EP2376229A1

EP2376229A1 - Pressurized impact mill

Info

Publication number: EP2376229A1
Application number: EP09838180A
Authority: EP
Inventors: Pentti Virtanen
Original assignee: Fractivator Oy
Current assignee: Fractivator Oy
Priority date: 2009-01-14
Filing date: 2009-12-21
Publication date: 2011-10-19
Also published as: WO2010081933A1; FI124439B; FI20090011A0; EP2376229A4; FI20090011A

Abstract

The invention concerns a method for maintaining of an overpressure in an impact mill during treatment of material to be carried out therein, and an impact mill that can be pressurized. The method is characterized in that the material components needed are fed into the rotor space by a feeding arrangement enduring pressure differences; the material exiting from the rotor space is discharged by a discharge arrangement enduring pressure differences, and the target pressure in the rotor space is secured by a pressurized gasket fluid, the pressure of which is kept at least the same as the target pressure of the rotor space, or preferably slightly higher than the target pressure of the rotor space. The gasket fluid is led beneath a gasket located between the rotor shafts, and/or beneath a gasket located between the rotor shaft and a support adjacent thereto.

Description

PRESSURIZED IMPACT MILL

This invention relates to a process for maintaining increased pressure in an impact mill during the treating of material therein and an impact mill that can be pressurized, as defined in the preambles of the independent claims hereinafter.

The impact mill is an apparatus comprising two rotor discs mounted on coaxial shafts, briefly rotors. Alternatively, one of the rotors is replaced by a stator. Onto the rotors are attached blades, parallel with the shafts, where said blades are arranged in blade rings, located within each other, wherein every other ring is located on the upper rotor and every other on the lower rotor (or stator). The rotors can be rotated in opposite directions or in the same direction with different speeds. This means that the blade rings do not touch each other or the second rotor. A housing is normally fitted around the rotors.

Impact mills have found versatile uses and they are described in many patent publications for different uses. As examples can be mentioned cleaning of gases and liquids (FI 98052), slurrying of materials into a liquid (WO 96/18454), defibrating of fibre-containing materials (WO 98/29596), treatment of reject from a paper mill (WO 99/54045), treatment of reject streams of fillers (WO 2001/038632), removing of printing ink from fibre material (WO 2003/031717), pre-treatment of organic wastes (WO 2004/062808) and processing of digestion sludge into useful products (WO 2005/121033). The Finnish patent FI 117711 discloses an impact mill equipped with a discharge screw conveyor. The patent publication WO 2008/122961 discloses an arrangement for lubrication of the bearings of the shafts arranged within each other in an impact mill.

OBJECT AND SUMMARY OF THE INVENTION

The object of the invention is to achieve an impact mill that can be pressurized and a method for maintaining increased pressure during treating of material therein. The target pressure in the impact mill is at least 0.1 bar overpressure, however, preferably at least 0.2 bar, most preferably about 0.5 bar overpressure.

The use of increased pressure in the apparatus enables treating of materials in water or steam phase at temperatures higher than 100 ⁰C. An increased temperature increases both chemical and physical reactions so that the reaction speed doubles for every increase of 10 degrees.

The method according to the invention is characterized in that - the material components needed are fed into the rotor space by a feeding arrangement enduring pressure differences, and

- the material exiting from the rotor space is discharged by a discharge arrangement enduring pressure differences, and

- the target pressure in the rotor space is secured by a gasket fluid, the pressure of which is kept at least the same as the target pressure of the rotor space, or preferably slightly higher than the target pressure of the rotor space, and which gasket fluid is led beneath a gasket located between the rotor shafts, and/or beneath a gasket located between the rotor shaft and the support adjacent thereto.

The impact mill according to the invention is characterized in that

- the feeding opening of the rotor space is equipped with a feeding arrangement enduring pressure differences, and

- the discharge opening of the rotor space is equipped with a discharge arrangement enduring pressure differences, and - into the rotor shaft and/or into the support of the rotor shaft is arranged a channel through which a gasket fluid, securing the target pressure of the rotor space, can be led beneath a gasket located between the rotor shafts, and/or beneath a gasket located between the rotor shaft and the support adjacent thereto.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows as a vertical section the impact mill, with rotor shafts mounted in bearings to each other and equipped with a flow route for the gasket fluid, in one embodiment of the invention.

Figure 2 shows enlarged the portion located beneath the rotor space shown in figure 1.

Figure 3 shows the apparatus of figure 1, where the flow route for the gasket fluid is changed.

Figure 4 shows the apparatus according to the invention, where one rotor is replaced with a stator.

Figure 5 shows the apparatus according to the invention, where the rotor shafts, located within each other, are mounted on bearings on a stationary support located between the shafts.

Figure 6 shows a feeding arrangement enduring pressure differences and a discharge arrangement enduring pressure differences, mounted in connection with the rotor space of the impact mill.

Figure 7 shows the apparatus according to figure 6, intended for non-continuous material treatment.

DETAILED DESCRIPTION OF THE INVENTION

For continuous processes, the wording "feeding arrangement enduring pressure differences" means that an arrangement for feeding from a lower pressure to a higher pressure of solid materials to be treated is mounted on the feeding opening or on a pressurized chamber connected to the feeding opening. As examples can be mentioned a feeding screw conveyor or a closing feeder. If fluids (liquids or gases) shall be fed into the rotor space, then "feeding arrangement enduring pressure differences" means a nozzle or valve, for example a pressure reducing valve for high-pressure steam, an ejector etc. which is mounted on the feeding opening or on a pressurized chamber connected to the feeding opening. For batch processes, the wording "feeding arrangement enduring pressure differences" means that a pressurized chamber is connected to the feeding opening. The material components needed are added into this chamber at atmospheric pressure. After the addition, the pressure is raised to the target pressure of the rotor space and the impact mill is started.

For continuous processes, the wording "discharge arrangement enduring pressure differences" means that an arrangement for discharging from a higher pressure to a lower pressure of materials is mounted on the discharge opening or on a pressurized chamber connected to the discharge opening. As examples can be mentioned a discharge screw conveyor or a closing feeder. If fluids (liquids or gases) shall be discharged from the rotor space, then "discharge arrangement enduring pressure differences" means a nozzle or valve which is mounted on the discharge opening or on a pressurized chamber connected to the discharge opening. For batch processes, the wording "discharge arrangement enduring pressure differences" means that a pressurized chamber is connected to the discharge opening. The material treated in the rotor space is collected in the pressurized chamber. After stopping of the impact mill and removal of the overpressure in the chamber, the material is discharged.

The feeding and discharge arrangements enduring pressure differences shall be such that they do not cause essential pressure reductions in the rotor space when the apparatus is operating.

The gasket fluid can be any fluid suitable for this purpose, such as a liquid, a gas, or a dispersion comprising a gas and a liquid.

The wording "rotor shaft" in the claims shall be understood to include also bodies fixed to said shaft such as rotor brackets etc. In the exemplified solutions described herein as well as in the claims below, wordings referring to direction, such as upper end, lower end, upper bearing, lower bearing etc. have been used. Such wording shall, however, not be interpreted to mean that the impact mill in operation must be in upright position. Instead, it may be inclined in different ways, for example as shown in patent publication WO 2006/123010, figure 8. The word upper shall throughout the text be interpreted to mean the end or element directed towards the rotor space, and word lower shall throughout the text be interpreted to mean the end or element directed away from the rotor space.

The solution according to the invention can also be adapted to an impact mill in which the rotor shafts, located within each other, are mounted on bearings on a stationary support located between the shafts.

If the lubricating material for the shaft or shafts is such that it can be allowed to enter into the rotor space, also the lubricating system may be connected to the pressurized rotor space.

The treatment of the material in the rotor space may be continuous or discontinuous.

The material to be treated may consist of several material components. The material components to be treated may be solid materials in the form of pieces or particles, or fluids (liquids or gases). In addition to the material components to be treated, also auxiliary components may be added, such as steam adjusted to a desired pressure. The material to be discharged may for example be finely divided solid material, or a dispersion (suspension, emulsion, aerosol).

The material treatment to be performed in the impact mill may be a physical process or a chemical process or both. As examples can be mentioned disintegrating of solid material, adsorbing of a gas or liquid to sectional surfaces created, mixing of substances of different forms to create homogeneous mixtures or solutions, dispersing of a liquid in a gas or another liquid to create an emulsion, dispersing of a solid material, consisting of small particles, in a liquid to create a suspension or into a gas to create an aerosol. The object of the process may also be the release of certain components from solid materials. As an example can be mentioned separation of lignin and other substances from cellulose fibers in defibrating of wood chips and/or fibrillating of cellulose fibers (see WO 98/29596) or removal of printing ink from fiber material (see WO 2003/031717). As examples can also be mentioned processes where starch is released from various plants such as grain, potatoes, maize, rice, or batata, and processes demanding efficient mixing where starch is further processed together with various components for various uses. As specific examples can be mentioned manufacture of coating paste and manufacture of starch gel for use in preparation of coating paste. As an example of chemical syntheses can be mentioned preparation of calcium carbonate (CaCO₃) from quenched lime (Ca(OH)₂) and carbon dioxide (CO₂).

The invention is described more in detail in figures 1 -7.

Figure 1 shows the impact mill according to the invention as a vertical section. The rotor space 1 of the impact mill comprises a housing 4 equipped with a feeding opening 2 and a discharge opening 3, and a rotor apparatus, located inside the housing, comprising a first rotor or an upper rotor 5, equipped with blades located in rings 51 and 52. The housing contains also a second rotor or a lower rotor 6, equipped with blades located in rings 61 and 62. The upper rotor 5 is via the bracket 7 joined to the shaft 8. The lower rotor 6 is via the bracket 9 joined to the shaft 10. The shafts 8 and 10 are arranged within each other so that shaft 8, the inner shaft, is located inside the hollow outer shaft 10. The shafts 8 and 10 are driven by one and the same motor (not shown) via the conic gears 11, 12 and 13. The inner shaft 8 rotates the upper rotor 5 and the outer shaft 10 rotates the lower rotor 6. The inner shaft 8 is on its upper end mounted in bearings onto the outer shaft 10 by the upper bearing 14, and on its lower end mounted on bearings onto the support by the bearing 14'. The outer shaft 10 is in turn mounted in bearings onto the support 16 by the bearings 15 and 15'. A gasket 20 is arranged between the bracket 7 of the upper rotor 5, fixed to the inner shaft 8, and the bracket 9 of the lower rotor 6, fixed to the outer shaft 10. A gasket 21 is arranged between the bracket 9 of the lower rotor 6, fixed to the outer shaft 10, and the support 16. Above the upper bearing 14 of the inner shaft 8 two gaskets 30 and 31 are arranged. Above the upper bearing 15 of the outer shaft 10 also two gaskets 40 and 41 are arranged. According to the solution according to this invention, the rotor space 1 can be made pressure-proof by mounting a pressure difference enduring feeding arrangement on the feeding opening 2 and a pressure difference enduring discharge arrangement on the discharge opening 3, respectively. These arrangements are described more in detail in figure 6. The pressure endurance of the rotor space has additionally been ensured by leading a suitable gasket fluid (for example a liquid or gas or dispersion) beneath the gaskets 20 and 21. In the solution shown in the figure, for feeding of the gasket fluid an axial channel 17 is arranged in the inner shaft. The channel 17 is in connection with the lateral channel 17'. The channel 17' is in connection with a channel 18, arranged into the bracket 9 of the lower rotor 6. The channel 18 is connected to the channel 19 made in the support 16. The gasket fluid is fed from beneath the rotor shaft 8 and it is removed from the opening of the channel 19 in the support. Alternatively, the gasket fluid can be fed through the opening of the channel 19 in the support, and it can be removed from the lower end of the channel 17 in the shaft 8. In both cases the gasket fluid touches the gaskets 20 and 21 from the underside. The pressure of the gasket fluid is preferably kept slightly higher (for example about 0.5 bar higher) than the target pressure in the rotor space. Thus the pressurized gasket fluid prevents the material components in the rotor space from escaping through the gaskets 20 and 21 and the subsequent pressure drop in the rotor space.

In the solution shown in the figure, the upper bearings 14 and 15, respectively, of the rotor shafts 8 and 10 are protected from optional influence of the gasket fluid so that on the upper side of both upper bearings has been arranged two gaskets 30, 31 and 40, 41, respectively. Further, an optional leakage of gasket fluid from the upper gasket 30 and 40 is led away via a channel 45 made into the rotor bracket 9, the shaft 10 and the support 16. In this way also the lubricating substance for the bearings 14 and 15 is prevented from entering into the rotor space 1. Figure 2 shows enlarged the portion beneath the rotor space of figure 1. The reference numbers have the same meaning as the corresponding reference numbers in figure 1.

Figure 3, in which the rotor space is not shown, demonstrates an alternative way for discharging the gasket fluid. The gasket fluid is led via channel 17 of the inner shaft 8, and channel 17' below the gasket 20. The gasket fluid is led below the gasket 21 via a channel 19 in the support 16. Contrary to figure 1, in the solution of figure 3 channels 1 T and 19 are not joined together by any channel in the rotor bracket 9. Thus the gasket fluid is discharged into the rotor space through the gaskets 20 and 21 as shown by the arrows. This solution is possible only in cases where the entrance of the gasket fluid into the rotor space is allowable in view of the material treatment to be carried out in the rotor space.

Figure 4 shows an apparatus where the lower rotor is replaced by a stator 60. The reference numbers have the same meaning as the corresponding reference numbers in figure 1.

Figure 5 shows a solution where the inner shaft 8 by bearings 14 and 14' is mounted in bearings onto support 16, which is located inside the hollow outer shaft 10. The outer shaft 10 is by the bearings 15 and 15' mounted in bearings on the support 16. A gasket 20 is arranged between the bracket 7 of the upper rotor 5 fixed to the inner shaft 8 and the bracket 9 of the lower rotor 6 fixed to the outer shaft 10. A gasket 21 is arranged between the bracket 9 of the lower rotor 6 fixed to the outer shaft 10 and the outer support 16'. Into the support 16 is made a channel 17 through which gasket fluid can be led below the gasket 20 and therefrom further via channel 18 below the gasket 21. The gasket fluid is discharged via the channel 19 made in the outer support 16'. An alternative way is of course to feed the gasket fluid in the opposite direction (i.e. from channel 19 to channel 17). By removing of the channel in the bracket 9 of the lower rotor, the gasket fluid can be discharged into the rotor space via the gaskets 20 and 21 (see figure 3).

Figure 6 shows a solution for a continuous process, where a pressure chamber, i.e. feeding chamber 71 is connected to the feeding opening 2 of the rotor space 1. Solid material is fed from atmospheric pressure to the pressure inside the feeding chamber 71 by a closing arrangement 72, which in the solution shown in the figure comprises two valves 72a and 72b, which are opened and closed in turn, and a pipe space 72c between the valves. Optional fluids (liquids, gases) can be fed separately via valves 73 and 74. The fluids to be fed are suitably already pressurized to a slightly higher pressure than the target pressure of the feeding chamber 71 and the rotor space 1 in order to compensate the pressure loss caused by the valves. Into the feeding chamber 71 is arranged a conveyor 75 for directing the solid material to the feeding opening 2. On the discharge opening 3 of the rotor space is mounted a discharge chamber 81 in which the pressure is that of the rotor space. If the material treated is in solid form it is preferably discharged by a closing discharger 82, which comprises valves 82a and 82b which can be opened and closed in turn, and a pipe space 82c between the valves. If the material to be discharged is a fluid its discharge is preferably made via the valve 83.

Figure 7 shows an alternative of figure 6, intended for batch treating of materials. The cover 76 of the feeding chamber 71 is opened and a batch of material to be treated is charged. Then the cover 76 of the feeding chamber 71 is fastened, and the discharge opening 84 of the discharge chamber 81 is closed. The pressure is increased for example by feeding steam through valve 73, the impact mill is started, the overpressure is removed and the material treated is discharged via the discharge opening 84.

If only liquid and/or gaseous components shall be treated in the impact mill, then the wall of housing 4 can cover the feeding opening 2 and the discharge opening 3. In this case a feeding valve or feeding valves 73, 74 are preferably mounted on the housing 4 at the position of the feeding opening 2. Correspondingly, a discharge valve 83 is fitted on the housing 4 at the position of the discharge opening 3.

Figures 1 , 4 and 5 show that the housing is located rather close to the rotor apparatus, which means that the rotor space is rather narrow. Alternatively, the housing could be considerably wider. In this case the housing could create a pressurized chamber into which the rotor pair (or the rotor/stator pair) is mounted. Also in apparatuses of this kind the material treating process can be continuous or batch process.

The invention is not intended to be limited to the exemplified embodiments presented above. On the contrary, the invention shall be broadly interpreted within the scope of the claims presented below.

Claims

1. A method for maintaining of an overpressure which is at least 0.1 bar in an impact mill during treatment of material to be carried out therein, wherein the impact mill comprises a rotor space (1) comprising

- a housing (4) equipped with a feeding opening (2) and a discharge opening (3),

- a first rotor (5) fitted into the housing, which rotor is equipped with blades having impact surfaces, said blades forming one or more, typically at least two rings (51 , 52) coaxial with said rotor, and - a second rotor (6), coaxial with said first rotor, fitted inside the housing, or a stator (60), which rotor or stator is equipped with blades having impact surfaces, said blades forming one or more, typically at least two rings (61, 62) coaxial with said rotor or stator, and which rings are arranged in an intermeshed fashion with respect to the ring or rings of the first rotor, characterized in that - the material components needed are fed into the rotor space (1) by a feeding arrangement (70) enduring pressure differences, and

- the material exiting from the rotor space (1) is discharged by a discharge arrangement (80) enduring pressure differences, and that

- the target pressure in the rotor space (1) is secured by a pressurized gasket fluid, the pressure of which is kept at least the same as the target pressure of the rotor space, or preferably slightly higher than the target pressure of the rotor space, and which gasket fluid is led beneath a gasket (20) located between the rotor shafts (8,10), and/or beneath a gasket (21 or 20) located between the rotor shaft (10 or 8) and a support (16 or 16') adjacent thereto.

2. The method according to claim 1, characterized in that the feeding arrangement (70) enduring pressure differences comprises a pressure chamber (71) arranged in connection with the feeding opening (2) of the rotor space (1), in which pressure chamber the target pressure of the rotor space is maintained, and into which a solid material component to be treated is fed from a lower pressure to said target pressure, and into which optionally needed liquids and/or gases are fed.

3. The method according to claim 1 or 2, characterized in that the discharge arrangement (80) enduring pressure differences comprises a pressure chamber (81) arranged in connection with the discharge opening (3), in which pressure chamber the target pressure of the rotor space is maintained, and from which the material exiting from the rotor space is discharged.

4. The method according to any of the foregoing claims, characterized in that the gasket fluid fed beneath the gasket (20) or gaskets (20, 21) is allowed to discharge through the gasket (20) or gaskets (20, 21) into the rotor space (1) of the impact mill.

5. The method according to any of the claims 1-3, characterized in that the discharge of the gasket fluid fed beneath the gasket (20) or gaskets (20, 21) into the rotor space of the impact mill is prevented by leading the gasket fluid away along a separate channel (17, 17', 18, 19).

6. The method according to any of the foregoing claims, characterized in that the upper bearings (14 resp. 15) of the rotor shaft (8) or rotor shafts (8, 10) are protected against an optional influence of the gasket fluid, and the lubrication agent of the bearings is prevented from entering into the rotor space by arranging above the said upper bearing (14 resp. 15) two gaskets (30, 31, resp. 40, 41), where a possible leakage of the gasket fluid from the upper gasket (30, 40) is led away along a separate channel (45).

7. An impact mill that can be pressurized to an overpressure of at least 0.1 bar, where said impact mill has a rotor space (1) comprising

- a first rotor (5) fitted into the housing (4), which rotor is equipped with blades having impact surfaces, said blades forming one or more, typically at least two rings (51, 52) coaxial with said rotor, and

- a second rotor (6), coaxial with said first rotor (5), fitted inside the housing, or a stator (60), which rotor or stator is equipped with blades having impact surfaces, said blades forming one or more, typically at least two rings (61, 62) coaxial with said rotor (6) or stator (60), and which rings are arranged in an intermeshed fashion with respect to the ring or rings of the first rotor (5), characterized in that

- the feeding opening (2) is equipped with a feeding arrangement (70) enduring pressure differences, and that

- the discharge opening (3) is equipped with a discharge arrangement (80) enduring pressure differences, and that

- into the rotor shaft (8) and/or into the support (16) of the rotor shaft is arranged a channel (17, 17', 19) through which a gasket fluid, securing the target pressure of the rotor space, can be led beneath the gasket (20) located between the rotor shafts (8, 10), and/or beneath the gasket (21 or 20) located between the rotor shaft (10 or 8) and the support (16 or 16') adjacent thereto.

8. The impact mill according to claim 7, characterized in that that the feeding arrangement enduring pressure differences comprises a pressure chamber (71) arranged in connection with the feeding opening (2) of the rotor space (1), which pressure chamber endures the target pressure of the rotor space, and which has means (72) for feeding of a solid material component to be treated from a lower pressure to said target pressure, and optionally also means (73, 74) for feeding of liquids and/or gases.

9. The impact mill according to claim 7 or 8, characterized in that the discharge arrangement (80) enduring pressure differences comprises a pressure chamber (81) arranged in connection with the discharge opening (3) of the rotor space (1), which pressure chamber endures the target pressure of the rotor space, and which comprises means (82, 83) for discharge of the material exiting from the rotor space.

10. The impact mill according to any of the claims 7-9, characterized in that a channel (17, 17', 18, 19) has been arranged in the rotor shaft (8) or rotor shafts (8, 10) and/or the support (16) of the shafts, along which channel the gasket fluid can be lead away from the lower side of the gasket (20) or gaskets (20, 21).

11. The impact mill according to any of the claims 7-10, characterized in that above the upper bearings (14, 15) of the rotor shaft (8) or rotor shafts (8, 10) has been arranged two gaskets (30, 31, resp. 40, 41), and that a channel (45) is arranged in the shaft (10) and/or support (16), through which channel a possible leakage of gasket fluid from the upper gasket (30 or 40) can be led away.