Burners
Burners on equipment used for asphalt heating can be either non-modulating, high-low, or fully modulating. A non-modulating burner has two operating states with no intermediate settings. It is either on or off. A high-low burner (Figure 29) has three operating states: off, low, and high. A fully modulating burner is one that can be fired at variable rates ranging from off to high with numerous intermediate rates.
Figure 29. High-Low Burner
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The non-modulating burner has the advantages of being simple, reliable and cost less than the other types. It is well-suited for applications where it does not need to frequently cycle on and off. Frequent cycling reduces its efficiency because of temperature overshooting. The non-modulating burner is well-suited for direct-fired tanks because they lose heat very slowly, allowing the burner to remain off for long periods of time.
The non-modulating burner is not well-suited for hot oil heaters that are subject to frequent on-off cycling. Hot oil heaters are subject to frequent cycling when the plant heat load varies a lot. Heat loads tend to vary a lot on plants with several asphalt tanks and a number of other plant components that are heated.
The high-low burner is a compromise between a non-modulating burner and a fully modulating burner. It doesn’t offer any real advantages for direct-fired tanks. And it is less suited for use with hot oil heaters than a fully modulating burner. Consequently, high-low burners are less popular for asphalt heating.
The fully modulating burner is the most efficient of the three types of burners (Figure 30). It can be fired at a rate that closely matches the heat demand. This conserves fuel, reduces temperature overshooting, and can eliminate constant on-off recycling. It is used extensively on hot oil heaters, especially larger ones that heat several asphalt tanks and other plant components.
Figure 30. Fully Modulating Burner
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