Jet-Fired Strip Steel Preheating With Inert Gas Heat Exchange
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Solution Overview
Problem
Existing continuous annealing furnaces face issues with low primary heat energy utilization, limited preheating temperature, and excessive oxidation of strip steel due to direct fire combustion exhaust gas contact, leading to inefficiencies and surface quality problems.
Innovation Solution
A jet direct fire preheating system with heat exchange and jet bellows units that utilize high-temperature exhaust gas for forced convection preheating, incorporating a secondary combustion chamber to prevent direct gas contact and an open flame burner for oxygen-rich secondary combustion, ensuring efficient heat exchange and reducing oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If direct fire combustion exhaust gas is used to preheat strip steel, then preheating temperature can be increased, but excessive oxidation occurs on strip steel surface
Solution Approach 1:
The patent introduces a sealing gas (nitrogen or other inert gas) as an intermediary substance between the direct fire combustion exhaust gas and the strip steel. The sealing gas forms a protective atmosphere that prevents direct contact between the oxidizing exhaust gas and the strip steel surface, thereby preventing excessive oxidation while still allowing heat transfer to occur. This mediator approach resolves the contradiction by decoupling the heating function from the oxidizing effect.
Solution Approach 2:
The patent creates an inert atmosphere using sealing gas (preferably nitrogen) that fills the preheating furnace chamber. This inert atmosphere replaces the oxidizing direct fire combustion exhaust gas environment, allowing the strip steel to be heated without direct exposure to oxygen-containing gases. The inert atmosphere maintains reducing conditions that prevent surface oxidation while permitting thermal energy transfer through conduction and convection.
2Productivity
If direct fire combustion exhaust gas is directly contacted with strip steel for preheating, then heating efficiency improves, but heat energy loss increases due to high emission temperature
Solution Approach 1:
The patent recovers the thermal energy from the direct fire combustion exhaust gas by using it to heat the sealing gas (nitrogen or other inert gas) in the preheating furnace. Instead of directly discharging the high-temperature exhaust gas, the system extracts its thermal energy to preheat the strip steel indirectly through the sealed inert atmosphere. This energy recovery approach reduces heat loss while maintaining heating efficiency, as the exhaust gas temperature is reduced before discharge.
3Productivity
If preheating temperature is increased to improve heating capacity, then heating efficiency improves, but oxidation of strip steel becomes more severe
Solution Approach 1:
The patent maintains a high preheating temperature (capable of heating strip steel to 350°C or higher) by using an inert atmosphere of sealing gas. This inert environment prevents oxidation even at elevated temperatures, allowing the system to achieve high heating capacity without the penalty of severe surface oxidation. The inert atmosphere acts as a protective barrier that enables aggressive heating while preserving surface quality.
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
The system achieves rapid preheating of strip steel to 350°C or higher, enhances heat utilization, and prevents excessive oxidation, improving heating efficiency and surface quality while reducing energy loss.
Implementation Method 1
heat exchange pipes, wherein the bellows body is provided with a plurality of nozzles on the side opposite to the threading channel
Implementation Method 2
the direct fire combustion exhaust gas is utilized to heat the shielding gas of nitrogen and hydrogen circulating in the bellows body
Implementation Method 3
at least one open flame burner is provided in the secondary combustion chamber for direct fire combustion exhaust gas
Implementation Method 4
the shielding gas of nitrogen and hydrogen heated under the action of circulating fan is sprayed on the upper and lower surfaces of the strip steel at high speed for forced convection and heat exchange
Implementation Method 5
a circulating fan, wherein an inlet pipeline port is arranged in the threading channel, and an outlet pipeline port is located in the bellows body
Implementation Method 6
The sealing device has a nitrogen gas sealing structure, which adopts a nitrogen gas sealing chamber with a nitrogen gas injection pipeline arranged thereon
Data Source
AI summary
A jet-type direct-fired preheating system, comprising a direct-fired furnace and a preheating furnace. The direct-fired furnace comprises a furnace casing, a direct-fired heating area being provided in the furnace casing. The preheating furnace comprises: a furnace body, wherein the upper portion of the furnace body is connected to the upper portion of the direct-fired furnace by means of a communicating pipe, the bottom of the furnace body is provided with a strip steel inlet, a sealing apparatus and a steering roller, an upper collection chamber of direct-fired waste gas and a secondary combustion chamber of direct-fired combustion waste gas are provided at the upper portion in the furnace body, and a lower collection chamber of the direct-fired waste gas is provided at the lower portion in the furnace body; and a plurality of heat exchange and jet bellows units, provided in the furnace body in the height direction of the furnace body, a threading channel being formed in the middle. Each heat exchange and jet bellows unit comprises: a bellows body, a heat exchange pipe being provided in the bellows body, and a nozzle being provided on the side surface opposite to the threading channel; a secondary waste gas mixing chamber provided between the bellows bodies; and a circulating fan, an inlet pipeline port being formed in the threading channel, and an outlet pipeline port being located in the bellows body. According to the present invention, strip steel can be quickly preheated to 350° or above and quickly heated to 750° or above; and waste heat of the waste gas is fully utilized, such that an over-thick oxide layer can be prevented from being generated on the surface of the strip steel.