GB2485642A

GB2485642A - Microwave heating apparatus

Info

Publication number: GB2485642A
Application number: GB1117802.7A
Authority: GB
Inventors: William Robertson Cunningham Erskine; Andrew Terah Gough
Original assignee: EMS Waves Ltd
Current assignee: EMS Waves Ltd
Priority date: 2010-10-21
Filing date: 2011-10-14
Publication date: 2012-05-23
Also published as: WO2012052743A1; GB201017787D0; GB201117802D0

Abstract

A microwave heating apparatus 100 comprises a thin walled receptacle within which a bulk material to be heated can be received and one or more elongate structural reinforcing members 170, 180, 190 secured to, or forming an integral part of, the receptacle which provide rigidity to the receptacle. At least one of the elongate reinforcing members 170, 180, 190 defines a channel through which microwave energy can pass along the member. The reinforcing member includes one or more openings which permit the energy guided along member to exit the member and enter the receptacle thereby to heat any material in the receptacle. The openings may be covered with ceramic windows 200,210,220 and liners500,510,520 defining the waveguides may be located within the members

Description

MICROWAVE HEATING APPARATUS

This invention relates to improvements in microwave heating apparatus suitable for heating bulk material, including solids, emulsions, suspensions, slurries and liquids. It is especially suited to heating of waste products.

It is known to provide for the uniform heating of bulk solids by placing the solid in a receptacle and directing microwave energy into the receptacle from one or more magnetrons located above the receptacle. To ensure uniform heating, the receptacle may be rotated relative to the source of radiation, or it may be vibrated to mix up the material.

Alternatively stirrers may be provided to mix up the material in the receptacle.

Heating material using microwaves can be used to trigger chemical changes in the product, and generally the apparatus of the present invention will have application in a far ranging number of industries.

Heating can be used to remove hydrocarbons from contaminated soil, or to break down rocks prior to grinding to extract minerals, or perhaps to pyrolise industrial waste which would otherwise have to be sent to landfill.

The applicant has appreciated that this method of heating is relatively inefficient and has sought alternative ways of heating bulk material.

According to a first aspect the invention provides a microwave heating apparatus comprising: a thin walled receptacle within which a bulk material to be heated can be received; and one or more elongate structural reinforcing members secured to, or forming an integral part of, the receptacle which provide rigidity to the receptacle, in which at least one of the elongate reinforcing members defines a hollow channel through which microwave energy can pass along the member, and further in that the reinforcing member includes one or more openings which permit the energy guided along the member to exit the member and enter the receptacle thereby to heat any material in the receptacle.

Large receptacles for bulk materials are typically made from thin walled sheets of material which are inherently insufficiently rigid unless reinforced with members. The present invention utilises these members as a carrier for distributing microwaves to appropriate openings in the wall of the receptacle. This allows microwaves to be introduced at a number of spaced locations, and eliminates the need for multiple magnetrons or additional waveguides to carry the microwaves to the receptacle by putting structural members to a double use.

The receptacle may be an open topped trough with a base wall and two opposing side walls. The members may be formed on one ore more of the sides walls and optionally also along the base.

Alternatively, the receptacle may be one of a range of different shapes. It may have a closed top, and may be sealed apart from an inlet and an outlet through which the bulk material to be heated or which has been heated can pass.

The receptacle may have a long axis, being longer than it is wide, and the members may extend generally along the long axis. They may extend from one end of the receptacle to the other end, or only part way along.

The walls of the receptacle may be metal, and the members may also be metal or may be of a different material to the walls.

The members may be integrally formed with the walls, perhaps by pressing or folding the walls into a ribbed shape, or secured to the wall (or walls) by suitable fastening means such as welds, nuts, rivets or bolts.

They may be secured to members which form part of the walls.

Most preferably the members are located wholly outside of the receptacle, where they are less likely to be damaged and do not form an obstruction to any material in the receptacle.

In an alternative one wall of the member may form a member which forms a part of the inner wall of the receptacle. The members may include one or more wings which extend outward from the one wall onto which panels can be attached to form other parts of the wall of the receptacle.

Three members may be provided, with one located at the base of the receptacle and one located on each side.

The at least one member that carries microwaves may be provided with more than one opening into the receptacle. The openings may be located at spaced locations along the length of the receptacle. There may be at least 5, or 10 or more than 20 in each member. The openings may be covered with a ceramic window, perhaps one window covering each opening or one window covering multiple slots through which microwaves can pass but the bulk product to be heated cannot pass.

The or each member that carries microwave may be a waveguide at the frequency of the microwaves that pass along them. The member may have a square or rectangular cross section, and may be designed to work in the H0,1 mode. It may have an aspect ratio (height to width) or 2:1 or greater with the width not less than half of the operating wavelength in free space of the microwave source. It may have electrically conductive walls and may generally be hollow.

All of the members, where provided, may have microwaves passing along them.

A liner may be provided within the or each member which guides the microwaves, and the liner may define a waveguide. The liner may include one or more openings and the openings in the member should then align with openings in the liner.

The liner may be removable. This allows it to be easily cleaned as required. Placing the liner in the member means that it is protected from damage and does not need to be as rigid as it would otherwise need to be.

The apparatus may include a microwave source, and means for connecting the source to the or each member which is to carry microwaves, or to the or each liner within the member. Each member may be connected to a separate source, or one source may feed microwaves to more than one member.

The connecting means may connect the source to an end of the member, or may connect to a point between the ends, preferably midway along the member. For instance, a magic tee connector may be provided along the length of the member which connects a waveguide to the member.

The receptacle may be supported by a vibrating mechanism that vibrates the receptacle.

The receptacle may be provided with mixing means which mix the material within the receptacle. For instance one or more mode stirrers may be located inside the receptacle that affect the distribution of microwaves within the receptacle.

The stirrers should be of a hard wearing material, depending on the bulk material to be heated. Most preferably they comprise ceramic coated metal parts. It has been found experimentally that electromagnetically induced chemical changes occur in some materials at elevated temperatures when this material is exposed to the microwaves which assist in the fluidising process without the need for the introduction of additional air to the receptacle to enable the process.

The receptacle may comprise a closed volume in which case provided that the level of microwave energy is sufficiently high, the apparatus may act as a self fluidising bed, turning solid material in the receptacle into a highly pulverised mix of fine particles and vapour released from the material due to the heating which will flow in a manner similar to a fluid.

This effect is enhanced with the use of stirrers in the receptacle. The closed receptacle may in itself form a closed waveguide.

The provision of liners, in particular, within reinforcing members is particularly well suited to retrofitting or conversion of prior heating receptacles.

Accordingly, in a further aspect the invention provides a method of converting a receptacle having reinforcing hollow members to an apparatus according to the first aspect of the invention by the steps of forming openings in the members, and inserting a liner which acts as a waveguide at microwave frequencies into at least one of the members, the liner having openings which communicate with the openings in the member.

It is unlikely that the members of existing receptacles will be suited to use as waveguides, perhaps being of the wrong dimensions or having a rough interior which would cause localised heating. The use of a liner overcomes this limitation and makes conversion simple.

The method may include steps of providing windows across the openings, and connecting a source of microwave radiation to the liners.

There will now be described, by way of example only, two embodiments of the present invention with reference to and as illustrated in the accompanying drawings of which: Figure 1 is a cross section through a first embodiment of a microwave heating apparatus according to the present invention; Figure 2 is a view from above of the apparatus of figure 1; Figure 3 is a perspective view of the apparatus of Figure 1; Figure 4 is a plan view of a coupler which can be used to connect microwaves to the members of the apparatus of figure 1; Figure 5 is a cross sectional view of a modification to the apparatus of Figure 1 which also falls within the scope of the present invention; and Figure 6 is a cross sectional view of a second embodiment of a microwave heating apparatus according to the present invention.

A microwave heating apparatus 100 for bulk material comprises an elongate trough, perhaps a metre or more across its width, with a length of at lest 3 or more metres. The trough has a generally U-shaped cross section with an upwardly curved base 110,120 and two opposing side walls 130,140 that extend vertically upwards from the a respective top edge of the curved base. An upper surface of the base 110,120 and side face of the walls 130,140 defines a smooth inner face 150 of the trough which will support the bulk material 160 to be heated. An optional lid (shown in dashed lines) may extend between the top edges of each side wall to form a closed container, and may be provided in conjunction with end walls (not shown). Where a lid is provided one or more openings may be provided in the lid or end walls The base 110,120 and side walls 130,140 are interconnected by three structural reinforcing members 170,180,190. Each member 170,180,190 comprises an elongate hollow metal tube with a square cross section along its length. An outer face 171,181,191 of one side of the member defines a further part of the inner surface 150 of the trough, and two wings 172,173, 182,183, 192,193 extend outwards from that face, set back by the thickness of the material used to form the base and two side walls.

One member 190 is located in the centre of the base 110,120 of the trough, and the long axis of the member extends along the long axis of the trough. A curved sheet of material 110 is fixed to one of the wings 192 and extends away for the member 190 to form one half 110 of the base of the trough. A similar curved sheet of material 120, typically steel, is fixed to the other wing 193 and extends away from the member 190 in the opposite direction to form the other half 120 of the base. The sheets 110,120 are fixed to the wings by rivets.

Two additional members 170,180 are provided with one at the top edge of each of the halves 110,120 of the base, and provides a join to a respective one of the side walls 130,140 of the trough in the same manner as the member 190 in the base connects together the two base half portions 110,120. Each side wall 130,140 also comprises a sheet of material, typically steel. Of course, additional members and sheets could be provided as required, depending on the size and shape of receptacle that is required, and the strength needed.

The base and walls therefore comprise a number of pressed metal sheets of a relatively thin gauge; strong enough to resist damage from shovels, pressure washers or hammers used to remove any bulk material stuck to the inside face of the trough, but not so thick as to make the trough unacceptably heavy. The members 170,180,190 that connect the sheets provide the rigidity needed for the trough to support the bulk material without deforming excessively.

Each member 170,180, 190 is provided with a plurality of openings, each comprising an elongate slot 175,185,195. The slots are provided in the outer face of the member 170,180,190 that forms a part of the inner surface 150 of the trough, effectively providing a connection between the inside of the hollow member and the inside of the trough. As shown the slots are provided in two parallel rows, with slots spaced equidistantly along the member. Each slot 175,185,195 is sealed with a window of ceramic material 200,210,220 which prevents the bulk material passing through the slot but which will, as will become apparent, allow microwaves to pass through the window.

As shown in Figure 4, a microwave source is connected to one of the members 170 so that microwaves produced by the source will enter the hollow inside of the member. A similar connection can be made to each of the other two members. In some embodiments only certain ones of the members, less than the total number of members, may carry microwave energy. The members 170, 180 and 190 are dimensioned (height/width) so that they act as a waveguide for the wavelengths of the microwave radiation, allowing the waves to pass along the inside of the members.

Where the waves come to a slot 175,185,195 they may pass through the slot and its corresponding window 200,210,220 into the trough. The waves entering the trough will then heat any bulk material 160 in the trough. In this embodiment the microwave source 400 is connected to the inside of the member by a waveguide 300 that is coupled to a magic tee coupler 310 which is coupled to a midpoint of the member. Microwave power P entering the member then splits up into two halves, 1/2P that pass along the member in opposing directions away from the magic tee coupler. In an alternative the source could be coupled to the end of the members.

Figure 5 shows a modification to the arrangement of Figure 1 in which each member 170,180,190 is provided with a liner 500,510,520. For clarity the liners are shown partially removed from the members. The liners 500, 510,520 each comprise elongate hollow tubes that have an outer profile that is complimentary to, but slightly smaller in width and height dimensions, than the profile of the inside of the member into which it is inserted. The liner 500,510,520 may be connected to a source of microwave radiation, so that the waves travel along the liner inside the member. The liner is protected from damage by the member. Each liner 500,510,520 is provided with slots 505,515,525 that align with corresponding slots 175,185,195 in the members, enabling the waves passing along the liner to enter the trough. As with the first embodiment the slots in the members are covered with a ceramic material to allow the microwaves to pass through but prevent bulk material from entering the member or liner from the trough.

The use of the liners 200,210,200 provides the additional benefit of allowing easy cleaning. It is has been observed by the applicant that any dirt inside the members may create localised heating which could cause damage, and so the inside of the members has to be kept clean. The use of liners which can be removed for cleaning, or perhaps replaced with new liners from time to time, may make cleaning simpler.

A second embodiment of a microwave heating device within the scope of the present invention is shown in Figure 6 of the accompanying drawings.

It is the same as the first embodiment apart from the position, shape and size of the slots 560 provided in the members. In this embodiment the slots are made larger than the slots in the liners 200,210,220 to make it easier to align the slots in the liner within the windows that cover the slots in the members.

Claims

CLAIMS1. A microwave heating apparatus comprising: a thin walled receptacle within which a bulk material to be heated can be received; and one or more elongate structural reinforcing members secured to, or forming an integral part of, the receptacle which provide rigidity to the receptacle, in which at least one of the elongate reinforcing members defines a channel through which microwave energy can pass along the member, and further in that the reinforcing member includes one or more openings which permit the energy guided along member to exit the member and enter the receptacle thereby to heat any material in the receptacle.
2. A microwave heating apparatus according to claim 1 in which a liner is provided within the or each member which guides the microwaves, the liner defining a waveguide for the microwave energy, the liner including one or more openings that are aligned with the one or more openings in the at least one member.
3. A microwave heating apparatus according to claim 1 or claim 2 in which the receptacle is an open topped trough with a base wall and two opposing side walls and the members are located on one ore more of the sides walls and optionally along the base.
4. A microwave heating apparatus according to any preceding claim in which the members are located wholly outside of the receptacle.
5. A microwave heating apparatus according to any preceding claim in which the at least one member that carries microwaves is provided with more than one opening into the receptacle, the openings being located at spaced locations along the length of the receptacle.
6. A microwave heating apparatus according to any preceding claim in which the openings are covered with a ceramic window through which microwaves can pass but the bulk product to be heated cannot pass.
7. A microwave heating apparatus according to any preceding claim in which the or each member that carries microwave is a waveguide at the frequency of the microwaves that pass along them.
8. A microwave heating apparatus according to any preceding claim in which a liner is provided within the or each member which guides the microwaves along the member from a source to the openings, the liner defining a waveguide.
9. A microwave heating apparatus according to claim 8 in which the liner includes one or more openings and the openings in the member align with openings in the liner.
10. A microwave heating apparatus according to claim 8 or claim 9 in which the liner is removable from the member.
11. A microwave heating apparatus according to any preceding claim which includes a microwave source, and means for connecting the source to the or each member which is to carry microwaves, or to the or each liner within the member where provided.
12. A method of converting a receptacle having reinforcing hollow members to an apparatus according to any one of claims 1 to 11 by the steps of forming openings in the members, and inserting a liner which acts as a waveguide at microwave frequencies into at least one of the members, the liner having openings which communicate with the openings in the member.
13. A microwave heating apparatus substantially as described herein with reference to and as illustrated in the accompanying drawings.