| JP2011161306 | BIOMASS MILL |
| JP06343888 | VERTICAL PULVERIZER |
| JP07008817 | ROLLER MILL |
HORNING, Bent (Kystvejen 17, Hornbaek, DK-3100, DK)
HELM, Alexander (Bakkevej 5, Allerod, DK-3450, DK)
HORNING, Bent (Kystvejen 17, Hornbaek, DK-3100, DK)
| Claims [Claim 1] 1. A method for controlling the material feed to a roller mill for continuous grinding of particulate material, such as cement raw materials, cement clinker and similar materials, which roller mill comprises a substantially horizontal grinding table (1) and a number of rollers (2) operating interactively therewith, said rollers rotating about separate roller shafts (3) being connected to a vertical central shaft (4) via a hinged connection (5) allowing a free circular movement of the roller up and down in a plane comprising the centreline (6) of the roller shaft, where material to be ground is continuously fed to the roller mill and ground material is continuously diverted from the roller mill, characterized in that an angle ( α ) between at least one of the roller shaft centrelines (6) and a reference line (18) is measured and used as input signal for a control circuit for controlling the material feed. [Claim 2] 2. A method according to claim 1, characterized in that the angles between several or all of the roller shaft centrelines (6) and one or several reference lines (18) are measured, and in that an average value of the angles is calculated and used as an input signal for a control circuit for controlling the material feed. [Claim 3] 3. A method according to claim 1 or 2, characterized in that the centreline through the vertical central shaft (4) is used as reference line (18). [Claim 4] 4. A method according to claim 1, characterized in that the angle between a roller shaft centreline (6) and a reference line (18) is measured using a displacement transducer. [Claim 5] 5. A roller mill for carrying out a method for controlling the material feed comprising a substantially horizontal grinding table (1) and a number of rollers operating interactively therewith, said rollers rotating about separate roller shafts (3) being connected to a vertical central shaft (4) via a hinged connection (5), allowing a free circular movement of the roller up and down in a plane comprising the centreline (6) of the roller shaft, means (7) for continuous feeding of material to be ground to the roller mill and means (12) for continuous diversion of ground material from the roller mill, characterized in that it comprises means (17) for measuring an angle ( α ) between at least one of the roller shaft centrelines (6) and a reference line (18) and means (19) for using the measured angle as an input signal for a control circuit for controlling the material feed. |
Title of Invention: METHOD FOR CONTROLLING THE MATERIAL FEED TO A ROLLER MILL AND SUCH SIMILAR
MILLS
[1] The present invention relates to a method for controlling the material feed to a roller mill for continuous grinding of particulate material, such as cement raw materials, cement clinker and similar materials, which roller mill comprises a substantially horizontal grinding table and a number of rollers operating interactively therewith, said rollers rotating about separate roller shafts being connected to a vertical central shaft via a hinged connection allowing a free circular movement of the roller up and down in a plane comprising the centreline of the roller shaft, where material to be ground is continuously fed to the roller mill and ground material is continuously diverted from the roller mill. The invention also relates to a roller mill for carrying out the method.
[2] A roller mill of the aforementioned kind is known e.g. from published patent application DE No. 2.061.422. This known mill is configured for rotation of the roller set with the grinding table at standstill, and moreover it is of the portion type which means that it cannot be operated continuously, instead being operated in portions involving charging, processing and emptying of one material portion at a time. However, continuous grinding of particulate material is known from other roller mills which comprise means for continuous feeding of material to the roller mill, and means for continuous diversion of ground material from the roller mill, as for example by means of an air stream being introduced via a nozzle ring. It is a common characteristic of these roller mills with continuous grinding that they need some form of control over the material feed to the mill so as to ensure that at all times the mill contains that for the grinding efficiency optimum amount of material, and that they are neither overfilled nor emptied in response to normally occurring variations in the grindability and other properties of the supplied material. For these known mills the control of the material feed is typically based e.g. on the pressure loss across the nozzle ring or the power consumption of the mill motor being used as an input signal for a control circuit. These control methods can be used despite their inherent disadvantages in that they are time-delayed, resulting in delayed control, and in that they are indirect and influenced by other operating parameters such as the circulation factor across the separator, the air consumption or other factors.
[3] It is the objective of the present invention to provide a method for controlling the material feed to a roller mill for continuous grinding of particulate material such as a roller mill whereby the aforementioned advantages are eliminated. [4] This is obtained by a method of the kind mentioned in the introduction, and being characterized in that an angle between at least one of the roller shaft centrelines and a reference line is measured and used as input signal for a control circuit for controlling the material feed.
[5] Hereby is obtained a fast and adequate control of the material feed which takes due account of the immediate operating environment in the roller mill in terms of material charge, ie the amount of material present in the roller mill at any given time. This is due to the fact that variations in the angular positions of the roller shafts will provide prompt and significant indication of any tendency towards overfilling or emptying of the mill.
[6] In roller mills of the mentioned kind with several rollers hinged independently of one another the rollers will during the operation of the mill move up and down independently of one another in response to variations in the grinding bed thickness, frequently giving rise to variations in the mutual angular positions of the roller shafts. However, the mean values for the angular positions of the roller shafts will normally lie within a very narrow range and, therefore, it may suffice to use only the angular position of one of the roller shafts as an input signal for the material control circuit. However, in certain cases it may be advantageous to use an average value of the angular positions of several or all the roller shafts, and in this scenario the angles between several or all of the roller shaft centrelines and one or several reference lines can be measured, and an average value of the angles be calculated and used as an input signal for a control circuit for controlling the material feed.
[7] In order to have just one reference line, it may be advantageous to use the centreline through the vertical central shaft.
[8] In principle, the angle between a roller shaft centreline and a reference line can be measured using any suitable measuring device capable of delivering reliable measurements inside a mill subject to hostile conditions in terms of temperatures and dust levels. As an example of a suitable device a displacement transducer can be mentioned.
[9] The implementation of the method according to the present invention will require a control unit which on one side is connected to the measuring device in order to receive an input signal while on the other side it is connected to the feed system for releasing an output signal to the latter.
[10] During start-up of the mill, the mill is run up to operation on the basis of a specific setpoint parameter being characterized by an ideal angel, after which the method according to the invention is started and takes over the control of mill feed. If the measured angle decreases, the control unit will release a signal to the feed system with instructions to reduce the material feed in order to avoid overfilling of the mill and vice versa. [11] The roller mill for carrying out the method for controlling the material feed comprises a substantially horizontal grinding table and a number of rollers operating interactively therewith, said rollers rotating about separate roller shafts being connected to a vertical central shaft via a hinged connection allowing a free circular movement of the roller up and down in a plane comprising the centreline of the roller shaft, means for continuous feeding of material to be ground to the roller mill and means for continuous diversion of ground material from the roller mill, and being characterized in that it comprises means for measuring an angle between at least one of the roller shaft centrelines and a reference line and means for using the measured angle as an input signal for a control circuit for controlling the material feed.
[12] The invention will now be explained in further details with reference to the drawing, the only figure of which shows a roller mill for carrying out the method according to the invention.
[13] In the figure is seen a roller mill which comprises a horizontal grinding table 1 and a number of rollers 2 rotating about separate roller shafts 3 being connected to a vertical central shaft 4 via a hinged connection 5 allowing a free circular movement of the roller up and down in a plane comprising the centreline 6 of the roller shaft. The roller mill further comprises means 7 in the form of a material container 8, an extraction band 9 and a feed duct 10 with a feed sluice 11 for continuous feeding material to be ground to the roller mill as well as means in the form of a not shown fan and a nozzle ring 12 for continuous diversion of ground material from the roller mill by use of gases.
[14] The shown mill further comprises a drive system 13 for rotating the grinding table 1 and/or the central shaft 4, and hence the rollers 2, as well as a separator 14 for sorting the ground material being diverted from the grinding zone into a fine fraction which suspended in gas stream is diverted via an outlet 15 and into a coarse fraction which via a hopper 16 is recirculated to the grinding table 2 for further grinding.
[15] In order to obtain fast and accurate control of the material feed to the roller mill with due account being taken of the immediate operating environment in the roller mill in terms of material charge, the roller mill according to the invention comprises means in the form of a measuring device 17 for measuring an angle α between a roller shaft centreline 6 and a reference line 18. The measuring device 17 is connected with means in the form of a control unit 19 which is capable of using the measured angle as an input signal for producing an output signal which is released to the feed system 7 for controlling the material feed at the given point in time.
[16] When the roller mill is in operation, the control unit 19 will release a signal, based on the signal received from the measuring device 17, to the feed system 7 with instructions to maintain, reduce or increase the material feed. If the measured angle decreases, the control unit 19 will release a signal to the feed system 7 to ensure reduction of the material feed 7 in order to prevent excessive filling the mill and vice versa.