Selection and design criteria
The flow behaviour and the discharge dynamics of the material being handled dictate the storage hopper design and dimensioning. The determining factors are
- the angle of internal friction of the material (material failure condition);
- the angle of friction between the material and the hopper;
- the inclination angle of the hopper wall with respect to the vertical (geometry/angle of the walls);
- the size of the outlet opening and the flow rate.
The evaluation of the operating and process conditions is also essential and takes into account
- the required storage capacity;
- the discharge frequency, rate and time;
- the operating temperature and pressure;
- the safety and environmental protection parameters.
The hopper geometrical shape is significantly affected by the material flow profile, which as a result of condensation, crystallization, fermentation reactions and moisture presence determines the material accumulation along the bin’s walls or edges, hindering the reliable discharge of the material. The hopper inclination angle as well as its discharge section are decisive for a uniform emptying.
In the hoppers,
- the filling (loading phase) takes place from the top, by gravity, by means of silos, FIBC emptying stations, mechanical, aeromechanical, screw and pneumatic conveyors;
- the emptying (discharge phase) occurs from the bottom, by gravity, through screw conveyors, rotary valves, butterfly valves and dedicated extracting devices.
Steep and smooth hoppers, with walls and angles that have an even finish, a cylindrical, rectangular or square shape and bottom
- with a square opening
- pyramidal wedge-shaped
suitable for fine powders, for not very fluid and easily degradable materials, designed to reduce storage time leading to product decomposition, segregation, oxidation. Emptying takes place in a first in – first out flow sequence.
Hoppers with low sides and reduced wall inclination, with a cylindrical, rectangular or square shape and bottom
1. pyramidal with a square opening
3. flat with slot opening
4. flat with circular opening
used only for coarse powders, free-flowing and nondegradable materials, so that the stationary material does not lead to abnormal segregation or efflux. Emptying takes place in a first in – last out flow sequence.
- Vibrating bottom
- Aerated bottom
- Plated bottom
- Butterfly valve
- Rotary valve
- Screw conveyor
- Ultrasonic level transmitters
- Capacitive level switches
- Conductive level switches
- Rotary level switches
- Membrane level switches