Method and apparatus for heat treatment

Abstract

A method and an apparatus for heat-treatment of materials, preferably metals, are provided. The method comprises the following steps: providing and maintaining a flame by supplying a burner with fuel and gas containing at least 80 percent by volume oxygen; creating an oxygen-hot exhaust mixture by recirculating exhausts from the flame to the gas containing oxygen by means of an ejector effect; mixing the oxygen-exhaust mixture and the fuel; and providing a secondary recirculation by recirculating exhausts from the flame to the oxygen-exhaust-fuel mixture. The method and apparatus allow for extremely low NOx emissions and high efficiency, resulting in an environmentally friendly and at the same time cost effective process.

Description

FIELD OF INVENTION [0001] The present invention relates generally to a method and an apparatus for heat treatment of materials, preferably metals, and more particularly to heat treatment involving low NOx emissions in open flame and radiant tubes as well as a very high thermal efficiency. BACKGROUND [0002] Conventional oxy-fuel technology has successfully been used for many years. It provides great benefits regarding productivity and fuel consumption. Conventional oxy-fuel technology can also be used to achieve considerable reductions in NOx emissions compared to conventional air-fuel burner technology. However, oxy-fuel technology is relatively sensitive to air in-leakage into the combustion zone and requires good pressure control in the furnace. In some processes and furnace types it is very difficult to keep air from leaking into the system [0003] Thus, fuel combustion in a furnace can result in large emissions of nitrous oxides (NOx). NOx (mainly NO2) emissions have been found t...

AI Technical Summary

Benefits of technology

[0006] An object of the present invention is to provide a method and an apparatus for heat treatment of metals wherein the drawbacks of prior art apparatuses are eliminated or at least mitigated. A particular object is to provide a method and an apparatus wherein emission of nitrous oxides (NOx) is kept to a minimum while maintaining a high degree of thermal efficiency and providing technology to use oxy-fuel combustion in radiant tubes.

Problems solved by technology

However, oxy-fuel technology is relatively sensitive to air in-leakage into the combustion zone and requires good pressure control in the furnace.

In some processes and furnace types it is very difficult to keep air from leaking into the system

Thus, fuel combustion in a furnace can result in large emissions of nitrous oxides (NOx).

NOx (mainly NO2) emissions have been found to have negative health effects, promote corrosion, and to be an environmental hazard, contributing among other things to eutrophication.

A further problem when using a conventional oxy-fuel burner for heat treatment of metals using radiant tubes is that the high flame temperature of an oxy-fuel burner will damage the tube material, which of course is unacceptable.

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