Maintaining proper burner function is crucial to the operation of a boiler, as the boiler will only run as well as the burner performs. A badly designed boiler with an efficient burner can actually perform better than a well-designed boiler with an inefficient burner.
Consider These Steps to Maintain Proper Performance:
- Do combustion efficiency tests at both full-load and part-load conditions.
- If excess oxygen exceeds three percent, or combustion efficiency values are low, consider upgrading the fuel-air control system to include solid-state sensors and controls without linkage.
- Consider investing in enhanced process controls, an oxygen trim system or a new energy-efficient burner.
- Install a smaller burner on a boiler that is oversized relative to its steam load.
Energy savings are guaranteed when upgrading to an energy-efficient burner. An upgrade should be considered if repair costs become extreme and reliability becomes an issue. Companies can also take advantage of utility energy conservation rebates that are available.
An efficient burner provides the proper air-to-fuel mixture throughout the full range of firing rates, without needing regular adjustments. Burners mix molecules of fuel with molecules of air and are designed to maximize combustion efficiency while minimizing the release of boiler emissions. However, many burners with complex linkage designs do not hold their air-to-fuel settings consistently over time. Many times, burners are adjusted to provide high levels of excess air to make up for the inconsistencies in the burner performance.
Servomotors are becoming increasingly popular on new burners. Servomotors provide an alternative to complex linkage designs by using parallel positioning to independently control the quantities of fuel and air distributed to the burner head. These controls without linkages give an operator accurate, pinpoint control to provide consistent performance and repeatability as the burner adjusts to different firing rates. The more modern controls also make tune-ups and minor adjustments easier.
A single drive or jackshaft is another alternative to electronic controls. However, linkage joints wear and rod-set screws can loosen and cause slippage, which will result in a decline in efficiency. For this reason, avoid purchasing standard burners that employ linkages to provide single-point or proportional control.
Upgrading to an Energy-Efficient Burner
Several steps are required to determine the potential energy saved by replacing an existing burner with an energy-efficient burner.
- Adjust your boiler and make sure all suggested burner maintenance has been completed.
- Perform combustion efficiency tests at full-load and part-load firing rates.
- Evaluate the measured efficiency values with the performance of the new burner. (Most manufacturers will provide guaranteed excess levels of oxygen, carbon monoxide and nitrous oxide).
Significant savings can be realized even with incremental improvements in burner efficiency. For example, on a 50,000 pound-per-hour process boiler with a combustion efficiency of 79 percent (E1), 500,000 million Btu (MMBtu) of natural gas will be consumed annually. Using the price of $5/MMBtu, the estimated annual cost would be $2.5 million. By improving the combustion performance, an annual savings of 20,000 MMBtus can be realized, totalling $100,000 in cost savings. With an installed cost of $250,000, the new burner will pay for itself in less than 2.5 years.
It is also important to note that fan selection is crucial. A backward-curved fan can provide more consistent air control than forward-curved fans. In addition, radial-damper designs provide air control that is easier to replicate at lower firing rates than blade-type damper assemblies.
Finally, always perform burner maintenance at regular intervals. It is crucial to avoid wear and tear on the firing head, diffuser and igniter, as this can cause air leakage or malfunction and cause the boiler not to start. Remember that weather can result in a change in combustion, so it is recommended that burner maintenance be performed quarterly or at the change in seasons.
This information was adapted from material supplied by the U.S. Department of Energy. For more information, visit the DOE’s Best Practices website at www.eere.energy.gov/industry/bestpractices.