[0001] This invention concerns a method for reducing the moisture content of stock piled
granular material.
[0002] Sand, and other granular material, is frequently required to be provided to the consumer
in a dry condition. For example, foundry sand, or sand utilised for glass making,
is generally required to be kiln dried to an appropriate degree of dryness. When substantial
moisture is present in the stock pile of sand, such a drying process is relatively
expensive. Accordingly, a method of reducing the moisture content of the stock pile
of sand itself would present significant advantages.
[0003] In accordance with the present invention, there is provided a method of reducing
the moisture content of a stock pile of sand or other granular material, which comprises
arranging beneath and/or within the stock pile a convoluted drainage tube of permeable
material, and coupling said drainage tube to a suction pump, whereby liquid is withdrawn
from the base of the stock pile.
[0004] Preferably, for the or each stock pile there is provided a single drainage line which
is set in a spiral pattern just below ground level beneath the stock pile. A suitable
suction pump comprises a self-priming centri-
fugal pump of the kind used for ground dewatering, for example a "Univac" (Registered
Trade Mark) pump. The drainage tube may, for example, comprise a flexible slotted
p.v.c. tube of 100 mm diameter, around which is placed a fibrous filter media of the
type used with wellpoints for ground dewatering, when installed in low permeability
or inter-stratified soil conditions. Coconut fibre material has proved especially
efficacious.
[0005] In order to enable a single pump to deal with the dewatering of several stock piles,
the drainage tubes set in a number of different stock piles may be coupled via appropriate
suction tubes to a manifold incorporating a valve bank whereby any one or more of
the suction tubes may be connected to the inlet of the suction pump, as desired. Such
a system is inexpensive to instal and requires the minimum of maintenance. If required,
it can be adapted so that the flow of liquid can be reversed to wash through the filter
pipes. Water extracted would then either be discharged to a settlement lagoon or the
like, or alternatively, recirculated back to the washing plant.
[0006] The arrangement according to the invention offers the advantage of easier handling
of the granular material stock piled, and, in particular, a reduction in the time
and cost when the product is kiln dried prior to use. Moreover, the accelerated drying
process enables a more rapid turnover of stock piled material to be dried, and thus
fewer stock piles are required, thus saving space. Additionally, the efficiency of
the drying process is not significantly effected by adverse weather conditions, as
would be the case with the natural drying process hitherto utilised.
[0007] The invention is illustrated by way of example in the accompanying drawings, in which
Fig. 1 is a diagrammatic plan view of an installation for carrying out the method
of the invention, and
Fig.2 is a diagram illustrating one arrangement of drainage tube according to a preferred
embodiment of the invention.
[0008] Referring to Fig. 1, a suction pump 1, for example a 'Univac' (registered Trade Mark)
150 mm pump, is coupled by way of a flanged manifold 2 and a plurality of control
valves 3 to a plurality of rigid vacuum pipes 4, each of which is coupled to a corresponding
drainage tube 5, each drainage tube being set in a spiral at., or just below, ground
level.
[0009] Sand or like granular material may be stock piled above the areas occupied by the
drainage tube 5, whereupon the moisture content of each stock pile may be regulated
by coupling the respective drainage tube 5 to the suction pump 1 via the appropriate
control valve 3.
[0010] A specific arrangement of drainage tube is illustrated in more detail in the diagram
of Fig. 2, wherein the circular line 10 represents the base of a stock pile of sand
having a nominal diameter of 17 m and the broken line 11 illustrates the longitudinal
axis of a coiled drainage tube arranged beneath the base of the pile of sand. Reference
numerals 12 to 19 designate radial axes extending from the centre of the circle defined
by the line 10, each adjacent pair of axes defining a angle of 45°, and the numerals
at the pointsof intersection of the line 11 and the axes 12 to 20 designate the radial
distance of the axis of the drainage tube from the point of origin of the radial axis,
in metres. The drainage tube 11 is closed at the free end located at the radially
outermost point, and its inner end is coupled to a rigid suction pipe 21 passing outwardly
below the drainage tube 11 to a suction manifold of the kind illustrated in Fig. 1.
The drainage tube comprises standard 60 mm diameter wellpoint tube approximately 94
metres long.
1. A method of reducing the moisture content of stockpiled granular material which
comprises disposing beneath and/or within a stock pile of granular material a permeable
drainage tube arranged in a convoluted pattern extending over a substantial portion
of the base area of said stock pile and coupling said drainage tube to a suction pump
whereby liquid is withdrawn from the base of the stock pile.
2. A method as claimed in Claim 1, wherein said drainage tube comprises a single drainage
line set in a spiral pattern just below ground level.
3. A method as claimed in Claim 1 or 2, wherein drainage tubes associated with a plurality
of said stock piles are coupled to a single suction pump via a manifold provided with
control valves.
