WO2021084071A1

WO2021084071A1 - Magnetic particle extraction device and method

Info

Publication number: WO2021084071A1
Application number: PCT/EP2020/080515
Authority: WO
Inventors: Teunis Christiaan VAN DER REE
Original assignee: Petrogas Gas-Systems B.V.
Priority date: 2019-11-01
Filing date: 2020-10-30
Publication date: 2021-05-06
Also published as: EP3815790A1; EP4051436A1

Abstract

There is provided a magnetic particle (e.g. black powder) extraction device and method for extraction of magnetic particles (e.g. black powder) from a fluid flow. The device comprises a housing having a first chamber and a second chamber, and a separator between the first chamber and the second chamber. A permanent magnet is provided, preferably more than one permanent magnet. The first chamber comprises a fluid-inlet; a fluid-outlet; and a flow-path from the fluid-inlet to the fluid-outlet. The first chamber may thus form a flow-path for the fluid that is to be cleaned of magnetic particles. The second chamber has an inner volume of a dimension to receive the at least one permanent magnet. The second chamber may in that manner accommodate the at least one permanent magnet. The at least one permanent magnet is movable between a filtering position enveloped by the fluid flow-path and a non-filtering position that is remote from the flow-path.

Description

Magnetic Particle Extraction Device and Method

Field of the invention

The invention relates to devices for extraction of magnetic detritus, especially black powder, from fluid flows, in particular from gases, most preferably from natural gas, and to processes for extracting magnetic detritus, especially black powder, from such fluid flows.

Background of the invention

In the natural gas industry, the presence of black powder in gas flows is a known problem. Black powder is the commonly used term in the technical field that refers to solid materials that are present in natural gas handling systems. The black powder is typically suspended in (fast-)flowing natural gas streams and can collect in pipe lines and other components associated with natural gas handling systems.

Black powder is typically comprised of very fine powder made up of very hard, abrasive particles of iron oxides, iron sulphides and further mineral contaminants, often having particle dimensions in the region of 10 microns or less. It can form through chemical reaction of the natural gas with the pipelines (which are mostly ferrous steel) and handling equipment, for example through a reaction of hydrogen sulphide with iron in the pipeline wall but may also be a by-product of microbes in the pipelines or result from mechanical erosion of ferrous materials such as the pipe line itself.

Black powder can clog and damage instrumentation, sensors and valves, prematurely wear pipes and other components e.g. through corrosion; give rise to flow losses, and lead to a need to overly frequently replace or service components of the gas handling system, e.g. in the gas transport systems, refining systems, and end use systems. Its presence in a natural gas stream can also result in a lower quality end product for its intended use, e.g. in gas fired power stations.

It is thus generally desirable to avoid and/or remove black powder from natural gas streams, preferably before it comes into contact with sensitive treatment equipment.

Conventionally, the industry has made use of various mechanical filters to remove black powder. These include the principle of passing incoming natural gas through a filter pad with pores dimensioned to balance the capture of black powder particles while minimizing pressure drop across the pad. Such pore-based filters are, however, less than perfect. For example, they may require frequent cleaning and/or replacement, for which the pipe line needs to be shut off at much expense, the pressure brought down, and the filter parts removed and replaced. Failure to timely clean or replace the filters can result in catastrophic failure of the pads leading to either a blockage or a sudden release of large concentrations of black powder to the downstream components. Filters may also struggle to provide a good balance between the need to capture the very finest black powder particles; the need for longevity of the filter; and the need to avoid large pressure drops across the filter.

Alternatives to mechanical filters have been attempted in the art. For example, cyclone centrifuge filters have been proposed for use in separating larger particles (5 microns and larger), however such techniques are not able to adequately capture smaller particles in black powder and may be considered to be overly flow restrictive for a proper clean of the gas in some circumstances, and even sensitive to collapse under back pressure when blocked.

A further alternative technique that has been proposed is the use of a magnetic filter assembly. In such an assembly rod-like magnets extend into an incoming flow of natural gas, and magnetic particles of the black powder are captured directly onto the surface of the magnet assemblies. In that manner, magnetic particles of the black powder are extracted from the gas stream.

An example is found in W009137930 Al, published in 2009, which considers the aim of black powder removal from gas pipelines. It discusses a pipeline magnetic separator system, wherein a magnetic separator assembly having a plurality of elongate magnetic members is provided. The assembly can be placed in line with the gas flow path to extract magnetic particles. To clean the magnets following black powder capture, a special operation is undertaken in which the magnetic separator assembly is removed from the pipeline by crane and moved to a complementary clean-out canister. The magnetic particles are removed from the magnet assemblies by way of a cleaning plate that scrapes or wipes along the surface of the magnetic rods. The magnetic rods are specially designed with non-magnetic ends to allow this. Shutting down of a pipeline, depressurization thereof, disassembly and removal of the filter, transport to and from a special cleaning station of strong magnets, and reassembly into the pipeline, can all result in excessive down-time of a facility (or at least a restricted throughput or need for other countermeasures) as well as increased risks of damage and wear to components.

Another example is US2010155336 AA, which discusses a pipeline filter with a pipeline mounting structure for mounting the pipeline filter in a pipeline, a screen support connected to the mounting structure and formed for releasably securing a screen filter to the pipeline filter and a magnetic filter support through which a magnetic filtering device is securable to the mounting structure. Cleaning again requires removal of filter and magnetic filtering device with associated shut down.

A more recent example is found in WO 2016/200427 Al, which discusses a still further alternative magnetic black powder removal system in which black powder flowing within a hydrocarbon pipeline is converted into a magnetorheological slurry by implementing wet scrubbing in the hydrocarbon pipeline using particular thixotropic agents. A magnetic field is then applied to the magnetorheological slurry to control the flow of the magnetorheological slurry through the hydrocarbon pipeline. The use of wet scrubbing and the need to use special thixotropic agents can be disadvantageous.

Although magnetic filter systems have offered some promise as compared to the more traditional mechanical filter pads and cyclones, there is still a need for improvement, for example in any of convenience, safety and cost-efficiency of use.

Summary of the invention

In accordance with one aspect of the invention there is provided a magnetic particle (e.g. black powder) extraction device for extraction of magnetic particles (e.g. black powder) from a fluid flow. The device comprises a housing having a first chamber and a second chamber, and a separator between the first chamber and the second chamber. At least one permanent magnet is provided, preferably more than one permanent magnet. The first chamber comprises a fluid-inlet; a fluid-outlet; and a flow- path from the fluid-inlet to the fluid-outlet. The first chamber may thus form a flow- path for the fluid that is to be cleaned of magnetic particles. The second chamber has an inner volume of a dimension to receive the at least one permanent magnet. The second chamber may in that manner accommodate the at least one permanent magnet. The at least one permanent magnet is movable between a filtering position enveloped by the fluid flow-path and a non-filtering position that is remote from the flow-path. The filtering position is preferably proximate a second-chamber side of the separator, and the remote position is preferably more distanced from the second chamber side of the separator. Remote preferably refers to a position in which the permanent magnet is removed to the extent that it no longer exerts a significant magnetic field in the fluid flow-path.

During extraction use of the magnetic particle extraction device, the permanent magnet is positioned in its filtering position. In that position the permanent magnets magnetic field attracts and captures magnetic (i.e. permanently or non-permanently magnetic) particles of the black powder entrained in the passing fluid, on the first chamber side of the separator.

As will be apparent, the captured particulates will continue to collect on the separator surface, in the magnetic field, until such time as the built-up particulates must be removed from the filtering device. At that time, flow of fluid may be stopped, and the permanent magnet may be moved from its filtering position to its non-filtering position remote from the flow-path, and remote from the separator collection surface, retreating inward to the second chamber.

Advantageously compared to prior art systems, this clearing of accumulated black powder from the extraction element, can be achieved by moving the permanent magnet from its filtering position enveloped by the flow-path to its non-filtering position in the second chamber. There is no requirement, (such as in the prior art) to disassemble the filter element from the pipeline, and to then transport the filter element to and from an independent cleaning station. This has advantages associated with reduced downtime and lower risk of wear and damage but may also make more frequent cleaning of the magnetic filter elements economical allowing for smaller and/or less expensive filter components.

It is preferable that the first chamber and the second chamber are substantially in pressure equilibrium, preferably wherein a pressure difference between the first chamber and the second chamber is maximally 500kPa, preferably 250kPa, preferably lOOkPa, preferably maximally 50kPa, and more preferably maximally lOkPa. This advantageously allows the separator between the first chamber and second chamber to be relatively thin because it does not need to withstand a pressure differential between the chambers. A generally thin separator (adjacent the magnet in its filtering position) is useful because it ensures minimal disruption of the magnetic field and minimal distancing of the separator collection surface from the magnet, ensuring a good magnetic field strength at the collection surface.

A high pressure differential between the first and second chambers, or for example if there was no second chamber and the separator was open to the atmosphere on one side, would require a strong (and thus bulky) separator to withstand the pressure and prevent escape of flow of the fluid and the magnetic particles (e.g. black powder) out of the first chamber and into the second chamber.

As mentioned, it may be advantageous to have a relatively thin separator delineating the first chamber and second chamber. In particular, in preferred embodiments of the invention said at least one permanent magnet is positioned in the second chamber in both its filtering and non-filtering positions. This advantageously provides shielding of the magnet from direct contact with black powder by way of the separator even in its filtering position. The separator preferably forms a barrier to transfer of black powder from the first chamber to the second chamber.

This avoids contamination of the permanent magnet with black powder such that removal of black powder accumulated during filtering does not require a scraping, wiping or other direct contact access with the permanent magnet’s surfaces.

For the permanent magnet to exert an optimal magnetic field strength in the flow-path, i.e. at the first chamber side of the separator, for example when the separator extends into the flow-path, the separator is preferably thin. In preferred embodiments, the separator may be from 0.5mm to 10mm thick, preferably from 0.5mm to 5mm thick, and preferably from 1mm to 3mm thick, adjacent to the permanent magnet when in its filtering position. Bringing the permanent magnet into proximity with second chamber side of the separator provides a magnetic field at the first chamber side surface of the separator causing collection of magnetic particles of black powder on the first chamber side surface of the separator, thus extracting it from the fluid stream.

The separator itself is preferably non-magnetic, preferably being composed of stainless steel. Other non-magnetic materials, including reinforced plastics, or aluminium are also contemplated as the material for the separator or in combination with stainless steel.

In a preferred embodiment the extraction device is provided with a pressure equalization conduit extending between the first and second chambers. The pressure equalization conduit may allow fluid (e.g. gas) to pass between the first and second chambers thereby allowing a substantial pressure equilibrium. To reduce or prevent ingress of black powder from the fluid flow of the first chamber into the second chamber, the pressure equalization conduit preferably comprises a particulate filter such as a filter tube or pad commonly known in the art. Any flow of gas through the conduit will be low and so the filter element will not be exposed to high levels of detritus from the fluid. The pressure equalization conduit may pass through the separator or may be an independent conduit, possibly external to the housing.

In an embodiment of the invention the separator may be provided with at least one sheath, preferably more than one sheath, as a protrusion of the separator. The sheath or sheaths may extend away from a generally planar base of the separator into the flow- path of the first chamber. This can increase the magnetic surface area to which the fluid is exposed as it flows past the separator surface.

Each sheath may form a blind channel having internal dimensions to receive a bar or rod-shaped permanent magnet. That is, each sheath has a closed end toward a first chamber end and an open end toward a second chamber end, and a sidewall joining the closed end and the open end. The sheath is preferably elongate having a hollow inner volume complementary in shape to a rod or bar shaped permanent magnet.

The permanent magnet is retractably positionable within the sheath via the open end. When in its filtering position within the sheath, the magnet exerts a magnetic field through the sheath’s sidewall and at a first chamber side surface of the sheath. This attracts magnetic particles and captures them upon the surface of the sheath. The magnetic particles do not come into direct contact with the permanent magnet because of the barrier function of the sheath.

Upon moving the permanent magnet to its non-filtering position at least partially withdrawn from the sheath, and thus distanced from the separator, the permanent magnet no longer exerts a magnetic field within the flow-path and the magnetic particles are no longer held against the separator (i.e. sheath) first chamber side surface. The magnetic particles can then be readily removed, even passively due to gravity, from the first chamber side surface of the separator.

In preferred embodiments, the permanent magnets are rods or bars, and may be a single magnet or more preferably comprised of a stack of magnets. In this manner a strong magnetic field can be closely concentrated around the rod or bar, as is known in the art of magnets.

In a preferred embodiment of the invention the black powder extraction device is provided with an array of permanent magnets retractably movable into the flow path of the first chamber, and preferably with an array of complementary sheaths as protrusions of the separator into the flow path, the sheaths accepting the array of permanent magnets.

It may be typical in the field of fluid treatment for black powder removal that high pressures and fluid flow rates are used.

It is preferable that the housing and/or other components of device are able to withstand internal pressures of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa. For example, the housing may be constructed of an appropriately thick (carbon-)steel shell with appropriately pressure resistant gaskets, seals and flanges.

In use the fluid inlet may be connected to a pressurized supply of fluid, preferably wherein the fluid is at a pressure of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa. Preferably the fluid is a hydrocarbon gas, natural gas, methane oxygen, carbon dioxide, hydrogen or nitrogen.

In some embodiments, in particular with high pressures and flow rates, a diffuser or baffle may be provided in the fluid-inlet to disperse the incoming fluid flow across the magnetic filter for optimal black powder capture.

In line with the preceding discussion, upon moving the permanent magnet to its non-filtering position, the permanent magnet no longer exerts a magnetic field within the flow-path and the magnetic particles are no longer held against the separator (e.g. the sheath outer surface) and can be readily removed. Preferably this is achieved by halting flow along the flow path, e.g. by closing the fluid inlet, thereafter moving the permanent magnet or magnets to the non-filtering position and allowing the captured magnetic particles to fall under gravity from the separator surface.

In this respect the first chamber is preferably provided with a a detritus collection area below the separator surface in the first chamber, preferably a sump.

It is also preferred that a detritus release outlet is provided in the detritus collection area for removal of detritus from the first chamber. The release outlet is preferably arranged in communication with the sump and is further preferably in communication with a pressure lower than that in the first chamber, preferably open to atmospheric pressure. Conveniently, the detritus release outlet can thus be opened so that back-pressure from the fluid pipeline will force the detritus in the sump through the release outlet for appropriate external collection and handling. In preferred embodiments a cyclone separator may be provided upstream of the fluid-inlet or downstream of the fluid-outlet.

In preferred embodiments a mechanical filter may be provided upstream of the fluid-inlet or downstream of the fluid-outlet.

In a preferred embodiment, a cyclone separator may be provided upstream of the fluid-inlet and a mechanical filter downstream of the fluid-outlet.

The magnetic filter removes magnetic particles before they encounter the barrier filter, the barrier filter does not become clogged with such contaminants and therefore the usefulness of the barrier filter is increased. Furthermore, while the barrier filter may not retain particles below a certain size, the magnetic filtration is not size-dependent. The overall efficiency of the filtration system is therefore greatly improved with use of the magnetic filter.

In another aspect of the invention there is provided a particle extraction device for extraction of magnetic particles from a fluid, (e.g. a stream of natural gas), the extraction device comprising a housing having a fluid-inlet, a fluid-outlet, and a flow- path from the fluid-inlet to the fluid-outlet along which the fluid can flow. Preferably a pipeline for fluid is adjoined to the fluid-inlet and the fluid-outlet. There is further provided a magnetic filter, preferably an array of magnetic filter elements, comprising one or more permanent magnets. The magnetic filter further comprises one or more sheaths that impinge upon or extend into the flow-path, and into which the array of magnetic filter elements can be retractably positioned. The sheaths form a physical barrier around the magnetic filter elements. This can help to prevent, or prevent, black powder from contacting the magnetic filter elements directly.

In this aspect, the magnetic filter preferably comprises an array of sheaths intruding into the flow-path, and a complementary array of permanent magnets retractably positioned within said sheaths.

In another aspect of the invention, there is provided a process for extracting detritus, preferably black powder, from a fluid stream, for example natural gas. The process comprises the steps of; a. providing at least one filter element, the filter element comprising a collection surface; b. providing a permanent magnet behind the collection surface to generate a magnetic field passing through the collection surface; c. passing a fluid containing magnetic particles through the magnetic field and trapping magnetic particles on the collection surface. d. moving the permanent magnet away from the collection surface to reduce or eliminate the magnetic field at the collection surface, and e. removing particles from the collection surface.

The process may preferably be implemented using the devices and apparatuses as described herein.

Preferably the flow speed passed the filter element is 25ms ¹ or less, more preferably 15ms ¹ or less, more preferably 10ms ¹ or less, most preferably 5ms ¹ or less. At lower speeds, magnetic particles may be more readily extracted by the magnetic filter elements.

Preferably the permanent magnet is shielded from direct contact with the magnetic particles by the filter element, the filter element forming separator membrane.

The step of reducing or eliminating the magnetic field from the collection surface preferably comprises moving the permanent magnet away from the collection surface, preferably rearwardly away from the collection surface.

A strong magnetic field at the collection surface of the filter element may provide for efficient and effective capture of magnetic particles.

In preferred embodiments the fluid is passed through a cyclone cleaning system, preferably before or after step c.

In preferred embodiments the fluid is passed through a mechanical filter, preferably before or after step c.

In a preferred embodiment, the fluid is passed through a cyclone separator prior to step c. and passed through a mechanical filter after step c.

In a preferred embodiment of the process, the filter element is positioned in a housing, said housing comprising a fluid-inlet, a fluid-outlet, and a flow-path from the fluid-inlet to the fluid-outlet, the filter element extending into the flow-path, wherein the fluid-inlet is connected to a pressurized source of fluid containing magnetic particles, and the fluid-outlet is connected to additional gas processing equipment. The source of fluid may be at a pressure of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa. Preferably the fluid is a hydrocarbon gas, natural gas, methane, oxygen, carbon dioxide, hydrogen or nitrogen. Removal of the collected particles from the filter element preferably comprises the steps of reducing or halting gas flow, reducing or removing the magnetic field at the collection surface, and thereafter allowing the particulate material to fall to a sump.

The process may further comprise a step of providing a sump-outlet and ejecting magnetic material in the sump via the sump outlet under back-pressure from the fluid outlet.

Gas in the present application refers to compositions that are predominantly in the gaseous state at the temperatures of pressures of use. Gas flows that include a minor weight portion of suspended solids or liquids, condensate or evaporated liquids, are considered to be gas flows within the meaning of the invention. For example, it is typical that a stream of natural gas, especially at its source, will contain a percentage of liquid hydrocarbons and/or water. Reference to gas thus includes instances in which the gas, especially if hydrocarbon gas, contains aerosolized aqueous or hydrocarbon liquids or separated aqueous or hydrocarbon liquids traveling along walls of a pipeline.

While the invention is preferably concerned with removal of magnetic particles from natural gas, the invention may also concern removal of magnetic particles from other gas streams, for example from flows of methane, carbon dioxide gas, oxygen, hydrogen, nitrogen, and mixtures thereof, for example air. Preferred gases of the invention

It is preferred that in the process the fluid is natural gas and preferably that the process further comprises steps of processing the natural gas to provide power-station grade natural gas, domestic-grade natural gas, compressed natural gas, or liquefied petroleum gas.

In an alternative aspect of the invention, the apparatus described above is used for extraction of magnetic particles from a flow of liquid, for example for extraction of black powder from a flow of crude oil, or other liquid hydrocarbon streams.

The various aspects of the invention discussed herein may provide for reliable extraction of magnetic particles (e.g. black powder) from a flow of fluid (e.g. natural gas), while at the same time avoiding the disadvantages of mechanical filter pads and the problems of cleaning of use of wetting/thixotropic agents found in the prior art.

Brief description of the drawings Various aspects of the invention will be further explained with reference to embodiments shown in the drawings wherein:

FIG. 1 shows a separator system for extracting magnetic particles from a fluid flow; FIG. 2 shows a side elevation of a single separator arrangement;

FIG. 3 shows a magnetic particle extraction device of the separator of figure 2;

FIG.4 shows a side elevation of the magnetic particle extraction device of figure 3; FIG.5 is a cross-section of the magnetic particle extraction device of figure 3;

FIG.6 is a cross-section of the magnetic particle extraction device of figure 4 along line A- A;

FIG.7 is top view into a lower shell of the magnetic particle extraction device of figure 3;

FIG.8 is a schematic illustration of magnetic fields in the view of figure 7;

FIG.9A is a schematic illustration of magnetic particle extraction device with an array of magnets in a filtering position;

FIG.9B is a schematic illustration of magnetic particle extraction device with an array of magnets in a non-filtering position; and

FIG.10 shows a diffuser suitable to be positioned within a fluid-inlet of the magnetic particle extraction device of Figure 3.

Description of illustrative embodiments

The following is a description of various embodiments of the invention, given by way of example only and with reference to the drawings.

FIG. 1 shows a separator system 100 comprising a gas inlet header (or manifold) 20 providing pressurized gas to separator system inlet pipe spools 40; and a gas outlet header 30, that receives pressurized, cleaned gas from the separator system outlet pipe spool 50.

The inlet pipe spools 40 are in communication with and provide the gas to inlets 65 of magnetic particle extraction devices 60. The outlets 66 of the magnetic particle extraction devices 60 connect to cyclone separators 90, downstream of the magnetic particle extraction devices 60.

In other embodiments, mechanical filters (not shown) may be used in place of or in combination with the cyclone separators 90, downstream of the magnetic particle extraction devices 60. Further alternatively mechanical filters and/or cyclone separators 90 may be included upstream of the magnetic particle extraction devices 60. In some embodiments, the magnetic particle extraction devices 60 may be directly coupled to the gas outlet, that is without other intervening filters or separators.

In use, a source of upstream pressurized gas (e.g. natural gas) is connected to the inlet header 20 from where it is then supplied via inlet pipe spools 40 to the magnetic particle extraction devices 60. As the gas passes through the magnetic particle extraction devices 60, magnetic particles are extracted from the gas. The system is preferably used for extracting black powder suspended in a hydrocarbon (e.g. natural gas) pipeline, preferably being an in-situ pipeline in service. The pipeline can be operational to transport hydrocarbons between locations.

The gas passes from outlets of the magnetic particle extraction devices 60 downstream to the cyclone separators 90 where remaining particles in the gas (if any) are removed from the gas by cyclonic separation.

The cleaned gas stream then passes to the outlet pipe spools 50, and outlet header 30 to exit the separator system. The outlet header 30 may be connected (directly or indirectly) to further transport gas pipelines, to gas handling equipment, to gas processing equipment, a gas compression system for provision of compressed natural gas or liquefied petroleum gas; to a power station; or to a domestic or industrial gas pipe network.

In the illustrated embodiment, three separator arrangements 80 (see fig. 2; comprising the magnetic particle extraction devices 60 and cyclone separators 90) are provided in parallel flow (as opposed to series flow). This preferred arrangement allows gas flow through one or two of the separator arrangements to be temporarily halted e.g. for cleaning operations, while maintaining continuous system gas flow through the remaining, open, separator arrangement(s). One or more inlet conduit valves 41, 42 and outlet conduit valves 43, 44 may be provided to selectively route the gas through one or more or all of separator arrangements. These valves may be operated manually or automatically via a pneumatic actuator or an electrical actuator.

Naturally, the separator system 100 could alternatively be provided with just two or more than three parallel separator arrangements. The separator system 100 may also comprise just one separator arrangement, without a parallel flow path, and in that case gas flow may be halted, or reduced in flow rate, during cleaning of maintenance of the separator arrangement. One of the separator arrangements shown in the system of figure 1 is illustrated in side elevation in figure 2. The gas flow enters via the header 20, and then follows a route passing through the magnetic particle extraction device 60, the cyclone separator 90, the outlet pipe spool 50, the inlet pipe spool 40, and then on to the outlet header 30 where it may recombine with gas from other parallel flow separator arrangements 80.

The magnetic particle extraction device 60 included in the separator system 100 of claim 1 is shown in more detail in figures 3 to 7.

Referring to figures 3 and 4, the magnetic particle extraction device 60 is provided with a pressure vessel having a housing 61 comprised of a lower shell portion 62 generally defining a first (preferably lower) chamber 601 therein; and an upper shell 63 generally defining a second (or upper) chamber 602 therein. The lower shell 62 and upper shell 63 are separably attached at a pressure resistant flange 64.

The pressure vessel 61 is preferably rated to withstand internal pressures of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa, in line with an ability to withstand typical pressures that may be found in industrial scale natural gas pipelines.

The lower shell portion 62 comprises a fluid-inlet 65 for receipt of a gas flow from an inlet pipe spool 40. There is further provided a fluid-outlet 66 for outlet of gas to an outlet pipe spool 50. A flow-path for gas is provided running from the fluid-inlet 65 to the fluid-outlet 66, through the interior of the lower shell 62 (first chamber).

A pressure equalization conduit 69 is provided to allow for pressure equalization between the first chamber 601 and the second chamber 602. The pressure equalization conduit 69 in a simple form may be an open line allow fluid communication between the first chamber 601 and the second chamber 602. In preferred embodiments, a filter element 70 e.g. a mechanical filter may be provided in the pressure equalization conduit 69 to prevent or reduce the passage of particulate material, e.g. particles of 3 micron or greater in a dimension, from the first chamber 601 to the second chamber 602.

At its lower end, the illustrated magnetic particle extraction device 60 is provided with a lower preferably funnelled end, forming a sump 67 into which particulate material extracted from gas can fall under gravity during a cleaning operation. The sump 67 is further provided with a sump outlet 68, preferably in the form of a valve, which is selectively openable to release particulate material that has collected in the sump 67.

At the upper end of the upper shell portion 63, the illustrated magnetic particle extraction device 60 is provided with an opening for receipt of lifting gear for affecting retractable movement of elements within the second chamber.

The housing may be composed of steel or other known materials capable of withstanding pressures in use.

Referring to figures 5 and 6, cross-sections of the magnetic particle extraction device 60 illustrated in figures 3 and 4 are provided illustrating the interior of the housing 61. The cross-section of figure 6 is a cross-section along the line A-A of figure 4.

The interior of the housing 61 is generally divided into a first (lower) chamber 601 in the lower shell 62, and a second (upper) chamber 602 in the upper shell 63.

The first chamber 601 and the lower chamber 602 are divided by a separator 603 delimiting the two chambers. The separator 603 comprises a separator plate and seals the chambers against exchange of particulate material and preferably also of liquids and gas. The separator has a first-chamber side 606 and a second chamber side.

The separator 603 extends as a plurality of blind-tubes into the interior of lower shell 62, which impinge upon a gas flow-path running from the fluid-inlet 65 to the fluid-outlet 66. The blind-tubes form sheaths 604 having a closed end 610 toward the first chamber 601 and an open end 611 toward the second chamber 602, with a sidewall 612 extending therebetween. In this manner magnetic rods 605 can be inserted into sheaths 604 for a filtering position and operation and withdrawn from sheaths 604 for a non-filtering position and/or cleaning operation.

A further inner-housing 608 may be provided in the second chamber 602, which may receive the retracted magnets 605, and provide additional protection against fouling of the magnets’ 605 surface.

Figure 7 is a view from above, into the lower shell 62 with separator 603 in place showing open ends 611 of the sheaths 604 with magnets 605 inserted therein in a filtering position. The magnets 605 are sheaths 604 are arranged in two offset rows to provide a large area of surface contact with a gas passing from fluid-inlet 65 to fluid-outlet 66. A greater number of rows, or only a single row, or more or fewer magnets may be provided as needed. Figure 8 schematically illustrates the magnetic field generated about the magnets 605. The magnetic field extends through the sheaths 604 of the separator 603 and into a gas flow as it passes over the first chamber side surface 606 of the sheathes. The magnetic fields of the magnets preferably overlap, e.g. as illustrated to exposure substantially all flowing gas to the magnetic fields.

As gas passes over the first chamber side surface 606 of the sheaths 604, magnetic particles (permanently magnetic or non-permanently magnetic) are captured within the magnetic field and forced into contact with and held against the first chamber side surface 606 of the sheaths 604 adjacent the magnets 605. The gas on a downstream side of the sheath 604 and magnet 605 array in this manner has a lower weight percent content of particulate material and is thus more readily handleable, treatable and useable than the upstream gas with its higher level of particulates. In preferred embodiments, the magnetic particle content of the gas at the fluid-outlet is less than 20% of the magnetic particle content of the gas at the fluid-inlet, by weight, preferably less than 5%, more preferably less than 1%.

Capture of magnetic particles within the magnetic field and against the first chamber side surface 606 of the sheaths 604 is best achieved at reduced gas speeds over the collecting surface 606. In this respect, in some embodiments, in particular with pipeline pressures and flow rates, a diffuser 72 or baffle may be provided in the fluid- inlet 65 to disperse the incoming gas flow across the magnetic filter. An example of a suitable diffuser 72 that may be inserted or incorporated into the fluid-inlet 65 is shown in figure 9.

It is preferable if the gas speed past the magnetic filter elements is 25ms ¹ or less, more preferably 15ms ¹ or less, more preferably 10ms ¹ or less, most preferably 5ms ¹ or less.

The separator 603 is substantial enough to prevent ingress of particulate material to the second chamber 602, it is also preferably thin to avoid damping of the magnetic field when the magnets 605 are in place for filtering. The present invention advantageously allows for the separator 603 and its sheaths 604 to be thin despite the high pressures involved in industrial handling of natural gas streams. This advantage can be achieved by maintaining the second chamber 602 at about pressure equilibrium with the first chamber 601. The pressure differential across the separator 603 can so be minimized and consequently the separator 603 can be made thin without risk of physical collapse or a breach. The sheaths 604, and preferably all of the separator 603, is are non-magnetic. Suitable materials for the sheaths and separator are preferably stainless steel, and may also include plastics, or other non-magnetic metals such as aluminium. Hard materials are preferred to avoid erosion.

The inclusion of a separator 603 provides for an advantageous cleaning of the magnetic particle extraction device 60 that is easy and/or speedy for an operator. For example, extracted magnetic particles such as black powder can preferably be removed without any need to internally access the housing 61 or preferably without a need to directly access a rod magnet’s surface for wiping or scraping of extracted material therefrom.

This is schematically illustrated in figures 9A and 9B. In figures 9A and 9B the array of magnets 605 and sheaths 604 has been rotated by 90° about a vertical axis as compared to figure 8, for ease of explanation.

In figure 9A the array of magnets 605 are in their filtering position, inserted within sheaths 604. The magnets 605 exert a magnetic field through a sidewall 612 of the sheaths 604 and into a gas flow passing from the fluid-inlet 65 to the fluid outlet 66 over the sheaths’ first chamber side surface 606. Magnetic particles suspended in a passing gas are thus extracted from that gas and held against the collecting surface 606. The pressures in the first chamber 601 and in the second chamber 602 are close to, or at, equilibrium so that there is only a small pressure differential across the separator 603, allowing the separator 603 to be thin. Operating pressures may be in the region of at least 3,000kPa, at least 6,000kPa, as much as 10,000 kPa, and possibly 20,000 kPa.

In figure 9B the array of magnets 605 has been retracted from the filtering position within the array of sheaths 604 and are retreated to a non-filtering position within the second chamber 602. Retraction of the magnets is achieved by lifting gear 609 which preferably lift the magnets pneumatically.

Prior to raising the magnets 605 to the non-filtering position, gas flow through the magnetic particle extraction device 60 is greatly reduced or preferably halted using e.g. valves 41-44. The housing magnetic particle extraction device 60 remains under pressure, but there is a minimal or no flow of gas.

In the non-filtering position, the magnets 605 no longer exert a magnetic field within the gas flow path so that the captured magnetic particles are no longer held against the first chamber side surface 606 of the sheaths 604. Those magnetic particles then fall under gravity to the sump 67 where they are collected. Once the magnetic particles have fallen away from the sheaths 604 so that they are suitably clean, the array of magnets 605 is reinserted in the array of sheaths 604 and the gas flow restarted whereby filtering of gas can recommence.

Advantageously, clearing of the extracted magnetic particles from the first chamber side surface of the separator’s 603 sheaths 604 can be done without depressurization, without disassembly and without exposure of the array of magnets 605 to the external environment. Downtime, complexity, risk of damage and wear can possibly be reduced.

In the illustrated embodiment, magnetic particles collected in the sump 67 can be expelled without disassembly or depressurization of the system. Sump 67 is provided with a magnetic particle release outlet 68. The outlet 68 comprises a valve leading to a lower pressure volume, such as atmospheric pressure. Under normal operation the magnetic particle release outlet 68 is closed to maintain pressure in the first chamber 601. To expel magnetic particles from the sump 67 the magnetic particle release outlet 68 can be opened so that pressure in the first chamber 601 drives magnetic particles in the sump 67 out via the magnetic particle release outlet 68.

Removal of particles form the sump 67 may be carried out at as necessary, possibly at every cleaning operation of the sheaths 604, more preferably every 3 to 10 cleaning operations, or most preferably based on a weight or volume threshold as may be detected in the sump 67.

Returning to figures 5 and 6, a downwardly facing conical vane 89 is provided around the lower end of the array of sheaths 604. This vane 89 acts as a baffle obstructing return of particulate material from the lower part of the first chamber 601 to upper part of the first chamber 601. This can maintain cleanliness and prevent re pollution of gas passing along the flow-path between the fluid-inlet 65 and fluid-outlet 66

The magnets 605 used in the invention are preferably elongate and constructed to provide a magnetic field along radially about the long axis. Such magnets are commercially available and are comprised of a plurality of magnets and soft ferrous metal spacers arranged in an alternating sequence to form a stack, adjacent magnets being arranged with like poles facing. A non-magnetic case may be provided sealed around the stack of magnets and spacers to create a rod-like magnet, which magnet 605 can then be used for retractable insertion into the sheaths 604 of the present invention.

While any type of magnet may be used, rare-earth magnets are preferred to maximize the magnetic force. The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.

Claims

1. A magnetic particle extraction device (60) for extraction of magnetic particles from a fluid flow, comprising: a housing (61), wherein said housing comprises a first chamber (601)and a second chamber (602), a separator (603) between the first chamber and the second chamber, and at least one permanent magnet (605), wherein the first chamber comprises a fluid-inlet (65); a fluid-outlet (66); and a flow- path from the fluid-inlet to the fluid-outlet; the second chamber has an inner volume of a dimension to receive the at least one permanent magnet; and the at least one permanent magnet is movable between a filtering position enveloped by the flow-path and a non-filtering position in the second chamber, which is remote from the flow-path.

2. The magnetic particle extraction device (60) of claim 1, wherein the first chamber (601) and the second chamber (602) are substantially in pressure equilibrium, preferably wherein a pressure difference between the first chamber and the second chamber is maximally 500kPa, preferably 250kPa, preferably lOOkPa, preferably maximally 50kPa, and more preferably maximally lOkPa

3. The magnetic particle extraction device (60) of claim 1 or claim 2, further comprising a pressure equalization conduit (69) between the first and second chambers (601, 602), preferably wherein the pressure equalization conduit comprises a particulate filter (70).

4. The magnetic particle extraction device (60) of any preceding claim, wherein the separator comprises at least one sheath (604) extending away from the second chamber (602) and into the flow-path of the first chamber (601), wherein the sheath has internal dimensions to receive the at least one permanent magnet (605), and the permanent magnet is retractably positionable within the sheath.

5. The magnetic particle extraction device (60) of the preceding claim, wherein the filtering position of the permanent magnet (605) is a position within the sheath (604) and the non-filtering position is a position at least partially withdrawn from the sheath.

6. The magnetic particle extraction device (60) of claim 4 or 5, wherein the permanent magnet (605) is elongate, for example is a magnetic bar or a magnetic rod, and wherein the sheath (604) is complementarily elongate and hollow to receive said permanent magnet.

7. The magnetic particle extraction device (60) of any of the preceding claims, comprising an array of permanent magnets (605) and wherein the separator (603) comprises an array of sheaths (604) complementary to the array of permanent magnets.

8. The magnetic particle extraction device (60) of any of the preceding claims, wherein the housing (61) is able to withstand an internal pressure of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa.

9. The magnetic particle extraction device (60) of any of the preceding claims, wherein the first chamber (601) further comprises a magnetic particle collection area (607) and a magnetic particle release outlet (608), preferably wherein the release outlet opens to a pressure lower than that in the first chamber (601), preferably to atmospheric pressure.

10. The magnetic particle extraction device (60) of any of the preceding claims, wherein the fluid-inlet (65) is connected to a pressurized supply of gas, preferably wherein the gas is at a pressure of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa.

11. The magnetic particle extraction device (60) of any of the preceding claims, wherein a cyclone separator (90) is provided upstream of the fluid-inlet (65) or downstream of the fluid-outlet (66).

12. The magnetic particle extraction device (60) of any of the preceding claims, wherein a cyclone separator (90) is provided upstream of the fluid-inlet (65) and a mechanical filter is provided downstream of the fluid-outlet (66).

13. The magnetic particle extraction device (60) of any of the preceding claims, wherein the magnetic particles are comprised in black powder suspended in a stream of natural gas.

14. A process for extracting magnetic particles from a fluid stream, wherein the process comprises the steps of; a. providing at least one filter element, the filter element comprising a collection surface (606); b. providing a permanent magnet (605) behind the collection surface to generate a magnetic field passing through the collection surface; c. passing a fluid containing magnetic particles through the magnetic field and trapping magnetic particles on the collection surface. d. moving the permanent magnet away from the collection surface to reduce or eliminate the magnetic field at the collection surface, and e. removing particles from the collection surface.

15. The process of claim 14, wherein the step of reducing or eliminating the magnetic field from the collection surface (606) comprises distancing the permanent magnet (605) and the collection surface.

16. The process of claim 14 or claim 15, wherein the fluid is at a pressure of at least 1000 kPa, preferably at least 3000 kPa, more preferably at least 10,000 kPa, and more preferably at least 20,000 kPa

17. The process of any of claims 14 to 16, wherein the filter element is positioned in a housing (61), said housing comprising a fluid-inlet (65), a fluid-outlet (66), and a flow-path from the fluid-inlet to the fluid-outlet, the filter element extending into the flow-path, wherein the fluid-inlet is connected to a source of fluid containing magnetic particles, and the fluid-outlet is connected to additional gas processing equipment.

18. The process of any of claims 14 to 17, wherein the removal of the collected particles from the filter element comprises the steps of reducing or halting gas flow, reducing or removing the magnetic field at the collection surface, and allowing the particulate material to fall to a sump (67).

19. The process of claim 18, wherein the sump (67) is provided with a sump-outlet (68) and the particulate material in the sump is ejected via the sump outlet under back-pressure.

20. The process of any of claims 14 to 19, wherein the fluid is natural gas and further comprising the steps of processing the natural gas to provide power-station grade natural gas, domestic-grade natural gas, compressed natural gas, or liquefied petroleum gas.

21. The process of any of claims 14 to 20, wherein the fluid is passed through a cyclone cleaning system (90), preferably before or after step c.

22. The process of any of claims 14 to 21, wherein the fluid is passed through a cyclone separator (90) prior to step c. and passed through a mechanical filter after step c.

23. The process of any of claims 14 to 22, wherein the magnetic particles are black powder and the fluid is natural gas.