Oxygen analyzer to improve boiler combustion efficiency

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Why using an oxygen analyzer helps improve combustion efficiency in boilers

Many industries rely on boilers and furnaces to carry out the fundamental process of using flames for heating purposes. For this type of equipment to operate effectively, a precise balance of oxygen and fuel is necessary to enable complete combustion.

In this blog we explore the role oxygen analyzers play as part of an O2 trim system that helps maintain this balance of oxygen and fuel, and thereby, efficient combustion.  

Combustion control

Several conditions exist that can affect the air/fuel ratio in a combustion process, including atmospheric changes (e.g., air pressure and temperature changes), and fuel composition and quality. To reduce potential risks in the combustion process, engineers typically design their boilers to use excess air in the combustion process. This reduces safety risks in varying operating conditions. However, despite creating a margin of safety, using a ‘fuel-lean’ approach reduces efficiency and increases the amount of fuel used in the combustion process.

If the air/fuel mixture has insufficient oxygen (fuel-rich), incomplete combustion can occur, resulting in carbon monoxide formation, sooting and even explosion if accumulated soot and other non-combusted components suddenly get enough oxygen to rapidly burn. If there is too much O2/air in the mixture (fuel-lean), efficiency is reduced due to the extra energy wasted heating the unnecessary volume of air. There are 3 primary considerations in achieving combustion control: 1. Safety of personnel and equipment 2. Reduction of fuel costs (efficiency) 3. Emissions control regulations

How do you keep a boiler operating as efficiently as possible?

Use an oxygen trim system. An O2 trim system is designed to continuously measure oxygen in the flue gas, sending the oxygen reading to a controller that maintains an optimum air-to-fuel ratio in the boiler combustion zone.

An oxygen analyzer (as part of an O2 trim system):

  • Improves safety – measuring O2 in combustion applications reduces risk of explosion, which can result in loss of life or major equipment damage. While accurate financial costs are difficult to measure, property damage due to boiler explosions is in the millions of dollars every year. And loss of life is never acceptable.

  • Improves combustion efficiency (fuel savings and ROI) – boiler efficiency is affected by the excess air concentration in the flue gas. For example, with 5% more excess air (1% more O2) in the combustion process than needed, efficiency drops by roughly 0.5%. If not adjusted, the boiler flue gas can vary by at least 2% oxygen per day (increasing or decreasing based on temperature, air density and fuel quality changes throughout the day). This 2% O2 swing corresponds to a 1% boiler efficiency loss. Saving just 1% efficiency over a year can result in huge fuel cost savings, especially with natural gas prices rising globally. If a normal fuel bill is $10,000,000 per year, a savings of 1% on fuel would equal $100,000. Adding an O2 analyzer and trim system would cost a fraction of that amount and provide an almost immediate ROI.

  • Reduces maintenance costs – using a real time O2 trim system will maintain a proper air/fuel mixture in the combustion process reducing the amount of soot build-up inside the heating chamber. Proper O2 trim also reduces blocked intake/exhaust ports, fouled burners and explosion risks due to unburned fuels or CO buildup.

  • Reduces emissions – When boiler equipment reaches a certain size, emission restrictions and compliance are placed on each application. A proper O2 trim system on these combustion devices reduces the amount of exhaust gas by-products they produce (typically CO2, CO, NOx, Sox) and keeps them within acceptable levels. Failure to maintain mandated emissions levels can result in fines, consent decrees, and even production shutdowns.

    • Oxygen analyzers for combustion control

    There are several types of oxygen analyzers used in combustion control, from TDL (tunable diode laser) to Zirconia and metal oxide. Many factors may influence the type of O2 analyzer/trim system a customer purchases. These include:

    1. Boiler size and fuel efficiency. Large industrial and commercial boilers consume massive quantities of fuel, (e.g., Natural gas, oil, coal, biogas) and will always want their combustion system tuned for maximum efficiency and fuel savings.

    2. Temperature. Package boilers are usually operated at temperatures less than 400degC (752degF). Heaters/furnaces can run at up to 1400degC (2552degF).

    3. Area Rating. Boilers that operate in hazardous area classified environments require an area-rated combustion analyzer.

    4. Cost. Always a factor, even a large boiler company will be looking for value in an O2 analyzer/trim system.

    5. Installation location. Installing a long probe into the flue or a small OEM sensor into the burner controller allows flexible installation in multiple types of systems.


    Boiler types and cost have a bearing on what technology customers will purchase for an O2 measuring/control system. Next to safety concerns, fuel savings/ROI is often the main justification for purchase.


    Summary

    An oxygen analyzer is a critical tool for improving combustion efficiency in boilers by providing operators with the ability to monitor the amount of oxygen in the combustion process, with real-time data to adjust and optimize combustion conditions.

    An oxygen analyzer measures the amount of oxygen in the flue gas produced by the combustion process and compares it to the theoretical amount of oxygen needed for complete combustion.

    With accurate data, plant operators can make adjustments to the air-to-fuel ratio to achieve optimal combustion efficiency. An excess of oxygen in the combustion process can result in incomplete combustion and increased emissions, while a lack of oxygen can cause carbon monoxide (CO) emissions and other safety hazards. By continuously monitoring oxygen levels and adjusting the air-to-fuel ratio as needed, plant operators can maintain a safe and efficient combustion process.



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