Field of the invention

The present invention relates to a damper assembly for controlling the flow of powders in pneumatically conveying pipelines, e.g. controlling the flow relative to other lines, and to methods of processing materials, especially powders.

Particularly the invention relates to a damper assembly comprising a grooved plate. Such a grooved plate can be positioned relative to the flow of powder in a pneumatically conveying pipeline such that a pressure drop can be generated based on the angular positioning of the damper assembly relative to the flow.

Background of the invention

There are many industries which involve conveying, e.g. pneumatically conveying, powdered material. These systems are generally required to balance the mass flow of air and the pneumatically conveyed powdered material. Many of these systems have an arrangement where several pipes of varying static pressure drop resistance are all sourced from the same reservoir. The arrangement of the several pipes can vary and can, for example, comprise one reservoir source feeding from 2 to 20 individual "outlet" pipelines, each with varying static pressure resistances. This arrangement can be seen in many applications which convey bulk materials, such as, limestone, cement or fossil fuels, e.g., coal. Generally, when fossil fuels, such as coal, are used in power generation plants, for example a coal fired power station, the fossil fuel will be pulverized to produce the fossil fuel in substantially powdered form. The bulk material, such as, limestone, cement or fossil fuel, even after pulverisation, will generally comprise powders of varying coarseness and generally there will be a large particle size distribution. In the multi-outlet pipe arrangement hereinbefore described, the flow of air will split in accordance with the ratio of the different static pressure drops of the various "outlet" pipes and generally, the material of certain coarseness will tend to follow the split of the mass air flow which might consequently lead to an uneven distribution of material of a given coarseness. Thus, it will be understood by the person skilled in the art that it is of importance to attempt to balance these static pressure resistances in order to achieve the desired even distribution of material. It has been shown that simple, square profile, orifice plates within the "outlet" pipes can be used to impose an additional pressure drop when balancing the static pressure resistance for clean air, i.e. air which contains no powdered material.

There are also numerous other devices that have been created for the purposes of balancing air flow in pipes in the arrangements hereinbefore described. However, generally, they all function on the same basis of imparting an additional static pressure resistance or pressure drop to the multiple pipelines to attempt to balance them equally. For clean air alone, i.e. air which contains no powdered material, the systems known in the art will work by balancing the air in accordance to the static pressure drop resistance. However, when powdered materials are involved in the pneumatic conveying process and the path to their destination is quite tortuous, as is the case in all practical (industrial) applications, the total pressure resistance will vary considerably from the static pressure drop resistance generated by the pipeline geometry alone.

Under lean phase pneumatic conveying, i.e. where the conveyed (powdered) material occupies less than 15% of the volume of the conveying conduit (pipeline), the powdered material is prone to the formation of so called "particle ropes". These "particle ropes" are formed by inertial and gravitational effects acting on the powdered material itself, for example, the powdered materials will generally gather in a particular area of the pipe and behave differently to a suspended transitory material.

These differences exhibited by the "particle ropes" hereinbefore described can usually be observed by the amount of energy required to convey the powdered material, which generally equates to an additional pressure resistance based on the position of the "particle rope(s)". As the position of the rope(s) within the conveying system changes according to, inter alia, the air.solid ratio; the air velocity; the particle size and the particle density, the conveying system can experience a range of different pressure resistances dependent on one or more of the factors described.

This means that, depending upon the arrangement of the conduit (pipeline) network, the position of one or more valves necessary to adjust the air or material flow within the conveying system, might need to be altered during operation of the system to maintain an equal pressure drop resistance and a steady flow powdered material. Many of the devices known in the art that impart a pressure drop in such conveying systems are fitted with actuators allowing them to be adjusted according to either a mass or pressure drop reading, Some of these systems are even connected to a feedback system.

In the operation of existing conveying systems in order to impart a change to the system whilst operating with air laden with powdered material it is usually necessary to close off the conduit (pipeline) either fully or at least to a significant degree. The operating system generally utilises a valve or a damper. However, the conventional design of a damper assembly is such that "particle rope(s)" can have a significant impact on one or more of the faces of the damper assembly. Under ordinary operating condition the "particle rope" loses momentum and when the material of the "particle rope" is re-entrained into the mainstream flow of air or the powdered material itself creates an additional localised pressure drop in or around that location. In addition, many conventional damper assemblies have long, flat, continuous areas, e.g. positioned behind the flow, which can create a ledge on which powdered material or "particle rope(s)" can gather, thus exacerbating the problem.

Summary of invention

Thus, the device of the present invention is designed to overcome these issues and more particularly it is designed to impart a pressure drop resistance which is desirably proportional to the angle of the damper plate within the conveying system.

The device described in this invention generally operates in a similar manner to prior art conveying systems, but is designed with the existence of the aforementioned "particle ropes" in mind. Thus, according to first aspect of the present invention there is provided a damper assembly which comprises a damper plate in the form of a grill, e.g. a plurality of blades positioned adjacent to one another and with channelled slots there between, such that the blades of the damper plate grill make up from 65 to 80% of the surface area of the damper plate, the damper plate being rotatably mounted about an axle.

Preferably, the blades of the damper plate make up from 65 to 70% of the surface area of the damper plate. Thus, the damper plate will comprise the general shape and dimensions of a cross section of the conduit in which the damper plate is intended to be positioned when in use.

The damper assembly of the present invention designed to work in unison with other damper assemblies of the same type to balance the relative mass flow of air and pneumatically conveyed powder down each line. The damper assembly consists of an elliptical cross section of conduit designed to interface with the existing conveying line. Into this cross section is placed a circular shape which will fill and leave approximately of greater of the cross section when fully closed. This is achieved by having profiled slots manufactured into the circular shape. The circular shape is actuated by use of a torsional rod to position the circular plate in relation to the flow.

In use, when the damper plate is fully closed in situ the total surface area of the damper plate that is not closed to the flow of air and/or entrained powdered material is from 20 to 35%, preferably from 25 to 35%, e.g. 30%, of the total cross section of the conduit, i.e. the area of the channelled slot(s) between the damper blades is from 20 to 35%, preferably from 25 to 35%, e.g. 30%, of the surface area of the damper assembly. The axle is substantially perpendicular to the longitudinal axis of the conduit or pipeline, i.e. perpendicular to the direction of flow of air or the (entrained) powdered material.

The damper blade may comprise any conventionally known size and/or shape of a conventional "fan" blade. The damper plate may comprise channelled notches as hereinbefore described that are constructed from ellipses, i.e. are elliptical in shape.

Hence the entire damper plate can be constructed of a set of elliptical shapes stacked together. Alternatively, the damper plate may be provided with notches that are constructed from diamond or rhombus shapes or an n-gonal pyramid shape or an n- gonal bipyramid shape. Hence the enter plate can be constructed from a set of diamond or rhombus shapes or an H-gonal pyramid shape or an n-gonal bipyramid shapes stacked together.

The number of damper blades which make up the damper plate or grill may vary according to, inter alia, the size, i.e. the cross sectional area of the conduit, the nature of the conveyed material, etc. Desirably the number of blades is substantially the same on either side of the damper axle, i.e. the damper plate is substantially symmetrical about the damper axle. The invention described has been created to balance the mass flow discrepancies between several conduits originating from a common source. It is designed to do so by affecting a change to the static pressure drop resistance in the respective conduits. The invention described here is designed so that material and air can freely flow round the device even when closed. The channelled slots allow the particle ropes to move through the plate without causing additional pressure drop resistance from having to re-entrain the material. The invention is shaped like a symmetrical aerofoil, from this shape it creates the pressure drop by creating gradually increasing area of increased turbulence in the pipe. The size of this area is directly proportional to the angle of attack that the circular plate adopts. This means that if the pressure drop resistance imposed to the flow is proportional to the position then a PID controller (Proportional Integral Derivative controller), reading various static pressure readings, can be used to control the position without losing control. The damper assembly may be actuated manually or as part of a simple PID feedback system monitoring operational conditions of a system and making changes to the position of the damper in response. Therefore, according to a further aspect of the invention we provide a material flow control system comprising;

(i) a damper assembly as hereinbefore described; and

(ii) a PID controller adapted to control the position of the damper assembly. The invention consists of a damper assembly which comprises an axle, conduit cross section and damper plate. The conduit cross section is arranged so that with the blade fully closed the total surface area not blocked is 30% of the total cross section of the conduit. This includes the area cut out of the damper blade.

Generally, the damper assembly as described herein comprises a portion of a conduit which is expanded (widened e.g. in diameter) so that when the damper plate is closed that the area not of the conduit that remains unblocked due to the gap and the plates notches is equal to approximately 30% of the surface area. The damper plate will be generally elliptical with an aerofoil profile, the damper has notches taken out of the elliptical shape giving the plate a fishbone or comb-like shape and an axle on which the damper plate is fixed and rotated. The channelled slots or notches cut into the elliptical damper plate are designed to make it easier for material to pass through the plate at large angles of approach, thus preventing additional unexpected static pressure drop resistance from having to re-entrain particles of material that may have lost significant momentum.

The damper plate is generally adjustable through, for example, up to 90 degrees of operation. When in use the angle of incline of the damper plate, relative to the mainstream fluid flow, is proportional to the intensity of the area of turbulence and is in turn proportional to the amount of static pressure drop resistance it contributes to the overall static pressure drop resistance in the conduit. The damper plate is designed to be able to be adjusted and held in any position from 0 to 90 degrees of rotation depending on the requirements for static pressure drop resistance. The damper plate itself is elliptical, and the plate and blades may be made from a variety of materials depending upon, inter alia, the intended use of the damper assembly, the powder to be conveyed, etc. Thus, the damper plate and blades may be made from the sane or different materials including, iron, e.g. cast iron, steel, e.g. white steel, ceramics, plastics, etc. The damper plate and blades may be cast from a hard wearing material such as cast iron. The cast iron may be enhanced by the inclusion of one or more alloying elements such as nickel (Ni), chromium (Cr), and/or molybdenum (Mo), for example, Ni-Hard, which is generally a white iron containing 4 to 5% nickel and up to 1.5% chromium. Alternatively, the plate and blades may be a high endurance ceramic, such as silicon carbide. The blade is cast in the shape of a symmetrical aerofoil. This shape is designed to generate the area of turbulence based on the angle of attack into the flow. The greater the angle of attack the greater the static pressure drop added to the system. When the damper plate is in the fully opened position, the shape helps contribute minimal pressure drop to the system.

The unique slots in the damper blade are arranged in such a way that material passing through the blade area does not cause a significant loss of momentum which can lead to additional and unstable static pressure drops. The slots' width and depth are variable based on the total diameter of the conduit and the predicted mainstream velocity.

The position of the damper plate will normally be positioned and actuated utilising an external pneumatic actuator. This pneumatic actuator might be controlled manually or by an automated system. The system is likely to be operated with a feedback circuit constantly monitoring the pressure difference between two points on the pipe work to determine the static pressure drop resistance difference.

According to a further aspect of the invention we provide a method of controlling the flow of material in a conduit which comprises the use of a damper assembly as hereinbefore described.

The method according to this aspect of the invention generally comprises altering the static pressure drop in a conduit by creating an area of turbulence behind the damper assembly.

Brief Description of the Drawings

The invention will now be described solely by way of example and with reference to the accompanying example and drawings in which:

Figure 1 is a perspective view of the damper assembly;

Figure 2a is a plan view of the damper assembly;

Figure 2b is a side view of the damper assembly;

Figure 3a is a perspective view of the damper;

Fig 3b is a cross-sectional perspective view of the damper;

Figures 4a, 4b and c are cross-sectional views of the conduit, illustrating the damper in the a) fully closed position, b) partially closed position, and c) fully open position;

Figure 5a is a perspective view of the damper with an alternative blade profile; and

Figure 5b is a cross-sectional perspective view of the damper with the alternative blade profile of 5a. Referring to Figure 1 a damper assembly 1 comprises a damper 2 housed in a conduit section 3. The conduit section 3 comprising an inner wall 4 and an outer wall 5 and being provided with a peripheral rim 6 and 7 at either end 8 and 9 of the conduit section 3. The damper 2 is in the form of a grill which comprises a plurality of blades 10 with spaces 11 therebetween. The blades 10 are shaped and dimensioned to form a substantially snug fit with the inner wall 4 of the conduit section 3. The damper 2 is also provided with an axle 12. It will be understood that whilst it is desirable that the axle 12 runs the length of the damper, it may be possible under certain uses for the axle to only comprise a portion of the length of the damper assembly. The axle 12 desirably protrudes through the outer wall 4 of the conduit section so as to enable it to mechanically engage with a motor 13. The damper 2 is shown in the fully "closed" position, i.e. the plane of the damper 2 is perpendicular to the longitudinal axis of the conduit section 3. The peripheral rims 6 and 7 are provided with one or more apertures 14 thus enabling the damper assembly 1 to be fastened in place in an existing pipeline assembly (not shown).

Referring to Figure 2a a damper 2 is housed in a conduit section 3. The damper assembly 1 comprises a damper 2 being made up of a damper body 15, the body 15 being provided with a plurality of blades 10 protruding from the damper body 15 with spaces 11 therebetween. The blades 10 are shaped and dimensioned to form a substantially snug fit with the inner wall 4 of the conduit section 3. The damper 2 is also provided with an axle 12 located on or through the outer wall 5. The axle 12 is also provided with a motor 13. The peripheral rims 6 (and 7 not shown) are provided with one or more apertures 14 thus enabling the damper assembly 1 to be fastened in place in an existing pipeline assembly (not shown). Referring to Figure 2b a damper assembly 1 comprises a conduit section 3. The conduit section 3 comprises an outer wall 5 and a peripheral rim 6 and 7 at either end 8 and 9 of the conduit section 3. The damper (not shown) is also provided with an axle 12 and a motor 13.

Referring to Figure 3a a damper plate 2 comprises a damper body 15 provided with a plurality of blades 10 extending therefrom and with spaces 11 therebetween. The blades 10 all being in substantially the same plane and being shaped and dimensioned to form a substantially snug fit within the inner wall of the conduit section (not shown). The damper 2 is also provided with an axle 12.

Figure 3b is a cross-sectional perspective view of the damper. Referring to Figure 3b, so as to generally reflect and form a snug fit within the inner wall of the conduit section (not shown) the length of each of the blades 10 of the damper 2 will vary so that the damper 2 substantially mirrors the internal profile of the conduit section (not shown). Each of the blades 10 is profiled, such that each blade is substantially thicker at one end and is tapered to be thinner at the other end. More precisely, an individual blade 10a comprises a first end 16 and a second end 17. The first end 16 of the blade 10a is adjacent, attached or integral to the damper body 15 and the second end 17 of the blade 10a is distal to the damper body 15. The second end 17 of the blade 10a is generally thinner, i.e. considering the thickness in the plane substantially perpendicular to the axis, than the first end of 16 of the blade. Referring to figures 4a, 4b and 4c are cross-sectional views of the damper assembly 1 comprising a damper 2 housed in a conduit section 3. The conduit section 3 comprising an inner wall 4 and an outer wall 5 and being provided with a peripheral rim 6 and 7 at either end 8 and 9 of the conduit section 3. The direction of air and/or entrained powdered material flow in use is indicated by the arrow. Thus, in figure 4a the damper 2 is substantially perpendicular to the direction of flow and the damper is fully closed. The flow of air or entrained powdered material is not fully blocked but is permitted by the spaces (11 not shown) between the blades 10. In figure 4b the damper is partially closed therefore a proportion of air or entrained powdered material can pass around the periphery 18 of the damper and the remainder will pass through the spaces (11 not shown) between the blades 10. In figure 4c the damper is fully open therefore no (or a minimal amount) air or entrained powdered material will pass through the spaces (11 not shown) between the blades 10 and substantially all of the air or entrained powdered material will pass around the periphery 18 of the damper 2.

Referring to figures 5a and 5b a damper 2 comprises a damper body 15 provided with a plurality of blades 10 extending therefrom and with spaces 11 therebetween. The blades 10 are generally in the form of fins in that they are generally thinner in the plane perpendicular to the axis. In addition, although generally the blades will be equidimensional on either side of the damper body 15 at the two axial ends 19 and 20 of the damper 2 the blade 10c and lOd protrudes on only one side of the body 15. In the illustration shown the blade 10c at one end 20 is on the opposite side 21 of the body 15 as the blade lOd at the other axial end 1 of the body 15. Example 1

Experimental Test Method.

The testing procedure involved using 1/3 test scale rig located in United Kingdom. The rig is capable of running at operating conditions which are dynamically and geometrically similar to the set ups present in UK power stations. The rig operated under a negative suction and utilises pumice as the powder fraction in the tests.

The set up for this experiment involved a large pipe, which had its material homogenised by a rope breaker, and then two pipes of differing lengths and number of bends. Both pipes terminated at the same height into weigh hoppers. Both pipes had the pressure drop across their complete length measured individually.

The shorter of the two pipes, which also corresponded to the pipe with the lowest pressure drop, had a 173 ^rd scale of a Coal Flo™ valve (the damper assembly of the present invention) installed in it. This had a differential pressure transducer attached across it to measure the individual pressure drop across it.

The experimentation on the rig was divided into three separate sections:

1.) To demonstrate that the Coal Flo™ blade could affect the pressure drop resistance down an individual line and that the change was linear and predictable across a range of conditions, including: different air velocities; with and without a powder fraction and with different loads of powder fractions. 2. ) To prove that by affecting this additional pressure drop it was possible to linearly affect on the split of the material in the pipes and to achieve a balance between the two lines.

3. ) To demonstrate that it was possible with an open loop feedback system to utilise a pneumatically actuated Coal Flo™ valve to balance the flow.

The tests demonstrated that the Coal Flo™ valve could be used successfully in all three cases.