As emission controls become increasingly stringent and the rising cost of fuel, furnace development demand techniques to obtain better thermal performance while also reducing emissions. Reheating Furnace equipped with low emission and combustion efficient burner combined with automation system has the prime focus.
Design may incorporate low oxygen combustion Burners, which is to have thin scale and its reduced formation. Usual capacity has through-put design 40-120 Ton/hr of slab/billet.
The pusher furnace is to reheat billet/slab,and producer gas as fuel is considered.
In Top and Bottom fired furnace, material moves over skid mouted on water cooled pipes. Charge is heated from both top and bottom sides, and recommended for cross-section above 150 mm x 150mm and heating of alloy steel/special steel.
A recuperative type combustion system with standard burner is also provided. Recuperate supplies preheated combustion air. Preheating of fuel gas is also feasible. Dimensions are 20m long, 7m wide,1.3-2.0 m high ( tunnel to center and soak zone ).In 60 T/hr Slab/Billet, charged from front and discharged by a discharging machine.
Waste gas leave the furnace through an uptake duct, conveyed to recuperate to preheat air and gas (optional), and finally emitted through Chimney on induced draft. Oxygen content in waste gas is measured at waste gas duct, which provides indication of excess air put into fuel combustion. NOx concentration in emission is also monitored which also has relationship to oxygen content in waste gas.
Usual capacity has throughput design 40-120 Ton/hr with regenerative burners.High temperature air combustion by Regenerative Burner is energy efficient,reduces scale formation and oxygen defient combustion leads to low NOx emission.
It permits heating of also bottom face of charge. Burner are divided in upper and lower arrangement and installed on both sides of furnace. Exhaust from furnace is used to preheat combustion air and gas in heat exchanges and finally led to chimney. Much of furnace is below level of work shed.
Advantages :
Shorter furnace length and shorter charge heating time better control of heating rate, Uniform discharge temperature reduced scale loss and operational flexibility.
Designs incorporates Regenerative Burner or Low oxygen concentration combustion Burners. Later is to have thin scale and its reduced formation.
Automation system comprises following in Pusher type furnace:
- Charge material handling control : Data of length, width, identity code of each slab/billet delivered to roller table PLC performs fuctions as under :
– Slab/billet centering in front of furnace
– Charging mechanism movement Discharging door movement
– Discharging machine control (extractor)
– Hydraulic system control
– Tracking of charging inside furnace - Fuel control combustion control : Burner engineered to low NOx emission, high fuel efficiency and giving temperature uniformity of giving temperature uniformity of reheated steel product. Automation in fuel combustion is handled by PLC as per Burner supplier.
- Furnace process control : This ensures that discharge temperature is not only in correct range but also temperature differential within body of reheated slab/billet must be minimized.
This facilitates in decrease in fuel consumption, decrease in scale formation, better surface and which effects yield and productivity.
The control methodology regulates heat transfer by reheating charge according to optimum cycle predetermined for each type of material over range of furnace production schedule including transitions and delays. Accuracy of heat supply control to zones using knowledge of actual temperature of steel. This has better benefits compared to traditional set-point temperature control fixed by operator.