GRINDER HOUSING FOR A PRESSURE CHAMBER GRINDER

Abstract: Grinder housing of a pressure chamber grinder, which said grinder housing comprises a substantially cylindrical outer mantle (1), end walls (2, 3), at least two accelerating nozzles (4) passing radially through the outer mantle (1), between which said nozzles there is an obtuse angle, as well as a discharge opening (5) made into one of the end walls (3) for the ground product. The invention is characterized in that the grinder housing is provided with a substantially cylindrical partition wall (6), which is in itself known, centrally located, and which surrounds the grinding chamber (7) proper and is provided with an inlet opening (9) facing the orifice of each accelerating nozzle, preferably terminating at the plane of the inner face of the outer mantle (1), that the annular space surrounding the partition wall (6) is a gas removing chamber (8) to which an exhaust duct (10) passing through the outer mantle is connected for the removal of the excess quantity of working gas discharged out of the solids-working-gas jets of the accelerating nozzles (4) into the gas removing chamber (8).

Description: Grinder housing for a pressure chamber grinder The present invention is concerned with the grinder housing of a pressure chamber grinder, which said grinder housing comprises a substantially cylin¬ drical outer mantle, end walls, preferably two acceler¬ ating nozzles passing radially through the outer mantle, between which said nozzles there is an obtuse angle, as well as a discharge opening made into one of the end walls for the ground product. In the pressure chamber grinder apparatuses known in prior art, the discharge ends of the acceler¬ ating nozzles extend into the interior of the grinding chamber, where the material-gas jets rushing out of the nozzles collide against each other at very high speeds so that the material particles in the jets are ground. In the main grinding chamber in the prior-art pressure chamber grinders, the material partiςles are, in prin¬ ciple, subjected to the grinding effect only once. In the case of materials that are difficult to grind, no satisfactory grinding result can be obtained with one passage through the grinder, but the discharge opening of the grinding chamber is directly connected to a classifier, whose discharge opening for the coarse fraction is directly connected to the grinding chamber, to the collision zone of the material-gas jets. The solution mentioned above is not fully successful, for, in order that the best possible grinding result should be achieved, the solids content in the material-gas jets colliding against each other must be kept relatively high, whereas, in order that a satis¬ factory classification result should be obtained, a very large excess quantity of gas is required in the classifier. In order that the material particles should reach an ultrasonic speed in the accelerating nozzles, the solids content in the material-gas jets rushing through the said nozzles must be kept relatively low. On the other hand, in principle, the working gas has accomplished its duty by the stage in which the material particles have been accelerated through the nozzles. It has, viz., been noticed that the working gas present in the grinding chamber has a mainly detrimental effect on the grinding process proper. Moreover, in the grinder apparatuses known in prior art, it is not possible to control the solids contents in the material-gas jets between different stages, but a compromise must be made in the choice of the grinding conditions, which does not yield a fully satisfactory result. The object of the present invention has been to eliminate the drawbacks mentioned above, which has been achieved by means of a grinder housing which is characterized in that the grinder housing is provided with a substantially cylindrical partition wall, which is in itself known, centrally located, and which sur¬ rounds the grinding chamber proper and is provided with an inlet opening facing the orifice of each accelerating- nozzle, preferably terminating at the plane of the inner face of the outer mantle, that the annular space surrounding the partition wall is a gas removing chamber to which an exhaust duct passing through the outer mantle is connected for the removal of the excess quantity of working gas discharged out of the solids-working-gas jets of the accelerating nozzles into the gas removing chamber. By means of this solution, it is possible to control the solids contents in the material-gas flows before they rush into the grinding chamber, where the grinding takes place highly efficiently, because in the grinding chamber there are no working-gas flows inter- fering with the grinding. Moreover, in this grinding chamber of new type, the grinding takes place in two stages, so that the grinding result is considerably more uniform than in the grinder apparatuses used in prior art. The first grinding stage takes place in the middle part of the grinding chamber, where the material particles rushing out of the different accelerating nozzles collide against each other at ultrasonic speed, and the second grinding stage takes place when the material particles that have passed through this first collision zone and that have retained their kinetic energy strike against the partition wall in the grinder housing. Since the quantity of working gas rushing into the grinding chamber can be kept relatively low, it is possible to dimension the grinding chamber so small that most of the kinetic energy of the material particles is still retained at the stage in which they strike against the partition wall. In order that the best classification result should be obtained, the classifi¬ cation must be carried out as an operation completely separate from the grinding process. Excessively large material particles are preferably returned, for example, into the feeding container or possibly feeding funnel of the pressure chamber grinder equipment. In the following, the grinder housing in accord¬ ance with the present invention will be described in more detail with reference to the accompanying drawing, wherein Figure 1 shows an example of the grinder housing in accordance with the invention as viewed from above, and Figure 2 is a sectional view along line A-A in Fig. 1. The grinder housing of a pressure chamber grinder in accordance with the present invention com¬ prises a substantially cylindrical outer mantle 1 , end walls 2, 3, preferably two accelerating nozzles 4 passing radially through the outer mantle 1 , between which said nozzles there is an obtuse angle, and a discharge opening 5 made into one of the end walls 3 for the ground product. In the grinder housing, a substantially cylindrical par¬ tition wall 6 is placed centrally, which said wall divides the grinder housing into a grinding chamber 7 proper and a gas removing chamber 8 surrounding the said chamber 7. The accelerating nozzles 4 terminate prefer¬ ably exactly at the plane of the inner face of the outer mantle 1. Into the partition wall 6 , an inlet opening 9 has been made facing the orifice of each accelerating nozzle 4. To the outer mantle 1 , a discharge duct 10 is attached for the working gas discharged into the gas removing chamber 8 from the material-gas jets rushing through the accelerating nozzles 4. The grinder chamber operates so that the pre-ground material-gas jet rushing out of a pressurized pre-grinding chamber is divided into equivalent component jets (not shown) , whose number equals the number of the accelerating nozzles 4. These component jets are passed into the said accelerating nozzles 4, wherein the velocity of the jets rises to the ultrasonic level by the_ effect of the pressure of the working gas. The major. " part of the quantity of working gas present in the material-gas jet is separated from the said jet in the gap B'etween the orifice of the accelerating nozzle 4 and the inlet opening 9 placed in the partition wall 6 and escapes through the said gap into the gas removing chamber 8 , whereby part of the fine fraction in the material-gas jet also follows along. It is only the coarser par¬ ticles that continue their movement straight into the grinding chamber 7, where, in the first grinding zone A formed in the middle part of the said chamber 7, the said particles collide with the material particles coming from the other accelerating nozzle 4 and are ground. Those particles which, by chance, pass through this grinding zone A without reaching contact with any of the material particles rushing in the opposite direction con¬ tinue their passage straight forwards and are finally struck against the partition wall 6 in the second grinding zone B formed at the opposite side of the grinding chamber 7. Such a method is possible because the coarser material particles, which require grinding, move along a linear path following the longitudinal axis of the accelerating nozzle 4, and the finer material particles, which correspond to the size of the finished product, move closer to the interior walls of the accelerating nozzles. In order to make sure that the solid particles still have the kinetic energy required for grinding even in the second grinding zone B, the pressure of the working gas in the final part of the accelerating nozzles 4 must be kept at a positive pres¬ sure of at least 0.3 bar. Thus, by means of the present grinder housing, it is possible to make sure that all the particles that require grinding indeed become ground. The size and shape of the inlet openings 9 in the partition wall 10 as well as the size of the grinding chamber 7 itself are chosen in accordance with the pro¬ perties and composition of the material to be ground as well as in accordance with the properties of the desired final product. If there is a high proportion of fine fraction in the material to bee ' ground, it is possible to use a partition -wall 6 with smaller inlet openings 9 than if there is only a very low proportion of fine fraction among the particles. In principle, the size of the grinding chamber 7 should be kept as little as pos- sible, in particular if the material to be ground is of a soft, non-abrasive nature. In stead, if the material to be ground is of highly abrading nature, the grinding chamber should be dimensioned so that most of the grinding of the material takes place in the grinding zone A. In the discharge duct 10 there is preferably a control valve (not shown) , by means of which the quantity of gas removed out of the material-gas jets of the accelerating nozzles 4 through the gas removing chamber 8 is adjusted. In order to prevent abrasion of the interior face of the partition wall 6 as a result of grinding, the inside of the partition wall 6 is lined with a wear-resistant material, such as ceramic tiles or hard- metal plates 6a. The said tiles or plates 6a must be installed so that the material particles to be ground col¬ lide against their faces substantially perpendicularly. In order to intensify the removal of working gas , the gas removing chamber 8 in the grinder housing may be advantageously provided with an inlet pipe 12 for flushing air, provided with a control valve 11. In such a case, the control valve placed in the discharge duct 10, mentioned above, can be omitted. The inlet pipe 12 for flushing air and the discharge duct 10 for working gas are preferably installed at opposite sides of the grinder housing in the centre plane between the acceler¬ ating nozzles 4 so that the inlet pipe 12 is placed at the side of the largest angle between the accelerating nozzles 4. In such a case, the material-gas jets rushing out of the accelerating nozzles 4 turn, by the effect of the flushing air, to a greater extent towards each other so that the grinding effect resulting from the collision is increased. If, besides working gas, material particles whose particle size is below a certain value are also supposed to be removed from the material-gas jets, it is possible to install flushing-air nozzles 13 between the orifices of the accelerating nozzles 4 and the corres¬ ponding inlet openings 9 in the partition wall 6, which said nozzles 13 comprise a first duct 13a, substantially following the shape of the flow ducts in the accelerating nozzles 4, for the material-gas jet rushing out of the accelerating nozzle (4) , and a second duct 13b, having the shape of a venturi tube and passing across the first duct, for the flow of flushing air at the side concerned. Since most of the working gas contained in the material-gas jets has been passed out of the grinder housing through the discharge duct 10, the discharge opening 5 for ground product in the grinder housing can be connected straight to the receiving and storage container (not shown) for ground product, wherein the remaining part, if any, of the working gas can be separated from the ground product. In order to exclude the possibility that a r" ϊ 5 particle in the material jet rushing out of one of the accelerating nozzles 4 might penetrate into the opposite accelerating nozzle 4, which is energy-economi- cally highly disadvantageous and, moreover, damages the final part in this accelerating nozzle 4, the obtuse 10 angle between the accelerating nozzles 4 should be kept preferably smaller than 170 . 15

Claims: WHAT IS CLAIMED IS: 1. Grinder housing of a pressure chamber grinder, which said grinder housing comprises a substan- 5 tially cylindrical outer mantle (1), end walls (2, 3), preferably two accelerating nozzles (4) passing radially through the outer mantle (1), between which said nozzles there is an obtuse angle, as well as a discharge opening (5)' made into one of the end walls (3) for the ground 10. product, c h a r a c t e r i z e d in that the grinder housing is provided with a substantially cylindrical partition wall (6) , which is in itself known, centrally located, and which surrounds the grinding chamber (7) proper and is provided with an inlet opening (9) facing 15 the orifice of each accelerating nozzle, preferably terminating at the plane of the inner face of the outer mantle (1) ,. that the annular space surrounding the par¬ tition wall (6) is a gas removing chamber (8) to which an exhaust duct (10) passing through the outer mantle is 0 connected for the removal of the excess quantity of working gas discharged out of the solids-working-gas jets of the accelerating nozzles (4) into the gas removing chamber (8) . 2. Grinder housing as claimed in claim 1, 5 c h a r a c t e r i z e d in that the size and shape of the inlet openings (9) in the partition wall (6) as well as the size of the grinding chamber (7) itself have been chosen in accordance with the properties and composition of the material to be ground. 0 3. Grinder housing as claimed in claim 2, c h a r a c t e r i z e d in that the exhaust duct (10) for working gas is provided with a control valve. 4. Grinder housing as claimed in claim 2 or 3, c h a r a c t e r i z e d in that the inside of 5 the partition wall (6) is lined with a wear-resistant material. 5. Grinder housing as claimed in claim 4, c h a r a c t e r i z e d in that an inlet pipe (12) for flushing air, provided with a control valve (11) , is connected to the gas removing chamber (8) . 6. Grinder housing as claimed in claim 5, c h a r a c t e r i z e d in that in the grinder housing, which is provided with two accelerating nozzles (4) , the inlet pipe (12) for flushing air and the exhaust duct (10) for working gas are installed at opposite sides of the grinder housing in the centre plane between the accelerating nozzles (4) so that the inlet pipe (12) is placed at the side of the largest angle between the accelerating nozzles (4) . 7. Grinder housing as claimed in claim 6, c h a r a c t e r i z e d in that in the gas removing chamber (8) , facing both of the accelerating nozzles (4) , flushing-air nozzles (13) are installed, which comprise a first duct (13a), substantially following the shape o.f the flow duct in the accelerating nozzle (4) , for the material-gas;jet rushing out of the accelerating nozzle (4) , and a second duct (13b), having the shape of a venturi tube and passing across the said first duct (13a) , for the flow of flushing air at the side concerned. 8. Grinder housing as claimed in claim 7, c h a r a c t e r i z e d in that the discharge opening (5) of the grinding chamber (7) for the ground product is connected straight to the receiving and storage con¬ tainer for the ground product. 9. Grinder housing as claimed in claim 8, c h a r a c t e r i z e d in that the grinding of the material takes place both in the first grinding zone (A) formed in the middle part of the grinding chamber as the material particles rushing out of the different accelerating nozzles (4) collide against each other and as the material particles that have passed through this first grinding zone (A) and retained their kinetic energy strike against the partition wall (6) in the second grinding zone (B) formed at the opposite side of the grinding chamber (7) . 10. Grinder housing as claimed in claim 9, c h a r a c t e r i z e d in that the angle between the accelerating nozzles (4) is at the maximum 170 .

Inventors: NIEMI JOUKO, NIEMI, JOUKO
Applicants: FINNPULVA AB OY, OY FINNPULVA AB
Application year: 1986
Main classification: B02C19
IPC codes: B02C19