AU771192B2

AU771192B2 - Method and apparatus for grinding of particulate material

Info

Publication number: AU771192B2
Application number: AU23915/01A
Authority: AU
Inventors: Jorn Touborg
Original assignee: FLSmidth and Co AS
Current assignee: FLSmidth and Co AS
Priority date: 2000-01-28
Filing date: 2001-01-19
Publication date: 2004-03-18
Anticipated expiration: 2021-01-19
Also published as: ES2307582T3; CZ20022579A3; ZA200204389B; PT1261431E; CA2397796A1; CA2397796C; EP1261431A1; DK1261431T3; MXPA02007282A; KR20020062776A; EP1261431B1; CZ299850B6; PL356139A1; AU2391501A; DE60134307D1; WO2001054818A1; KR100729026B1; TW466136B; JP2003520676A; CN1139431C

Abstract

A description is provided of a method as well as an apparatus for grinding particulate material, such as cement raw materials, cement clinker or similar materials, in a roller mill (1) by subjecting the material to pressing action in a zone (13) between opposite, rotating surfaces where the material is directed to the grinding zone via a feed shaft (11). The method is peculiar in that the material in the feed shaft (11) is accelerated through the action of gravity to a desired velocity without involving essential air admixture, whereas the apparatus is peculiar in that the feed shaft is essentially of a vertical configuration, with a downwardly reduced cross-section, where the reduction of the shaft´s cross-sectional circumference per height unit is downwardly decreasing.The described configuration of the feed shaft has, surprisingly, proved that the material over a given height of fall may attain high velocities and that this is achievable without involving admixture of air into the material. It has thus been established that it will be possible for the material to attain velocities which are close to the velocity achievable in connection with the free fall of individual particles.

Description

METHOD AND APPARATUS FOR GRINDING OF PARTICULATE MATERIAL The present invention relates to an apparatus for grinding of particulate material such as cement raw materials, cement clinker or similar materials, in a roller mill, such as a roller press, ring-roller mill, vertical mill or a similar unit.

In recent years, developments in grinding technology have primarily been devoted to improving the cost efficiency of the grinding process. In this context, the primary focus has been to improve the operating economy of the grinding process and to reduce the capital cost of the grinding machines relative to their capacity ratings. A method widely used to lower the investments costs involves uprating of the operating speed of a machine, and hence its productivity. Needless to say, the operating speed of a machine can only be increased up to a certain point, and, furthermore, it is a recognized fact that problems are likely to occur in connection with the operating of, for example, a roller press if the peripheral velocity of the rollers is increased arbitrarily.

Such operating problems may be ascribable to many different causes. One explanation could be the difficulty of achieving S 25 an acceleration of the material which is to be ground in the roller press to an extent which corresponds to the peripheral velocity of the rollers. Such acceleration of the material is usually achieved by means of the rollers by physical contact with the latter and/or through the action of gravity. However, 30 the capability of the rollers is restricted to a very short range of operation, thereby severely limiting the rate of acceleration, and in a shaft the force of gravity will either be counteracted by the friction of the material against the shaft and/or the friction present in the material itself.

o: W:AnaryNODELETE\23915-01l.doc 2 Also, acceleration accomplished in a traditional shaft will also entail significant admixture of air, which is undesirable, and this will also adversely affect the grinding process. Use of a vertical shaft with a circular or rectangular crosssection and with an identical cross-sectional area across the entire length will enable the force of gravity to accelerate the material to a high velocity, but in this scenario there will be a simultaneous increase in the distance between the particles, thereby decreasing the density of the material and involving air admixture. By using a shaft of a pyramidal or conical configuration, it will be possible to maintain the distance between the particles, but in a shaft of this type the material will be influenced by forces of friction which are so substantial that the terminal velocities attainable are quite small. In such ordinary shafts the cross-sectional circumference is a linearly decreasing function of the height.

The reduction of the cross-sectional circumference per height unit thus remains constant for these shafts.

It is the objective of the present invention to provide a plant for remedying the aforementioned deficiencies.

According to one aspect, the present invention provides an apparatus for grinding of particulate material such as cement 25 raw materials, cement clinker or similar materials, which !apparatus includes a roller mill as well as a shaft for feeding particulate material to the grinding zone of the roller mill, the shaft being of a substantially vertical configuration and with a downwardly reduced cross-section wherein the reduction :0.60, 00 30 of the shaft's cross-sectional circumference per height unit is downwardly decreasing.

eoe• The described configuration of the feed shaft has, surprisingly, proved that the material over a given height W:may\NODELETE\23915-0l.doc WO 01/54818 PCT/IB01/00057 3 of fall may attain high velocities, and that this is feasible without involving admixture of air into the material. It has thus been established that it will be possible for the material- to attain velocities which are close to the velocity achievable in connection with the free fall of individual particles.

The material can be accelerated to a velocity of more than m/s. However, it is preferred that the material be accelerated to a velocity of more than S m/s, and preferably of more than 10 m/s.

An example of the cross-sectional characteristics according to the invention is known from the form of a free-falling water jet, for example from a slow-running water tap. At the top, at the outlet of the water tap, the water flow rate is quite small, with the width of the water jet corresponding roughly to the outlet. Further downstream of the jet the force of gravity has increased the water flow rate, but since the water flow throughout the jet is the same, and since the density throughout the jet is also the same, this means that the cross-section of the water jet is smaller. In this way the water jet will attain an almost hyperbolic shape and the characteristics of the cross-sectional area as a function of the height of fall can be expressed by means of the formula: where 2gh A is the cross-sectional area V is the volume flow g is the gravity acceleration h is the height of fall A is a correction element which describes the friction in the material, assuming for water a small value which is close to C WO 01/54818 PCT/IB01/00057 4 The water jet must be assumed to roughly circular and, therefore, its circumference can be calculated on the basis of the formula: O= rD=n where V 7 .J2gh 0 is the circumference D is the diameter of the water jet As it appears from the aforementioned formula, the circumference is proportional not to the height of fall but to the height of fall to power +U.

According to the invention it is preferred that the shaft be configured so that its cross-sectional area as a function of the fall of height is essentially as defined in the formula above. To make allowance for the friction which occurs when feeding particulate material via a shaft according to the invention, the correction element A must be within the range 0 and 0.2, preferably lower than 0.1.

The shaft may, for example, be made up of a number of pyramidal or conical sections so that the reduction of the cross-sectional circumference of the shaft exhibits a gradual, downwardly decreasing trend. To ensure that the shape of such a shaft does not deviate too much from the formula indicated above, it is preferred that the number of sections incorporated is at least 3, but preferably at least 5, and most preferably at least However, it is preferred that the reduction of the crosssectional circumference of the shaft exhibits a continuous downwardly decrease, and that for example the shaft is of a trumpet-shaped configuration.

4' .*n WO 01/54818 PCT/IB01/00057 In principle, it will be possible to use the shaft according to the invention for conveying any particulate material from one level to a lower level by the action of gravity, and for this purpose the shaft should be of a substantially vertical ccnfiguration, with a downwardly reduced cross-section where the reduction of the cross-sectional circumference of the shaft is downwardly decreasing.

The invention will be explained in further details in the following with reference being made to the drawing, which is diagrammatical, and where Fig. 1 shows a roller press installation comprising a feed shaft according to the invention.

In Fig. 1 is seen a roller press installation comprising a roller press 1 with two oppositely rotating rollers 3 and During the operation of the roller press, the material to be ground is fed from a bin 7 via a feed conveyor 9 and a feed shaft 11 to a grinding zone 13 between the rollers 3 and According to the invention the depicted shaft is formed with a downwardly reduced cross-section in such a way that the reduction of the shaft's cross-sectional circumference per height unit is also downwardly decreasing. Ideally the shaft is formed with a downwardly decreasing cross-section which is inversely proportional to the steadily downwardly increasing velocity of the material due to the gravityinduced acceleration. Hence it will be possible for the material to achieve a velocity close to the velocity of a free fall without admixture of air, allowing the roller press to be operated at higher roller velocities, thereby increasing its rate of production.

The applicant filing the present patent application has conducted tests with a shaft configured in accordance with the aforementioned guidelines, with a final cross section of 0.1 x 0.1 metres and a heiaht of 5 metres, and has recorded WO 01/54818 PCT/IBOI/00057 a material- velocity which is close to io rn/s without air admixture.

Claims

2. An apparatus according to claim 1 the cross-sectional area of the shaft as a function of the height of fall is in accordance with the formula V A (1+A) ,2gh where A is the cross-sectional area V is the volume flow g is the gravity acceleration h is the height of fall 20 A is within the range 0 and 0.2, preferably lower than 0.1.
3. An apparatus according to claim 1 wherein the shaft is made up of at least 3 pyramidal or conical sections.
4. An apparatus according to claim 1 or 2 wherein the reduction of the cross-sectional circumference of the shaft S•exhibits a continuous downwardly decrease.
5. An apparatus according to claim 4 wherein the shaft is of a trumpet-shaped configuration. W:maUANODELETE23915-1O.doe 8
6. An apparatus for grinding of particulate material substantially as herein described with reference to the accompanying drawing figure. DATED: 27 November 2003 PHILLIPS ORMONDE FITZPATRICK Patent Attorneys for: F.L. SMIDTH CO. A/S *e W:\mar~nODELETE\23915-01doc