Improving productivity while reducing fuel consumption and emissions are high priorities for industrial furnace, oven and dryer manufacturers. Because such equipment heats in-process materials to very high temperatures, they need a lot of fuel to operate, driving up your costs and complicating your plant’s emissions goals.
Fortunately, you can meet your productivity, fuel consumption and emissions goals with the right combustion system design and control strategy. For example, implementing a combustion control strategy known as pulse firing can reduce fuel consumption, improve temperature uniformity within the combustion chamber, lower nitrogen oxides (NOx) emissions and achieve a better, more efficient Turndown Ratio.
One of the goals of combustion systems is to be able to change the heat output depending on process needs. In traditional modulating systems, the burners are always firing at greater or lesser intensities. Pulse firing, on the other hand, engages the burners by “pulsing” them repeatedly in an ON/OFF or high-fire/low-fire cycle.
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Pulsing the burners creates turbulence and airflow, evenly distributing heat within the combustion chamber and maximizing the ratio of heat transfer to fuel consumption. Improving air circulation and temperature homogeneity within the furnace chamber provides efficiency by reducing fuel consumption and emissions. In fact, fuel consumption can decline by as much as 20–30 percent when switching from traditional combustion to pulse firing.
Because of the heat uniformity and superior convection, pulsing the burners lowers the excess air level within the combustion chamber, reducing the amount of NOx that is emitted. When air gets really hot — usually 1,300°C (2,600°F) — the oxygen starts to bind with nitrogen to form NOx. Pulsing enables more efficient heat transfer, meaning the burner is ON less, cutting down on the NOx. Homogenizing the heat within the furnace also reduces these NOx-forming zones.
Turndown Ratio is a comparison between the highest and lowest output temperature of the burner. Changing the duty cycle maximizes this ratio, while adjusting the temperature achieves different heat outputs, ensuring the burner only uses what it needs for the process. Because it improves a system’s efficiency, pulse firing is a good way to upgrade burners that weren’t originally designed for a high Turndown Ratio. Traditional systems typically have a Turndown Ratio often between 2:1 and 10:1.
Combined with the proper settings, pulse firing methods based on high-fire/low-fire cycles can usually achieve a Turndown Ratio of 20:1, while ON/OFF pulsing cycles can achieve an infinite Turndown Ratio as long as you change the duty cycle as needed.
Pulse firing systems are easy and flexible to control, requiring a controller to modify the cycling speeds and achieve quick heating and cooling effects in furnaces. In applications with many burners, this setup improves flexibility by allowing you to have different zones with different temperatures.
To learn more about pulse firing, visit www.emerson.com/combustion
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