Abstract:
A cyclone separator including vanes along the inside wall of the conical section of the separator to regulate the pitch and thus the axial velocity of the gas flow stream in the separator. By adjusting the pitch of the gas flow stream, the collection efficiency of the separator can be optimized so as to minimize the amount of dust particles which are re-entrained in the gas flow stream exiting the separator.

Description:
BACKGROUND OF THE INVENTION 
   This application claims priority from U.S. Provisional Application Ser. No. 60/374,595 filed on Apr. 22, 2002, which is hereby incorporated by reference. 
   The present invention relates to a cyclone separator. More particularly, it relates to a cyclone separator which includes adjustable vanes along the inside surface of the cone of the cyclone separator. These vanes are adjusted in order to direct the gas flow so as to optimize the separation of particulates from the gas flow. 
   Cyclone separators are often used as primary gas pollution control equipment, ahead of baghouses, for instance, to knock out the larger particles and reduce the particulate loading on the baghouse. It is desirable to optimize the performance of the cyclone separator by minimizing the emission of particulates from the cyclone separator so as to minimize the discharge of particulates into the environment, or to reduce the loading on downstream equipment such as baghouses. 
   Current design practices do not optimize the combination of axial and tangential velocities of the gas flow in the cyclone separator. This results in a stagnation level in some cyclone cones, and in excessive re-entrainment of the dust particles back into the effluent gas flow stream in other cases. 
   SUMMARY OF THE INVENTION 
   The present invention provides vanes in the inside conical wall of the cyclone separator in order to control the axial velocity of the gas flow stream in the cyclone separator. In a preferred embodiment, the angle of the vanes is adjustable. Thus, if the pitch of the gas flow into the cyclone is too steep and the axial flow is too high, the vanes may be adjusted to a shallow angle to flatten the pitch and reduce the axial flow rate. On the other hand, if the pitch of the gas flow is too shallow and the axial flow is too low, the vanes may be adjusted to a more pronounced angle to increase the pitch angle and increase the axial flow rate. 
   In a preferred embodiment, the surface vanes are readily adjustable from the outside of the cyclone separator body so that tests can be performed measuring deposition rates against vane position in order to empirically determine the optimum setting of the vanes for any given gas flow rate, particulate loading, and particle size distribution. 
   In yet another embodiment, the cyclone may have more than one set of vanes at a given elevation of the cyclone, and the angle setting of each set of vanes may be set independently of the angle setting of any other set of vanes. 
   BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1  is a side view, partially broken away, of a cyclone separator with vanes made in accordance with the present invention; 
     FIG. 2  is an enlarged view of the broken-away section of  FIG. 1 , showing the vanes adjusted at a shallow angle so as to reduce the pitch of the gas flow stream; 
     FIG. 3  is the same as  FIG. 2  except the vanes are adjusted to a steeper angle so as to increase the pitch of the gas flow stream; 
     FIG. 4  is a section view taken along line  4 — 4  of  FIG. 1 , showing the vanes; 
     FIG. 5  is an enlarged view of one of the vanes of  FIG. 4 ; 
     FIG. 6  is a broken away view along line  6 — 6  of  FIG. 5 ; 
     FIG. 7  is a perspective view of the portion of the cyclone shown in  FIG. 6 , but also including a lever arm for adjusting the vane; 
     FIG. 8  is the same view as  FIG. 7  but partially exploded; and 
     FIG. 9  is a side view, partially broken away, of another embodiment of a cyclone separator with vanes made in accordance with the present invention, depicting two sets of vanes. 

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  shows a cyclone separator  10  made in accordance with the present invention. The cyclone separator  10  has a continuous side wall  11 , which has a circular cross-section and defines a central vertical axis  13 . The side wall  11  defines a tangential inlet  12  to allow a particulate laden gas, such as air, to enter the body of the cyclone separator  10 . The side wall  11  of the cyclone separator  10  includes an upper cylindrical section  14 , connected to an intermediate frustroconical section  16  (hereinafter referred to simply as the conical section  16 ), followed by a lower cylindrical section  18 . A cylindrical, solids outlet section  22  is connected to the lower cylindrical section  18  via a concentric reducer  20 . A cylindrical, clean-gas-outlet section  28  is located at the top of the cyclone separator  10 , and this outlet section  28  extends a distance into the body of the cyclone separator  10  as shown in FIG.  1 . Typically, particulate laden gas is drawn into and through the cyclone separator  10  by a fan (not shown) located downstream of the cyclone separator  10  and connected to the outlet section  28 . 
   As the gas enters the cyclone separator  10 , the tangential inlet section  12  induces a swirling action to the gas. As more gas enters the cyclone separator  10 , it displaces the gas already in the cyclone separator  10 , causing it to move downwardly along the inside surface  26  of the side wall  11  of the conical section  16 . This creates a downwardly spiraling vortex  24 . As the cross-sectional area of the conical section  16  decreases, the velocity of the gas flow increases, and the centrifugal forces acting on the dust particles carried by the gas flow force these particles against the inside surface  26  of the conical section  16 . These dust particles are carried down along the inside surface  26  and, in a properly sized and designed cyclone separator  10 , these dust particles are deposited into the cylindrical section  18  to be evacuated via the solids outlet section  22 , while the gas flow makes a sharp change in direction to flow up along the central axis  13  of the cyclone separator  10  and out the outlet section  28 . 
   Only those particles which are heavy enough for the centrifugal force acting on them to overcome the force of the gas flow are likely to be removed in the cyclone separator  10 . If the downwardly spiraling vortex  24  is too steep, the gas flow tends to pick up dust particles which have been deposited in the lower cylindrical section  18 , causing these particles to become re-entrained and carried away to the gas outlet section  28 , thereby decreasing the deposition efficiency of the cyclone separator  10 . On the other hand, if the downwardly spiraling vortex  24  is too shallow, the gas flow tends to stall, which causes the dust particles to stall in some portion of the cone, allowing the gas flow stream to carry some of the dust particles away to the gas outlet section  28  before they are collected, once again decreasing the deposition efficiency of the cyclone separator  10 . This condition, also known as roping, not only causes losses in collection efficiency; it also causes undue erosion in the inside surface  26  of the side wall  11  of the conical section  16 . 
   Thus, it is important to find and establish the optimum axial velocity of the gas flow stream to assist in sending the “centrifuged” dust particles to the solids outlet section  22 . The optimum axial velocity will establish the right balance between too much axial velocity (which has the gas stream once again picking up the settled dust particles) and not enough axial velocity (which causes the dust particles to stall in some portion of the cone, allowing the gas flow stream to carry the dust particles away before they settle down). 
     FIG. 2  shows that, if the pitch of the vortex  24  is too steep (the axial velocity of the gas flow stream is too high), the vanes  30  may be adjusted to a shallow angle, which flattens the pitch of the gas flow (as shown schematically by the lines  48  representing the new pitch of the gas flow stream after correction by the vanes  30 ). At this flatter pitch, the gas flow stream is less likely to re-entrain the settled dust particles in the lower cylindrical section  18 , thus optimizing the collection efficiency of the cyclone separator  10 . 
     FIG. 3  shows that, if the pitch of the vortex  24  is too shallow (the axial velocity of the gas flow stream is too low), the vanes  30  may be adjusted to a steep angle, which increases the pitch of the gas flow (as shown schematically by the lines  48  representing the new pitch of the gas flow stream after correction by the vanes  30 ). At this steeper pitch, the gas flow stream is less likely to stall the dust particles as they move downwardly along the inside surface  26  of the side wall  11  of the conical section  16 . The dust particles are conveyed and collected in the lower cylindrical section  18  instead of being carried away to the outlet  28 , thus optimizing the collection efficiency of the cyclone separator  10 . 
   On site tests at different particulate size distributions, different particulate loading, and different pressure drops across the cyclone separator  10  will establish the pitch angle of the vanes  30  which maximizes collection efficiency for differing operational parameters. 
     FIGS. 4 and 5  show the vane assemblies  30  used in the present invention to alter the gas flow stream so as to increase or reduce the axial velocity of the gas steam as required to optimize the collection efficiency of the cyclone separator  10 . Referring to  FIG. 5 , the vane assembly  30  comprises an arcuately-shaped flat plate  32  which, in this preferred embodiment, is made from steel. The plate  32  has an outer edge  34  with a radius which closely matches the radius of the cross-section of the conical section  16  at the location where the plate  32  is installed. The inner edge  36  of the plate  32  generally matches the shape of the outer edge  34 . Toward the middle of the arcuate segment formed by the outer edge  34 , one end  40  of a threaded rod  38  is attached (preferably by brazing or welding) to the plate  32 . A hole  41  through the side wall  11  of the conical section  16  allows the threaded rod  38  to extend from the inside of the cyclone separator  10  to the outside. A rubber washer  42 , a metal washer  44 , and a wing nut  46 , in that order, are threaded onto the rod  38  to secure the plate  32  to the inside of the cyclone separator  10 . The pitch of the vane assembly  30  may be readily adjusted from the outside of the cyclone separator  10  by loosening the wing nut  46 , turning the rod  38  until the plate  32  is at the desired angle, and then re-tightening the wing nut  46  to keep the vane assembly  30  in this new position. As the wing nut  46  is tightened, the rubber washer  42  is compressed against the outside wall of the conical section  16  of the cyclone separator  10 , pulling the outer edge  34  of the plate  32  against the inside surface  26  of the wall  11  of the conical section  16  and holding it in place. 
     FIGS. 6 ,  7 , and  8  show one embodiment of a mechanism for turning the rod  38  to adjust the plate  32 . The threaded rod  38 , which is secured to the plate  32  at one end  40 , has a slotted keyway  48  at its opposite end. A lever arm  50  has a hole  52  and a projection  54  within the hole  52 . The threaded rod  38  extends through the hole  52  (as seen in FIG.  7 ), and the projection  54  slides into the slotted key way  48  in such a way that the longitudinal dimension of the arm  50  is parallel to the longitudinal dimension of the plate  32  inside the separator  10 . In order to adjust the position of the plate  32 , the wing nut  46  is loosened; the arm  50 , installed over the threaded rod  38 , is moved to the desired angle, and the plate  32  follows the movement of the arm  50 . Once at the desired angle, the wing nut  46  is tightened and the arm  50  may be removed, or it may be left in place to give a visual indication of the angular setting of the plate  32  inside the cyclone  10 . The dial face  56  with graduations in degrees is provided on the outer surface of the wall  11  surrounding the rod  38  as a reference to assist the user in setting all the vane assemblies  30  to the desired angular setting. 
     FIGS. 1 ,  2  and  3  show a plurality of spaced-apart plates  32  mounted at evenly spaced angular positions at one level (or height) around the conical section  16 . In this particular embodiment there are eight vane assemblies  30 . However, as shown in  FIG. 9 , two or more levels of vane assemblies  30  could be used within a single cyclone separator  10 , and the vane assemblies  30  at a first axial level may be set at a different pitch than the vane assemblies  30  at a second axial level to progressively affect the pitch of the gas flow stream. In a preferred embodiment (not shown), there are four vanes at a first elevation and four vanes at a second elevation. 
   Empirical testing has established that a single level location of the vane assemblies  30  has been effective in reducing emissions by between 14% and 70%, and it is preferred to provide vanes at two different levels or elevations. The angle of the vane plates  32  relative to the horizontal may be adjusted from zero degrees to 180 degrees. It is preferred that the angle be between plus or minus twenty (20) degrees from the horizontal and most preferable that the angle be between minus five (−5) and plus five (+5) degrees from the horizontal, whether one or two sets of vanes are present, as described later. 
   The axial elevation of the vane assemblies  30  along the wall  11  of the conical section  16  of the cyclone  10  may vary. It may be that the most effective location for the vane assemblies  30  would be to place them within the lowermost 20% to 30% of the vertical height of the conical section  16 . If a second set of vanes is installed, it may be that the most effective location for this second set of vane assemblies  30  would be to place them within the lowermost 20% to 50% of the vertical height of the conical section  17 ′, as described later. 
   The number of vane assemblies  30  may vary depending on the size of the cyclone separator  10 , and particularly depending on the diameter of the conical section  16  at the height at which the vane assemblies  30  are installed.  FIG. 4  shows a preferred configuration of eight (8) vanes  30  evenly distributed around the circumference of the conical section  16 , with each vane  30  extending through an arcuate segment of approximately 22.5 degrees, for a total of 180 degrees, or half of the circumference, occupied by the vanes. It is preferred that any elevation of vanes occupies no more than 270 degrees or three-fourths of the circumference, with the remaining one-fourth or more being spaces between the vanes. This 22.5 degree arc length dimension represents the length of the vane plate  32 . The width of the vane plate  32  is the radial distance between the outer edge  34  and the inner edge  36 , and this width typically is approximately 10% of the diameter of the cyclone at the axial elevation of the vane, which, for a cyclone having a diameter of 10 inches, would be one inch. 
   It is most helpful to change the pitch of the gas flow stream close to the inside surface  26  of the wall of the conical section  16 , as this is the stream which is likely to stall or to re-entrain the dust particles which have been “centrifuged” and are thus being carried downwardly along the inside surface  26  of the wall of the conical section  16 . 
     FIG. 9  depicts another embodiment of a cyclone made in accordance with the present invention. This cyclone  10 ′ is very similar to the cyclone  10  of the first embodiment, except that this cyclone  10 ′ incorporates a second set of vanes  31 ′ in a second conical section  17 ′ of the cyclone  10 ′. This second set of vanes  31 ′ may be oriented at any desired angle, which need not be the same angle at which the first set of vanes  30 ′ are set. It has been determined that this second set of vanes  31 ′ is preferably located from 20% to 50% up the axial height of the second conical section  17 ′. The angle of the vanes  31 ′ from the horizontal may be adjusted from zero degrees to 180 degrees, but it is preferred that the angles be between plus and minus 20 degrees and most preferably between plus and minus 5 degrees from the horizontal. 
   While the embodiment described above shows a simple means for adjusting the angle of the vanes, various other mounting mechanisms could be used to adjust and control the angular position of the vane assemblies  32 . It will be obvious to those skilled in the art that modifications may be made to the embodiments described above without departing from the scope of the present invention.