Abstract:
A new valve is designed for the transport of solids using a motive fluid. The valve includes an inlet conduit for carrying solids, where the solids are fed through gravity. The solids are carried by fluid transport out an outlet where the outlet conduit has a smaller diameter than the inlet conduit carrying the solids. The conduit should be sufficiently smaller to prevent instability in the flow. A second inlet provides the source of motive fluid to drive the transport of solids.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the conveying of particulate solid materials, and particularly the handling of solid particulate materials where the solids are transported by a fluid. 
     BACKGROUND OF THE INVENTION 
     There are many processes in the petrochemical industry that use catalysts and adsorbents. The catalysts and adsorbents are frequently transferred between operational units and regeneration units, and often there is a continuous flow of the catalyst and/or adsorbent through the system comprising the operational unit and the regeneration unit. 
     One common system that requires the continuous flow of solids is a transport reactor. In hydrocarbon processing, transport reactors are commonly used. In a transport reactor the catalyst bed moves through the reactor where the catalyst contacts the reactants. This is different from fixed bed reactors where the catalyst is held in place by screens or other devices, or ebullated bed reactors where the catalyst particles circulate within the reactor, but are not carried out of the reactor. In a transport reactor, the catalyst is carried through the reactor by the fluid reactants passing through the reactor. Although the general direction for a transport reactor is in an upward direction, it can also be downward, horizontal, or at some angle in between horizontal and vertical. In the case where the reactor is vertical and the transport is in the upward direction, the reactor is called a riser reactor, where the catalyst is introduced in the bottom of the reactor and is carried up through the reactor. 
     Riser reactors are commonly used in hydrocarbon processing. A fluid hydrocarbon reactant contacts a solid catalyst carried along by a fluid, where the catalyst and fluid are introduced at the bottom of the reactor and the fluid and catalyst rise up through the reactor in a fluidized state during which the process reaction takes place. Upon exiting the riser reactor, the fluid and catalyst enter a separation zone where the catalyst disengages from the fluid and settles by gravity to the bottom of the separation zone. The catalyst is then withdrawn and sent to a regeneration unit, before recirculation to the riser reactor. 
     Several methods are used for controlling the introduction of solid catalysts to the bottom of a riser reactor, or for any process unit where a solid is introduced and carried through the process unit. The means for control include slide valves, lock hoppers, screw conveyors and L-valves, to name a few. The L-valve is a specific type of a non-mechanical valve. These valves have no moving parts and control the flow of solids through the introduction of a fluid to carry the solids along. In an L-valve, solids are fed by gravity to a downcomer, or a vertical pipe. The downcomer intersects a horizontal pipe, or exit arm, giving the appearance similar to the letter “L”. A motive fluid inlet located at the junction opposite the exit arm, or intersecting the vertical leg proximate to the “L” junction provides the energy to carry the solids out the exit arm. Control of the L-valve is through the control of the flow of a motive fluid to carry the solids out the exit arm. The solids flow includes fluid transported with the solids down through the vertical pipe, where the fluid in the horizontal pipe provides a motive force to facilitate all of the fluid carrying solids out the second arm, or exit of the L-valve. Generally, the solids flow rate can be controlled by adjusting the rate at which fluid is introduced at the junction. However, there are control problems due to flow instabilities for certain flow regimes, and notably when the fluid is a liquid. 
     Accordingly, there is a need for improved apparatuses to reliably feed solids at a controlled and reproducible rate while reducing the attrition of catalysts and adsorbents in systems with continuous solids circulation. 
     BRIEF SUMMARY OF THE INVENTION 
     In a transport reactor, where a solid catalyst is circulated through the reactor, the flow of solid catalyst can be controlled by several means. One method is the use of an L-valve. An L-valve is a valve for controlling the flow of solids without the use of mechanical parts, but through control of a motive fluid to carry the solids. An L-valve of the present invention comprises a first inlet conduit for carrying solids and having a first diameter, and an outlet conduit having a second diameter, where the second diameter is less than 80% of the first diameter. The outlet conduit is oriented at an angle between 45 degrees and 135 degrees relative to the first inlet conduit. The L-valve further includes a second inlet for the admission of a motive fluid, and where the second inlet is substantially aligned with the outlet conduit. The use of the L-valve generally has the first inlet conduit oriented vertically and the solids are fed by gravity to the first inlet conduit. And the outlet is substantially oriented horizontally at a right angle to the first inlet conduit. 
     Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of the instability control problem; 
         FIG. 2  is a diagram of an embodiment of the L-valve of the present invention; 
         FIG. 3  is a diagram of a second embodiment of the present invention with the outlet conduit end extending partially across the first inlet conduit end, and with a portion of the upper part of the conduit wall removed; 
         FIG. 4  is a diagram of a third embodiment of the present invention where a dam or other obstruction is used in the outlet conduit instead of a conduit diameter reduction; and 
         FIG. 5  is a diagram of an embodiment with the motive liquid positioned on the downcomer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is important to transport a solid material in a smooth manner with little or no holdup, and to prevent the solid from being ground up, thereby reducing the usefulness of the solid. It has been found that with a liquid flowing medium in an L-valve, there is a region of instability and where good control is not achievable, particularly in a liquid medium, with an L-valve as described in the literature. Physical modeling tests were performed to determine how to overcome the instability flow problem, and it was discovered that the control problem was overcome by making the horizontal line in the L-valve smaller than the vertical downcomer, or providing a restriction in the horizontal line, such as a flat plate with an orifice of smaller diameter than the vertical downcomer. It was found that providing the line size reduction was most effective, providing stable control with a minimum of additional pressure loss, if the change was a sudden contraction at the inlet of the horizontal line. 
     The instability problem can be seen in the representational diagram of  FIG. 1 . Without the instability, the flow should follow a smooth curve  52  providing control of the solids flow through adjusting the motive fluid flow. With the instability flow  54 , the flow of solids suddenly becomes very high, and stays at a higher level of solids flow, or circulation, through a broad range of motive fluid flow. The solids flow increases gradually to a threshold level  56 , where a jump in solids flow occurs, resulting in loss of control over the rate of solids flow. While the preferred operation is with a liquid motive fluid, a dense gas is also believed to have similar behaviors, and therefore the term fluid will be used hereinafter to encompass the use of either a liquid or a dense gas or vapor. 
     In experiments to understand the flow problems, the motive fluid used was liquid water and the particulate solids were glass beads. The experiments consisted of operating L-valves constructed of standard steel or plastic pipe fittings varying from ¾″ to 4″ nominal size over a range of solids flows from zero to the point where no increase in solids rate could be achieved, or the solids get fluidized in the L-valve vertical inlet line. The solids flow was controlled by adjusting the liquid flow to the L-valve junction, and at a threshold liquid addition rate the solids flow jumped out of control, where the solids flow increased to a high level and remained at that level. 
     The invention is a valve for the transport of solids with a fluid. The control of the flow of solids is important for the control of processes that have a continuous flow of solids, such as transport reactors where a fluid carries solid catalyst into a reactor. The valve  10 , as shown in  FIG. 2 , comprises a first inlet conduit  12  for carrying solids, and having a first inlet conduit end  14 . The valve  10  further includes an outlet conduit  16  oriented at an angle between 45 degrees and 135 degrees relative to the first inlet conduit  12 . The inlet conduit  12  has a first diameter  18 , and the outlet conduit  16  has a second diameter  20 , where the second diameter  20  is less than 80% of the first diameter  18 , and the outlet conduit  16  has an outlet conduit end  22 . The first inlet conduit  12  has a side  24  proximate to the outlet conduit end  22 , and a side  26  distal to the outlet conduit end  22 . While the configuration in  FIG. 2  shows the T intersection for the L-valve, the inlet conduit  12  includes a vertical pipe that extends upward for the complete vertical portion of the inlet conduit. The length and pressure differential in the entire inlet conduit is a factor in determining the amount of motive fluid required in the operation of the L-valve. The configuration in  FIG. 2  indicates the use of a flanged T for the L-valve. This facilitates the maintenance and/or replacement of parts, but is not necessary for this invention. In one embodiment, the outlet conduit end  22  is substantially aligned with the proximate side  24  of the first inlet conduit  12 . The valve further includes a second inlet for carrying fluid, and where the second inlet  30  is substantially aligned with the outlet conduit  16 . 
     In an L-valve, the general configuration is that the outlet is approximately at a right angle to the solids inlet conduit  12 , and it is preferred that the outlet conduit  16  be oriented at an angle between 80 degrees and 100 degrees relative to the first inlet conduit  12 . The operation of the L-valve is partially controlled by the gravity feeding of solids into the solids conduit  12 , and it is preferred that the first inlet conduit be oriented at an angle within 20 degrees of vertical, where the vertical is the direction parallel to the direction of gravity. 
     In a preferred configuration, the second diameter  20 , or diameter of the outlet conduit  20 , is between 50% and 75% of the first diameter  18 , or diameter of the solids inlet conduit  12 . By reducing the outlet diameter  20  size relative to the solids inlet diameter  18 , the flow produced by the motive fluid carrying the solids and fluid entering from the first inlet  12 , is stabilized and can be smoothly controlled through the desired range of motive fluid and solid flows as depicted by curve  52  in  FIG. 1 . 
     In an alternate embodiment, the L-valve  10  includes an outlet conduit  16  with an outlet conduit end  22  where the outlet conduit end  22  extends a distance across the solids inlet conduit end  14 . In this embodiment, as shown in  FIG. 3 , the valve  10  comprises a first inlet conduit  12  for carrying solids and having a first diameter  18  and a first inlet conduit end  14 . The valve  10  further includes an outlet conduit  16  having a second diameter  20 , where the second diameter  20  is less than the first diameter  18 , and where the outlet conduit  16  is oriented at an angle between 45 degrees and 135 degrees relative to the first inlet conduit  12 . The valve  10  includes a second inlet  30  for carrying the motive fluid, and is substantially aligned with the outlet conduit  16 . The outlet conduit end  22  extends at least 20% of the distance across the first inlet conduit end  14 . It is preferred that the outlet conduit which comprises an outlet conduit wall  28  has a portion of the outlet conduit wall nearest the first inlet conduit end  14  removed from the outlet conduit end  22  to a position on the outlet conduit that intersects the first inlet conduit  12 , at the first inlet conduit side  24  that is proximate to the outlet conduit  16 . 
     For this valve, the general configuration is for the solids inlet conduit  12  to have a vertical orientation, and the outlet conduit  16  to have a horizontal orientation, and it is preferred that the outlet conduit  16  is oriented at an angle between 80 degrees and 100 degrees relative to the solids inlet conduit  12 . The outlet conduit  16  is preferred to have a diameter less than 80% of the diameter of the first inlet conduit  12 , and more preferably to have a diameter between 50% and 75% of the first diameter  18 . 
     In this embodiment, the configuration of the outlet conduit  16  relative to the first inlet conduit  12  allows for a smoother transition of particle flow into the outlet conduit  16 . The portion of the outlet conduit wall  28  that is removed creates an open section of the outlet conduit  16  where solid catalyst can flow down from the inlet conduit  12  to the outlet conduit  16 . The portion of the outlet conduit wall is between 25% and 95% of the outlet conduit wall  28  for the section that extends across the first inlet conduit end  14 . In a preferred embodiment, the removed portion is between 50% and 70% of the outlet conduit wall  28  and forms a partially open channel  32  on the end of the outlet conduit  16 . 
     With this embodiment, the outlet conduit  16  extends preferably at least 50% of the distance across the first inlet conduit end  14  as measured by the diameter  18  of the first inlet conduit  12 , and more preferably at least 100% of the distance. The outlet conduit  16  with a portion of the outlet conduit wall  28  removed is preferred to have the exposed edges along the removed section rounded. 
     The construction of the L-valve of the present invention can be made through the use of standard pipe fittings. This saves considerable expense over custom casting of L-valves, and especially for systems where the operating pressures are high, and for example can exceed 4 MPa. Standardized materials can be chosen that have already been fabricated for operating conditions one expects to encounter. A T-intersection provides the base, with a first standard pipe attachment to form the vertical leg of the L-valve. A second standard pipe having an inside diameter  20  less than 80% of the first standard pipe&#39;s inside diameter  18  is then attached through a blind flange with appropriate standard fittings and seals to join the second pipe with the T-intersection. Other fittings and arrangements are available with standard piping materials, with the criteria of an outlet conduit size reduction relative to the solids inlet conduit controlling the decision process. 
     In a second alternate embodiment, the L-valve  10  includes an outlet conduit  16  that is the same diameter as the inlet conduit, but includes a “dam” or other partial obstruction of the outlet conduit. In this embodiment, as shown in  FIG. 4 , the valve  10  comprises a first inlet conduit  12  for carrying solids and having a first diameter  18  and a first inlet conduit end  14 . The valve  10  further includes an outlet conduit  16  having a diameter  20 , where the second diameter  20  is the same as the first diameter  18 , and where the outlet conduit  16  is oriented at an angle between 45 degrees and 135 degrees relative to the first inlet conduit  12 . The valve  10  includes a second inlet  30  for carrying the motive fluid, and is substantially aligned with the outlet conduit  16 . The outlet conduit includes an obstruction  34  that reduces the cross sectional area of a portion of the outlet conduit  16  to between 25% and 75% of the cross sectional area of the first inlet conduit  12 , and preferably less than 50% of the cross sectional area of the first inlet conduit end  14 . The opening at the point of the obstruction  34  may be of a shape appropriate to the requirements of the flowing fluid properties. It may be an orifice plate  36  centered in the outlet conduit  16 , or placed eccentrically and aligned with the top or bottom edge of the conduit, as may be dictated to make the line free draining or able to pass entrained vapor. The orifice plate  36  may also comprise an opening such as a semi-circular section, or other shape opening, to block a portion of the cross-sectional area. 
     An alternate construction of the present invention, the motive fluid inlet  30  can be positioned above the junction of the first inlet conduit  12  with the outlet conduit  16 , as shown in  FIG. 5 . In this embodiment, the valve  10  comprises a first inlet conduit  12  for carrying solids having a substantially vertical orientation. The valve  10  further includes an outlet conduit  16  having a substantially horizontal orientation. The inlet conduit  12  has a first diameter  18 , and the outlet conduit  16  has a second diameter  20 , where the second diameter  20  is less than 80% of the first diameter  18 , and preferably less than 75% of the first diameter  18 . The second inlet  30  for admission of the motive fluid is disposed in the first inlet conduit  12  and can be positioned near the outlet conduit  16 , or substantially above the junction of the first inlet conduit  12  with the outlet conduit  16 . This embodiment can also include a construction where the outlet conduit  16  has the same diameter as inlet conduit  12 , but a restriction is disposed within the outlet conduit  16 , such as an orifice plate, or other restriction as described above, where the cross-sectional area is reduced to between 25% and 75% of the cross-sectional area of the first inlet conduit  12 . 
     While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.