Consulting-Specifying Engineer - December 2008 - (Page A8)

SEARCHING FOR A Better Boiler Burner Combustion Air and Flue Gas Swirl Vanes and Gas Injectors External Recirculation Zone Internal Recirculation Zone Flue Gas Rapid Mixing Furnace Section Wall THE LAST DECADE SHOWED IMPROVEMENTS IN THE BURNERS used in natural gas-ﬁred and combination fuel boilers, resulting in reductions in boiler NOx emissions, gradual improvements in combustion efﬁciency, and improved burner reliability. Among the leaders in boiler burner technology are the John Zink Company and Coen Company, both divisions of Koch Chemical Technology Group, as well as Cleaver-Brooks’ Pro-Fire and NatCom burner divisions, and Johnston Boiler. John Zink develops and markets burners under the Gordon Piatt brand, and Coen is a licensed manufacturer of the TODD Combustions burners, as well as its own Coen burners. Both companies manufacture burners sold as original equipment in new boilers from many manufacturers, as well as replacement burners for existing boilers. Looking for Lower NOx The past 15 years has been an interesting and challenging period for burner designers. Tim Webster from John Zink Company explains, “Today the lowNOx burner – with emissions less than 30 ppm – is quite a mature technology. There are a lot of products on the market that can meet this number.” But he explains that the last decade or more has seen development of ultralow NOx (ULN) burners. “This is where the more recent development has taken place, and we are continuing to reﬁne this technology.” Webster notes that the ULN technology has been driven by increasingly rigorous standards for NOx emissions, coming ﬁrst in Southern California and the San Joaquin Valley, and today in many other regions of the country. He notes, “When we started offering this ULN technology, virtually all the burners went to California. Now we have placed these burners in 29 different states in the U.S., and in several locations in Canada.” FGR an Essential Strategy According to Webster, the most widespread strategy for achieving low-NOx numbers is ﬂue gas recirculation (FGR) – in effect taking a portion of the combustion exhaust gas and recycling it back through the combustion zone. The only alternative is to use drastic amounts of excess air through the combustion zone air in the combustion process. The excess-air approach has major penalties in efﬁciency, however. The challenge with FGR, Webster says, is to recycle the exhaust products in a way that continues to allow stable, efﬁcient combustion. “That’s where the developments of the last 10 to 15 years have been critical.” He explains that John Zink and Coen burners have been improved through extensive laboratory testing and ﬁeld experience over the last decade. “We’ve learned that we need to keep ﬂame temperatures to less than 2700°F, and we need to achieve an optimum and very uniform mixture of fuel, combustion air and recirculated exhaust gas.” Diagram shows typical fuel, recirculated ﬂue gas and air injection points. Illustration courtesy Coen Company. NOx Performance Continues to Improve A8 gastechnology / WINTER 08 Boiler Replacement vs. Burner Retroﬁt According to Webster, the facility operator looking to reduce NOx emissions has the alternatives of replacing the burners on existing boilers, or installing replacement boilers with low or ULN burners. “It may be practical to simply replace the burners if the existing boiler is in good condition and otherwise has a good remaining life expectancy.” Webster indicates the decision does not so much depend on the age of the boiler as its condition. He notes however that many older boilers do not have membrane wall construction. “In those situations, it is more challenging to maintain the furnace at a WWW.ENERGYSOLUTIONSCENTER.ORG http://WWW.ENERGYSOLUTIONSCENTER.ORG

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - December 2008

Consulting-Specifying Engineer - December 2008 Contents Viewpoint News M/E Roundtable ARC Awards New Construction Gold New Construction Silver New Construction Bronze Renovation Gold Renovation Silver A Green Approach to Air Conditioning Systems Turning Down the Lights Case Study New Products Equipment Lifecycles Advertiser Index Green Space Gas Technology Pure Power Supplement

Consulting-Specifying Engineer - December 2008

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