 |  | Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.) | ||
 |  | Technical Chapter 17: Drying | ||
|  | 17.1 Drying oven | ||
| | 17.2 Solar houses | ||
| | 17.3 Drying areas, drying surfaces | ||
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Mining General
Beneficiation, Drying
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germ.: |
Trockenofen |
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span.: |
horno de secar, horno secador |
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TECHNICAL DATA: | |
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Dimensions: |
approx. 2 × 1 m hearth area, 10-cm-high rim for oven plate |
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Weight: |
several 100 kg |
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Form of Driving Energy: |
thermal from combustion of wood, peat, diesel, gasoline, oil, gas, coal |
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Alternative Forms: |
mechanical heat generator (by METZLER) |
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Technical Efficiency: |
very low |
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Operating Materials: |
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Type: |
fuels |
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Quantity: |
very high, approx. 0.05 - 0.1 t coal/t concentrate |
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ECONOMIC DATA: | |
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Investment Costs: |
approx. 200 DM when self made |
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Operating Costs: |
high fuel costs |
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Related Costs: |
fuel transportation costs, which could vastly increase for biogenic fuels due to lumbering requirements |
CONDITIONS OF APPLICATION:
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Operating Expenditures: |
low |————————| high |
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Maintenance Expenditures: |
low |————|————| high |
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Personnel Requirements: |
minimal |
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Grain Size of Feed: |
theoretically no restrictions; however, drying of fine grains is lengthy and expensive due to the large proportion of adhesive water which requires high energy input to separate it |
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Replaces other Equipment: |
drying areas |
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Regional Distribution: |
very rare, known from Bolivia, Thailand |
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Operating Experience: |
very good |————————| bad |
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Environmental Impact: |
low |————|————| very high |
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especially when temperatures exceed 1 05°C and sulfides begin to roast |
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Suitability for Local Production: |
very good |————|————| bad |
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Lifespan: |
very long |————|————| very short |
Bibliography, Source: Priester, Gast, Inversin
OPERATING PRINCIPLE:
The drying surface of the oven - the oven plate - is formed like a pan for holding the feed, which is periodically stirred by means of shovels or scrapers. Gast describes an oil-fired oven for drying of wet concentrate: the cylindrical outer wall is perforated and the inner wall (cone shaped) serves as the oven's chimney. The material is fed by shovel and percolates through the oven automatically as the dried concentrate trickles out through the holes and piles up around the oven.
AREAS OF APPLICATION:
For drying of concentrates.
REMARKS:
It is absolutely necessary to ensure that the drying temperature of products containing sulfide minerals remains below 105° C; above this temperature the sulfides begin to roast, releasing sulfide-containing acids, sometimes at very high concentrations.
For preliminary dewatering, the concentrates need to be processed in a raffination barrel following the Schanz-method or in a tossing kieve.
SUITABILITY FOR SMALL-SCALE MINING:
Due to the negative environmental effects of drying in drying ovens, this process should only be employed when alternative methods cannot be used.
Mining General
Beneficiation, Drying
|
engl.: |
solar tents, solar tunnel dryer |
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germ.: |
Solarhauser, Solarzelte, solare Tunneltrockner |
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span.: |
cases solares, carpas solares, tuner de secado solar |
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TECHNICAL DATA: | |
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Dimensions: |
size depends on drying requirements, specific drying duration and radiation energy |
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Weight: |
e.g. solar tunnel dryer for drying harvested crops: 3 × 20 × 0.1 m |
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Extent of Mechanization: |
not mechanized |
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Form of Driving Energy: |
heat of radiation (solar thermal energy or insolation) |
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Alternative Forms: |
in solar tunnel dryer with small fan: electric or photovoltaic |
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Mode of Operation: |
semi-continuous |
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Throughput/Capacity: |
up to approx. 100 kg/m² drying area |
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Technical Efficiency: |
40° - 70° C drying temperature, drying duration is around half that of simple ground drying |
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ECONOMIC DATA: | |
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Investment Costs: |
dependent on construction material, minimum of approx. 500 DM; also dependent on intensity of solar radiation (insolation), less sun means more collector surface area is required. |
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Operating Costs: |
when fan-operated, low energy costs |
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Related Costs: |
possibly wind protection measures |
CONDITIONS OF APPLICATION:
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Operating Expenditures: |
low |————|————| high |
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Maintenance Expenditures: |
low |————|————| high |
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Personnel Requirements: |
minimal |
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Location Requirements: |
feasibility can only be calculated when solar radiation fluctuations are measured over the entire year |
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Grain Size of Feed: |
all sizes |
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Special Feed Requirements: |
no restrictions |
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Output: |
the drying speed in solar houses and solar tents is notably higher than that of drying areas, especially when the material to be dried is spread out on tables, etc. (see Diderot). This is a result of air circulation through convection. |
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Replaces other Equipment: |
drying areas, drying ovens |
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Environmental lmpact: |
low |————|————| very high |
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Suitability for Local Production: |
very good |————|————| bad |
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Under What Conditions: |
depends upon the available possibilities using the following building materials: transparent corrugated sheets, glass, black plastic-foil, etc.; imported material (Nicolon) or nationally produced material, UV-stabilized transparent foil, insulation material, sealing material |
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Lifespan: |
very long |————|————| very short |
Bibliography, Source: Diderot, Landtechnik Wethenstephan, Bine
OPERATING PRINCIPLE:
Diderot describes southward-facing glass houses for solar drying of beneficiation products where the feed is spread out on tables. A similar effect can be achieved in foil tents made of black cloth foil, whereby the warming principle varies somewhat: with transparent materials, the enclosed space is warmed through the solar irradiation, and with opaque material the covering itself is heated by the solar energy.
Of simpler design, due to their compactness, are solar tunnel dryers. These consist of two flat, parallel tunnel channels, one of which serves as the air collector and the other as the concentrate dryer. Both channels are covered with a transparent foil. The collector is lined on the inside with a black absorbent-foil, black cloth, black stones, or similar heat-asbsorbing material. Towards the bottom, the dryer is thermally-insulated with, for example, plastic foam, rock wool, coconut fiber, straw or other dry organic materials. The walls of the channel are made of wood, brick or metal. The foil covering can be rolled up around a pipe to enable the dryer to be charged. A small fan is used for blowing air into the collector, where it warms up before entering a ventilation duct directing it into the tunnel dryer; the now warm, dry air passes over the thinly-spread layer of feed material and dries It out.
AREAS OF APPLICATION:
Drying of mining products especially in humid or semi-humid locations where open drying in direct sunlight is not possible. In locations at higher elevations, for example in Andean mining where the radiation intensity is particularly high, solar houses and solar tents offer an alternative to oven dryers.
Self-built air collectors are widely used in the agricultural industry for drying of herbs, hay, grains, peanuts, fuel materials, etc, One of the best foil-covering materials has proven to be Nicolon 66530 (from NICOLON B.V., Box 236, 7600 AE Almelo, the Netherlands). This material is a black PE-fabric with monofilament threads in the warp and stretched bands in the woof; It is 0,5 mm thick, 2.4 m or 5 m wide, weighs 182 g/m², has a tensile strength of 227 kg/5 cm in the warp and 104 kg/5 cm In the woof, and is characterized for its high resistance to radiation and long service-life (more than 5 years). Nicolon is air-permeable, thereby allowing air collectors to operate either with blower-fan drive or as gravity dryers. In gravity dryers, the collector unit must be positioned below the drying unit. In windy locations, collectors yield poor results. Air collectors can also possibly be used for ventilation purposes (exhaust of mine air).
SUITABILITY FOR SMALL-SCALE MINING:
This is suitable in locations where drying outside in the open air is not possible for climatic reasons. Simple, reasonably-priced and environmentally compatible constructions are possible.
Fig.: Solar tent made of syntetic
fabric, from Landtechnik Weihenstephan
(Germany).
Mining General
Beneficiation, Drying
|
germ.: |
Trockenflachen |
|
span.: |
superficies de secado |
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TECHNICAL DATA: | |
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Dimensions: |
up to 20 × 20 m |
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Form of Driving Energy: |
solar radiation (insolation) |
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Throughput/Capacity: |
several tons per day depending on grain size, climate etc. |
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ECONOMIC DATA: | |
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Investment Costs: |
approx. 10 to 20 DM/m² area |
CONDITIONS OF APPLICATION:
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Operating Expenditures: |
low |————|————| high |
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Maintenance Expenditures: |
low |————|————| high |
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Location Requirements: |
also employable in humid climates, however high radiation intensity necessary |
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Regional Distribution: |
Bolivla, Chile |
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Operating Experience: |
very good |————|————| bad |
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Environmental Impact: |
low |————|————| very high |
|
|
large space requirements |
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Suitability for Local Production: |
very good |————|————| bad |
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Under What Conditions: |
cement foundation |
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Lifespan: |
very long |————|————| very short |
Bibliography, Source: Priester, Diderot
OPERATING PRINCIPLE:
The dewatered ore or concentrate is thinly spread over the drying surface and allowed to dry in the sunlight. Wooden rakes are used for turning the feed material over, rubber scrapers for gathering and distributing the material and brooms to sweep together the dried material.
AREAS OF APPLICATION:
Drying of concentrate prior to selling, processing by magnetic separation, etc.
REMARKS:
The drying duration depends greatly on the grain size of the material to be dried. The finer the material, the more water is adhesively bound to the surface, and the longer it takes to dry. Drying time can total 8 hours or more.
SUITABILITY FOR SMALL SCALE MINING:
Drying on drying areas is the simplest method of drying products, and plays an important role particularly in arid and semi-arid climates.
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