To the east of Cape Town is the area called the "Overberg" which, together with the "Swartland" area to the north west, produces most of the grain grown in the Western Cape. Grain types include wheat, barley (used by SA Breweries for malting at Caledon) and small quantities of oats, rye and canola seed (for the manufacture of vegetable oils).

Grain is mostly stored in concrete silos which are ventilated for the storage of barley. The product is kept dry and free of insects and vermin.

GPB has been involved in the upgrading of a number of grain storage depots. Typically our work would entail improvements to the grain handling machinery and to the grain flow layout including modernisation of the process control.

The process at depots entails the taking of samples of the grain, weighing of the load, intake, storage and loading out for road or rail transport. Equipment usually comprises a mix of bucket elevators, chain and belt conveyors, chutes, mass measurement, drying, screening and cleaning equipment, etc.

By increasing the intake and discharge rates and improving the traffic flow, the average queue length at intake silos is reduced. This results in a more productive use of the producer's transport vehicle. A further major advantage which flows from faster intake and discharge of grain is the reduced risk of ripe grain being damaged by rain which can occur during the harvesting period.

Grain delivery trucks queue at a grain silo to off-load


In one instance it was found that the average service time at a grain intake point was 3.65 minutes. Queuing theory was used to determine the expected number of vehicles in a queue should the equipment work at maximum capacity. This analysis indicated that very long queue lengths would result which is not acceptable.

The options available are:

  • increase the number of intake points, or
  • decrease the service time per vehicle at an intake point.

The graph below shows how daily intake increases should the intake time be decreased from 3.65 minutes per vehicle to 3.2 minutes per vehicle. It also indicates what the effect is of increasing the queue length from 1 to 4 vehicles and how this would be affected should the queue be infinitely long.

Click to go back to Projects