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Online Tours
Redding Plant Online Tour
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1.
Raw Materials - The Quarries
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Limestone and shale are the primary components
of cement. Limestone contains calcium carbonate, while shale
contains silica, iron and alumina. When the correct proportions
are heated, they form calcium silicates, the primary ingredient
in Portland cement. When mixed with water, the calcium silicate
forms a gel that binds rock and sand together to form concrete.
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2.
Raw Materials - The Quarries
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Lehigh Southwest mines limestone and shale from
separate quarries within the cement plant. Three 60-ton trucks
transport the rock from the blasted muck pile to the primary
crusher approximately 1200 feet above the plant. The crusher
can reduce a 42" diameter boulder to 6" rocks.
After passing through a 487 ft. vertical raise the limestone
is transported 7260 feet by a conveyor to the plant to continue
processing.
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3. Reclaimer, Dome Storage
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A radial arm stacker blends and stacks the
raw materials. Cables rake the pile across. As the cables
cross the pile, they pull down a small cross- section. Blades
at the base of the reclaimer drag the material to the center
of the dome where it drops to a conveyor and is transported
to storage tanks. The rock storage tanks hold the primary
raw materials: shale, limestone, and diatomaceous earth. Feeders
from below the tanks supply raw materials to the roller mill.
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4. Materials Blending:
The First Grind
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The roller mill blends and grinds the limestone
and shale components to the proper consistency. The roller
mill has two grinding wheels that pulverize the rocks to form
a powder-like consistency called ‘kiln feed.’ Kiln feed
is conveyed to homogenizing silos where the powder is analyzed
and further treated prior to firing in the kiln.
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5. & 6. Heating
it Up: The Preheat Tower and Kiln
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Kiln feed is transported to the preheater
tower, the highest location on the plant site. The tower contains
four vessels and an inline calciner. In the preheater tower,
heat is recovered from the kiln exhaust gases and is used
to heat the raw kiln feed from approximately 50°C (120 °F)
to over 830°C (1520°F) in less than 1 minute. In this process
the kiln gases are cooled from approximately 1050°C (1920°F)
to less than 380°C (720°F). The feed continues into the rotary
kiln where it is fired to over 1450°C (2,650° F), the temperature
required to form tri-calcium silicate, a key component of
‘clinker’. As the clinker cools, the heat is recovered to
preheat the secondary combustion air.
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7. Tire Feed
The plant at Redding feeds used tires into the
preheater tower just below the calciner. The heat released when
the tires burn provides some of the energy required to convert calcium
carbonate into calcium oxide.
8. Coal
Feed
In addition to the tires, coal, coke and natural
gas are used to heat the kiln to the temperature required to form
clinker.
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9. Laboratory
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Laboratory testing at numerous stages of
the process ensures quality control, and includes setting
time tests and strength gain testing, both crucial to producing
a consistently high quality product.
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10. Control Room
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From the control room, operators monitor
and control every step in the process. Feedback systems continually
deliver statistics on feed rates, temperatures, conveyor speeds
and other vital information. From this intelligence, the plant
operator can make informed decisions.
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11. The
Final Grind: Finishing
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Gypsum is mixed with the clinker before
being fed into the three finish mills. Each mill contains
approximately 105 tons of steel grinding balls that pulverize
the combination into a fine powder. Gypsum is added to the
clinker to control the reaction time of the cement so that
concrete workers can place the concrete before it sets.
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12. &13. Storage
Silos & Shipping
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The ground cement is stored in silos for
loading trucks and rail cars. The cement is also packaged
and shipped in 94- lb. bags.
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14. Maintenance Shop
On-site buildings house a maintenance shop which
enables Lehigh Southwest to service equipment integral to the cement manufacture
process.
15. Administration Building
Lehigh Southwest administrative staff provide support
services, such as accounting and order processing to the plant from
inside this building.
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