# Environmental Science/Sulphur calculation

Question
Dear Sir,
How do i can exactly calculate the sulphur content in a sour gas. if the gas capacity is 30 mmscfd with the system design of 0.12% H2S content.

It depends on how the Sulfur Content is measured, whether by weight or by volume.
Since you specified the measurement is about 30mm scfd, that indicates temperature and pressure, but the remaining question is what's in the gas stream besides H2S?  Usually, "sour gas" is a term reserved for petrolum gases, and they have higher molecular weight than Methane or Natural gas ( one in the same thing). You need to find out the average molecular weight of the gas,and for the sake of argument, I'll assume that it is all ethane or C2H6 which has an average density of 1.24 gm/cm3 and a molecular weight of 30.07 gm/ Mole. The Mol Wt. of H2S is 30.0908
One mole is 22.7L and there are 28.3168 L/ ft3.  Now there is a slight temperature conversion problem because a mole is defined at 0C and STP is often at 68F (or 20C). The gas laws indicate that the volume of the 22.7L is multiplied by 293/273 for the volume to correct it for temperature, and that gives 24.363 L as the volume of 30.07 gm of ethane at 20C. Since most gases are set by weight, the revised Mol wt of the gas is 30.07*0.9988+0.0012*30.0908 or about 30.1 gm
Now there are 28.316/24.363 about 1.1225 mol/Cubic foot. 1,000,000 cubic feet of gas at STP will weigh 1.225*10E6 moles *30.1 grams/mole * 1 pound/453.6 grams  or about 81,288.5 lb of  mixed gas, of which 0.0012 is H2S or 97.54 lb of H2S per 1,000,000 Cubic feet.
I assume you can do the multiplication by 30.
Dave

Environmental Science

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#### David L. Russell, PE

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