Bucket Elevators for Process Plants

in the Cement, Lime, Gypsum and Mineral Industries



Testing system to analyse full emptying of buckets and increasing the elevating efficiency at high capacity bucket elevators.

High capacity bucket elevators are increasingly used in the mining, power, and coal handling industry, as well as for fertilizers and ports/terminals.

As far as capacities are more and more increasing, the efficiency of elevating the materials considered as the ratio between the material elevated and the material really discharged becomes very important.

One of the most important matters about bucket elevators is the full discharge of material from the buckets, that means of the elevating efficiency .

We have 100% efficiency at bucket elevators if the the buckets are completely discharged at outlet. The elevated material which is not discharged at outlet, and therefore is taken with again in the bucket, in the descendent run, creates the so called recirculation.

Recirculation means wasting of energy because material which was already lifted up to the drive station and to the outlet, falls down again and must therefore be "elevated up again".

The fall of material causes moreover premature wear of all parts of bucket elevator such as casings, buckets, chains.

This is very more important at high capacity bucket elevators with capacities of 1500 m3/h and more where only a small percentage of recirculated material means many tons/h of material falling down to bottom station .

Very important regarding this matter is the analysis of the emptying process of buckets.

This depends on many factors, which we list in the following:

a) Geometry of bucket elevator

- diameter of sprockets

- distance between axses of sprockets and discharg outlet in the vertical and in the horizontal

- general shape of drive station

b) Geometry of bucket

- deepness of bucket

- angle of discharging at dragging side of bucket

- general shape of bucket

- material the buckets are made on

c) Exercise data

- speed of buckets

- filling ratio

- pitch of buckets as far as the material coming out from one

bucket could hit or could interfere with the other buckets

d) Conveyed material data

- specific weight

- moisture content

- grain size and distribution of grain size

- inner friction coefficient of conv. material

- friction coeff. of the considered material on the material the buckets are made on.

- content of additives

- falling speed of material in the air

It is obviously very difficult to develop a reliable software which can take into consideration all above mentioned data in the correct manner. Additionally it must be said that in any case detailled analysis of material conveyed should be performed with additional costs.

The result of the theoretical analysis requests a huge work for “adjusting” the software that means to match the theorectical results with the real ones. At any way a pilot plant would be needed, in order to check "on the field" if the calculated values are really reliable. Even a small error, let say 10%, would cause a material recirculation in the bucket elevator of 10% of total capacity.

If a bucket elevator with f.ex. 800 t/h capacity recirculates 10 % of total capacity, this means:

a) 10 % of 800 ton /hr = 80 t/h, considering a center distance of only 60 mt , takes to 30 kW of wasted energy.

b) 80 t/h bulk material falling down the bucket elevator causing additional wear on chains, buckets, casings.

This situation results from the fact that in many cases shape of buckets, geometry, speed, etc. are chosen and bucket elevators installed, without the support of data from full scale tests.

About recirculation:

If we consider the section of a bucket we can divide it in a square area A , at the bottom of bucket, corresponding to the part of material which is gone to be recirculated and in a area B over it correspondig to the material which will be correctly discharged at outlet.

Area A + Area B = 100 % filling of bucket ( H2O = level)

The area A creates the recirculation flow Q3, the area B creates the effective elevated flow Q2.

The whole elevator is a system in which a material flow Q1 goes in and a flow Q2 comes out / is elevated.

Depending on the amount of recirculation we can have three situations:

A) Q2 = O , that means Q3 = Q1 , the incaming material is totally recirculated. No material is coming out from the elevator. In short time the bucket elevator is filled up with material

B) 0< Q2 >Q1

- part of bucket section (section A) doesen't convey and the material recirculates .

- only section B is available for conveying

We have then additionally situations:

B1) area B is sufficient for elevating incoming capacity Q1.

The elevator is able to elevate the incoming flow but with high recirculation and energy waste, the buckets digs at bottom but the elevator doesen't fill up even after long time.

Premature wear of elevator parts .

Efficiency of bucket elevator < 100%

B2)

The area B is not sufficient for elevating the flow Q1 and therefore the elevator is going to fill up in a longer or shorter time depending on the ratio Q1/Q2 .

Efficiency of bucket elevator << 100%

C) Q2 = Q1 that means Q3 = 0

The recirculating area A in the bucket is = 0 .

All material is discharged. The bucket has no dead areas.

The efficiency of bucket elevator = 100%

Testing System:

To test the buckets geometry in a practical system without using software programms, a full scale pilot plant is normally needed ,complete with silo, elevators , conveyors etc. This system needs relatively big amounts of material for the test ( tens of m3) ,which is not allowable or only at high costs.

Verifying the efficiency is not very easy with this system and it is connected with long testing time, filling and empting the silo etc) .

Gambarotta Gschwendt GmbH developed a system were only about 1 m3 of testing material is needed and the test series can be performed in short time in conditions which are almost the same as the real exercise conditions.

Certified tests can be carried out for different speeds, shapes of buckets, pitch, etc. for the considered material.

We investigated cases with difficult materials, in which it was possible to increase the efficiency of bucket discharge from 70 % to 97 %.

The testing system takes into consideration all parameters described above and we are able in this way to develop absolutely customer retailed solutions for new bucket elevators, or to increase the efficiency on existing ones.

Special solutions can be developed where the place available is already given and standard bucket elevators are too big for the capacity requested.

We can give answers to the following problems:

- revamping of existing bucket elevators which recirculate

- design of high capacity bucket elevators for installation in small place sites .

- difficult materials must be elevated ( sticky, umid )

- big size materials must be elevated / conveyed

The testing system can be used on all types of buckest / buckets elevators such as:

a)belt bucket elevators

b)round link chains b.el.

c)bushed chains bucket elevator

The attached drawings show the various types of buckets and related bucket elevators in our production program, used for elevating different types of material regarding grain size, temperature, moisture, etc., at different speeds.

In particular:

1) Belt Bucket elevators:

- EVN type for fine materials , high capacity

2) Bushed chain bucket elevators:

- type ESP-C : central chain bucket elevator, centrifugal discharge

- type ESP : double chain bucket elevator, slow speed

- type ESP-LV : double chain, high capacity

- type ESP-BS : double chain, for very big size material

3) Round link chain bucket elevators:

- type ELD : double chain, slow speed

- type EVD : double chain, centrifugal discharge

- type ELR : double chain, slow speed high capacity

- type EVR : double chain, centrifugal discharge, high capacity

- type ETR : double chain, for big size material

We can design and supply bucket elevators for elevating materials in the cement and minerals industry, with:

a) grain size up to 400 mm

b) temperature up to 600°C

c) moisture up to 20 %

d) capacities up to the range of 2000 m3/h and more

Depending on the task round link or bushed chains ( double chain or central chain ), textile belt or steel reinforced belt for bucket elevators can be used .

Please contact us for more information.

Fabriizio Gambarotta

fgambarotta@gambarotta.it

https://edir.bulk-online.com/profile...-gschwendt.htm



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