Improved Method for Flare Gas Measurement

Sage Metering recently released a white paper describing an improved method for determining flare gas flow using insertion style thermal mass flow meters. The innovative approach features an easy method for inserting the mass flow measuring system into the flow stream, which results in significant cost savings versus measuring flare gas with ultrasonic flowmeters. Additionally, using the Sage Thermal Mass Flow Meter for vent gas monitoring meets the accuracy requirements of  ±5% and calibration requirements, as referenced in 40 CFR 98.3.

In an eight-part series, we will bring you key aspects of the white paper if you desire to see the paper in its entirety visit measuring flare gas.

Part I: Introduction

flaring gas
Gas flaring or venting is the process of burning off combustible gas (flare gas).

Flare gas and vent gas systems are used worldwide in various industries, including oil and gas production, refining, chemical processing, gas plants, wastewater treatment facilities, and landfills. The systems are utilized to burn off waste gases, dispose of surplus gases, and protect people, equipment, and the environment. The measurement and monitoring of flare gas are necessary to ensure that the flare system is operating correctly. Additionally, strict environmental regulations often require the measurement of flare gas emitted into the atmosphere. Unfortunately, there are inherent challenges to measure and monitor flare gas that needs to be overcome, which include: extreme flow variation, the potential for changing gas composition, and working in hazardous locations. Thermal mass flow meters offer solutions for flare gas measurement and monitoring in many of these applications.

What is Flare Gas?

Flare gas systems are commonly used in industrial plants all over the world. Flare gas is the surplus gas or vapor that is typically burned through a gas flare, also known as a flare stack. Gas flaring or venting is the process of burning off combustible gas (flare gas). A gas flare is a gas combustion device used to burn off excess hydrocarbons that cannot be processed. This is a safety measure. If the gases were not burned and released into the atmosphere, it could create a combustible condition.

The purpose of gas flaring has historically been to dispose of excess combustible gases or relieve the gas pressure within a system. When global warming wasn’t considered an issue, gas flaring became a widely accepted process. Back then, there were no significant concerns relating to the environmental impact of emissions, and no incentives were given to maximize or recycle the gas destroyed in the flaring process.

Today there is a shift from burning flare gas to reducing the amount of flare gas released into the atmosphere. Natural gas is a valuable resource, and efforts to capture and recycle flare gas into renewable energy takes precedence over destroying it. Additionally, increasing pressure from global organizations, federal and state legislation encourages reducing emissions, and flare reduction is deemed a significant method to achieve the desired goal. By recycling the waste gas, we reduce the CO2 footprint and provide a source for on-site energy.

Today, gas flares are subject to stringent regulations, frequently requiring operators to measure, record, and report the amount of flared gases. Aside from the gas measurement, it is often necessary to monitor flare gas flow at various points within a complicated run of pipes, including the actual flare stack. Flow monitoring provides the user with an understanding of the gas source flowing to the flare and a relative flow rate.

Typically, gas flows to the flare system during the following:

  • Operational upsets, interruptions, or emergencies when process equipment must be quickly depressurized to avoid equipment damage
  • During start-up or shutdown, the gases cannot be safely channeled back to the system’s storage or process. Venting gas may also be required for maintenance or regeneration.
  • Continuous flare operation may include uninterrupted sweep gas through the piping systems to maintain positive pressure and prevent the buildup of combustible gases. It is also typical to provide process venting of equipment such as analyzers, gas seals, and pressure control. Additionally, pressure relief valve leakage is commonly flared.

In part II of the Sage Metering flare gas series, we will explore some of the challenges engineers and operations face when selecting the proper flow meter for flare gas flow measurement.