40ppm sulfure in boiler fuel gas

[GenB]

Gentlemen:

I am to build a small water boiler
(1,000,000BTU/Hr); Temp: 250d.F.
The fuel is:
Wastewater digester gas (bio gas) 75% CH4 gas
-H2S content: 40 ppm (0.004%) of Sulfur as H2S form.

I am to choose the best carbon steel for the job or if not c/s will be stainless.
What about the burner materials? (a power burner will be used)

How rusty is this 40ppm (.004%)amount of sulfure?

Thanks, genb

 

[mbeychok]

GenB:

40 ppm by volume of H2S (and I am assuming that you meant ppm by volume rather than ppm by weight) is good enough for a fuel gas. Here in Los Angeles, California, the local governmental air quality management agency would accept that. The national Environmental Protection Agency of the USA would accept 159 ppm by volume.

When that gas is burned, the H2S will be converted to SO2 (sulfur dioxide) and some small amount of SO3 (sulfur trioxide) and the CH4 (methane) will be converted to carbon dioxide and water vapor. That means that your combustion flue gas stack or vent may be subject to excessive corrosion if any of the water vapor condenses in the flue gas stack and combines with the SO2 and SO3 to form a weak acid. You really should talk to a knowledgeable boiler manufacturer about how to protect your flue gas stack and what materials to use for that stack.

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

 

[GenB]

mbeychok,
Thanks,
I will use stainless steel for the stack.
my concern are the boiler because is of carbon steel.
according to your suggestions: the boiler will not be a problem but the after burning acids.
What about the burner, will I experience any rust?
genb

 

[mbeychok]

GenB:

I don't consider myself to be an expert on burner design, but I have never heard of very small amounts of H2S in fuel gas causing burners to "rust". Again, I suggest that you consult a good boiler design manyfacturer.

As for the stainless steel flue gas stack, I would suggest it be well insulated to prevent heat loss and condensation of the water vapor in the flue gas ... especially if you live in a cold climate and the flue gas stack will be subjected to very cold external temperatures.

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

 

[dcasto]

I would not make the stack out of stainless unles you start/stop the unit several times a week, the stack will last for a decade before it may need replacement. The condensation temperature for sulphuric acid is slightly higher than that of water, so about 212F. Just make sure that when you shut it down to dry out the fire tubes or stack so the acid won't go to work.

 

[kenvlach]

GenB,
Are you in California?
You will need Air Permits (one to construct, one to operate).
Find your local Air Pollution Control District here:

http://www.arb.ca.gov/capcoa/dismap.htm

It's not a good idea to build your own boiler in CA -- Initial equipment testing for air emissions cost $18k about 5 years ago, probably more now. Better to buy equipment that's been pre-certified by the SCAQMD, as the other APCDs accept their certs. Low-NO_x burners, etc. List of certified Large Water Heaters and Small Boilers and Process Heaters is available here:

http://www.aqmd.gov/rules/doc/r1146/r1146table.html

Also, maybe not a good idea to buy a 1-Million BTU boiler; get one that's mfr-rated 990,000 BTU, as the air regulations are less strict, both initially & for annual testing. Check your APCD rules.

Some CA vendors:

http://www.ajaxboiler.com/

http://www.parkerboiler.com/

http://www.rfmacdonald.com/boilers/ajax.html

You can find more from the SCAQMD certified equipment list.

 

[GenB]

kenvlach,
Who are you that know so much about our environ in CA?
I am in the SCAQMD LIST (not the big & famous ones in you list) but a small one with a whole bunch of models with a small production 'generalboiler'


I found that my standard unit will run on the type of gas;
this one is going outside the District's jurisdiction so there is no restriction.The stack is responsibility of the installer, i can only suggest on that.
Note that: The installation of the stack is done by starting horizontally with a drip elbow so the condensation will not get into the boiler.

Thanks for all the replies, I appreciate the input.
genb