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© [email protected], [email protected] Department of Mining, Dressing and Transport Machines AGH tel/fax +48126335162

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Department of Mining, Dressing and Transport Machines AGH

Silos, hoppers and bunkers

Piotr Kulinowski, Ph. D. Eng.

Piotr Kasza , Ph. D. Eng.

- [email protected]

( 12617 30 92

B-2 first-floor /US/ room 6

consultations: Mondays 11.00 - 12.00

Conveyors

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Hoppers

Hoppers are used in industry for protection and storage of powdered

materials.

Hoppers come in a variety of shapes and designs, not just conical.

Common designs for mass flow hoppers

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Storage bins and bunkers Zasobniki i zbiorniki

1 Bunker wall Ścianka zbiornika

2 Structure Rama wsporcza

3 Lining material Wykładzina

4 Stiffeners Ożebrowanie usztywniające ścianki zbiornika

5 Outlet Wylot

6 Grid Krata, ruszt

7 Anti-pressure device Element osłaniajacy wylot ze zbiornika

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Silos and hoppers Silosy i zbiorniki zasypowe

1 Multiple silos Silos wielokomorowy

2 Single silos (round) Silos jednokomorowy (okrągły)

3 Single silos (polygonal) Silos jednokomorowy (wielokątny)

4 Conical bottom Dennica stożkowa

5 Structure Konstrukcja wsporcza

6 Inlet Otwór wlotowy

7 Inspection or cleaning manhole Otwór rewizyjny

8 Outlet Wylot

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Hand operated bin gates Ręcznie otwierane zamknięcia wylotów ze zbiorników

1 Swinging gate arrangement Układ z klapą wahadłową

2 Rack and pinion gate arrangement Układ z klpą przesuwną

3 Gate body Wylot , zsyp

4 Gate (swinging) Klapa wahadłowa

5 Sliding gate Zasuwa

6 Rack and pinion Mechanizm zębatkowy

7 Guides Prowadniki

8 Hand operating chain and wheel Łańcuch lub koło zębate obsługiwane ręcznie

9 Hand operating cable or chain Lina lub łańcuch obsługiwane ręcznie

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Mechanicaly operated bin gates Mechanicznie zamknięcia wylotów ze zbiorników

1 Swinging gate Układ z klapą wahadłową

2 Rack and pinion gate Układ z zasuwą

3 Hydraulic actuated cylinder

Pneumatic actuated cylinder

Electromagnetic actuated cylinder

Napęd hydrauliczny

Napęd pneumatyczny

Napęd elektromagnetyczny

4 Support brackets Wsporniki

5 Chute Zsyp

6 Gate (swinging) Klapa wahadłowa

7 Sliding gate Zasuwa

8 Geared motor unit Motoreduktor

9 Rack and pinion Mechanizm zębatkowy

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HOPPER DESIGN

Andrew W. Jenike developed the theory and methods to apply the

theory, including the equations and measurement of the necessary

material properties. His primary works are published in 1961.

Designer should to choose the geometry of the bin (specifically the

hopper angle and the outlet size) on a rational basis, based on

measurement of the flow properties of the bulk solid to be

discharged.

Measure

- powder cohesion/interparticle friction

- wall friction

- compressibility/permeability

Calculate

- outlet size

- hopper angle for mass flow

- discharge rates

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TESTING REQUIREMENTS

To design storage hoppers, the

following material properties are

needed:

Internal friction coefficient

The powder sample is sheared within itself

Wall friction coefficient The powder sample is in contact with

a wall sample. Shearing occurs

between the powder and wall samples.

Permeability

Compressibility

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Hopper Flow Modes

A - Mass Flow - all the material in the hopper is in motion, but not

necessarily at the same velocity

B - Funnel Flow - centrally moving core, dead or non-moving annular

region

C - Expanded Flow - mass flow cone with funnel flow above it

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Advantages (+) and Disadvantages (-) of Mass Flow

Hoppers

+ flow is more consistent

+ reduces effects of radial segregation

+ stress field is more predictable

+ full bin capacity is utilized

+ first in/first out

- wall wear is higher (esp. for abrasives)

- higher stresses on walls

- more height is required

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Advantages (+) and Disadvantages (-) of Funnel Flow

Hoppers

+ less height required

- ratholing

- a problem for segregating solids

- first in/last out

- time consolidation effects can be severe

- silo collapse

- flooding

- reduction of effective storage capacity

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Hopper Design Problems

RATHOLING/PIPING. Ratholing or piping occurs when the core of

the hopper discharges (as in funnel flow) but the stagnant sides are

stable enough to remain in place without flowing, leaving a hole

down through the center of the solids stored in the bin

Stable

Annular

Region

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FLOW IS TOO SLOW. The material does not exit from the hopper

fast enough to feed follow on processes.

NO FLOW DUE TO ARCHING OR DOMING. The material is

cohesive enough that the particles form arch bridges or domes that

hold overburden material in place and stop the flow completely.

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SEGREGATION. Different size and density particles tend to

segregate due to vibrations and a percolation action of the smaller

particles moving through the void space between the larger particles.

INCOMPLETE EMPTYING. Dead spaces in the bin can prevent a

bin from complete discharge of the material.

TIME CONSOLIDATION. For many materials, if allowed to sit in a

hopper over a long period of time the particles tend to rearrange

themselves so that they become more tightly packed together. The

consolidated materials are more difficult to flow and tend to bridge or

rat hole.

CAKING. Caking refers to the physiochemical bonding between

particles what occurs due to changes in humidity. Moisture in the air

can react with or dissolve some solid materials such as cement and

salt. When the air humidity changes the dissolved solids re-solidify

and can cause particles to grow together.

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FLUSHING. Flushing occurs when the material is not cohesive

enough to form a stable dome, but strong enough that the material

discharge rate slows down while air tries to penetrate into the packed

material to loosen up some of the material. The resulting effect is a

sluggish flow of solids as the air penetrates in a short distance

freeing a layer of material and the process starts over with the air

penetrating into the freshly exposed surface of material.

Uncontrolled flow from a hopper due to powder being in an aerated

state

- occurs only in fine powders (rough rule of thumb - Geldart group

A and smaller)

- causes --> improper use of aeration devices, collapse of a

rathole

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Silo Discharging Devices

Slide valve/Slide gate

Rotary valve

Vibrating Bin Bottoms

Vibrating Grates

others

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Sliding Gate Options

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Rack & Pinion Drive

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Slide valve/Slide gate

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Rotary valve

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Vibrating Bin Bottoms

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Level Measurement of Bulk Solids in Bins,

Silos and Hoppers

Measuring the level of bulk solids or powders in a bin

or silo can be difficult for several reasons:

Many materials produce large amounts of dust

during filling and discharging

Ratholing

The angle of repose, or shape of the surface,

can vary with filling, discharging, the location of

filling and discharging, angled or multiple fill

points, multiple draw points, etc.

The coarser the material, the more likely it is to

clump, bridge, leave voids and pile up.

It also can be difficult to know the exact

dimensions of the silo the material is stored within

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Level Measurement Systems

Weight & Cable Level Systems

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Weight & Cable Level Systems

Conclusion - The increased durability of the

state-of-the-art weight & cable designs, added to

the low purchase cost of the weight & cable

system, makes this technology a very cost

effective solution, compared to other level

measurement devices, for a wide range of

applications.

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Ultrasonic Level Systems

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Ultrasonic Level Systems

Conclusion - There is some doubt as to whether

all problems, particularly heavy dust, have been

satisfactorily dealt with by the new technology

advances. You should have confidence in the

reliable performance of a state-of-the-art

ultrasonic system that has been approved by

the manufacturer for your specific

application.

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Guided Wave Radar (GWR) Level Systems

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Guided Wave Radar (GWR) Level Systems

Conclusion - GWR and TAR systems

have different pros and cons. One may

be more advantageous than the other for

specific applications, however, either

should be equally reliable and dependable

on any application approved by the

manufacturer.

Thru-Air Radar (TAR)

GWR units are highly recommended for

dusty applications

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Thru-Air Radar (TAR) Level Systems

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Thru-Air Radar (TAR) Level Systems

TAR has the advantage of being truly continuous

versus weight & cable units, however, we still

feel that the best course of action is to choose

the most economical option that fits the

application and your most important needs.

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Laser Level Systems

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Laser Level Systems

Conclusion -These units are non-

invasive, highly accurate and respond

quickly to changes in material level. If

true continuous measurement is

needed they are a good option.

However, the trade-off is price. You

should still choose the most

economical option that fits the

application and your most important

needs.

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Load Cell Weight Systems

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Load Cell Weight Systems

Conclusion - Load cell systems do not

really compete with level systems. The

high cost of the weight system is not a

factor because there are rarely any other

candidates at a lower cost that offer the

required performance.

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Underground bunker in copper ore mine

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Bibliography

Karl Jacob: Bin and Hopper Design,The Dow Chemical Company,

Solids Processing Lab, [email protected]

Joseph D. Lewis, Sr: Technology Review Level Measurement of Bulk

Solids in Bins, Silos and Hoppers

George G. Chase: SOLIDS NOTES 10, The University of Akron

Dietmar Schulze: Storage of Powders and Bulk Solids in Silos

mailto:[email protected]

Department of Mining, Dressing and Transport Machines AGH · 3 © [email protected],...

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