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Natural gas flaring and venting systems on offshore platforms and in oil extraction are used globally to burn off waste gas, excess gases and are also a means to protect process equipment, the system’s processes, and the environment.
In Part VI of this continuing series on flare flow measurement, we consider flaring natural gas in applications at offshore oil platforms, crude oil extraction, oil refineries, and chemical plants, as well as venting at atmospheric storage tanks.
If you are interested in more information, see the Sage Metering white paper, Flare Gas Measurement Using Sage Thermal Mass Flow Meters.
Offshore Platforms
On offshore production platforms, when natural gas is a byproduct, and the gas cannot be recovered or disposed of in any other manner, the gas is flared or burnt off. The operator can measure the gas with the SAGE Thermal Mass Flow Meter.
30 CFR Part 250 subpart K
Federal Regulation Title 30 CFR Part 250 subpart K Oil and Gas Requirements require operators to meter flare and vent gas volumes for deepwater facilities processing more than an average of 2000 barrels per day during a calendar month. As stated by 30 CFR 250.1163 (a) (2), “The flare/vent meters must measure all flared and vented gas within 5 percent accuracy.”
Crude Oil Extraction
Natural gas is produced during petroleum crude oil extraction. When the oil pumps from the ground, it typically contains water and natural gas. For oil and natural gas to be considered pipeline quality, it must be separated through a separator. Here, the gas is removed and sent to a separate pipeline while the remaining oil and water are heated and treated, separating the constituents. Residual natural gas or hydrocarbons are typically vented to the atmosphere or processed further while the oil goes to storage tanks. The vented vapors are typically low flow within small pipes (4”). Alternatively, when oil wells lack the infrastructure required to recover the natural gas, typically because the wells are in remote locations, much of the associated gas is flared as waste gas.
Oil Refineries and Chemical Plants
At refineries, the facility may consist of a flare system with many branch lines connecting secondary process units to the main flare header. Throughout this system, the waste gas is recycled through a vapor recovery system where the gas is recovered and returned to the process. As previously indicated, the thermal flow meter is not traditionally suitable for accurate emission measurement or obtaining a mass balance for the main flare header due to the extreme variations in gas composition. However, thermal mass flow meters can be used in refineries or chemical plants to discern which particular operation is sending flow to the flare.
Oil Refinery Regulations: EPA 40 CFR Part 60 Subpart Ja
EPA 40 CFR Part 60 Subpart Ja are performance standards for petroleum refineries and include flare flow measurement. The regulations require that all flares, except for emergency flares, be continuously monitored for gas discharges to the flare. The thrust of this regulation is that the EPA encourages refineries to install flare gas recovery systems which will “reduce emissions of SO2 by 3,200 tons/year, NOx by 1,100 tons/year, VOC by 3,400 tons/year and CO2 by 1,900,000 metric tons/year from the baseline.”1 While these regulations apply to refineries only, the oil and gas industry is looking at this as a possible future model. As previously indicated, thermal flowmeters are not suitable for this application due to the potential for significant gas composition modifications.
Atmospheric Storage Tank Vent
Atmospheric storage tanks are large aboveground containers commonly used in oil and gas production, containing liquids of oil or gas condensate. Storage tank emissions from venting are mostly volatile organic compounds (VOC) and considered hazardous air pollutants (HAP). Regulatory agencies may require that the emissions be quantified and reported. Additionally, reporting tank venting for greenhouse gas emissions is required under 40 CFR part 98.
More information on using thermal mass flow meters to measure flashing and working losses of oil and gas atmospheric storage tank emissions are on Atmospheric Storage Tank Vent.
In our next post on flare flow measurement, we explore various flow measurement technologies for flare gas measurement, including ultrasonic flow meters, averaging pitot tube, and thermal mass flow meters.
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