Question 1
– Narrative Process Description of Furnaces 5 and 6

Furnaces 5 and 6 are the final step in the pellet

- making process, which consists of converting crude ore into a final product. In this stage, the green balls that are delivered from the balli ng circuit are dried, fire

- hardened, and cooled before being sent to the yard or boat loading. The furnace converts the green balls that consist of magnetite (Fe 3 O 4 ) and additives into a hardened hematite (Fe 2 O 3 ) pellet capable of enduring the handling re quired during stockpiling, reclaiming, boat loading, and shipping.
Furnaces 5 and 6, which consists of approximately 200 6

- foot by 2

- foot pallets that have 15

- inch side plates, are continuous traveling grate furnaces. Each pallet has approximately 40 gr ate 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 with reduction gears is the bull gear for moving the pallets. The weight of the pallets on th e return strand along with a gravity

- sloped rail feed the empty pallets into the feed end.
The upper strand of pallets accepts layer of green pellets via a roll feeder that are produced in the balling drums. The green pellets dry, fire, harden, cool, and discharge while the pallets ride over 28 6

- foot square windboxes in Furnace 6 while Furnace 5 has one less windbox. The windboxes are connected by a series of downcomers to the main furnace air ducts, breechings, and six process fans. Each windbox has a dust leg with a dump valve that allows the dumping of dust, fines, or pellets that infiltrate the system through the grate bars on the pallets. A conveyor that runs the entire length of the underside of the furnace, reclaims this product. Dripping hoppe rs under the return grate strand also collect spillage and discharge onto the conveyor.

Roll feeder
– Location B 1Pellets entering furnace
– Location B 2

Firing of pellets
– Location B 3

Pellets after firing
– Location B 4 .1Windbox
– Location B 5

The energy source that ignites and hardens the green pellets as they travel through the furnace comes from natural gas. The furnace has a natural gas system with 22 natural gas pilot burners. The furnace has three combustion sections that operate in the range of 1,600°; 1,900°; and 2,400° Fahrenheit (F).

Burner controls
– Location B 6

The furnace has a Fluid Ionics emission control system that consists of three electrostatic precipitators. The precipitators remove particulate matter and scrub the emissions from the hood exhaust and waste gas fans.
The discharge ends of Furnaces 5 and 6 each are equipped with a vibrating feeder that conveys pellets to a discharge screen.Discharge end of Furnace
– Location B 7

Pellet feeder
– Location B 8

Discha rge screen – Location B9PROCESS FAN SYSTEM

All process fans are located on the bottom floor, east of the furnace. The forced draft fan is the only updraft fan. The other five fans are downdraft fans. During normal operation of the process fan syste m, ambient air is drafted down through the pellet bed at windboxes Nos. 15, 16, 17, 18, 19, 20, 21, 22, and 23 by the recuperation fan. This air passes through a duct system to the forced draft fan intake and also supplies roof air to the furnace. The re cuperation fan has a main inlet damper and a tempering air damper and supplies combustion air for the pilot burners and the main burners. This fan also supplies roof air to the ignition zone through the 4E damper. The 4E damper is also called the recuper ation

- air

- to

- ignition

- furnace damper.
The forced draft fan receives a volume of air from the recuperation fan and forces it upwards against and through the wet pellet bed at windboxes Nos. 1, 2, 3, 4, and 5. The forced draft fan has a main inlet damper (10E).
Ambient air is drafted down and through the pellet bed at windboxes Nos. 24, 25, and 26 by the first stage cooling fan. This air passes through a duct system that has an intake damper (5E) called the first

stage

- cooling

- air

- to

- preheat

- and

- downdraft damper. The first stage cooling fan has a main fan damper (3E) and a tempering air damper.
Ambient air is drafted down through the pellet bed at windboxes Nos. 27 and 28 by the second stage cooling fan. This air passes through a duct system and is force d down on top of the pellet bed at windboxes Nos. 6 and 7. This is the downdraft drying section, and the air is drafted into the waste gas fan. The second stage cooling fan has a main inlet damper (9E) and a tempering air damper.

The volume of air that i s supplied to the firebox from the recuperation fan, the first stage cooling fan, and the second stage cooling fan is drawn down through the pellet bed at windboxes Nos. 6, 7, 8, 9, 10, 11, 12, 13, and 14 by the waste gas fan. This air exhausts to the atm osphere through the Fluid Ionics system. The waste gas fan has a main damper (1E) and a tempering air damper.
The hood exhaust fan accepts the volume of air that is discharged from the forced draft fan and has been forced up and through the wet pellet bed through windboxes Nos. 1, 2, 3, 4, and 5. The hood exhaust fan does not have a damper.
Atomizing air is used to supply air for the gas mixture to the pilot burner , cool the flame monitors and the pilot burners and gas burners.