WO 2008/122122 PCT/CA2008/000644 1 "APPARATUS AND METHODOLOGY FOR COMMINUTING MATERIALS" 2 BACKGROUND OF THE INVENTION 3 Many different types of material are comminuted for reducing the 4 size of the particulates forms of the material. For example, coal excavated from 5 a mine is frequently comminuted to make the particulate size smaller and more 6 uniform to facilitate the coal's transportion and/or to provide consistent 7 combustion in a furnace. In another example, food stuffs, such as wheat, are 8 frequently comminuted to produce flour. Rock containing a desirable ore is 9 frequently comminuted to provide easier access to the ore and the metal 10 included in the ore. 11 A common way of comminuting material is to collide a particle of 12 the material with an impact surface. The collision generates a force on and 13 inside the particle that causes the particle to fracture into two or more smaller 14 pieces. The amount of force generated in the collision is directly proportional to 15 the impact speed of the particle. The impact speed of the particle is relative to 16 the impact surface at the moment of collision. The generated force increases as 17 the impact speed increases. As the force applied to the particle increases, the 18 size of the pieces that result from the collision of the particle with the impact 19 surface decreases. 20 There are many different comminuting devices that collide a 21 particle of material with an impact surface. For example, hammer mills 22 comminute particles of material with a rotating set of hammers having impact 23 surfaces. In operation, the material is dropped into the mill and fed by gravity to 24 the hammers. The hammers smash the particles of the material into smaller
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WO 2008/122122 PCT/CA2008/000644 1 pieces and also throw some of the particles and pieces against a side of the mill. 2 In a hammer mill the impact speed of the particles largely depends on the 3 rotational speed of the hammers. 4 Another type of comminuting device is a pin mill. The pin mill 5 comminutes particles of material with multiple rings of pins spinning in opposite 6 directions. In operation, the material is dropped into the center of the mill and 7 moves outwardly through the paths of the pins in each ring. As the particles of 8 material move, the pins knock the particles. In a pin mill, the impact speed of the 9 particles largely depends on the speed of the pins moving along the paths. 10 Another type of comminuting device is a jet mill. Jet mills 11 comminute particles by accelerating the particles with a jet of air and directing 12 the accelerated particles against an impact surface, which may or may not be 13 stationary, or against an opposing jet of particles. In operation, a jet of air is 14 generated and the particle is then fed into the jet to accelerate it. Once 15 accelerated to a desired speed, the particle is directed toward and collides with 16 the impact surface or another particle of an opposing jet. In a jet mill, when the 17 impact surface is stationary, the impact speed of a particle largely depends on 18 the speed of the particle, and when the impact surface moves, or an opposing jet 19 of particles is used, the impact speed of a particle largely depends on the 20 combined speed of the particle and the impact surface or particle of the opposing 21 jet. 22 The aforementioned comminuting devices are energy intensive 23 which can be related to a given particulate size. Hammer mills and pin mills 24 typically generate a maximum impact speed of about 350 ft/sec and about 550 25 ft/sec respectively. A significant reduction in a material's particulate size typically 2 WO 2008/122122 PCT/CA2008/000644 1 requires the material to be run through these mills more than once. Thus, the 2 amount of energy consumed during the comminuting process includes the 3 amount of energy required to operate these mills during multiple runs. 4 Furthermore, to generate impact speeds greater than about 550 ft/sec, the 5 hammers and pins would have to rotate/move faster than their conventional 6 structures will allow without sustaining substantial wear or catastrophic failure. 7 Although jet mills can generate higher impact speeds than hammer and pin mills, 8 the amount of energy jet mills consume can also be significant because they 9 generate a jet of air to accelerate a particle, which typically requires a substantial 10 amount of energy. 11 As shown in French patent application published as FR 2538718A1 12 to Vannier, another type of device is the centrifugal throwing wheel for 13 accelerating particles from a central axis and through radially extending slots 14 formed in the wheel for impacting the accelerated particles against a spaced 15 peripheral target. In 1933, German Patent DE 576895 to Meffert, the target is a 16 ribbed funnel ring counter-rotating with respect to the rotating throwing wheel. 17 The known throwing wheels can suffer from inefficiencies in 18 moving the particle to the wheel's periphery. The harsh environment results in 19 rapid erosion of components and as a result, and inherent in the dynamics of 20 comminuting apparatus, imposes great challenges in maintaining integrity of the 21 components and in driving and rotationally supporting such components. 22 Erosion of components is inevitable and ease of access to the throwing wheel 23 and related equipment is desirable. 24 3 1 SUMMARY OF THE INVENTION In embodiments of the invention, an improved comminuting apparatus 3 comprises a throwing wheel having improved construction and material flow I characteristics. An improved wheel enables use of particularly wear-resistant 5 components only where required. Generally radially extending flow channels through 3 the throwing wheel can be configured to minimize energy loss for maximum r acceleration of the materials. The channels can converge towards the particle exits 3 for minimizing eddies and the like. Further, in other embodiments, the comminuting apparatus further ) comprises a housing which is readily accessible for maintenance. The housing 1 comprises a two-part housing which is reversibly separable for accessing the 2 comminuting chamber, throwing wheel and impact rotor within. 3 In one broad aspect, the present invention provides a throwing wheel 1 for accelerating and discharging particles for impact against impact surfaces of a 5 particle fragmenting device, the throwing wheel comprising: a body having a central 3 inlet port along an axis of the body and a periphery having a plurality of particle exits, 7 the port being adapted for receiving particles; and a plurality of channels within the 8 body extending generally radially from the central inlet port to the plurality of particle 9 exits, each channel having a top wall, a bottom wall, and side walls, wherein the side 0 walls of each channel preferably converge towards the particle exits at the periphery. 1 In an embodiment, the body further comprises: a top plate; a bottom 2 plate; and a plurality of inserts sandwiched between the top plate and the bottom 3 plate for mounting the inserts in a circumferentially spaced position, each insert 4 having a leading side wall and a lagging side wall, the leading side wall and lagging 5 side wall of adjacent inserts forming the side walls of each channel. 4 1 In an embodiment, the material of the inserts has a greater wear 2 resistance than that of the top and bottom plates. In an embodiment, the inserts are 3 pie-shaped, each having an apex oriented generally radially inwardly towards the $ central port. 5 In an embodiment, the throwing wheel further comprises: a plurality of 3 bosses axially extending from at least one of the top plate or bottom plate, and r wherein the inserts have an axially extending cavity formed between the leading and 3 lagging side walls, and wherein the cavity of each insert engages each axially ) extending boss as the top plate and bottom plate sandwiches the plurality of inserts ) therebetween. In an embodiment, each boss is generally pie-shaped, and the cavity 1 in each insert is generally pie-shaped. In an embodiment, at least some of the 2 bosses are axially extending from the bottom plate. In an embodiment, the bosses 3 are integral with the bottom plate. In an embodiment, the throwing wheel further $ comprises a plurality of fasteners extending between the top plate and the bottom 5 plate for sandwiching the plurality of inserts therebetween. 3 Preferably the body can comprise an assembly of replaceable generally 7 pie-shaped inserts for forming the channels sandwiched between a top and a bottom 8 plate. The inserts can be supported by bosses extending from one of the top of 9 bottom plates and into cavities in the inserts. 0 In another aspect, the present invention provides an apparatus for 1 fragmenting particles comprising: a throwing wheel comprising a body having a 2 central inlet port along an axis of the body and a periphery having a plurality of 3 particle exits, the port being adapted for receiving particles and a plurality of channels 4 within the body extending generally radially from the central inlet port to the plurality 5 of particle exits, each channel having a top wall, a bottom wall, and side walls, 6 wherein the side walls of each channel converge towards the particle exits at the 4a 1 periphery, and wherein the throwing wheel is rotatable in a first direction and 2 operable to receive the particles for accelerating and directing the particles from a 3 periphery of the throwing wheel along a particle trajectory; an impact rotor having a 1 peripheral impact surface positioned concentrically about the throwing wheel for 5 intersecting the particle trajectory; the impact rotor rotatable in a second direction 3 opposite to the throwing wheel for increasing an impact speed of the particles and 7 fragmenting the particles when the particles collide with the impact surface; a first 3 motor directly coupled to the impact rotor and operable to power the impact rotor; 3 and a second motor directly coupled to the throwing wheel and operable to power the 3 throwing wheel. 1 In an embodiment, the apparatus further comprises a housing within 2 which the throwing wheel and impact rotor are housed. 3 In an embodiment, the housing further comprises: an upper housing for 4 rotatably supporting one of the throwing wheel or impact rotor; and a lower housing 5 for rotatably supporting the other of one of the impact rotor or throwing wheel, the 3 upper and lower housings being separable at about the throwing wheel for access to 7 the throwing wheel and impact rotor. 8 In an embodiment, the apparatus further comprises: a housing support 9 for maintaining the upper housing in a substantially fixed position; and an actuator for 0 moving the lower housing between a closed position wherein the throwing wheel and 1 impact rotor are axially coupled for aligning the particle trajectory with the impact 2 surface, and an open position wherein the throwing wheel and impact rotor are 3 axially decoupled for access to each throwing wheel and impact rotor independently. 4 In an embodiment, the actuator further comprises one or more 5 actuators positioned between the upper housing and the lower housing. In an 6 embodiment, the one or more actuators further comprise two or more actuators, 4b 1 circumferentially spaced about a periphery of the upper housing and extending 2 axially between the upper housing and the lower housing. In an embodiment, the one 3 or more actuators further comprise three actuators equally spaced about a periphery I of the upper housing. 5 In an embodiment, the housing support further comprises one or more 3 supports positioned between the upper housing and a surface. In an embodiment, r the one or more supports further comprise three supports equally spaced about a 3 periphery of the upper housing. In an embodiment, a gap is formed between the 3 throwing wheel and the impact rotor further comprising an elastomeric anti-wear ) surface applied to at least one of the impact rotor or throwing wheel facing the gap. 4c WO 2008/122122 PCT/CA2008/000644 1 In another aspect, a fragmenting apparatus comprises the throwing 2 wheel coupled with an impact wheel. More preferably, the throwing wheel and 3 impact rotor are operable within a housing. The housing can comprise an upper 4 housing for rotatably supporting one of the throwing wheel or impact rotor; and a 5 lower housing for rotatably supporting the other of one of the impact rotor or 6 throwing wheel, the upper and lower housings being separable at about the 7 throwing wheel for access to the throwing wheel and impact rotor. Preferably the 8 upper housing is supported and the lower housing can be actuated between a 9 closed position wherein the throwing wheel and impact rotor are axially coupled 10 for aligning the particle trajectory with the impact surface, and an open position 11 wherein the throwing wheel and impact rotor are axially decoupled for access to 12 each throwing wheel and impact rotor in dependently. 13 The above apparatus enables practicing a methodology for 14 fragmenting particles comprising: rotating a throwing body about a substantially 15 vertical axis, the throwing body having a central inlet at a top of the body at the 16 axis and a plurality of channels within the body and extending generally radially 17 from the central inlet port for forming a plurality of flow paths to a plurality of 18 particle exits at a periphery of the body, each channel having a top wall, a 19 bottom wall, and side walls; introducing particles to be fragmented through the 20 central inlet for accelerating the particles through the channels; converging the 21 flow path as the particles flow from the central inlet to the particle exits for 22 favoring streamline flow of particles between the side walls; discharging the 23 particles from the particle exits; and impacting the discharging particles against 24 impact surfaces arranged about the periphery of the throwing body. Preferably, 25 the impacting of the discharging particles against impact surfaces further 5 WO 2008/122122 PCT/CA2008/000644 1 comprises rotating an impact rotor co-axially with the throwing body, the impact 2 rotor supporting a plurality of impact surfaces arranged concentrically about the 3 periphery of the throwing body thereon and wherein the impact rotor is counter 4 rotated relative to the throwing body. 5 6 BRIEF DESCRIPTION OF THE DRAWINGS 7 Figures 1-9 illustrate the prior art as described and claimed in 8 Applicant's related US Patent 7,207,513, more particularly 9 Figure 1 is a partial cross-sectional view of an embodiment 10 of the prior art comminuting device; 11 Figure 2A is a larger view of the cross-sectional view in Fig. 12 1 of a throwing wheel and impact rotor incorporated in the prior art 13 comminuting device; 14 Figure 2B is a cross-sectional view of an embodiment of the 15 prior art comminuting device that incorporates a throwing wheel and two 16 impact rotors; 17 Figure 3 is a perspective view of the throwing wheel in Figs. 18 1, 2A and 2B; 19 Figure 4A is a perspective view of a throwing wheel, of the 20 prior art comminuting device; 21 Figure 4B is a perspective view of another embodiment of a 22 throwing wheel, of the prior art comminuting device; 23 Figure 4C is a perspective view of another embodiment of a 24 throwing wheel, of the prior art comminuting device; 6 WO 2008/122122 PCT/CA2008/000644 1 Figure 5 is a perspective view of the impact rotor in Figs. 1 2 and 2A; 3 Figure 6A is a perspective view of another embodiment of 4 an impact rotor, of the prior art comminuting device; 5 Figure 6B is a cross-sectional view of the impact rotor in Fig. 6 6A; 7 Figure 7A is a perspective view of another embodiment of 8 an impact rotor, of the prior art comminuting device; 9 Figure 7B is a side view of the impact rotor in Fig. 7A. 10 Figure 8 is a side view of an embodiment of the prior art 11 comminuting device; and 12 Figure 9 is a top view of the comminuting device in Fig. 8; 13 Figure 10 is a cross-sectional view of a comminuting device or 14 apparatus according to an embodiment of the invention; 15 Figure 11 is a top view of the comminuting device according to Fig. 16 10; 17 Figure 12 is a cross-sectional view of the comminuting device of 18 Fig. 10 illustrated in an open state for accessing the throwing wheel and impact 19 rotor according an embodiment of the invention; 20 Figure 13 is a side cross-sectional view of an embodiment of a 21 throwing wheel axially coupled with an embodiment of an impact rotor; 22 Figures 14A and 14B are side cross-sectional and underside views 23 of an embodiment of the impact rotor of Fig. 13; 24 Figures 15A through 16 illustrate an embodiment of the throwing 25 wheel of Fig. 13. More particularly, 7 WO 2008/122122 PCT/CA2008/000644 1 Figs. 15A and 15B are side cross-sectional and underside views 2 respectively of a top plate for an embodiment of the throwing wheel; 3 Figs. 15C and 15D are top and side cross-sectional views 4 respectively of the structure of a bottom plate for the throwing wheel; 5 Fig. 15E illustrates a top view of the plurality of elements for 6 installation to the bottom plate of Fig. 15F for the throwing wheel of Fig. 13; 7 Fig. 15F illustrates a top view of the bottom plate of Fig. 13, with % 8 of the plurality of elements of Fig. 15E for installation to the rightmost illustrated 9 bosses; 10 Fig. 16 is a side cross-sectional view of the impact rotor poised 11 axially over a partially exploded view of the throwing wheel comprising the top 12 plate, the leftmost one half of the elements shown before installation to the 13 bottom plate, and the rightmost one half of the elements installed to the bottom 14 plate; 15 Figure 17 illustrates particle velocity results of Computational Fluid 16 Dynamics (CFD) analysis illustrating the effect of a narrowing channel between 17 elements of the throwing wheel according to one embodiment of the invention; 18 Figure 18 illustrates particle velocity results of CFD analysis 19 illustrating the effect of a parallel channel between elements of the throwing 20 wheel according to another embodiment of the invention; 21 Figure 19 is a side cross-sectional view of the throwing wheel of 22 Fig. 13; and 23 Figure 20 is a cross-sectional view of a comminuting device 24 according to Fig. 10. 8 WO 2008/122122 PCT/CA2008/000644 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 2 3 Appicant's prior art device 4 Fig. 1 is a partial cross-sectional view of a first embodiment of 5 Applicant's prior art comminuting device 20. This embodiment, and exemplary 6 variations therefrom and shown in Figs. 2 - 9, are detailed in Applicant's US 7 Patent 7,207,513. Applicant's prior art Figs. 1 - 9 and portions of the 8 specification of US Patent 7,207,513 are reproduced herein to assist the reader. 9 As shown in Fig. 1, Applicant's prior art comminuting device 20 10 includes a throwing wheel 22 to accelerate particles of material (omitted for 11 clarity of the apparatus) toward an impact speed, and toward an impact rotor 24 12 that includes an impact surface 26 (see also Fig. 3) to fragment particles that 13 collide with the impact surface 26 after exiting the throwing wheel 22. Applicant's 14 prior art comminuting device 20 also includes an impact motor 28 to rotate the 15 impact rotor 24 about a rotor axis 30 and a throwing motor 32 to rotate the 16 throwing wheel 22 about a wheel axis 34 in a direction opposite to the rotation of 17 the impact rotor 24. In addition, Applicant's prior art comminuting device 20 18 includes an inlet hopper 36 to receive particles of material, a conduit 38 to direct 19 the particles of material from the hopper 36 to the throwing wheel 22, and an 20 outlet hopper 40 to collect processed material. 21 By rotating the throwing wheel 22 and the impact rotor 208 in 22 opposite directions, the impact speed of the particles become a combination of 23 the particles' speed and the impact surface's speed. If, at the moment of 24 collision, the trajectory of the particle is aligned but opposite in direction to the 25 trajectory of the impact surface 26, then the particle's impact speed will be the 9 WO 2008/122122 PCT/CA2008/000644 1 sum of the particle's speed and the impact surface's speed. Thus, the 2 comminuting device 20 can generate impact speeds exceeding those generated 3 by conventional comminuting devices. This increase in impact speed combined 4 with an orientation of the impact surface 26 that aligns the direction of the impact 5 surface 26 with the trajectory of the particles increases the force generated on 6 and in the particles at the moment of collision. Consequently, particles of the 7 material may be fragmented into smaller pieces after one run through the 8 comminuting device 20, which allows the comminuting device 20 to comminute 9 material more efficiently. 10 As shown in Figs 1, 2A and 2B, Applicant's prior art comminuting 11 device 20 uses tangential and centrifugal force to accelerate particles of material 12 toward an impact speed. Fig. 2A is a larger view of the cross-sectional view in 13 Fig. 1 of the throwing wheel 22 and the impact rotor 24 incorporated in the 14 comminuting device 20. 15 First, material is poured in the hopper 36 and flows through the 16 conduit 38 to a hub 42 of the throwing wheel 22. The conduit 38 may include a 17 valve (not shown) to allow one to control the flow rate of the material to the 18 throwing wheel 22. Once particles enter the hub 42, the rotation of the throwing 19 wheel 22 exerts a tangential force on the particles and generates centrifugal 20 force in each particle that propels each particle radially away from the hub 42 21 toward an exit of the throwing wheel 22. As each particle moves away from the 22 hub 42, the tangential and centrifugal forces accelerate the particles toward an 23 impact speed. Upon exiting the throwing wheel 22, each particle continues to 24 move on a trajectory and then collides with an impact surface 26 of the impact 25 rotor 24 that is moving toward the particles. After colliding with the impact 10 WO 2008/122122 PCT/CA2008/000644 1 surface 26, the particles and/or fragments of the particles may collide with other 2 portions of the impact rotor 24 and/or throwing wheel 22 eventually fall 3 downward into the hopper 40. 4 The throwing wheel 22 and the impact rotor 24 are mounted in the 5 comminuting device 20 such that the wheel axis 34 and the rotor axis 30 are 6 aligned or substantially aligned. The throwing wheel 22 is mounted to the 7 throwing motor 32, and the impact rotor 24 is mounted to the impact motor 28. 8 The motors 32 and 28, for example electric motors, are designed to power their 9 respective throwing wheel 22 and impact rotor 24 at a desired rotational speed 10 for a given material flow rate through the comminuting device 20. 11 With reference to Fig. 2A, in one embodiment, the hub 42 of the 12 throwing wheel 22 receives particles of material through a central port hole 43 in 13 the impact rotor 24 via the conduit 38. The throwing wheel 22 comprises a 14 plurality of channels 44 to direct the particles of material from the hub 42 toward 15 a periphery of the wheel 22. The particles accelerate toward an impact speed 16 and exit through wheel exits 46. The use of centrifugal force to accelerate each 17 particle toward an impact speed is less than the amount of energy frequently 18 required by conventional comminuting devices. 19 As shown in Figs. 1 and 5-7B, the impact rotor 24 comprises a 20 rotor hub 48 having hole 43 that allows the particles of material to enter the 21 throwing wheel's hub 42 from the conduit 38. Further, impact rotor 24 includes 22 an impact surface 26 about a rotor periphery 50. When the impact rotor 24 23 rotates about the rotor axis 30, the impact surface 26 revolves around the 24 throwing wheel 22 in a concentric and contra-rotating circular path. Thus, after a 11 WO 2008/122122 PCT/CA2008/000644 1 particle leaves the throwing wheel 22 through the exit 46, the particle and the 2 impact surface 26 collide to fragment the particle into smaller pieces. 3 The throwing wheel 22 accelerates particles of material toward an 4 impact speed and throws the particles from an exit 46 on a trajectory away from 5 the wheel 22. To increase the impact speed of the particle, the throwing wheel 6 22 is designed to throw the particles on a trajectory that is aligned with or is as 7 closely aligned as possible with the direction of the impact surface 26 (Figs. 1 8 and 2) at the moment of collision. 9 When a particle leaves the throwing wheel 22 through an exit 46, 10 the trajectory of the particle includes a first directional component that is tangent 11 to the periphery 54 and at least a second directional component that is radial to 12 the hub 42. The magnitude of each of these directional components depends on 13 the velocity and acceleration of the particle as the particle leaves the wheel 22. 14 By modifying the direction of each channel 44 as they extend toward the 15 periphery 54, and the angle that each channel 44 intersects the periphery 54, 16 one can modify the two directional components of the particle's trajectory. 17 As shown in Fig. 3, in one embodiment, the throwing wheel 22 18 includes channels 44 that extend substantially radially from the hub 42 toward 19 the periphery 54 in a straight or substantially straight direction and intersect the 20 periphery 54 at about 90 degrees to a tangent. Alternate embodiments of the 21 throwing wheel include angled channels 58 which are angled slightly off of a 22 radial, either lagging (Fig. 4A) or leading (Fig. 4B). An example of other 23 embodiments includes arcuate channels 70 of arcuate shape (Fig. 4C). 24 Figs. 6A and 6B are views of an impact rotor 88, according to 25 another embodiment of Applicant's prior art device. Fig. 6A is a perspective view 12 WO 2008/122122 PCT/CA2008/000644 1 of another impact rotor 88, and Fig. 6B is a cross-sectional view of the impact 2 rotor 88. The impact rotor 88 is similar to the impact rotor 24 of Fig. 5 except the 3 impact surfaces 90 are angularly positioned such that a (Alpha) is greater than 4 0 *, and a particle of material can not pass between adjacent impact teeth 92. 5 Angularly positioning each impact surface 90 greater than 00 relative to the rotor 6 axis 30 and preventing a particle of material from passing between adjacent 7 impact teeth 92 may be desirable to decrease the number of collisions a particle 8 may have with one or more impact surfaces 90. 9 Other embodiments were contemplated. For example, each impact 10 surface 90 may be angularly positioned such that a is greater than 0* but canted 11 opposite to the direction shown in Figs. 6A and 6B. This may be desirable to 12 increase the number of collisions a particle may have with one or more impact 13 surfaces 90. 14 Figs. 7A and 7B are views of an impact rotor 94 according to yet 15 another embodiment of Applicant's prior art device. Fig. 7A is a perspective view 16 of the impact rotor 94, and Fig. 7B is a side view of the impact rotor 94. The 17 impact rotor 94 is similar to the impact rotor 24 of Fig. 5 except the impact teeth 18 96 extend from the body 98 in the same direction as each tooth's respective 19 radius 100. This may be desirable when the impact rotor 94 and throwing wheel 20 24 (Fig. 3) are not concentric during operation. Each impact plate 102 is 21 mounted on a respective one of the impact teeth 96 by inserting the curved end 22 104 into a groove 106 and applying adhesive to hold the impact plate 102 to the 23 respective impact tooth 96 in the direction along the rotor axis 108. The impact 24 plate 102 may be mounted such that its impact surface 110 may be facing away 25 from the rotor axis 108 or toward the rotor axis 108, as desired. 13 WO 2008/122122 PCT/CA2008/000644 1 Figs. 8 and 9 are views of another embodiment of Applicant's prior 2 art comminuting device 112. Fig. 8 is a side view of the prior art comminuting 3 device 112, and Fig. 9 is a top view of the prior art comminuting device 112. 4 Applicant's prior art comminuting device 112 can efficiently generate impact 5 speeds around 950 ft/sec. 6 Applicant's prior art comminuting device 112 includes an impact 7 rotor 114 that is cylindrical and has impact surfaces 116 to collide with and 8 fracture particles of material, and two particle accelerators 118 to accelerate the 9 particles of material and direct them toward the impact rotor 114. Applicant's 10 prior art comminuting device 112 comminutes particles of material by first 11 accelerating the particles with one of the accelerators 118 to an approximate 12 speed of 200-300 ft/sec. Then, the particles are directed toward the impact rotor 13 114 that rotates to move the impact surfaces 116 at a speed 650 ft/sec or 14 greater toward the particles leaving the accelerators 118. Thus, Applicant's prior 15 art comminuting device 112 can generate impact speeds of approximately 850 16 ft/sec or greater. 17 In one embodiment of Applicant's prior art device, the particle 18 accelerator 118 includes a throwing wheel 120 (shown in Fig. 9 and omitted from 19 Fig. 8 for clarity) having an outer diameter 122 (shown in Fig. 8 and omitted from 20 Fig. 9 for clarity) and blades 124 (shown in Fig. 9 and omitted from Fig. 8 for 21 clarity) that rotate about an axis 126 to accelerate particles of material toward an 22 impact speed, and a motor 128 to rotate the throwing wheel 120. The accelerator 23 118 also includes a hopper 130 to receive particles of material and feed them to 24 an inlet 132 that is located at the axis 126, and an outlet 134 to direct the 25 particles of material toward the impact rotor 114. 14 WO 2008/122122 PCT/CA2008/000644 1 Because the speed of a particle exiting the accelerator 118 largely 2 depends on the throwing wheel's outer diameter 122 and rotational speed, the 3 accelerator 118 may be designed to accelerate particles to any desired exit 4 speed. The exit speed may be substantially determined by multiplying the 5 rotational speed of the throwing wheel 120 times the distance of the particle from 6 the axis 126 (half of the outer diameter 122). Thus, the exit speed may be 7 increased by increasing the throwing wheel's outer diameter 122 and/or 8 rotational speed, and may be decreased by decreasing the throwing wheel's 9 outer diameter 122 and/or rotational speed. 10 In operation, the accelerator 118 receives particles of material 11 through the hopper 130, which directs the particles toward the inlet 132. Once in 12 the inlet 132, the particles move away from the axis 126 and are picked up and 13 accelerated by a blade 124 of the rotating throwing wheel 120. As the particles' 14 speed increases, centrifugal force moves the particles toward the outer diameter 15 122 and through progressive regions of the blade 124 whose respective speed 16 increases. Thus, as the particles continue to move toward the outer diameter 17 122, the blade 124 continues to accelerate the particles toward an impact speed. 18 Then, the outlet 120 receives and directs the particles toward the impact rotor 19 114. 20 The impact rotor 114 includes impact surfaces 116 to collide with 21 and fracture the particles of material that have been accelerated by the particle 22 accelerator 118. To increase the impact speed of the particles, a motor 134 23 (shown in Fig. 9 but omitted in Fig. 8 for clarity) rotates the impact rotor 114 24 about an axis 136 (shown in Fig. 8 and omitted in Fig. 9 for clarity). A belt 138 15 WO 2008/122122 PCT/CA2008/000644 1 couples the motor 134 with the impact rotor 114 to transmit the output power of 2 the motor 134 to the impact rotor 114. 3 The throwing wheel imparts the initial energy to the particles. It is 4 advantageous both to provide a design which maximizes the energy imparted 5 and retains that design as long as possible despite the erosive environment. 6 Components will wear out and it is advantageous to replace them in an 7 expeditious manner. 8 9 EMBODIMENTS OF THE INVENTION 10 With reference to Figs. 10-20, further embodiments of the 11 invention are presented which improve one or more of comminution efficiency, 12 endurance and maintainability. 13 As shown in Figs. 10, 11 and 12, an improved comminuting 14 apparatus 200 includes another embodiment of a throwing wheel 202 having 15 improved construction and material flow characteristics. The throwing wheel 202 16 enables use of particularly wear-resistant components only where required. 17 Flow channels 204 through the throwing wheel 202 are provided which minimize 18 energy loss for maximum acceleration of the materials. The throwing wheel 202 19 is rotatably driven with a drive shaft and motor arrangement 206. The 20 arrangement 206 is secured to the throwing wheel 202 with an erosion-avoidant 21 arrangement. An impact rotor 208 is similarly rotatably driven with a drive shaft 22 and motor arrangement 210 which is secured to the impact rotor 208 with an 23 erosion-avoidant arrangement. 24 Preferably the impact rotor 208 is contra-rotating to the throwing 25 wheel 202. Not detailed for this embodiment, however as described above in the 16 WO 2008/122122 PCT/CA2008/000644 1 co-pending application, a first motor is directly coupled to the impact rotor and 2 operable to power the impact rotor and a second motor directly coupled to the 3 throwing wheel and operable to power the throwing wheel. 4 Further, the comminuting apparatus further comprises an 5 embodiment of a housing 212 which is readily accessible for maintenance, 6 particularly the throwing wheel 202 and impact rotor 208. The housing 212 7 comprises an upper housing 213 and a lower housing 214 which are reversibly 8 and axially separable for accessing a comminuting chamber 215 and for 9 accessing the throwing wheel 202 and impact rotor 208 operable within the 10 chamber 215. 11 The upper housing 213 is supported in space by stands 216. The 12 lower housing 214 is suspended from the upper housing 213 by actuators 218. 13 Actuators 218 are operated for raising and lowering the lower housing 214 14 relative to the upper housing 213 between a raised operating position (Fig. 10) 15 and a lowered maintenance position (Fig. 12) for enabling access to the throwing 16 wheel 202 and impact rotor 208. The upper and lower housings 213,214 seal at 17 an interface 220 in the raised operating position and position the throwing wheel 18 202 and impact rotor 208 in co-axial operably-spaced arrangement. As shown in 19 the top view of the housing 212 in Fig. 11, there can be multiple supports 216, 20 equi-spaced circumferentially about the upper housing 213, three supports 21 216,216,216 being shown spaced about 1200 apart with three actuators 218 22 circumferentially spaced therebetween. 23 With reference to Fig. 13, the impact rotor 208 and throwing wheel 24 202 rotate about a substantially and concentric, vertical axis A. In one 25 embodiment, as shown, the impact rotor 208 is arranged co-axially above the 17 WO 2008/122122 PCT/CA2008/000644 1 throwing wheel 202. In this arrangement, particulate materials M or particles to 2 be comminuted pass through the axis A of the impact rotor 208 to access the 3 throwing wheel 202. In a mirror arrangement (not shown) wherein the throwing 4 wheel 202 is above the impact rotor 208, the particles M can fall along the axis A 5 of the throwing wheel directly. Terms such as bottom and top are used herein in 6 the illustrated context of the impact rotor 208 arranged over the throwing wheel 7 202. 8 The impact rotor 208 and throwing wheel 202 is an assembly of a 9 body 222 and a plurality of impact teeth 223 spaced about the periphery of the 10 body 222 and extending axially therefrom. The throwing wheel 202 can be an 11 assembly of a bottom plate 212, a top plate 213 and a plurality of inserts 226 12 sandwiched therebetween. The inserts 226 determine the configuration of the 13 channels 204 formed therebetween. As discussed later the inserts can be pie 14 shaped for forming channels 204 of substantially parallel side walls. The 15 plurality of channels 204 extend from a central inlet 227 to a plurality of particle 16 exits 229. An apex 228 of each insert 226 is oriented generally radially inwardly 17 towards the axis A. 18 In more detail in Figs. 14A and 14B, impact rotor 208 shown above 19 the throwing wheel 202 comprises a plurality of teeth 223 extending downwardly 20 therefrom and mechanically fastened to body 222 for ease of replacement. A 21 central hole 230 in the body 222 passes particles M to the throwing wheel 202 22 co- axially arranged therebelow. One embodiment of each tooth 223 is a 23 triangular form, providing one or more impact surfaces 231 which can be 24 oriented for optimal impact with particles thrown from the throwing wheel 202. 18 WO 2008/122122 PCT/CA2008/000644 1 Each tooth 223 can be secured with a single fastener 215 enabling rotation 2 positioning of the impact surfaces 231. 3 The throwing wheel 202 is a sandwiched assembly 225,226,224 for 4 ease of replacing wear components. The inserts 226 are spaced 5 circumferentially about the wheel 202 and spaced from one another for forming 6 energy imparting side walls of the generally radially extending channels 204. As 7 described in Applicant's co-pending application, a variety of channel 8 configurations are contemplated. A further configuration is described herein. 9 As shown in Figs. 15C and 15D, the bottom plate 224 comprises a 10 mounting means for securing the inserts 226 in a position for forming the 11 channels 204. In this embodiment, the mounting means comprise a plurality of 12 axially extending bosses 240 which form mounting and positioning structure for 13 the inserts 226 (see Fig. 15E). Each boss 240 corresponds to a cavity or socket 14 241 formed in each insert 226. The bosses 240 extend axially from at least one 15 of the top or bottom plates 225,224. As shown, the bosses 240 can be formed 16 integrally with the bottom plate 224 or otherwise secured thereto. The bosses 17 240 need not be designed for wear-resistance as each insert 226 encapsulates 18 the boss 221. 19 Each insert 226 has a leading side wall 250 and a lagging side wall 20 251. Between the leading side wall 250 and lagging side wall 251 of adjacent 21 inserts is formed each channel 204. The bottom plate 224 and top plate 225 22 form the bottom and top of the channel 204 respectively. As shown in Figs. 13, 23 15A and 15B, particles M can enter the throwing wheel 202 through the central 24 inlet port 227 formed in the top plate 225. The leading and lagging side walls 25 250,251 can be parallel or non-parallel. 19 WO 2008/122122 PCT/CA2008/000644 1 As discussed above, the channels 204 guide the particles M and 2 urge them along a vector including a tangential component, applying significant 3 wear on the side walls 250,251 of the channels 204. Implementation of this 4 arrangement of replaceable inserts 226 enables selection of differing, greater 5 wear-resistant materials for the side walls 250,251 than those used for the top 6 and bottom plates 225,224. 7 With reference to Figs. 15E and 15F, each insert 226 has cavities 8 or sockets 241, each of which corresponds in shape to each boss 240. A 9 plurality of inserts 226 are shown in Fig. 15E arranged for superpositioning their 10 respective sockets 241 over each insert's corresponding boss 240, a subset of 11 the fourteen illustrated inserts 226 being shown installed over a respective 12 subset of bosses 240 of Fig. 15F. As shown, one form of corresponding boss 13 240 and socket 241 include a pie or triangular shape which both orients each 14 triangular insert 226 and fixes its position in the throwing wheel 202. The apex 15 228 of each pie-shaped insert 226 is oriented generally radially inwardly towards 16 the central inlet port 227. Other boss 240 and socket 241 combinations are 17 contemplated within the scope of this application. 18 With reference to Fig. 16, an assembled impact rotor 208 is shown 19 poised over an exploded-view of the throwing wheel 202 and demonstrating 20 installation of inserts 226 to bosses 240 for assembly of the throwing wheel 202. 21 With reference also to Fig. 15E, one can see the inserts 226 right of the 22 illustrated centerline have been fit to the rightmost bosses 240 and the remaining 23 inserts 226 left of the centerline are ready for fitting to the remaining bosses 240. 24 Means for fastening the sandwiched assembly are contemplated, including pairs 25 of counter-sunk base holes 243 through the bottom plate 224 at each boss 240 20 WO 2008/122122 PCT/CA2008/000644 1 for fasteners to secure to top holes 244 in the top plate 225, the fasteners being 2 omitted from the view. 3 In some more detail, the top plate 225 is secured to the bottom 4 plate 224 using fasteners which extend through the bosses 240 and inserts 226, 5 securely mounting the inserts 226 against the inertial forces generated while 6 rotating and accelerating particles. The material properties of the insert 226 can 7 be selected dependent upon the particles being processed including metallic 8 alloys, hardfaced materials and ceramics. The materials choices for the top 9 plate 225, bottom plate 224 and bosses 240 are less subject to erosion and can 10 be based more so upon mechanical assembly principles and need not be 11 restricted to wear-resistance. 12 The side walls 250,251 of the inserts 226 direct and accelerate the 13 particles in a curved radial path in global coordinates and thus are subjected to 14 maximal forces and erosion as they impart acceleration forces in redirecting the 15 particles M. The bottom and top of the channels 204 are not directly involved in 16 redirecting particles except to the extent that they constrain gravity, random 17 movement and some circulation. Accordingly, adaptation of the materials or 18 surface of the top and bottom plates for wear resistance can less critical. The 19 impact surfaces 231 of the impact rotor 208 are also designed for, and subjected 20 to, near instantaneous deceleration of the particles thrown from the wheel 202 21 and thus are also subject to extreme erosive forces. The teeth 223 themselves 22 can form the impact surface 231 and accordingly be formed of wear-resistant 23 materials or, as described in Applicant's US Patent 7,207,513, separate wear 24 resistance impact surfaces 231 can be fit to each tooth 223. 21 WO 2008/122122 PCT/CA2008/000644 1 Another area of direct particulate erosion occurs when the particles 2 from the hopper impinge on the bottom plate 224 through the central port 227 3 through the top plate 225. The trajectory of the particles from the hopper are 4 redirected from a substantially vertically downward flow along the axis A to a 5 radial flow through the channels 204. This redirection results in wear. A 6 substantially planer surface 245 on the bottom plate 224 has been employed 7 successfully. This is an area which could be protected by an anti-wear 8 treatment. In embodiments having the throwing wheel mounted to the drive 9 through the bottom plate 224, the planer surface 245 is not penetrated by any 10 mounting hardware and the planer surface 245 can be fit with ceramics or 11 elastomeric materials without compromising the integrity of either the wear 12 surface or the throwing wheel. 13 With reference to Fig. 19, the channels 204, the impact surface 231 14 and to a lesser extent the central port 227 in the wheel 202, are not the only 15 components subject to wear. A circulation of comminuted particles adjacent the 16 impact rotor at the impact surfaces 231, and between the generally planer 17 contra-rotating surfaces of the impact rotor 208 and the throwing wheel 202 is 18 also a known erosive factor. These planer surface are not subjected to the same 19 energy of impact and other anti-wear solutions are available, in structure and in 20 material choices. Accordingly, in another aspect of the invention, an area of 21 consideration for protection is the planer underside 261 of the impact rotor 208 22 which faces a top surface 262 of the top plate 225. There is necessarily a gap 23 263 therebetween for enabling contra-rotation of the components. 24 This gap 263 is not a processing path for comminuting particles 25 however, due to the inherent distribution of comminuted dust throughout the 22 WO 2008/122122 PCT/CA2008/000644 1 housing 212, some particles circulate into and out of the his gap 263, causing 2 wear. As the exposed surfaces in the gap 263 are not energy transferring 3 surfaces, such as the hard materials of the inserts 226 and impact surfaces 231, 4 one can install wear-resistant, resilient, elastomeric materials such as urethane 5 to one or the other of the impact rotor or the throwing wheel facing the gap 263. 6 For example, it has been noted that wear has been more predominant on the 7 underside 261 of the impact rotor 208. Accordingly an anti-wear surface or 8 protective layer 265, such as an elastomeric material including urethane, is 9 employed along the rotor's underside 261. 10 Further, the gap 263 extends radially to a peripheral interface 11 between the throwing wheel 202 and the impact teeth 231, is formed an annular 12 impact area 270. Above the impact areas 270, the underside 261 is also subject 13 to wear and is preferably also coated with a protective layer 265. In addition, the 14 life of the impact rotor 208 can be extended by mounting the impact teeth 231 on 15 an optional annular ring 271 which is easily replaced when worn. 16 Turning to the performance of the particle movement, and as 17 shown in Figs. 17 and 18, the flow characteristics of the multiphase flow of 18 particles or material through air is modeled to demonstrate the effectiveness of 19 the channel design 204. 20 Surprisingly, the use of parallel side walls 250,251 for the channel 21 204, while functional, is not necessarily optimal. Figs. 17 and 18 illustrate 22 particle velocity results of Computational Fluid Dynamics (CFD) analysis. The 23 reference for the velocity vectors is relative to the throwing wheel. The velocity 24 vectors are those viewed from the throwing wheel as it rotates. As shown in Fig. 25 18, where side by side inserts 226,226 form a parallel; wall channel 204p 23 WO 2008/122122 PCT/CA2008/000644 1 therebetween, The flow mechanics can result in eddies E, illustrating some 2 areas of substantially stationary particles, which result in a loss of some of the 3 energy capable of being imparted to the particles. As shown in Fig. 17, the side 4 by side inserts 226,226 form a converging wall channel 204c therebetween. The 5 particles in the converging channel 204c achieve near or substantially streamline 6 flow. Modeling programs such as ANSYS@ can be used to ascertain the proper 7 convergence for optimal flow characteristics to avoid eddies. 8 One example of a suitable convergence is as shown in Fig. 15F, 9 the angle of each insert's side wall 250,251 to a radial from the axis A of the 10 throwing wheel 202 being about 50 or an included angle of about 9 - 100 11 between the side walls 250,251 of adjacent inserts 226,226. The modeling was 12 based upon particles diameters 3mm, wheel rotational speed of 3,000 RPM and 13 channel dimensions of 25mm x 15mm. One approach to determination of 14 channel convergence is to reduce the cross-section area as the flow accelerates 15 to minimize flow separation and eddy currents. Another approach is to establish 16 the convergence angle based upon achieving a channel exit cross section area 17 times the radius of the approximately equal to the channel inlet cross section 18 area times the inlet radius. 19 In operation, the throwing wheel 202 is rotated about the 20 substantially vertical axis A. Particles to be fragmented through the central inlet 21 227 for accelerating the particles through the channels 204. The particles 22 accelerated generally radially along a converging flow path in the channels 204 23 as the particles flow from the central inlet 227 to the particle exits for favoring 24 streamline flow of particles between the side walls 250,251. The particles 25 discharge from the particle exits 229 and impact against impact surfaces 231 24 1 arranged about the periphery of the throwing wheel 202. Preferably the impact rotor 2 208 is rotated co-axially with the throwing wheel 202 and the impact rotor 208 is 3 counter-rotated relative to the throwing wheel 202. 4 With reference to Fig. 20, another embodiment of the invention 5 concerns product and dust management. The housing 212 is fitted with atmospheric 3 flow controls for minimizing re-entrainment of product and dusts into the area about 7 the throwing wheel 202 and impact rotor 208. 3 As shown, the upper housing 213 is fitted with a tubular skirt 300 3 extending axially downward into close proximity with the wheel/rotor assembly 301 of ) the comminuting apparatus 200. Similarly, lower housing 214 is fitted with a tubular 1 skirt 302 extending axially upward into close proximity with the wheel/rotor assembly 2 301. Within skirts 300 and 302 are formed exclusion chambers 303 which can be 3 swept with a flow of clean gas such as air. Air fittings 304 can direct air into the 4 exclusion chambers 303,303 for flow out of the chambers adjacent the wheel/rotor 5 assembly 301 for excluding particular material therefrom. Dust extraction from the 3 comminuting chamber 215 can be through dust ports 305. Comminuted material 7 product exits the comminuting chamber 215 via a lower exit 306. 8 Although a preferred embodiment of the present invention has been 9 described in the foregoing detailed description, it will be understood that the invention 0 is not limited to the embodiment disclosed, but is capable of numerous 1 rearrangements, modifications and substitutions without departing from the scope of 2 the invention. 3 Throughout this specification the word "comprise", or variations such as 4 "comprises" or "comprising", will be understood to imply the inclusion of a stated 5 element, integer or step, or group of elements, integers or steps, but not the 25 1 exclusion of any other element, integer or step, or group of elements, integers or 2 steps. 3 All publications mentioned in this specification are herein incorporated I by reference. Any discussion of documents, acts, materials, devices, articles or the 5 like which has been included in the present specification is solely for the purpose of 3 providing a context for the present invention. It is not to be taken as an admission T that any or all of these matters form part of the prior art base or were common 3 general knowledge in the field relevant to the present invention as it existed in ) Australia or elsewhere before the priority date of each claim of this application. 26