Low NOx Burners (LNBs)
	Combustion Modifications
	Burner Management and Combustion Controls
	Cold Flow Modeling

AUS LNBs - AUS VEM-LNBs

The heart of the Applied Utility Systems, Inc. (AUS) combustion system offering is the AUS VEM-LNB. This burner design, known commercially as the Vortex Enhanced Mixing (VEM) LNB, incorporates years of experience in designing and applying LNBs to utility boiler applications. The VEM-LNB emphasizes the combustion processes required to establish stable combustion and low emissions.

Air is introduced to the burner in the form of a plug flow with a flat velocity profile. A VEM zone is created by the positioning of a combustion air swirler, which separates the combustion air into primary and secondary combustion zones. Fuel(s) (both oil and/or gas, as applicable) are injected into the primary combustion zone to establish ignition and a stable flame. The air-to-fuel ratio in the primary combustion zone is maintained fuel-rich to control NO_x formation and to enhance flame stability. Flammability limits under fuel-rich conditions are much broader than under fuel-lean conditions. Therefore, operating the primary combustion zone fuel-rich not only offers the control of NO_x formation, but also ensures stable combustion. In a fuel-rich environment, stable combustion is maintained, even if a fluctuation in the combustion air-feed system is experienced.

The combustion air swirler has been the subject of extensive product development. A swirl number is selected to balance the competing requirements of ensuring flame stability and minimizing emissions. The swirler is surrounded with a four-inch wide shroud to guide combustion air flow in and out of the swirler. The swirler establishes a strong recirculation zone internal to the flame that brings hot furnace gas to the base of the flame, thus augmenting flame stability. The swirler axial position within the burner throat is adjustable to allow for flame shaping and optimizing emissions.

The swirler axial position within the burner throat is made adjustable. Retracting the swirler position toward the boiler windbox generally reduces the flame included angle and extends flame length. This swirler position also reduces operating excess O₂ level and results in an increase in NO_x emissions. Positioning the swirler further towards the furnace generally produces a bushy short flame, offering some reduction in NO_x emissions. However, this swirler position may increase operating excess O₂ levels and promote particulate emissions. The swirler’s adjustability provides the operational flexibility that ensures optimum performance in a broad range of field applications.