Potato Flour Storage, Conveying and Dosing system
Customer: Saarioinen Oy.
Time span: 02/2015 – 04/2016.
The delivery was a turnkey delivery where everything works together through an automation system delivered by Kopar. Main components of the delivery are the following:
- 50m³ potato flour storage silo
- low-pressure conveying equipment
- and two dosing bins.
Potato flour receiving
The potato flour storage silo is filled by truck. Automation system detects when a cap is detached from the end of the filling pipeline, this tells the automation system that the silo is about to be filled. A hose from a truck is connected to DN100 silo filling pipeline, the truck then blows a mixture of potato flour and conveying air to the silo. Air is separated from the flour by silo filter, filter purging is essential during silo filling as there is lots of flour to be separated. Silo filter elements are automatically purged by reverse air pulse.
Rotary feeder feeds ejector with potato flour from the silo, at the same time conveying air is blown to the ejector, potato flour and air are combined forming a mixture which is blown forward in DN65 stainless steel conveying pipeline. Dosing bin works as a receiving cyclone in which the air is separated from the conveyed material. Separated conveying air is then sucked back by silo filter fan, the filter further separates any potato flour left in the air.
Tuning the conveying system is essential, if the rotary feeder doses too much potato flour in comparison to the conveying air the pipeline clogs and if there is too much air in comparison to potato flour the system is inefficient energy wise. Usually, in low-pressure conveying systems one can tune the capacity of the rotary feeder by inverter, conveying air pressure by pressure control valve and conveying air amount by air flow control valve. We were able to reach potato flour conveying capacity of 3 t/hr in this system.
The most essential part of the project was the dosing system, as factory operators directly use this part of the delivery in the plant. The dosing system consisted of two near identical dosing sets. Dosing set consists of 100 liter dosing bin, dosing bin agitation equipment, weighing sensors and a rotary feeder.
The operator decides the amount of flour to be dosed. The system then begins dosing and goes through coarse, accurate and if needed proof dosing phases. In coarse dosing phase the rotary valve doses flour quickly until it reaches certain limit value in comparison to the set point. When the limit value is reached the accurate dosing phase begins, the rotary valve rotates more slowly and the bin agitation is limited to reach maximum accuracy, when the set point is reached rotary vale stops. A control weighing is automatically done after this, if the dosed amount is not in negative tolerance the system enters proof dosing phase, in which more flour is dosed. The accuracy of the dosing system is 2,5%, with a dosing capacity of 10kg/min.