Stack Height

by Constantin

Gas Flaring

Gas Flaring

I need to size the height of a dispersion stack for the hydrogen sulphide.

Barry's Response - Hi Constantin:

Determining the optimal height for these stacks is what I do mostly. What I use for inputs in this type of assessment is:

If the stack is to be used as a gas flare:
1 - Flow rate (cubic metres per day for example) at standard temperature and pressure
2 - Gas composition with mole fraction (or percent) for each component, or at least gas heating value and H2S content
3 - The stack exit diameter, at the tip
4 - Location of stack (longitude and latitude)
5 - The applicable air quality standards in your country for one-hour, 24-hour and/or annual H2S and SO2 concentrations (in ppm or µg/m3).

If the stack has no flame coming from the tip:
1 - The stack diameter
2 - The exit temperature
3 - The exit velocity
4 - The H2S and/or SO2 emission rate (in grams per second for example)
5 - Location of stack (longitude and latitude) and position relative to nearest buildings, along with building dimensions.
6 - The applicable air quality standards in your country for one-hour H2S and SO2 concentrations (in ppm or µg/m3).
7 - These same parameters will also work for sources of NOx particulate and various other species.

This information will allow a simple screening assessment. To make for a more refined study I would need:

1 - Stack base elevation and terrain maps with elevations in the general region of the flare site, usually within 10 kilometres.
2 - At least one year (preferably five) of hourly observed meteorological data. Temperature, wind direction, wind speed, sunshine intensity are useful input parameters for the ISC-PRIME model (for instance).

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Stack tip exit temperature
by: Anonymous

Does the stack tip exit temperature take into account the ambient air temperature. For example, if the stack tip exhaust gas temperature is 100 degrees F and the ambient air temperature is 90 degrees F is the stack exit temperature 190 degrees F? What temperature would be used in air dispersion modeling?

Thank you,

Barry's Response - In most cases of atmospheric dispersion modelling, meteorological data is encoded into hourly records for a total of 5 years. Each record includes an ambient temperature reading which is used in the buoyancy and dispersion calculations. Generally speaking, the difference between the stack temperature and the ambient is of greatest importance.

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