GB2129707A - Grinding installation - Google Patents

Abstract

Grinding installation comprising a preliminary crushing unit (1) which is charged with raw material and a grinder (2) downstream thereof, the discharge line (3) of which leads to a separator (4) having a grit return line (5) back to the feed side of the grinder. With a view to improving the efficiency of the installation, the preliminary crushing unit (1) is connected to the feed side of the grinder 2 via a separating chamber (6) which also has a connection (7) to the discharge line (3) of the grinder. <IMAGE>

Description

SPECIFICATION Grinding installation The invention relates to a grinding installation and, in particular, to an installation of the type comprising a preliminary crushing unitwhich is charged with raw material and has a grinder downstream thereof, the discharge line of which leads to a separator.

A problem generally encountered with such grinding installations is that, while optimum comminution of the raw material is always desired, the result achieved in practice is greatly affected by the nature of the material to be comminuted, especially by its moisture content. It has therefore proved generally advantageousforthe grinding stockto be subjected to drying processes in separate steps, in orderto reduce this variable and damaging effect.

Afurther particular problem encountered when optimising the grinding processes is that, as far as possible, only grinding stock which still requires to be comminuted should be subjected to the grinding process. Maximum effort should therefore be made to remove, from the grinding process, grinding stock which is already ofthe desired particle size.

A grinding and drying installation is already known (DE-AS 1 281 817) which comprises a crushing mill which is charged directly with raw material, and a grinding mill through both of which hot gas flows and the discharge lines ofwhich open into a common pipe leading to a separator, the separator having a grit return line backto the input of the grinding mill.

This installation can sufferfrom the problem already described that raw material which has already reached the final particle size stays mixed for too long with the raw material to be communited further, with the result that an uneconomical burden is placed on the crushing process and on the comminuting tools in particular. It is also found that it can sufferfrom internal circulation of material in the preliminary crushing mill and from the fact that the preliminary crushing mill effectsafinecommunition of a high proportion of the raw material, which could be effected more efficiently in the grinding mill.

An object ofthe invention isto enable sufficiently broken - up grinding stock to be separated as directly as possible from the material which has to be processed further.

The present invention provides a grinding installation comprising a preliminary crushing unit for receiving raw material and a grinder downstream thereof the discharge side of which leads to a separator, in which the crushing unit is connected to the feed side of the grinder via a separating chamber which is also connected to the discharge side of the grinder.

In a grinding and drying installation in accordance with the invention, hot gas flows through the grinder, and the separator has a return line,forcoarse material, back to the feed side ofthe grinder.

Preferably, the preliminary crushing unit is equipped with a grid for limiting the particle size of material leaving the crushing unit.

Preferably also,the separating chamber has a hot gas supply line. In operation, the material in the separating chamber is dried by hot gas supplied thereto and is separated according to particle size.

The installation may include a feed shaft which is located upstream of the preliminary crushing unit and has a hot gas supply line.

By way of example, an embodiment ofthe invention is described below with reference to the accompany ing drawing which is a diagrammatic illustration of a grinding and drying installation.

The installation shown in the drawing has a preliminary crushing unit 1 which is charged with raw material, and a grinding mill 2 (in the form of a tube mill through which hot has flows) downstream thereof. The discharge line 3 ofthetube mill leads a separator4, the grit return line5 which is connected to thefeed side ofthetube mill 2.

The preliminary crushing unit 1 of of bottomless construction and is connected via a separating chamber 6 to the feed side of the tube mill 2, the separating chamber6 also being connected via a line 7, to the discharge line 3 of the tube mill 2. A grate 8 is provided in the preliminary crushing unit 1 to ensurethatthe particle size ofthe material removed from the crushing unit is limited.

The separating chamber 6 has a hot gas supply line 9, and a feed shaft 10, located upstream of the preliminary crushing unit 1 to supply raw material thereto, also has its own hot gas supply pipe 11.

The raw material to be processed is fed into the shaft 10 ata supply point 12: this can be effected in a manner known perse, forexample using swinging gates. The feed shaft 10 can be provided with baffles, known perse, for extending the dwell time of the raw material in this zone. In addition, air-valve members 13, 14are provided downstream ofthe separating chamber6 and in the grit return line 5 atthe points of connection to the feed side of the tube mill 2.

Forthesake of completeness,the drawing also shows a cyclone 15 for separating offthe fine material from the separator and, connected to the cyclone, a fan 16 and a cleaning arrangement 17 downstream thereof. A mixing chamber 18 is also connected downstream of the fan, in which gas which is being recirculated is mixed with fresh hot gas entering the mixing chamber art 19.

The path of the gas within the installation is indicated in the drawing: from the mixing chamber 18, a partial stream is supplied viathe hot gas supply pipe 11 (and any optional control members therein) to the feed shaft 10; a further partial stream is supplied via the hot gas supply line 9to the separating chamber 6; athird partial stream is supplied viaa linetothetube mill 2, and the final remaining partial stream circumvents the tube mill 2, parallel thereto, and is used as an auxiliary supplyforthe discharge line 3 ofthe tube mill 2, which line leads to the separator 4.

The supply of hot gas via pipe 11 to the feed shaft 10 is an advantageousfeature particularly if the raw material hasa high moisture content or in general tends to stick together: without this hot gas supply, the grate 8 at the bottom of the crushing unit can not be used with raw material of this nature. The hot gas supply via line Sto the separating chamber 6 enables the raw material which has undergine preliminary crushing to be dried and also to be separated according to particle size. This separation is affected especially bythe speed and the amount of the hot gas supplied via line and makes it possible for very fine particles ofthe desired final sizeto be removed directly atthis point, via the transport line 7 to the separator 4.

Claims (10)

1. A grinding installation comprising a preliminary crushing unit for receiving raw material and a grinder downstream thereofthe discharge side of which leads to a separator, in which the crushing unit is connected to the feed side ofthe grinder via a separating chamberwhich is also connected to the discharge side of the grinder.

2. A grinding and drying installation comprising a preliminary crushing unit for receiving raw material and a grinder downstream thereof through which hot gas flows and the discharge side of which leads to a separator having a return line back to the feed side of the grinder, in which the crushing unit is connected to the feed side ofthe grinder via a separating chamber which is also connected to the discharge side of the grinder.

3. An installation according to claim 1 or claim 2, in which the preliminary crushing unit is equipped with a grid for limiting the particle size of material leaving the crushing unit.

4. An installation according to any one of the preceding claims in which the separating chamber has a hot gas supply line.

5. An installation according to any one of the preceding claims, in which a feed shaft is located upstream of the preliminarycrushing unit and hasa hot gas supply line.

6. A method of operating an installation according to claim 4, in which the material in the separating chamber is dried by hot gas supplied thereto and is separated according to particle size.

7. A method according to claim 6, in which the separation according to particle size is effected by the amount and speed of the hot gas supplied.

8. A method according to claim 7 in which particles of a desired size are removed from the separating chamberto the discharge side of the grinder.

9. A method according to any one of claims 6to 8, substantially as herein described.

10. Agrinding and drying installation substantially as described herein with reference to, and as shown in, the accompanying drawing.