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Reduce Steam Energy Losses

May 1, 2015

Condensing Economizer

The fuel spent in a manufacturing or process operation is a significant part of the company’s operating budget. Studies show that plants waste as much as $0.27 to $0.39 of every dollar due to poor energy practices. Identifying and correcting steam energy losses can add thousands of dollars to a company’s bottom line.

The boiler room is a plant’s primary energy culprit. Some of the common causes for excessive energy loss:

  • Boiler stack. This is the biggest loss area at about 20%. 
  • Fouled waterside and fireside surfaces. For every 40-degree rise in stack temperature over the base point (same firing rate, operating pressure, and ambient tempera- ture), there is a 1% loss in efficiency. 
  • Excessive cycling. Cycling causes pre- and post-purge losses that waste significant energy but often go undetected. 
  • Improper burner setup. This leads to overly high or low excess air that causes inefficient and possibly un- safe combustion. 

To stop these issues and losses, the first step is to work with an experienced service technician who can properly inspect the boiler. The best time is during the boiler’s annual inspection, when it is down and drained. 

The technician will check the water- side and fireside surfaces for cleanliness. If the waterside is fouled, and the pressure vessel is still salvageable, an acid cleaning may be recommended, and/or if there is a soot fouling on the fireside, a good cleaning should be done. After this, the boiler’s gasketing (fireside and water- side) will be checked for possible replacement before closing and refilling the unit. The next step is a complete tune-up of the burner, including the resetting of combustion and performing a combustion analysis throughout the burner’s complete turndown range.

After the boiler has been cleaned, properly gasketed and tuned, it is important to watch the operation of the boiler during normal production hours to see if it is cycling more than 10 times per hour. If it is, the boiler is either oversized for the load or the burner doesn’t have the turndown required to match the varying conditions. To resolve excessive cycling, consider a smaller capacity boiler or retrofitting the existing boiler with a new burner that has higher turndown capability.

With the burner, maintaining 3% O2 at mid- to high-fire is optimal. For every 2% increase in O2 above this base, another 1% is lost in efficiency. For instance, if a burner is originally set up to maintain 3% O2, and the system drifts unknowingly to 7%, there is a loss of 2% overall. Again, this often goes undetected.

 

There are several equipment options that can help recover steam energy loss in a boiler system; however, before installing new equipment, it is important to establish an energy baseline. Many times, plants that burn natural gas have only one meter to measure the boiler as well as other commonly connected energy users. It’s important to install a second gas meter that shows only the boiler’s fuel consumption, providing a benchmark to substantiate improvements.

Following are equipment options that can recover energy from wasted heat or steam, thereby reducing fuel usage while increasing system efficiency.

  • Stack Economizer. Recovers heat from flue gases that would otherwise be wasted, and is used to preheat boiler feedwater. Multiple size options are available to accommo- date space constraints while maximizing heat recovery. 
  • Two-Stage Condensing Economizer. Captures heat through both a traditional stack economizer section and a condensing section. One section recovers energy by pre- heating boiler feedwater. The second (condensing) section preheats cool liquid streams, such as make-up water, pro- cess water, or domestic water for sinks and showers. 
  • One-Stage Condensing Economizer. Saves fuel by pre- heating virtually any cool liquid stream (e.g., make-up wa- ter, process water) by capturing the wasted heat from the boiler stack. It increases the amount of heat recovered by capturing both sensible and latent heat energy. 
  • Flash Tank Economizer. Captures high-temperature flash steam and condensate from a non-modulating pro- cess load, providing (sensible) heat for make-up water and low-pressure flash steam (latent heat) for the deaerator. This system quickly pays for itself with fuel savings result- ing from recycled heat that would otherwise be wasted through exhaust. 
  • Blowdown Heat Recovery System. Captures waste heat from the boiler surface blowdown to increase make-up water temperature (sensible heat) going to the feedwater tank. Continuous boiler surface blowdown heat recovery is the most optimized method of controlling total dissolved solids (TDS) levels within the boiler because it captures otherwise wasted energy normally purged to the sewer. These units are available for boilers of all sizes, including multiple boilers.

One website that can help justify energy-saving initiatives for a facility is energypathfinder.com. This site includes a tool that demonstrates the process of recovering capital for energy-saving initiatives, calculates the results, and shows how much money is being wasted by not proceeding with the recommended action.

In addition, Cleaver-Brooks has a Boiler Plant Optimization Process led by a team of engineers, who generate boiler room recommendations specific to a facility along with the estimated payback.

To learn more about reducing steam energy losses, go to cleaverbrooks.com/energyloss to watch a webinar titled Identifying and Capturing Parasitic Steam Energy Losses or visit cleaverbrooks.com

Steve Connor is an industry expert in steam and hot water generation. He has more than 50 years of experience in a variety of positions, including: engineering, marketing, aftermarket services, field application sales, and training. He recently retired from Cleaver-Brooks as Director of Technical and Marketing Services.

Source: Today's Boiler