Air Assisted Flares

AIR ASSISTED FLARES

NAO’s air assisted flares deliver reliable smokeless combustion for onshore and offshore applications where steam is unavailable or where air assist is operationally preferred. With six engineered burner configurations and VFD blower control, NAO air assisted flare systems are sized and designed to your specific smokeless capacity requirements, relief gas pressure, and site conditions.

What Is an Air Assisted Flare?

An air assisted flare is a combustion device that uses a motor-driven blower to force air into the flare burner, mixing it with waste gas to achieve smokeless combustion. Unlike steam assisted flares, which require an active steam supply to promote air entrainment and complete combustion, air assisted flares generate the necessary combustion air mechanically. This makes them the preferred solution for offshore platforms, remote onshore locations, and any site where steam generation is unavailable, impractical, or cost-prohibitive.

Air assisted flares are used across the oil and gas, petrochemical, and chemical processing industries to combust relief gases, vent streams, and waste hydrocarbons without visible smoke. They comply with EPA smokeless combustion requirements under 40 CFR Part 60 and are designed in accordance with API Standards 521 and 537, which govern flare design and pressure-relieving system engineering.

The core operating principle is straightforward: a blower draws in ambient air and delivers it to the flare burner at a controlled rate, creating turbulent mixing with the incoming relief gas stream. This mixing promotes complete combustion, eliminating the soot and black smoke produced when hydrocarbons burn in an oxygen-starved environment. The result is a clean, stable flame that meets smokeless operation requirements across a wide range of flow conditions.

How Does an Air Assisted Flare Work?

Air assisted flares operate by mechanically delivering combustion air directly to the flare burner. Here is how the system works from inlet to flame:

1. Relief gas arrives at the flare header. Waste gas from process relief valves, blowdown systems, or continuous venting flows to the flare through a dedicated header. Gas composition, pressure, and flow rate vary depending on the process and operating conditions.

2. The blower delivers forced air to the burner. A motor-driven centrifugal or positive displacement blower supplies air at a controlled pressure and flow rate. The blower is sized based on the required air-to-fuel ratio for smokeless combustion of the specific gas stream. For heavier hydrocarbons and high-carbon gases, a higher air-to-fuel ratio is required to achieve full combustion.

3. Air and gas mix at the burner. Depending on the burner design, mixing occurs at the tip, through jet mixing, vortex action, or Coanda-effect attachment. The goal in all configurations is to create a well-mixed, turbulent air-gas stream that burns completely before leaving the visible flame envelope.

4. The VFD adjusts blower speed in real time. A Variable Frequency Drive (VFD) monitors the smokeless relief flow rate and continuously adjusts motor speed to maintain the correct air-to-fuel ratio across all operating conditions. When relief flow increases, blower speed ramps up. When flow drops, speed decreases. This prevents over-airing — which wastes energy and creates noise — and under-airing, which produces smoke.

5. Combustion is completed in the flare flame. With proper air delivery and mixing, the combustion reaction is completed within the flame, destroying hydrocarbons and volatile organic compounds with high efficiency.

VFD control is a significant operational advantage over fixed-speed blower systems. A fixed-speed blower operates at one air delivery rate regardless of relief flow, meaning it either under-airs at high loads or wastes energy at low loads. VFD-equipped systems can achieve turndown ratios of 10:1 or greater, maintaining smokeless operation and combustion efficiency across the full operating range at minimum energy cost.

When Should You Choose Air Assist Over Steam Assist?

Air assisted flares and steam assisted flares both achieve smokeless combustion, but they do so through different means and are suited to different site conditions. The right choice depends on utility availability, operating costs, site environment, and the composition of the gas stream.

Choose air assist when:

• Steam is not available at the flare location. This is the most common driver. Offshore platforms, remote production facilities, and smaller industrial sites often lack the infrastructure to supply steam at the flare stack.
• Generating or distributing steam to the flare is cost-prohibitive. Even where steam exists on a facility, running a steam line to a remote flare location adds capital cost and ongoing maintenance.
• Water consumption or steam losses are a concern. Steam assisted flares consume significant quantities of water. In water-scarce environments or where steam losses affect plant efficiency, air assist eliminates this demand entirely.
• The operating environment creates freezing risk. Steam lines and condensate systems are vulnerable to freezing in cold climates. Air assisted systems have no water-based components at the flare tip, removing this failure mode.
• You want continuous, modulated control. VFD blower control provides precise, real-time adjustment of air delivery. Steam-based turndown is more dependent on steam pressure, which can be variable.

Choose steam assist when:

• Steam is already available at the flare location at adequate pressure. If steam supply is reliable and the capital cost of steam injection infrastructure is already built in, steam assist can be the more economical choice for a new installation.
• High Flow Rates: The application involves very high smokeless flow rates where steam injection is the established design practice.

Air Assisted vs. Steam Assisted Flares: Comparison

Key Design Factors for Air Assisted Flare Selection

Selecting the right air assisted flare system requires two primary design inputs, along with gas composition data:

1. Smokeless Capacity

Smokeless capacity is the maximum gas flow rate, expressed in MMSCFD, lb/hr, or equivalent units, at which the flare must operate without producing visible smoke. This is not the same as the total design flare capacity. Many flare systems are designed for large emergency relief cases that rarely or never occur in practice. Smokeless capacity is typically set at a lower flow rate that covers normal operations and minor relief events. Oversizing smokeless capacity drives up blower size and operating cost without operational benefit.

Determining the correct smokeless capacity requires a careful review of the relief load cases, distinguishing between continuous and intermittent flows, and understanding the composition of the gases that will be flared during smokeless operation. NAO engineers work with clients to establish the right design basis before selecting a burner model.

2. Available Relief Gas Pressure

The pressure of the incoming relief gas at the flare tip affects burner selection and mixing performance. Higher gas exit velocity improves air-gas mixing in jet-type burners, reducing the required external air assist. Lower gas pressures require more aggressive air injection and burner designs optimized for low-momentum mixing. Available relief gas pressure varies widely between applications and must be defined as part of the design basis.

3. Gas Composition

Gas composition determines the air-to-fuel ratio required for complete, smokeless combustion. Heavier hydrocarbon streams — those high in ethane, propane, butane, and higher carbon compounds — require more combustion air per unit of gas than lighter streams predominantly composed of methane. Hydrogen-rich streams behave differently again. NAO sizes the blower and selects the burner configuration based on the heat release characteristics of the specific gas stream.

With these three inputs established, NAO engineers select and size the appropriate burner model, blower, motor, and VFD to deliver smokeless performance at minimum operating cost.

NAO Air Assisted Flare Burner Models

NAO offers six air assisted flare burner configurations, each engineered for specific applications and performance requirements. All models are available for onshore and offshore service and are designed and manufactured to ISO-9001 quality standards.

NFF-AA: NAO Fluidic Flare Burner with Air Assist

The NFF-AA integrates NAO’s proven Fluidic Flare Burner design with an air assist system. The Fluidic Flare design, which NAO pioneered, uses a multi-baffle fluidic seal to minimize purge gas consumption while maintaining internal combustion protection. The air assist version extends this platform to applications where steam is not available, delivering the efficiency and flame stability of the Fluidic Flare in a forced-air configuration. The NFF-AA is well-suited for refinery and chemical plant applications transitioning away from steam assist or installing in locations without steam supply.

NFAV: NAO Forced Air Vortex Flare Burner

The NFAV uses a vortex mixing principle to achieve highly efficient air-gas mixing at the burner tip. Forced air enters the burner in a swirling pattern, wrapping around the rising gas stream and creating a stable, rotating combustion zone. This vortex action promotes complete combustion with a compact, stable flame profile and relatively low noise generation compared to high-velocity jet designs. The NFAV is particularly suited for sites with noise sensitivity requirements or where a controlled, predictable flame shape is operationally important.

NMEC-AA: NAO Multi External Coanda Flare Burner with Air Assist

The NMEC-AA applies the Coanda effect — the tendency of a fluid jet to attach to and follow a curved surface — to enhance air entrainment and mixing around the flare gas stream. In this design, the relief gas exits through multiple ports arranged around the burner body, and the external curved geometry promotes natural air entrainment supplemented by the forced air assist system. The multi-tip configuration improves mixing performance at higher smokeless flow rates and heavier hydrocarbon compositions. The NMEC-AA is used in staged flare systems alongside NAO’s control panels, where multiple tips may be sequenced on and off based on relief load.

NJM-AA: NAO Jet Mix Air Assist

The NJM-AA uses high-velocity jet mixing to drive turbulent air-gas interaction at the burner exit. Forced air is delivered through a ring or nozzle arrangement that creates high-momentum air jets intersecting with the outgoing gas stream. The result is rapid, thorough mixing that supports smokeless combustion across a wide range of gas compositions. The NJM-AA is effective for applications with moderate smokeless capacity requirements and where a proven, mechanically simple design is preferred. It offers reliable performance and straightforward maintenance.

NMJM-AA: NAO Multi Jet Mix Air Assist

The NMJM-AA is a multi-tip version of the NJM-AA design, used in applications requiring higher smokeless capacity or staged operation. Multiple burner tips are arranged on a common header, allowing the system to distribute the gas flow across several combustion zones rather than concentrating it in a single tip. This configuration is used in NAO’s staged flare systems, where tips are sequenced on and off by UL-listed NAO control panels based on real-time relief flow monitoring. The NMJM-AA is installed at facilities worldwide and is suitable for both onshore refinery and offshore production applications requiring high-capacity smokeless performance.

NVCF: NAO Vapor Control Flare

The NVCF is designed specifically for vapor control and low-pressure vent applications, including storage tank breathing losses and vapor recovery bypass streams. These applications involve low-pressure, low-velocity gas streams that require a burner design optimized for stable combustion at minimal inlet pressure. The NVCF provides controlled, smokeless combustion of storage vapors and low-BTU vent gases that would otherwise be challenging to handle in a conventional elevated flare system. It is commonly used at tank farms, terminals, and facilities with vapor control requirements under EPA regulations.

VFD Blower Control: How NAO Maximizes Combustion Efficiency

Variable Frequency Drive (VFD) blower control is central to the operating efficiency of NAO’s air assisted flare systems. The principle is simple but impactful: rather than running the blower at a fixed speed and delivering a constant air volume regardless of conditions, the VFD continuously adjusts motor speed based on the actual smokeless relief flow at any given moment.

A flow monitoring system measures the relief gas flow in the flare header. The VFD controller compares this measured flow to the required air-to-fuel ratio for the specific gas composition and adjusts blower RPM to deliver exactly the right air volume. If relief flow increases — due to a process upset or increased venting — the blower speeds up. If relief flow drops back, the blower slows down.

This real-time control delivers two simultaneous benefits:

1. Maximum combustion efficiency: The burner always receives the optimal air supply for the current load condition. There is no period of under-airing (which produces smoke and incomplete combustion) or over-airing (which dilutes the flame, increases noise, and wastes electrical energy driving the blower harder than necessary).
2. Minimum operating cost: Because the blower only works as hard as the current smokeless load requires, electrical consumption tracks the actual demand curve rather than running at peak capacity continuously. Over the operating life of a flare system, this efficiency difference is significant.

Fixed-speed blower systems cannot achieve this balance. A fixed-speed blower is sized for a specific operating point. At any other flow condition, it is either over- or under-performing. VFD-equipped systems eliminate this compromise, maintaining smokeless compliance across the full turndown range at optimized energy use.

Onshore vs. Offshore Air Assisted Flare Applications

NAO engineers air assisted flare systems for both onshore and offshore environments, with design differences driven by site conditions and utility availability.

Offshore Applications

Offshore platforms represent one of the most demanding environments for flare system design. Space is constrained, weight budgets are tight, corrosive salt air demands material upgrades, and utility systems are often limited. Steam is frequently unavailable offshore — generating steam for a flare system adds significant topside weight and complexity, making air assisted designs the standard choice for smokeless offshore flaring.

NAO offshore air assisted flares are designed with:

• Corrosion-resistant materials and coatings appropriate for marine environments
• Compact footprints optimized for platform deck space constraints
• No dependency on steam infrastructure — the blower and VFD are the only required utilities beyond electrical power
• Reliable ignition systems and pilots designed for offshore wind and weather conditions

Onshore Applications

Onshore sites offer more flexibility in configuration, utility access, and installation space, but the fundamental design requirements — smokeless capacity, gas composition, relief pressure — drive the same engineering process. Onshore air assisted flares are used at refineries, petrochemical plants, chemical manufacturing facilities, gas processing plants, and production sites where steam is not available at the flare location.

Onshore configurations may include ground-level blower packages with above-grade piping runs to the flare stack, staged multi-tip systems for wide load ranges, and integration with facility SCADA or DCS systems through NAO’s UL-listed control panels.

Quality Assurance: All NAO flare systems are designed, manufactured, installed, and serviced to ISO-9001 quality standards. NAO provides turnkey services across the full project scope — design, fabrication, installation, and operator training — eliminating the need to coordinate multiple contractors.

Regulatory Compliance for Air Assisted Flares

Air assisted flare systems in the United States must comply with federal regulations governing flare design and smokeless operation. NAO engineers flare systems to meet applicable requirements, and understanding the regulatory framework is important for facility planning and permitting.

• EPA 40 CFR Part 60, Subpart Ja (Standards of Performance for Petroleum Refineries) establishes specific requirements for refinery flares, including that flares must maintain a net heating value of at least 270 BTU/scf in the combustion zone and must operate in a smokeless manner. Facilities subject to Subpart Ja must also meet requirements for flare gas recovery and combustion device monitoring. Similar smokeless and efficiency requirements exist under other subparts applicable to chemical plants, LDAR programs, and other regulated source categories.
• API Standard 521 (ISO 23251), “Pressure-relieving and Depressuring Systems,” is the foundational engineering standard for pressure relief and flaring system design. It establishes the methodology for sizing relief systems, defining flare design loads, and selecting appropriate disposal methods. API 521 is the standard referenced by most engineering specifications and is required by many owner companies and EPC contractors for flare system design.
• API Standard 537, “Flare Details for General Refinery and Petrochemical Service,” provides detailed engineering requirements for flare tip design, ignition systems, purge gas, seal systems, and operational parameters. It is the companion standard to API 521 for the detailed design of the flare burner and tip assembly.
• International Initiatives: Internationally, the World Bank’s Zero Routine Flaring by 2030 initiative has increased regulatory and investor pressure on upstream oil and gas operators to eliminate routine flaring. This has accelerated demand for high-efficiency, smokeless flare systems — including air assisted configurations — on production facilities and platforms where flaring is being scrutinized.

NAO designs air assisted flares to comply with applicable federal, state, and international standards. Our engineering team works with clients during the design phase to confirm that the selected system meets the regulatory requirements for the specific facility and jurisdiction.

Frequently Asked Questions About Air Assisted Flares

What is an air assisted flare?

An air assisted flare is a combustion device that uses a motor-driven blower to force air into the flare burner, mixing it with waste gas to achieve smokeless combustion. It is used when steam is unavailable or when air assist is operationally preferred. Air assisted flares are standard equipment at offshore platforms, remote production facilities, and onshore sites without reliable steam supply.

What is the difference between an air assisted flare and a steam assisted flare?

Steam assisted flares inject high-pressure steam around or into the flare gas stream to promote air entrainment and complete combustion. Air assisted flares replace the steam function with a motor-driven blower that delivers forced air directly to the burner. Air assisted systems are preferred where steam is unavailable, where water consumption is a concern, or where VFD-controlled turndown is operationally advantageous. Steam assisted systems can be the lower capital cost option where an existing steam supply is already available at adequate pressure.

What does VFD control do in an air assisted flare system?

A Variable Frequency Drive (VFD) adjusts blower motor speed in real time based on the monitored smokeless relief flow rate. This allows the system to deliver exactly the right volume of combustion air for any flow condition, maintaining smokeless performance while minimizing electrical energy consumption. VFD-equipped systems can achieve turndown ratios of 10:1 or greater — far exceeding what is possible with fixed-speed blowers.

What regulations apply to air assisted flares?

In the United States, flare operations at petroleum refineries are governed by EPA 40 CFR Part 60, Subpart Ja, which requires smokeless operation and sets combustion zone heating value requirements. API Standard 521 and API Standard 537 provide the engineering frameworks for flare system design and flare tip selection. NAO designs all air assisted flare systems to comply with applicable federal standards and will work with clients to address specific state or permit requirements.

Can air assisted flares be used offshore?

Yes. Air assisted flares are among the most common flare types used offshore because they do not require a steam supply. NAO designs offshore air assisted flares with corrosion-resistant materials, compact configurations for platform deck constraints, and ignition and pilot systems suited to marine environments.

How is the right NAO air assisted flare burner model selected?

NAO selects and sizes the burner model based on three primary design inputs: smokeless capacity (the maximum gas flow rate requiring smokeless combustion), available relief gas pressure at the flare tip, and gas composition. These inputs determine the required air-to-fuel ratio, the blower sizing, and the burner geometry that will deliver complete, smokeless combustion across the operating range. Contact NAO’s engineering team to begin the design review.

Request a Custom Air Assisted Flare Design

NAO has designed and manufactured air assisted flare systems for onshore and offshore applications around the world, drawing on over 107 years of combustion equipment experience. Every system is engineered to your specific smokeless capacity, gas composition, relief pressure, and site requirements.

NAO provides complete turnkey services: design, fabrication, installation, and operator training. There is no need to coordinate multiple contractors or integrate separate vendors for the blower package, burner, and controls. NAO supplies the complete system and supports it through its operating life.

To begin a design review, contact NAO with your relief load data, gas composition, available utilities, and site location. Our engineering team will recommend the appropriate burner model and system configuration.

Contact NAO to Discuss Your Air Assisted Flare Requirements

NAO, Inc. designs and manufactures air assisted flares, steam assisted flares, enclosed flares, sonic flares, and a full range of flare burner types for onshore and offshore service. All equipment is designed and manufactured to ISO-9001 quality standards.

NFF-AA
NAO Fluidic Flare Burner with Air Assist

NFAV
NAO Forced Air Vortex Flare Burner

NMEC-AA
NAO Multi External Coanda Flare Burner – Air Assist

NJM-AA
NAO Jet Mix-Air Assist

NMJM-AA
NAO Multi Jet Mix- Air Assist

NVCF
NAO Vapor Control Flare