GAS: Afrox Installs State-Of-The-Art Vessel Preheating Systems
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Afrox applications engineer Gareth Jones says the introduction of this new low-temperature flame technology is a first for Afrox.
“We’re able to supply this pioneering technology as a total package for fast and fuel-efficient oxyfuel preheating of vessels up to 50 tonnes in size Â— in a kit that is small enough to fit into the boot of a car,” says Jones. “The new technology offers several distinct advantages. For instance, compared to air-fuel, oxyfuel allows for fuel savings of up to 55% and there is a 25% shorter heating cycle. The system is very compact, simple and powerful, yet easy to fit on any vessel preheating.
“The flameless oxyfuel promotes a more uniform heating method which increases refractory lining life, reduces the number of vessels in circulation and effectively lowering carbon dioxide (CO2) and nitrogen oxide (NOx) emissions.”
How The Preheating Systems Work
Silicon Smelters, the largest producers of Silicon and Ferrosilicon on the African continent, were the first to use the OXYGON technology in an operating environment in South Africa. Says Bennie Bierman – Unit Manager, Furnaces at Rand Carbide “The OXYGON 400 system rapidly heats our 3.5 tonne capacity ladles to 1000Â°C, frequently in less than one hour. This significantly saves fuel and increases ladle availability. In addition, the system is fully automated and one press of a button is all it takes to get ladles to the desired end temperature”.
Within the metals production industry various types of vessels and runners are used to transfer hot, liquid metal between melting and casting operations. Typical examples are ladles, converters, tundishes, runners and pouring chutes. These vessels and runners have ceramic lining of different types and quality that requires preheating to minimise refractory wear and to secure the right metal quality.
Preheating Systems Helping Systems Going Green
Preheating temperature is based on optimisation factors such as fuel economy, refractory lifetime, refractory quality and liquid metal temperature, as well as the vessel design and tapping system used.
“The issue of reducing greenhouse gases emission, such as from CO2 and NOx, is not only an environmental concern, but also an economic aspect of modern metals production,” says Jones.
“Flameless oxyfuel combustion in preheating of various vessels, such as ladles, AOD converters and tundishes has long since been proved to be an efficient method of cutting heating times, improving fuel economy and extend vessel refractory lining life. The OXYGONÂ® 400 system now makes this energy-efficient preheating application available for use in smaller vessels and runners, targeting for example, foundries and micro steel mills. To further improve the performance, flameless oxyfuel is applied. Flameless oxyfuel combustion technology is uniquely designed to boost capacity, reduce fuel consumption, improve temperature uniformity and reduce emissions.”
Combustion occurs under a diluted oxygen concentration as flue gases are mixed into the combustion zone. This slows down the oxyfuel combustion reactions and results in lower flame temperatures, which are below the point at which thermal NOx is created.
The mixing of flue gases into the flame also disperses the energy throughout the entire vessel for a faster and more uniform heating. The dispersed flame contains the same amount of energy, but with a much more effective heat distribution.
The overall result is a more homogenous heating, a further decrease in fuel consumption and reduced NOx emissions. The OXYGONÂ® 400 preheating systems work in a flameless mode with only the pilot flame continuously visible.
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