GB2490409A - Apparatus and method comprising agitator elements for use in the heat treatment of feedstocks - Google Patents

Abstract

An apparatus 100 suitable for the heat treatment of a bulk feedstock comprises a receptacle 101 suitable for receiving a bed of feedstock, an inlet 105 through which microwaves may pass to enter the receptacle, causing the feedstock bed to heat up due to volumetric heating effects, to release inbound moisture to regions within the bed. The apparatus further comprises a stock of reusable agitator elements 200 mixed within the bed of feedstock, the elements preferentially absorbing at least some of the microwave energy thereby heating up to cause additional heating of the moisture or vapour or gas released from the feedstock. A vibratory means 110 is operable to cause the receptacle to vibrate and agitate the feedstock and agitator elements and the released liquid or vapour in the receptacle so as to produce a fluidised bed of feedstock, in which the agitator elements are shaped so as to assist in the formation and collapse of microvoids within the bed to drive released moisture or vapour out of the bed. In a further aspect, a method of drying or otherwise treating a feedstock by a combination of heating, vibrating and agitating the feedstock is disclosed.

Description

APPARATUS AND METHOD FOR TREATMENT

OF FEEDSTOCKS

BACKGROUND OF THE INVENTION.

This invention relates to apparatus and methods for the treatment of bulk feedstocks such as fragmentary or fluid feedstock materials in a manner that allows physical or chemical processing of the materials in conjunction with the efficient removal of gases, vapours and microparticulates resulting from such processing.

It is well known that it is possible to heat feedstocks by conveying them through a heated region. The heating can be achieved by direct radiation of the heated region with infrared radiation or by microwave radiation. In the later case, where the feedstock is lossy (typically containing water or other polar solvent) then inevitably the heating of the feedstock creates thermal energy which heats other feedstock in the heated region.

In W02010/073013A2(Nodesys) it is proposed to combine heating of a feedstock by microwave energy with vibration of the receptacle containing the bed so as to cause the bed as a whole to be turned through a helical path, constantly moving feedstock from the base of the bed to the top before folding back in on itself. This relatively slow helical motion is said to help expose the bed to uniform heating, improving the drying process.

It has also been proposed to deliver thermal energy to feedstocks using sensitizers, small elements of solid material that can be mixed in with a feedstock and which are capable of dissipating microwave energy as heat In US61 84427 there is disclosed a process in which high molecular organic waste material undergoes cracking by mixing a pulverized sensitizer with the waste and treating the mixture with microwave energy.

The sensitizers and waste are combined in such a way that it is difficult to separate and recover the sensitizer from the carbonised waste.

BRIEF SUMMARY OF THE INVENTION.

According to a first aspect the invention provides apparatus suitable for the heat treatment of a bulk feedstock comprising: a receptacle suitable for receiving a bed of feedstock, an inlet through which microwaves may pass to enter the receptacle when the inlet is exposed to a source of microwave energy, the microwaves causing the feedstock bed to heat up due to volumetric heating effects to release inbound moisture as vapour or gas from the feedstock to regions within the bed, a stock of reusable agitator elements which in use are placed in the receptacle mixed within the bed of feedstock, the elements preferentially absorbing at least some of the microwave energy thereby heating up to cause additional heating of the moisture or vapour or gas released from the feedstock, and a vibratory means which is operable to cause the receptacle to vibrate at a frequency and amplitude so as to agitate the feedstock and agitator elements and the released liquid or vapour in the receptacle so as to produce a fluidised bed of feedstock, and in which the agitator elements are shaped so as to assist in the formation and collapse of microvoids within the bed to drive released moisture or vapour out of the bed.

In the context of this specification, the terms "fluidised" and "self-fiuidising" refer to a fragmentary material that acts as a fluidised material through the use of mechanical vibrations, without the need for externally-sourced gases or fluids flowing through that material.

Previous attempts at providing fluidised beds have required air to be blown through the bed of feedstock through holes in the base of the bed. This requires a lot of energy and so is inefficient. It also limits the environment that can be achieved within the receptacle. The present invention achieves such a bed through heating of the agitator elements and vibration alone, which can enable a more efficient processing to be achieved. The fluidised bed allows released moisture to transfer through the bed more easily than non-fluidised beds.

The Rate of heat and mass exchange in the materials is increased under the vibratory effect as a result of which productivity is raised and energy / power consumption is reduced.

The agitator elements, or FLOPOIDS, which are heated by the microwaves and move due to movement of the bed by vibration, assists in the formation of the self-fluidised bed and help to drive the released vapour out of the bed. The microwave energy fed into the receptacle heats them to a temperature above that of steam (100 degrees celcius at atmospheric pressure) so that as released moisture contacts the elements it is heated and turned to steam, helping create the fluidisation. The formation of the self fluidising bed is also assisted, at least in part, by the shape of the elements. They help mix the feedstock as they move through the bed when vibrated. They may, for example, increase or retard flow of the feedstock, reduce or increase the effective viscosity of the bed of feedstock, and assist in the flow of gas or vapour through the bed by the formation of microvoids. These microvoids may vary from microns to a few mm in size. The heating of the agitator elements by microwave or radiant healing effects helps maintain and transfer heat throughout the bed of feedstock.

The elements should be reusable, by which we mean that they are thermally stable within the range of temperatures they are likely to be used, so they can be used over extended periods of time. Ideally they should not degrade when in use so they can be reused almost indefinitely. Preferably they have the same density, or substantially the same, as the solids feedstock that forms the bed, so that they are suspended throughout the self fluidised bed rather than sinking to the bottom or floating on the top. This can be achieved through correct selection of agitator elements for any given feedstock.

It is envisaged that, in at least some embodiments, the apparatus will be suitable for use in heat treating the following feedstocks: liquids, slurries, acids, solvents, oils/waters, industrial effluents in both onshore and offshore environments, emulsions, granular solids, powders, particulates, aggregates, biomass, organics, mixtures, algaes, bio-oils, furfanols, dismantling gases, glass, asbestos, tyre cuttings etc. The elements may be of any three dimensional shape that assists the flow of material and the creation of microvoids. They are preferably non-spherical in shape with at least one concave portion, forming a groove, trough or dimple, on their outer surface.

The concave portion may form a pocket or void which has been found to be beneficial in creating voids in the bed as the elements move. For instance, as two agitator elements move away from one another with theft concave portions facing each other, a void may tend to open up in the feedstock. As they move together, the facing concave regions entrap material and gas or moisture and create a micropumping effect pushing the entrapped material away from the elements.

In a most preferred embodiment the shapes of the elements may be described as geoidal.

The elements may have a length and a width and may be generally uniform in cross section along their length. They may comprise a concave polygon when viewed in cross section, for instance shaped like a figure of eight in cross section, or an approximately figure of eight shape (like a peanut shell), or an oval. Providing elements which have a uniform cross section along their length makes them simple to produce, perhaps using an extrusion process. Of course, they may have a non-uniform cross section along their length in some applications.

The elements may have a length greater than their width, typically two to three times greater. This sleek shape helps the elements to move around easily between the feedstock within the bed.

In use the receptacle may typically contain between 10 and 20 percent agitators relative to feedstock by volume, although any ratio up to approximately 100 percent agitators. The agitators are preferably relatively low in mass (for a given volume relative to a given volume of feedstock) so that they do not damage the feedstock as they move around within the bed.

The agitator elements may be at least partially porous. They may be of any one or more pure chemical elements, alloys or compounds, perhaps of ceramic material or metals and their alloys, metal carbides or nitrides or polymers. They may be monophasic or polyphasic, including homogenously mixed solid phases, liquid phases absorbed into solid phases, laminated materials, or a core surrounded by a shell.

The ceramic material may comprise one or more of the following: steatite, alumina, silica, magnesium sulphate, mullite, zeolites or alkali aluminosilicates (e.g. molecular sieves). If they are specially manufactured to be porous, the elements can absorb moisture or vapour released from the feedstock, subsequently heating up the absorbed moisture as the elements heat up, causing the element to release the moisture, typically as steam from the element.

The agitator elements may comprise a surround part which has a relatively low dielectric loss which surrounds a core which has a relatively high dielectric loss. The core may be completely encased by the surround part. In use, the core will be heated up by the microwave energy and will radiate this heat outward through the surrounding material. The surround part may be relatively less dense than the core part so that, for a given size, the element is lighter than it would be if it was made purely from the material used for the core.

Depending on the dimensions of the core it may also/alternatively scatter the microwave energy back out through the surround. These actions may result in strong heating at the surface of the elements. This, in turn, may permit chemical modifications to take place at the surface that advantageously alter the physico-chemical properties of the surface, including changes in the surface coefficient of friction..

The elements may be coated with a catalyst, or a catalyst may be dispersed throughout at least the surround part of the element. This will typically comprise a heterogeneous catalyst, examples being:: graphite, elemental metals, alloys, vanadium oxides, iron oxides. This is beneficial in breaking down chemicals in the released moisture or vapour. Placing them on the outer surface of the elements ensures they are evenly spread throughout the bed of feedstock and move around to be exposed to the released moisture or vapour. Using a catalyst, the apparatus of the present invention may produce a self-fluidising and ebulating bed within the receptacle, all without the need to blow additional air through the bed. The catalyst may take an active part in modifying the chemical or physical properties of the feedstock materials or byproducts created in heating.

The core, in a preferred arrangement, may comprise a sheet, rod, bar or other shape, and may be a perforated metal sheet, which may be sandwiched between two half surround portions of material, preferably ceramic. The perforations may have a diameter that is less than one quarter of a wavelength of the microwave radiation.

The core of the elements may have a length equal to one quarter of the wavelength of the microwave energy used so that it absorbs the energy, or one half of a wavelength so that it scatters the energy and works as a mode stirrer or mode mixer within the bed.

Other core/surround arrangements may include a microwave absorbing material such as carbon contained within a chemically inert shell of alumina, or a catalytically active but largely microwave transparent material such as a zeolite interspersed with a microwave absorbing material such as silicon carbide.

The elements may include a conductive antenna, typically a metal pin or rivet, that passes through the element from one side to the other. This antenna will, under correct application of microwave energy, temperature and pressure within the receptacle generate plasma which can assist during the treatment process. This pin may pass perpendicularly through any metal insert provided within the element.

The agitators may be larger in size than the feedstock items, or smaller in size.

Generally, the larger feedstocks may be treated with smaller agitator elements.

It is most preferred that all the agitator elements are of the same size and shape within the bed.

The agitator elements may, in some arrangements, assist in the grinding, crushing or polishing of the feedstock. They may, in some arrangements, convert vibration energy into electrical energy if they are made at least in part of piezo-electric material, and this may effect electrochemical modification of the feedstock material that is treated.

To provide a self fluidising bed, the vibration means must cause the feedstock and agitator elements to move around sufficiently vigorously in the receptacle whilst the microwave source provides enough energy to drive out inbound moisture. This action is assisted by the radiant heating from the agitator elements. This will depend on the dimensions and mass of the receptacle, and any parts rigidly attached to it, any damping provided by the support of the receptacle, the mass and volume of feedstock and agitator elements that are in the bed, the nature of the feedstock and size and shape of the feedstock pieces and agitator elements, and the amount of radiation applied from the microwave source.

The vibrator means, as the source of vibration, may be electro-mechanical and may include at least one unbalanced motor fixed to the receptacle or a support platform for the receptacle, the receptacle or support platform in turn being supported by one or more springs such that it can move around as the motor rotates, causing the feedstock in the bed to move side to side or back and forth or with a circular motion or any combination relative to the support platform. The vibration may be arranged to cause feedstock in the bed to advance from one end of receptacle where feedstock is fed in to another end at which it can leave the receptacle. A brake may be provided to stop the vibrations when the vibration means is switched off In the case of an electric S motor, an electro-mechanical brake may be provided. This can help ameliorate the sometimes violent uncontrolled vibrations due to resonance and such like that might otherwise arise as the motor slows to a standstill.

The vibrations from the motor(s) may be adjustable in amplitude and frequency and in mode of vibration dependent on the feedstock and agitator elements that are used.

Vibrations of individual agitator elements and feedstock of around 1mm to 3mm in magnitude are preferred for the creation of the fluidised bed.

It is most preferred that the vibrations created by the vibrator means are such that the bed of feedstock moves mainly up and down, side to side and with little circular motion, either in a horizontal plane (similar to a whirlpool) or in the vertical plane, so called "rolling" similar to a collapsing wave. This circular motion tends to cause moisture in the bed to be folded back in making it hard for it to be released from the bed, and can lead to relatively cold regions within the bed where released moisture may tend to condense.

The base of the receptacle may include one or more flow conditioning ridges, which act to control the motion of the bed preventing the bed of feedstock from moving in a bulk helical motion. This may comprise an inverted U or V shaped ridge that extends along at least part of the base of the receptacle. The ridge may form a channel through which heated gas or fluid may be passed to help heat the lower part of the bed of fee dstock.

To assist in removing the released vapour and gas that is driven out of the bed, the receptacle may include an outlet suitable for connecting to a means of generating pressure below atmospheric pressure, such as a vacuum pump, where "atmospheric" S refers to the pressure outside of the receptacle.

The walls and base of the receptacle may be of solid material, no holes in particular being needed or provided in the base for the inflow of air as has previously been used to create a self-fluidised bed.

The actual pressure in the vessel may itself be maintained above or below the outside "atmospheric" pressure by forcing air or other gas into the receptacle, or the use of restrictors to control the inflow of air into the vessel relative to the rate at which it is drawn out. Where the receptacle is pressurised to a level above the outside atmospheric pressure, pumping is not needed as the hot gas and vapour mixed with the air in the vessel will force its own way out of the receptacle. Because there is no need for holes to allow air to be blown through the bed, it is simpler to evacuate the inside of the receptacle.

The use of reduced pressure creates a "modified atmosphere" and provides the advantage that the temperature at which liquid or vapour is released from the feedstock is lowered. The vacuum pump may form a part of the apparatus. Positive pressure in the vessel may be used to reduce the processing time of reactions that occur during drying. It is notable that a reduced or elevated pressure, and the resulting improvements in energy efficiency that can be obtained by the present invention, cannot be achieved using prior art fluidised bed dryers which require a constant flow of air through the bed to create the fluidisation.

The applicant has appreciated that for many feedstocks there will be a large volume of dust driven out of the bed as it vibrates which could clog any vacuum pump connected to the outlet. The apparatus may therefore include a filter which traps particles of dust that pass through the outlet, or would otherwise pass through the outlet and which are above a predetermined size. This filter will typically be located just outside or just inside the receptacle across the outlet, although it could be located some distance away along a pipe connected to the outlet.

The filter may comprise a self-cleaning filter, comprising two layers of filter material separated by a gap which contains a plurality of individual cleaning elements (which may or may not be spherical balls) sized so that the they are free to move around between the layers, air and vapour and other gas drawn off from the receptacle entering one filter, passing across the gap and leaving through the other layer, the cleaning elements moving as the receptacle vibrates to strike the filter layers thereby causing dust built up on the filier layers to fall away.

The layer through which the air is drawn off first may have larger filter holes than the other layer, so dust knocked off by the balls can fall back through the openings into the receptacle or a catch tray. The other layer may have holes that are too small for the dust to pass through. En each case the holes should be smaller than the balls so that they are entrained between the layers. Holes of less than one quarter wavelength in size are preferred for the lower layer.

At least one layer may comprise a layer of filter cloth. This may be the uppermost layer, and the material may be resilient so that upon being struck by a ball the openings in the material open up slightly to allow entrapped material to fall away.

The lower layer of the filter may be stainless steel and optionally may be heated to assist in drying any dust that may under normal operating conditions contain a lot of moisture. Drying the dust reduces the chance of it sticking to the upper filter cloth layer.

The opening through which microwaves can enter the receptacle may be sealed by a window that is at least partially transparent to microwave radiation, such as a ceramic window of quartz, or alumina or aluminium nitride, or a polymer such as Perfiourpolymer, PEEK or polyamide. The window may be enhanced by the use of a low friction surface coating on the side facing into the receptacle, to improve the flow of the self-fluidised bed. PTFE would be a suitable low friction coating that can be used with a wide range of windows. Other coatings may be used to improve the wear resistance of the window, such as diamond or titanium nitride coatings.

The apparatus may include a coupler which is fixed at one end to the receptacle and at the other to a source of microwaves, the two ends being mechanically decoupled to reduce the vibration from the receptacle being passed to the microwave source.

The applicant has appreciated that microwaves that enter the receptacle through an inlet that is above the bed will result in the top of the bed being warmer than the lower part. Therefore, the apparatus may include one or more inlets by which microwave energy can enter the receptacle from the side, or sides, and/or the base which are below the level of the top of the bed of feedstock. They may, for example, be located in the bottom half or bottom third of the receptacle.

The inlet for microwaves may comprise a set of slots along the sides and/or base which are located within one or more hollow reinforcing beams that extend along or around the receptacle and provide rigidity to the receptacle. The beams may act as waveguides to guide microwave energy towards the slots, or may be lined with a waveguide that provides that function.

The apparatus may include a source of ultrasound and be arranged to direct the ultrasonic energy onto the bed of feedstock. The applicant has appreciated that this is beneficial in some cases in that it can help to crack open feedstock, helping to release inbound moisture or gas.

The receptacle may comprise a trough, and may be linear, circular, oval or other shape, for instance an oval trough curved to form a double helix or a spiral etc. The trough may be lower at one end than the other to form a flight conveyor-linear or spiral, with the vibration causing the bed material to move form one end to the other.

The receptacle may be arranged, for example as a spiral conveyor of the kind generally disclosed in United Kingdom patent application No.1000748.2.

The apparatus may include one or more load cells which produce a signal indicative of the weight of the bed of feedstock, enabling a controller or human operator to determine the amount of reduction in weight of the bed of feedstock due to healing releasing water or other liquids from the feedstock. The output of the load cell(s) may be passed to a controller which varies the amount of applied microwave energy and/or the vibration amplitude/frequency to ensure an optimal self-fluidising bed is maintained and that the energy consumed in the drying process is optimised.

The receptacle may include one or more relief panels or blow-off valves which automatically release pressure from within the receptacle if it exceeds a predetermined safe level, A bromo-chloride safety pressure bottle may be provided to meet safety requirements in the event of a failure in the monitoring or control of the apparatus S when in use.

The receptacle may include one or more inlets through which heated air removed from the receptacle can be passed back into the receptacle, reusing the removed heat energy to make the process more efficient or drive up the temperatures in the receptacle.

The receptacle may be made of any suitable material, but in at least one embodiment at least one of the receptacle, a liner to the receptacle which supports the bed of feedstock, a part of the receptacle or liner, may be of stainless steel.

According to a second aspect the invention provides a heating system for feedstock comprising the apparatus of the first aspect, a bed of feedstock placed in the receptacle, agitator elements mixed into the bed and a microwave source coupled to the inlet of the receptacle whereby in use feedstock that is fed into the receptacle is heated by the microwave energy to cause inbound moisture to be released, the released moisture being further heated by contact with the heated agitator elements so form steam and the mixture of steam, elements and feedstock forming a fluidised bed due to vibration of the receptacle.

It is preferred that the vibration as well as helping fluidise the bed causes the feedstock to move along the receptacle to an outlet where it leaves the receptacle.

The microwave source may provide sufficient microwave energy to heat the agitator elements to a temperature which is at least 2 or 3 degrees above the temperature required for moisture to be released from any feedstock in the bed to be turned to steam when it contacts the elements. This will depend on the material used for the agitator elements and the amount of feedstock and agitator elements in the bed. The microwave source may emit electromagnetic radiation of approx 2Ghtz.

The system may include a vacuum pump connected to the receptacle, preferably through a self-cleaning filter as described in relation to the first aspect of the invention.

A wide range of feedstocks can be dried using the method of the present invention, including (but not limited to) any one or more of the following: oils, waters, slurries, oil/drilling cuttings, chemicals, organics, liquids or solids or any stock that requires fragmentation.

The system may include means for recirculating the extracted air from receptacle back into the receptacle, or otherwise extracting the heat from the extracted air and reusing this extracted heat energy to heat the interior of the receptacle. For example, a heat exchanger may be provided with the extracted air being passed over it and heating fresh air which is then fed into the receptacle.

Similarly, the system may include means for taking agitator elements removed from the receptacle along with treated feedstock, and adding them back in with fresh feedstock, thus reusing the heat energy stored in the elements.

The preferred frequency of the electromagnetic radiation that is used for heating within any particular embodiment of the embodiments of the invention described herein will depend upon a variety of factors, including the size of the process vessel and, the physical properties of the fccdstock, but may be any frequency within the RF/Microwavc region of the electromagnetic spectrum (3 kHz to 300 0Hz).

Typically, the electromagnetic radiation will have a frequency that lies within the ISM frequencies (as defined by the ITTJ Radiocommunication Sector) appropriate to the location of the processing unit. In preferred embodiments, frequencies of approximately 2.45±0.050Hz, or 915±13MHz would be used.

In a preferred embodiment, a continuous single frequency of microwave radiation would be employed for heating. Where it is advantageous in alternative embodiments, two or more frequencies of microwave/RF radiation may be used to heat the same volume of material simultaneously. Alternatively, two or more frequencies of microwave/RF radiation may be used to heat the material sequentially. Alternatively, the microwave power may be pulsed. As a further option, combinations of these irradiation regimes may also be used; in a hypothetical example, a feedstock may be simultaneously heated by 915MHz and 2.450Hz radiation, and then immediately processed using pulsed 5.8 0Hz radiation.

In other embodiments, the spatial or temporal absence of microwavc/RF radiation within sections of the processor may also be advantageous and would be regarded as a further embodiment of the microwave heating regime.

According to a third aspect the invention provides a method of drying or otherwise treating a feedstock by a combination of heating, vibrating and agitating the feedstock comprising: passing the feedstock into a receptacle to form a bed layer of feedstock, adding re-usable agitator elements in with the bed of feedstock, directing microwaves, or other RF radiation, onto the feedstock and agitator elements so as to heat the agitator elements above the temperature at which water in the S receptacle turns to steam whilst simultaneously vibrating the receptacle, the mode of vibration applied and the microwave energy causing the feedstock and agitator elements to form a fluidised bed in which the motion of the feedstock and agitator is such that micro-voids are formed and then collapsed within the bed between adjacent agitators to cause vapour released from the feedstock and heated by the agitator elements to form steam to be pushed out of the layer of feedstock by a micro-pumping action.

The self fluidised bed, containing microvoids of a few microns to a few millimetres in size, combined with the micropumping and mixing effect of the agitator elements helps to drive the released moisture and steam and other gas out of the bed, drying the feedstock. The formation of the self-fluidising bed is a stochastic process and depends at least in part on the frequency of vibration used, and it is preferred that the method comprises vibrating the receptacle in the range of lkh to 100khz, with a frequency around 20khz typically working very well for a range of feedstocks, especially granular solids.

The method may include applying a vacuum source to the receptacle to draw off the released vapour or gas from within the receptacle. This also lowers the temperature at which the released inbound moisture turns to steam, which reduces the amount of heating needed or speeds up the process for a given input of heat energy.

The method may include steps of conveying the feedstock through the receptacle so that it exits from an outlet after drying or other treatment, recovering the heated agitator elements and reintroducing them into the receptacle. In this way, the heat energy in the elements is retained, making the process more efficient. The feedstock may be conveyed by the vibrational mode of the receptacle.

The method may include providing shredded used printed paper or cardboard into the bed of feedstock. The applicant has found that this greatly helps draws out inbound moisture from feedstock as the paper is porous, and the carbon print will be preferentially heated by microwaves to further heat absorbed moisture turning it into steam to release it from the bed.

A wide range of feedstocks can be used, and the applicant has found the invention works very well with agitator elements that are generally homogenous in size and granular feedstocks that are also generally homogenous.

The method may comprise providing sufficient microwave energy and other heat to the inside of the receptacle to raise the temperature of the agitator elements in the bed to a level which is at least 2, and most preferably at least 5 degrees C above the level of steam released from the bed. This will depend on the nature of the agitator elements and the pressure in the vessel as well as other parameters such as the mass of agitator elements and feedstock provided.

The method may also include a step of adding additional water to the feedstock prior to, or during heating.

The method may comprise applying appropriate temperature, pressure and microwave (or other RF) energy together with suitable agitator elements that include metallic portions such as pins, or rivets that function as antennae to create an artificial plasma within the bed.

S

In a refinement, the method may include a step of introducing water to the receptacle to mix with the bed of feedstock and agitator elements. This water will be heated to create steam, and contact of this hot water and steam with the feedstock may be used to sterilise the feedstock. In addition to, or as an alternative to the steam, another Gas such as Chlorine dioxide could be introduced into the receptacle. As such the method may therefore provide the functionality of an autoclave. An advantage is that the self fluidised bed increases contact of the water with the feedstock, and the steam does not particularly absorb the microwave energy so a lot of the energy goes into heating the water that contacts the feedstock. The process can therefore be more efficient than a standard autoclave process.

The method applied in this way may be used, for instance, to sterilise organic municipal waste typically after removal of metals, ceramics and plastics. The sterilised material produced by the present method can be used to form fuel pellets, or could later be dried and burnt by incineration or perhaps passed through a bio-digester.

The method may comprise pressurising the receptacle to increase the temperature of the steam and water that sterilises the feedstock.

The method may also include a step of introducing an inerting mixture which may be a gas or a steam, into the cavity. This provides additional safety when heating feedstocks which might otherwise trigger an exothermic reaction.

According to a fourth aspect the invention provides a set of agitator elements for use in a vibrating bed of feedstock in which the elements are so shaped as to assist in the formation and collapse of voids within the bed to drive released moisture or vapour out of the bed, the elements being made at least partially of a material which, in use, preferentially absorbs microwave energy thereby heating up.

The elements are preferably non-spherical in shape with at least one concave portion on their outer surface. They may approximate a concave polygon in cross section, albeit preferably being devoid of any sharp radius corners. The concave portion may form a pocket of void or groove. The elements may have a length and a width and may be generally uniform in cross section along their length. They may be shaped like a figure of eight in cross section, or a peanut, or an oval. Providing elements which have a uniform cross section along their length makes them simple to produce, perhaps using an extrusion process. They may have a non-uniform cross section along their length.

In a most preferred arrangement, the agitator elements may comprise porous elements, perhaps of ceramic material. The ceramic may comprise one or more of the following: steatite, alumina, silica, magnesium sulphate, and mullite. By being porous, the elements can absorb moisture or vapour released from the feedstock, subsequently heating up the absorbed moisture as the elements heat up, causing the element to release the moisture, typically as steam from the element.

The elements may all generally be equal in size, weight, density, shape, microwave attenuation, porosity so as to assist in the creation of a homogenous, ebulating, self fluidising bed when forming part of the apparatus of the first aspect of the invention.

The agitator elements may comprise a surround part which has a relatively low dielectric loss which surrounds an core which has a relatively high dielectric loss. The core may be completely encased by the surround part. In use, the core will heat up by the microwave energy and radiate this outward through the surrounding material.

Depending on the dimensions of the core it may also/alternatively scatter the microwave energy back out through the surround. These actions cause strong heating at the surface of the elements which can be used to make them self cleaning, burning away any material that builds up on the surface.

The elements may be coated with a catalyst, or a catalyst may be dispersed throughout at least the surround part of the element. The catalyst may comprise one or more of: zeolites, metals such as nickel, platinum or palladium, and supported metal catalysts.

This is beneficial in breaking down chemicals in the released moisture or vapour.

Placing them on the outer surface of the elements ensures they are evenly spread throughout the bed of feedstock and move around to be exposed to the released moisture or vapour.

The core may comprise a perforated metal plate which may be sandwiched between two half surround portions of material, preferably ceramic. The two surround portions may be bonded to the core.

The insert of the elements may have a length equal to one quarter of the wavelength of the microwave energy used so that it absorbs the energy, or one half of a wavelength so that it reflects the energy and works as a mode stirrer within the bed.

The elements may include an antenna, such as a metal pin, that passes through the element from one side to the other. This pin will, under correct application of microwave energy, temperature and pressure within the receptacle generate plasma which can assist during the treatment process.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

There will now be described, by way of example only, one embodiment of the present invention with reference to and as illustrated in the accompanying drawings of which: Figure 1(a) is a side view of an embodiment of a key part of a heating apparatus according to the first aspect of the invention comprising a receptacle for feedstock that is to be treated; Figure 1(b) is a perspective view of the embodiment of Figure 1(a); Figure 2 is an exploded perspective view of a filter assembly incorporated in the apparatus of Figure 1; Figure 3 is a cutaway view of the apparatus of figure 1 along the section line A-A' in Figure 1; Figure 4 is an isometric view of a first embodiment of an agitator clement used in the apparatus of Figure 1, Figure 5 is a schematic of a complete system incorporating the apparatus of Figure 1 when in use to dry a bed of fccdstock, Figure 6(a) is a cross sectional view and 6(b) is a perspective view of an alternative form of agitator clement that can be used, and Figure 7 shows an alternative shape of receptacle base that can be used that includes a channel for applying heat to the lower region of the fccdstock bed.

DETAILED DESCRIPTION OF THE INVENTION.

Referring to Figures 1 and S of the accompanying drawings, an apparatus and system for treatment of fccdstock using heating is shown. The apparatus comprises a receptacle 101, in the form of a trough having stainless steel walls defining a curved base. The receptacle can be of a wide range of sizes, but for this example a large receptacle able to hold several hundred kilos of material at any time is shown. The side walls of the arc reinforced by two elongate box section reinforcement ribs 102, 103 welded in place on the outside of the receptacle. The top of the receptacle 101 is scaled by a plate 104 forming a cover. An inlet 105 is provided at one end through which fcedstock can be introduced to the receptacle pre-treatment through a shutc lOSa, and an outlet 106 is provided at the other end through which fccdstock exits post treatment.

The receptacle 101 is provided with a load bearing flange 107,108 on each side that sits on springs 109 that hold the receptacle suspended above a base (not shown) so that it is free to move, constrained only by the lateral compliance and vertical stiffness of the springs. A motor 110 is connected to the base of the receptacle 101 which S drives an unbalanced weight. Thus as the motor 110 rotates the weight will rotate causing the receptacle to vibrate. The speed of the motor, and the mass of the weight and its position relative to the receptacle determine the mode at which the receptacle will vibrate. A motor controller (not shown) allows an operator to alter the speed of the motor, altering the severity of the vibration. Other vibratory means could be used to cause the receptacle to vibrate, such as linear electromagnetic actuators.

The receptacle 101 also includes one or more openings through which microwave radiation can enter the receptacle to irradiate fecdstock inside the receptacle. The manner in which the radiation enters is not critical to the invention, but it is preferred that it enters through a set of elongate slots (not shown in Figure 1 but visible partially as slots 111 in Figures 3 and Figure 7) or windows located in the wall of the receptacle. These slots are located within the hollow box section reinforcement ribs 102,103 that extend along the length of the receptacle. The microwaves are fed into the reinforcement ribs which act as waveguides, or are lined with a waveguide. Any suitable source of microwaves can be used. As most microwave sources are sensitive devices which can be readily, a decoupler 300 is provided which mechanically isolates the receptacle from the microwave source. The decoupler guides waves into the reinforcement ribs 102,103.

As shown in the cutaway of Figure 2, the cover 104 includes a large rectangular aperture 120 which is covered by a raised lid 121. The lid 121 is provided with three exhaust ports 122 through which air and vapour can be drawn out of the receptacle 101. The lid 122 covers a self cleaning filter 123 which is fitted across the rectangular aperture. This can best be seen in exploded form in Figure 3. The filter 123 comprises two upper layers of filter cloth 124,125 that are both trapped along their peripheral edges between the lid 121 and the outer edge of the plate 104. The filter cloth has S small holes which prevent dust passing through to the exhausts 122. Below the aperture is a depending perimeter wall 126 which extends downwards from the edges of the aperture. The wall 126 is sealed at its base by a lower plate 128 that slots into the box section formed by the walls and sits on an inwardly turned lipped 129 of the wall. The plate 128 has a plurality of small slots 127 in it, and forms a lower filter layer. The slots are less than 1/4 of the wavelength of the microwave radiation in length so that the radiation cannot escape past the plate.

Between the lower plate 128 and the filter clothes 124,125 is a plurality of balls 130, made of stainless steel. In use, the balls 130 bounce around in the space between the lower plate and the filter cloth, and as they collide with the cloth they dislodge any dust or other material that is stuck to it, the dislodged material falling back through the holes in the lower plate into the receptacle.

A further key part of the invention are agitator elements 200. A typical element 200 is shown in Figure 4 of the drawings. It comprises an extruded element having a central core of perforated metal sheet 210 surround by two half shells 220,230 of porous ceramic material. In practice, a large length of extruded core and shells can be produced before it is cut up into small sections to form the agitator elements. The element 200 has a cross section which approximates a smoothed concave polygon, defining two opposing concave regions 205,215 or grooves that extend along opposing sides of the element. Optionally the shells arc coated with a catalyst.

Other shapes of agitator element could be used, and they can be formed in many different manners within the scope of the present invention. One alternative is shown in Figures 6(a) and (b). Here, an agitator element 300 includes an additional central pin 310 which passes through a central meshed metallic sheet 320 to connect both S sides of the element. This pin acts as a microwave antenna when in use and may be used to create artificial plasma within the bed when subjected to microwave radiation.

A nut 330 holds the pin in place.

Figure 5 is a schematic diagram showing how the system can be used to dry a feedstock. In use, the receptacle 101 is loaded with a mix of feedstock 400 from a hopper and agitator elements 200 or 300 to form a layer or bed of feedstock/elements on the base of the receptacle 101. The ratio of feedstock to agitator elements will vary depending on the type of feedstock to be processed.

Once the receptacle 101 is loaded with the bed of feedstock and agitator elements, the motor 110 is then switched on to cause the bed to vibrate, making the feedstock and agitator elements 200 move around vigorously. As the agitator elements 200 move, small voids, so-called microvoids ranging from microns to a few millimetres in size, form and collapse within the bed.

The microwave source 500 is then switched on, to cause the feedstock and agitator elements to heat up as microwave energy is fed into the receptacle through the decoupler 300. The feedstock will heat up as the inbound water or solvent in the feedstock absorbs the microwave energy, and as the temperature rises this inbound moisture will be released. The agitators 200 will also heat up to a temperature above that at which the released water or other solvent turns to steam/vapour by controlling the level of radiation applied. Any released water which is not already steam, on contact with the agitator elements 200 will be heated on contact with the agitator elements to form steam. The elements therefore assist in further heating the feedstock and the released moisture. Because the elements are porous, they will absorb any released water and then as they heat up the water will be released as steam.

As the temperature reaches a critical level, the vibration of the bed combined with the released vapour and gas in the bed will cause the bed to self-fluidise, meaning that the mix of solid feedstock and agitator elements and steam act as a fluid. In this state, the elements and feedstock can move around relatively freely within the bed, and frequent collisions will occur. Small voids that form and collapse as the elements move act as pumps to drive the vapour through and out of the bed. This is helped by a pumping action created due to the concave shape of the agitator elements.

A vacuum applied to the exhausts 122 from a vacuum pump 600 then starts to draw the hot air, vapour and gases out from within the receptacle. This hot exhaust mixture is filtered by the self cleaning filter to remove dust particles, and is then at least partially dried outside of the receptacle before being recirculated back into the receptacle using a fan 700 forcing the steam re-gen back in through openings 720 in the side of the receptacle. The recirculated air retains a proportion of the heat energy from the process and adds it back to the receptacle, helping to dry the feedstock bed.

Over time, the recirculated gas can reach quite high temperatures, perhaps forming super heated steam/hot gas mix. Additional water can be added to the receptacle through a top inlet 710 as shown in Figure 1 to help start the fluidising process.

The applicant has appreciated that the weight of the feedstock and agitator elements in the bed may affect the drying process. As the trough shape may be 600mm -1 meter or more in depth, and the bed may fill at lease half of the depth of the trough, it follows that the weight of the feedstock will influence the "pressing" of the feedstock, albeit that vibration is present. The feedstock will be more densely packed at the bottom of the trough than it is at the top. Therefore the area most affecting the migration of moisture/steam will be at the approximately first 1/3rd of the fill. To counter this, an additional heating device may be provided which is located within the relatively cool lower region of the bed, helping migration of released vapour up and out of the bed.

An example of a modified receptacle 800 which includes a raised, inverted, U-shaped channel 810 along the base of the receptacle is shown in Figure 7, through which hot steam is passed. The shape of the channel also affects how the bed moves around in the receptacle as it is vibrated.

Whilst the bed is heating and drying, the vibration of the receptacle caused by the motor also causes the bed of feedstock/elements to advance towards the outlet, where it exits, in the manner of a vibratory conveyor. As the mixture falls out of the exit the elements are separated from the drier feedstock by passing them across a separator mesh and are then returned to the inlet along with fresh feedstock. This ensures that the heat energy held in the agitator elements is added back to the receptacle, reducing the amount of energy needed to heat the feedstock.

The apparatus of the present invention, and its method of use, can be employed with a wide range of feedstocks. The embodiments of the invention are particularly suited to processes where conventional fluidised bed methods are unsuitable or less efficient processing options.

The following are three examples of feedstocks which can be treated.

Example 1: Drying Grains and Seeds Globally, there is a huge and ongoing requirement for the drying of grains, beans and seeds, such as rice, for the purposes of storage, preservation and preparation for other processes. The moisture levels required vary according to the seed type, but are typically less than 10% moisture content. In many cases, there are practical limitations on the rate at which drying may be effected using conventional methods.

In the case of seeds, for example, drying air temperatures in excess of 43°C overheats the grain and kills the germ, preventing subsequent germination. Acceleration of conventional seed drying processes tbrough the use of elevated temperatures is therefore precluded. Even where later germination is not required, for example when drying grains in preparation for grinding, the simple use of elevated temperatures may lead to rapid drying of the grain with concomitant surface modification that lowers moisture transport from the core. In such cases, the use of tempering may be useful, but requires extended processing times.

The apparatus within the scope of the present invention may be advantageously used with these feedstocks. Volumetric heating is a defining characteristic of microwave processing and in these applications proves advantageous at both a macroscopic and microscopic level. A specific benefit is that improved drying methods reduce the time during which conditions exist that are conducive to fungal growth. This, in turn, is beneficial in reducing the levels of mycotoxins that could be produced in these stored foodstuffs. Where feedstock requirements permit higher electromagnetic power levels and elevated temperatures, bacterial sterilisation may also be effected.

Macroscopic volumetric heating ensures that the heating is essentially uniform throughout the entire volume of the sample, which is clearly advantageous in ensuring that the energy is dissipated effectively uniformly throughout the grains and seeds that require treatment. This macroscopic heating uniformity is assisted by the continuous motion and mixing of the vibrating containment vessel, resulting in grains that have experienced effectively uniform process conditions.

S It is an important consequence of the use of microwave and RF energy is that it ensures heating uniformity at the sub millimetre scale within individual grains. This ensures that the moisture is uniformly heated and flows more efficiently through to the surface of the individual grains, without the need for conventional tempering processes. In combination with airflow through the voids created around individual grains by the mechanical vibration of the containment, highly efficient drying conditions are created.

In practical embodiments, "pilot"-scale processors may be employed as in-situ drying systems even on remote agricultural locations, where they may be powered through the use of renewable energy systems (wind or water turbines, for example). Such arrangements would represent a carbon-neutral processing system that is advantageous in the rapid preparation of dried products with reduced risk of mycotoxin formation.

Furthermore, these systems may also be used for other applications (e.g. vegetable oil production) when not required for drying grains.

Example 2. Drilling residues. From Recovery of Oil/Gas Drilling operations Including Shale oil/Shale Gas and other commercial drilling residues.

Drilling residues are an inevitable by-product that results from both onshore and offshore oil, gas extraction. The residues contain potentially toxic chemicals that prevent direct disposal and they therefore require processing to remove these toxins or render them biochemically inert. Ideally, the materials should be removed in a form that has the economic potential.

A significant problem with the processing of drilling residues is the viscosity and related physical properties of the feedstock. Conventional methods of mass transfer such as pipes or Archimedean screws are either unsuitable, have high energy costs or experience large stresses in forcing the movement of these fluids. The present invention uses a vibratory self-fiuidising processor that uses vibrations to move and fluidise the feedstock. In contrast to conventional mass transfer methods, which may compact the feedstock, self-fluidising processors create voids and induce significant motion in the feedstock; a process that assists the release of materials into, and subsequent isolation from, the space above the feedstock. Motion of the feedstock within the vibrating applicator may be facilitated through the addition of microwave suscepting units; these may also be recovered as hot objects that may be returned to the cool feedstock as it enters the processor, to improve its initial heating rate.

As the drill cuttings contain water and polar organic molecules, in addition to solid microwave susceptors, they are suitable for heating with microwaves or radio frequency radiation. As with other dielectric heating processes, this results in volumetric heating of the feedstock. A specific advantage of this direct heating process is that water is preferentially heated and vapourised. In doing so, the water facilitates the movement of oils from interstitial spaces and may assist in steam-assisted distillation of organic compounds. In cases where a feedstock possesses moisture levels that are exceptionally low, it may be advantageous to add moisture to the feedstock as either a vaporised I atomised water or steam in order to initiate or enhance this process.

The direct nature of microwave heating means that energy is imparted either directly into the water or polar molecules; or, in the worst case, directly into lossy mineral components of the cuttings; in the latter case, this may also assist in the mechanical breakdown of the rocks. This results in a significant reduction in the amount of energy required to heat both the surroundings and the containment vessel, thereby increasing energy efficiency and lowering carbon emissions relative to those of a conventional process.

The efficiency of residue extraction through the combination of microwave heating and vibratory self-fiuidisation means that processing temperatures may also be significantly reduced relative to conventional processes. The formation of micro-voids in the self-fluidised feedstock, which provide a space into which vapours may pass, is a significant contributory factor in this. Steam/oil vapours resulting from process may be removed under reduced pressure, with the oils being recovered from the vapour stream. Heat from these gases may be returned via a heat exchanger into the feedstock.

In a practical embodiment, a processor may be capable of any throughput, depending upon its size and the available microwave power, but 3-10 tonnes per hour would be typical. Such a processor would be capable of attaining its normal operating conditions within 15 minutes of starting from cold. By the nature of both the mechanical vibration and microwave heating, both the motion of the fluid and its temperature can be controlled virtually instantaneously, permitting tight control of the process conditions and rapid response to variation in the properties of the feedstock.

In the event of an emergency shutdown, dynamic cooling to ambient temperature may be effected within 15 minutes.

Example 3. Biochar.

Biochar is carbon (charcoal) created by the pyrolysis of biomass. As the carbon is stable and ultimately originates from atmospheric C02, it is produced for the specific S purpose of biosequestration of carbon from the atmosphere.

The nature of products produced from biomass pyrolysis varies with the process temperature and heating rate, with lower temperatures favouring the formation of greater proportions of biochar. Microwave processing is already in use for the industrial scale production of biochar using batch processing or conventional continuous process methods. The combined use of self-fluidising vibration processor and microwaves permits an efficient and directed energy source for the process along with an efficient method for movement of the feedstock, in a manner that facilitates the removal of other byproducts. As the other byproducts are bio-oils and syngas, they may be used to generate power for both a microwave source and the vibrating motor. Existing systems powered by this means generate by-products that may be used to produce up to 9 times the energy required by the process itself Various modifications are possible within the scope of the invention. It is possible to use other forms of heating rather than microwaves, such as RF radiation, as required.

Ultrasound radiation may be introduced to the receptacle to help break up large portions of feedstock, reducing drying times. The agitator elements could be omitted in some embodiments, dependent upon the properties of the feedstoek that is being treated.

Also, in some arrangements under appropriate conditions of temperature, pressure, flopoid density and other parameters, the use of metallic or metal-containing agitator elements will result in the formation of electrical discharges and transient plasma formation within the bulk of the fcedstock. Such high energy conditions, when brought about in close contact with chemical compounds will result in chemical degradation of those compounds. This is particularly important, in the current context, when toxic intractable organic compounds are present in the process materials, and it is therefore proposed that the use of metallic or metal-containing flopoids may be used to facilitate the remediation of contaminated materials. The advantage of this approach when compared to plasma formation in large spacial volumes is that the energy is imparted in the direct presence of the contaminants and is not wasted through absorption into the bulk plasma and re-emission as UV, JR and visible light.

A specific example is the use of metal-containing agitator elements in this manner for the remediation of soils from brown-field sites that are contaminated with polychlorinated biphenyls (PCB5), polycyclic hydrocarbons (PAH5) and similar highly toxic but chemically relatively inert materials. With sufficient treatment under the conditions described above, the PCBs and PAHs will be broken down by localized microscopic plasma discharges into materials that display relatively benign biochemical properties, resulting in a non-hazardous product that is available for immediate use.

Claims (46)

1. CLAIMS1. Apparatus suitable for the heat treatment of a bulk feedstock comprising: a receptacle suitable for receiving a bed of feedstock, an inlet through which microwaves may pass to enter the receptacle when the inlet is exposed to a source of microwave (or other RF) energy, the microwaves causing the feedstock bed to heat up due to volumetric heating effects to release inbound moisture as vapour or gas from the feedstock to regions within the bed, a stock of reusable agitator elements which in use are placed in the receptacle mixed within the bed of feedstock, the elements preferentially absorbing at least some of the microwave energy thereby heating up to cause additional heating of the moisture or vapour or gas released from the feedstock, and a vibratory means which is operable to cause the receptacle to vibrate at a frequency and amplitude so as to agitate the feedstock and agitator elements and the released liquid or vapour in the receptacle so as to produce a fluidised bed of feedstock, and in which the agitator elements are shaped so as to assist in the formation and collapse of microvoids within the bed to drive released moisture or vapour out of the bed.
2. 2. Apparatus according to claim 1 in which the agitator elements have the same density, or substantially the same, as the solids feedstock that forms the bed, so that they are suspended throughout the self-fluidised bed rather than sinking to the bottom or floating on the top.
3. 3. Apparatus according to claim 1 or 2 in which he elements are non-spherical in shape with at least one concave portion, forming a groove, trough or dimple, pocket or void.
4. 4. Apparatus according to 3 in which the shapes of the elements is geoidal.
5. 5. Apparatus according to any preceding claim in which the elements have a length and a width and are generally uniform in cross section along their length and comprise a concave polygon when viewed in cross section.
6. 6. Apparatus according to any preceding claim in which in use the receptacle contains up to 10 percent, or up to 20 percent agitators relative to feedstock by volume.
7. 7. Apparatus according to any preceding claim in which the agitator elements are at least partially porous.
8. 8. Apparatus according to any preceding claim in which they elements are of any one or more pure elements, alloys or compounds, perhaps of ceramic material or metals and their alloys, metal carbides or nitrides or polymers.
9. 9. Apparatus according to any preceding claim in which the agitator elements comprise a surround part which has a relatively low dielectric loss which surrounds a core which has a relatively high dielectric loss.
10. 10. Apparatus according to claim 9 in which the elements are coated with a catalyst, or a catalyst may be dispersed throughout at least the surround part of the element.
11. 11. Apparatus according to claim 9 or claim 10 in which the core comprises a perforated metal sheet sandwiched between two half surround portions of material, the perforations having a diameter that is less than one quarter of a wavelength of the microwave radiation.
12. 12. Apparatus according to any preceding claim in which the elements include a conductive antenna, typically a metal pin or rivet, that passes through the element from one side to the other so that in use the apparatus generates plasma within the bed.
13. 13. Apparatus according to any preceding claim in which the vibrator means, as the source of vibration, is electro-mechanical and includes at least one unbalanced motor fixed to the receptacle or a support platform for the receptacle, the receptacle or support platform in turn being supported by one or more springs such that it can move around as the motor rotates, causing the feedstock in the bed to move side to side or back and forth or with a circular motion or any combination relative to the support platform.
14. 14. Apparatus according to any preceding claim in which in use the vibration is arranged to cause feedstock in the bed to advance from one end of receptacle where feedstock is fed in to another end at which it can leave the receptacle.
15. 15. Apparatus according to any preceding claim in which the base of the receptacle includes one or more flow conditioning ridges, which act to control the motion of the bed preventing the bed of feedstock from moving in a bulk helical motion.
16. 16. Apparatus according to claim 15 in which the flow conditioning ridge comprises an inverted U or V shaped ridge that extends along at least part of the base of the receptacle.
17. 17. Apparatus according to claim 15 or claim 16 in which the ridge forms a channel through which heated gas or fluid may be passed to help heat the lower part of the bed of feedstock.
18. 18. Apparatus according to any preceding claim in which the receptacle includes an outlet suitable for connecting to a means of generating pressure below atmospheric pressure, such as a vacuum pump, where "atmospheric" refers to the pressure outside of the receptacle.
19. 19. Apparatus according to claim 18 in which the apparatus includes a filter which traps particles of dust that pass through the outlet, or would otherwise pass through the outlet and which are above a predetermined size.
20. 20. Apparatus according to claim 19 in which the filler comprises a self cleaning filter, comprising two layers of filter material separated by a gap which contains a plurality of individual cleaning elements sized so that the they are free to move around between the layers, air and vapour and other gas drawn off from the receptacle entering one filter, passing across the gap and leaving through the other layer, the cleaning elements moving as the receptacle vibrates to strike the filter layers thereby causing dust built up on the filler layers to fall away.
21. 21. Apparatus according to claim 20 in which the layer through which the air is drawn off first has larger filter holes than the other layer, so dust knocked off by the balls can fall back through the openings into the receptacle or a catch tray and the other layer has holes that are too small for the dust to pass through, the holes in both layers being smaller than the cleaning elements so that they are entrained between the layers.
22. 22. Apparatus according to claim 20 or claim 21 in which the lower layer of the filter is stainless steel and optionally may be heated to assist in drying any dust that may under normal operating conditions contain a lot of moisture.
23. 23. Apparatus according to any preceding claim in which the receptacle includes one or more inlets by which microwave energy can enter the receptacle from the side, or sides, and/or the base which are below the level of the top of the bed of feedstock.
24. 24. Apparatus according to claim 23 in which the inlet for microwaves comprises a set of slots along the sides and/or base which are located within one or more hollow reinforcing beams that extend along or around the receptacle and provide rigidity to the receptacle.
25. 25. Appparatus according to any preceding claim in which the receptacle includes one or more inlets through which heated air removed from the receptacle can be passed back into the receptacle, reusing the removed heat energy to make the process more efficient or drive up the temperatures in the receptacle.
26. 26. A heating system for feedstock comprising the apparatus of any preceding claim, a bed of feedstock placed in the receptacle, agitator elements mixed into the bed and a microwave source coupled to the inlet of the receptacle whereby in use feedstock that is fed into the receptacle is heated by the microwave energy to cause inbound moisture to be released, the released moisture being further heated by contact with the heated agitator elements so form steam and the mixture of steam, elements and feedstock forming a fluidised bed due to vibration of the receptacle.
27. 27. A heating system according to claim 26 in which the vibration as well as helping fluidise the bed causes the feedstock to move along the receptacle to an outlet where it leaves the receptacle.
28. 28. A heating system according to claim 26 or claim 27 in which the microwave source provides sufficient microwave energy to heat the agitator elements to a temperature which is at least 2 or 3 degrees above the temperature required for moisture to released from any feedstock in the bed to be turned to steam when it contacts the elements.
29. 29. A heating system according to any one of claims 26 to 28 which includes a vacuum pump connected to the receptacle through a self-cleaning filter.
30. 30. A heating system according to any one of claims 26 to 29 which includes means for recirculating the extracted air from receptacle back into the receptacle, or otherwise extracting the heat from the extracted air and reusing this extracted heat energy to heat the interior of the receptacle.
31. 31. A heating system according to any one of claims 26 to 30 which further comprises means for taking agitator elements removed from the receptacle along with treated feedstock, and adding them back in with fresh feestock, thus reusing the heat energy stored in the elements.
32. 32. A method of drying or otherwise treating a feedstock by a combination of heating, vibrating and agitating the feedstock comprising: passing the feedstock into a receptacle to form a bed layer of feedstock, adding re-usable agitator elements in with the bed of feedstock, directing microwaves (or other RF energy) onto the feedstock and agitator elements so as to heat the agitator elements above the temperature at which water in the receptacle turns to steam whilst simultaneously vibrating the receptacle, the mode of vibration applied and the microwave or other RF energy causing the feedstock and agitator elements to form a fluidised bed in which the motion of the feedstock and agitator is such that micro-voids are formed and then collapsed within the bed between adjacent agitators to cause vapour released from the feedstock and heated by the agitator elements to form steam to be pushed out of the layer of feedstock by a micro-pumping action.
33. 33. A method of claim 32 which further comprises a step of applying a vacuum source to the receptacle to draw off the released vapour or gas from within the receptacle.
34. 34. A method according to claim 32 or 33 which includes steps of conveying the feedstock through the receptacle so that it exits from an outlet after drying or other treatment, recovering the heated agitator elements and reintroducing them into the receptacle.
35. 35. A method according to any one of claims 32 to 34 which further includes a step of providing shredded used printed paper or cardboard into the bed of feedstock.
36. 36. A method according to any one of claims 32 to 35 which further includes a step of adding additional water to the feedstock prior to, or during heating.
37. 37. A set of agitator elements for use in a vibrating bed of feedstock in which the elements are so shaped as to assist in the formation and collapse of voids within the bed to drive released moisture or vapour out of the bed, the elements being made at least partially of a material which, in use, preferentially absorbs microwave energy thereby heating up.
38. 38. A set of agitator elements according to claim 37 in which the elements are non-spherical in shape with at least one concave portion on their outer surface and approximate a concave polygon in cross section, the concave portion forming a pocket of void or groove.
39. 39. A set of agitator elements according to claim 37 or claim 38 in which the elements have a length and a width and are generally uniform in cross section along their length.
40. 40. A set of agitator elements according to any one of claims 37 to 39 in which the agitator elements are porous.
41. 41. A set of agitator elements according to any one of claims 37 to 40 in which the agitator elements are of ceramic material.
42. 42. A set of agitator elements according to any one of claims 37 to 41 in which the agitator elements comprise a surround part which has a relatively low dielectric loss which surrounds a core that has a relatively high dielectric loss.
43. 43. A set of agitator elements according to any one of claims 37 to 42 in which the elements are coated with a catalyst, or a catalyst may be dispersed throughout at least the surround part of the element.
44. 44. A set of agitator elements according to claim 42 in which the core comprises a perforated metal plate sandwiched between two half surround portions of material, preferably ceramic.
45. 45. A set of agitator elements according to claim 44 in which the insert of the elements has a length equal to one quarter of the wavelength of the microwave energy used so that it absorbs the energy, or one half of a wavelength so that it reflects the energy and works as a mode stirrer within the bed.
46. 46. A set of agitator elements according to any one of claims 37 to 45 in which the elements include an antenna, such as a metal pin, that passes through the element from one side to the other.