|Upgrade Boilers with Energy-Efficient Burners|
|Written by USDOE Office of Industrial Technologies|
|Thursday, 01 July 2010 08:20|
Upgrade Boilers with Energy-Efficient Burners
A power burner mechanically mixes fuel and combustion air and injects the mixture into the combustion chamber. All power burners essentially provide complete combustion while maintaining flame stabilization over a range of firing rates. Different burners, however, require different amounts of excess air and have different turndown ratios. The turndown ratio is the maximum inlet fuel or firing rate divided by the minimum firing rate.
An efficient natural gas burner requires only 2% to 3% excess oxygen, or 10% to 15% excess air in the flue gas, to burn fuel without forming excessive carbon monoxide. Most gas burners exhibit turndown ratios of 10:1 or 12:1 with little or no loss in combustion efficiency. Some burners offer turndowns of 20:1 on oil and up to 35:1 on gas. A higher turndown ratio reduces burner starts, provides better load control, saves wear-and-tear on the burner, reduces refractory wear, reduces purge- air requirements, and provides fuel savings.
Efficient Burner Technologies
An alternative to complex linkage designs, modern burners are increasingly using servomotors with parallel positioning to independently control the quantities of fuel and air delivered to the burner head. Controls without linkage allow for easy tune- ups and minor adjustments, while eliminating hysteresis, or lack of retraceability, and provide accurate point-to-point control. These controls provide consistent performance and repeatability as the burner adjusts to different firing rates.
Alternatives to electronic controls are burners with a single drive or jackshaft. Avoid purchasing standard burners that make use of linkages to provide single-point or proportional control. Linkage joints wear and rod-set screws can loosen, allowing slippage, the provision of suboptimal air-to-fuel ratios, and efficiency declines.
Cost Savings = Fuel Consumption x Fuel Price x (1 - E1/E2)
If the installed cost is $75,000 for a new burner that provides an efficiency improvement of 2%, the simple payback on investment is:
Simple Payback = $75,000 / $98,760/year = 0.76 year
Steam Tip Information is adapted from material supplied by PBBS Equipment Corp. and Blesi-Evans Company and reviewed by the DOE BestPractices Steam Technical Subcommittee. For additional information, refer to Steam Tip Sheet #4, Improve Your Boiler’s Combustion Efficiency, available online at www.eere.energy.gov/industry/bestpractices.