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The watertube boiler market has been hit especially hard by the recent economy, but Preferred Utilities’ W.N. Best burner division was able to win a large order for two 50,000 pph gas and oil fired burners through Rentech Boiler Systems in Abilene, TX. These PAF burners were developed in the 1970’s to provide very low excess air performance for multiple burner utility boilers. In the last ten years, this burner design was applied to packaged watertube boilers and delivered 5% excess air performance (1% stack oxygen) from 50% firing rate up to high fire. In addition, turndown rates of 10 to 1 or greater were achieved with good CO performance at all firing rates.
Preferred burner windbox being hung on one of two 50,000 pph Rentech boilers. Note the eight bolts that will be used to attach the fuel skid below on site. This was done to expedite windbox delivery to Rentech’s plant in Abilene, TX. Also, the fuel skid can be crated to offer more protection during shipping.
Gil Sy, head of the W.N. Best burner division at Preferred, won this order beating out Peabody and the Coen/Zink/Todd collective. “Our price was lower than Coen, and Rentech was uncomfortable with the Peabody proposal,” Sy said. “The Peabody proposal was somewhat vague and they weren’t exactly sure what was included and what wasn’t.” Preferred was able to provide a very complete package to Rentech including the burners, burner controls, pump set, and plant master controls. Preferred engineers coordinated this entire package to ensure the pieces work together as a system and eliminate the possibility of mis-matched equipment and “finger-pointing” at the jobsite.
These burners are equipped with Preferred’s BurnerMate Universal Industrial control system. Like the original BurnerMate Universal, the BMU Industrial includes flame safeguard, drum level, and draft control, and the combustion control strategy is fully metered using a unique and patented position pacing servo logic. The combustion control system uses air and fuel flow metering, servo position, and stack oxygen to maintain tight fuel air ratio control and fast response to changing boiler loads. The BMU Industrial is also controlling FGR valves and fresh air dampers on this project.
The burners were designed with externally adjustable “candy cane” gas carrier tubes (hidden under bubble wrap) to allow for adjusting the flame during commissioning. If gas nozzle adjustments are necessary, this feature will save a great deal of time in the startup compared to shutting down the boiler, cooling it down, and making the adjustments from inside the boiler. Dick Potts was the project manager for this burner order, and Gil and Darrel Scribner will start up the burners once they are installed at OSI Pharmaceutical’s facility in Ardsley, New York.
Rentech boilermakers getting ready to weld the Preferred windbox to the boiler front.
The burners on this order carry a NOx guarantee of 0.05 lbs/mmBtu or about 41 ppm NOx using flue gas recirculation. As seen from the photograph below, these burners feature a very aggressive swirler that fills almost the entire burner throat. This high intensity swirler, sized for relatively high pressure drop, is essential to the low excess air performance of this burner. It also provides for very clean oil firing. For even more swirl, this burner can be combined with adjustable windbox louvres for applications that require extremely short flames. NOx is controlled by FGR and very low excess air operation.
Rentech watertube boilers feature a fully welded membrane front and rear wall construction. This greatly reduces the amount of refractory in the boiler, enables the boiler to warm up faster from a cold start, and generates lower NOx emissions. Rentech’s specialty is high pressure superheated steam, high capacity utility plant auxiliary boilers, and high quality saturated steam boilers for industrial applications.
Internal view of the Rentech boiler showing the PAF burner swirler, Rentech ring header, and fully welded membrane front wall.
Preferred Utilities works closely with Rentech to package a total solution for the project’s needs. Preferred Utilities' industrial factory is located in Danbury, CT (Connecticut).
