Question 1

– Narrative Process Description of Furnaces 11 and 12

The No. 11 and No. 12 indurating furnaces provide the final step in the pellet

- making process of converting crude ore into a finished product. In this process stage, the green balls that ar e delivered from the balling circuit are dried, fire

- hardened, and cooled before being sent to the yard or loaded into a boat.
The furnace converts the green balls consisting of magnetite (Fe 3 O 4 ) and additives into a porous, hardened hematite (Fe 2 O 3 ) pelle t capable of enduring the handling required during stockpiling, reclaiming, boat loading, and shipping. Daily pellet quality controls on furnace production ensure good performance of the product in the customer’s blast furnaces.
The No. 11 and No. 12 gr ate furnaces, that consist of approximately 280 8

- foot by 24

- inch pallets that have 20

- inch side plates, are continuous traveling conveyor

- type furnaces that have upper and lower return strands of pallets. The pallets ride on the top and bottom rails and in double rails at the feed and discharge ends of the furnaces. Each pallet has approximately 57 grate bars with air spaces between the bars. The pallets move along the top strand through the furnace zones from the feed, or drive end, of the furnace. A motor that is equipped with reduction gears is the driving force for moving the pallets. The weight of the pallets on the return strand along with a gravity

- sloped rail feed the empty pallets into the feed end.
Pellets on grate leaving firing zone

– Locat ion B 4Turning gear

– Location B 10

The upper strand of pallets accepts layer of green pellets that are produced in the balling drums. The upper strand of pallets also accepts a hearth layer of fired pellets. Pellets are added to the furnace via a roll feeder. The green pellets dry, fire, harden, cool, and discharge while the pallets ride over 27 8

- foot

square windboxes. The hearth layer of pellets helps to protect the grate bars from excessive heat and ensures good quality pellets in the b ottom layer of green balls by reducing the influence of the heat transfer effect.Roll feeder

– Location B 1

Green balls entering furnace

– Location B 2

### Hearth layer pellets in furnace

– Location B 3

The windboxes are connected by a seri es of 27 downcomers to the main furnace air ducts, breechings, and six process fans. Each windbox has a dust leg with a dump valve that allows dust, fines, or pellets that infiltrate the system through the grate bars on the pallets to be dumped.

Windbox

– Location B 5

The energy source that ignites and hardens the green pellets as they travel through the furnace comes from natural gas (though No. 2 fuel oil is also permitted). The furnace has a fuel oil system and anatural gas system with 28 natural gas pilot burners and 28 main oil or gas burners. The furnace has three combustion sections that operate in the range of 1,600°; 1,900°; and 2,400° Fahrenheit (F).
Each furnace has a Fluid Ionics emission control system that consists of five electrostatic precipitators. The precipitators remove particulate matter and scrub the emissions from the hood exhaust and waste gas fans. There are two precipitators for the waste gas fan and three precipitators for the hood exhaust fan.
After passing through the fu rnace, the pellets enter the discharge end system. The fired pellets are discharged onto a vibrating feeder, which in turn feeds the vibrating fired

- pellet screen. This screen allows pellets that have broken up or are undersize to fall through. Pellets that do not fall through the screen are considered the correct size and are directed to the No. 60A conveyor for screening or to the No. 160 conveyor for boat loading.

Furnace discharge

– Location B7Pellet screening

– Location B 8

PROCESS F AN SYSTEM
The process fan system consists of the recuperation fan, the updraft drying fan, the hood exhaust fan, the updraft cooling fan, the furnace fan, and the waste gas fan.
The recuperation fan receives its air volume from the recirculation hood. The air is drafted down through windbox Nos. 13, 14, 15, 16, 17, 18, l9, 20, and 21 on the bottom side of the pallet strand for the No. 11 and No. 12 furnaces. This air, which is pulled down through the bed, burns the pellet bed. After passing through the p ellet bed, the air discharges from the recuperation fan at an average temperature of 800° F. The air is discharged through duct systems to the updraft drying fan intake.
The updraft drying fan receives its air volume from the recuperation fan through the duct system. The air volume leaving the updraft drying fan di scharges through a duct system t o windbox Nos. 1, 2, 3, 4, and 5 to the updraft drying section of machine.The hood exhaust fan removes the moisture and waste gases that are discharged from the top of the pellet bed and discharges them through the Fluid Ionics dust control system. This is the updraft drying section of the machine and is over windbox Nos. l, 2, 3, 4, and 5.
The updraft cooling fan receives its air volume through ductwork, the inl et of which is located underneath the roof of the pelletizing building. For furnaces No. 11 and No. 12, the updraft cooling air discharges through the duct system to Nos. 22, 23, 24, 25, 26, and 27 windboxes. The air cools the pellet bed and supplies air to the recirculation hood. This air, in turn, is supplied to the furnace fan to maintain furnace combustion and pressure and to the recuperation fan for burning and drying the pellets. The cooling fan supplies all the process air to the furnace.

The furna ce fan receives air from the top of the recirculation hood and maintains 860° F automatically, using tempering air from the atmosphere. This fan supplies combustion air to the top of the furnace and operates the automatic pressure control system for the fu rnace.
The waste gas fan drafts air from beneath the furnace firebox through windbox Nos. 6 through 12 and exhausts the combustion wastes and downdraft drying air. The fan exhausts through the Fluid Ionics dust control system.