If your boiler/burner package is like the more than 200,000 commercial- and industrial-boiler packages currently in operation, it probably is more than 20 years old. It most likely is only 60- to 70-percent efficient, and large amounts of fuel and associated cash are wasted with every minute the equipment is operated.

Burning money unnecessarily in the current economy simply is unacceptable. While a new boiler package would fix the problem, such a significant investment (usually $100,000 or more) may be difficult to justify during these challenging economic times.

Fortunately, less costly retrofits and upgrades can be made to an existing boiler package, increasing efficiency and reducing fuel usage. Assuming a boiler vessel is in good shape, the most immediate opportunities to cut boiler-room fuel use and electricity costs involve burners, burner components, and controls. This article will examine various burner retrofit options.

Replacing a Burner

The burner is the true driver of a boiler system's fuel use and costs. After about 20 years of service, a typical burner simply gets tired. Linkage joints, cams, and other moving parts wear out, and a burner's ability to keep tight control of its air-to-fuel ratio degrades. The result commonly is referred to as “hysteresis,” which, in turn, results in a burner's inability to maintain desired excess-air levels across the firing range for optimum combustion. Higher excess air means lower combustion efficiency. A legacy burner can suffer from a host of other issues, including plugged or deteriorated nozzles and gas orifices and deterioration of other combustion-head components responsible for proper fuel and air mixing. All of this results in unburned fuel (carbon monoxide, hydrocarbon, etc.) and higher-than-required excess-air levels, leading to poor performance, overall efficiency reduction, and unnecessary spending.

If a burner has too many worn-out parts or is based on outmoded technology, adding new controls probably is not going to fix the underlying issues. Instead, the old burner can be replaced with a new one that features advanced controls, higher turndown capability, and lower excess-air requirements. Depending on a variety of factors unique to each system, replacing a burner can reduce fuel usage by 5 to 10 percent.

Older burners also are out of step with modern, more stringent emissions regulations established by the U.S. Environmental Protection Agency (EPA) and related air-quality-management districts. For systems that include a legacy burner, the looming threat of financial penalties for violations of EPA standards more than likely outweighs the upfront costs of replacing old burners with newer models that emit significantly less pollutants.

High Turndown

Replacing a legacy burner with a new burner that incorporates high-turndown (HTD) capability is one of the most beneficial upgrades available. While older burners typically operate in a narrow turndown range, HTD burners continue operating at even lower firing rates to meet lower loads.

With greater turndown capability, a burner experiences fewer cycles. Before each firing cycle, a burner must perform an automatically controlled pre-purge, during which fresh air is blown through flue-gas passages for a specified amount of time. Depending on several factors, such as agency and insurance approvals, a burner also may be required to perform a post-purge sequence. The purges rid the furnace of any unburned fuel that may have pocketed and, therefore, could have ignited in an uncontrolled condition. In many applications, a post-purge must commence once a load is satisfied, after which the burner proceeds to shutdown or standby mode. Any time cooler air is blowing through a hot boiler or heat exchanger, heat loss occurs. Therefore, on subsequent firing cycles, the burner must raise the temperature of the water or fluid to be heated to make up for the heat losses associated with pre- and post-purging. The fan motor must be activated for each purge, adding to unnecessary energy costs.

HTD burners can reduce these cycling occurrences and related expenses dramatically. When an HTD burner is used, the boiler is hotter when a new cycle begins, reducing the amount of energy required to return to set point. Additionally, an HTD burner is less likely to overshoot the desired set point and waste more fuel as the burner oscillates (over- and undershooting) while trying to meet the desired pressure or temperature.

A reduction in cycles also means a decrease in failures brought on by cyclic fatigue, reducing ongoing maintenance costs.

Upgrading an Existing Burner

If a burner meets emissions standards and retains a satisfactory ability to track at good excess-air levels throughout its firing range, it may be a candidate for various retrofit-technology upgrades.

New burner controls incorporating a programmable logic controller (PLC) or microprocessor-based technology offer additional opportunities to improve a boiler package's performance and efficiency through precise and customized control.

Parallel positioning

While traditional controls use “single-point” positioning, incorporating shafts and linkages for air-to-fuel-ratio control over a firing range, parallel positioning allows independent control of air and fuel flows. Because desired and exact air-to-fuel ratios can be set at each point in the range, proper oxidation is ensured.

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