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We are excited to announce the launch of the new Air Monitor Corporation YouTube channel! This channel is dedicated to practical airflow measurement insights for commercial HVAC, industrial process, and power generation applications.

Inside the Air Monitor Factory Tour

To kick things off, our first video is live! Our brief factory tour video brings our engineered airflow solutions to life in our 42,000 sq ft facility. Notably, Air Monitor’s manufacturing team design and produce airflow probes, stations, and systems. Beyond fabrication, you’ll see wind tunnel calibration site and quality checks that support AMCA-certified accuracy. Thus, the video gives engineers, facility managers, and operators a behind-the-scenes look at the Air Monitor facility. Air Monitor products perform in challenging duct configurations, low and high velocities, clean airflow, and particulate-laden airstreams. Watch the tour here: https://www.youtube.com/watch?v=5iAhCpl0GYE.

Upcoming Animated Airflow Measurement Videos

Coming soon, this channel will feature a growing series of animated, application-focused and technology-focused videos. Topics range from ducted airflow measurement and fan inlet monitoring to combustion air, dirty air process, and building pressurization. The short explainer video series is designed to show where to apply multi-point averaging pitot technologies. In addition, you’ll see how to solve low-flow and large-duct measurement challenges, and how to get the most from your Air Monitor systems.

Subscribe to the Air Monitor YouTube Channel

Now is the perfect time to subscribe so you don’t miss upcoming videos. Visit the Air Monitor Corporation YouTube channel, watch the factory tour, and click Subscribe and the notification bell to stay up to date as we release new animated application and technology content in the weeks ahead.

In Part 1, we explored how pitot averaging technology delivers superior accuracy by capturing true airflow velocity across entire duct cross-sections. But in real-world industrial environments—cement kilns, baghouse inlets, coal mills, and material handling systems—airflows don’t flow through clean ducts. They carry dust, moisture, sticky residue, corrosive gases, and abrasive particles that rapidly degrade conventional measurement equipment.

This is where the challenge deepens: How do you maintain accurate, reliable airflow measurement when the environment itself is clogging or fouling the sensors?

Facilities monitoring cement kiln exhausts, baghouse inlet/outlet flows, material handling conveyor air, or coal-fired power plant ash systems encounter airflows contaminated with fine particulates, sticky dust, moisture, or abrasive materials. These contaminants present four critical measurement challenges:

#1 – Sensor Fouling and Drift

Dust particles, moisture, or sticky residue accumulate on unprotected sensor elements, degrading accuracy, causing erratic readings, or leading to complete sensor failure within days or weeks rather than months or years. An averaging pitot probe placed at a baghouse inlet, where dust concentration is highest, can become fouled within 48–72 hours of operation. Once fouled, the probe delivers less reliable data—it becomes a liability consuming maintenance resources while providing less confidence in measurements.

#2 – Pressure Line Blockages

Fine dust can plug pressure sensing lines or orifices, preventing true differential pressure measurement. When pressure lines clog, the transmitter receives zero or erratic differential pressure signals, making the system useless for control or compliance documentation. Operators then resort to manual portable measurements which are episodic, labor-intensive, and incapable of supporting continuous process optimization.

#3 – Corrosion

Acidic gases, moisture, or reactive dust can corrode unprotected metal components, shortening equipment life and increasing maintenance costs. In cement production, kiln exhaust contains sulfuric acid vapor and hygroscopic dust that accelerates corrosion. In power generation, coal dust and fly ash create corrosive, abrasive environments. Without protective measures, sensor housings, orifices, and internal passages degrade, requiring premature replacement.

#4 – Temperature Extremes

High-temperature kiln exhausts or cooler ambient air can stress sensor elements and electronics, requiring specialized materials and designs. A pitot probe positioned at a 400°F kiln outlet faces thermal cycling that expands and contracts materials differently, creating micro-cracks and sensor drift. Conventional transmitters designed for HVAC comfort applications (70–80°F) simply cannot tolerate these extremes.

The Hidden Cost of Conventional Sensors

Without active protection mechanisms, conventional airflow measurement equipment in dirty environments often becomes a liability rather than an asset. Consider a typical scenario:

A facility installs an electronic airflow sensor at a baghouse inlet to monitor collection efficiency. Initial cost: $3,000–$5,000. Within three weeks, dust accumulation causes erratic readings. The sensor requires removal and cleaning—requiring ductwork access, mechanical labor, and production disruption. After cleaning, it functions briefly, then fouls again. After the third cleaning cycle and two replacement cycles in 18 months, the facility has spent $15,000–$20,000 in equipment and labor, plus the cost of missed compliance documentation or inefficient baghouse operation. This cycle repeats because the root problem—sensor fouling—was never addressed. The sensor works only when clean, but the environment constantly fouls it.

The Real-World Impact: Why Continuous Measurement Matters

In contrast, a facility with reliable, continuous airflow measurement can:

Optimize process operation:

For instance, in cement baghouses, operators adjust pulse-jet cleaning frequency, duration, and intensity. Based on actual airflow trends, unnecessary cleaning cycles are reduced, and filter life is extended.

Detect filter blinding early:

Real-time airflow trends show when filters are approaching saturation, allowing scheduled cleaning before bypass or visible emissions occur.

Maintain regulatory compliance:

Continuous data streams provide compliance records for EPA, OSHA, and provincial emission standards. Up-to-date data can eliminate the risk of violations during unannounced inspections.

Identify system problems before they escalate:

Declining airflow trends can indicate duct leaks, damper failures, or fan degradation—problems that remain hidden until equipment fails catastrophically.

Optimize energy consumption:

Knowing true airflow allows fan operators to run at minimum speed necessary to maintain target efficiency. This reduces energy waste and lowers operating costs.

Why Standard Sensors Fail in Dirty Environments

The fundamental problem is that conventional airflow sensors assume relatively clean air. Many are engineered for commercial HVAC (typical 50–100 microns dust). Few are constructed for industrial settings (1–50 microns fine dust, often at high concentration). Conventional pressure sensing elements, orifices, and internal passages are too small, too exposed, or too sensitive to fouling to handle:

• Baghouse inlet dust loads (10–100+ mg/m³)
• Cement mill outlet particulate (50–500 mg/m³)
• Coal pulverizer exhaust (100–1000+ mg/m³)

Any of these environments will foul a conventional sensor within days or weeks.

The Solution: Engineered Sensor Protection

Air Monitor’s AUTO-purge III system addresses this challenge through continuous or on-demand active sensor protection. By injecting clean, compressed air or inert gas through internal passages within the probe, the purge system creates a protective barrier that:

– Prevents dust accumulation: The purge flow gently dislodges and sweeps away dust, moisture, and residue from sensing elements before they can build up, clog, or degrade sensor accuracy.

– Maintains measurement integrity: By keeping pressure taps and sensing elements clean, AUTO-purge III ensures that differential pressure readings remain true and representative of actual airflow conditions.

– Extends probe lifespan: Proactive cleaning dramatically reduces the frequency of probe removal, recalibration, or replacement, lowering total cost of ownership and minimizing production disruptions.

– Enables continuous, unattended operation: Unlike manual cleaning methods that require system downtime and operator intervention, AUTO-purge III operates automatically, allowing measurement systems to run 24/7 with minimal supervision.

From Reactive Maintenance to Proactive Protection

The shift from conventional sensors that foul and require frequent cleaning to AUTO-purge III systems that prevent fouling represents a fundamental change in philosophy. Instead of accepting degraded performance as normal and planning for frequent maintenance, facilities adopt a proactive approach where sensor cleanliness is maintained continuously.

This shift has downstream implications:

– More confident operational decisions: Operators know that airflow data is reliable, not degraded by fouling artifacts.

– Better regulatory documentation: Continuous, clean data streams provide auditable compliance records.

– Lower total cost: Despite higher initial investment, fewer maintenance interventions and emergency repairs drive down long-term operating costs.

– Higher system availability: Without scheduled probe removal for cleaning, airflow monitoring runs uninterrupted.

Bringing Technology and Application Expertise Together

Understanding these challenges is critical. It frames why pitot averaging technology alone—while superior to single-point measurement—is insufficient in dirty environments. The technology must be protected through engineered solutions like AUTO-purge III which address the contaminant challenges of dirty industrial airflows. In Part 3 of this series, we’ll explore how these two technologies offer a comprehensive solution in harsh industrial environments. We’ll examine real-world applications, integration with facility control systems, and why this combination delivers unmatched reliability and value.

Industrial facilities handling cement, materials, or process gases face a critical challenge: accurately measuring airflow through dust-laden, particle-heavy air streams while maintaining sensor reliability and measurement accuracy. Standard airflow measurement devices often fail or degrade rapidly in these harsh environments, leading to missed process control, regulatory non-compliance, and unexpected downtime. Air Monitor’s pitot averaging flow stations paired with the AUTO-purge III system deliver a robust, engineered solution specifically designed to overcome these obstacles, providing continuous, accurate airflow monitoring even in the most demanding industrial conditions.

Pitot tubes measure airflow velocity by sensing the difference between dynamic pressure (total pressure) and static pressure in a moving air stream. This fundamental principle has remained reliable for over a century, making it an industry standard for airflow measurement.

Why Averaging Matters

Non-uniform velocity distribution is the reality in most industrial ductwork. Air flowing through a duct doesn’t move at the same speed—velocity is typically higher toward the center and slower near the walls. A single-point measurement might capture flow near a wall (slow) or near the center (fast), delivering misleading data that doesn’t represent true system performance.

• Flow disturbances from elbows, dampers, or other upstream obstructions
• Ductwork geometry variations
• Natural velocity distribution patterns that develop in moving air streams

Multi-Point Advantages Over Single-Point Measurements

The technical superiority of multi-point averaging becomes evident when comparing measurement consistency. A single-point pitot tube might vary by ±5% to ±10% depending on where it’s positioned and how flow patterns shift due to operational changes. A properly designed averaging pitot probe typically delivers ±1% to ±3% accuracy, with real-world industrial performance in the ±3% to ±5% range—a significant improvement that compounds when used for continuous process control decisions.

This consistency is critical for facilities that rely on airflow measurement to:

• Optimize baghouse cleaning cycles
• Balance flows across multiple collection zones
• Maintain precise dust collection efficiency
• Document regulatory compliance over extended periods

Why Industrial Facilities Need Better Airflow Measurement

Consider a cement plant kiln outlet or a baghouse inlet—two critical measurement points where airflow drives operational decisions. Baghouse efficiency, pressure drop trends, filter health, and emission compliance all depend on accurate, consistent airflow data. When a measurement system delivers unreliable or inconsistent readings, operators cannot make confident adjustments, regulatory inspectors cannot validate compliance claims, and hidden inefficiencies persist.

Averaging pitot technology directly addresses this need by ensuring that airflow readings remain stable and representative of true conditions, not artifacts of measurement location or transient flow disturbances.

Technical Characteristics That Enable Accuracy

Several design features make averaging pitot probes effective:

• Multiple Averaging Taps: Averaging pitot probes typically feature 4–10 pressure sensing ports strategically positioned to account for velocity gradients across the duct.
• Low Permanent Pressure Loss: Pitot tubes generate minimal permanent pressure drop (typically 5–15% of measured dynamic head), meaning they don’t waste fan energy like high-restriction differential pressure devices.
• Consistent Calibration: Factory calibrated and field-verified, averaging pitot probes remain accurate over years of continuous operation when properly maintained.

The Foundation for Reliable Process Control

Understanding pitot averaging technology is the first step toward reliable airflow monitoring. This foundation becomes even more powerful when combined with active sensor protection—a challenge that becomes critical in dirty, particulate-laden environments.

In Part 2 of this series, we’ll explore the unique measurement challenges posed by dust, moisture, and contaminants in industrial airflows, and how Air Monitor’s AUTO-purge III system actively protects pitot averaging probes to maintain measurement integrity in the harshest conditions.

Air Monitor’s latest Application Guide—focused on Primary Airflow in Coal-Fired Power Plants—presents invaluable insights and practical solutions for professionals seeking greater efficiency, safety, and reliability in their operations. This application guide addresses both the challenges and advanced methods for accurate primary airflow measurement, which is crucial to optimal mill and burner performance.

The Importance of Primary Airflow Measurement

Precise primary airflow measurement is fundamental for several reasons in coal-fired power plants:​

• It optimizes combustion and reduces fuel costs by ensuring the right amount of air for burning coal.
• It helps stabilize the process, limiting operator intervention and increasing equipment capacity.
• It is essential for safe operation, preventing hazards such as pipe fires and mill puffs.
• Accurate airflow ensures stable flame positions and reduces issues like slagging, burner pluggage, and coal layout—all critical for plant efficiency and compliance.

Key Challenges in Coal-Fired Environments

Coal-fired power plants face several obstacles when monitoring airflow:​

• Limited straight duct runs restrict where devices can be installed, impacting measurement accuracy.
• Hot and tempering air convergence, along with barometric damper inlets, complicate traditional sensor placement.
• High particulate matter, especially fly ash, can erode probes and interfere with sensor readings, especially for devices like annubars and venturis.
• Excess air increases NOx emissions and tube erosion; insufficient air can cause fires and instability.

Air Monitor’s Proven Solutions

Air Monitor addresses these challenges with robust, field-tested products and integrated systems:​

• The Fechheimer-Pitot Combustion Air CA station and VOLU-probe/SS arrays are designed to maintain accurate, continuous measurements—regardless of hot, dusty, or challenging duct layouts. These technologies work even in the presence of straight duct runs.
• The Combustion Airflow Management System (CAMS) features the AUTO-purge III to keep sensing ports and lines clear of fly ash, ensuring reliability.
• Advanced compensation technologies deliver true density compensated mass flow outputs with accuracy within 2% over a 10:1 turndown range.
• For extremely harsh applications, Air Monitor offers tungsten carbide coated VOLU-probes, addressing probe erosion and extending equipment life.

Real-World Applications and Upgrades

These solutions integrate seamlessly into Raymond Bowl Mills, MPS/EL Mills, Atrita Mills, and many more common coal pulverizer systems. Air Monitor also provides integrated bell mouth CA stations for sites with barometric damper openings to improve tempering air management. These upgrades create minimum straight runs for improved accuracy.​

Why Industry Leaders Trust Air Monitor

With over five decades of experience engineering and deploying field-tested solutions, Air Monitor’s products continue to set the standard for process stability, safety, and compliance in coal-fired power generation. The new Application Guide delivers actionable information for power plant engineers and operators—empowering them to:​

• Reduce fuel costs
• Lower emissions
• Prevent system failures
• Streamline maintenance

For more details, industry professionals are encouraged to consult Air Monitor’s new Application Guide for Primary Airflow in Coal-Fired Power Plants. It’s an essential resource for optimizing your plant’s performance in today’s demanding regulatory and economic environment.

If you have specific questions, feel free to reach out to our experts on your process needs.

In cement manufacturing, dust control is both an operational necessity and a regulatory requirement. Baghouse performance directly impacts product quality, energy efficiency, and environmental compliance. The key to unlocking peak baghouse performance lies in implementing comprehensive airflow measurement systems. Such systems provide operators with the real-time data needed to optimize dust collection processes throughout the facility.

The challenging operating environment found in cement plants is characterized by high temperatures, abrasive dust, and moisture variations. These place extraordinary demands on baghouse systems.

Implementing effective airflow management is essential for improvement:

Airflow Measurement Technologies for Cement Applications

Air Monitor’s Solutions for Peak Performance

• Application-specific challenges and how to overcome them
• Ideal product recommendations for:
  • Natural gas-fired industrial boilers
  • Process heaters
  • Regenerative thermal oxidizers (RTOs)
  • Dust collection systems
  • Clean room environments
• Primary elements like VOLU-probe/SS, CA Station, and ACCU-flo
• Advanced transmitters including MASS-tron II, VELTRON DPT-Plus, and AUTO-purge III
• Integrated systems for automatic purging and density-compensated flow output
• Industry coverage from refineries and chemical plants to semiconductor manufacturing and carbon capture

• Regulatory compliance with EPA and air quality standards
• Process efficiency and reduced downtime
• Safety and reliability in combustion and exhaust systems
• Customization for corrosive, high-temperature, or particulate-laden environments

We’re excited to announce the release of the new Application Optimizer for Clinker Coolers. This document is designed to help cement manufacturers optimize their clinker cooler operations through precise airflow measurement. This Application Optimizer maps out key airflow measurement points across the clinker cooler system. It offers actionable insights to improve cooling efficiency, reduce energy consumption, and enhance clinker quality.

In cement manufacturing, the clinker cooler plays a critical role in the pyroprocessing stage. After raw materials are pre-heated and fired in the kiln to form clinker, the cooler rapidly reduces the clinker temperature. This stabilizes its phase composition and preparing it for grinding. But this process is far more than just cooling—it’s a delicate balance of airflow dynamics that directly impacts:

Proper airflow management ensures uniform cooling. It prevents the formation of problematic zones like “snowmen” or “red rivers” and maximizes the recovery of secondary and tertiary air for combustion in the kiln, suspension preheater, and precalciner. Uneven or insufficient airflow can lead to incomplete cooling, elevated discharge temperatures, and damage to cooler components. Moreover, excess air must be carefully vented to maintain environmental compliance and operational stability.

The new document outlines a range of airflow measurement technologies tailored to the unique challenges of clinker cooler environments. These include:

• VOLU-probe/SS with Temp Probe: A cost-effective, robust solution for dirty airflow conditions, suitable for duct-mounted installations.
• MASS-tron II: Offers accurate flow measurement with 100:1 turndown, temperature and pressure compensation, and AUTO-zero functionality to eliminate drift.
• CA Station and CAMS: Ideal for limited straight runs and high-turndown applications, with integrated AUTO-purge for reliability.
• Custom Material Options: Including Inconel for high-temperature durability.

These products are strategically mapped to monitor cooling airflow, secondary/tertiary air, and exhaust air streams. Each zone is essential for maintaining optimal combustion, calcination, and heat recovery.

Airflow measurement is just one piece of the puzzle in pyroprocessing optimization. As highlighted in recent industry analyses, cement plants are increasingly turning to advanced monitoring solutions to:

With energy consumption accounting for up to 60% of production costs and contributing to CO₂ emissions, finding efficiency is more important than ever.

Whether you’re troubleshooting cooling inefficiencies or planning a system upgrade, the Clinker Cooler Application Optimizer provides a roadmap for improvement. By leveraging precision airflow measurement, cement manufacturers can achieve more consistent product quality, lower maintenance costs, and better environmental performance.

Get Your Copy:

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To learn more or schedule a consultation, CONTACT one of our experts.

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For more information on airflow measurement in the Cement Industry, visit Air Monitor’s Cement Manufacturing Applications page.

FAQs

The efficiency of industrial boiler systems can be maximized by tightening the control over the air-to-fuel ratio in the burners. Increased effectiveness in monitoring and controlling airflow in these systems makes tighter control possible. But which combustion control systems offer the best solution for efficiency improvements?

Combustion Control Challenges

The objective of combustion air control is to minimize excess air without creating a fuel-rich environment that ultimately could lead to an explosion. A small level of excess oxygen is desirable to prevent calamity and to ensure complete combustion, so as not to waste fuel. However, a larger excess of air/oxygen also degrades the combustion efficiency because exhaust gas leaving the system at an elevated temperature also represents a loss of energy.

A common margin of excess oxygen is about 2-4% as a target to maximize efficiency and minimize formation of NOx, while still ensuring complete combustion of fuel. However, effectively and accurately monitoring airflow to maintain this small excess margin in industrial combustion systems is more complicated than monitoring the fuel flow.

For better boiler control, maintaining a balanced fuel and air mixture can be accomplished in a couple of different ways.

Parallel Positioning (PP) Systems

In a parallel positioning system, the objective is to link the position of the air damper with the position of the gas valve to maintain an acceptable air-to-fuel ratio that is based on a process setpoint, such as a required steam pressure.

In this type of cross-limiting system, the damper/valve controls are physically linked, so it is not possible to control fuel flow and airflow individually. PP systems may work reasonably well initially but will drift away from the desired fuel-air ratio over time as valve seals and damper linkages wear. 

Additionally, a PP system will not respond to fluctuations in process temperature, duct static pressure, and barometric pressure changes, which alter air density and affect the air-fuel ratio.

Adding O2 Trim to PP Systems

A second option for airflow control is known as parallel positioning with O2 trim. In this control scheme, O2 trim systems are used to continuously monitor the amount of oxygen in the exhaust gas and provide feedback to an automatic positioner for the air damper. 

The objective is to “trim” the airflow to drive excess oxygen lower (closer to 2-4% excess O2). PP with O2 trim is the most common type of control that is applied to combustion systems across many industries.

Fully Metered Combustion Air Control Systems

In this scheme, flow measurement devices are added for both fuel and air flow measurement to provide instant feedback for maintaining the air-to-fuel ratio at its most efficient point. In a fully metered system, accurate mass-based airflow measurement is crucial.

The rationale behind fully metered systems is to address multiple issues simultaneously: promote efficient fuel use, control emissions, extend burner lifetime (especially with ultralow-NOx burners), and expand the efficient operating range. Fully metered systems typically include O2 trim, as well. This provides the ultimate in control and final operation.

Advanced Control Technology for Increased Efficiency

The fully metered combustion control system is only as good as the measurement technologies used as inputs. These can include flow conditioners followed by multipoint Pitot averaging arrays that are used to accurately sense the stratified velocity profile.

Next, a low-range multivariable transmitter is used to amplify the differential pressure and compensate for changes in atmospheric pressure, static pressure, and process temperature. This provides a 4–20mA output with a linear relationship to mass flow to the fully metered control system.

In cases where particulates are present, an automatic purge system also is integrated into the flow measurement system, ensuring that the measurement is never lost due to the sensing ports plugging. During this purge cycle, the signals are held at their last values.

Benefits of Fully Metered Combustion Control Systems

The degree of actual control enabled with a PP/O2 trim system is not very large. In contrast, state-of-the-art fully metered systems have the best ability to optimize the efficiency of burners and can address multiple challenges at once, including efficiency, maintenance, safety, and emissions.

Fully metered systems allow tighter control of the air-fuel ratio throughout the full operating range of the boiler and ensure that emissions are within specifications. They also allow a much higher degree of control for operations over tuning the system, so operators can closely match the optimal air-fuel ratio even throughout process temperature swings, barometric pressure, and static pressure changes.

The greater degree of combustion air control means there are fewer boiler trips, so less downtime across full operating ranges of the combustion burner when the air-fuel ratio gets out of balance. Fully metered systems also can easily adapt to fuel type or composition changes such as switching between natural gas and fuel oil or changing natural gas suppliers.
The challenge of realizing fuel savings while maintaining the ideal air-to-fuel ratio for process controls is felt by plant managers everywhere. Discover more information about Air Monitor’s combustion air flow measurement technologies and how they can benefit your industrial boiler application by clicking below.

As the economy tightens, operators of industrial combustion systems such as steam boilers, thermal oxidizers, fired heaters, waste-heat boilers, dryers, furnaces, incinerators, and kilns are called upon to save fuel costs and minimize downtime. Each of these applications burns fuel in the presence of air (oxygen) to create process heat.

Saving fuel costs and minimizing downtime requires maximizing the combustion efficiency by tightly controlling the flow of both air and fuel introduced to the burner. The trick is knowing how much of each to provide—and that goes back to understanding the stoichiometric air-fuel ratio.

Efficient Air-to-Fuel Ratio

In chemistry, stoichiometry is the method for balancing chemical equations to calculate the exact amount of individual reactants needed to ensure that all the reactants are used up with no excess left over from the reaction. For example, a simple combustion equation for burning the methane (CH₄) in natural gas is:

CH₄ + 2O₂ → CO₂ + 2H₂O + Heat

According to this stoichiometric equation, a perfectly balanced combustion process would require exactly two oxygen (O₂) molecules to burn each methane molecule. The reaction would produce one molecule of carbon dioxide (CO₂) and two molecules of water (H₂O) along with excess heat to be used for the process.
If the equation is not perfectly balanced, for example, if there is not enough O₂  to completely combust or burn each CH₄ molecule, the reaction will produce some carbon monoxide (CO) instead of CO₂.

Real-World vs. Ideal Air-to-Fuel Ratio

In theory, a perfectly efficient combustion system would operate with a perfect stoichiometric ratio of fuel to oxygen. But in practice, real-world industrial combustion systems need to operate with a slight excess of oxygen in the ratio of air to fuel. 

This ensures complete combustion and avoids potential safety issues associated with burning fuel-rich mixtures, which can lead to safety issues.

The result, as you can see from the illustration, is that operators try to maintain a slightly lean mixture of fuel with only a small amount of excess oxygen because too much excess oxygen degrades the combustion efficiency and increases cost. This happens for a few reasons.

First, by requiring the system to heat a larger volume of gas than is needed decreases the ability for the system to transfer heat from the flame to the steam (in the case of a boiler) or to the process fluid.

Second, too much excess oxygen will force the fan to operate at elevated speeds, which wastes energy over time and increases emissions. A common margin of excess air is about 2-4% more air than fuel. 

This target maximizes efficiency and minimizes formation of NOx—a pollutant generated from nitrogen in the air reacting with oxygen—while still ensuring the complete combustion of fuel.

3 Methods for Maintaining an Efficient Air-to-Fuel Ratio

To accurately maintain this small excess margin in industrial combustion systems, combustion control systems need accurate airflow measurement and control in addition to fuel flow monitoring. In general, operators use one of three different methods to monitor and maintain the proper amount of air and fuel in an industrial plant:

• Parallel positioning (PP)
• PP with O₂ trim
• Fully metered airflow control systems

Parallel positioning systems are relatively straightforward technically and are generally the least expensive option for controlling airflow. These provide some degree of control for stable loads and consistent burner function and offer the lowest capital cost of the three options. 

However, PP is not effective for variable loads or rapid swings and is the least able to maintain optimal efficiency.

PP with O₂ trim systems continuously monitor the amount of oxygen in the exhaust gas and provide feedback to an automatic positioner for the air damper. The objective is to “trim” the airflow in order to drive excess oxygen lower (closer to 2-4% excess O₂).

PP with O₂ trim is the most common type of control that is applied to combustion systems across a number of industries. This type of system, however, is best applied to boilers at steady-state operation, while real-world boilers run at constantly varying steam loads. The degree of actual control enabled with a PP/O₂ trim system is not very large and this system is not the best choice for boilers with broad load ranges.

Fully metered airflow control systems

Minimizing the amount of excess air without creating a fuel-rich environment can best be achieved with the help of fully metered systems that effectively monitor and control airflow. These systems have the best ability to optimize the efficiency of burners and can address multiple challenges at once including efficiency, maintenance, safety, and emissions. 

They allow tighter control of air-to-fuel ratio throughout the full operating range of the boiler and ensure that emissions are within specifications.

Fully metered systems allow a much higher degree of control for operations over tuning the system using PP with O₂ trim. With a fully metered system, operators can closely match the optimal air-fuel ratio even throughout process temperature swings, barometric pressure, and static pressure changes. 

The greater degree of control means there are fewer boiler trips and therefore less downtime across full operating ranges of the combustion burner when the air-to-fuel ratio gets out of balance. Fully metered systems also can easily adapt to fuel type or composition changes such as switching between natural gas and fuel oil or changing natural gas suppliers.

Because a poor ratio of air to fuel can contribute to failures of burner internals as well as soot buildup, there is a connection to unplanned shutdowns. Better airflow control enabled by fully metered systems results in fewer chronic maintenance issues, such as burner replacements.

For large-sized boilers, good air monitoring allows the possibility of using a predictive emissions control system (PEMS) versus continuous (CEMS) to report emissions to air districts or the EPA. 

A PEMS system is one-third the cost of a CEMS but requires that plant operators can maintain high levels of confidence in the control system for airflow to ensure the measurement is accurate.

A Fully Metered Airflow Control System Can Benefit Your Industrial Application

The benefits of a fully metered airflow control system come with costs and added complexity— however, the benefits far outweigh the costs. The cost of this type of system varies but is slightly more than that of a PP with O2 trim.
The challenge of maximizing fuel economy using the stoichiometric air-to-fuel ratio is felt by plant managers everywhere. With a fully metered combustion airflow measurement system, operators can expect to see measurable efficiency improvements and emissions reductions that will increase their bottom line.