Calculating H2S in the Gas Phase 2

[griz76]

I've applied the pomeroy and parkhurst equation to calculate the amount of sulfides generated at forcemain discharge structure. I've been asked to calculate the concentration of hydrogen sulfide in the gas phase. Is there a way to convert the 2 mg/l of dissolved sulfides to a ppm of hydrogen sulfide?

Does anyone have any references I can go back to??

Thanks for any responses.

 

[dicksewerrat]

Is the 2mg/l H2S what comes out of solution at the discharge or the amount in solution?

 

[griz76]

Hi there,

The 2.0 mg/l is the amount in solution. To be conservative, I would assume the 2.0 mg/l will come out of solution. But how do i relate this to a H2S gas concentration. Is there a way to calculte the 2.0 mg/l to a ppm level and get an indication of the H2S concentrations that would be expected at the discharge.

Thanks

 

[bimr]

You need to assume a temperature, a wastewater flow rate and an air flow.

2 mg/l X (the waste water flow rate) will give you mass flow rate of H2S. Example:

Lbs of H2S = 2 MGD x 2 mg/l X 8.34 = 33.36 lb/day. (or 15.13 kg/day).

Once you know the mass of H2S, you need to assume the volume of air that the H2S is being dipersed into, then you will have mg H2S)/m3 air.

ppm - Parts (of vapor or gas) per million (parts of air) by volume.

The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). At an ambient pressure of 1 atmosphere, the general equation is:

ppmv = (mg/m3)(273.15 + °C) / (12.187)(MW)


where: ppmv = ppm by volume (i.e., volume of gaseous pollutant per 106 volumes of ambient air)

mg/m3 = milligrams of gaseous pollutant per cubic meter of ambient air

MW = molecular weight of the gaseous pollutant

°C = ambient air temperature in degrees Centigrade



As an example, for gaseous pollutant NOx, convert 20 mg/m3 to ppmv at 25 °C:

ppmv = (20)(273.15 + 25) / (12.187)(46.01) = 10.6

where: 46.01 = molecular weight of NO2 (i.e., NOx expressed as nitrogen dioxide)

NOTES:
(1) The pollution laws and regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. However, in other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values.
(2) 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
(3) For all practical purposes, degrees Centigrade and degrees Celsius are synonymous.

 

[KernOily]

One way to do this is with a process simulator like HYSYS, Aspen, or PRO-II. If you have a ChemE or MechE friend, maybe they could do it for you if they have the software.

This is just a flash calculation where you are calculating the equilibrium volume of gas that is flashed out of the water. Some H2S stays in solution and some flashes to the gas phase. It is a hassle to do this by hand, so you really need the software. Hope this helps - Pete

Thanks!
Pete

 

[mbeychok]

Bimr:

This is a quote from your contribution to this thread:

The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). At an ambient pressure of 1 atmosphere, the general equation is:

ppmv = (mg/m3)(273.15 + °C) / (12.187)(MW)

where: ppmv = ppm by volume (i.e., volume of gaseous pollutant per 106 volumes of ambient air)

mg/m3 = milligrams of gaseous pollutant per cubic meter of ambient air

MW = molecular weight of the gaseous pollutant

°C = ambient air temperature in degrees Centigrade

As an example, for gaseous pollutant NOx, convert 20 mg/m3 to ppmv at 25 °C:

ppmv = (20)(273.15 + 25) / (12.187)(46.01) = 10.6

where: 46.01 = molecular weight of NO2 (i.e., NOx expressed as nitrogen dioxide)

NOTES:
(1) The pollution laws and regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. However, in other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values.
(2) 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
(3) For all practical purposes, degrees Centigrade and degrees Celsius are synonymous.

I am flattered that you took the above quoted information from my website at

http://www.air-dispersion.com/formulas.html

but the next time you do this, please include credit for the source of your information.

Regards,

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