The following article by
Alagasco Questline addresses the increased interest in boiler efficiency and the trends towards smaller, more economical boilers. Soaring energy prices and tighter emissions standards are a few of the many challenges that have been placed upon numerous facilities in the U.S., and according to the American Boiler Manufacturers Association sales data, 76% of existing boilers are more than 30 years old. This article provides helpful suggestions on how to improve boiler efficiency by identifying energy losses and lowering
emissions. This article can be found at
http://www.questline.com/Article.aspx?userID=973219&articleID=8602&NL=5221. Enjoy!
In Boiler Rooms, Green Is Red Hot
Key Points
· Boilers make up about 40 percent of total energy use in commercial and industrial facilities.
· Most operating boilers are over 30 years old and may operate below current efficiency standards.
· Improving boiler system efficiency can help cut energy costs and improve your environmental profile.
It is not exactly late-breaking news that boilers use a lot of energy. Currently, an estimated 163,000 commercial and industrial boiler systems are in operation nationwide [1]. Boilers make up about 40 percent of the total energy consumption in these sectors. It is also no secret that boilers emit air pollutants, such as nitrogen and sulfur compounds, that contribute to acid rain, ozone depletion, and other environmental problems.
Soaring energy prices and tighter emissions standards have created additional challenges for facilities all across the country that are already struggling to cut costs and meet operating budgets. Age is another factor. According to American Boiler Manufacturers Association sales data, 76 percent of existing boilers are more than 30 years old. These boilers likely operate well below the efficiency standards of current technology and are probably less reliable than newer models. Some units may even violate state and federal emissions standards, contributing further to greenhouse gas emissions.These issues have combined to increase interest in boiler efficiency and to drive sales trends toward smaller, more economical boilers. If you are one of the many facilities looking to cut boiler operating costs and improve your environmental profile, there are a number of steps that you can take to identify energy losses, improve efficiency and lower emissions.
Install Energy Efficient BurnersThe purpose of a burner is to mix air and fuel. Burners are designed to maximize combustion efficiency while minimizing the release of emissions. A boiler will run only as well as the burner performs. An efficient burner provides the proper air-to-fuel mixture throughout the full range of firing rates, without constant adjustment. Consider purchasing a new energy-efficient burner if your existing burner is cycling on and off rapidly or if repair costs become excessive and reliability becomes an issue. For further details, see the U.S. Department of Energy document "
Upgrade Boilers with Energy Efficient Burners."
Flue Gas RecirculationUpgrading or adding options to the burner is the most effective way to cut down on boiler emissions. While there are a number of combustion and post-combustion emissions control options, flue gas recirculation (FGR) has the potential to offer the greatest emissions reduction. FGR involves recirculating part of the relatively cool exhaust gases back into the combustion process in order to lower the flame temperature and reduce nitrogen oxide (NOx) formation. It is currently the most effective and popular low NOx technology for firetube and watertube boilers. In many cases, it does not require any additional reduction equipment. For information about other emissions control options, see the Energy Solutions Center's
Boiler Efficiency Improvement Guide.
Increase Turndown RateAnother energy-saving option for burners is to increase the turndown rate. Boiler turndown is a ratio of a boiler's capacity at full fire to its lowest firing point before shut-down. Old boilers may have only two firing positions: low and high. Newer boilers offer a wider range of firing capacities. A higher turndown ratio reduces burner starts, provides better load control, saves wear-and-tear on the burner, increases refractory life, reduces purge-air requirements and provides fuel savings.
Consider Condensing BoilersMany currently installed boilers, especially older ones, are oversized, wasting energy and emitting more pollutants than necessary. In many applications, it is a good idea to replace an older boiler with a smaller, more efficient condensing boiler. A condensing boiler is a hot water heating device designed to recover energy normally discharged to the atmosphere through the flue. The real energy savings from a condensing boiler come from the drop in the temperature of flue gases flowing through the stack, multiplied by the mass-flow rate of the flue gases. A typical non-condensing boiler has a flue gas temperature of 135°C (275°F). A properly-sized condensing boiler may drop the flue gas temperature to 77°C (170°F) or lower, condensing the flue gases and transferring the absorbed heat into the water flow. This can raise the effective seasonal thermal efficiency of these boilers from below 80 to 90 percent or higher. See
Condensing Boilers for Maximum Efficiency.
Boiler Blowdown Heat RecoveryThe boiler blowdown process involves the periodic or continuous removal of water from a boiler to remove accumulated dissolved solids and/or sludges. Boiler blowdown wastes energy, however, because the blown-down liquid is about the same temperature as the steam produced. Much of this heat can be recovered by routing the blown-down liquid through a heat exchanger that preheats the boiler's makeup water. Blowdown heat recovery systems can offer a payback in as little as 12 months. Several boilers can be attached to a single recovery unit, thus reducing capital costs. Any boiler with continuous surface blowdown exceeding 5% of the steam generation rate is a good candidate for blowdown waste heat recovery. For more information, see
"Recover Heat From Boiler Blowdown," a U.S. Department of Energy fact sheet.
[1] Characterization of the U.S. Commercial/Industrial Boiler Population, Energy and Environmental Analysis, Inc., Arlington, VA, 2005.