Method of operating a wall fired duct heater

Abstract

A heater for heating gases such as turbine exhaust gases to facilitate the extraction of the heat energy carried by such gases or flue gases to reduce their corrosiveness. The heater is defined by burners installed on walls of the duct through which the gases flow. The burner can be operated with heavy fuel oil and normally uses no more primary air than is necessary to ignite the fuel oil atomized by the burner and sustain a flame. The flame is relatively long and narrow and is directed transversely to the gas flow into the duct. Upstream of the burner is a shield to protect the flame from the gas flow. The shield communicates with a register which collects an amount of gas sufficient to provide the balance of the combustion oxygen to fully combust all fuel. From the register the gas flows along inclined passages to the side of the shield facing the flame, the passages directing the gas in the direction of the flame and at an oblique angle in regard thereto. The flame shield is shaped to approximate the outline of the flame. Gas not collected by the register is guided by the shield past the flame so as to achieve a uniform heating of the gas and thereby prevent the formation of hot spots in the gas downstream of the heater. For operation in gas streams having a low oxygen content the burner is constructed so that the fuel-to-combustion oxygen ratio in the upstream and downstream portion of the flame (relative to the exhaust gas flow) is substantially equalized.