Low-Profile, Bin-Bottom Design
Suits Cement
Guest article by Reinhardt Matye, President, DCL Inc.Introduction
Southern Nevada is one of the fastest
growing areas in the United States and is expected to grow for the
next 20 years. In response to increasing demand for cement and
cement-products, California Portland Cement constructed a transfer
terminal in the city of North Las Vegas capable of transferring
500,000 tons of cement per year to the Nevada market.
Operational Requirements
 The
terminal was designed to off load 100 ton railcars at a rate of 200
tons per hour of cement which is then loaded into three 1,200 ton
capacity steel silos using a pneumatic conveyor system. A dedicated
double rail spur was specified to accommodate up to 30 railcars by
simply feeding cars from one spur to the other. The three silos
permit the handling of more than one cement product and three
adjustable loading spouts were included in the this arrangement to
accommodate a variety of truck configurations.
Additionally, the city of North Las
Vegas, surrounding landowners, and developers required that the
terminal height be minimized to mitigate the visual impact of the
terminal on other developments. A maximum overall height of 62 feet
was considered acceptable. The terminal configuration was designed
to blend with the surrounding land use and be aesthetically
acceptable to the city and local developers.
Railcar Unloading
Railcars containing 100 tons of
cement each deliver the cement to the terminal. The cement is
unloaded through two unloading boots which seal against the rail car
discharge doors. The cement is discharged into two inclined drag
conveyors and conveyed to a dilute phase dual pod conveying system
that delivers the cement to one of the three selected silos. The
pneumatic conveyor was chosen to maintain a low elevation profile on
top of the silos and to allow for the future expansion of the
conveying system.
Low Profile Design Storage Silos
The total storage capacity of the
terminal is 91,000 cubic feet. The three silos are identical in size
and have a cement capacity of 1,200 tons each.
 The
center silo can discharge to either of two loading spouts and can be
used for alternate products. Also, the center silo can also be
discharged to a pneumatic conveyor to transfer cement from one silo
to the others, allowing more operational flexibility.
To accommodate the local height
restrictions and accommodate the storage requirements, a +38 feet
diameter fully aerated 8° silo bottom was designed. The silo bottom
incorporates special aeration pads covering 90% of the bin-bottom
surface. The pads are segmented and selectively valve controlled,
this reduced the blower size to only 600 CFM. The resultant design
offers the ability to reclaim 99.6% of the stored product from any
given silo.
Dust-Free, Quick-Loading Truck
Spouts
The cement is conveyed from the silo
bin bottoms to the loading spouts by aeration conveyors.
 The
two outboard loading spouts incorporate horizontal positioners. A
third spout and positioner is used in the center to accommodate
"triple trailer" rigs. Each loading point is provided with
an integral dust collector eliminating the need for duct and
maintenance associated with a remotely mounted dust collector.
Dual trailer 120,000 LB Nevada rigs
are loaded in 5 minutes. A 130 feet long above ground scale is
supplied as two independent platforms allowing the simultaneous
loading of each trailer reducing the loading time. The loading
spouts are fitted with self sealing cones which close the discharge
when not seated in the hatch. The self sealing cones reduce
housekeeping by eliminating cement dust dribbling from the spout
when it is retracted.
Unified Control System
 The
operator aligns the spouts to the hatches with the aide of video
cameras. The filling as well as the silo aeration sequence is
automatic once initiated through the start button. The scale is of a
twin platform design allowing the filling of two trailers
simultaneously reducing the filling time while maintaining control
of each trailer weight. Inventory and shipping data is transmitted
to the cement company's offices via data line.
The control building is of a block
structure and houses the managers office, operators control room,
motor control center and spare parts storage with workshop. The
terminal is controlled through an Allen Bradley PLC SLC 500 with a
PC interface. The truck filling is PLC controlled with a manual
override.
For more information, contact our
author:
Mr. Reinhardt Matye
DCL Inc.
P.O. Box 125
Charlevoix, MI 49720
Telephone: 800-748-0563 or +1-231-547-5600
Fax: +1-231-547-3343
Email: rmatye@dclinc.com
Web site: http://www.dclinc.com/
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