DE3124649A1 - METHOD FOR CONTROLLING A MILLING PLANT - Google Patents

Description

-λ- Ρ 4976

Method for controlling a grinding plant

The invention relates to a method for regulating a grinding plant in which the material discharged from a mill The ground material is sighted and the resulting amount of semolina is fed back to the mill will.

It is known to regulate and control the feed quantity of the mill via the (air flow) differential pressure of the mill and / or via the filling level of the mill (the latter measured via the sound pressure of the mill) in grinding systems, especially in IQ air-flow grinding systems equipped with ball mills in this way to maintain optimal conditions for the grinding process in the mill. If, for example, the material to be ground is very soft, the mill is operated with a large throughput and accordingly is switched on and off frequently. If the ground material is very hard, the mill can run longer or a reduced throughput is accepted. To compensate for these fluctuations in grindability and throughput, the grinding system is usually followed by a buffer bunker.

However, there are also cases in which, on the one hand, such buffer bunkers should be dispensed with, which Mill on the other hand, however, with regard to the requirements of the downstream process for the the material is ground, must be operated with different throughput. In such Cases it proves to be difficult to

- Si

to comply with the specified fineness of the ground material. In general, one becomes too large grinding capacity the ground

Well finer than desired and vice versa. 5

One could now think of the fineness of the grist to measure continuously (e.g. to determine the residue on a certain sieve) and by a corresponding intervention in the grinding system (for example a changed setting des Sichtera) the Foinhc.lt back on dun desired Bring value. However, such a method proves to be extremely cumbersome in practice and also suffers from considerable dead time.

The invention is therefore based on the object of developing a method of the type mentioned at the beginning, which allows the fineness to be achieved regardless of fluctuations in throughput and grindability to keep the ground material in a simple manner at a predetermined value.

The task is founding <yes no food solved by that the semolina is measured and the mill speed is regulated in such a way that the ratio of the amount of semolina to the mill feed quantity remains constant. ·

As detailed investigations have shown, in practice it can be assumed that with a constant ratio The fineness of the ground material is constant from the amount of semolina to the amount fed into the mill.

In order to explain the invention in more detail, let us first consider the various variants of the method described with the aid of the schematic representation according to FIG.

The grinding plant according to FIG. 1 contains a mill 1, a classifier 2 and a device 3 for recycling and measuring the amount of semolina.

To the. Explanation of the invention on the basis of a few simple mathematical relationships are as follows Abbreviations introduced:

A = mill feed rate Qt / hJ Sa = classifier feed quantity

SG = amount of classifier meal

SF = finished sifter quantity
= Mill feed quantity

N = power consumption of the mill LkW_ [ η = speed of the mill £ rpm] N = specific grindability rkWh /

The following dependencies exist:

'' If the circulation factor (UF) measured on the classifier remains constant, the fineness of the finished quantity sifter (SF) also remains constant.

SA

By definition, UF = - ^ = - const. = c

The following applies to the classifier: SG + SF = SA

From this it follows: UF = = const. = c

OI

This results in: SG = SF (c-1)

or (since SF = A): ~ = (c-1) = C. (1)

This relationship therefore exists with a constant fineness of the finished sifter.

In the case of a constant throughput, the following dependency exists:

N ₁ 15 _Y

^N sp1 ^N sp2

= SF = A = const. = C ₀ (2)

Finally, there is the following empirically found dependency between the power consumption a mill and its speed:

Ü2 Γη2 | N ₁ = [nij

1.3

Such a grinding plant can now be operated in 25

several variants take place:

Version 1:

Mill feed quantity A and throughput = constant. 30th

Specific eligibility (N,) = variable.

t> p

Fineness of the finished product = constant.

the end (1) results themselves SG ₁ (4) ^N 2 the end (2) follows ^N 1 ^N sp2 ^N sp1

From (4) and (5) results

^SG i * N ^ ₁ SG ₁ · N _-

N ₁ = -JL SEI (6) N ₂ = P ² (7)

ι U ₁ ζ O ₁

From (3) and (7) it finally follows

^M i · »ι ¹ ' ³ ..] T73

(8th)

In this case, the mill speed is only a function of the changed specific Material grindability.

The mill feed quantity and the fineness of the finished product are set according to the needs of the consumer. The ratio of the amount of semolina to the amount fed into the mill then has a certain value (C ₁ ). If the grindability of the material becomes worse, the material to be ground leaves the mill more coarsely than before. A larger amount of semolina is therefore separated in the sifter, which is then sent to the mill

go is returned. This measurand (amount of semolina) is set in relation to the feed quantity and

V "

used to control the speed of the mill. As the mill speed is now increased to the value n2, the fineness of the ground material that leaves the mill increases. The mill speed is increased until the ratio of the amount of semolina to the amount of the mill feed has returned to the original value: * The grinding system thus delivers the specified throughput rate with a constant IQ fineness (with reduced specific grindability).

Variant 2:

Throughput and mill feed quantity = variable (selected).

Grindability = constant.

Fineness of the finished product = constant.

SG ₁

From (1) we get A ₁ = γτ— (9)

¹ 1

as

. - ^SG 2

(10)

From (2) follows

"1

(11)

A ₀ = φ- (12)

^A 2 ^C 1 ^A 1 ^N 1 ^N s _P 1 ^A 2 N ₂ ^N s _P 1

From (3) and (9) to (12) can be derived

n ~ =

Vt m ¹ ' ³

SG,

1.3

(13).

In this case, the mill speed is only a function of the changed amount of semolina, where the amount of semolina is directly proportional to the amount added. The speed of the mill is regulated So according to the amount of semolina, which changes with the amount of semolina, until the original again Relationship of the amount of semolina to the mill feed amount is established.

Variation 3:

Throughput and feed quantity = variable. Material grindability = variable. Fineness of the finished product = constant.

This is the most common case in practice, in which the mill with different throughput and variable material grindability with the required constant fineness of the finished product should be operated.

Here, too, the speed of the mill is regulated so that the ratio of the amount of semolina to the amount of the mill feed remains constant.

A summary of the above relationships is provided for this case

ⁿ 2 ⁼

ⁿ 1

1.3

* ^N SP2 ' ^SG 2

1.3

(14)

The mill speed is therefore a punctuation of the changed amount of semolina (SG-) and the changed material grindability (N ₂ ).

If the mill with strongly variable throughput rates and strongly fluctuating material grindability is to be operated, it can be useful to set the desired value of the ratio of the amount of semolina to be adjusted accordingly to the mill feed quantity. This can either be done automatically or according to a specific one Program.

Variation 4:

If the fineness of the finished product is to be changed for a given throughput and a given material grindability, a new ratio between the amount of semolina (SG) and the amount of mill feed (A) must be determined. A new setpoint ratio C2 · This ratio is then - as described above for the three previous variants - kept constant by regulating the mill speed from _{C 1} , which was kept constant above for the first three variants mentioned.

AO '

The method according to the invention is suitable for the most varied types of mills and grinding systems, in particular for air-flow mills and mills with mechanical material discharge, and also for ball and roller mills. In the context of the method according to the invention, a wide variety of types of separators can be used, such as static separators, turbo separators, cyclone air separators, etc. Mill feed quantity the fineness of the finished product remains approximately constant.
15th

The amount of semolina can be measured using belt scales, flow meters, nuclear scales or by Determination of the power consumption of conveyors such as belts, augers and the like. 20th

The amount of gas flow generated by the system fan, which the Well promoted by the grinding plant, included and the changed throughput rates, grindabilities and subtleties to be adjusted.

Likewise, to regulate the fineness of the finished product, an either automatic or manual process can be used Adjustment of the classifier can also be used.

η a * η

4f

2 shows the essentials in schematic form Components of a system for carrying out the method according to the invention.

The mill 1 is connected to the sifter 2 via a pipe 4, the grit here via a Measured as a conveyor belt scale device 3 and returned to the material feed side of the mill 1 will.

The material to be ground is fed from a storage container 5 via a weighfeeder 6 to the mill 1. A controller 7 controls the weighfeeder 6 as a function of a signal (arrow 8) sent by the consumer of the ground material is delivered.

The finished product arrives from the classifier 2 to a filter system 9 in which the finished product is separated (Arrow 1 0), while the air flow is drawn off by a fan 11. Part of this air flow can be via lines 12, 13 and 14 on the airflow discharge side the mill 1 or (together with another hot gas stream, see arrow 15) the material feed side the mill 1 are fed.

On the one hand, a controller 16 receives a signal (arrow 17) from the controller 7, which signal corresponds to the current mill feed quantity (Fresh product quantity), on the other hand, a signal (arrow 18), which from the device 3 is delivered and corresponds to the amount of semolina returned from the classifier 2 to the mill 1. From these two The controller 16 forms an actual signal and values

compares it with an adjustable setpoint signal (arrow 20), which is a measure for the desired The fineness of the finished product. The delivers according to the deviation of the actual value from the setpoint Controller 16 sends a control signal (arrow 21) to a drive 22 of the mill 1. This speed-controlled drive can be formed, for example, by a DC motor or a subsynchronous converter cascade will. 10

ο 25

Claims (2)

Patent claims: Method for controlling a grinding plant in which the ground material discharged from a mill sighted and the resulting amount of semolina is fed back to the mill, characterized in that the amount of semolina is measured and the mill speed in such a way it is regulated that the ratio of GrießjQ the amount of the mill feed remains constant. 2. The method according to claim 1, characterized in that the target value of the ratio of The amount of semolina for the mill feed amount is adjustable depending on the desired fineness of the finished product.