Direct Flame Heating Section for Metal Strip Annealing
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Solution Overview
Problem
Direct flame ovens in metal strip annealing and galvanizing processes face inefficiencies due to temperature drops in downstream sections, leading to reduced heating capacity and non-reducing conditions, which require additional radiant tube furnaces, increasing costs and environmental impact.
Innovation Solution
Implementing a 'SUROX' process with a direct flame heating section divided into upstream and downstream zones, using a sub-stoichiometric mixture of air and superoxygenated fuel to maintain high combustion gas temperatures and control oxidation/reduction conditions, reducing unburned gases and NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stoichiometric air/gas ratios or slight excess of air are used to improve combustion efficiency and heating capacity, then combustion efficiency increases, but surface oxidation occurs on the steel strip
Solution Approach 1:
The patent changes the chemical composition parameters of the combustion atmosphere by injecting reducing gases (hydrogen and carbon monoxide) to alter the redox potential. This allows maintaining high combustion efficiency while creating a reducing atmosphere that prevents surface oxidation of the steel strip.
Solution Approach 2:
The patent introduces reducing gases (hydrogen and carbon monoxide) as intermediary substances that mediate between the oxidizing combustion process and the steel strip surface. These gases form a protective reducing atmosphere that shields the strip from oxidation while allowing heat transfer to continue.
2Object-affected harmful factors
If excess fuel is used to maintain reducing conditions with CO and H2, then surface reduction is improved, but combustion efficiency decreases and heating capacity is reduced
Solution Approach 1:
The patent merges two previously separate functions into one combustion process: (1) heating the steel strip through combustion, and (2) maintaining reducing conditions at the strip surface. By simultaneously optimizing both the combustion zone and the atmosphere near the strip, the system achieves high heating capacity while preventing oxidation.
Solution Approach 2:
The patent changes the atmospheric parameters by actively injecting reducing gases (hydrogen and carbon monoxide) into the combustion zone. This alters the chemical composition to maintain high concentrations of reducing agents near the strip surface while preserving efficient combustion characteristics.
3Productivity
If temperature of combustion gases is increased to improve heating capacity, then heating efficiency increases, but NOx emissions increase
Solution Approach 1:
The patent converts the harmful effect of high-temperature combustion (NOx formation) into a beneficial outcome by using the heat from efficient combustion to drive the decomposition of organic matter and generate reducing gases, while the injected reducing gases simultaneously suppress NOx formation through chemical reactions.
Solution Approach 2:
The patent changes the chemical parameters of the combustion atmosphere by injecting reducing gases that chemically interact with NOx precursors and formed NOx, converting them into nitrogen and water. This chemical parameter change reduces NOx emissions while maintaining high heating capacity.
4Temperature
If radiant tube furnace capacity is increased to compensate for temperature drop in downstream section, then temperature maintenance is improved, but device complexity and cost increase
Solution Approach 1:
The patent changes the thermal parameters in the downstream section by injecting reducing gases that burn exothermically, locally increasing the temperature and maintaining it without requiring a larger radiant tube furnace capacity. This reduces device complexity while achieving the same temperature maintenance goal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances heating and production capacity, improves metal strip cleaning, decreases fuel consumption, and reduces environmental impact by maintaining controlled oxidation/reduction conditions while being economically viable and compatible with existing furnaces.
Implementation Method 1
the heating of the metal strip is obtained by combustion of a sub-stoichiometric mixture of air and superoxygenated fuel
Implementation Method 2
Heating of the steel strip is ensured both by radiation and by convection in contact with the burnt gases or combustion gases
Implementation Method 3
Heating of the steel strip is ensured both by radiation and by convection in contact with the burnt gases
Implementation Method 4
the capacity for the furnace atmosphere to oxidize or reduce the surface of the steel strip
Implementation Method 5
An excess of fuel, on the contrary, releases carbon monoxide and hydrogen which are reducing elements
Implementation Method 6
the temperature rise time and therefore the total length of the oven... Steel strips can be heated in radiant tube furnaces
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for operating a continuous annealing or galvanisation line for a metal strip, comprising a section for heating by direct flame (9) with an upstream zone (10) and a downstream zone (11), the section for heating by direct flame (9) being followed by a section for heating by radiant tubes, the metal strip being indirectly hearted in the section for heating by direct flame (9). According to the invention, the heating of the metal strip is achieved in the upstream zone (10) by combustion of a mixture of atmospheric air and fuel such that the temperature of the combustion gas is between 1250°C and 1500°C, preferably close to 1350°C and in the downstream zone(11), the heating of the metal strip is achieved by combustion of a superoxygenated sub-stoichiometric mixture of air and fuel such that the temperature of the combustion gas achieved at the end of the upstream zone (10) is maintained until the end of the downstream zone (11) of the section for heating by direct flame (9).