well.

If you are in the U.S., i would think that no regulatory agency will allow you to burn gas containing 2% (20,000 ppm) of hydrogen sulfide.

As for your "Sour water stripper gas, which is basically wet fuel gas containing 2% H2S (800 kg/hr)", sour water stripper gas (in petroleum refineries) is usually water vapor, hydrogen sulfide and ammonia. It is not a "fuel gas". It is usually sent to a Claus sulfur recovery unit for conversion into elemental sulfur.

Also, sour water stripper gas (in petroleum refineries) usually has a hydrogen sulfide concentration of perhaps about 25 wt% or 16 vol% ... so I am confused about your 2% hydrogen sulfide. Is your sour water stripper in a petroleum refinery? And is your 2% by volume or by weight?

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[rogered]

Milton

The Hydrogen sulphide is 2% by volume. The sour water stripper is a fuel gas stripped unit which was originally to discharge to an incinerator. The current plan is to send to a fired heater instead. Ultimately whether from fired heater or incinerator the gas ends up converted to SOx - my question is more how effectively the H2S is burnt in a fired heater, and more importantly perhaps, whether the mercaptans will burn effectively. And whether there is a reference to this in published literature.

rogered

 

[rneill]

Usually the heater/burner manufacturer will provide you fuel gas quality specifications and will not warranty the equipment if you operate outside these limits so it would be worthwhile to see what the fuel gas spec said. Regardless, the degree of combustion of the contaminants is not going to be as good in the heater vs. an incinerator.

Section 22 of the old GPSA "Engineering Data Book" is on Sulphur Recovery and has a section talking about incineration of H2S and conversion to SO2. Unfortunately, I only have this in hardcopy.

Other than that, this is not quite on target but this document may have something of use in it?

http://www.ercb.ca/docs/documents/directives/Directive060.pdf

Also,
Paper 03362 from NACE 2003 "Corrosion Issues - Incinerators and Incinerator Air Pollution Control Systems".