WO1998045042A1

WO1998045042A1 - Process for grinding temperature-sensitive products and grinding installation for carrying out this process

Info

Publication number: WO1998045042A1
Application number: PCT/EP1998/001957
Authority: WO
Inventors: Gerhard KÄPPELER; Wolfgang Peukert; Joachim Galk; Peter Hoffmann; Jörg KRAHNEN
Original assignee: Hosokawa Mikropul Gesellschaft Für Mahl- Und Staubtechnik Mbh
Priority date: 1997-04-04
Filing date: 1998-04-03
Publication date: 1998-10-15
Also published as: DE19714075A1

Abstract

A process and device are disclosed for grinding temperature-sensitive products cooled with cold gas, preferably gaseous or liquid nitrogen. The products are ground in a grinder (11) with several superimposed grinding zones (17, 18, 19). The products are introduced through the top of the grinder (11) and exit through the bottom of the grinder (11).

Description

Process for grinding temperature-sensitive products and suitable for carrying out this process

Grinding plant

The invention relates to a method for grinding temperature-sensitive products, in which the product is cooled with cold gases, preferably with gaseous or liquid nitrogen. The invention also relates to a grinding plant suitable for carrying out this method.

In currently known mills used in so-called cold grinding, there is no defined stress on the product to be reduced. The grinding result is often only controlled via the grinding intensity and the dwell time. Long residence times in the mill are particularly disadvantageous for temperature-sensitive products. Impairment of product quality can only be avoided by using relatively large amounts of cold gases, especially nitrogen.

The object of the invention is not only to achieve an improved grinding result in the cold grinding of products, but also to reduce the operating costs.

This object is achieved in a method of the type mentioned at the outset in that the grinding is carried out in a mill with a plurality of grinding stages lying one above the other and in that the product is fed into the mill from above is abandoned and leaves the mill below. Because the product is crushed in several stages, a defined particle load is achieved. The solids transport does not require any additional transport gases (eg air) when loading goods from above and delivering goods downwards. The product sediments downwards by gravity. It is no longer necessary to additionally cool relatively large air volume flows that serve to transport the product. The result is a reduction in nitrogen requirements and thus a significant reduction in operating costs.

Good product quality and economical production nowadays require very defined particle size distributions. The main reasons are the optimization of material properties and the minimization of material losses. Crushing is of great importance for the production of such particle size distributions.

The particle size distributions that arise during the comminution often do not correspond to the desired target, so that a downstream wind sighting is necessary. Its task is to determine the maximum particle size or to determine the amount of the fine fraction.

It is known to use a mill with a built-in air classifier for producing products with a defined upper grain (ACM grinding system from the applicant). The solids are crushed by an initial load when they enter the ACM classifier mill. The maximum particle size of the finished product is determined by the internal wind classification. Particles with sufficient fineness are returned to the grinding zone. Particles that are smaller than the specified target size can leave the mill. This means that the classifier not only defines the top grain, it also prevents over-grinding of finished products.

An advantage of the ACM classifier mill is that the particle size distribution is relatively narrow. It is about a power of ten. In many applications, however, a higher fines content is desirable. In addition, the energy consumption of the ACM classifier mill is comparatively high due to internal flow and pressure losses.

As a result of the multistage of the grinding plant according to the invention, several particle stresses corresponding to the number of stages take place under different conditions. The type of stress can be optimally determined for each of the stages by selecting the conditions (radius of the grinding zone, height of the grinding zone, peripheral speed, impact angle, type of grinding tools, etc.). This allows the total stress on the grinding plant to be precisely defined.

Another special feature of the mill according to the invention is its low air volume requirement. Since it is operated “downstream”, that is to say in a position in which the solids are transported by gravity, its air volume requirement is practically zero. As a result of the low air requirement, the use of relatively small filters and blowers is sufficient a significant reduction in operating costs can be achieved with cold grinding.

The content of US-A-1 656756 also belongs to the prior art. It discloses a three-stage mill which is interspersed with the product (preferably ore) from top to bottom. The cited document does not contain any indications of modifying a mill of this type for cold grinding.

Further advantages and details of the invention will be explained on the basis of exemplary embodiments schematically illustrated in FIGS. 1 to 15. Show it:

FIGS. 1 and 2 flow diagrams of grinding plants which are suitable for the cold grinding according to the invention,

FIGS. 3 to 5 mills with several grinding stages, the diameter of which increases discontinuously,

FIGS. 6 to 10 different designs for grinding tools,

Figures 1 1 to 1 3 different arrangements and bearings of the

Mill as well Figures 14 and 15 versions with different designs

Solids supply.

The solid to be comminuted is located in a bunker 1 in the grinding plants according to the process flow diagrams (FIGS. 1 and 2). It is conveyed into the mill 11 via a screw feeder 2 and a rotary valve 3. The screw feeder 2 is equipped in a known manner with a cooling screw. Liquid nitrogen, as a coolant, is preferably applied directly to the product and to the screw. The cooled product to be comminuted reaches the mill 11 from above via the rotary valve 3. During the stressing of the product in the mill 11 there is a risk, despite previous cooling, that the product and the mill heat up to impermissibly high temperatures. To avoid this, one or - as required - several grinding zones of the mill 1 1 coolant (also liquid nitrogen, arrow 4) can be added.

The crushed product leaves the mill 1 1 through an outlet located in its lower area. Another cellular wheel lock 5 can be connected directly to the outlet, so that the product can then be bagged (FIG. 1). In the embodiment according to FIG. 2, a filter process follows the comminution process. For this purpose, the product is fed to the filter 8 via the line 6 with the aid of a conveying gas, preferably air, let in at 7. The transport air leaves the filter 8 via the fan 9. The outlet of the filter 8 is followed in a known manner by a rotary valve 10. Since the solid passes through the mill 1 1 “downstream”, it can be operated without transport air. Even if air is supplied to one or more grinding stages to influence the grinding result and the grinding system is operated according to flow diagram 2, the fact that transport air is omitted , a significantly smaller filter and a smaller blower can be used, which means that both acquisition and operating costs are reduced compared to the prior art.

In the other figures, the mill according to the invention is denoted by 1 1, its rotor by 12 (or 12, 13), its rotor axis by 14 and its stator or mill housing by 1 5.

In the exemplary embodiments according to FIGS. 3 to 5, the multi-stage design of the mill 11 is achieved in that the rotor 12 (or 12, 13) and stator 15 are of stepped design. The rotor axes 14 are arranged vertically. The solids supply 16 is on the top. As a result of the multi-stage arrangement of the rotor 12 (or 12, 13) and the stator 15, there are several annular gap-shaped grinding zones 17, 18, 19 (or 17 to 20 in FIG. 4), the geometry of which can be adapted to the grinding result desired in each case. In all of the exemplary embodiments according to FIGS. 3 to 5, the radius of the grinding zones increases with the direction of flow of the product. Grinding tools, possibly designed differently in the different grinding zones, are not shown in detail. During operation, the solids fed centrally at 1 6 are accelerated radially outwards and reach the first grinding zone 1 7, where the first stress takes place. Further comminution takes place in the subsequent grinding zones, in which the solid is used with higher energy due to the increase in the radius of the grinding zones.

In the exemplary embodiment according to FIG. 5, rotor and stator grinding tools are shown schematically and designated 21 and 22, respectively. The product discharge located on the circumference of the last grinding zone 9 is shown and designated 23. FIG. 5 also shows that the rotor 12 is supported by the shaft 24 in bearings 25 located below the mill housing 15. The drive takes place via the belt 26.

In the embodiments according to FIGS. 3 to 5, the solids supply takes place centrally from above. Immediately below this is the end face of the rotor 12 or the rotor section of the upper annular gap-shaped grinding zone 17. In FIG. 5 it is indicated schematically that this end face of the rotor 12 is equipped with radially directed product guide elements 27. Due to these star-shaped elements, the product is thrown outwards (centrifugal wheel principle). There is a first particle stress by impacting the product on the outer grinding track, through which coarse particles are crushed. Further comminution takes place in the lower gap below. The first stage is followed by two more, which also enable a very targeted impact load. Due to the increase in radius, the solid is fed a defined, larger comminution energy per stage. In the exemplary embodiment according to FIG. 4, the rotor consists of two rotor sections 12, 13 which can be operated at different speeds. This means that the energy with which the solid is used in the grinding zones can be adjusted. For example, the lower stress energy due to the smaller diameter of the first grinding zones can be increased by increasing the speed of the upper section 12 of the rotor. On the other hand, the grinding result can be improved in terms of its grain size by high speeds of the lower section 13 of the rotor.

FIGS. 6 to 10 show examples of grinding tools that can be used in the grinding zones. The designs according to FIGS. 6 (blow bars 32) and 7 (profiled surfaces 33) are toothless, the designs according to FIGS. 8 (pins 34), 9 (gable roof-shaped impact elements 35) and 10 (knives 36) interlocking solutions. Toothed solutions have proven to be particularly advantageous in the context of the invention.

Figures 1 1 to 13 show different arrangements and bearings of the modular mill according to the invention and its drive 37. A flying bearing (two bearings 38, 39 on one side, together with the drive 37) is shown in Figure 13, also Figure 5 (bearing 25). It is useful to keep one end of the mill freely accessible. Other solutions in which the mill 1 is supported on both sides are shown in FIGS. 1 1 and 12. Figures 14 and 15 show different ways of feeding solids. These designs do not require air during operation. At 6, the solids are fed either on the principle of the centrifugal wheel (FIG. 14) or via a distributor cone 31. The product discharge 23 is arranged either radially or below the last grinding zone.

Claims

Expectations

1) Process for grinding temperature-sensitive products, in which the product is cooled with cold gases, preferably with gaseous or liquid nitrogen, characterized in that the grinding in a mill (II) with a plurality of grinding zones (17, 18, 19) one above the other is carried out and that the product is fed into the mill (11) from above and leaves the mill (11) from below.

2) Method according to claim 1, characterized in that the product is cooled with gaseous, preferably liquid nitrogen before and / or during the grinding process.

3) Method according to claim 1 or 2, characterized in that the mill (11) is operated without transport gases.

4) Method according to claim 1, 2 or 3, characterized in that the particle loading is initially effected in that the product is thrown onto an impact surface (17) according to the centrifugal wheel principle, and that the further comminution in the annular gap-shaped grinding zones (17, 18 , 19) is brought about, which are equipped with rotating and stationary grinding tools (32 to 36). 5) Method according to claim 4, characterized in that the peripheral speed of the grinding tools rotating in the grinding zones (17, 18, 19) increases from grinding zone to grinding zone.

6) Method according to one of claims 1 to 5, characterized in that a filtering process follows the grinding of the product.

7) Device for carrying out a method for grinding temperature-sensitive products, in which the product is cooled with cold, preferably with gaseous or liquid nitrogen, and in which the grinding is carried out in a mill (11) with a plurality of grinding zones (17, 18, 19) one above the other ) is carried out, the product being fed into the mill (11) from above and leaving the mill (11) at the bottom, characterized in that the mill (11) is constructed in several stages so that the grinding stages are annular gap-shaped grinding zones (17, 18, 19) ) in which there are rotating and stationary grinding tools (32 to 36), and that the radius of the grinding zones (17, 18, 19) increases from top to bottom.

8) Device according to claim 7, characterized in that the grinding stages formed by annular gap-shaped grinding zones (17, 18, 19) is preceded by a further grinding stage (27, 17) which is designed in the manner of an impact mill. 9) Device according to claim 8, characterized in that the central end of the rotor (12) facing the central product feed (16) is equipped with star-shaped product guide elements.

10) Device according to claim 7, 8 or 9, characterized in that the rotor has several, preferably two sections (12, 13) which can be driven at different speeds.

1 1) Device according to one of claims 7 to 10, characterized in that there are toothed grinding tools (34, 35, 36) in the grinding zones (17, 18, 19).

12) Device according to one of claims 7 to 1 1, characterized in that the rotor (12 or 12, 13) is overhung and that the bearings (25,38,39) on the outlet side of the mill (1 1) are located.

13) Device according to one of claims 7 to 12, characterized in that three or four annular gap-shaped grinding zones (17, 1 8, 19) are present.