Technical notes
Three reference points for project developers
Written by our design office and publishable as they stand. They describe no particular project: they are points of method, useful before any investment.
NOTE 01 · ENERGY
Why drying decides the operating cost
In a processing unit, mechanical operations — grating, grinding, pressing, shelling — consume energy of the order of a few tens of kilowatt-hours per tonne processed. Thermal operations are counted in another unit altogether: evaporating one kilogramme of water requires at minimum the latent heat of vaporisation, about 2.26 megajoules, to which dryer losses must be added. A dryer of poor efficiency can consume twice that theoretical minimum.
The practical consequence is counter-intuitive: on a line where the energy bill is to be cut, the first lever is almost never the motor, but the quantity of water the dryer is asked to remove. Every point of moisture removed mechanically — by better-conducted pressing, a more gradual pressure rise, an adjusted cycle time — is thermal energy that will not have to be spent. This is why we always examine the press setting before sizing the dryer.
Technical note from the SOTIC design office — reference physical values, with no data specific to any installation.
NOTE 02 · SIZING
Oversizing, the leading cause of unit failure
An oversized unit does not merely cost more to buy. It costs more every hour it runs, because the fixed costs — amortisation, supervision, scheduled maintenance, contracted power — are spread over a tonnage lower than the one that justified the investment. A line operated at forty per cent of its nominal capacity can show a cost per tonne twice that of a more modest line running at full load.
The error almost always comes from the same place: capacity is set from the theoretical agricultural potential of an area, rather than from the tonnage the project developer is actually able to collect, pay for and transport within the delays imposed by the material. Between the two, a factor of two to three is common. The rule we apply is simple: size on the flow that can genuinely be mobilised in the first year, planning for extension rather than anticipating it in concrete and steel.
Technical note from the SOTIC design office — a point of method, illustrated without reference to any identifiable project.
NOTE 03 · PURCHASING
Reading a machine data sheet without being misled
Three traps recur systematically when comparing equipment offers. The first is the stated throughput: it often corresponds to nominal operation on an ideal material, without the stoppages for emptying, cleaning and adjustment. Useful throughput over a real production day is lower, sometimes by thirty per cent. Always ask under what conditions the figure was recorded.
The second is installed power, often confused with absorbed power. A machine fitted with a twenty-two kilowatt motor does not draw twenty-two in normal running; but it is on installed power that the electrical supply and the back-up generator must be sized. Both figures are useful and serve different calculations.
The third is silence about wear parts. A machine is judged as much on the price and availability of its spares as on its initial performance. Before signing, ask for the list of wear parts, their estimated life, their unit price and their lead time. Equipment that is slightly more expensive but whose parts are available in-country is almost always the better investment.
Technical note from the SOTIC design office — generic purchasing advice, applicable to any supplier.
