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Stewart portable
spreads
optimize product quality
By Andy Bateman,
Engineering Editor
 All
crushing was completed at the Lacombe pit by this 1371 mm Cedarapids
Rollercone II cone crusher
Two
simple but effective portable spreads operated by Stewart Construction
(1996) Ltd. of Innisfail, Alberta demonstrate how the choice of aggregate
process equipment can impact on the quality of the finished product.
The family-owned aggregate business operates four portable processing
spreads throughout southern Alberta.
Pine Lake pit
During Aggregates & Roadbuilding's site visit
to the company's Pine Lake sand pit near Red Deer, Stewart's portable
sand wash plant was being utilised to extract saleable sand grades from
a difficult deposit. The customer base for this seasonal pit includes
Inland Concrete Ltd.'s ready mix concrete plant and Border Paving's
asphalt plant, both in Red Deer, and custom orders such as 3 000 tonnes
of "beach" sand for a man-made lake at an executive subdivision in Oakatooks,
south of Calgary. Owner Ken Stewart explained that good aggregate deposits
in the Red Deer area are in short supply, so the challenge here is to
extract the maximum ratio of quality product while dealing with some
4 per cent naturally occurring coal. To meet this challenge, Stewart
teamed a wet screen with a classifying tank and three screw washers.
With an average total throughput rate of 150 tonnes/h, the plant was
delivering concrete sand, golf course sand and reject sand in about
equal quantities, together with a small quantity of pond fines.
Pit run was first separated over a 6x20 Pioneer
triple-deck screen fitted with 25.4 mm, 11.1 mm and 4.8 mm opening screen
cloths on the top, middle and bottom decks, respectively. Plus 11.1
mm rock retained on the middle screen was stockpiled for later crushing,
while material between 11.1 mm and 4.8 mm (retained on the bottom deck)
was taken off as a gravel product. The bottom deck was fitted with trellis
screens and consisted of sixty 609 mm long x 305 mm wide urethane panels,
mounted so that there was a 25.4 mm longitudinal step between panels.
As material passed down the screen, the steps imparted a tumbling action
that improved the separation of sand particles from the larger sizes.
All sand passing the screen's bottom deck was pumped by a Linatex 6x6
pump to a 7.3 m long Eagle Iron Works (EIW) Autospec classifying tank
which separated the three sand sizes. From there, each sand size was
dewatered by 914 mm diameter x 7.6 m long EIW single screw dewatering
screw before being carried on in-house shop-built field conveyors to
Strongco stackers including two 762 mm x 36.6 m units and a 609 mm x
30.5 m unit. Wash water was provided from a pond some 366 m from the
plant, with the plant utilizing about 2275 litres /min when on sand
production. Power was provided by a portable Caterpillar genset with
a 3406 engine driving a 320 kW generator.
The overall set up provided effective separation
of the coal present in the feed; about one-third was floated out with
the plant's wash water, while the balance reported to station five of
the classifying tank and included in the reject sand. Stewart added
that this reject sand has been utilised successfully in hot mix asphalt
where any residual coal particles have no impact effect on the product.
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| At Stewart's
Lacombe spread, a Caterpillar 988F wheel loader discharged diretly
into a 20 tonnes capacity feeder that regulated material flow to
the crushing and screening plant. |
Twin
6x20 Clemro inclined screens completed the screening job on Stewarts'
portable spread at Lacombe. |
 The
uniform stockpile at the Lacombe
pit was produced by this Thor T36-800 programmable stacker.
Lacombe pit
Further north at Lacombe, another of Stewart's portable spreads was
producing granular base material on a contract basis for pit owner DMD
Rock Products. Here, pit run was hauled at an average rate of 350 tonnes/h
by a Caterpillar 988F wheel loader equipped with a 6.1 cu.m toothed
spade nose bucket. There was no primary crushing stage on this spread,
with the 988 discharging directly into a 20 tonne-capacity feeder that
regulated material flow to the crushing and screening plant.
Downstream of the feeder, a 1066 mm wide belt
fed the 200 mm pit run to the first of two 6x20 Clemro inclined screens
working in closed circuit with a 1371 mm Cedarapids Rollercone II cone
crusher. The bottom deck of the first screen was fitted with 9.5 mm
opening screen cloths to direct a high proportion of the pit run to
the crusher and thereby obtain high ratio of fractured faces in the
finished product. Finished 22.2 mm minus product from the second screen
was conveyed to a Thor T36 - 800 programmable stacker. (The 36 designation
refers to the stacker's belt width in inches while the 800 denotes its
rated capacity in tonnes/h.)
 A
7.3 m long Eagle Autospec classifying tank was teamed with three Eagle
Iron Works (EIW) 914 mm diameter by 7.6 m long single dewatering screws
to produce three sand grades at Stewart's Pit Lake pit.
Stewart reports that the programmable stacker
has helped the company secure work by providing uniform stockpiling
and avoiding the compacted layers that can occur with loader or truck
built stockpiles. As a footnote on the topical subject of fuel efficiency,
Stewart is obtaining good fuel efficiency numbers from the new engine
powering this plant. The Detroit Series 60 engine with electronic controls
is teamed with a 450 kW generator and is using about 41.7 litres/h of
diesel fuel, or nearly 40 per cent less than the 68.2 litres/h consumed
by the previous unit.
January/February
2003 issue
Aggregates
and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca
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