NOTE: All industry standards and practices should be observed when installing
a powered metering device on a tank battery.
Case Study: Monitoring VOC Emissions from Oil and Condensate Storage Tanks
A recent study conducted for the Texas Environmental Research Commission (TERC) to support the Texas Commission on Environmental Quality (TCEQ) evaluated emission factors and regional emissions of speciated VOCs from oil and condensate storage tanks at wellhead and gathering sites in East Texas. Thirty-three tank batteries in the Dallas and Houston areas were used to sample vent gas emissions.
Storage tank emissions were measured by determining vent gas flow rates and sampling the vent gas for chemical composition. Tank batteries having multiple tanks were sampled through common vent gas gathering pipes located at the tops of the tanks. All vent gas (flash gas) measurements and samplings were conducted at atmospheric pressure and all potential sources of fugitive emissions were sealed before making measurements.
Flow rates were measured using a FOX Model 10A thermal mass flowmeter. The monitoring system consisted of an “instrumentation tube”, a two-inch diameter four-foot long pipe into which
all vent gas (flash gas) was routed so as to flow across the thermal mass flow sensor. The instrument probe of the flowmeter was inserted horizontally at ninety degrees into the instrumentation probe.
Vent gas (Flash gas) samples were collected from within the instrumentation tube with flowing vent gas. Vent gas (Flash gas) composition was measured using gas chromatography with flame ionization and thermal conductivity detectors. Emission factors for vent gas were derived from these field measurements and used to estimate regional emissions.
FOX flowmeters provide these advantages in emissions monitoring applications:
- Exceptional low-flow sensitivity provides accurate measurement over a wide range of venting and flaring operations
- Heated stainless steel sensor is suitable for corrosive, particulate-laden gas streams
- No temperature and pressure compensation required
- Direct Mass Measurement
- Built-in alarms, totalizers and a wide variety of communications protocols available for easy interfacing with emissions management systems
