Abstract:
“A flow control valve for fluidized material comprises a valve housing having a valve chamber with a valve seat and a valve plug having a flow passage, the valve plug being arranged inside the valve chamber in front of the valve seat ( 30 ) so as to be rotatable about an axis of rotation for controlling a flow through the flow control valve. It further comprises spring means biasing the valve plug against the valve seat perpendicularly to the axis of rotation, for achieving a sealing contact between the valve seat and the valve plug. According to an important aspect of the invention, the spring means comprises at least one cantilever spring ( 40 ) arranged in a clearance space opposite to the valve seat ( 30 ) so as to bias the valve plug against the valve seat.”

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a flow control valve for fluidized material, in particular for use in pneumatic conveying systems of fluidized material. 
       BRIEF DISCUSSION OF RELATED ART 
       [0002]    In conveying systems for fluidized material, fluidized materials are conveyed in bulk through conduits by means of a carrier fluid such as a carrier gas or carrier liquid. A specific example of a 
         [0003]    pneumatic conveying system using a carrier gas is a pulverized coal injection system for injecting pulverized coal of fine grain size through tuyeres into a blast furnace. 
         [0004]    In order to allow metering of bulk material, it is well known within the field of fluidized material conveying to provide a flow control valve in a conduit for controlling the flow rate of the carrier fluid and hence also the flow rate of bulk material passing through the valve. 
         [0005]    A common example of a flow control valve, used e.g. in pulverized coal injection systems, is a plug valve. A plug valve conventionally comprises a valve housing having a valve chamber with a valve seat and a valve plug having a flow passage. The valve plug is arranged inside the valve chamber in front of the valve seat and rotatable about an axis of rotation. Rotation enables controlling a flow through the valve by setting the position of the flow passage of the valve plug relative to the valve seat. 
         [0006]    Obviously, sealing contact between the valve seat and the valve plug is an important requirement for any valve. When a flow control valve is to be used in a system where the operating temperature of the carrier fluid and/or ambient temperature and hence temperature of the valve itself are subject to significant variations, achieving a sealing contact between the plug and the seat can be problematic. In fact, temperature variations may cause leakage of the valve e.g. due to differing thermal expansion of the valve housing and the valve plug and/or the valve seat. This problem occurs for example in pulverized coal injection. In such cases, it is known for plug valves to provide the valve with spring means biasing the valve plug and the valve seat against each other in a direction perpendicular to the axis of rotation of the valve plug. In a first possible design, the seat is spring biased against the plug. In a second possible design, which is of concern for the present invention, the plug is spring biased against the seat. 
         [0007]    In many known spring biased plug valves, the spring means consist of helical springs arranged in guiding bores of the valve housing so as to bias the plug and the seat together. It has been found that this type of spring biased plug valve does not sufficiently warrant fluid-tightness in certain applications and especially in a pulverized coal injection system operated at high temperatures and pressures. Furthermore, in conveying systems for fluidized bulk material, fine particles originating from the fluidized bulk material flow tend to accumulate in cavities inside the valve housing and hence also inside the guiding bores of the helical springs. Hence helical springs are susceptible to being blocked in a certain position. Once spring biasing is impeded, fluid-tightness obviously becomes deficient, in particular with temperature variations. This is especially problematic in a pneumatic conveying system where gas-tightness is an important requirement. As a further detrimental consequence of potential blocking, damage to the valve or, in case of a motor operated valve, damage to the motor unit may occur when the valve is operated in such a blocked condition. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The invention provides a flow control valve for fluidized material which improves fluid tight contact between valve plug and valve seat, irrespective of operating conditions and fine particle accumulation. 
         [0009]    The invention further proposes a flow control valve for fluidized material comprising a valve housing having a valve chamber with a valve seat and a valve plug having a flow passage, the valve plug being arranged inside the valve chamber in front of the valve seat so as to be rotatable about an axis of rotation for controlling a flow through the flow control valve. The flow control valve further comprises spring means biasing the valve plug against the valve seat perpendicularly to the axis of rotation, for achieving a sealing contact between the valve seat and the valve plug. According to an important aspect of the invention, the spring means comprises at least one cantilever spring arranged in a clearance space opposite to the valve seat so as to bias the valve plug against the valve seat. 
         [0010]    The flow control valve according to the invention achieves improved fluid-tightness, irrespective of the operating conditions of the valve. Furthermore, the use of cantilever type flexion springs eliminates the need for helical springs with guiding bores and hence the spring biasing function of the valve is rendered insensitive to clogging by fine particles. 
         [0011]    In a preferred embodiment, the at least one cantilever spring is a rod spring. The rod spring has a first end portion spring biasing the valve plug against the valve seat and a second end portion fixed to the valve housing. Although other cantilever type flexion springs such as leaf springs could be used, rod springs are preferred. 
         [0012]    In order to achieve a more uniform distribution of bending stress over the length of the rod spring, the rod spring preferably tapers towards its first end portion. 
         [0013]    Advantageously, the cantilever spring comprises a saddle member mounted on a first end portion of the cantilever spring and having a contact surface conformed to the outer surface of the valve plug. This configuration enables an intimate surface contact of a certain area between spring and plug. 
         [0014]    As a further benefit of cantilever springs, the flow control valve can comprise, in a preferred embodiment, an adjustment device supporting the second end portion of the rod spring, the adjustment device allowing the axial position of the rod spring with respect to the valve plug to be set. Since the pre-tension of each cantilever spring and hence the contact pressure between valve plug and valve seat can be set, the adjustment capability proves beneficial to warrant fluid-tightness. Initial adjustment enables adapting the valve for a certain application (different pressures, temperatures, fluid types, etc.). Adjustment during service life enables taking into account process variations or wear of the valve parts for example. For setting the axial position of the rod spring, the adjustment device preferably comprises an operating portion which protrudes from the valve housing. Adjustment during operation of the valve is thereby enabled. 
         [0015]    In order to achieve a uniform contact between valve plug and valve seat, is advantageous to provide two pairs of cantilever springs that are arranged in corresponding clearance spaces tangentially with respect to the valve plug and on opposing sides of a flow channel through the valve housing. In this configuration, the cantilever springs of each pair are preferably arranged in parallel and two cantilever springs of either pair are arranged in opposing coaxial relationship. 
         [0016]    Advantageously, the flow control valve further comprises an actuating shaft mounted rotatable in the valve housing and an Oldham coupling which couples the valve plug to the actuating shaft. This configuration represents a simple and reliable manner of floatingly mounting the valve plug inside the valve chamber, in order to allow displacement of the valve plug against the valve seat. 
         [0017]    In order to facilitate access to the cantilever springs, and especially their respective adjustment devices, the clearance space of each cantilever spring is preferably arranged perpendicular to the axis of the actuating shaft in the valve housing. 
         [0018]    Although plug valves with spherical plugs could also benefit from the use of cantilever springs, it is preferred, especially in pneumatic conveying systems, that the valve plug comprises an essentially cylindrical hollow body having a cylindrical plug sealing face in contact with a corresponding sealing face of the valve seat and a cylindrical plug biasing face in contact with a first end portion of the cantilever spring or, if provided, the contact surface of the saddle member. 
         [0019]    As will be appreciated, the flow control valve according to the present invention is especially suitable for use in a pulverized coal injection system for a blast furnace. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: 
           [0021]      FIG. 1 : is a longitudinal cross sectional view of a flow control valve according to the invention; and 
           [0022]      FIG. 2 : is cross sectional view of the flow control valve along the line II-II in  FIG. 1 . 
       
    
    
       [0023]    Further details and advantages of the present invention will be apparent from the following detailed description. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  shows a flow control valve for fluidized material, generally identified by reference numeral  10 . The flow control valve  10  is designed to be used in a conduit of a conveying system for fluidized bulk material, in particular a pneumatic conveying installation such as pulverized coal injection system for a blast furnace. 
         [0025]    The flow control valve  10  comprises a valve housing  12  having an inlet port  14  and an outlet port  16 . The valve housing  12  delimits therein a valve chamber  18  communicating with the inlet port  14  and the outlet port  16 . A valve plug  20  is arranged inside the valve chamber  18 . The valve plug  20  has a body of generally cylindrical hollow configuration with a first aperture  22  and a second aperture  24  arranged laterally in the cylindrical shell of the plug body. The apertures  22 ,  24  provide a flow passage through the valve plug  20 . The valve plug  20  further comprises a coupling portion  26  for coupling the valve plug  20  to an actuating shaft  28  which is rotatably mounted in the valve housing  12 . 
         [0026]    The flow control valve  10  further comprises a valve seat  30  which is fixed in the valve housing  12  on the periphery of the valve chamber  18 . The valve seat  30  has a generally tubular, cylindrical shape and is arranged in a conjugated socket  32  in the valve housing  12 . The valve seat  30  provides a further flow passage through which the valve chamber  18  communicates with the outlet port  16 . As seen in  FIG. 1 , the valve plug  20  is arranged in front of the valve seat  30 . The valve plug  20  is rotatable about an axis of rotation A by means of the actuating shaft  28 . In a manner known per se for plug type valves, the rotational position of the valve plug  20  relative to the valve seat  30  allows to control the flow through the valve  10  by setting the degree of coincidence between the flow passages in the valve plug  20  an the valve seat  30  respectively. In this respect, it may be noted that the second aperture  24  of the valve plug  20  has the combined shape of a tapered generally triangular first portion and a generally semi-circular second portion (seen in planar projection). This shape allows to improve flow control by making the intersecting flow passage area an essentially linear function of the angular position of the valve plug  20  (when coincidence is limited to the first generally triangular portion of the aperture  24 ). As further seen in  FIG. 1 , two mounting flanges  34 ,  36  are mounted to the valve housing  12  in extension of the inlet port  14  and the outlet port  16  respectively. 
         [0027]    As best seen in  FIG. 2 , the valve plug  20  has a cylindrical outer sealing surface portion. The valve plug  20  need not be cylindrical however, other types are also possible, e.g. spherical plugs, provided that the sealing surface portion is a surface portion of a solid of revolution. The valve seat  30  is provided with a sealing surface portion precisely conformed to the sealing surface of the valve plug  20  such that sealing contact between both is possible. 
         [0028]    As further seen in  FIG. 2 , spring means are provided for biasing the valve plug  20  against the valve seat  30  in a direction perpendicular to the axis of rotation A, for achieving a sealing contact between the valve seat  30  and the valve plug  20 . According to the invention, these spring means comprises cantilever springs  40 . It will be understood that the cantilever springs  40  are flexion springs functioning by elasticity of flexure. Although other types of cantilever springs such as leaf springs could be used, it is preferred that the cantilever springs are rod springs  40  of circular cross section, for reasons that will become apparent below. As appears from  FIG. 1  and  FIG. 2 , four rod springs  40  are arranged in respective clearance spaces  42  adjacent to the valve chamber  18  and opposite to the valve seat  30 . Each rod spring  40  has a first end portion tangential to the valve plug  20  and spring biasing the valve plug  20  against the valve seat  30  and a second end portion fixed to the valve housing  12 . As will be understood, the direction of the resultant spring biasing force F produced by the rod springs  40  is perpendicular to the axis of rotation A and directed towards the valve seat  30 . 
         [0029]    As seen in  FIG. 2 , each rod spring  40  is configured as conical rod tapering towards its first end portion. A more uniform bending stress distribution over the length of the rod spring  40  is thereby obtained when compared to cylindrical rods. In order to provide a surface contact between each rod spring  40  and the valve plug  20  each rod spring  40  has a saddle member  44  mounted on its first end portion. Each saddle member  44  has a contact surface conformed to the cylindrical outer surface of the valve plug  20 . 
         [0030]    As further seen in  FIG. 2 , each rod spring is mounted to the valve housing  12  by means of a respective adjustment device  46 . The adjustment device  46  supports the second end portion of the associated rod spring  40  in a manner which allows setting, i.e. adjusting the axial position of this rod spring  40  with respect to the valve plug  20  and hence the tangential contact point between them. As will be understood, axial positioning of the rod spring  40  allows to reduce or increase the distance between its first end portion and the axis of rotation A, while maintaining tangential contact with the valve plug  20 . Hence, by virtue of the adjustment devices  46 , the flexion of the rod spring  40  and consequently the magnitude of the force F, i.e. the degree of spring biasing can be adjusted. To this effect, each adjustment device  46  comprises a hollow cylindrical sleeve  48  fixed in a bore in elongation of the respective clearance space  42  so as to protrude from the valve housing  12 , an internally threaded bushing  50  fixed inside the sleeve  48 , which cooperates with a corresponding external thread  52  on the second end portion of the rod spring  40 , and a locknut  54  screwed onto the external thread  52  in abutment with the sleeve  48 . When the locknut  54  is loosened, the axial position of the rod spring  40  can be adjusted precisely by turning i.e. screwing the rod spring  40 , for example using a torque wrench. To this effect, the body of the rod spring  40  has rotationally symmetrical shape with circular cross sections tapering towards the front end. As will be appreciated, the adjustment device  46  has an operating portion  55 , formed by the locknut  54  and the external portions of the sleeve  48  and the spring rod  40 , which protrudes from the valve housing  12 . By virtue of this design, the adjustment device  46  can be operated without the need to dismantle the valve housing  12  i.e. during operation, e.g. to readjust sealing contact pressure or to recover from a blocking condition. It will also be appreciated that besides adjusting, the construction of the adjustment device  46  allows easy disassembling and removal of the rod spring  40  e.g. for maintenance or inspection purposes. Two retention pins  56  are provided in the valve housing  12  in order to avoid dislocation of the valve plug  20  when the rod springs  40  are removed. In order to maintain engagement of the saddle members  44  on the valve plug  20  in any axial position and during rotation, each saddle member  44  is mounted on its rod spring  40  so as to be rotatable about the longitudinal axis of the rod spring  40  and preferably slightly pivotable about an axis parallel to axis A, e.g. by means of a spherical joint. 
         [0031]    It will be understood from  FIG. 1  and  FIG. 2  that two pairs of rod springs  40  are arranged, on opposing sides of the flow channel through the valve housing  12 , in corresponding clearance spaces  42  tangentially with respect to the valve plug  20 . The rod springs  40  of each pair are arranged in parallel (i.e. with parallel longitudinal axes and assuming no pretension). Two rod springs  40  of either pair are arranged in opposing coaxial relationship as seen in  FIG. 2 . This arrangement of the four rod springs  40  warrants a uniform contact pressure on the sealing surfaces of the valve seat  30  and the valve plug  20 . 
         [0032]    As seen in  FIG. 1 , the valve plug  20  is coupled to the actuating shaft  28  by means of a coupling member  60 . The coupling member  60  is generally disc shaped and configured as Oldham coupling. To this effect, the coupling member  60  has a linear recess on a first side, which cooperates with a conjugated rib of the actuating shaft  28 , and a linear rib on a second side which is perpendicular to the recess on the first side and cooperates with a conjugated recess in the coupling portion  26  of the valve plug  20 . This configuration enables a floating mounting of the valve plug  20  inside the valve chamber  18  to allow some displacement between the rotational axis A of the valve plug  20  and the axis of the actuating shaft  28 . Parallelism of both axes is maintained by this Oldham coupling configuration in combination with a suitable rest for the valve plug  20  on the side opposite to the coupling member  26 . 
         [0033]    As further seen in  FIG. 1 , the essentially cylindrical clearance spaces  42  are arranged perpendicular to the axis of the actuating shaft  28  in the valve housing  12 . By virtue of this arrangement access for personnel to the adjustment devices  46  is facilitated. 
         [0034]    Regarding preferred materials, it will be understood that each spring rod is made of spring steel. The valve plug  20 , valve seat  30  and the saddle members  44  are in turn made of a hard metal or hard alloy. The valve housing itself can be made of any suitable material, e.g. conventional steel. 
         [0035]    Finally, some important advantages obtained by the flow control valve  10  according to the invention remain to be mentioned:
       Using cantilever flexion springs  40  in combination with suitable clearance spaces  42  renders the required spring biasing function much more reliable and virtually insensitive to clogging and blocking caused by fine particle accumulation.   As a result, the flow control valve  10  offers more reliable fluid-tightness in virtually any condition and can therefore be used in safety critical applications and/or severe environments, e.g. in a pulverized coal injection system on a blast furnace.   By virtue of the cantilever flexion springs  40 , the flow control valve  10  has improved tolerance with respect to differing thermal expansion of the constituent material of the valve housing  12  and of the valve plug  20  and/or the seat  30 .   In combination with the adjustment device  46 , the cantilever flexion springs  40  allow to precisely and optimally set the sealing contact pressure. This allows adapting the valve  10  to different working conditions and reducing wear of the plug  20  and the seat  30 . Furthermore, the required actuation torque can be reduced when compared to conventional valves that are often over-biased for safety reasons.   The construction of the flow control valve  10  in general, and the adjustment device  46  in particular, allows to set the sealing contact pressure during operation time such that no downtime is required.   Since the risk of blocking of the valve plug  20  in a given position is drastically reduced, the risk of resulting damage to the valve and, if provided, its actuation motor is also reduced.   The construction of the flow control valve  10 , in general and the adjustment device  46  in particular, facilitates maintenance of the internal parts of the valve  10  when compared to conventional spring biased valves using helical springs.