Elevator and intake systems
May 01, 1994
by Teresa Acklin
By David Sugden, a consultant to the grain industry.
This article describes a large elevator and intake system serving a flour, maize, soybean and/or feed mill complex. The accompanying diagram and plan view highlight the system's major features and may be used to generate ideas according to the needs of individual operators.
The facility's intake of grain by ship be it wheat, maize, rye, barley, oats, soybeans and even soybean meal is accomplished from two intake pneumatic suction pumps at up to 400 tph. Road intake in this example is 100 tph.
The elevator or silo itself is made up of 30 main and 12 interspace bins, each with a capacity of 1,350 tonnes and 400 tonnes, respectively. The total storage capacity of the elevator is 45,300 tonnes, split into three silo block sections or buildings (silo A, silo B and silo C). Delivery from the three silo blocks is rated mainly at 100 tph, although a 50-tph conveyor can be seen underneath.
Flexibility is an important feature of this system. The whole is fully automatic and remote-controlled by Programmable Logic Controller (P.L.C.).
THE DIAGRAM: SPECIFIC FEATURES.
The two pneumatic pump ship unloaders illustrated at (1) discharge ships by chain conveyor to the electronic weigher (2), which records movement into the elevator.
These and all the other horizontal chains are fully protected individually by motor overload detectors and choke or plug probes. The detectors and probes, if activated, immediately close down all equipment.
After passing the weigher, grain moves through two drum sieves (3), which act as a rubble separator. Grain then moves to the bucket elevator (4), which feeds the main chain conveyors over the bin tops of silos A, B and C.
The bucket elevator is protected by two features, a bottom drum rotary underspeed sensor and an elevator belt alignment instrument. Both, if activated, will stop all machinery behind. With this system of detectors and sensors, both bucket elevators and chain conveyors are fully protected.
Each bin is remotely filled and emptied according to the schedule or queue “punched in” to the P.L.C. All bins have remote-controlled slides operated by compressed air solenoid valves for entry and exit. Further, each bin has a high- and low-level control to monitor full and empty status.
The intake system also feeds a flat storage area (5), which can be used for any material, including millfeed pellets or soymeal.
The all-important turnover system (6) can take from any bin and feed any other, a critical feature because it allows refreshing heated or pest-attacked grain, as well as moving stocks for convenience. The truck shown at (7) is ready to receive any type of grain.
The machinery between points (8) and (9) weighs grain out of the silo, runs it over a powerful magnet, aspirates the grain and dampens it with water before sending the grain to the mill bins at a rate of 100 tph.
The machinery between points (5) and (10) shows a number of optional destinations, such as soybean, maize or feed mills. This machinery includes a weigher, magnet and a grain separator with aspirator.
The whole system at every point is totally enclosed and exhausted by fans and dust collectors. The total air requirement is 900 cubic meters per minute when all sections are in use.
Each bin top has an explosion panel, which is interlocked to shut the whole system if activated. The same shut-down feature applies to each filter dust collector and bucket elevator.
Most countries have laws that put the onus of safety, in any guise, on the operator. Agreement even among scientists as to exactly what is required in grain elevators is missing. The operator is left to hope no explosion takes place.
Nonetheless, a well-engineered and enclosed exhaust system, coupled with proper and reasonable maintenance, usually is more than enough to avoid problems, barring the totally exceptional and freak circumstance. By its nature, the elevator described here is very easy to keep clean because of the exhaust system.
Features not shown on the diagram include sampling devices, continuous temperature monitoring within each bin, fumigation facilities and dosing elements for stored product insects.
THE PLAN VIEW: FACILITY LAYOUT.
The intake suction pumps are located at position (1) on the waterfront. The weigher, down sieves, bucket elevator, turnover system and machinery (points 2 through 10) are in the tall elevator housing itself. Grain delivered to the various mills is shown by the arrow marked “to mill bins.” The flat grain storage area is positioned at (5), and the truck receiver weighbridge or scale is shown at (7).
The silos' height is 30 meters to the bin tops. The entire site measures some 200 meters by 55 meters, with the highest point, the elevator housing, at 38 meters.
Note the other facilities, including a cafeteria, shipping office, pumphouse and power house, which contains the site generator. Also visible is the route taken by the horizontal intake conveyors.
The total number of employes would be about 20 for a facility of this size, with five to operate the intake and elevator systems, five for maintenance and the remainder for office, laboratory and cleaning functions. Automatic sampling devices can be used at particular points to take samples and send them to the laboratory with the date, time and location marked for tracking.
The laboratory would include quick-test apparatus to measure such items as weight, dockage, moisture and sprout damage. Near-infrared equipment also could be used to speedily estimate not only moisture but protein and oil content.
This modern system is very efficient when taking into account P.L.C. process control, automatic inventory data collection, reconciliation, storage and retrieval, combined with modern office and laboratory functions.
Mill-feed pellets occasionally are stored in large elevators, depending on climate. Such pellet storage is not recommended in hot and humid areas because of sweating, mold and bacteria growth. Loading warm pellets in very cold climates also should be avoided.
In the more temperate zones, it is not uncommon to store pellets in large elevators. Pellets' specific gravity is about 90% of wheat with the same volume, and pellets flow similarly to wheat. Pellet machines should be set correctly to prevent breakage.
Dockage disposal from a large elevator and mill facility can be made to a number of outlets. Rubble, such as sticks, stones, string, wood or rodents, should be turned out for garbage under all circumstances. The remaining dockage, with the exception of metal caught on magnets, usually is ground and can be included with mill dockage for disposal as millfeed.
A stand-alone elevator either may sell dockage, except rubble and metal, for animal feed or may burn some, such as straw and chaff, for steam generation to save energy costs.
In conclusion, there are many options to contemplate in designing and operating elevator and intake systems. While the system described here is comprehensive and relatively large, thousands of country elevators worldwide have incorporated some of these features.