One goal in any foundry, which transfers metal, is to reduce the amount of energy lost in the ladle. With typical air-fuel ladle heating burners, ladles require long preheating times and produce ladle temperatures appreciably lower than the metal temperature. Oxy-fuel burners eliminate these problems due to the highly radiant flame produced by combustion with pure oxygen.
By replacing air with industrial grade oxygen, the nitrogen ballast is eliminated from the combustion process. Oxy-fuel burners provide higher flame temperature, better emissivity and higher heat transfer. Therefore, oxy-fuel burners are most often used in high temperature processes.
An oxy-fuel burner can rapidly heat a ladle to the metal tapping temperature. This means that instead of superheating the metal to compensate for ladle losses, the metal can be tapped at a lower temperature. Oxy-fuel burner technology used for ladle preheating has become more common for the following reasons:
1. Faster heat up
Due to the higher available heat, which is defined as the gross energy delivered to the ladle minus exhaust gas losses, a ladle can typically be at temperatures in half the time of a conventional air-fuel burner at the same power. This results in fuel savings and high system flexibility.
2. Higher ladle temperature with energy savings
Oxy-fuel burners are excellent in maintaining temperature in hot ladles. The temperature of an air-fuel flame is only 1900°C, versus 2700°C for oxy-fuel. Due to the above, and the highly radiant flame of oxy-fuel, more available heat is provided to the ladle. Therefore a higher ladle temperature (up to 1485°C) can be achieved in a shorter time, with substantially less fuel. This means that the oxy-fuel flame not only maintains a higher ladle temperature, but it can also do it at lower energy consumption.
3. Longer refractory life
Since oxy-fuel provides a ladle temperature much closer to that of liquid iron, there is less thermal shock on the refractory when compared to a standard air-fuel system. As a result, refractory life is usually extended.
4. Reduced flue gas volume
When combustion air is replaced with oxygen the flue gas volume is drastically reduced. From approximately 11,7 to 3,04 Nm3 (normal cubic metres... not Newton metres cubed) of exhaust gas per Nm3 of natural gas, which gives a 75% reduction in flue gas volume - this means a much better environment for an operation.
Other benefits of using oxy-fuel burners
* Elimination of air blowers.
* Elimination of electricity consumption for air blowers.
* Lower investment costs.
* Energy savings in melting furnace.
* Flexible ladle heating.
* Universal tool for different ladle sizes.
* Controllable ladle heating temperature.
Significantly increased billet furnace throughput
With the revival of global steel prices, many manufacturers are seeking to restart idled equipment and improve the performance of older units. One Ohio manufacturer of forged steel pipe has found a method to dramatically improve the throughput of billet reheating furnaces by integrating Maxon Xytherm LE FF burners.
These burners produce a flat, sheet shaped flame that maximises the surface area of the flame over products. By maximising the flame surface area radiant heat transfer to products is increased promoting more rapid, more efficient exchange of heat.
In this application, a large reheat furnace with over 200 MMBTU (62 MW) of heat input was boosted to increase production throughput. As a side benefit, the Oxytherm also provided part of a furnace balancing solution that helped the end user provide more consistent, better quality final products. In this integration, the Maxon Smartfire intelligent combustion control system was used to ensure optimal adjustment of the fuel and oxygen ratios feeding each burner.
For more information contact Quentin Korff, The Combustion Group, 011 452 5060.
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