Run your boiler at its best

Maintaining Efficiency Is a Continuing Goal

12/07/2012


Today’s boilers are rugged and finely-tuned machines. Digital burner controls and on-board flue gas analysis make the job easier, but it’s as important as ever to keep an eye on the goal of optimum efficiency.Too often a high-efficiency package boiler is purchased at a premium price and then allowed to decline in performance from lack of proper maintenance or from incorrect operation. Today’s boilers are rugged and finely-tuned machines. Digital burner controls and on-board flue gas analysis make the job easier, but it’s as important as ever to keep an eye on the goal of optimum efficiency. 

Feedwater is Critical

Perhaps the single most important item to watch is feedwater quality. Good feedwater is critical for the life and efficient operation of a boiler. Rakesh Zala, Director of Product Engineering for Cleaver-Brooks Packaged Boiler Systems, points out that poor feedwater quality can lead to premature boiler failure. “It can also lead to fouling and scale buildup on heat transfer surfaces, raising stack temperature and reducing efficiency.”

It is important to follow manufacturers’ recommendations for feedwater pH and to use the recommended anti-scaling treatments. A modest investment in feedwater treatment chemicals and periodic tube cleaning can pay large rewards in boiler integrity and efficiency. Follow the recommended blowdown frequency, and inspect the boiler interior regularly for signs of erosion or scaling. 

Keep Controls in Calibration

Zala also points out that newer boiler controls often use an O2 sensor to optimize combustion. This means many fewer adjustments of draft and fuel linkages are needed than with older mechanical controls. However, he says, “Typically the sensor requires periodic calibration. Some control systems are designed to perform automatic calibration.” Check with the control system provider to confirm the status of your system.

Chad Fletcher from Hurst Boiler emphasizes the importance of regular maintenance and echoes comments of others on the importance of maintaining feedwater quality. He points out, “The newer technology digital controls do offer easier maintenance and offer easier setup and dealing with problems.” He notes that much of this maintenance work can be done during the bi-annual boiler inspection.

Flue gas analysis will give information on boiler efficiency. Typically you want excess air less than 15% and no measurable carbon monoxide (CO). This will indicate clean combustion. Higher excess air or the presence of CO indicates adjustments are needed. If your boiler offers on-board flue gas analysis, then be sure to take advantage of  this very useful tool.

Find the Sweet Spot and Stay There

Most steam boilers have efficiency “sweet spots” when firing somewhere between 60% and 80% of maximum capacity. Condensing hot water boilers are most efficient at rates somewhat below this. If you have a single boiler, you may not have a choice of the firing rate, but if you have multiple boilers, you should be trying to operate as many as possible at or near the sweet spot. Ask your system designer or the boiler manufacturer for information on what firing rates offer the highest efficiency.

Related to the discussion of sweet spots is the reality that for many industrial and institutional systems, there is a year-round need for steam. Yet summer steam requirements are much less, so a boiler has to operate far from its optimum rate, or cycle an unacceptable number of times a day. This hurts year-round efficiency. 

A Place for Ponies

The solution may be a small “pony” boiler for off-season minimum loads. Small horizontal or vertical tube or tubeless boilers are available to match up with your off-peak pressure and volume requirements. Adding a pony boiler can make your entire plant more efficient year-round.

According to the DOE, boilers are commonly the single largest energy using device in many plants and institutions. Doesn’t it make sense to closely watch the efficiency of this system and try for the best?



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