FIELD OF THE INVENTION

This invention relates to apparatuses and methods for recovering particles from a slurry. It finds particular application to the recovering of buoyant particles (such as hollow ceramic microspheres) from a slurry (such as a water-based slurry) in which they are contained. However, in an inverted configuration, the apparatuses and related methods can be applied to the recovering from a slurry, of particles having a specific density greater than that of the slurry.

BACKGROUND TO THE INVENTION

Hollow ceramic microspheres consisting of alumina and silica filled with air or inert gas are produced as a by-product of coal combustion at temperatures of between about 1500°C and 1750°C. These hollow ceramic microspheres are referred to as“cenospheres” and are found in the pulverised fuel ash of thermal power plants. Their chemical composition and physical characteristics vary depending on the combustion process and the composition of the coal used. Each such ceramic microsphere typically has a diameter of about 5 to 500 micron with a density between about 0,4 to 0,8 g/cm ³ making it less dense than water.

Hollow ceramic microspheres where initially thought of as an unwanted and difficult waste product since, once dry, it would become a persistent airborne dust. The low density thereof furthermore rendered it unsuitable for landfill as groundwater would push it to the surface. However, it has become a valuable commodity having an approximate commercial value of about USD1 ,000 per ton at the time of filing this application. Depending on the grade thereof, hollow ceramic microspheres have various industrial applications, including the use thereof in lightweight insulating products; fillers for paints, lacquers and plastics; lightweight aggregates in concretes; and fillers for bituminous rubbers to name but a few examples. The benefits of using hollow ceramic microspheres as a filler in such applications include weight reduction, reduced viscosity, shrinkage reduction, and improved fireproofing properties.

The main by-products of coal-fired thermoelectric power plants are slug, bottom ash and fly ash. The heavier slug and bottom ash may be removed at the bottom of the power plant’s boiler whereas light fly ash soars up and is generally transported with exhaust gases from which it is separated, and transported to the ash dam either by means of a dry method or a wet method.

Wet transport of the fly ash may form a slurry which drains into settling lagoons. Here, most of the ash would settle and the buoyant hollow ceramic microspheres would rise to the surface. However, the density difference between the hollow ceramic microspheres and the water is such that the rate at which the microspheres rise toward the surface of the water is dreadfully slow. Workers need to collect the floating hollow ceramic microspheres manually by skimming the floating microspheres from the water surface. This process may therefore be quite labour intensive and time-consuming.

Furthermore, approximately 80% of the hollow ceramic microspheres contained in the fly ash either become damaged along its transport to the settling lagoons, trapped under or contaminated by the ash, or otherwise rendered unusable. Since these hollow ceramic microspheres form only about 0.2% to 2% of the fly ash at its origin, such a high percentage of further losses is untenable.

There is therefore room for improvement in this regard and the invention disclosed herein addresses these and other inadequacies, at least to some extent. Furthermore, with the apparatus being invertible to separate from a slurry, particles having a specific density greater than that of the slurry, the invention is capable of fulfilling a dual purpose.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided an apparatus comprising:

a body defining a slurry flow region and having an inlet and an outlet at opposing first and second regions of the body respectively, the slurry flow region extending between the inlet and the outlet;

at least one operatively inclined corrugated plate contained within the body, the corrugated plate including at least one corrugation forming a peak or a valley that extends within the slurry flow region; and a collector provided on an inlet side of the plate and associated with:

the at least one peak, with a mouth of the collector positioned at an edge of the plate to allow particles in a slurry within the slurry flow region, having a specific density lower than that of the slurry to riseand be guided along an underside of the peak towards the mouth of the collector; or

the at least one valley, with a mouth of the collector positioned at an edge of the plate to allow particles in a slurry within the slurry flow region, having a specific density greater than that of the slurry to sink and be guided along an upperside of the valley towards the mouth of the collector.

Further features provide for the apparatus to have a plurality of spaced apart and operatively inclined corrugated plates contained within the body, each plate including at least one corrugation forming a peak or a valley that extends within the slurry flow region; and for each plate to have a plurality of corrugations forming a plurality of peaks and a plurality of valleys.

A still further feature provides for the valleys of the corrugated plates to be arranged such that higher density particles contained in the slurry are guided downward along an operative topside of the valleys.

Where the particles to be recovered have a specific density lower than that of the slurry, the opposing first and second regions of the body may be respective operative upper and lower regions. Further features provide for the corresponding corrugations of adjacent plates to form a group of peaks; and for each group of peaks to have a collector associated therewith provided on the inlet side of the plates with a mouth of each collector positioned against the edges of the plates.

A still further feature provides for each collector to be in fluid communication with a riser pipe extending operatively upward from the collector for guiding low density particles from the mouth of the collector and out of the body via the riser pipe. A further feature provides for the collector to taper operatively upwardly to meet the riser pipe thereby to aid the low density particles in the slurry to travel into and along the riser pipes.

Alternatively, where the particles to be recovered have a specific density higher than that of the slurry, the opposing first and second regions of the body may be respective operative lower and upper regions. Further features provide for the corresponding corrugations of adjacent plates to form a group of valleys; and for each group of valleys to have a collector associated therewith provided on the inlet side of the plates with a mouth of each collector positioned against the edges of the plates.

A still further feature provides for each collector to be in fluid communication with a sink pipe extending operatively downwardly from the collector for guiding high density particles from the mouth of the collector and out of the body via the sink pipe. A further feature provides for the collector to taper operatively downwardly to meet the sink pipe thereby to aid the high density particles in the slurry to travel into and along the sink pipes.

A still further feature provides for the body to define an intermediate space between the inlet and the corrugated plates and for the intermediate space to contain one or more baffle plates positioned transverse the slurry flow region.

Still further features provide for the body to have an operatively vertical section and an inclined section downstream of the operatively vertical section with the inlet provided at the operatively vertical section and the one or more corrugated plates located within the inclined section; and for the second region of the body to funnel into the outlet.

Further features provide for the operative incline of each corrugated plate to be between 60° and 80° from the horizontal, preferably 70°; and for the inclined section of the body to have substantially the same incline as the corrugated plates.

Further features provide for the slurry to include a mixture of water, fly-ash and hollow ceramic microspheres; for the low density particles to be the hollow ceramic microspheres; and for the hollow ceramic microspheres to be cenospheres.

The invention extends to a method of extracting low density particles from a slurry, the method comprising:

providing an apparatus as defined above;

receiving into the body, through the inlet, a slurry containing the low density particles; causing the slurry to flow along the slurry flow region;

causing the low density particles to rise and be guided along the underside of the at least one peak formed by the at least one inclined corrugated plate;

causing the low density particles to enter the mouth of the collector associated with each of the peaks. The invention also extends to a method of extracting low density particles from a slurry comprising the steps of:

flowing the slurry into a body via an inlet and through a flow region having at least one operatively inclined corrugated plate contained therein, the corrugated plate including at least one corrugation forming a peak that extends along such flow region;

causing the low density particles to rise and be guided along the underside of the at least one peak formed by the at least one inclined corrugated plate;

collecting the low density particles rising from the at least one peak formed by the at least one inclined corrugated plate in one or more collectors associated with each peak; and directing the low density particles from the collectors operatively upwardly beyond the level of the inlet into the body via riser pipes.

The invention further extends to a method of extracting high density particles from a slurry, the method comprising:

providing an apparatus as defined above;

receiving into the body, through the inlet, a slurry containing the high density particles; causing the slurry to flow along the slurry flow region;

causing the high density particles to sink and be guided along the upperside of the at least one valley formed by the at least one inclined corrugated plate;

causing the high density particles to enter the mouth of the collector associated with each of the valleys.

The invention even further extends to a method of extracting high density particles from a slurry comprising the steps of:

flowing the slurry into a body via an inlet and through a flow region having at least one operatively inclined corrugated plate contained therein, the corrugated plate including at least one corrugation forming a valley that extends along such flow region;

causing the high density particles to sink and be guided along the upperside of the at least one valley formed by the at least one inclined corrugated plate;

collecting the high density particles sinking from the at least one valley formed by the at least one inclined corrugated plate in one or more collectors associated with each valley; and directing the high density particles from the collectors operatively downwardly, where they are extracted from the body, beyond the level of the inlet, via sink pipes.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a three-dimensional view of an apparatus in accordance with the invention for the seperation of low density particles from a slurry;

Figure 2 is a cross section of corrugated plates contained within the body of the apparatus of Figure 1 ;

Figure 3 is a sectional view of two adjacent corrugated plates;

Figure 4 is a three-dimensional view of the corrugated plates and collectors associated with the peaks of the corrugated plates;

Figure 5 is a three-dimensional view of the corrugated plates and an alternative embodiment of the collectors associated with the peaks of the corrugated plates;

Figure 6 is a flow diagram illustrating a method of separating low density particles from a slurry using the apparatus of Figure 1 ;

Figure 7 is a three-dimensional view of a second embodiment of the apparatus in accordance with the invention for the seperation of high density particles from a slurry; and

Figure 8 is a sectional view of two adjacent corrugated plates of the apparatus of

Figure 7.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An apparatus is provided for separating low density particles from a slurry. It finds particular application in removing hollow ceramic microspheres from a water-based slurry that originates as part of a wet separation method of fly-ash from a coal-fired thermoelectric power plant. These hollow ceramic microspheres may, in one exemplary embodiment, be cenospheres. The apparatus has a body that defines a region along which the slurry may flow in use. The body has an inlet at an operatively upper region of the body for receiving the slurry and an outlet through which the remainder of the slurry, that is the part of the slurry remaining after the low- density particles have at least partially been extracted therefrom, may exit the body.

The body contains at least one operatively inclined corrugated plate that has at least one corrugation forming a peak. For efficiency reasons, the body may typically contain multiple corrugated plates, each having a plurality of corrugations and thus forming a plurality of peaks and valleys. Adjacent corrugated plates are spaced apart to create a flow region between them through which the slurry may flow. The direction of the inclined peaks and valleys of the corrugated plates extend generally in the flow path.

The apparatus further includes one or more collectors, each associated with a peak and provided on an inlet side of the plate. A mouth of each collector is positioned at an edge of the plate. Where multiple corrugated plates are used, the corresponding corrugations on the adjacent plates may form groups of peaks. A collector may therefore be associated with each of the peaks such that a group associated with the mouth of the relevant collector is provided where the group of peaks terminate on the inlet side of the plates.

In use, a low density particle containing slurry, for example a slurry containing hollow ceramic microspheres, may enter the body via the inlet and may flow toward the outlet. The low density particles may rise and be guided along the underside of each of the peaks towards the mouth of each collector. The particles that travel along the underside of a particular group of peaks may therefore enter a common collector.

Since the operation of the apparatus is dependent on gravity and the relative densities of the components of the slurry, it should be understood that where reference is made to“vertical” or “horizontal” throughout the description, it refers to the orientation of the apparatus when in use. Similarly, relative directions such as“below” and“above” refers to the apparatus being in an upright orientation.

Figure 1 shows an exemplary embodiment of an apparatus (1 ) for separating low density particles from a slurry. For illustration purposes, the apparatus (1 ) and its operation will be explained at the hand of an example wherein the low density particles are hollow ceramic microspheres contained in a fly-ash slurry. However, it will be apparent to those skilled in the art that the apparatus may be used to separate any particle or selection of particles having a lower density or densities than that of the remainder of the components contained in the slurry.

The apparatus (1 ) has a body (3) with a vertical section (5) and an inclined section (7) below the vertical section. Both the vertical section (5) and the inclined section (7) have a substantially rectangular cross section. An inlet (9) is provided at the vertical section (5) and thus near the top of the apparatus (1 ) through which a slurry may be received into the body (3). At a lower region of the inclined section (7), the body defines a funnel (11 ) with an outlet (13) of the body provided at the narrow end of the funnel (1 1 ). In use, slurry may flow through the body (3) from the inlet (9) towards the outlet (13) in a flow region (12) of the body defined between the inlet and outlet.

In the present embodiment, the inclined section (7) is angled at about 70° from the horizontal. Within the inclined section (7), a plurality of spaced apart and substantially parallel corrugated plates (15) are contained that are also inclined at about 70° from the horizontal. Each corrugated plate (15) has multiple corrugations and therefore defines a plurality of peaks (17) and valleys (19) formed by the corrugations.

As shown more clearly in the width-wise cross-sectional view of Figure 2, the corresponding peaks (17) of adjacent corrugated plates together form parallel groups of peaks (21 ). Turning now to Figure 4, a collector (25) is provided at the inlet side edges (23) of the corrugated plates (15) at each of the groups of peaks (21 ), each collector therefore being associated with the peaks (17) of its corresponding group (21 ). A mouth (27) of each collector is positioned against the edges (23) of the plates and is arranged to collect the upward outflow of microspheres from groups of peaks (25) as will be described in more detail below.

Each collector (25) is in fluid communication with a riser pipe (29) that extends upward from the collector for guiding microspheres from the mouth (27) of the collector (25) and out of the body (3) via the riser pipe (29).

In an intermediate space (31 ), generally between the inlet (9) and the corrugated plates (15), vertically spaced apart baffle plates (33) are provided and are therefore positioned transverse the direction of flow.

Figure 6 shows a flow diagram of a method (500) of separating low density particles from a slurry using the apparatus (1 ). As a first step, fly-ash slurry is fed (501 ) into the body (3) through the inlet (9). The slurry may be gravity fed, pumped into the body or a combination thereof. The slurry will enter the intermediate space (31 ) in the vertical section (5) and will trickle downward through the baffle plates (33). The baffle plates (33) help to reduce turbulence in the flow of the slurry since the results may be more efficient when the downward flow through the apparatus is uniform or as near possible.

As a second step, the slurry is caused to flow (502) along the slurry flow region and through the spaces between adjacent corrugated plates (15). The flow parameters of the slurry through these spaces between adjacent plates, and particularly the flow rate thereof, is configured such as to allow the separation of the hollow ceramic microspheres from the heavier remainder of the slurry as is described further with reference to Figure 6.

Figure 3 shows a length-wise cross section of two adjacent corrugated plates (15). The upper plate shown is sectioned at a peak (17) with the plate shown at the bottom being sectioned at a valley (19). Figure 3 illustrates a condition in which the space between adjacent plates (50) is completely filled with the slurry, which in this exemplary embodiment is water-based. The slurry is a mixture of low density hollow ceramic microspheres (51 ) and higher density ash particles (53) and other heavier impurities. It will be understood that the remainder of the space (50) between the adjacent plates is therefore filled with water.

The fact that the hollow ceramic microspheres (51 ) are less dense than the water, will cause the microspheres to rise (503) within the water, provided that the flow rate is sufficiently slow to prevent the microspheres from being swept along. As the hollow ceramic microspheres (51 ) move upward within the space (50) between the adjacent plates (15), the microspheres will eventually encounter the underside of the upper plate. The hollow ceramic microspheres (51 ) will be guided toward the peak (17) of the upper plate along the upwardly slanted edges of the corrugation. Once the microspheres (51 ) reach the peak (17) of the upper plate, the microspheres will be guided upward along the peak at the underside of the upper plate.

Conversely, due to the fact that the ash particles (53) and other higher density impurities are more dense than the water, the ash particles (53) move downward within the space (50) between the adjacent plates (15). As the ash particles (53) move downward, it will eventually encounter the upper surface of the lower plate. The ash particles (53) will be guided toward the valley (19) of the lower plate along the downwardly slanted edges of the corrugation. Once the ash particles (53) reach the valley (19) of the lower plate, they will be guided downward along the valley at the upper surface of the lower plate toward the funnel (11 ) and thus also the outlet (13). When the microspheres (51 ) travelling upwards along the peaks reach the inlet side edges (23) of the corrugated plates (15), the microspheres will enter the mouth (27) of the collector (25) that is associated with the relevant group (21 ) of peaks. The microspheres (51 ) will continue to rise within the riser pipes (29) and will eventually exit the body (3) from where the microspheres may be further transported. The remainder of the slurry, including the higher density ash (53) and other impurities, may exit the outlet (13) from where it may be transported for further treatment.

Figure 4 shows the parallel plate arrangement. The fact that the sheets are corrugated plays a very important role in the collection of the microspheres. When the microspheres float upwards along the underside of the sheets, they migrate towards the peaks in the sheets, which are higher, where they concentrate and travel along these peaks ridges to the top of the sheets. There they float into the inverted collection channels. These inverted channels cover all the points where the microspheres exit the peaks in the sheets. From there they float upwards through the riser tubes and are collected at the top.

Figure 5 shows the parallel plate arrangement of Figure 4, with an altenative tapered embodiment of the collectors (25) to better aid the travel of the microspheres (51 ) upwardly into and along the riser pipes (29). Although the tapered collectors (25) have been illustrated as tapering operatively upwardly from each end to meet the respective riser pipe (29) midspan of such collector (25), it will be appreciated that the riser pipe (29) may be positioned anywhere along the length of the collector (25) with the collector (25) appropriately tapering upwardly to meet the riser pipe.

Similarly, the ash will slide downwards along the sheets and migrate to the valleys in the sheets, and are discharged via the drainage chute to the outlet.

The apparatus (1 ) and the method (500) described above may address two problems associated with separating hollow ceramic microspheres by floatation as per the prior art. The first such addressed problem is that the microspheres float at a very slow rate. They usually rise in water at a rate of about 100 mm per minute, depending on the density and size of the particular microspheres. By passing the slurry between the closely spaced parallel sheets, which may typically be spaced about 10 mm apart, the microspheres only need to rise about 15 mm upwards before reaching the bottom surface of the plate directly above it. Thereafter, its upward travel path is defined by the peak in the corrugations and when reaching the upper edge of the plate will enter the mouth of a collector and move further upwards in the riser tubes. In contrast, using normal floatation methods, one would need a very large floatation tank to allow enough residence time for the hollow ceramic microspheres to escape to the surface of the ash slurry. For example, in a traditional 5 m deep flotation tank, the microspheres will typically take up to 30 min to reach the surface.

The second problem addressed is that this apparatus and the method by which it is used may increase the purity at which the microspheres are extracted in comparison to the purity of extraction by means of conventional methods. Such increased purity may be due to the fact that once the microspheres have reached the inverted collection channels or peaks, they may no longer be in contact with the ash particles, and only microspheres will float up toward the riser tubes (with as little impurities as possible). The extraction of the microspheres from the riser tubes will be above the water level, away from the ash slurry below.

Throughout the specification unless the contents requires otherwise the word ‘comprise’ or variations such as‘comprises’ or‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

The apparatus may further be manufactured in a modular construction, so as to provide custom setups for varying slurry flow rates and/or cenosphere recovery. The modular construction will be made up of a standard apparatus removable corrugated plates receivable therein such that the number of corrugated plates can be varied as required. Alternatively, the modular construction will be made up of a standard apparatus with a fixed number of corrugated plates, which number of standard apparatus making up an installation can be varied as required.

Although the invention has been described above with reference to preferred embodiments, it will be appreciated that many modifications or variations of the invention are possible without departing from the spirit or scope of the invention. For example, and with like references designating like components, the apparatus (10) may be used in an inverted configuration as depicted in figure 7 for operative use as a clarifier or similar.

Figure 7 shows an exemplary embodiment of an apparatus (10) for separating high density particles from a slurry. The apparatus (10) has a body (30) with a vertical section (50) and an inclined section (70) above the vertical section. Both the vertical section (50) and the inclined section (70) have a substantially rectangular cross section. An inlet (90) is provided at the vertical section (50) and thus near the bottom of the apparatus (10) through which a slurry may be received into the body (30).

At an upper region of the inclined section (70), the body defines a funnel (1 10) with an outlet (130) of the body provided at the narrow end of the funnel (110). In use, slurry may flow through the body (30) from the inlet (90) towards the outlet (130) in a flow region (120) of the body defined between the inlet and outlet.

The inclined section (70) is angled at about 70° from the horizontal. Within the inclined section (70), a plurality of spaced apart and substantially parallel corrugated plates (150) are contained that are also inclined at about 70° from the horizontal. Each corrugated plate (150) has multiple corrugations and therefore defines a plurality of peaks (170) and valleys (190) formed by the corrugations.

The corresponding valleys (190) of adjacent corrugated plates together form parallel groups of valleys at which collectors (210) are providedfor in use collecting the downward outflow of particles having a greater specific density than the slurry.

Each collector (210) is in fluid communication with a sink pipe (290) that extends downward from the collector for guiding the heavier particles from the mouth of the collector (210) and out of the body (30) via the sink pipe (290).

Figure 8 shows a length-wise cross section of two adjacent corrugated plates (150). The upper plate shown is sectioned at a valley (190) with the plate shown at the bottom being sectioned at a peak (170). Figure 8 illustrates a condition in which the space between adjacent plates (500) is completely filled with the slurry, which in this exemplary embodiment is water-based containing high density particles (530).

The fact that the high density particles (530) are more dense than the water, will cause them to sink within the water, provided that the flow rate is sufficiently slow. As the high density particles (530) move downward within the space (500) between the adjacent plates (150), they will eventually encounter the upperside of the lower plate and ultimately guided toward the valley (190) of the lower plate along the upwardly slanted edges of the corrugation. Once the high density particles (530) reach the valley of the lower plate, the high density particles (530) will be guided downward along the valley, into the collectors and ultimately downwardly out of the apparatus via the sink pipes.