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The initial pulsing systems used in this country were generally based on the idea of firing each burner for a fixed amount of time-say 8-12 seconds-and then forcing the burner to low-fire for a variable amount of time. While these types of systems worked adequately, they often caused somewhat cyclical heating and cooling due to the relatively long high-fire time and sometimes exceedingly long minimum-fire times.
The DataPaq curve shown in Figure 1 illustrates the cyclical heating associated with this type of pulsing logic. At the start of the cycle, no pulsing occurred at all because the kiln temperature was above set point. As the kiln approached 350-400°F, pulsing initiated and cyclical heating and cooling occurred in products set close to the burners.
The smoother heating shown in Figure 2 occurred because the high-fire time was much shorter. The burner fired in pulses as short as a half-second, and pulsing occurred regularly every 8-10 seconds. The combination of short periods of input and frequent pulsing allowed for smooth temperature control with all of the benefits of pulse firing, including the minimum use of required excess air, which translates to better efficiency, and reduced NOx formation due to reduced excess air and high-velocity entrainment, which lowers the flame temperature.
As you upgrade your kilns or purchase new kilns, be aware that while pulse firing is the best current combustion solution, the details of the pulsing can make a huge difference in ultimate performance and efficiency.
Any views or opinions expressed in this column are those of the author and do not represent those of Ceramic Industry, its staff, Editorial Advisory Board or BNP Media.