GB2390043A

GB2390043A - Shredding apparatus to facilitate the burning of bales of packaging material

Info

Publication number: GB2390043A
Application number: GB0215016A
Authority: GB
Inventors: Ross Donovan
Original assignee: ASGARD SYSTEMS Ltd; CLUBBS PROJECTS Ltd
Current assignee: ASGARD SYSTEMS Ltd; CLUBBS PROJECTS Ltd
Priority date: 2002-06-28
Filing date: 2002-06-28
Publication date: 2003-12-31
Also published as: GB0215016D0

Abstract

A system to burn bales 12 of packaging material sheets comprising cardboard, paper, packaging plastic, etc includes a bale feeder 2, a bale shredder 4, a shredded material conveyor 6, a shredded material feeder 8, and a boiler 10. The bale feeder 2 transports the bales 12 to the bale shredder 4, which has a plurality of rotating ripping blades(40 fig 5) to rip, tear and pull material from the bale 12, and a plurality of stationary cutting blades (44) to cut material removed by the ripping blades (40) into smaller pieces. Upon detection of jamming of the ripping blades (40), the bale feeder 2 is controlled to withdraw the bale 12 from the shredder 4, and the ripping blades (40) are driven in reverse direction in an attempt to free trapped material. The shredded material feeder 8 includes a hopper (100 fig10) air airlock plate (104) and a transfer drawer (124) to receive shredded material and transfer it to the hopper (100). Both the airlock plate (104) and transfer drawer (124) have "closed" positions in which they substantially block air flow through the hopper (100) to the boiler 10. Movement of the airlock Plate (104) and drawer (124) is controlled so that least one of them is always in the "closed" position during use. The boiler 10 has a water jacket (202 fig 13) which includes a water filled wall (244) between chambers through which exhaust gases passes, thereby increasing the surface area in contact with the gases. The hearth (200 fig14) of the boiler is designed to allow ash to fall to the base of the boiler rather than accumulating in the hearth, thereby facilitating easier ash removal.

Description

APPARATUS TO FACILITATE THE BURNING

OF BALES OF PACKAGING MATERIAL

The present invention relates to apparatus to facilitate 5 the burning of bales of packaging material comprising sheets of cardboard, paper, packaging plastic, such as shrinkwrap, etc. Many businesses have considerable amounts of packaging 10 material which requires disposal each year.

Often, to ease transport and disposal, sheets of packaging are placed in a compacting machine which compacts the material sheets and binds them to form 15 laminated bales having a typical size of 1 to 2m by 0.5 to lm by 0.5 to lm and a typical weight of 100kg to 200kg. The present invention aims to provide apparatus to 20 facilitate the burning of such bales of packaging material, thereby releasing heat energy which can be used for heating purposes etc. According to the present invention there is provided a 25 shredding machine for shredding bales of packaging

material sheets, the shredding machine having ripping means operable to rip and dislodge material from a bale and cutting means for cutting material dislodged by the ripping means. In use, the shredding machine produces 5 pieces of material suitable for burning.

The present invention also provides apparatus for shredding bales of packaging material comprising shredding means for shredding the packing material in a 10 bale, transport means for moving the bale towards and away from the shredding means, means for determining if the shredding means becomes jammed, and control means for controlling the shredding means and transport means in the event of jamming detection to move the bale away from 15 the shredding means and control the shredding means to attempt to remedy the jam.

The present invention also provides apparatus for transferring solid fuel, such as shredded packaging 20 material, into a receiving apparatus, such as a boiler, without allowing significant amounts of air into the receiving apparatus, comprising a housing, feeding means for feeding solid fuel into the housing and releasing means for releasing fuel from the housing, wherein each 25 of the feeding means and releasing means is independently

movable between first and second positions, and wherein each of the feeding means and releasing means engages the housing in one of the positions to prevent significant amounts of air leaving the apparatus to the receiving 5 apparatus, such that the feeding means can be moved to a position to receive solid fuel while the releasing means engages the housing to prevent significant amounts of air leaving the apparatus, and the releasing means can be moved to a position to release solid fuel from the 10 housing while the feeding means engages the housing to prevent significant amounts of air passing through the housing. The present invention also provides a boiler for burning 15 shredded packaging material and heating water, having a water jacket which includes a waterfillable wall between first and second chambers through which exhaust gases pass. 20 The present invention further provides a boiler having a hearth arranged relative to the rest of the boiler such that ash does not accumulate in the hearth, but instead falls from one end of the hearth into a lower part of the boiler for removal.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which like reference numbers are used to designate like parts, and in which: Figure 1 is a perspective, partially cut away, view of the components of a system embodying the invention; Figure 2 is a perspective view showing the functional 10 components of the bale feeder and bale shredder of the system in Figure 1; Figure 3 is a side elevation of the bale feeder and bale shredder; Figure 4 is a front elevation of the bale shredder and shredded material conveyer; Figure 5 is a perspective view showing the arrangement 20 of the blades of the bale shredder; Figure is a plan view of the bale shredder; Figure 7 is a front elevation of part of the shredded 25 material conveyer in use;

Figure 8 is a front elevation of the shredded material feeder; Figures 9 and 10 are perspective views of the functional 5 components of the shredded material feeder to illustrate the operation thereof; Figure lla and Figure llb are plan views of the shredded material feeder, Figure lla showing the shredded material 10 feeder in its "open" position to receive shredded material, and Figure llb showing the shredded material feeder in its closed position to feed the shredded material to the boiler; 15 Figures 12a, 12b and 12c comprise, respectively, a front view of the boiler, a right-hand side view of the boiler with hidden details shown dotted, and a left-hand side view of the boiler; 20 Figure 13 is a perspective, partially cut away, view of the water jacket of the boiler; Figure 14 is a schematic block diagram illustrating the electrical control components of the system in Figure 1;

Figures 15a, 15b and 15c comprise a flow chart showing the control procedure of the system in Figure 1; and Figure 16 is a flow chart showing the control processing 5 performed as the shredder de-jamming routine at step S15 46 in Figure 15c.

Overview 10 Referring to Figure 1, the system in this embodiment comprises a bale feeder 2, a bale shredder 4, a shredded material conveyer 6, a shredded material feeder 8, and a boiler 10.

15 The system is designed to handle bales 12 of packaging material comprising cardboard, paper, packaging plastic (such as shrinkwrap plastic, etc.) and similar packaging material, which has been compacted and bound by plastic straps 13 into a bale having a typical size of the order 20 of l.lm by 0.8m to 0.7m and a typical weight of the order of 120kg to 150kg.

In use, the bale feeder 2 transports the bales 12 of packaging material to the bale shredder 4, which shreds 25 the material into smaller pieces using a plurality of

blades 15.

The conveyor 6 transfers the shredded material pieces from the shredder 4 to the feeder 8.

The feeder 8 transfers the shredded material pieces to the boiler 10, where it is burnt to release heat energy which is used to heat water.

10 Bale Feeder The components and operation of the bale feeder 2 will now be described.

15 Referring to Figures 2 and 3 in addition to Figure 1, the bale feeder 2 includes a plurality of horizontal rollers 14 coupled together by a roller chain 16 between each adjacent pair of rollers. In use, the horizontal rollers 14 are driven by a motor 18 through a gear arrangement 20 20 to transport bales 12 to the bale shredder 4.

In this embodiment, the motor 18 is a 0.75kW motor and the gear arrangement 20 is such that the bales 12 are transported by the rollers 14 at approximately 30mm per 25 second.

Each bale 12 is placed on the horizontal rollers 14 so that the sheets of material therein lie in planes which are perpendicular to the planes of the blades 15 in the bale shredder 4. AS will be explained below, this 5 assists in the removal and shredding of the material from the bale 12. In this embodiment, the blades 15 of the bale shredder 4 are arranged in substantially horizontal planes so that each bale 12 is placed on the horizontal rollers 14 of the bale feeder 2 with the sheets of 10 material in vertical planes, as shown in Figure 1.

In Figures 1 and 3, only one bale 12 is shown in the bale feeder 2. However, in practice, two (or more) bales may be placed on the horizontal rollers 14 so that they abut 15 each other. In this case, the second bale assists in pushing the first bale into the blades of the bale shredder 4 when the horizontal rollers 14 are driven by the motor 18.

20 As will be explained in further detail below, the motor 18 may be run in reverse direction to withdraw a bale 12 from the bale shredder 4 in the event that the bale shredder 4 jams.

25 A plurality of horizontal top rollers 22 are provided,

which are linked together by a roller chain 24 between each pair of adjacent rollers, but which are not driven in this embodiment. The top rollers 22 assist in the transport of bales 12 to the bale shredder 4, and also 5 stabilise each bale 12 against any upward forces when the bale is being shredded by the bale shredder 4.

A plurality of side rollers 26 are provided on each side of the front part of the bale feeder 2, that is, the part 10 adjacent the bale shredder 4. In addition, a single side roller 28 is mounted on the rear of the bale shredder 4 on the side towards which each bale 12 is forced by the motion of the blades 15 of the shredder 4 (in this embodiment, the shredder blades rotate in a clockwise 15 direction and therefore the side roller 28 is mounted on the right-hand side of the rear of the shredder 4 when viewed from the front).

The side rollers 26 and 28 stabilise the bale 12 against 20 sideways movement caused by shredding of the bale 12 by the bale shredder 4. This stabilization has been found to be particularly important when the front part of each bale 12 has been removed by the bale shredder 4 such that the part of the bale 12 remaining in the bale feeder 2 25 is sized so that the length of the horizontal faces of

the bale 12 (that is the faces in contact with the bottom rollers 14 and top rollers 22) is less than the horizontal width of the bale (that is, the horizontal width of the face of the bale in contact with the blades 5 15 of the bale shredder 4). In this case, the side rollers 26, 28 prevent the bale 12 skewing on the horizontal bottom rollers 14.

Each horizontal roller 14, 22 and each vertical roller 10 26, 28 has a plurality of longitudinal gripping ribs 30 to provide additional force on each bale 12 during the transport thereof.

A binding cutter 32 is provided to cut the binding straps 15 13 of each bale 12. In this embodiment, the binding cutter 32 comprises a thin blade mounted in a fixed position near the top of the bale shredder 2. The thin width of the blade 32 enables the blade to pass between the vertical sheets of material in a bale so that, as the 20 bale 12 is transported towards the bale shredder 4, each binding strap 13 is cut in turn when it reaches the blade 32. Since the material in each bale is compacted, the sheets 25 of material "flare'. out when a binding strap 13 has been

cut, which facilitates the shredding of the material by the bale shredder 4. More particularly, the shredder 4 pulls and tears the sheets of material more easily when a binding strap 13 has been cut. On the other hand, when 5 the binding straps 13 are not cut, the shredder 4 produces very small pieces of material together with considerable amounts of material dust.

Bale Shredder The components and operation of the bale shredder 4 will now be described with reference to Figures 1 to 6.

Referring to Figure 5, the blades 15 of the bale shredder 15 4 comprise four sets of toothed ripping blades 40, each set being mounted on a respective rotating shaft 42a, 42b, 42c and 42d, and fixed cutting blades 44 arranged in three respective sets 46, 48, 50. (It should be noted that, for clarity, not all of the cutting blades 44 are 20 shown in Figures 1 to 4.) The ripping blades 40 are arranged to rotate to rip, tear and pull relatively large pieces of material from a bale 12, rather than to cut through the material.

25 Consequently, a stream of relatively large pieces of

material is produced by the rotating ripping blades. The relatively large pieces of material produced in this way are then forced across the fixed cutting blades 44 due to the force imparted by the rotation of the rippling 5 blades 40, with the result that the material is cut into smaller pieces by the fixed cutting blades 44.

To achieve this effect, the face of each tooth on each ripping blade 40 which is to contact the material in the 10 bale 12 is blunt relative to the cutting edge of each cutting blade 44, and each tooth of each ripping blade 40 is curved.

Material removed from a bale 12 by the ripping blades 40 15 will first be cut by the cutting blades 44 in set 46, then by the cutting blades 44 in set 48, and finally by the cutting blades 44 in set 50. To reduce unwanted forces imparted by the material on the cutting blades 44, the number of cutting blades 44 increases in each 20 successive set 46, 48, 50. In this embodiment, the number of cutting blades 44 in the sets 46, 48 and 50 is three, seven and eleven, respectively. In this way, pieces of material removed from a bale 12 are progressively cut into smaller pieces by the cutting 25 blades in sets 46, 48, 50. Consequently, forces created

by a large piece of packaging material hitting a large number of cutting blades 44 are avoided because the material is first cut by relatively few cutting blades and then subsequently cut by an increasing number of 5 cutting blades.

The rotating shafts 42a, 42b, 42c, 42d and the ripping blades 40 thereon are arranged over an area to cover the face of a bale 12 fed to the bale shredder 4 by the bale 10 feeder 2.

Referring to Figure 4, in this embodiment, eleven ripping blades 40 are provided on rotating shafts 42b and 42d, with each ripping blade 40 arranged in a substantially 15 horizontal plane. On each of rotating shafts 42a and 42c, ten ripping blades 40 are provided, with adjacent blades being arranged at an angle relative to each other.

The rotation shafts 42a, 42b, 42c and 42d are positioned 20 sufficiently close together that the ripping blades on adjacent rotating shafts are interleaved (as best seen in Figure 4).

On each respective rotating shaft 42a, 42b, 42c, 42d, the 25 ripping blades 40 are arranged so that the positions of

the teeth thereon are offset between the blades on the shaft (that is, each blade 40 on a given shaft is positioned so that it is rotated relative to the other blades on the shaft). In this way, when a given shaft 5 rotates, the ripping blades on the shaft make contact with the material in the bale 12 at different times, thereby reducing the force applied to the bale 12 at any given time, and also reducing the counterrotation force applied to the rotating shaft. In a similar way, the 10 ripping blades 40 are, as far as possible, arranged in an offset way across the different rotating shafts 42a, 42b, 42c, 42d so that the ripping blades 40 at the same height on different respective rotating shafts 42a, 42b, 42c, 4d, contact the bale 12 at different times.

The rotating shafts 42a, 42b, 42c, 42d are driven by a motor 60 via a drive shaft 62, drive gear 64, idler gears 66a, 66b, 66c and driven gears 68a, 68b, 68c, 68d.

20 In this embodiment, the motor 60 is a 5.5kW, 44 rpm motor, and the drive gear 64, idler gears 66a - 66c and driven gears 68a - 68d provided a stepped down gear arrangement to drive the ripping blades 40 at approximately 20 rpm.

As will be explained in more detail below, the motor 60 can be controlled to run in reverse in order to reverse the direction of rotation of the ripping blades 40 to remove any packaging material which becomes stuck 5 therein. In addition, the bale shredder 4 is pivotably connected to the bale feeder 2 by means of hinges 72a, 72b so that it can be swung away from the bale feeder 2 to allow 10 access to the blades for maintenance. In use, the bale shredder 4 is locked to the bale feeder 2 by means of locking pin arrangements 74a, 74b.

A current overload sensor (not shown) is provided in the 15 bale shredder 4 to detect any current overload from the motor 60 indicating jamming of the ripping blades 40 (jamming occurring when the ripping blades 40 are caused to stop or substantially slow in their rotation by trapped packaging material). Output signals from the 20 current overload sensor are used in the overall control of the system, as will be described in detail below.

Shredded Material Conveyor 25 The components and operation of the shredded material

conveyor 6 will now be described with reference to Figures 1, 2, 4 and 7..

The shredded material conveyor 6 comprises a conveyor 5 belt 80 within a housing 82 to shield shredded material pieces on the conveyor belt 80 from wind, rain etc. As best seen in Figure 2, the conveyor belt 80 extends beneath the blades 15 of the bale shredder 4 so that 10 pieces of packaging material shredded by the bale shredder 4 fall on to the conveyor belt 80 for transport thereby. Referring to Figures 4 and 7, in this embodiment, the 15 housing 82 of the shredded material conveyor 6 is shaped to provide a shredded material ''reservoir", generally designated as 86. This reservoir 86 is provided because the shredder 4 may produce shredder material at a faster rate than the conveyor belt 80 can transfer it to the 20 shredder material feeder 8. Should this occur, the reservoir 86 provides space for the shredded material to accumulate before it is removed by the conveyor belt 80.

To detect when the reservoir 86 is full of shredded 25 material, a microswitch 88 is provided together with a

plate 90, which is pivoted at 92 and counterbalanced by a weight 94. In use, if the reservoir 86 fills with shredder material, then the material causes the plate 90 to pivot about the pivot 92 thereby closing the 5 microswitch 88 and generating an electrical signal. The use of the electrical signal from the microswitch 88 in the overall control of the system will be described in detail below.

10 A conveyor motor (not shown) is provided to drive the conveyor belt 80 to transfer shredder material from beneath the bale shredder 4 to the shredded material feeder 8.

15 Shredded Material Feeder The components and operation of the shredded material feeder 8 will now be described with reference to Figures l and 8 to 11.

The shredded material feeder 8 includes a hopper lOO through which shredded material can fall to a screw auger 102 driven, in use, by a screw auger motor (not shown) to transfer the shredded material to the boiler lo via 25 a screw auger tube 103.

An airlock plate 104 is provided having a horizontal front portion 104a and a horizontal rear portion 104b with a vertical step 104c therebetween. The rear portion, 104b in sliding contact with the vertical side 5 walls of the hopper 100 at a position substantially midway up the sidewalls.

The front portion 104a of the airlock plate 104 is provided with rolling bearings comprising, in this 10 embodiment, four wheels 106a, 106b on each side thereof which run within U-shaped channel frames 108. The wheels 106a are arranged to run in a horizontal plane contacting the vertical side walls of the frames 108, and the wheels 106b are arranged to run in a vertical plane contacting 15 the inner bottom and top horizontal surfaces of the frames 108. The rear portion 104b of the airlock plate 104 is subjected, in use, to intense heat from the boiler 10 which reaches the airlock plate 104 via the screw auger tube 103. For this reason, the wheels 106a, 106b 20 for the airlock plate 104 are provided on the front portion 104a which is not subjected to the same intense heat. A linear actuator 110 is provided on one side of the 25 shredded material feeder 8 to move the airlock plate 104

between a "closed" position and an "open" position". In the "closed" position, the rear portion 104b of the airlock plate 104 closes the channel through the hopper 100 (as shown in Figure 10) and provides a substantially 5 air-tight seal with the sidewalls of the hopper 100 so that significant amounts of air cannot enter the boiler 10 via the hopper 100 and screw auger tube 103. In the "open position, the rear portion 104b of the airlock plate 104 is clear of the hopper log, so that the channel 10 through the hopper 100 is open to allow shredded material to fall into the screw auger 102. Limit switches (not shown) are provided to determine when the airlock plate 104 is in its "closed" position and in its "open" position. A weighing and feeding unit, generally designated as 120, and comprising a weigh cell 122 and a transfer drawer 124, is provided to weigh shredded material received from the conveyor 6, and to transfer a predetermined weight 20 of shredded material to the hopper 100.

The transfer drawer 124 has four vertical side walls comprising a front wall 125a, a rear wall 125b and side walls 125c, but no bottom or top walls. Consequently, 25 the drawer 124 is open at the top to allow shredded

material to enter, and is open at the bottom to allow shredded material to fall on to the weight cell 122 or into the hopper 100 (depending upon the position of the drawer 124).

The front wall 125a of the transfer drawer 124 extends beyond each of the side walls 125c to define flanges on each side of the front of the transfer drawer 124. When the transfer drawer 124 is in its.tclosed't position 10 inside the housing of the feeder 8, the flanges defined by the front wall 125a abut the feeder housing forming a substantially air- tight seed therewith and preventing any significant amount of air from entering the housing and hence entering the hopper 100.

Two front wheels 126a are provided on the front of the drawer 124 on respective sides at the bottom thereof, and two rear wheels 126b are provided on respective sides at the rear of the drawer 124 at the top thereof. The front 20 wheels 126a run along L-shaped frames 128 provided along the sides of the weigh cell 122, while the rear wheels 126b run along L-shaped frames 130 provided inside the housing of the feeder 8.

25 A linear actuator 132 is provided on one side of the

to l shredded material feeder 8 to move the transfer drawer 124 from an ''open" position (shown in Figures 1, 8, 9, 10 and lla) in which shredded material received from the conveyor 6 can be accumulated in the drawer 124 and 5 weighed by the weigh cell 122, to a closed position (shown in Figure lib) in which the transfer drawer 124 is above the hopper 100, thereby allowing the shredded material to fall into the hopper 100 and onto the airlock plate 104.

Limit switches (not shown) are provided to determine when the transfer drawer 124 is in the..open" position and when it is in the enclosed" position.

15 The way in which the transfer drawer 124 and airlock plate 104 are moved to transfer shredded material to the screw auger 102 without allowing significant amounts of air into the boiler 10 will now be described.

20 To load the transfer drawer 124 with shredded material and to weigh the shredded material on the weigh cell 122, the transfer drawer 124 is moved to its "open" position above the weigh cell 122, while the airlock plate 104 is moved to its "closed" position with the rear portion 104b 25 thereof blocking the passage through the hopper 100 and

preventing significant amounts of air reaching the screw auger tube 103. This situation is illustrated in Figure lla. 5 When the required weight of shredded material has been accumulated in the transfer drawer, the transfer drawer 124 is moved to its "closed' position above the hopper 100. As the transfer drawer 124 is moved, the shredded material therein falls onto the airlock plate 104 within 10 the hopper 100. In its fully closed position, the flanges on the front wall 125a of the transfer drawer 124 abut the housing of the feeder 8 preventing any significant amount of air reaching the hopper 100 from outside the feeder 8. Consequently, once the transfer 15 drawer 124 is in its "closed" position, the airlock plate 104 can be moved to its "open" position to allow the shredded material to fall through the remainder of the hopper 100 to the screw auger 102 without significant air being drawn into the boiler 10.

Boiler The components and operation of the boiler 10 will now be described with reference to Figures 12 and 13.

Referring first to Figures 12a and 12b, the boiler lo includes a hearth 200 and a water jacket 202.

Shredded material is fed into the hearth 200 by the screw 5 auger 102 through the screw auger tube 103 which, in this embodiment, connects to the tube 204 which passes through the front of the boiler 10.

The hearth 200 comprises three axis-aligned tubes, namely 10 an inner tube 203 defining the hearth in which shredded material is burned, a central tube 206 defining a water jacket for the hearth, and an outer tube 207 defining an air passage tube.

15 The hearth 200 is water-cooled with water being pumped into the water jacket 206 through a water inlet 208 by a pump (not shown) and out through a water outlet 210.

Air is blown into the outer tube 207 by two fans (not 20 shown) through air intakes 220 and 222, with the air passing through the water jacket 206 to the hearth 200 via a plurality of passages 224 through the water jacket 206. The air passages 224 are positioned to substantially surround the perimeter of the hearth 200 25 and also to occupy positions along the length of the

hearth 200. In this way, a vortex is created in the exhaust gases from the hearth 200.

The hearth 200 is provided at a position substantially 5 midway in the height direction of the boiler 10. In use, the pieces of shredded material fed into the hearth 200 burn as they pass along the length of the hearth 200.

The pieces are of a sufficient size that burning is typically not complete until each piece is substantially 10 at the end of the hearth 200 remote from the end at which it was introduced into the hearth 200. As a result, ash from the burnt material does not accumulate in the hearth 200, and instead falls from the end of the hearth 200 because it is pushed out by material passing down the 15 hearth as it burns. In this way, it is not necessary to remove ash from the hearth 200.

A screw auger 230 is provided along the base of the boiler lO and the water jacket 202 is of tapered shaped 20 along its length so that any ash falling from the hearth 200 or deposited by the exhaust gases falls and is funnelled by the water jacket 202 into the screw auger 230. A motor 232 is provided to drive the screw auger 230 to remove accumulated ash to a pneumatic ash removal 25 system (best seen in Figures 12a and 12c), which is

operable to deposit the ash in a receiving container 236.

Referring to Figure 13, the water jacket 202 of the boiler 10 is shaped to define a primary chamber 240 and 5 a secondary chamber 242 for the exhaust gases from the hearth 200.

More particularly, the water jacket 202 is shaped to define an inner water-cooled wall 244 with a circular 10 hole 246 therein defining a passage between the primary and secondary chambers.

This arrangement of water jacket 202 provides a number of advantages. Firstly, by providing the inner wall 244, IS increased contact surface area is provided between the water jacket 202 and the hot exhaust gases, thereby improving the efficiency of the boiler. In addition, by providing the wall 244 to define primary and secondary chambers with a relatively small hole therebetween, it 20 has been found that the exhaust gases are forced to move between the primary and secondary chambers in a way which causes ash contained in the gases to be deposited substantially within the first chamber, with very little ash deposited within the second chamber.

Water is pumped into the water jacket 202 by a pump (not shown) through two water inlets 250 and 252 (Figure 12a) arranged on different sides of the water jacket 202. By providing a water inlet on each respective side of the 5 water jacket 202, problems are avoided whereby the water on one side of the water jacket 202 is warmer than the water on the other side thereof. The water pumped into the water inlets 250, 252 includes the water from the water outlet 210 of the hearth 200, which has already 10 been heated by the exhaust gases from the hearth.

A water outlet (not shown) is provided near the top of the water jacket 202. Water output from the water jacket 202 may be used for a number of different purposes. For 15 example, the water may be fed into pipes to provide central heating for a building, or the water may be fed to heat exchanges so that the heat from the water can be used to heat air, for example in a greenhouse, etc. 20 A number of thermometers (not shown) areprovided to measure the temperature of the water in the water jacket 202. The arrows 260 shown in Figures 12a and 12b indicate the 25 path taken by exhaust gases through the boiler 10.

The exhaust gases leave the hearth 200 as a vortex depositing ash within the primary chamber 240 before passing through the hole 246 in the inner wall 244 of the water jacket 202 into the secondary chamber 242.

From the secondary chamber 242, the exhaust gases pass into exhaust tubes 262 within the top portion of the water jacket 202. It should be noted that, for clarity, the exhaust tubes 262 are not shown in the right-hand 10 view of Figure 12b.

Upon leaving the exhaust tubes 262, the exhaust gases enter an L-shaped grit box 264. Within the grit box 264, an internal plate 266 directs the exhaust gases downwards 15 before they change direction by 180 to exit the boiler 10 to the flue stack. The change of direction of the exhaust gases and the associated change in the flow speeds causes any small pieces of debris caught up in the exhaust gases to be deposited at the bottom of the grit 20 box 264, from which it can be removed periodically by an operator by removing access plate 268.

Process Control 25 The control of the system described above will now be

described with reference to Figures 14 to 16.

Referring to Figure 14, the control components of the bale feeder 2, shredder 4, conveyor 6, shredded material 5 feeder 8 and boiler 10 described above are electrically connected to a control unit 200 (not shown in previous Figures). The control unit 200 includes a microprocessor 202 lo operating in accordance with a stored control program and having associated therewith a plurality of timers 204 and counters 206 in a conventional way. A plurality of audio and visual warning devices 208 are provided, which are controlled by the microprocessor 202 to warn an operator 15 when the system requires human intervention as will be described below.

Referring to Figures 15 and 16, the control of the system by the control unit 200 will now be described.

At step S15-2, microprocessor 202 starts the screw auger motor of the shredded material feeder 8. This is done at the start before any shredded material drops through the hopper 100 so that the material does not accumulate 25 in the screw auger 102 before the screw auger is rotated

to transport the material. In this way, strain on the screw auger motor at start-up is avoided since there is no accumulated material in the screw auger tube 103.

5 As steps S15-4 and S15-6, microprocessor 202 starts the fans and the water pumps in the boiler 10 to feed air into the hearth 200 and to pump water through the hearth water jacket 206 and through the main water jacket 202.

10 At step S15-8, microprocessor 202 reads the temperature from the thermometers in the boiler 10 and determines whether the water in the boiler has reached a temperature greater than the required operating temperature (which, in this embodiment, is 85 C).

If it is determined at step S15-8 that the water temperature is greater than the required operating temperature, then at step S15-10, microprocessor 202 determines whether the water has reached 100 C and, if it 20 has, shuts down the system and outputs a warning via the warning devices 208 at step S15-12.

On the other hand, if it is determined at step S15-8 that the water temperature has not yet reached the required 25 operating temperature, then at step S15-14,

microprocessor 202 sets a weight limit for the weigh cell 122 in the shredded material feeder 8 to a first predetermined value (which, in this embodiment, is lkg).

5 Alternatively, if it is determined at step S15-10 that the water temperature is between the required operating temperature and 100 C, then at step S15-16, microprocessor 202 sets the weight limit for the weigh cell 122 to be a second predetermined value (which, in 10 this embodiment, is 0.25kg).

Following step S15-14 or step S15-16, processing proceeds to step S15-18, at which microprocessor 202 determines from the signals received from the top limit switches of 15 the shredded material feeder 8 whether the transfer drawer 124 of the feeder is in its "closed" position.

If it is determined at step S15-18 that the transfer drawer 124 is already in its "closed" position, then at 20 step S15-20 microprocessor 202 controls the linear actuator 110 of the airlock plate 104 to move the airlock plate 104 to its "open" position and then to its "closed" position. In this way, any shredded material lying on top of the airlock plate 104 is allowed to fall through 25 the hopper 100 onto the rotating screw auger 102.

On the other hand, if it is determined at step S15-18 that the transfer drawer 124 is not in its ''closed" position, then at step S15-22, microprocessor 202 controls the linear actuator 110 to move the airlock 5 plate 104 to its "closed'' position.

Following step S15-20 or step S15-22, processing proceeds to step S15-24, at which microprocessor 202 controls the linear actuator 132 of the transfer drawer 124 to move 10 the transfer drawer 124 to its "open" position to receive shredded material from the conveyor 6.

The processing performed at steps S15-18 to S15-24 as described above ensures that, the first time the steps 15 are performed when the system is started, the transfer drawer 124 and airlock plate 104 are set in their correct relative positions to receive shredded material - that is with the transfer drawer 124 in its "open" position and the airlock plate 104 in its "closed" position.

At step S15-26, microprocessor 202 reads the electrical signals from the weigh cell 122 to determine whether the weight of shredded material thereon is equal to or greater than the weight limit previously set at step S15 25 14 or S15-16.

If it is determined at step S15-26 that the weight limit has been reached or exceeded, then processing proceeds to step S15-28, at which microprocessor 202 stops the shredder motor 60, the bale feed motor 18 and the motor 5 of the conveyor 6.

Subsequently, at step S15-30 microprocessor 202 controls the linear actuator 132 of the shredded material feeder 8 to move the transfer drawer 124 to its "closed" 10 position, thereby transferring the shredded material that has accumulated in the transfer drawer 124 into the hopper 100 and on to the top of the airlock plate 104 therein. 15 After step S1530, the processing returns to step S15-8 and the processing proceeds from there as described above. In this way, when step S15-20 is reached again, the airlock plate 104 is moved to its "open" position so that the shredded material deposited thereon by the 20 transfer drawer 124 now falls onto the rotating screw auger 102.

On the other hand, if it is determined at step S15-26 that the predetermined weight limit on the weigh cell 122 25 has not yet been reached, then processing proceeds to

step S15-32, at which microprocessor 202 starts the shredder blade motor 60 to rotate the ripping blades 40 in their working direction to rip, tear and pull material from the bale 12 to be cut by the cutting blades 44 as 5 described above.

At step S15-34 microprocessor 202 starts the motor of the conveyor belt 80.

10 At step S15-36 microprocessor 202 determines whether a signal has been received from the material level switch 88 indicating that the reservoir 86 in the housing 82 of the conveyor 6 is now full of shredded material.

15 If it is determined at step S15-36 that the material level switch 88 has been activated, then at step Sl5-38, microprocessor 202 stops the shredder blade motor 60 for a predetermined period of time (which, in this embodiment, is set to two minutes) so that the conveyor 20 belt 80 has time to remove the accumulated shredded material to the shredded material feeder 8. Processing then returns to step S15-36.

When it is determined at step S15-36 that the material I 25 level switch 88 has not been activated, then processing

proceeds to step S15-40, at which microprocessor 202 controls the roller motor 18 of the bale feeder 2 to drive the bale 12 a predetermined distance towards the shredder 4. In this embodiment, the predetermined 5 distance is set to 50mm.

At step S15-42, microprocessor 202 resets a counter 206 which has been allocated to count the number of shredder jamming occurrences if a predetermined time has elapsed 10 since the counter was last reset. If the predetermined time has not yet elapsed, then the current count value of the counter 206 is retained. In this embodiment, the predetermined time used at step S15-42 is set to 10 seconds. At step S15-44, microprocessor 202 determines whether a signal has been received from the current overload sensor associated with the shredder blade motor 60 indicating that the shredder ripping blades 40 have jammed.

If it is determined at step S15-44 that the shredder has not jammed, then processing returns to step S15-26 and proceeds from there as described above.

25 On the other hand, it is determined at step S15-44 that

the shredder 4 has jammed, then processing proceeds to step S15-46, at which microprocessor 202 controls the system to perform a shredder dejamming routine. The processing then returns to step S15-44.

Figure 16 shows the steps in the shredder de-jamming routine performed at step S15-46.

Referring to Figure 16, at step S16-2 microprocessor 202 10 increments the value of the counter 206 allocated to count shredder jamming occurrences by one.

At step S16-4, microprocessor 202 determines whether the current shredder jamming occurrence is the first 15 occurrence in the current predetermined time period (10 seconds in this embodiment). This is carried out by reading the value of the counter 206, because, as explained above, the counter value is reset to zero at step S15-42 whenever the predetermined time period 20 elapses. If it is determined at step S16-4 that the current shredder jamming occurrence is not the first occurrence in the current time period, then at step S16-6, 25 microprocessor 202 reads the counter 206 to determine

whether the threshold number of gemming occurrences in the current time period has been reached. In this embodiment, the threshold number of jamming occurrences is set to five.

If it is determined at step S16-6 that the threshold number of jamming occurrences has been reached for the current time period, then processing proceeds to step S16-8 at which microprocessor 202 shuts down the system 10 and controls the warning devices 208 to output a warning to the operator.

On the other hand, if it is determined at step S16-4 that the current jamming occurrence is the first jamming 15 occurrence, or if it is determined at step S16-6 that the threshold number of jamming occurrences has not yet been reached in the current time period, then processing proceeds to step S16-10.

20 At step S16-10, microprocessor 202 controls the roller motor 18 of the bale feeder 2 to reverse the direction thereof so as to withdraw the bale 12 away from the shredder 4 at high speed by a predetermined distance (set to 100mm in this embodiment). At the same time, 25 microprocessor 202 controls the blade motor 60 in the

r shredder 4 to drive the ripping blades 40 in reverse in an attempt to free any material from the bale 12 tangled in the ripping blades 40.

5 At step S16-12, once the bale 12 has been withdrawn the predetermined distance (step S16-10), microprocessor 202 stops the roller motor 18 of the bale feeder 2 and controls the blade motor 60 in the shredder 4 to drive the ripping blades in their normal Working direction 10 again. Although not specifically included in the process control flowcharts of Figure 15 and Figure 16, control unit 200 periodically controls the ash auger motor 232 and IS pneumatic ash removal system 234 to remove ash from the inside of the boiler 10 into the ash receiver 236.

Modifications and Variations 20 Many modifications and variations can be made to the embodiment described above.

For example, the system may be designed to handle bales of different size and height to those described above.

In the embodiment described above, a current overload sensor is provided in the bale feeder 4 to determine whether the rotating ripping blades 40 have jammed.

However, other jamming-detection devices may be used 5 instead. For example, a shaft rotation detector may be provided on the drive shaft 62 to determine when the drive shaft 62 substantially slows or stops, thereby indicating jamming of the ripping blades 40.

10 In the embodiment described above, the vertical side roller 28 provided to resist forces imparted on a bale 12 by the rotating ripping blades 40 may be replaced by other forms of restraining means, such as a fixed vertical plate.

In the process control described above with reference to Figure 15, if step S15-18 and the subsequent steps are entered via steps S15-10 and S1516 (rather than via steps S15-8 and S15-14), then an additional step may be 20 introduced between steps S15-26 and S15-28 in which a delay of a predetermined time is introduced before step S15-28 is performed. The predetermined time would be set to allow the water temperature to drop below the required operating temperature.

In the embodiment described above, the amount of shredded material fed by the shredded material feeder 8 into the boiler 10 is controlled using a weigh cell 122. However, instead, a sensor (such as an optical sensor) may be 5 provided in drawer 124 to determine when shredded material has accumulated therein to a predetermined depth. In this case, the airlock plate 104 may then be provided as the base of the drawer 124 (as it is no longer necessary for the drawer 124 to have no base so 10 that the shredded material can fall onto the weigh cell).

In the embodiment described above, the rotating blades 40 of the shredder 4 are stopped when the load switch 88 within the shredded material conveyor 6 is activated 15 (S15-38 in Figure 15c). However, in addition or instead, the motor 18 of the bale feeder 2 may be stopped to prevent further transport of the bale 12.

In the embodiment described above, the water jacket 202 20 of the boiler 10 has a single hole 246 within the wall 244 between the primary and secondary chambers 240, 242.

However, more holes may be provided in the wall 244.

In the embodiment described above, a speed controller may 25 be provided on one or both of the fans which draw air

into air-intakes 220 and 222 surrounding the hearth 200 of the boiler 10. The speed controller(s) may be arranged to control the fan(s) to draw air into the tube 207 at a rate dependent upon the temperature of the 5 exhaust gases.

In the embodiment described above, the shredded material feeder 8 is arranged to feed shredded packaging material into the boiler 10. However, the shredded material 10 feeder 8 may be used in other systems to feed different types of solid fuel, such as wood chip waste, wood pellets etc. into a boiler.

Claims

CLAIMS:

1. A shredder for shredding bales of packaging material, comprising: 5 a plurality of parallel rotatable shafts, each respective shaft having thereon a plurality of ripping blades spaced apart along the length of the shaft to rotate therewith; and a plurality of cutting blades unconnected to the 10 rotatable shafts; wherein the ripping blades are substantially blunt relative to the cutting blades, and the cutting blades are positioned relative to the ripping blades so that, in use, the ripping blades tear and pull material from 15 a bale, and the cutting blades cut the material removed from a bale by the ripping blades.

2. A shredder according to claim 1, wherein the rotatable shafts are arranged to be driven in the same 20 direction of rotation.

3. A shredder according to claim 1 or claim 2, wherein the rotatable shafts are positioned in relation to each other such that the ripping blades on adjacent shafts are 25 interleaved.

4. A shredder according to any preceding claim, wherein each ripping blade has a plurality of teeth, and wherein, for each respective shaft, at least some of the ripping blades thereon are arranged such that the teeth on 5 different blades are relatively offset in the direction of rotation of the shaft.

5. A shredder according to any preceding claim, wherein each ripping blade has a plurality of teeth, and wherein, 10 for at least some of the shafts, at least some of the ripping blades thereon are arranged such that the teeth on different blades provided on different shafts at substantially the same position along the length of the shafts are relatively offset in the direction of rotation 15 of the shafts.

6. A shredder according to any preceding claim, wherein at least some of the ripping blades are arranged in planes inclined relative to the planes of the other 20 ripping blades.

7. A shredder according to any preceding claim, wherein the cutting blades are arranged in a plurality of sets, each respective set having a different location and 25 having a plurality of blades in an array extending

parallel to the rotatable shafts.

8. A shredder according to claim 7, wherein the number of cutting blades provided in at least two of the sets 5 is different.

9. A shredder according to claim 8, wherein the sets are positioned relative to the rotatable shafts and relative to each other such that: 10 at least some of the pieces of material removed from a bale by the ripping blades will pass across two sets of cutting blades; and of the sets across which a piece of material removed from a bale by the ripping blades will pass, the first 15 contains the fewest cutting blades.

10. Apparatus according to any of claims 7 to 9, wherein a stream of pieces of material is created by the rotation of the ripping blades, and wherein the sets of cutting 20 blades are positioned relative to the ripping blades so as to lie within the stream, and the number of blades in each set increases in the stream direction.

11. Apparatus for shredding bales of packaging material, 25 comprising:

] a bale shredder having a plurality of rotatable shafts, each respective shaft having thereon a plurality of blades for rotation therewith to shred material in a bale, means for driving the rotatable shafts in a first, 5 shredding rotation direction, and in a second, opposite rotation direction, and jamming-detection means for detecting when the blades are jammed by packaging material; a bale transporter having means for transporting lo bales of packaging material in a first direction towards the shredder and in a second direction away from the shredder; and control means arranged to receive an output from the jamming-detection means and to control the bale shredder 15 and the bale transporter such that, in the event that it is determined from the output of the jamming- detection means that the blades are jammed, the means for transporting the bales is driven in the second direction to move the bale away from the blades, and the rotatable 20 shafts are driven in the second rotation direction to attempt to dislodge any trapped packaging material.

12. Apparatus according to claim 11, wherein the bale transporter includes a cutter positioned to cut straps 25 binding the bales of packaging material as they are

transported towards the shredder.

13. Apparatus according to claim 11 or claim 12, further comprising a conveyor belt arranged in a housing for 5 transporting shredded material produced by the bale shredder, the housing being shaped to provide space within which material can accumulate if shredded material is produced by the shredder at a rate faster than the rate at which the conveyor belt transports the material, 10 and wherein: means is provided within the space to detect when the space is substantially full of shredded material; and the control means is arranged to receive an output from the detection means and to stop at least one of the 15 bale shredder and the bale transporter in dependence upon such an output.

14. Apparatus according to any of claims 11 to 13, further comprising restraining means positioned in the 20 vicinity of the bale shredder to restrain a bale against forces imparted thereto by the rotating blades of the shredder, so as to prevent the bale skewing substantially relative to the blades.

25

15. Apparatus for transferring solid fuel into a

receiving apparatus without allowing significant amounts of air into the receiving apparatus, comprising: a hopper, through which solid fuel can fall; a hopper closing member and means for moving the 5 hopper closing member between a enclosed" position in which the member engages the walls of the hopper to close the passage for solid fuel through the hopper and to prevent significant amounts of air passing through the hopper, and an "open" position in which the passage 10 through the hopper is open to solid fuel and air; and a solid fuel feeder for receiving solid fuel and for transferring it to the hopper, and means for moving the solid fuel feeder between an "open" position in which the feeder can receive and accumulate solid fuel, and a 15 "closed" position in which the feeder is positioned relative to the hopper to transfer solid fuel from the feeder to the hopper, and in which the feeder prevents significant amounts of air entering the hopper.

20

16. Apparatus according to claim 15, wherein the solid fuel feeder has the form of a drawer having side walls but open top and bottom portions, thereby allowing solid fuel to enter through the top when the feeder is in the Aspen" position and allowing the accumulated solid fuel 25 to fall into the hopper through the bottom when the

feeder is in the "closed'' position.

17. Apparatus according to claim 16, further comprising weigh means for weighing solid fuel, the weigh means 5 being provided at a position so that it is substantially below the solid fuel feeder and forms a bottom wall for the drawer when the feeder is in its "open t. position, thereby allowing solid fuel fed into the feeder to accumulate on top of the weigh means while being retained 10 by the side walls of the feeder.

18. Apparatus according to any of claims 15 to 17, wherein the hopper closing member is provided with rolling bearings to facilitate the movement thereof, and 15 wherein the rolling bearings are positioned on the closing member such that they are not inside the hopper for any position of the closing member.

19. Apparatus according to any of claims 15 to 18, 20 further comprising control means operable to control the movement of the hopper closing member and the solid fuel feeder such that, in use, at least one of the hopper closing member and the solid fuel feeder is always fin its 'closed' position.

20. Apparatus according to claim 19, wherein the control means is operable to control the movement of the hopper closing member and the solid fuel feeder such that: when the solid fuel feeder is in its "open" position 5 to receive solid fuel, the hopper closing member is in its closed position to prevent significant amounts of air passing through the hopper, and the hopper closing member is maintained in its "closed' position whenever the solid fuel feeder is not in its enclosed position"; 10 the hopper closing member is moved to its "open" position when the solid fuel feeder is in its enclosed" position so that the feeder prevents significant amounts of air from entering the hopper, thereby allowing solid fuel to fall through the hopper.

21. A boiler for burning shredded packaging material and heating water, the boiler having: a hearth for burning shredded packaging material; and 20 a water jacket through which water can be passed to be heated by heat generated from the burning of the packaging material; wherein the water jacket defines at least part of the output route for exhaust gases from the hearth, and 25 wherein the water jacket is shaped to define first and

second chambers for the exhaust gases to pass through and to define a wall between the chambers through which the water can be passed, the wall having a hole through which the exhaust gases can pass from the first chamber to the 5 second chamber.

22. A boiler according to claim 21, wherein the water jacket is shaped to define cylindrical first and second chambers.

23. A water jacket for use in a boiler, comprising a housing through which water can be passed having a shape which defines first and second chambers for exhaust gases to pass through and which defines a wall between the 15 chambers through which the water can be passed, the wall having a hole through which the exhaust gases can pass from the first chamber to the second chamber.

24. A boiler for burning shredded packaging material and 20 heating water, the boiler having: a hearth for burning shredded packaging material; and a water jacket through which water can be passed to be heated by heat generated from the burning of the 25 packaging material;

wherein the hearth comprises an elongated chamber open at both ends to allow shredded packaging material to be fed into one end and to allow exhaust gases and ash to escape from the other end, and wherein the hearth is 5 arranged at a position spaced apart from the base of the boiler to allow ash to fall from the open end of the hearth into the base.

25. A boiler according to claim 24, wherein the water 10 jacket surrounds at least the end of the hearth from which the ash and exhaust gases exit, and wherein the water jacket is shaped to channel falling ash towards a collection area at the base of the boiler.

15

26. A boiler according to claim 24 or claim 25, wherein the boiler includes ash removal means operable to remove ash accumulated in the base of the boiler.

27. A boiler according to any of claims 24 to 26, 20 wherein the hearth chamber walls prevent ash falling therethrough.

28. A boiler according to any of claims 24 to 27, wherein the hearth has air inlets along its length and 25 around its perimeter.

29. A shredder for shredding bales of packaging material substantially as described herein with reference to, or as shown in, any of accompanying Figures 1, 2, 3, 4, 5 and 6.

30. A combination of a shredder for shredding bales of packaging material, a transporter for transporting the bales to the shredder and a method of controlling the shredder and transporter substantially as described 10 herein with reference to, or as shown in, accompanying Figures 1, 2, 3, 15 and 16.

31. Apparatus for transferring solid fuel received from a conveyor system into a boiler substantially as 15 described herein with reference to, or as shown in, any of accompanying Figures 1, 8, 9, 10 and 11.

32. A boiler substantially as described herein with reference to, or as shown in, any of accompanying Figures 20 12a, 12b and 12c.

33. A water jacket for a boiler substantially as described herein with reference to, or as shown in, accompanying Figure 13.