Wall fired duct heater

Apparatus for heating an exhaust gas comprising in combination:

• a duct defined by opposing duct walls through which the exhaust gas can flow;
• first and second burners mounted to opposing duct walls and including fuel oil atomizing means for discharging fuel oil in a manner which forms a flame that extends transversely to the gas flow, each flame having a relatively elongate, pencil-like shape and a predetermined, cross-sectional extent in a direction perpendicular to the gas flow;
• a means for shielding the flame associated with each burner and mounted to the duct walls, each flame shield means being positioned upstream of the associated burner and forming a trough for each flame which is protected from the gas flow by the shield, each shield means further having an outline in the flow direction of the gas flow which approximates the shape of the flame and which is selected so that a portion of the shield facing the gas flow has a width in a direction perpendicular to the gas flow which is less than the cross-sectional extent of an associated part of the flame so that peripheral sections of the flame extend beyond the shield, adjoining shield means further having proximate edges which are spaced apart so as to define unobstructed paths between adjacent shield means which permit gas flowing through the paths to intersect the peripheral flame sections;
• additional means associated with each flame shield for defining an elongate passage for flowing flame combustion sustaining oxygen through the shield means, said passage being disposed axially intermediate its respective longitudinal ends, from an upstream side of the shield to the trough, and means for regulating the amount of combustion sustaining oxygen which flows through the passage;
• whereby the flame in the trough is sustained with oxygen entering the trough through the passage and the formation of gas flow eddies in the trough and resulting carbon deposits are substantially prevented;
• and whereby the gas flow is further substantially evenly heated over its full cross-section to prevent the formation of hot spots in the gas flow downstream of the burners.

Apparatus for heating of an exhaust gas stream comprising in combination:

• a duct defined by opposing duct walls through which the exhaust gas stream can flow;
• a plurality of burner means each for producing an elongate flame having a controlled outline with a base of the flame adjacent the burner having a transverse extent greater than a transverse extent of an end of the flame remote from the burner, said burner means being mounted to opposing duct walls, each burner means including a nozzle having an axis oriented transversely to the duct and means for mixing fuel discharged by the nozzle with primary combustion air and for flowing a resulting fuel-air mixture transversely to the exhaust gas stream into the duct towards the opposing duct wall;
• means for mounting the burner means in a substantially common plane, adjacent burner means in such plane being alternatively mounted to the opposing duct walls so as to interleave the flames formed by such burner means;
• shield means for each burner positioned relative to the gas stream on the upstream side of the burner to define a flame trough which is open in a downstream direction, the shield means having an outline approximating the outline of the flame so that edges of the shield means extending transversely to the gas stream flowing in the duct are proximate the flame outline, the shield means for the burners being further sized so as to define between them substantially like paths through which the exhaust gas stream can flow to assure an even heating of the exhaust gas stream flowing through such paths;
• means for anchoring the shield means to the duct;
• and supply means connected with the shield means for supplying the trough with sufficient oxygen to assure the substantially complete combustion of the fuel introduced into the trough.

Apparatus for heating an exhaust gas comprising in combination:

• a dust defined by opposing duct walls through which the exhaust gas can flow;
• a burner means for forming a flame that extends transversely to the gas stream into the duct, said means mounted to a duct wall and including a fuel oil atomizing nozzle;
• a means for shielding the flame mounted to the duct and positioned upstream of the burner for forming a trough within which the flame can burn and which protects the flame from the gas flowing in the duct;
• register means disposed upstream of the shield for collecting a gas including oxygen, the register means being disposed within the duct;
• means defining a passage communicating the trough with the register means so that the gas including the oxygen can flow from the register means to the trough and the oxygen can sustain the combustion of fuel oil in the trough;
• and means for regulating the rate with which the gas including the oxygen flows through the passage as a function of the rate with which fuel oil is discharged by the nozzle to assure a substantially complete combustion of all fuel oil discharged by the nozzle.

A method for heating an exhaust gas stream flowing through a duct defined by opposing walls comprising the steps of:

• generating an elongated flame of a well-defined outline with a fuel and an off-stoichiometric amount of primary combustion air;
• directing the flame transversely to the exhaust gas stream from one duct wall towards the other duct wall by forming a mixture of fuel and primary air in an amount substantially less than the required amount of air to fully combust the fuel by directing such mixture into the duct;
• defining a first path for a plurality of exhaust gas streams which path substantially intersects the periphery of the flame and generally follows a longitudinal contour of the flame;
• defining a second path which leads directly into the flame and passes a portion of the exhaust gas along the length of the flame;
• and controlling the extent of the portion so that the portion furnishes the flame with sufficient oxygen to effect the substantially complete combustion of all fuel in the mixture directed into the duct;
• whereby the exhaust gas can be heated to the desired temperature with a minimum amount of additional air and is substantially uniformly heated and the formation of hotspots in the exhaust gas downstream of the flame is prevented.