The disclosed device generally relates to devices used to separate solids from liquids, and specifically to an improved centrifugal separator which includes internal structure which enable the attainment of preferred flow regimes through the separator, resulting in superior separation of solids from the liquid and greater efficiency in operation of the separator.
Centrifugal separators are generally known as a means to separate solids from flowing streams of fluid in which the solids are entrained. The typical configuration of a centrifugal separator is to inject a stream of the influent through a nozzle tangentially into a cylindrical separation barrel. As the injected stream whirls around the inside wall of the separation barrel, the high g forces within the stream cause the solid particles to migrate toward the wall as the whirling stream flows from one end of the separation barrel to the other, typically from an upper elevation to a lower elevation within the separation barrel. The force required to move the particles to the side wall is defined by the equation F=mv2/r, where m equals the mass of the particle, v is the tangential velocity of the particle, and r is the radius of the separator.
At or near a lower end of the separation barrel there is a spin plate which induces a spiral motion to the stream, thus creating a vortex, the liquid of which flows away from the spin plate toward a centrally located structure typically referred to as the vortex finder, and into the exit port. The filtrate exiting the separator is, ideally, substantially free from entrained solids. There is an opening or slot near the spin plate at the lower end of the barrel through which a substantial portion of the entrained solids which are nearer the wall of the separator barrel will pass. These solids accumulate at the bottom of the barrel within a collection chamber. This general type of centrifugal separator is shown in U.S. Pat. Nos. 4,072,481, 5,811,006 and 6,143,175, which are incorporated herein by reference in their entireties for their showing of the theory and practice of such separators.
The function and efficiency of this type of separator are in large part derived from the velocity and smoothness of flow of the stream within the separator. The desired flow regime within the separator is laminar flow, which is characterized by smooth, constant fluid motion. On the other hand, turbulent flow produces random eddies and flow instabilities. Turbulence anywhere in the system results in the need for more power to provide a higher injection pressure, or a reduction in separation efficiency. As turbulence increases, particle entrainment increases in the stream reflected from the spin plate and exiting the separator through the vortex finder.
The increase in power demand can be significant, particularly where high flow rates are required, such as in cooling tower applications where the required flow rate may be 13,000 gpm or higher. Turbulence in the separator can significantly impact the energy demands of the pumps required to drive the stream through the separator.
Turbulence also aggravates abrasion of the internal components of the separator. The solids entrained in the influent are abrasive. In order to generate the substantial g forces required for centrifugal separation of the solids from the liquid, the velocity of the particles and the force of their contact with parts of the separator will result in a substantial wear rate that can only partially be compensated for by the use of abrasion resistant materials such as steel alloys. Thus, non-turbulent and smooth flow results in reduced wear throughout the entire system. However, notwithstanding improvements which have been made in the art in reducing turbulence throughout various zones within the separator, the inventor herein has discovered that there remain portions of the known cylindrical centrifugal separators which continue to present a challenge in achieving non-turbulent flow. In particular, as the whirling stream approaches the portion of the separator in axial adjacency to the spin plate, the smooth flow is prone to transition into turbulent flow, resulting in reduced separation efficiency and abrasion of the spin plate and associated structures. It is desirable that the collection chamber be maintained in a quiescent condition to facilitate the settling of the solids in the collection chamber, and reduce the re-entrainment of solids into the liquid which is returned from the collection chamber to the separation chamber.
It follows that reduction of turbulence throughout the system can importantly improve separation, reduce power cost, extend the time between repairs, and extend the useful life of the device. The present invention is directed toward reducing turbulent flow throughout centrifugal separators, particularly in the portions of the separator adjacent to the spin plate.
A centrifugal separator which incorporates this invention includes a separator barrel. This barrel has a cylindrical internal wall which forms an axially-extending separation chamber. The stream is injected tangentially into the separation chamber, typically at an upper elevation, swirling down the wall in a helical pattern to a portion of the barrel, usually, but not necessarily, at a lower elevation, where the stream encounters a central structure for reversing the direction of flow of the stream, and inducing rotation in the stream. This structure is referred to herein as the spin structure or as the spin plate. Below the spin plate there is a collection chamber and there is conduit means between the spin plate and the internal wall through which the solids can pass through to the collection chamber. In accordance with known principles, the spin plate causes the central portion of the whirling stream to reverse its axial direction, and flow upwardly through an outlet barrel centrally aligned within the separator barrel, exiting the separator through outlet port at the top of the separation chamber.
In accord with the present invention, a rod having an upper end and lower end is disposed within the separation barrel such that the rod is centrally aligned within the separation barrel, and the lower end of the rod is affixed to or disposed within the spin structure and the upper end is positioned within a portion of the outlet barrel. As noted above, the term spin plate may refer to the spin structure. However, because the term suggests a two-dimensional configuration, the term spin plate may refer specifically to the top surface of the spin structure, while the term “spin structure” may also refer to three dimensional structures, such as the conical embodiments disclosed herein.
Surprisingly, the inventor herein has observed that the presence of the axially-centered rod between the spin plate and the outlet barrel reduces the occurrence of turbulence in the portion of the separation barrel in axial adjacency with the spin plate. Moreover, the presence of the rod stabilizes the axial position of the vortex. This stabilization reduces the tendency of the vortex, particularly in the portion of the separation barrel near the spin plate, to migrate into the path of the oncoming solids-laden stream, which is flowing tangentially along the inner wall toward the spin plate.
Decreasing the turbulence in the barrel adjacent to the spin plate and also decreasing the intrusion of the vortex into the oncoming solids-laden stream substantially reduces the entrainment of solids in the vortex, and thus increases the efficiency of the separator. The inventor herein has further found that there is even greater stabilization of the vortex and reduced tendency for turbulent flow to be induced if the spin plate itself is formed by the top surface of a truncated cone, where the truncated cone comprises the top surface, a base, and a conical surface extending from the base to the top surface and the truncated cone is disposed between the separation chamber and the collection chamber. The collection chamber may also have a larger diameter than the separation barrel.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings.
An acceptance chamber 118 is formed by the outer housing 104 around the upper end of the separation barrel 102. The acceptance chamber 118 is annularly-shaped and fits around and in fluid-sealing relationship with the separation barrel 102 and is separated from the lower portion of the outer housing 104 by dividing wall 126. An injector nozzle 120 through the wall of the outer housing 104 is directed tangentially into the acceptance chamber 118. The injector nozzle 120 injects the solid-laden liquid stream under pressure into the acceptance chamber 118. This creates a circular flow between wall 122 of the outer housing 104 and the outside wall of the separation barrel 102. Entrance slots 124 through the wall of the separation barrel 102 pass the stream from the acceptance chamber 118 into the separation barrel.
The separation of solids from liquids is derived from fields of g force. The stream is injected into the separation barrel 102 at a high velocity, and whirls as a swiftly flowing helically moving stream from the upper end to the lower end of the separation barrel. In the separation barrel, the centrifugal forces are much greater than the gravitational force, and particles P are forced outwardly by centrifugal action.
The smaller the diameter of the separation barrel 102, the greater the centrifugal force becomes for the same linear speed along the inner surface of the barrel. At or near a lower end of the separation barrel 102, the spin plate 110 induces a spiral motion to the stream, thus creating a vortex. The liquid of the vortex flows away from the spin plate upward towards the outlet barrel 114, as depicted by the upwardly pointing arrows in
At or near the lower end of the separation barrel 12 there is a spin structure 20 which generally extends normal to the central axis of the separation barrel. Spin structure 20 may comprise a spin plate similar to that of spin plate 112 of the separator 100 depicted in
An annular opening 22, or other conduit means is left between the spin structure 20 and the inside wall of the outer housing 14, which allows the passage of solids from the separation barrel 12 into the collection chamber 16. An outlet barrel 24 is centrally located within the upper end of the separation barrel 12. The outlet barrel 24 includes an exit tube 26 for exit of treated liquid.
An acceptance chamber 28 is formed by the outer housing 14 around the upper end 36 of the separation barrel 12. The acceptance chamber 28 is annularly-shaped and fits around and in fluid-sealing relationship with upper end 36 of the separation barrel 12 and is separated from the lower portion of the separation barrel by dividing wall 30. An injector nozzle 32 through the wall of the outer housing 14 is directed tangentially into the upper end of the acceptance chamber 28, above the upper end 36 of the separation barrel 12. The injector nozzle 32 injects the solid-laden liquid stream under pressure into the acceptance chamber 28. This creates a circular flow between wall 34 of the outer housing 14 and the outside wall of the upper end 36 of the separation barrel 12. Entrance slots 38 through the wall of the upper end 36 of the separation barrel 12 pass the stream from the acceptance chamber 28 into the separation barrel. Entrance slots 38 may be tangential to promote the tangential flow pattern of the fluid. However, it is to be appreciated that other mechanisms may be employed to promote a tangential flow pattern.
As with the separator depicted in
The smaller the diameter of the separation barrel 12, the greater the centrifugal force becomes for the same linear speed along the inner surface of the barrel. At or near a lower end of the separation barrel 12, the spin structure 20 induces a spiral motion to the stream, thus creating a vortex. The liquid comprising the vortex flows away from the spin structure 20 upward towards the outlet barrel 24 (or vortex finder) and out through the exit tube 26.
Distinctive from the known separators is the disposition of rod 40 between the spin structure 20 and the outlet barrel 24. Rod 40 may be hollow or solid. Rod 40 is centrally aligned within spin structure 20 and maintained in position by hub 42. Rod 40 comprises an upper end 50 and may comprise a lower end 52, which extends below the spin structure 20. The upper end 50 is disposed within a portion of outlet barrel 24. As shown in
The internal support structure 54 may not be necessary on smaller units and very large units. The support structure 54 may comprise a central hub 56 into which the upper end 50 of the rod 40 is inserted. The support structure 54 may further comprise flow vanes 58, through which the rising fluid stream flows. The flow vanes may be comprise a shape and pitch which further stabilizes the flow of the fluid stream. The benefits of the flow vanes 58 are particularly noticed in the start up and shut down of the separator, and during the opening and/or closing of valves. The flow vanes 58 help keep the flow trajectories inside the separator intact for longer periods of time, thus minimizing the drops of solids removal efficiency which are typically observed when there are abrupt changes in flow. As depicted in
Rod 40 may also comprise radial support members 60 which attach to the lower end 52 of the rod, where the radial support members are affixed to the inside wall of the collection chamber 16. It is to be appreciated that the beneficial flow characteristics of the present invention are induced, in part, by the portion of the rod 40 which is between the top 23 of spin structure 20 and the outlet barrel 40. Therefore, while the portion of rod 40 inserted within spin structure 20 may be beneficial in terms of supporting the spin structure and providing stability to the rod, other embodiments of the present invention may have rods which are configured differently below the spin structure.
As shown in
While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. Thus the scope of the invention should not be limited by the specific structures disclosed. Instead the true scope of the invention should be determined by the following appended claims.
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Number | Date | Country | |
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20110294643 A1 | Dec 2011 | US |