Burners for Reheating Furnaces
Danieli Centro Combustion (DCC) proposes a wide range of burners, either wall or roof mounted, designed for gaseous fuels (from 1.000 to 22.000 kcal/Nm3) or liquid fuels (heavy and light fuel oil).
Lateral Burners – FXB, MAB and MAB-FLTM
The thermal power of lateral burners varies from 500 Mcal/h to 5.000 Mcal/h, with preheated combustion air (typical temperature 500-550°C).
* FXB burners
are suitable for gases with low calorific values (usually preheated), where flame temperature is relatively low, and NOx emissions tend to be minimal without using any complex combustion technique. The FXB design is focused on guaranteeing flame stability in all firing conditions (cold and hot chamber), and the required flame length depending on the application. Further improvements to the FXB series have recently been incorporated to allow firing with gas and liquid fuels simultaneously. Achieved NOx emissions are 80 mg/Nm3 @ 3% O 2 @ 1250°C when firing gas with LCV lower than 2.000 kcal/Nm3.
* MAB burners
were developed with the cooperation of the Polytechnic University of Milan and systematic laboratory tests, in order to achieve lower NOx emissions. The applied combustion techniques are“air staging, whereby combustion air is injected in multiple steps (Multi Air Burner), and waste gas recirculation, which contributes to minimizing peaks in flame temperature. The benefits of MAB technology are particularly interesting in furnaces firing liquid fuels or gaseous fuels with a calorific value exceeding 2.000 kcal/Nm3. Achieved NOx emissions are 130 mg/Nm3 @ 3% O2 @ 1250°C when firing natural gas.
*MAB-FLTM flameless burners
represent the ultimate development of lateral firing technology, with the following main benefits:
*50% reduction of NOx emissions
*Invisible flame, with no temperature peaks.
These results are achieved by the high-speed injection of fuel through a dedicated lance, and by a specific design which allows an extremely high waste gas recirculation factor. The operation of MAB-FLTM burners is extremely flexible thanks to two firing modes: the standard MAB mode is used for cold start and for low chamber temperatures; above the self- ignition temperature, the burner is automatically switched to the flameless mode. MAB-FLTM flameless burners are mechanically compatible with MAB and FXB burners, allowing for easy retro-fits. All lateral burners (FXB, MAB and MAB-FLTM) can be equipped with a pilot burner and a flame detection system with UV cell.
is the flameless version of the FXB burner, to be used when the pressure of the gas is lower than 70 mbar and very low NOx are required. Significant advantages are reached in terms of emissions and flame uniformity when firing Coke Oven Gas, which produces a very high flame temperature and it is usually supplied at low pressure; using the FXB-FLTM the NOx emissions are drastically reduced to 100 mg/Nm3 @ 3% O2 @ 1250 °C in flameless mode.
Radiant Roof Burners – RAD-VG, RAD-VG Low NOx and RAD-FLTM
The thermal power of radiant burners varies from 150 Mcal/h to 800 Mcal/h, with preheated combustion air (up to 500-550°C); typical fuels are gas and light diesel oil.
*RAD-VG and RAD-VG Low Nox burners
are usually installed in the furnace roof. The refractory block is designed so that fuel is injected into the powerful vortex produced by the air speed; this leads to a perfect mix and to a completely flat flame profile. Excellent reliability and long burner life are achieved by the careful selection of the materials for the refractory block and the metallic anchors. Burner ignition can be either by pilot burner or by spark plug, with flame detection by UV cell. Achieved NOx emissions are 160 mg/Nm3 @ 1250°C when firing natural gas.
burners combine radiant design with state-of-the-art flameless technology; NOx levels are drastically reduced (- 60%), without impacting the flat flame profile, by recirculating waste gas into the refractory block, and injecting the fuel through dedicated Lances. Two separate gas inlets are used: one for flame mode (cold start) and one for flameless mode (above self-ignition), with automatic switching between the two modes. CO emissions remain near zero in all conditions. Achieved NOx emissions are 70 mg/Nm3 @ 1250 °C when firing natural gas.
High Speed Burners
High-speed burners are usually recommended in applications where the product must be heated by controlled convection, and where excellent temperature chamber uniformity is required.
*TFB-SIKTM and TFB-REKTM
*TFB (Treatment Furnace Burner)
is DCC’s new series of low-power burners, developed to drastically reduce NOx levels while maintaining high flame stability in all operating Conditions. Low emissions are obtained by multi-staging of air and gas, so that the temperature peaks responsible for thermal NOx formation are minimized. The first reaction zone, operated in sub-stoichiometric ratio, is followed by a second zone that completes the combustion reaction at lower flame temperature. The burners are designed for direct flame ignition using spark plugs and flame detection with ionization rods or UV cells.
is the conventional version of the burner, with thermal input from 150 Mcal/h to 500 Mcal/h; combustion air can be either cold or preheated in a centralized recuperator (temperature up to 550°C).
is the self-recuperative version, where each burner has an integral recuperator for air preheating; the range of thermal power is from 80 Mcal/h to 250 Mcal/h. For chamber temperatures up to approx. 1000°C, the recuperator is metallic type (air at approx. 650-700 °C). For higher chamber temperatures (up to 1250°C) a ceramic recuperator is used (air above 800 °C) Both types are also available with flameless combustion (TFB-FL-SIKTM , TFB-FL-REKTM), for Ultra-Low NOx emissions (lower than 80 mg/Nm3).
BURNERS FOR Continious Strip Annealing Lines
DCC has developed a specific line of burners for application in annealing furnaces for strip galvanizing lines.
Free Flame Burners
*LAT-HG4 and RAD-HG4 burners
are installed in the sidewalls respectively of Horizontal and Vertical Annealing Furnaces. A powerful vortex is produced by high combustion air speed inside the refractory block; fuel gas is then injected into the air vortex to obtain both a perfect gas mix and an intense combustion well inside the cone. The flame profile generated by air swirling is short and compact for LAT-HG4 (horizontal application, approx flame length 1500mm), and completely flat for RAD-HG4 (vertical furnaces, distance from strip 300mm). Both versions are designed to fire in sub-stoichiometric conditions in order to maintain a reducing atmosphere inside the furnace. A special application has been customized for the cleaning section of the free flame zone on Vertical Annealing Furnaces for Hot Dip Galvanising Lines.
*The RAD-MIX6 burners
are designed to premix air and gas in the burner body and can operate either with natural gas or LPG in sub- stoichiometric ratio. The typical high-speed, compact flame produces both a de-oxidising and a cleaning effect on the steel strip. It is possible to reduce the number of active burners according to strip width to avoid edge overheating.
Reku-Burners for P-shaped and 2 P-shaped Radiant Tubes
Radiant tube heating is at the heart of the strip annealing process; DCC has developed specific burners for this application, keeping in mind the following key targets:
- excellent heating quality (uniform heating of the strip)
- high reliability and long service life of the burner/tube system Preassembled panel with RAD-MIX6 burners
- low energy consumption (high air preheating temperature)
- low NOx emission.
for radiant tubes meet all the above goals, and are perfectly suited for all shapes of radiant tubes, including P and 2P, both cast-alloy and Inconel (welded) types. A specific optimization program has been focused on the most up-to-date 2P radiant tube technology leading to these outstanding results:
- tube temperature uniformity better than 45°C (guaranteeing excellent process and long tube life)
- air preheat temperature up to 650-700°C
- very low thermal inertia (allowing fast production Thermal efficiency vs air preheating increases)
- NOx below 100 mg/Nm3
- TFB-REKTM installed on a double P tube shows a 90 thermal efficiency enhanced by 15% if compared to conventional plug-in recuperator burner on a W tube, thanks to the higher air preheating effect.
Source: Steel 360 Magazine May’16 Issue