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News
World Dredging Mining &Construction 2001
Vulcan Twin 20 Yard
The Calmat S&G operations in Irwindale California began in the 1930’s and continues today at an accelerated pace.
In 1989 they purchased a Rohr twin-12yd bucket clamshell (BC/M) dredge for the Durbin Aggregate pit and operated it until 1999.
The dredging operations were followed by dry mining methods until acquiring a new, Rohr BC/M dredge twin 20 yd bucket dredge which began operations February 2001.
A separation system is used to remove the silt accumulation in the pit, after pumping through cyclones then discharging by pipeline to another part of the pit away from S&G mining. A complete description of the dredge mining equipment with photos follows.
Summary
The new dredge is a Rohr Twin 20 yd 3 dredge, with two (2) 20 yd capac-ity clamshell buckets for digging in water depths up to 200 ft.
This dredge consists of two separate units, each with its own bucket, hoist, and associated on-board processing and material handling equipment. In addition, there are some common components for material processing (e.g. jaw crusher).
The dredge is a complex assembly of many different equipment components, including those pieces of equipment required for excavation, on-board processing (including de-watering, fines removal, and primary crushing), and material handling to discharge of material onto the existing floating conveyor system.
The primary components for the dredge were designed and supplied by Rohr Corporation, a German-based company specializing in dredges.
Rohr supplied all mechanical components except for some of the processing equipment that Vulcan Materials Company (VMC) Vulcan Materials Company (VMC) Vulcan Materials Company (VMC) Vulcan Materials Company (VMC) Vulcan Materials Company (VMC) elected to supply separately. VMC did all electrical work necessary to supply power to the DC drives and motor control centers, and Rohr did all electrical wiring beyond the motor control centers and DC drives.
Total weight of dredge as installed ~ 1,000 t
Total connected electrical load = 3,022 hp (including power for 9 floating conveyors receiving powerfrom the dredge)
Rated maximum digging capacity (for 100' water depth) = 2,300 tph.
Actual average production rate (in good material) = 1,600 – 1,800 tph.
Rohr Supplied Equipment
Rohr supplied the flotation structure for the dredge, approximately 100 ft 2 , consisting of 12 separate pontoons, with total deck space of 7,300 ft 3 . The total weight of the pontoons is approximately 260 t.
(1) Four (4) bank winches (one for each corner of dredge) for dredge travel and to anchor to bank when digging.
(2) 15-t service crane over jaw crusher and fresh water pump.
(3) Gantries supporting trolley houses for both dredge units with rail elevation approximately 48 ft above pontoon deck elevation. Length of each gantry beam is ap-proximately 94 ft in length.
(4) Two (2) Trolley houses, each with a 20 yd 3 capacity clam shell bucket and motor grab including the following components:
(a) Hoisting mechanism consisting of a two-line winch and two (2) cable drums powered by two 500 hp motors (one per cable) with variable speed DC drives to vary lifting and lowering speeds;
(b) Two (2) disc hoist brakes (one per cable);
(c) Trolley travel mechanism;
(d) Bucket with hydraulic grab and motor consisting of 20 yd 3 bucket, a deep water-rated 200 hp electric motor driven by variable frequency AC drive with hydraulic package for opening and closing bucket;
(e) Underwater-rated power cord to supply power to bucket, with gravity take-up to maintain constant tension in power cord and triple reaved sheaves to keep counterweight above water level.
(5) Two 15' X 25' stationary grizzlies with 5-in. openings over hoppers (one for each dredge unit).
(6) Two reversible rake grids (one for each dredge unit) for transferring oversized material on top of grizzlies to jaw crusher or overboard.
(7) Four hopper discharge gates (two for each dredge unit, one per 8 X 20 screen) operated by two skid-mounted hydraulic units (one for each dredge unit) for discharge of material from bottom of hopper to 8 X 20 vibrating screens.
Rohr supplied the operator’s cabin with control panels, automatic bucket monitoring system, and programming for automatic operation of all equipment on the dredge or manual operation with joy stick from operator’s cabin.
All equipment is operated from the operator’s cabin with the exception of the bank hoists which are operated by push buttons located near each hoist.
VMC Supplied Equipment
VMC supplied the majority of the processing and material handling equipment on the dredge, with sup-port structures, discharge chutes and boxes, and installation primarily by Rohr.
(8) Four (4) Deister 8 X 20 double deck, horizontal wet vibrating screens (two for each dredge unit, one for each hopper gate), with spray bars on both decks, polydeck synthetic media and each powered by two (2) 30 hp electric motors.
(9) Four (4) 8 in. Galigher Pumps with No. 5 bearing assemblies (one pump for each 8 X 20 screen, two for each dredge unit), powered by a 125 hp electric motor with a V-belt drive to produce an impeller speed of 800 rpm. Each pump is designed for 2,010 gpm of sand slurry with a specific gravity of 1.28 and a total head of 83 ft.
(10) Eight (8) 20" Warman CAVEX (two cyclones for each Galigher pump) with discharge onto 6 X 12 dewatering screens. Each cyclone is designed for underflow of 334 gpm (w/ specific gravity of 1.8) and overflow of 674 gpm (w/ specific gravity of 1.01).
The cyclone overflow (primarily minus 200 mesh waste silts and clay) is transferred to a floating wastewater line, 18 in. dia. HDPE pipe, that is discharged approximately 500 ft away from digging area.
(11) Four (4) Deister 6 X 12 high frequency single deck de-watering screens (two for each dredge unit, one for each Galigher pump), with polydeck synthetic media and each powered by two (2) 15 hp electric motors.
(12) Two (2) 42" x 43' belt conveyors (one for each dredge unit) collecting discharge from on top of screen decks for both 8 X 20 and 6 X 12 screens, powered by a 30 hp electric motor with discharge onto a 48 in. belt conveyor.
(13) One 48" X 66' belt conveyor collecting discharge from both 42" conveyors as well as from the jaw crusher, powered by a 50 hp electric with discharge onto the first floating conveyor for transporting material to shore.
(14) One Deister 48" X 16' vibrating feeder, with rubber lining, powered by a 30 hp electric motor collecting oversize material from rake to feed the jaw crusher.
(15) One 30 X 42 Pioneer jaw powered by a 150 hp, 900 rpm electric motor, and including an automatic lube sys-tem.
(16) One freshwater Peerless verticle turbine pump, designed for 4000 gpm flow and 160 ft of total head, powered by a 200 hp electric motor to supply all fresh water needs for dredge operation
(17) Two (2) electrical equipment stations; each including a 35 ft long enclosed container housing the DC drives, motor control centers, PLC panels, and variable frequency drives; a raised electrical equipment platform including a 2000 kVA 12 kV-480V transformer and a 480 v switchboard; and access walkways and stairs. The platform for Dredge A also includes 15 kV switchgear.
VMC provided a new electrical supply system for the dredge independent from the rest of the plant.
This new system includes a new metering section near the main plant location, a 12 kV overhead pole line from this metering section to the shore, and two 12 kV portable power cables that run along the floating conveyors and terminate at the 15 kV switchgear on the dredge. to the cyclones and for discharge of the cyclone overflow away from the dredge location.
VMC supplied and installed all sup-ply water piping from the freshwater pump to the spray bars for the 8 X 20 screens, wash down stations, manifolds for adding water to screen unders boxes, and other water needs on the dredge.
VMC supplied and installed all slurry piping from the Galigher pumps to the cyclones and for discharge of the cyclone overflow away from the dredge location.
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Rohr Corporation
http://www.rohrcorp.com
ROHR Corporation, 6295 Dry Fork Road, Cleves, OH 45002
Tel: 513-202-0800 Fax: 513-202-0888 Email: sales@rohrcorp.com