Low velocity staged combustion for furnace atmosphere control

Abstract

An improved staged combustion method useful with oxy-fuel combustion and in a furnace which contains a charge, wherein substoichiometric combustion and low velocity injection of fuel and primary and secondary oxidant are carried out in an orientation which forms a reducing atmosphere proximate the charge surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]The present invention claims priority to U.S. provisional patent application Ser. No. 60 / 937,768, filed Jun. 29, 2007, the entire contents of which are incorporated herein by reference in its entirety.TECHNICAL FIELD[0002]This invention relates generally to staged combustion within a furnace which contains a charge to be heated by heat generated by the combustion.BACKGROUND OF THE INVENTION[0003]In many industrial heating processes fired with fuel and oxidant, products of fuel combustion interact or react with furnace charge and often cause undesirable effects. For example, fuel rich flame impinging over glassmelt in a glass melting furnace is known to cause color change in glass product due to redox change of the glassmelt exposed to the fuel rich flame. In a steel reheat furnace oxide scale is formed during heating resulting in loss of metal or surface defects. In the direct reduction of iron oxide by the process disclosed in U.S. Pat. N...

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Benefits of technology

[0022]As used herein the term “products of complete combustion” means one or more of carbon dioxide and water vapor.

[0023]As used herein the term “products of incomplete combustion” means one or more of carbon monoxide, hydrogen, carbon and partially combusted hydrocarbons.

[0024]As used herein the term “unburned fuel” means material that comprises one or more of fuel which has undergone no combustion, products of incomplete combustion of the fuel, and mixture

Problems solved by technology

In many industrial heating processes fired with fuel and oxidant, products of fuel combustion interact or react with furnace charge and often cause undesirable effects.

For example, fuel rich flame impinging over glassmelt in a glass melting furnace is known to cause color change in glass product due to redox change of the glassmelt exposed to the fuel rich flame.

In a steel reheat furnace oxide scale is formed during heating resulting in loss of metal or surface defects.

There are drawbacks with this approach.

The melting process requires a significant amount of heat which is typically provided by combustion of natural gas with air.

The reactions of CO2 and H2O with carbon are endothermic and consume heat and increase the consumption of natural gas.

Although this technology has been used commercially in glass melting furnaces where hearth areas are controlled to have a more oxygen rich atmosphere, the degree of atmosphere stratification was limited due to the relatively high momentum required for this method.

Although the process could be applied in a direct reduction furnace to create a reducing atmosphere in the lower half of the furnace and oxidizing atmosphere in the upper half of the furnace, the large number of special low velocity burners required for the process makes the process more complex to operate.

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