California’s Central Valley region recently passed a regulation requiring that many existing industrial boilers be upgraded to meet a NOx requirement of less than 9 parts per million (ppm). As part of the rule’s implementation, an extension was given to users who agreed to meet a NOx level of 6ppm. The current versions of Coen Company’s Rapid Mix Burner (RMB™) operate at 6 to 7 ppm, which easily meets a 9 ppm NOx requirement. In order to meet a 6 ppm NOx requirement, a burner was required that would operate at 5 ppm or less.


Engineers developed a variant of the rapid mix technology, the Cell-Rapid Mix Burner (C-RMB™), which consists of multiple burners operated in unison. In this way, combinations of smaller single-zone registers could be used in configurations like one over one, or three rows of two, to meet the required capacity, maintain the fully swirling flow through each burner, and fit within the confines of the given furnace geometry.

FIGURE 1 A Cell-Rapid Mix Burner (C-RMB) installation.


The first commercial application of the burner was installed at TomaTek, a tomato processing facility in central California. The application involved the retrofit of two 80,000 lb/hr “D” style package watertube boilers. The customer was required to meet an emission limit of 6 ppm NOx and 90 ppm CO on both boilers.

The system’s design incorporated two burner cells in a vertically stacked configuration with each cell having a heat release of 50 million Btuh. A new combustion air fan was supplied to provide up to 25% excess air and 45% flue gas recirculation, (FGR) and it was mounted directly above the burner windbox. No boiler modifications were required to allow operation at these ultra-low emission levels, and the burners were installed into an existing windbox. A new burner management and combustion control system was installed to allow precise control of fuel, air, and FGR during operation.

The burners demonstrated the ability to operate at less than 5 ppm NOx between 35% and 45% FGR. The burner excess air levels ranged from approximately 35% at low fire to 25% at high fire. Both units were set up to operate below 5 ppm NOx and have been operated in automatic with a ramp rate from 20% to 100% firing rate within three minutes.

A picture of the burner installation is shown in Figure 1 and operating data from the emissions source test is shown in Table 1. The testing demonstrated that the burners were able to operate at NOx levels as low as 3.5 ppm before CO emissions would exceed 50 ppm.


The two-cell concept has proven extremely successful for operating at less than 5 ppm NOx, and it can accommodate boilers with heat inputs up to 120 million Btuh. The C-RMB not only reduces costs and space requirements, but it is a proven alternative to the catalytic control of NOx emissions. Based on the success of the first two units, TomaTek ordered another C-RMB to retrofit a third boiler at this site.TB