Flash Gas Calculation Methods

The following methods for measuring flash gas emissions have been approved by the administrative authority in accordance with LAC 33:III.2104.G.1. Measurements should be done so as to represent a worst-case, highest emission scenario.
  1. Direct measurement of emissions: Test Method 1-4 (40 CFR part 60, Appendix A) for determining flow rate, and Test Method 18 (40 CFR part 60, Appendix A) for measuring gaseous organic compound emissions by gas chromatographic analysis.
  2. Measurement of gas to oil ratio: A pressurized sample of crude or condensate is obtained from an upstream vessel (separator or heater treater) and flashed in the lab. This involves bringing the sample to sampling temperature and pressure conditions and bringing a portion of the sample to storage tank (or downstream vessel) conditions of temperature and pressure (via a pressure drop). The amount of gas released per volume of oil generated is measured to estimate gas to oil ratio. The chemical composition of the flash gas is then analyzed. Appropriate sampling and laboratory techniques require prior approval of the Air Quality Assessment Division, Engineering Support Group.
As an alternative to the measurement methods above, the calculation methods below may be approved by the administrative authority on a case-by-case basis. Cases where the alternate methods may be approved include:
  •  New fields or facilities not yet in production for which testing cannot be performed; and
  • Process equipment which has a very low throughput in barrels per day, and/or a low API gravity.
Calculations should be done so as to represent a worst-case, highest emission scenario.
The alternate methods are:
  • E&PTANK program: Published by the American Petroleum Institute.
  • Process simulator: Process design programs such as HYSIM and PROSIM can be used to estimate flash losses.
  • Vazquez-Beggs correlation using a representative flash gas analysis (Vazquez, M. and H.D. Beggs. "Correlations for Fluid Physical Property Prediction," Journal of Petroleum Technology, Society of Petroleum Engineers, 1980.)