WO2013038184A1

WO2013038184A1 - Microwave processing of feedstock

Info

Publication number: WO2013038184A1
Application number: PCT/GB2012/052260
Authority: WO
Inventors: Martin PARMENTER
Original assignee: E2V Technologies (Uk) Limited
Priority date: 2011-09-14
Filing date: 2012-09-12
Publication date: 2013-03-21
Also published as: GB2494664A; GB201115914D0

Abstract

A method and apparatus (10) for processing feedstock such as vermiculite (34)or oil- contaminated drill cuttings using microwaves is described. The method involves removing ferrous material form the feedstock by magnetic separation (46) before exposing the feedstock to microwaves. This reduces arcing in the microwave cavity.

Description

Microwave processing of feedstock

Technical field

The present invention relates to techniques for processing feedstock with microwaves, such as the microwave exfoliation of vermiculite and the microwave treatment of oil- contaminated drill cuttings. Background

It is known to use microwaves to expand, or 'exfoliate', minerals such as vermiculite, which contain water trapped within their structure. Vermiculite has water molecules trapped between silicate layers. The microwaves selectively heat the 'interlayered' water, turning it to steam. The steam forces the silicate layers apart, which results in a net expansion in volume of the vermiculite. The vermiculite is then suitable for a number of uses, including as a water absorbent for horticultural applications, as a friction product in brake pads, as a thermal insulator, and as a building material. A continuous process for exfoliating vermiculite is described in PCT patent application WO2010/070357A2, the content of which is incorporated herein by reference. In this process, a conveyor belt is used to transport raw vermiculite through a microwave treatment region. A continuous supply of raw, unprocessed vermiculite is dispensed onto the conveyor belt on one side of the treatment region. The conveyor belt carries the vermiculite through the microwave treatment region, where the vermiculite is expanded by exposure to microwave radiation. The expanded vermiculite is then collected at a discharge station on the other side of the treatment region.

WO2010/070357A2 also describes a process for separating oil from oil-contaminated drill cuttings (OCDC), which may be used in the oil exploration industry. This process involves conveying untreated drill cuttings (which comprise a mixture of water, oil and rock) through a microwave treatment region. The microwaves preferentially heat the water in the drill cuttings, which causes thermal desorption of the oil component of the drill cuttings, leaving substantially oil-free solid treated drill cuttings. Extensive trials of these processes have shown that arcing in the microwave cavity of the treatment region can present a problem. Whilst low-levels of arcing may be acceptable, excessive arcing can damage the machinery. In particular, arcing may damage the microwave generator (typically a magnetron) or the conveyor belt. Replacement of these components can be expensive and may require skilled personnel. In addition, the equipment is often located in remote locations, such as on an oil rig in the case of drill cuttings, so accessing the equipment for maintenance and repair can be challenging.

It has been discovered that arcing is caused by a number of factors, and it is an object of the present invention to provide an improved apparatus and associated process that reduces or eliminates arcing in the microwave cavity.

The term 'microwave' is used herein for convenience and should be understood to mean any electromagnetic radiation that is capable of selectively heating water in a bulk material; typically this radiation has a frequency of between 1 MHz and 3 GHz.

Summary of the invention

According to a first aspect of the present invention there is provided a method of processing feedstock using microwaves, the method comprising removing ferrous material from the feedstock using a self-cleaning magnetic separator configured to remove the ferrous material from the feedstock by magnetic attraction and carry the ferrous material away from the feedstock in a continuous process before exposing the feedstock to microwaves.

Analysis has shown that bulk vermiculite may contain traces of metallic impurities such as magnetite. Magnetite and vermiculite are often extracted from the same mine, for example in Palabora, South Africa, which explains this cross-contamination. Also, vermiculite, or other bulk raw materials, may acquire small quantities of iron oxide from being transported in rusty containers. It has been found that these metallic impurities can cause arcing in the microwave cavity when the vermiculite is exfoliated.

As mentioned above, drill cuttings comprise a mixture of oil, water and rock. The rock component may include traces of ferrous metals, which can cause arcing in the microwave cavity when the drill cuttings are exposed to microwaves. Removing ferrous material from the feedstock prior to exposing the feedstock to microwaves ensures that the ferrous material does not enter the microwave cavity where it may otherwise cause arcing. The process is therefore more reliable than prior art methods, which risk damage to the equipment as a result of arcing. The improvements provided by the present invention reduce servicing requirements and increase the longevity of system components thereby increasing the overall robustness of the system.

In preferred embodiments, the microwave process is a continuous process, but batch processes are also envisaged. The raw feedstock may be pre-processed to remove ferrous contaminants. However, in preferred embodiments, the feedstock is processed on a production line and the ferrous material is removed from the feedstock on the production line. Accordingly, the method may comprise moving the feedstock through a microwave treatment region and removing the ferrous material from the moving feedstock upstream from the microwave treatment region.

The feedstock may be moved through the microwave treatment region in a number of ways. Embodiments are envisaged in which the feedstock falls under gravity through an inclined chute. However, in preferred embodiments the feedstock is moved on a conveyor, such as a belt conveyor.

It is important to control the depth and distribution of the feedstock on the conveyor belt because it has been found, for example, that variations in depth of the feedstock on the conveyor belt can alter the effectiveness of the process. The process typically involves ordering the unprocessed feedstock on the conveyor belt to control precisely the geometry of the feedstock that is conveyed through the microwave cavity. Ordering the feedstock on the conveyor belt may be achieved by controlling the belt speed and the feed rate, i.e. the rate at which the feedstock is supplied to the belt, in order to achieve a uniform depth of feedstock on the conveyor belt. Alternatively or additionally,

the feedstock may be ordered by passing the feedstock through baffles or paddles on the conveyor.

Removing ferrous contaminants from ordered feedstock may disorder the feedstock, especially for particulate feedstock such as vermiculite where ferrous contaminants may be drawn through the bulk of the feedstock by the magnet. Consequently, the method preferably comprises removing the ferrous material from the feedstock before the feedstock is ordered on the conveyor belt. This avoids disrupting the controlled geometry of feedstock that is conveyed through the microwave cavity. The method may comprise removing the ferrous material from the feedstock on the conveyor. In this case, the feedstock may be ordered on the conveyor (for example using the baffles or paddles) after the removal step. Preferably, the ferrous material is removed from the feedstock before the feedstock is supplied to the conveyor. In preferred embodiments, the method comprises removing ferrous material from feedstock in a feed device supplying the conveyor. In this case, removing the ferrous material cannot disrupt or disorder the feedstock on the conveyor. The feed rate can be controlled using a vibratory feeder or equivalent feed device, which induces movement in the feedstock and causes the feedstock to behave like a fluid. The flow of feedstock onto the conveyor belt can be controlled by adjusting the frequency and/or amplitude of vibration of the feeder. It has been found that inducing movement such as this in the feedstock can improve the effectiveness of the magnetic separation by freeing ferrous material in the bulk feedstock, and allowing it to move through the bulk feedstock toward the magnet. Accordingly, the method may advantageously comprise inducing movement in the feedstock to cause the feedstock to become fluid and removing the ferrous material from the fluidised feedstock. According to a second aspect of the present invention within the embracing inventive concept there is provided an apparatus for processing a flow of feedstock using microwaves, the apparatus comprising a self-cleaning magnetic separator configured to remove ferrous material from the flow of feedstock and carry the ferrous material away from the flow of feedstock in a continuous cycle, the magnetic separator being arranged upstream from a microwave cavity.

The magnetic separator may comprise any suitable magnet, for example a permanent magnet or an electromagnet. In preferred embodiments of the invention, the apparatus comprises a conveyor such as a belt conveyor for moving the feedstock through the microwave cavity. As mentioned above, the apparatus may further comprise a feed device for supplying feedstock to the conveyor. The 'self-cleaning' magnetic separator of the present invention essentially removes ferrous material from a moving supply of feedstock and carries the ferrous material away from the moving feedstock in a continuous process. It thus advantageously permits large quantities of feedstock to be processed or the processing of feedstock having relatively high levels of ferrous contaminants, such as certain varieties of vermiculite. In preferred embodiments of the invention, an 'overband' magnetic separator is employed, which is typically suspended above the feedstock flow, for example above the conveyor belt. The overband separator is self-cleaning and comprises a magnet surrounded by a continuous moving conveyor belt. The magnetic field of the magnet generally covers a central region of the conveyor belt. Ferrous material is attracted by the magnet and is held on the belt by the magnetic field of the magnet acting through the belt. As a portion of the belt moves clear of the magnetic field, ferrous material falls away from that portion of the belt under gravity into bins for collection and disposal.

The overband separator may be arranged with its belt transverse to, and preferably substantially perpendicular to, the feedstock flow. Conveniently this allows the collection bins to be arranged adjacent to the main conveyor belt.

Alternative types of magnetic separator may be used in other embodiments of the invention. For example, a self-cleaning magnetic drum separator may be used, which has a magnet located inside a revolving drum. The magnetic field covers only part of the drum, so ferrous material is held on the surface of the revolving drum until it moves out of the magnetic field, at which point it separates from the surface of the drum and is collected in a bin. The magnetic separator may be suspended above (or otherwise located adjacent) the conveyor belt or the feed device. It is advantageous to locate the magnet adjacent to the feed device, because this ensures that the ferrous contaminants are separated from the feedstock before the feedstock reaches the conveyor belt. As explained above, this avoids disrupting the feedstock on the conveyor belt, which ensures efficient microwave processing.

Preferably the feed device is a vibratory feed device or equivalent, which fluidises the feedstock resulting in a controlled flow of feedstock onto the conveyor. The magnet is preferably located adjacent, and more preferably suspended above, the vibratory feed device. In this way, ferrous contaminants are removed from the fluidised feedstock, which is particularly effective for reasons already explained above. In preferred embodiments of the invention, the feedstock is vermiculite. However, it will be appreciated that the method and apparatus of the present invention are also suitable for processing any other type of feedstock, including drill cuttings or other water- containing minerals, for example perlite.

It will be appreciated that optional and preferred features described in relation to the method of the first aspect of the invention apply equally to the apparatus of the second aspect of the invention and vice-versa.

Brief description of the drawings

In order that the invention may be more readily understood, reference will now be made, by way of example, to the following figures, in which:

Figure 1 is a schematic side view of an apparatus for exfoliating vermiculite according to the present invention;

Figure 2 is a schematic view of the apparatus taken along the line A-A in Figure 1 ; and

Figure 3 is a perspective view of an alternative arrangement of the apparatus, also in accordance with the present invention. Detailed description

Figure 1 shows an apparatus 10 for expanding vermiculite according to the present invention. The apparatus 10 includes a central microwave heating unit 12, which comprises a microwave cavity 14 and a microwave generator 16, which in this example is a magnetron. A tubular choke 18a, 18b for attenuating microwave radiation is provided at each end of the cavity 14. The cavity 14 and chokes 18a, 18b together form a tunnel through which a conveyor belt 20 of a belt conveyor 21 passes. The belt conveyor 21 is arranged to transport vermiculite from a feed station 22 at a first end 24 of the belt 20, through the microwave heating unit 12, where the vermiculite is expanded, and to a discharge unit 26 at a second end 28 of the belt 20, where the expanded vermiculite is collected. The feed station 22 comprises a hopper 30 and a feed device 32. The hopper 30 contains raw, unprocessed vermiculite 34. The feed device 32 is a vibratory feeder, in the form of an elongate open chute 36 having a first end 38 adjacent an outlet of the hopper 30, and a second end 40 located above the conveyor belt 20. The chute 36 is inclined downwardly from the hopper 30 towards the conveyor belt 20. The vibratory feed device 32 is configured to oscillate in a direction perpendicular to its direction of extension, as shown by the double-headed arrows 42 in Figure 2. Referring still to Figure 1 , a control unit 44 for controlling parameters including feed rate, belt speed and microwave power is shown in communication with the hopper 30, vibratory feeder 32, belt conveyor 21 and microwave generator 16. The control unit 44 comprises a Human Machine Interface (HMI), which allows a user to control the various operating parameters of the apparatus 10.

An overband magnetic separator 46 for removing ferrous material from the raw vermiculite 34 is suspended above the vibratory feeder 32. The overband magnetic separator 46 can be seen more clearly in Figure 2, which is a schematic cross-sectional view of the apparatus 10, taken along the line A-A in Figure 1 .

Referring to Figure 2, the magnetic separator 46 comprises a conveyor belt 48 arranged over a pair of rollers 50. A strong permanent magnet 52, in the form of a plate, is mounted substantially centrally between the rollers 50. In this arrangement, the magnetic field of the magnet 52 covers the central region of the conveyor belt 48, but does not extend to the end parts of the conveyor belt 48, near the rollers 50.

As shown in Figure 2, the magnetic separator 46 is located in front of the hopper 30 (with respect to the general feed direction of the vermiculite) and above the open chute 36 of the vibratory feeder 32. The magnetic separator 46 is arranged with its conveyor belt 48 substantially perpendicular to the main conveyor belt 20. A bin 54 for collecting ferrous material 56 removed by the magnetic separator 46 is located beside the main conveyor belt 20. As shown in Figure 1 , the magnetic separator 46 is connected to the control unit 44, which may be used to control the belt speed of the magnetic separator 46. The method of operation of the apparatus 10 will now be described with reference still to Figures 1 and 2. Referring to Figure 1 , the HMI of the control unit 44 is used to set the microwave power, the speed of the main conveyor belt 20 and the feed rate. Unprocessed vermiculite 34 in the hopper 30 is fed onto the main conveyor belt 20 via the vibratory feeder 32. The feed rate is determined by the frequency of oscillation of the vibratory feeder 32, which causes the vermiculite to flow under gravity along the open chute 36 of the vibratory feeder 32 in the direction of arrow 58. When the unprocessed vermiculite 34 reaches the second end 40 of the chute 36, it falls onto the first end 24 of the main conveyor belt 20. The unprocessed vermiculite 34 is transported on the main conveyor belt 20 in the direction of arrow 60 towards the microwave heating unit 12. The unprocessed vermiculite 34 enters the tunnel comprising the chokes 18a, 18b and is conveyed through the microwave cavity 14 in the direction of arrow 61 . The magnetron 16 generates microwave radiation in the cavity 14. The microwave radiation selectively heats water trapped between the silicate layers of the vermiculite, causing the trapped water rapidly to turn to steam and expand the vermiculite within the cavity 14. The expanded vermiculite 62 is conveyed out of the cavity 14, through the choke 18b and towards the second end 28 of the conveyor belt 20 in the direction of arrow 64. At the second end 28 of the belt 20, the expanded vermiculite 64 falls into the discharge unit 26. The process operates continuously, but may of course be suspended for cleaning or maintenance of the machinery, to re-fill the hopper 30 or for any other reason.

In order to reduce or avoid arcing within the microwave cavity 14, the overband magnetic separator 46 is arranged to remove ferrous material 56 continuously from the supply of unprocessed vermiculite 34. As the unprocessed vermiculite 34 moves along the vibratory feed device 32, ferrous material 56 in the vermiculite 34 is drawn towards the magnet 52 as shown by the dashed arrow 66, and separated from the vermiculite feed.

Referring to Figure 2, the conveyor belt 48 of the magnetic separator 46 moves in a direction from left to right as illustrated above the open chute 36 of the vibratory feed device 32. Ferrous material 56 in the chute 36 is attracted to the magnet 52 and is lifted out of the unprocessed vermiculite 34 towards the magnet 52. The ferrous material 56 is held on the conveyor belt 48 of the magnetic separator 46 under the influence of the magnet 52. As the conveyor belt 48 moves from left to right, it transports the ferrous material 56 away from the chute 36 until the ferrous material 56 is clear of the magnetic field. At this point, the ferrous material 56 separates from the belt 48 and falls under gravity into the bin 54 beside the main conveyor belt 20 for collection and disposal. The process of separating and releasing the ferrous material 56 is continuous, hence the magnetic separator 46 is described as 'self-cleaning'. The speed of the main conveyor belt 20 and the frequency and/or amplitude of oscillation of the vibratory feeder 32 are carefully controlled to provide a steady flow of vermiculite 34 onto the conveyor belt 20. This ensures that a uniform distribution 68 of vermiculite is conveyed through the microwave cavity 14 and avoids uneven piling of vermiculite, which can adversely affect the microwave process. The magnetic separator 46 removes the ferrous material 56 before the vermiculite 34 falls onto the main conveyor belt 20, which avoids disrupting the uniform distribution 68 of vermiculite on the conveyor belt 20. Thus, ordering of the vermiculite 34 on the conveyor belt 20 takes place after removal of the ferrous material 56. The vibratory feeder 32 causes the unprocessed vermiculite feed to behave substantially as a fluid. Consequently, any ferrous material 56 within the vermiculite 34 can move freely through the bulk of the vermiculite 34, which increases the effectiveness of the magnetic separation. An alternative embodiment of the invention is shown schematically in the perspective view of Figure 3. In this embodiment, the magnetic separator 46 is arranged directly above the main conveyor belt 20. Whilst not shown in Figure 3, the apparatus may optionally include means such as paddles or baffles for ordering the feedstock on the conveyor belt 20 after the magnetic separation stage. This arrangement also works well when the properties of the feedstock are such that removing ferrous material from feedstock on the belt 20 does not significantly affect the ordered distribution of feedstock on the belt 20. This may be the case when the ferrous material is very fine, or is present in a low concentration. This arrangement is also effective in situations where disrupting the feedstock on the belt 20 is not detrimental to the microwave processing. In such cases, subsequent ordering of the feedstock may not be required.

Whilst the above examples relate to the microwave exfoliation of vermiculite, it will be appreciated that other types of feedstock may be employed in this process. Analogous examples could employ other water-containing minerals, such as perlite. Alternatively, the feedstock may be oil-containing drill cuttings, or indeed any other feedstock that may contain ferrous material.

Claims

1 . A method of processing feedstock using microwaves, the method comprising removing ferrous material from the feedstock using a self-cleaning magnetic separator configured to remove the ferrous material from the feedstock by magnetic attraction and carry the ferrous material away from the feedstock in a continuous process before exposing the feedstock to microwaves.

2. The method of Claim 1 , further comprising moving the feedstock through a microwave treatment region and removing the ferrous material from the moving feedstock upstream of the microwave treatment region.

3. The method of any preceding claim, further comprising removing the ferrous material from a fluidised mass of feedstock.

4. The method of any preceding claim, further comprising removing the ferrous material before ordering the feedstock on a conveyor.

5. The method of Claim 4, comprising removing the ferrous material from a flow of feedstock supplying a conveyor.

6. The method of Claim 4, comprising removing the ferrous material from the feedstock on the conveyor.

7. An apparatus for processing a flow of feedstock using microwaves, the apparatus comprising a self-cleaning magnetic separator configured to remove ferrous material from the flow of feedstock and carry the ferrous material away from the flow of feedstock in a continuous cycle, the magnetic separator being arranged upstream from a microwave cavity.

8. The apparatus of Claim 7, wherein the magnetic separator is an overband magnetic separator.

9. The apparatus of Claim 8, wherein the overband magnetic separator comprises a conveyor belt arranged transverse to a direction in which the feedstock is conveyed.

10. The apparatus of any of Claims 7 to 9, further comprising a conveyor for conveying feedstock through the microwave cavity and a feed device for supplying feedstock to the conveyor, wherein the magnetic separator is configured to remove the ferrous material from feedstock on the feed device.

1 1 . The apparatus of Claim 10, wherein the feed device is configured to fluidise the feedstock.

12. The method of any of Claims 1 to 5 or the apparatus of any of Claims 7 to 1 1 , wherein the feedstock is a water-containing mineral, such as vermiculite or perlite, said mineral being expanded by microwaves in the method or by the apparatus.

13. The method of any of Claims 1 to 6 or the apparatus of any of Claims 7 to 12, wherein the feedstock comprises oil-contaminated drill cuttings.