MATERIALS DRYING SYSTEM

TECHNICAL FIELD

This disclosure relates to a system and method for drying bulk materials. The system is described specifically in relation to drying materials such as coal, ores and sands but it will be understood that the system may be utilised for drying any bulk materials.

BACKGROUND ART

Processes to dry bulk materials such as coal, lignite, ores and sands along with other inorganic and organic bulk materials may allow for more improved storage, more efficient transportation and more efficient use.

For example, in Victoria, brown coal or lignite has approximately 66% moisture content. Each tonne (t) of coal produces 2t of water so that when burned lignite has a very low calorific value. Burning lignite requires larger power stations to account for additional steam, has low energy efficiency and is a high producer of carbon emissions as a result. Drying the coal improves the overall efficiency of power generation and delivers calorific content more akin to black coal which attracts a premium price because of its calorific content and efficiency. Australian lignite is amongst the 'wettest' brown coals in the world, but brown coal deposits are significant in Germany and Indonesia. Developing a process to dry lignite opens up access to premium coal markets by improving power station efficiency and reducing carbon emissions.

Brown coal as a primary energy source in Australia will become increasingly important in energy supplies in the future because of its abundance, easy access and low mining cost. Therefore, there is considerable interest in the drying of coal prior to transport and usage. There are many technologies available for the drying of coal in various stages of technical and commercial development. Some technologies involve squeezing the water out of the coal, others involve heating the coal with steam via fluid bed drying processes, microwaving, or through a combination of pressure and high temperature. There are numerous evaporative drying technologies for coal that are in principle suited for coal drying, each with their respective merits. Hot air, combustion flue gas or superheated steam may be used as the heating medium during the convective and evaporative drying process. Coal is highly reactive and more susceptible to fire and explosion hazards due to spontaneous combustion. Each of these technologies is high cost, delivers inconsistent outputs, and cannot deliver throughput at a sufficient scale production to drive higher volume lower price, high margin returns. There is a high and continuing demand for an economical solution to drying coal products.

Further, sand is an integral element in an array of manufactured products and industrial practices, ranging from cement to the production of silicon chips for PV panels, other electronics, glass manufacture and fracking. Drying the sand is initially required in the process of producing various types and grades. Again primarily heat based technologies such as rotary kilns are used which are costly both in the initial capital outlay and ongoing running costs. Again there is a high and continuing demand for an economical solution to drying sands.

It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

SUMMARY Disclosed is a system for drying bulk materials such as, for example, coal and coal fines, lignite, petroleum coke, mineral and ore-bearing sand, sands or ores, gravel, plaster, slag, salts, grains and bulk foodstuffs. Broadly, the system uses principles of conveyance in a swirling pipe material dryer and applies them to drying bulk materials. In some forms, disclosed is an apparatus for drying bulk materials using a swirling flow, the apparatus comprising a delivery pipe configured to convey bulk materials from an inlet end to an outlet end in an induced swirling flow; an air inlet configured to introduce air or a gaseous fluid into the delivery pipe such that a swirling flow is induced in the delivery pipe; a materials inlet configured to introduce bulk materials to the delivery pipe; wherein an air stream into the delivery pipe induced by the air inlet is out of line with the material stream induced by the materials inlet.

In some forms the materials stream enters the delivery pipe through an end of the delivery pipe while the air stream enters the delivery pipe through a peripheral wall of the delivery pipe at a location proximal the end of the delivery pipe.

In some forms the air inlet comprises at least two inlet ducts spaced apart around the perimeter of the delivery pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with reference to the accompanying drawings in which

Fig. 1 shows an overview of the system of one embodiment of the disclosure;

Fig. 2 shows a perspective view of a delivery pipe assembly and cyclone of one embodiment of the disclosure;

Fig. 3 shows a perspective view of the delivery pipe assembly of Fig. 2 with a swirling vortex therein;

Fig. 4 shows a cross-sectional plan view of a delivery pipe inlet of one embodiment of the disclosure from the top; Fig. 5 shows a cross sectional side view of the delivery pipe inlet of Fig. 4 Fig. 6 shows a cross-sectional plan view of a delivery pipe inlet of one embodiment of the disclosure from above;

Fig. 7 shows a cross sectional side view of the delivery pipe inlet of Fig. 6;

Fig. 8 graphs experimental measurements of pipe centreline velocities at various generator speeds;

Fig. 9 shows experimental measurements of streamwise centreline velocity profile at two generator speeds of 450 rpm and 700 rpm at x = 13.8 m, where z = 0 is at the pipe wall and z =150 mm is closer to the centreline of the pipe;

Fig. 10. graphs temperatures recorded at the x=2.2 m and 13.8 m for various generator speeds;

Fig. 11 graphs temperature variation at differing pipe lengths.

DETAILED DESCRIPTION

In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Disclosed is an apparatus for drying bulk materials using a swirling flow, the apparatus comprising a delivery pipe configured to convey bulk materials from an inlet end to an outlet end in an induced swirling flow; an air inlet configured to introduce air or a gaseous fluid into the delivery pipe such that a swirling flow is induced in the delivery pipe; a materials inlet configured to introduce bulk materials to the delivery pipe; wherein an air stream into the delivery pipe induced by the air inlet is out of line with the material stream induced by the materials inlet. The configuration of the inlet assembly is such that the air stream and materials stream are angled with respect to one another, for example the air stream enters the delivery pipe at an angle while the material inlet enters the pipe substantially aligned with the pipe. The configuration allows for separate streams of material and air resulting in lower wear and a more controlled swirl and flow rate. A configuration with a plurality of pipes entering through the periphery of the delivery pipe while the materials enter at one end of the pipe allows for the impeller or air stream to be out of line with the material flow.

In some forms the materials stream enters the delivery pipe through an end of the delivery pipe while the air stream enters the delivery pipe through a peripheral wall of the delivery pipe at a location proximal the end of the delivery pipe.

In some forms the air inlet comprises at least two inlet ducts spaced apart around the perimeter of the delivery pipe.

In some forms the inlet ducts are oriented such that air entering the delivery pipe enters at an angle with respect to a radius of the pipe. In some forms the inlet ducts are angled away from parallel with respect to the pipe. In some forms the inlet ducts are angled to between 90° and 180° with respect to the pipe.

In some forms the inlet ducts are oriented such that air entering the pipe is directed at an angle close to parallel to an inner surface of the pipe. In some forms the inlet ducts have at least two different diameters.

In some forms the materials inlet and the air inlet are angled away from parallel with respect to one another. In some forms the air inlet is angled with respect to the delivery pipe such that inlet ducts extending from the air inlet meet the delivery pipe at an acute angle with respect to the horizontal

In some forms the apparatus further comprises a mixing chamber from which the material is delivered to the materials inlet.

In some forms the apparatus further comprises a cyclone unit engaged with the delivery pipe such that materials exiting the delivery pipe enter the cyclone unit for further drying.

In some forms the air stream is out of line with the materials stream in more than one plane.

Disclosed is a method of drying bulk materials using a swirling flow, the method comprising inducing a swirling flow in a delivery pipe through introduction of an air stream into the delivery pipe; delivering bulk materials to the delivery pipe through a materials stream; conveying the bulk materials in the delivery pipe in the induced swirling flow; wherein the materials stream and the air stream are off set from one another.

In some forms the bulk materials are delivered to an end of the pipe and the air is delivered through a peripheral wall of the pipe at a position proximal the end of the pipe. Also disclosed is an inlet assembly for an apparatus for drying bulk materials using a swirling flow, the inlet assembly comprising a materials inlet for introducing a materials stream to a delivery pipe and an air inlet for introducing an air stream to the delivery pipe, the air stream being out of line with the materials stream at entry. In some forms the materials inlet introduces a materials stream at an end of the pipe and the air inlet introduces an air stream through a peripheral wall of the pipe. Referring first to Fig. 1, shown is a drying system 1. The system 1 comprises a bulk materials delivery apparatus 2 configured to deliver bulk materials to a mixing chamber.

The materials delivery apparatus 2 in some forms includes a one-way valve to prevent blowback of materials from the system. The one-way valve may be in the form of a rotary lock valve which operates on similar principles to a revolving door. Alternatively, the one-way valve may be in the form of an extruder discharge screw, a flap valve or a counterweight valve, or any valve which acts in one direction and allows flow of bulk materials into the mixing chamber 3. The material is delivered from the mixing chamber 3 into a delivery pipe 4 which is elongate. In the illustrated form the delivery pipe has a circular cross-sectional area.

In some forms, material is delivered to the delivery pipe by means of an augur which moves material into the delivery pipe. It will be clear that alternatives to an augur are available .

A swirling vortex or spiral flow is created in the delivery pipe by means of air (or other fluid) delivery into the pipe. The air is input into the delivery pipe 4 in the illustrated form by means of a dual pipe inlet 5 (not shown in Fig. 1).

The delivery pipe 4 extends from the mixing chamber 3 to a cyclone 8. The material moves along the delivery pipe in a swirling vortex and is dried by conveyance within the vortex.

In the illustrated form a cyclone unit 8 is attached at the exit of the delivery pipe 4. This may have the benefit of increasing drying without using a very long pipe.

It has been found that a strong swirling flow is generated after the flow enters into the cyclone unit. The cyclone unit includes a plurality of outlets. Some flow is observed to leave the cyclone unit through the bottom outlet while the others is found to rise into the centre pipe inside the cyclone unit and leave through the top outlet. Referring to Fig. 2 the delivery pipe 4 is defined by a peripheral wall 9 having a perimeter extending about the pipe 4. The inlet assembly 10 comprises a dual air inlet 5 engaged with and in communication with the delivery pipe. The dual air inlet 5 is designed to deliver air or an alternative gas to the delivery pipe 4 and comprises a first inlet duct 11 and a second inlet duct 12 each entering the delivery pipe. In the illustrated form, the first and second ducts 11 and 12 enter the delivery pipe 4 at an angle to the pipe. That is, the first and second inlet ducts are neither parallel to nor perpendicular with the delivery pipe but enter the delivery pipe at an angle of between 90 degrees and 180 degrees with respect to the pipe. Moreover, the first and second input pipes enter the delivery pipe 4 at locations that are spaced apart around the perimeter of the delivery pipe 4. In some forms the locations are offset with respect to one another.

The delivery pipe 4 extends to the cyclone unit 8.

Fig. 3 shows the delivery pipe of Fig. 2 and includes streamline tracers to show direction and velocity of the flow. As shown in this Figure, the air flow instigated by the dual inlet duct 5 creates a swirling vortex having a helical shape in the pipe 4. The velocity and angle of the swirl decreases through swirl decay as the swirl moves through the pipe so that on entry the vortex has a high velocity and a tight helical shape while at the distal or output end of the pipe 4 the vortex is looser and the velocity slower. As illustrated, strong swirl is shown at the beginning of the horizontal pipe, which decays quite quickly to very little swirl at the entrance to the cyclone unit.

Turning now to Figs. 4 through 7, the inlet assembly 10 comprises a materials inlet 16 in the form of a materials inlet duct 17 containing an augur 18 which is adapted to rotate about the longitudinal axis of the material inlet duct 17 to deliver bulk material to the delivery pipe 4. The materials inlet 16 is adapted to put the materials delivery apparatus 2 in communication with the delivery pipe 4 for movement of materials from the delivery apparatus 2 to the delivery pipe 4. The inlet assembly 10 further comprises a dual air inlet 5 which delivers air or an alternative gas under force into the delivery pipe 4. The air inlet 5 comprises a first inlet duct 11 and a second inlet duct 12. The first inlet duct 11 enters the delivery pipe 4 through the peripheral wall of the delivery pipe 4 at inlet position 13 while the second inlet duct 12 enters the delivery pipe 4 through the peripheral wall of the delivery pipe 4 at inlet position 14. At the point where the inlet ducts meet the delivery tube, the inlet ducts 11 and 12 are angled with respect to the delivery pipe 14.

As shown best in Fig. 5 and 7, the materials inlet 16 extends substantially in line with the delivery pipe while the air inlet 5 is angled to the x axis with respect to the delivery pipe. Thus, the air inlet 5 slopes down toward the delivery pipe in ordinary use. This has the benefit of allowing the air inlet and the materials inlet to avoid interference with one another while the material and air enters the pipe in a position proximal to one another. In the illustrated form the angle of entry is an acute angle with respect to the horizontal x axis. As illustrated in Fig. 5, the first inlet duct 11 enters the delivery pipe at 8° to the horizontal. As illustrated in Fig. 7, the second inlet duct 12 enters the delivery pipe at 10° to the horizontal. These angles are a selection only and entry may occur between 2 and 30° to the horizontal. The entry of the inlet ducts 11 and 12 are also angled in the horizontal plane, that is the inlet ducts 11 and 12 enter the delivery pipe 4 at between 90° and 180° angling into the delivery pipe 4 from either side.

In the illustrated form, the air comes from a single air pipe 19 but it will be clear that multiple impellers or air pipes may be utilised to deliver air or other gas to the system.

The angle of entry allows for creation of the swirling vortex within the delivery pipe while the impeller or air inlet assembly is out of line with the material flow. Experimental observations

In some forms a 10 m straight pipe section is utilised as a delivery pipe. The pipe may be extended, for example, to 20 m and a constant mass flow rate applied at the inlet boundary to achieve a constant pipe centreline velocity of 55 m/s (equivalent to a generator speed of 750 rpm in the experiment). Through examining two different particle sizes of 1 mm and 2 mm are examined with a total of 20,000 coal particles, injected through the feeder and tracked throughout each of the simulations we can observe the effect of pipe length on drying.

It can be observed that the in-plane tangential velocity is reduced significantly by extending the pipe, which means the swirl strength decays very rapidly within the horizontal pipe. It can be seen that the coal particle moisture level is reduced by 0.3% by doubling the pipe length. It also confirms that the drying efficiency can be improved significantly by reducing the coal particle size. Although the swirl strength is weakened significantly in the second 10 m section of the pipe, the drying curve doesn't seem to be affected as badly. This suggests that the coal drying process is not strongly influenced by the swirl strength in the pipe.

However, swirl could be important in terms of coal particle transport.

In some forms, a velocity measurement was performed at 40 m pipe length and speed of 450 and 600 rpm. Weak velocity swirl was measured. As later observed however, the swirl strength did not seem sufficient to circulate the sand grains (heavy particles) at this length.

In some forms, coal was circulated through the system. The moisture level of the coal particles dropped from the original level of 65.5% to 64% with the first 0.3 s of being conveyed in the swirling vortex of the delivery pipe 4. It is observed that the coal particles continuously to dry from 64% to approximately 60.8% at t = 1.4 s within the cyclone.

In some forms, coarse and fine batches of sand were used for testing. The first test was at 40 m pipe length, then we gradually removed each pipe section and re-run the test. Final pipe length tested was 6 m. Sand samples were collected by GHD Australia, and the results have been tabulated. Note that sand samples were not taken at last few shorter lengths. Particles were conveyed at the bottom of the pipe when swirl is weak and will circularly distributed close to the pipe inner wall when strong swirl was present. Field observation suggested that moisture can be felt outside sand flow stream (at pipe exit), but only happens when particles were swirling, and at higher speed. When pipe length is too short, however, particles exit the pipe at very steep angle and scattered violently.

The cyclone was installed, following pipe length of roughly 24 m. Since the cyclone structure is tall, inlet from pipe is roughly 5 m above the ground. This made the pipe curve upwards from length 7 - 24 m, with approximate angle of 25 - 30°. Coal particles were tested throughout, with and without the cyclone. The dryness results can be referred to the table provided by GHD.

The most obvious problem during the field test is the blow back from material delivery system. Irregular particle size and very large objects within the coal lump may have prevented easy delivery, hence counteracting higher pressure within the pipe became very difficult. This problem was solved by providing a one-way valve for entry from the material delivery system 2.

In some forms, the bulk material may be granulated prior to drying or may be divided according to particle size.

(a) Mean centreline velocity comparison (generator speed at 750 rpm)

Experimental measurements of pipe centreline velocities at various generator speeds and mean centreline pipe velocity at a generator speed of 750 rpm are shown in Figure 8 which shows experimental measurements of pipe centreline velocities at various generator speeds, and right: the mean centreline pipe velocity at a generator speed of 750 rpm. The mean centreline velocity from the simulation is approximately 42 m/s, which agrees well with the experimental measurements.

(b) Streamwise velocity profiles comparison (generator speed 750 rpm) Experimental measurements of centreline velocity profile at two generator speeds of 450 rpm and 700 rpm at x = 13.8 m are shown in Figure 9. This Figure shows experimental measurements of streamwise centreline velocity profile at two generator speeds of 450 rpm and 700 rpm at x = 13.8 m, where z = 0 is at the pipe wall and z =150 mm is closer to the centreline of the pipe. It can be seen that the maximum velocity is not at the centreline but at location towards the pipe wall.

(c) Air temperature comparison (generator speed 750 rpm)

As shown in Figure 10, Temperatures were recorded at the x=2.2 m and 13.8 m for various generator speeds and no measurable temperature change as the air moves from the inlet to the outlet of the pipe. Same behaviour of the air temperature can also be observed in the numerical data at a generator speed of 750 rpm.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word“comprise” or variations such as“comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.