WO2014199185A2

WO2014199185A2 - Method and rotary processor for processing waste into fertilizer

Info

Publication number: WO2014199185A2
Application number: PCT/GB2014/051848
Authority: WO
Inventors: Derek REFFELL; Colin STACEY
Original assignee: Global Advanced Recycling Company Limited
Priority date: 2013-06-14
Filing date: 2014-06-16
Publication date: 2014-12-18
Also published as: WO2014199185A3; GB2515119A; GB201310699D0

Abstract

A rotary processing machine comprises a rotor arranged in a housing, the rotor including an impeller and multiple rotor assemblies adapted to generate a high velocity vorticial airflow for comminuting a feedstock. In one embodiment the rotor shaft is axially adjustable to adjust the airflow by varying the position of the rotor elements. In another embodiment an angle of incidence of the rotor elements is adjustable to suit a mechanical characteristic of the feedstock. In another embodiment the machine comprises rotor elements having upper and lower surfaces defining lines which are symmetrical about a first plane and converge in a convergent region to a trailing edge. The machine may be used to process municipal solid waste in combination with biochar so as to impregnate the biochar with the waste, providing an improved fertilizer. Preferably the biochar is derived by pyrolysis of a separated fraction of a mixed waste stream in a self sustaining process.

Description

Method and rotary processor for processing waste into fertilizer

This invention relates to methods and apparatus for processing waste, e.g.

municipal solid waste, in a high velocity airflow in a rotary processing machine.

It is known, for example from US5192029 and US2010327096, to process waste in a vertical mill having a housing containing a rotor, the rotor comprising multiple cutter or striker blade assemblies wherein each striker blade assembly is separated in the axial direction of the rotor from a fixed shelf in the housing by a gap. Usually in machines of this type the housing is a regular polygon with an odd number of sides, nine sides being generally preferred, and a lowermost blade assembly may be adapted to act as a fan. The striker blades are generally solid or angled rectilinear bars but may have swept tips or other shapes. The feedstock is comminuted by impacting it against the armoured housing and rotating striker blade assemblies which together with the fan generate a high volume airflow which dries the feedstock and carries it downwardly through the machine to the outlet. In order to obtain an end product having a desired particle size and final moisture content, the position and inclination of the blades and the axial position of each striker blade assembly on the shaft can be adjusted so as to regulate the airflow and hence the residence time of the feedstock in the machine.

In a commercial installation for processing municipal solid waste (MSW) a mill of this type will typically be driven by an electric motor rated at several hundred kilowatts. Since the large motor imposes a very heavy starting load on the electrical supply system, the mill will generally be set up to suit a specific feedstock and thereafter run as far as possible in continuous operation.

In practice it is found that in machines of this type the striker blade assemblies and internal armour plating of the housing can wear rapidly, necessitating frequent maintenance. Moreover, when processing a mixed waste stream such as MSW, the applicant has found that variations in the rotor blade settings can have a significantly different effect on different waste materials, making it difficult to achieve an end product of consistent quality.

Usually the mill is set up with a progressively downwardly diminishing gap size, and the applicant has also found that when the smallest gap at the lowermost striker blade assembly is widened, instead of improving the flow of waste through the machine, the increased airflow can lead to jamming of the feedstock in the upper striker blade assemblies.

When processing manure into fertilizer, it is known that bacterial content can be greatly reduced by "thrashing", i.e. by mechanically impacting the waste at high speed against the rotors and walls of a vertical mill. Fertilizers manufactured according to this principle are available from Perfect Blend Organics of Bellevue, Washington, USA, as set out in their brochure entitled "Perfect Blend Fertilizers - Pathogen Destruction Program - Process Manufacturing Flow Chart"

(http://www.perfect-blend.com/pdf/Brochures/PathogenDestructionProgram.pdf).

US3987970, US4151794, and US4877531 teach methods of processing refuse, sewage and smoke in a vertical mill to produce fertilizer.

US4493459 teaches a similar method wherein nutrient enriching additives are added to a liquid carrier medium.

For more specific applications it is known to design a rotary mill and to run it at sufficiently high rotational speed to generate an airflow in which multiple vortices cause particles to collide with each other rather than impacting against the striker blades and housing. WO201 1146896 for example teaches a high speed rotary mill running at over 5000RPM which is configured to generate a vorticial airflow.

US6227473 teaches processing organic sludge or animal waste in a rotary vertical mill in which the feedstock is broken up by pulsed standing shock waves which also cause temperature fluctuations and piezoelectric effects.

US2004169096 teaches the manufacture of carbon black by micronizing a feedstock such as used tyres or pyrolytic char in a resonance disintegration mill, wherein the processing conditions make the surface of the carbon more

hydrophilic.

It is also known, for example from US2002027173 and US2011 114766 to process a feedstock in a high speed vortex which is generated without the use of a rotor.

More generally, it is well known to enrich a waste feedstock with nutrients, mycorrhizal fungi and the like so as to produce an improved fertilizer.

For example, US 20041 1 1968 teaches saturating biochar with a solution of ammonia and then holding it in suspension while impregnating it with flue gases to produce a soil improving additive.

Biochar is known to have a very large surface area and to be beneficial to the soil. In particular it is known that the very large surface area encourages the

development of mycorrhizal fungi and other beneficial soil organisms. However, it is very difficult to impregnate biochar with other substances to sustain and promote this beneficial action. In order to introduce gases or liquids of low viscosity it has been found necessary firstly to remove the gases already present in the microscopic pores of the biochar, and since it is difficult or impossible to impregnate biochar with more dense or viscous substances the use of biochar as a soil improver is relatively limited.

US 8317892 teaches producing thin sheets of biochar from biomass which is subjected to heat and pressure pulses generated by pistons or explosive devices. The biochar can be treated ultrasonically or by vacuum, impact, or water infiltration to remove adsorbed gases and render it more hydrophilic before impregnating it with soluble nutrients.

In one aspect, an object of the present invention is to provide a rotary processing machine and a method of operation which is more convenient and effective for use in processing mixed waste such as MSW.

In a further aspect, the invention sets out to provide a sustainable method for processing waste, particularly mixed waste such as MSW, to produce an improved fertilizer.

According to the present invention in its various aspects there are provided a rotary processing machine and a method as variously defined in the claims.

A preferred embodiment provides a rotary processing machine in which a feedstock is comminuted by interparticle collisions or pressure fluctuations in a vorticial airflow.

In a first aspect, the machine includes a shaft which is axially adjustable in the housing to simultaneously adjust all of the rotor gaps, whereby the machine is rapidly reconfigurable to process a heterogeneous feedstock.

In a second aspect, at least one rotor assembly of the machine is adjustable to vary an angle of incidence of the rotor elements. In a related method, the angle of incidence is adjusted in accordance with at least one mechanical characteristic of the feedstock. It has been found that this significantly improves the effectiveness of the machine when processing a variable feedstock.

In another aspect, the machine comprises rotor elements having upper and lower surfaces defining lines which are symmetrical about a first plane and converge in a convergent region to a trailing edge. This configuration is found to be particularly effective in generating a vorticial airflow and maintaining the feedstock in suspension in the path of the rotor elements until it has attained the desired particle size.

In another aspect, the machine is used to process a nutrient rich waste stream in combination with biochar so that the comminuted biochar is impregnated with the waste, resulting in an improved fertilizer.

The above mentioned features may be used individually or may advantageously be combined to produce an environmentally sustainable method and apparatus which is particularly well adapted for processing a mixed waste stream, particularly MSW.

These and other features and advantages of the invention will be understood from the illustrative embodiments of the invention which will now be described, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which:

Fig. 1 shows a first rotary processing machine;

Fig. 2 shows the first machine with the housing and rotors partially cut away; Fig. 3 is a cross section at III of Fig. 2 showing the upper rotor assembly; Fig. 4 is a cross section at IV of Fig. 2 showing the impeller;

Figs. 5A - 5C show an adjustment mechanism respectively in a lowered position with the clutch disengaged (Fig. 5A); a lowered position with the clutch engaged (Fig. 5B); and a raised position with the clutch disengaged (Fig. 5C);

Fig. 6 shows part of one rotor assembly comprising a rotor element;

Fig. 7 shows a section in the second plane P2 through the rotor element of Fig. 6;

Figs. 8A - 8C illustrate three interchangeable rotor elements having different angles of incidence, wherein:

Fig. 8 A is a simplified view of the section of Fig. 7; and

Figs. 8B and 8C are simplified views corresponding to Fig. 8A of two alternative rotor element sections; and

Fig. 9 shows a process for converting a mixed waste stream into fertilizer.

Corresponding reference numerals indicate corresponding features in each of the figures.

Referring to Figs. 1 - 4, a rotary processing machine for comminuting MSW or other feedstock comprises a polygonal housing 1 having an upper portion 2 and a lower portion 3 with an access door 4. A rotor 20 is mounted in the housing for rotation about an axis X. An electric motor 5 is mounted in fixed relation to the housing and coupled to the rotor by a centrifugal clutch 50 so as to drive the rotor in rotation about an axis at a service speed. In this specification, "axially" means in a direction of, e.g. parallel with, the rotor axis X; and a "motor" means any drive means, such as an electric motor, an engine, or other prime mover.

The upper portion 2 of the housing has a polygonal cross section with nine flat sides 6 made from armoured steel plate, with an inlet 7 at an upper end, while the lower portion 3 has a smoothly curved cross section, with an outwardly widening outlet 8 having a wall 9 arranged tangent to the curved housing; this outlet configuration advantageously avoids blockages and increases the flow rate of the feedstock through the machine. Preferably a snatch roller (not shown) is fitted at the inlet to break long filamentary material into shorter lengths.

Three horizontal walls 10, 1 1, 12 extend inwardly from the sides of the upper portion of the housing, the walls being spaced apart axially between the inlet and the outlet, each wall having a circular central aperture 13 through which the rotor 20 extends.

The rotor 20 includes an impeller 21 and at least two rotor assemblies. In the illustrated embodiment the rotor includes three rotor assemblies 22, 23, 24 which together with the impeller 21 are fixed on the rotor shaft 25 in axially spaced relation so that they all rotate together with the shaft, the impeller being arranged in the lower portion 3 and the rotor assemblies in the upper portion 2 of the housing.

The impeller 21 (Fig. 4) comprises six blades 26 arranged to generate a large volume airflow through the housing from the inlet 7 to the outlet 8 sufficient to draw the feedstock through the housing from the inlet to the outlet when the rotor is driven in rotation at the service speed, and also sweeps the comminuted feedstock 28 from the lower portion of the housing out through the outlet. Each rotor assembly 22, 23, 24 comprises a circular steel plate 27 which carries an array of replaceable rotor elements 22', 23', 24'. There may be for example from four to eight rotor elements on the uppermost rotor assembly 22, and from four to twelve rotor elements on each of the lower rotor assemblies 23, 24. The plate 27 is fixedly mounted on the shaft 25 by means of a collar 29 which is releasable and re-engagable in a known manner so that each rotor assembly is axially adjustable on the shaft independently of the other rotor assemblies. Of course, this

adjustment requires the rotor to be stopped so that the door can be opened to release and re-engage the collar using suitable tools.

Each rotor element 22', 23', 24' is fixed (e.g. with bolts 30) to the plate 27 so that a radially outer end portion 31 of the rotor element extends radially outwardly from the plate 27 above the respective one of the walls 10, 1 1, 12, so that each array of rotor elements 22', 23', 24' is spaced axially from the respective one of the walls 10, 1 1, 12 by a respective rotor gap G defined between their respective axially opposed surfaces 32, 33. Preferably the downwardly facing surfaces 32 of the rotor elements are arranged to overlap the respective upwardly facing surfaces 33 of the walls so that the feedstock is caused to flow around or between the outer end portions 31 of the rotor elements as it travels through the machine.

The apertures 13 and rotor gaps G decrease downwardly from the inlet to the outlet as shown. A radial gap 34 is defined between each plate 27 and its respective fixed wall 10, 1 1, 12, and at a minimum rotor gap setting (for example, lmm or 2mm) the respective plate 27 is received substantially within the aperture 13 in the respective fixed wall. The rotor gaps G are adjustable individually or simultaneously, as further described below.

Importantly, even at the minimum setting, there is no contact between the rotor assemblies and the fixed walls or other parts of the housing. Instead, the impeller and rotor assemblies are arranged as known in the art to generate a vigorous airflow which interacts with the polygonal housing to create multiple vortices, subjecting the feedstock to rapidly fluctuating pressure pulses.

In practical applications for processing MSW it is necessary to operate

substantially continuously at high volume, and so the motor will generally have a power consumption of at least about 1 OOkW. It is found that multiple vortices begin to be generated when a radially outer tip 35 of each rotor element travels at a speed about 15m/s (metres per second), equating to a rotational service speed of about 200RPM in a machine having rotor assemblies of about 1.5m in diameter. It is preferred however to operate at a tip speed of at least about 60 m/s, more preferably about 75 m/s, which a machine of this size corresponds to a rotational service speed of about 750RPM or 950 RPM.

In the illustrated embodiment, the service speed is about 1000 RPM and the motor has a power consumption of about 450kW in continuous normal operation at the service speed, so that the rotor tips travel at about 80m/s. When the rotor gaps are adjusted to the maximum, the airflow is estimated to be approximately 200,000 standard cubic feet per minute (i.e. 200,000 cubic feet at ambient pressure).

In use, the illustrated machine is found to reduce one tonne of MSW in 150 seconds to a commingled, odour free, confetti sized flock with a moisture reduction of 50% and a volume reduction of 70%, while wooden pallets and coarse limestone aggregate are processed into a finely comminuted form with average residence times of about 36 seconds and 43 seconds respectively.

Without wishing to be bound by theory, it is believed that the airflow comprises a vortex or vortices which extend axially from the inlet to the outlet, and within or between this vortex or vortices a complex pattern of multiple smaller vortices which are generated at the radially outer end portions 31 of the rotor elements. The contra-rotating vortices cause rapid pressure fluctuations and inter-particle collisions so that the particles of feedstock entrained in the airflow collide with each other rather than with the rotor elements or the housing, probably due to a boundary layer effect which tends to prevent contact with the machine.

In normal operation of the illustrated machine it is calculated that the airflow in the vortices at the tips of the rotor elements reaches a speed of about 750 m/s, indicating an interparticle collision speed as high as 1500m/s. The very high velocity interparticle impacts and pressure fluctuations are believed to give rise to other difficultly detectable transient phenomena such as fluctuating magnetic fields and piezoelectric effects, sonic and ultrasonic resonance, and extreme temperature fluctuations of very short duration at a micro scale which rapidly disintegrate and sterilise the feedstock.

The presence of vorticial airflow can be ascertained in operation by the relatively low rate of wear of the housing and particularly the rotor elements, compared with the much higher rate of wear in machines which operate by impacting the feedstock against the rotor elements and the housing, such machines tending to have rectilinear rotor elements which are ineffective in creating a vorticial airflow as they rotate.

The uppermost rotor assembly 22 is configured as a breaker assembly with four rotor elements 22' (Fig. 3). Unlike the lower rotor assemblies 23, 24, the rotor elements of the breaker assembly directly impact against the feedstock to break it into pieces which are entrained in the airflow and carried down into the lower rotor assemblies. These rotor elements 22' are configured as rectilinear bars.

In normal operation the rotor elements 23', 24' of the two lower rotor assemblies 23, 24 do not contact the feedstock, but instead serve to generate vortices in the airflow which comminute the feedstock by interparticle collisions and pressure fluctuations as described above.

Referring to Figs. 5A - 5C, the processing machine is adapted so that the shaft 25 is axially adjustable in the housing to simultaneously adjust all of the rotor gaps G In the illustrated example, each rotor gap G between the axially opposed surfaces 32, 33 of the rotor elements and the fixed walls may be adjustable for example from about 1mm or 2mm to about 130mm, with the smallest gap being at the lowermost rotor assembly 24.

The gap size G is adjusted to regulate the airflow through the machine, which in turn determines the residence time of the feedstock and hence the particle size of the end product. Different feedstocks with different mechanical characteristics (e.g. hardness, plasticity, flexibility) require different gap settings to achieve the required particle size, and factors such as moisture content will also influence the adjustment. In the past, airflow has been increased by adjusting the gap G at the lowermost rotor assembly. Advantageously, by simultaneously adjusting all of the gap sizes, when the airflow is increased by increasing the gap on the lowermost rotor assembly 24, although the rotational speed of the rotor remains constant, the increased gap G in the uppermost rotor assembly 22 is found to make the machine less prone to jamming, plausibly because the increased airflow causes more vigorous vorticial turbulence which transfers a greater proportion of the

mechanical work to the lower rotor assemblies.

Preferably the rotor 20 is axially adjustable relative to the motor 5, and the adjustment means is operable while the motor is in operation, so that the motor can be fixedly mounted to minimise vibration and the machine can be frequently adjusted for a heterogeneous feedstock without stopping and re-starting the motor. In the illustrated embodiment this is accomplished by a hydraulic raising and lowering mechanism 60 (not shown in Figs. 1 and 2) in combination with the clutch 50, which comprises first and second surfaces 51, 52 which are engageable together (Fig. 5B) to couple the rotor 20 to the motor 5 and disengageable (Fig. 5A, Fig. 5C) to decouple the rotor 20 from the motor 5; and the rotor 20 is axially adjustable relative to the motor by axially displacing the first surface relative to the second surface.

In the example illustrated, the gap size is thus increased by raising the shaft 25 along its axis X, displacing the first surface from a lower position (Figs. 5A, 5B) to a higher position (Fig. 5C). The first surface 51 is arranged as an internal surface of a drum which rotates about the second surfaces 52, which are outer surfaces of pads 53 of friction material. The clutch operates automatically in a known manner to retract the pads so as to disengage the first and second surfaces when the motor operates at an idle speed below the service speed, and re-engages the pads when it is accelerated to the service speed.

The hydraulic mechanism 60 comprises an annular piston 61 housed in an annular casing 62 fixed to an upper surface of the housing 1. A thrust carrier 63 is fixed to the shaft 25 so that it transfers the dead weight of the rotor to the piston 61 via a thrust bearing 64. The upper end of the shaft 25 is supported in a rotary bearing 65 located in a sleeve 66 which has axial ribs 67 on its outer surface so that it can slide freely together with the shaft in the axial direction of the shaft in the casing 62. Hydraulic fluid is pumped from a reservoir 68 into the space beneath the piston to raise the rotor, and allowed to return when it is desired to lower the rotor. Of course, a double acting piston could be provided.

In alternative embodiments, the clutch could be selectably rather than

automatically releasable. The shaft could be axially slidable relative to the motor by means of a splined or other slidable connection. Alternatively, the shaft and motor could be axially adjusted together relative to the housing.

The shaft could be adjusted by inserting shims or spacers at one of two bearing assemblies, wherein the shims are removably located between a bearing

supporting the shaft and a fixed housing which supports the shim, the bearing resting on the shim. For example, spacers could be removed from beneath a fixed lower bearing housing wherein the lower bearing is located below the spacers, the rotor raised until the lower bearing rests axially against a lower surface of the lower bearing housing, and then the spacers replaced above a fixed upper bearing housing so that the upper bearing rests on an upper surface of the spacers to support the shaft in a raised position; and vice versa. In such an embodiment, the spacers could be provided with a central recess surrounded by a raised, inwardly tapering rim so as to centralise the bearing in the spacer, and each spacer could be made in two halves so that it can be dismantled and re-assembled around the shaft.

In yet further embodiments, the rotor could be raised and lowered by a

screwthread or any other suitable mechanism.

The rotor could be driven by a non-electric motor, e.g. an internal combustion engine. The polygonal housing could have a different, preferably odd number of sides; alternatively, instead of or in addition to using a polygonal housing, internal fixed elements could be used to interact with the airflow to create multiple vortices as known in the art. The impeller can be any suitable shape for inducing a large volume airflow through the machine while expelling the comminuted feedstock from the outlet. The machine can advantageously be used for processing a wide variety of feedstocks in addition to MSW, including for example stone, rubble, wood, agricultural and industrial waste and the like, and may be used to comminute combustible feedstock so as to increase its recoverable calorific value and reduce bottom ash by ensuring complete combustion in incineration, gasification or other processes.

Referring to Figs. 6 - 8, at least one of the rotor assemblies 23, 24 is adapted to be adjustable to vary an angle of incidence of the rotor elements 23', 24'.

The rotor elements 23', 24' of the lower rotor assemblies 23, 24 are arranged to generate a vorticial airflow as described above. In the illustrated example, a radially outer end portion 31 of each rotor element 23' of the rotor assembly 23 includes a leading edge 70, a trailing edge 71, a first, upper surface 72 and a second, lower surface 73, the first and second surfaces acting on the airflow so that a partial vacuum and vortex are created behind the rotor element as the rotor rotates. The angle of incidence is a measure of the bluntness or pointedness of that radially outer end part of the rotor element which is exposed to the airflow. The shape of this part including its converging region which tapers to the trailing edge is found to be more effective in creating a vortex behind the rotating rotor element, and by adjusting it to suit the mechanical characteristics of the feedstock, an improved processing action is obtained.

It can be seen that the leading edge 70 includes a first point 74 which lies at an intersection of first, second and third mutually orthogonal planes, the first plane P 1 being normal to the axis X, the second plane P2 being normal to the first and third planes and intersecting the third plane P3 at a vertical line 75, the third plane P3 containing the axis X.

The first surface 72 intersects the second plane P2 at a first line 72', while the second surface 73 intersects the second plane P2 at a second line 73', the first and second lines extending from the first point 74 to the trailing edge 71 respectively on opposite sides of the first plane PI . Each of the first and second lines 72', 73' passes through a respective second point 72", 73", the second point being that point closest to the first point 74 at which the respective first or second line lies at a maximum distance from the first plane PI .

Each of the first and second surfaces has a respective angle of incidence al, a2 in the second plane P2, the angle of incidence being defined between the first plane PI (at its intersection with the second plane) and a respective straight line 76, 77 joining the first point 74 and the respective second point 72" or 73".

The leading edge is taken to be that portion of the surface of the radially outer portion of the rotor element which leads in the direction of rotation Dl of the rotor. (It will be noted that the direction of rotation of the example shown in Fig.s 6 - 8 is opposite to that in the example of Figs. 1 - 4.) Since the leading edge 70 includes a first point 74 which lies in a plane (the third plane P3) containing the rotor axis, this means that the first and second surfaces terminate exactly at the third plane P3.

In the case where the whole of the region of the leading edge is smoothly curved, the first point 74 will therefore be the only point on the first and second surfaces which lies in the third plane P3. This case is illustrated in Fig. 8 A.

In the case where the region of the leading edge 70 is a flat region defining a straight line lying at the intersection 75 of the second and third planes, the first point 74 is taken to be equidistant between the extremities of that straight line. This case is illustrated in the examples of Fig. 8B and Fig. 8C.

It will be understood therefore that an "edge" may be construed accordingly as a line or a flat surface. Where as in the illustrated embodiments the rotor element is fixed to a surface of a solid disc or plate 27, the radially outer portion 31 of the rotor element will form at least a part of that region whose upper and lower surfaces are exposed to the airflow. The novel configuration is preferably applied over substantially all of that region, but may be applied in a more limited part of that region.

Preferably at least two sets of interchangeable rotor elements having different angles of incidence are provided (Figs. 8A, 8B, 8C) so that the angles of incidence of each rotor element can be adjusted by removing the bolts 30 and interchanging the rotor elements.

In each of the rotor elements of Figs. 8 A, 8B and 8C the first plane PI is a plane of symmetry of the radially outer portion 31 of the rotor element, so that the first and second lines 72', 73' are symmetrical about the first plane PI and the first and second surfaces have equal angles of incidence. This is found to be particularly advantageous because it causes the feedstock to remain in the region behind the rotor element so that it is acted upon by all of the rotor elements in succession. It is possible for the section to be asymmetrical about PI, but this is less preferred because the feedstock would tend to move out of the path of the rotor elements, resulting in slower or less complete comminution.

Preferably each of the first and second surfaces is adjustable to have a maximum angle of incidence from 80° - 90° and a minimum angle of incidence from 20° - 40°. This range is found to suit the constituents of MSW.

In the example of Fig. 8A, the first and second surfaces are smoothly curved from the first point to the second point, and from the second point to the trailing edge, and each of the first and second surfaces has an angle of incidence of 35°. The first and second lines 72', 73' converge in a convergent region 79 from the second points 72", 73" to the trailing edge 71. A smoothly curved configuration with a low angle of incidence of about 30° - 60° is found to give best results when processing biochar and MSW in combination, since the vorticial action is relatively more gentle which allows the soft MSW to blend with the biochar while the biochar is reduced to a suitable granular consistency to form an homogeneous end product 28 comprising mixed particles of MSW and impregnated biochar.

In the example of Fig. 8B, the leading edge is flat with square corners, and the upper and lower surfaces have a parallel portion extending from the square corners back to a transition point 78 which marks the beginning of a convergent region 79 in which the first and second lines converge to the trailing edge. The second points 72", 73" are therefore formed by the square corners, so that the angle of incidence of each of the upper and lower surfaces is 90°. The convergent region extends for at least half the distance between the leading and trailing edges. This configuration produces a more radical vorticial comminution suitable for harder materials, while the convergent region forms the vortex behind the moving rotor element.

In the example of Fig. 8C the leading edge comprises a short flat region from which the upper and lower surfaces diverge towards the second points 72", 73", which form the transition to the convergent region 79 in which the first and second surfaces converge towards the trailing edge. Again, the convergent region extends for more than half the distance between the leading and trailing edges.

Advantageously, the leading edges of the deflector elements in particular show remarkably little wear, which is believed to be due to the development of a high pressure region which deflects particles of feedstock around the profiled upper and lower surfaces.

In another embodiment, as illustrated and described above with reference to each of Figs. 8A, 8B and 8C, the rotor assembly and rotor elements may be either adjustable or of fixed geometry, wherein the first and second lines 72', 73' are symmetrical about the first plane PI and converge in a convergent region 79 to the trailing edge 71. Preferably, as shown in each of Figs. 8 A, 8B and 8C, the convergent region extends for at least half the distance between the leading and trailing edges. This configuration is found to be particularly effective in creating a vortex behind the trailing edge and maintaining the feedstock in suspension in the path of the rotor elements until it is comminuted to the desired particle size. The leading edge may be smoothly curved for example as shown in Fig. 8A.

As described above and illustrated in Fig. 7 and Fig. 8A, the radially outer portion of the rotor element may advantageously be configured as an aerofoil, preferably a symmetric aerofoil wherein the chord lies at the intersection of the first and second planes.

A method of operating a rotary processing machine comprises determining at least one mechanical characteristic of the feedstock; in particular, the mechanical characteristic may be a resonant frequency of the feedstock, which can be determined from reference sources as known in the art. In the case of a mixed waste feedstock, an average resonant frequency of the feedstock is determined. Alternatively the mechanical characteristic could be for example the hardness, plasticity or flexibility of the feedstock. At least one rotor assembly is then adjusted to vary the angle of incidence of the respective rotor elements, the angle of incidence being selected according to the at least one mechanical characteristic of the feedstock to give optimal processing. The selection of the optimal angle of incidence for the value of the respective mechanical characteristic may be determined by routine experimentation, but as a rule of thumb, the angle of incidence may be increased with the resonant frequency or hardness of the feedstock.

Preferably, after adjusting the at least one rotor assembly to vary the angle of incidence, at least one rotor gap is adjusted to achieve the desired particle size of the comminuted feedstock at the outlet. The motor is then operated to drive the rotor in rotation about the axis at the service speed so that the rotor elements of the at least one rotor assembly generate multiple vortices in the airflow, and the feedstock is fed into the inlet so that it is comminuted by interparticle collisions or pressure fluctuations in the vorticial airflow.

In this manner the machine may be tuned for improved performance when processing a range of different materials.

Referring to Fig. 9, in a method of processing waste into fertilizer a first waste stream 91 comprising solid waste having a nutrient and moisture content is processed in combination with biochar 93 in a vorticial airflow to obtain a homogeneous particulate end product 28, wherein the biochar and the solid waste are comminuted and the biochar is impregnated with the solid waste.

The processing takes place in a processing machine 1 ' ' including a housing, a rotor, and a motor for driving the rotor, the rotor including at least an impeller for generating an airflow through the housing, wherein the rotor is driven in rotation about an axis at a service speed to generate the vorticial airflow through the housing from an inlet to an outlet.

It has surprisingly been found that when biochar is comminuted by interparticle collisions or pressure fluctuations in a vorticial airflow in combination with a relatively soft and nutrient rich waste material such as food waste or partially dried sewage or manure, the biochar becomes intimately impregnated with the waste material so that the waste material is driven deep into its pores. Where the biochar is added to soil, the waste material together with any chemical additives (e.g. phosphate or potash) intermixed with it becomes available to beneficial soil organisms which populate the very large surface area within its pores. This impregnation is found to occur even without any special treatment to remove adsorbed gases from the pores of the biochar prior to introducing it into the vorticial airflow. This surprising effect is believed to be due to the very rapidly fluctuating pressures within the vortices of the airflow which cause the waste material to behave in a very fluid manner and to replace the adsorbed gases in the pores. The effect is observed in rotary machines in which a vortex is generated at each of a plurality of salient rotor elements, which are found to cope well with a feedstock having a relatively high moisture content because the multiple vortices generated by the rotating rotor elements tend to keep the moist feedstock in suspension in the airflow. The resulting end product 28 is rich in nutrients and of outstanding benefit to the soil.

Advantageously, the method is carried out in the novel machine 1 ' as described above, wherein the angles of incidence and the rotor gaps may be adjusted to provide optimal processing of the waste stream; this is particularly useful where a mixed waste stream is separated into two dissimilar waste streams which are separately processed as further described below.

Advantageously, the aforementioned effects of the vorticial airflow effectively sterilise the waste by thrashing to reduce odour and destroy weed seeds, insect eggs, spores and pathogens including bacteria and viruses while reducing its moisture content and flocculating and precipitating fine particles. Without wishing to be bound by theory, it is believed that living DNA is dissociated by extreme temperature fluctuations on a micro scale resulting from transient sonic and pressure phenomena in the vorticial airflow, and by processing the waste in combination with chemical nutrients such as phosphate or potash, these nutrients prevent the DNA fragments from re-combining, leading to more complete sterilisation of the first waste stream 91.

It is possible that a similar effect may be obtained from vortex generating machines which do not have any rotor elements, although such machines tend to cope less well with moist materials and so are generally used for comminuting rock and other hard, dry materials.

In a preferred embodiment as illustrated, a mixed waste stream 90 is screened to remove metals and other inert materials before being separated into the first waste stream 91 having a relatively higher nutrient and moisture content, and a second waste stream 92 comprising combustible materials having a relatively lower nutrient and moisture content than the first waste stream.

The mixed waste stream may be MS W. The first waste stream 91 may include at least one of food waste, green waste, animal products, and semi-dry sewage or manure. The second waste stream 92 may include at least one of wood, plastics, fabrics, paper, and cardboard.

Preferably the biochar 93 is obtained by pyrolysis of the second waste stream 92 in a pyrolysis plant (pyrolyser) 94 in which the second waste stream is pyrolysed to yield the biochar 93 together with a liquid or gaseous hydrocarbon fuel 95. More preferably, before pyrolising the second waste stream, the second waste stream is comminuted in the vorticial airflow in the at least one processing machine 1 " to produce a comminuted second waste product 92' which is more efficiently pyrolysed.

Where the novel machine 1 ' is used as the processing machine, the respective angle of incidence al, a2 of each of the first and second surfaces when processing the first waste stream and the biochar is preferably less than 60°, which is found to more effectively impregnate the particles of biochar with the first waste stream. When the second waste stream is comminuted in the same machine, the angle of incidence of each of the first and second surfaces may be more than 60° to suit the nature of the feedstock, wherein the first and second waste streams are batch processed alternately. Alternatively, more than one processing machine may be provided, and each of the machines adjusted for processing a respective one of the two feedstocks.

The fuel 95 may be burned to produce an exhaust gas 96. Preferably, the fuel 95 is burned in an internal combustion engine to power a generator 98 to produce energy 99 which may be used to drive the rotor of the machine 1 ' ' and/or sold to the electricity grid.

The exhaust gas 96 may be used to heat the first waste stream in a drier 97 to reduce its moisture content, preferably to around 7% - 10% before processing the first waste stream in the processing machine.

The exhaust gas 96 may then be combined with the first waste stream 91 when processing the first waste in the machine 1 ".

More preferably, the exhaust gas 96 is processed in combination with the second waste stream 92 in the processing machine 1 " so that the gaseous carbon contained in the exhaust is impregnated into the processed second waste product 92' and subsequently sequestered in the biochar when the waste product 92' is pyrolysed.

The first waste stream 91 is combined in the machine 1 " with the biochar 93 from the pyrolysis plant and optionally chemical additives 100 such as phosphate and potash to provide a desired nutrient profile in the end product. After processing, the end product 28 comprises a homogeneous blend of particles of the first waste and biochar in which the first waste is deeply impregnated.

The end product is blown by the impeller into a cyclonic separator 101 in which it is separated from the airflow, and then stored in a reaction chamber 102 in which the first waste undergoes an exothermic reaction with the chemical additives, raising the temperature to further sterilise it. The end product is then treated by spraying with a mycorrhizal fungus 103, which is able to rapidly colonise the pores of the biochar due to the impregnated waste, creating a very large reservoir of beneficial soil organisms. Finally the treated end product 28' is fed into a pelletiser 104 where it is pelletised, and the pellets 28" are packed in bags 105 for sale.

It will be understood that the novel method can be practiced as a self sustaining process in which the mixed waste stream is converted into energy and an improved fertilizer product without any external energy input and with virtually no emissions. Advantageously, the impregnated biochar acts as a carbon sink as well as a more effective fertiliser.

In summary, a preferred rotary processing machine comprises a rotor arranged in a housing, the rotor including an impeller and multiple rotor assemblies adapted to generate a high velocity vorticial airflow for comminuting a feedstock. In one embodiment the rotor shaft is axially adjustable to adjust the airflow by varying the position of the rotor elements. In another embodiment an angle of incidence of the rotor elements is adjustable to suit a mechanical characteristic of the feedstock. In another embodiment the machine comprises rotor elements having upper and lower surfaces defining lines which are symmetrical about a first plane and converge in a convergent region to a trailing edge. The machine may be used to process municipal solid waste in combination with biochar so as to impregnate the biochar with the waste, providing an improved fertilizer. Preferably the biochar is derived by pyrolysis of a separated fraction of a mixed waste stream in a self sustaining process.

Claims

1. A rotary processing machine for comminuting a feedstock, including a housing;

a rotor arranged in the housing;

and a motor for driving the rotor in rotation about an axis at a service speed;

the housing including an inlet, an outlet, and at least two inwardly extending walls spaced apart axially between the inlet and the outlet, the rotor extending through a respective aperture in each wall;

the rotor including a shaft, an impeller, and at least two rotor assemblies, the impeller and the rotor assemblies being fixed on the shaft in axially spaced relation;

the impeller being arranged to generate an airflow through the housing from the inlet to the outlet sufficient to draw the feedstock through the housing from the inlet to the outlet when the rotor is driven in rotation at the service speed; each rotor assembly comprising a respective array of rotor elements spaced axially from a respective one of the walls by a respective rotor gap;

wherein the shaft is axially adjustable in the housing to simultaneously adjust all of the rotor gaps.

2. A rotary processing machine according to claim 1, wherein the rotor is axially adjustable by an adjustment means, the adjustment means being operable while the motor is in operation.

3. A rotary processing machine according to claim 1, wherein the motor is mounted in fixed relation to the housing, and the rotor is axially adjustable relative to the motor.

4. A rotary processing machine according to claim 3, wherein a clutch is provided, the clutch comprising first and second surfaces which are engageable together to couple the rotor to the motor and disengageable to decouple the rotor from the motor; and the rotor is axially adjustable relative to the motor by axially displacing the first surface relative to the second surface.

5. A rotary processing machine according to claim 4, wherein the clutch is a centrifugal clutch which disengages the first and second surfaces when the motor operates at an idle speed below the service speed.

6. A rotary processing machine according to claim 1, wherein each rotor assembly is independently axially adjustable on the shaft.

7. A rotary processing machine according to claim 1, wherein in normal operation at the service speed of the rotor, the motor has a power consumption of at least lOOkW and a radially outer tip of each rotor element travels at a speed of at least 15m/s.

8. A rotary processing machine according to claim 1, wherein the rotor elements are arranged to generate multiple vortices in the airflow so as to comminute the feedstock by interparticle collisions or pressure fluctuations when the rotor is driven in rotation at the service speed.

9. A rotary processing machine according to claim 1, wherein the housing comprises an upper portion and a lower portion, the upper portion having a polygonal cross section and containing the rotor assemblies, the lower portion having a smoothly curved cross section and containing the impeller.

10. A rotary processing machine according to claim 1, wherein a radially outer portion of each rotor element includes a leading edge, a trailing edge, and first and second surfaces;

the leading edge including a first point which lies at an intersection of first, second and third planes, the first plane being normal to the axis, the second plane being normal to the first and third planes, the third plane containing the axis;

the first and second surfaces intersecting the second plane respectively at a first and second line;

the first and second lines extending from the first point to the trailing edge respectively on opposite sides of the first plane;

each of the first and second lines passing through a respective second point, the second point being that point closest to the first point at which the respective first or second line lies at a maximum distance from the first plane;

each of the first and second surfaces having a respective angle of incidence in the second plane, the angle of incidence being defined between the first plane and a straight line joining the first point and the respective second point;

wherein at least one rotor assembly is adjustable to vary a said angle of incidence of the rotor elements.

11. A rotary processing machine according to claim 10, wherein the first and second surfaces are smoothly curved from the first point to the second point.

12. A rotary processing machine according to claim 10, wherein the first and second surfaces are smoothly curved from the second point to the trailing edge.

13. A rotary processing machine according to claim 10, wherein the first and second surfaces have an equal angle of incidence.

14. A rotary processing machine according to claim 10, wherein the first plane is a plane of symmetry of the radially outer portion of the rotor element.

15. A rotary processing machine according to claim 10, wherein each of the first and second surfaces has a maximum angle of incidence from 80° - 90°.

16. A rotary processing machine according to claim 10, wherein each of the first and second surfaces has a minimum angle of incidence from 20° - 40°.

17. A rotary processing machine according to claim 10, wherein at least two sets of interchangeable rotor elements having different angles of incidence are provided.

18. A rotary processing machine for comminuting a feedstock, including a housing;

a rotor arranged in the housing;

and a motor for driving the rotor in rotation about an axis at a service speed;

wherein a radially outer portion of each rotor element of at least one rotor assembly includes a leading edge, a trailing edge, and first and second surfaces; the leading edge including a first point which lies at an intersection of first, second and third planes, the first plane being normal to the axis, the second plane being normal to the first and third planes, the third plane containing the axis;

the first and second surfaces intersecting the second plane respectively at a first line and a second line;

and the at least one rotor assembly is adjustable to vary a said angle of incidence of the rotor elements.

19. A rotary processing machine according to claim 18, wherein the first and second surfaces are smoothly curved from the first point to the second point.

20. A rotary processing machine according to claim 18, wherein the first and second surfaces are smoothly curved from the second point to the trailing edge.

21. A rotary processing machine according to claim 18, wherein the first and second surfaces have an equal angle of incidence.

22. A rotary processing machine according to claim 18, wherein the first and second lines are symmetrical about the first plane.

23. A rotary processing machine according to claim 18, wherein the first and second lines converge in a convergent region to the trailing edge, and the convergent region extends for at least half the distance between the leading and trailing edges.

24. A rotary processing machine according to claim 18, wherein each of the first and second surfaces has a maximum angle of incidence from 80° - 90° and a minimum angle of incidence from 20° - 40°.

25. A rotary processing machine according to claim 18, wherein at least two sets of interchangeable rotor elements having different angles of incidence are provided.

26. A rotary processing machine according to claim 18, wherein in normal operation at the service speed of the rotor, the motor has a power consumption of at least lOOkW and a radially outer tip of each rotor element travels at a speed of at least 15m/s.

27. A rotary processing machine according to claim 18, wherein the rotor elements of the at least one rotor assembly are arranged to generate multiple vortices in the airflow so as to comminute the feedstock by interparticle collisions or pressure fluctuations when the rotor is driven in rotation at the service speed.

28. A rotary processing machine according to claim 18, wherein the housing comprises an upper portion and a lower portion, the upper portion having a polygonal cross section and containing the rotor assemblies, the lower portion having a smoothly curved cross section and containing the impeller.

29. A method of operating a rotary processing machine;

the machine including a housing;

a rotor arranged in the housing, the rotor having an axis of rotation; and a motor for driving the rotor;

the impeller being arranged to generate an airflow through the housing from the inlet to the outlet sufficient to draw the feedstock through the housing from the inlet to the outlet when the rotor is driven in rotation at a service speed; each rotor assembly comprising a respective array of rotor elements spaced axially from a respective one of the walls by a respective rotor gap;

the method comprising:

determining at least one mechanical characteristic of the feedstock; adjusting the at least one rotor assembly to vary a said angle of incidence of the respective rotor elements, wherein the said angle of incidence is selected according to the at least one mechanical characteristic of the feedstock;

operating the motor to drive the rotor in rotation about the axis at the service speed so that the rotor elements of the at least one rotor assembly generate multiple vortices in the airflow;

and introducing the feedstock into the inlet so that the feedstock is comminuted by interparticle collisions or pressure fluctuations in the vorticial airflow.

30. A method according to claim 29, wherein the mechanical characteristic is a resonant frequency of the feedstock.

31. A method according to claim 30, wherein the said angle of incidence is increased with the resonant frequency of the feedstock.

32. A method according to claim 29, wherein the said angle of incidence is increased with the hardness of the feedstock.

33. A method according to claim 29, wherein after adjusting the at least one rotor assembly to vary the said angle of incidence, at least one rotor gap is adjusted to achieve a desired particle size of the comminuted feedstock at the outlet.

34. A method according to claim 29, wherein in normal operation at the service speed, the motor has a power consumption of at least lOOkW and a radially outer tip of each rotor element of the at least one rotor assembly travels at a speed of at least 15m/s.

35. A method according to claim 29, wherein the housing comprises an upper portion and a lower portion, the upper portion having a polygonal cross section and containing the rotor assemblies, the lower portion having a smoothly curved cross section and containing the impeller.

36. A method of processing waste into fertilizer, comprising:

receiving a first waste stream, the first waste stream comprising solid waste having a nutrient and moisture content;

providing a stream of biochar;

providing at least one processing machine including a housing, a rotor, and a motor for driving the rotor, the rotor including at least an impeller for generating an airflow through the housing;

driving the rotor in rotation about an axis at a service speed to generate a vorticial airflow through the housing from an inlet to an outlet;

and processing the first waste stream and the biochar in combination in the vorticial airflow to obtain a homogeneous particulate end product,

wherein the biochar and the solid waste are comminuted and the biochar is impregnated with the solid waste.

37. A method according to claim 36, wherein the biochar is obtained from a second waste stream, the second waste stream comprising solid combustible materials having a relatively lower nutrient or moisture content than the first waste stream.

38. A method according to claim 37, including separating a mixed waste stream into the first and second waste streams.

39. A method according to claim 37 or 38, wherein the second waste stream is pyrolysed to yield the biochar together with a liquid or gaseous hydrocarbon fuel.

40. A method according to claim 39, wherein the fuel is burned to produce energy to drive the rotor.

41. A method according to claim 39 or 40, wherein the fuel is burned to produce an exhaust gas, and before pyrolising the second waste stream, the exhaust gas is processed in combination with the second waste stream in the at least one processing machine.

42. A method according to claim 41, wherein the exhaust gas heats the first waste stream to reduce its moisture content before processing the first waste stream in the processing machine.

43. A method according to claim 36, wherein the rotor includes at least two rotor assemblies arranged in the housing, each rotor assembly including an array of rotor elements,

and the housing includes at least two inwardly extending walls spaced apart axially between the inlet and the outlet, the rotor extending through a respective aperture in each wall,

each rotor assembly comprising a respective array of rotor elements spaced axially from a respective one of the walls by a respective rotor gap;

and the rotor elements of at least one rotor assembly are arranged to generate multiple vortices in the airflow so as to comminute the biochar and the solid waste by interparticle collisions or pressure fluctuations in the vorticial airflow.

44. A method according to claim 43, wherein a radially outer portion of each rotor element of the at least one rotor assembly includes a leading edge, a trailing edge, and first and second surfaces; the leading edge including a first point which lies at an intersection of first, second and third planes, the first plane being normal to the axis, the second plane being normal to the first and third planes, the third plane containing the axis;

and the angle of incidence of each of the first and second surfaces when processing the first waste stream and the biochar is less than 60°.

45. A method according to claim 44, wherein the biochar is obtained by pyrolising a second waste stream, the second waste stream comprising solid combustible materials having a relatively lower nutrient or moisture content than the first waste stream;

and before pyrolising the second waste stream, the second waste stream is comminuted in the vorticial airflow in the at least one processing machine, wherein when comminuting the second waste stream the angle of incidence of each of the first and second surfaces is more than 60°.

46. A method according to claim 36, wherein the first waste stream includes at least one of food waste, green waste, animal products, sewage and manure.

47. A method according to claim 37 or 38, wherein the first waste stream includes at least one of food waste, green waste, animal products, sewage and manure, and the second waste stream includes at least one of wood, plastics, fabrics, paper, and cardboard.

48. A method according to claim 36, wherein after said processing in the vorticial airflow the end product is treated with a mycorrhizal fungus.

49. A method according to claim 36, wherein after said processing in the vorticial airflow the end product is pelletised.

50. A method according to claim 36, wherein the first waste stream is processed in the processing machine in combination with chemical additives; and then the end product is separated from the airflow in a cyclonic separator and stored in a reaction chamber in which it undergoes an exothermic reaction.

51. A rotary processing machine for comminuting a feedstock, including a housing;

a rotor arranged in the housing;

and a motor for driving the rotor in rotation about an axis at a service speed;

wherein the first and second lines are symmetrical about the first plane and converge in a convergent region to the trailing edge.

52. A rotary processing machine according to claim 51, wherein the convergent region extends for at least half the distance between the leading and trailing edges.

53. A rotary processing machine according to claim 51, wherein the leading edge is smoothly curved.