Assist air (flare)

Assist air means all air that intentionally is introduced prior to or at a flare tip through nozzles or other hardware conveyance for the purposes including, but not limited to, protecting the design of the flare tip, promoting turbulence for mixing or inducing air into the flame. Assist air includes premix assist air and perimeter assist air. Assist air does not include the surrounding ambient air.

Elevated Flare definitions and calculation methods from 40 CFR 63 Subpart CC section 63.641

Assist steam (flare)

Assist steam means all steam that intentionally is introduced prior to or at a flare tip through nozzles or other hardware conveyance for the purposes including, but not limited to, protecting the design of the flare tip, promoting turbulence for mixing or inducing air into the flame. Assist steam includes, but is not necessarily limited to, center steam, lower steam and upper steam.

ref: Elevated Flare definitions and calculation methods from 40 CFR 63 Subpart CC section 63.641

Black smoke (black plume)

A plume of black smoke with soot. It indicates low combustion efficiency – incomplete combustion of hydrocarbons can lead to emissions of soot (solid carbon).

Can I identify a flare with a performance issue?

Where the are a large number of flares in an operating environment it is necessary to have methods to ensure that every flare is operating to design. Flares can become extinguished for a wide range of reasons including intermittent flow, variable composition and crosswinds.

This challenge is greater where a flare operates without direct supervision for extended periods of time, such as those encountered in dispersed (unconventional) oil and gas fields.

A wide range of technologies are available to help identify a flare that has a problem.

Can I measure flare efficiency?

Historically, it has been assumed that all flares irrespective of design, operation or age perform at the same level of efficiency – with flares in production environments thought to by 98% efficient. That means that 2% of methane being sent to flare would be lost to the atmosphere.

There are now a range of technologies becoming available that allow this assumption to be improved upon by conducting measurements specific to the flare.

Where flaring is thought to be a major contributor to methane emissions, moving away from a generic emission factor to actual measurements can make a substantive difference to reported methane.

Identifying a flare that has lower efficiency than expected allows the operator to explore technical options to improve it.

Cavity ring-down spectrometer (CRDS)

 is a highly sensitive optical spectroscopic technique that enables measurement of absolute optical extinction by samples that scatter and absorb light. It has been widely used to study gaseous samples which absorb light at specific wavelengths, and in turn to determine mole fractions down to the parts per trillion level. The technique is also known as cavity ring-down laser absorption spectroscopy (CRLAS)


Centralised facility

An oil and gas production, refining or processing facility  in which the majority of equipment is within a clearly defined area with distinct boundaries. Examples include, but are not limited to offshore production facilities, refineries, LNG terminals, petrochemical plants

ref: Wiki


is a branch of fluid mechanics that uses numerical analysis and data structures to analyse and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering, fluid flows and heat transfer, and engine and combustion analysis. 

Cold Flare

A process control system that can operate as both a vent and a flare. As a vent all of the gas emitted is unburnt. When operated as a flare, hydrocarbons are combusted and emitted as CO2

Combustion zone net heating value (NHVcz)

The energy released as heat when a combustion zone gas undergoes complete combustion with oxygen to form gaseous carbon dioxide and gaseous water (also referred to as lower heating value). The net heating value in the combustion zone (NHVcz) gas correlates well with combustion efficiency for steam assisted 

flares. It is a better indicator of efficiency than the heating value of the Vent Gas alone.

Elevated Flare definitions and calculation methods from 40 CFR 63 Subpart CC section 63.641

Continuous flare

A flare that is intentionally lit for the majority of the time, usually as part of the safety critical equipment on a facility


Cross winds may lead to recutions in combusiton efficiency and destruction efficiency. Each facility shall have its own unique weather patterns which need to be considered during flare specification and operation. Insights into the effects of crosswinds come from both empirical studies and models.

Destruction (removal) efficiency (DE or DRE)

It is a percentage conversion of the hydrocarbon components entering the flare combuston zone to other compounds – CO2, CO, soot. It is calculated from the concentrations of individual flare plume components. It is always higher than combustion efficiency (except when CE is 100% – then DE is also 100%) as the latter measures complete combustion (to CO2), while destruction efficiency measures incomplete hydrocarbon combustion (to CO2, CO, soot).

Elevated Flare definitions and calculation methods from 40 CFR 63 Subpart CC section 63.641

Dispersed facility

An oil and gas production or distribution facility in which the main equipment is located across a large geographical area. Examplesi nclude, but are not limited to, gas distribution networks or unconventional oil production whereby multiple small well-pads are managed collectively.

Do I know the gas composition?

Knowing the exact makeup of gas being sent to flare has a key role in assessing exactly how much methane may be emitted to the atmosphere. This includes the proportion of methane to other hydrocarbons and the mole fraction of other gases such as carbon dioxide.

There are a number of technologies available that can assess composition operating either periodically or continuously.

Do I understand the impacts of the environment on my flare?

Each flare is subject to a unique mixture of local environmental conditions such as wind speeds.

Understanding how these may impact upon flare performance – and where possible taking action to compensate for adverse weather is an integral part of flare management.

Eddy dissipation concept

EDC model is an extension of the Eddy dissipation model. Detailed Arrhenius chemical kinetics can be incorporated in turbulent flames. However, typical reaction mechanisms are invariably stiff, and their numerical integration is computationally costly. Hence, the model should be used only when the assumption of fast chemistry is invalid, such as modelling the slow CO burnout in rapidly quenched flames, or the NO conversion in selective non-catalytic reduction (SNCR). 

ref: ANSYS Fluent Theory Guide

Empirical studies

The challenges in measuring flare efficinecy in the field have led to a number of empirical studies being designed using both full scale and reduced sacale flares with additional instrumentation designed to analyse the flare products. Whilst these provide useful insights in to flare performance cautuion is required to consider how close the experimental design replicates in-field conditions including environmental effects.

Extractive sampling

The process of measuring flaring combustion by extracting part of the plume and analysing the absolute quantities of burnt and unburnt gas by measn of a traceable method such as mass spectrometry.

ref: McDaniel et al. 1983 Flare Efficiency Study. EPA report 600/2-83-052

Flare pilots (pilot burners)

A source of ignition is needed to assure the safe destruction of any hydrocarbons sent to the flare, including hydrocarbons in the purge or sweep gas. Reliable ignition is obtained by continuous pilot burners designed for stability and positioned around the outer perimeter of the flare tip.

ref: http://Chapter 1 – Flares (

Flare sweep gas

for a flare with a flare gas recovery system, the gas intentionally introduced into the flare header system to maintain a constant flow of gas through the flare header in order to prevent oxygen buildup in the flare header; flare sweep gas in these flares is introduced prior to and recovered by the flare gas recovery system. For a flare without a flare gas recovery system, flare sweep gas means the gas intentionally introduced into the flare header system to maintain a constant flow of gas through the flare header and out the flare tip in order to prevent oxygen buildup in the flare header and to prevent oxygen infiltration (backflow) into the flare tip.

ref: Elevated Flare definitions and calculation methods from 40 CFR 63 Subpart CC section 63.641

Fugitive emissions

Unintentional emissions of gas from equipment and processes. Typical equipment components where fugitive emissions can occur are valves, screwed connections, flanges, open-ended lines and pump seals.

ref: Methane glossary | IPIECA

Glint mode measurements

Satellite measurements at more acute angles, positioning the spacecraft’s sensor so it focuses on the point where the sun’s light reflects most strongly off the sea – the “glint spot to overcome challenges associated with measurement over water

How is the flare designed to minimise methane?

There are a wide range of flare designs – configured to operate effectively in the different operating environments in which they are used, the amount of gas that they may need to be able to burn, variability in volumes and composition.

Selection of an appropriate flare can have significant impact upon the reliability of the flare and to minimise the amount of methane that is emitted to atmosphere – either through reducing the amount of gas consumed which in pilot mode  or through the efficiency of combustion.

Improve efficiencies

Maintaining effective cobustion efficiency and destruction efficiency are key to minimising methane from flaring. This can be achieved through improving the mixing of flare gas and air to enable complete combustion and/or by only lighting the flare when required using ignition and pilot-light systems that avoid the risk of venting.


A wavelength just greater than that of the red end of the visible light spectrum but less than that of microwaves. Infrared radiationhas a wavelength from about 800nm to 1 mm, and is emitted particularly by heated objects.

ref: ISO20473


Lidar is a method for determining ranges (variable distance) by targeting an object with a laser and measuring the time for the reflected light to return to the receiver. LiDAR is an active remote sensing system – the system itself generates energy – in this case, light – to measure things on the ground. In a LiDAR system, light is emitted from a rapidly firing laser.  This light travels to the ground and reflects off of objects. The reflected light energy then returns to the LiDAR sensor where it is recorded.

Net heating value

The energy released as heat when a compound undergoes complete combustion with oxygen to form gaseous carbon dioxide and gaseous water (also referred to as lower heating value).

Net Heating Value of Dilution (NHVdil)

the Net Heating Value, in BTU/ft2 , of dilution zone gas in a Flare.   This is to ensure that there is enough combustible material available to adequately combust the gas and pass through the flammability region and also ensure that degradation of flare performance from excess aeration does not occur

Offshore facility

An oil or gas production or processing facility that is designed to operate in water. The size, function and designs vary and includes, but is not limited to, jacketed structures permanently anchored to the seabed, semi-submersible strcutures and floating  production and storage facilities. For the purposes of this toolkit it does not include shipping.

Parametric model

A Parametric Model is a concept used in statistics to describe a model in which all its information is represented within its parameters. In short, the only information needed to predict future or unknown values from the current value is the parameters. Parametric models often deal with discrete values, whereas non-parametric models will frequently incorporate continuous values and are described as having infinite dimensions. 


Perimeter assist air

the portion of assist air introduced at the perimeter of the flare tip or above the flare tip. Perimeter assist air includes air intentionally entrained in lower and upper steam. Perimeter assist air includes all assist air except premix assist air.

Periodic flaring

Any flare that is not operated continuously but is integral to the design and/or operation of a facility.

Permanent flare

Any flare that is installed as an integral part of a facility design and operated either on a continuous  basis

Predictive feedback and control

The inclusion of feedback systems into flare monitoring allows adjustments to be made to how the flare is operated to maintain good combustion efficiency. As many influences on flares are transient – such as corsswinds, these systems need to operate in near real-time to afford the maximum benefits to the operation.

Predictive systems and calculations

The efficiency of combustion can be calculated based upon the flare gas composition, volumes, and data on the flare design from which exit velocities and mixing can be estimated. These calculations can either be done by the operator directly or obtained from pre-built simulation software. Recent advances in computing have supported the development of predictive systems providing real-time feedback on calculated values. In all cases, the quality of calculations is dictated by the quality of data that is available on flare volumes, composition, and flare design.

Premix assist air

the portion of assist air that is introduced to the flare vent gas, whether injected or induced, prior to the flare tip. Premix assist air also includes any air intentionally entrained in center steam.

Probabilistic density function

The composition PDF transport model, like the EDC model, should be used when you are interested in simulating finite-rate chemical kinetic effects in turbulent reacting flows. With an appropriate chemical mechanism, kinetically controlled species such as CO and NOx, as well as flame extinction and ignition, can be predicted. ANSYS FLUENT has two different discretizations of the composition PDF transport equation, namely Lagrangian and Eulerian. The Lagrangian method is strictly more accurate than the Eulerian method but requires significantly longer run time to converge. Turbulent combustion is governed by the reacting Navier-Stokes equations. While this equation set is accurate, its direct solution (where all turbulent scales are resolved) is far too expensive for practical turbulent flows. In Species Transport and Finite-Rate Chemistry, the species equations are Reynolds averaged, which leads to unknown terms for the turbulent scalar flux and the mean reaction rate. 

ref: ANSYS Fluent Theory Guide


Radiometry is the science of measurement of optical radiation at any wavelength, based simply on physical measurements. Radiant energy cannot be measured quantitatively directly, but must always be converted into some other form such as thermal, electrical, or chemical. Radiometry applies over the entire electromagnetic spectrum, not just the optical region. 


Reduce purge consumption

Flares are a safety device and many designs require the flare to remain permanently lit. To ensure that there is no ingress of air into the system (which may lead to an explosion) a minimum amount of gas passing through the flare is required. This purge gas is part of safe and reliable operations. For flares that spend extended periods in this standby state the amount of gas consumed is a significant contributor to overall emissions including methane. This may be reduced in a range of flare designs.

Remote sensing

Remote sensing is the process of characterizing an area at a distance by analyzing reflected and emitted electromagnetic radiation. In recent years there have been a range of developments that allow this methodology to be used to assess flare efficiency. In general, they are either based around measurement of methane itself or infer flare volumes from the heat signature. In all cases, information on flaring volumes is also required to fully assess efficiency.


Any change of design or functionof a flare that can be effectively made after the original commissioning has been completed.

Satellite monitoring

Remote sensing using satellite technology is emerging as a powerful tool for investigating methane emissions of all kinds. Where a large number of flares are operated over wide or inaccessible areas the satellite may be effectively used to highlight locations that require closer inspection. Monitoring technology is either based upon methane itself or the distinct thermal signature of a lit flare.

Secondary data (inferred performance)

Secondary data – such as the appearance or increase of soot may be used to infer that the performance of a flare has changed. Whilst this is not a measure of methane itself it may act as an indicator for further investigation.

Sensor arrays

Sensors are devices that measure physical properties such as methane concentration, temperature, or radiance. When permanently installed they can be used to identify changes in emissions, such as when flare performance has deteriorated.


Sensors are devices that measure physical properties such as methane concentration, temperature, or radiance. For measuring flare efficiency the sensor must be capable of measuring methane and in some cases other combustion products. The sensor has to be manouvered in to a location where it intersects with the flare plume – either through the use of drone technology or aircraft. Where only methane is being measured, additional data on flare volumes is required to derive combusiton effificiency estimates.


Spectrometry is the observation and measurement of wavelengths of light or other electromagnetic radiation. Once a range of wavelengths, or a spectrum, for a gas mixture has been measured, by observing the intensity or amplitude of individual wavelengths, the method allows for the determination of the chemical composition of that gas mixture. Spectrometry is typically performed with the use of a spectrometer which is an instrument that separates and measures the spectral components of the sample or object being studied. Various types exist, but the most used are either a mass spectrometer or an optical spectrometer.


Spectrometry is the measurement of the interactions between light and matter, and the reactions and measurements of radiation intensity and wavelength. In other words, spectrometry is a method of studying and measuring a specific spectrum, and it’s widely used for the spectroscopic analysis of sample materials. It’s the practical application where results are generated, helping in the quantification of, for example, absorbance, optical density or transmittance.



Spectrometry inlcudes a broad range of technologies that measure electromagetic spectra. These include energy emitted by the flare itself (such as infra red radiation) or how the flare interacts with energy from a knowen source such a a tuneable laser. By measuring these spectra detailed information can be obtained on the nature and emissions from the flare allowing efficinecy to be calculated.


Spectroscopy is the analysis of the interaction between matter and any portion of the electromagnetic spectrum. Spectroscopy can involve any interaction between light and matter, including absorption, emission, scattering, etc. Emitted and absorbed spectra can be used to gain information about the material.


Temporary Flare

A flare that has been installed for a limited time period for the purposes of non routine operations, such as to permit maintenance on another part of a facility.


Infrared thermography (IRT), thermal video and thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object

Tip deterioration and inspection

Regular inspection of the flare is essential to maintaining safe and reliable operations. A range of techniues are now available to allow inspection to be carried out whilst the flare remains operational which reduces the risk of poor combustion efficiency

Turndown (turndown ratio)

Turndown ratio refers to the width of the operational range of a device, and is defined as the ratio of the maximum capacity to minimum capacity.

ref: Wiki

Ultrasonic flow meter

Ultrasonic Measurement uses sound waves to interrogate the fluid or object and determine various key properties. The sound waves are typically sent and received by a piezo electric transducer which converts electric signals to pressure waves and vice versa. Ultrasound spectrum includes wave frequencies from 20kHz to several gigahertz depending on the application. For example, for flowmeters, the range is typically 50kHz-2Mhz. In most flowmeters, the ultrasonic signals are typically used to precisely measure downstream and upstream transit time in a pipe. Transit time is then converted to a flow rate. The transit time also allows accurate determination of the gas sound speed, which in turn enables further properties to be calculated such as molecular weight.

Visual indicators (non-quantitative)

Visual indictors of flare performance can be used to provide basic insights in to whether the flare is combusting as designed but provide very limited data on the efficiency.

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