Patent Document

[0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/618,488 filed Oct. 13, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the field of systems for cleaning the interiors of tanks and, more particularly, to a system and method for altering the axis of rotation and diameter of spray nozzles in such a cleaning system to maximize the efficiency of the cleaning process.  
       BACKGROUND OF THE INVENTION  
       [0003]     Most tanks in chemical plants, refineries, and similar factories are custom designed vessels that have to be cleaned periodically. Since the tanks are custom designed and thus may have different interior geometries, no one cleaning system will work adequately for all tanks. Furthermore, vessels are typically divided with dividing plates which include centered through-holes or partially removable dividing plates.  
         [0004]     Commonly, such a tank has an entry point or access way which is small relative to the interior diameter and height of the tank. On the other hand, a typical tank has relatively large inner surface areas which require periodic cleaning to remove the buildup of materials left by the material kept in the tank, such as calcium and magnesium carbonates and similar residues. Thus, a single manufacturing facility may have a wide variety of tanks of varying sizes, each requiring this sort of periodic maintenance and at least some of the tanks presenting a different aspect of interior geometry versus the size of the entry point or access way.  
         [0005]     That restriction presents the engineering dilemma of having to insert the tool through a small opening (so the tool has to be small), but requiring a substantial range for a water jet from the tool, in order to reach the farthest surfaces of the interior of the tank.  
         [0006]     With all of these factors in mind, one can see that it is difficult to find a single cleaning tool that fits all tank sizes and applications while doing a good job of cleaning the interiors of all of the tanks. One current proposed solution available on the market uses a small volume, high pressure water cleaning tool that is positioned inside the vessel and moved along the center axis of the tank while several water jets rotate around one or two axes simultaneously. Since the water jets are directed more or less radially from one point inside the tank, the distances from the water jet exit ports to the vessel walls are substantial and change continuously.  
         [0007]     Thus, surface coverage cannot be exactly controlled since the water jet tracks contact the interior surface of the tank at more or less random locations. For proper surface coverage, each track of the water jet should overlap the previous track by a small amount. If the track does not overlap a previous track, then a portion of the interior surface of the tank will not be cleaned. If there is too great an overlap, then the track will be directed too much to a portion of the interior surface which has already been cleaned and the process is therefore inefficient.  
         [0008]     However, in many known systems, the tracks of the jets are directed more or less randomly. That means that in order to insure that the entire interior surface of the tank is cleaned, the cleaning process must be continued for a much longer period of time than would be required if the direction of the spray of the jets could be more closely controlled. Such systems are also inefficient since the majority of time the spray from the jets is not effective directed to the wall of the vessel, but either up or down away from the surface to be cleaned.  
         [0009]     Furthermore, since the distance from the center axis of the tank, where the jets are typically located, to the interior surface of the tank may be several feet, hard deposits cannot be adequately removed and thus the cleaning process is more a flushing process.  
         [0010]     Systems for cleaning the interior surfaces of a tank encounter another serious problem in that the inside of the tank typically includes structural support plates extending laterally inwardly toward the axis of the tank. These plates represent surfaces which must be cleaned, and also present obstacles for the movement of the cleaning tool within the tank or vessel. As the cleaning tool is lowered into a tank from an access point at or near the top of the tank, the interior obstacles within the tank must be considered when directing a high velocity jet from a point off the axis of the tank.  
         [0011]     Another proposed solution to the problem of the variations in interior geometries of tanks to be cleaned takes advantage of automation technology. The interior geometry of the tank, including inside diameter, height, and interior obstacles, are set into a programmable controller and the tool is then run into the tank. Unfortunately, such systems are highly complex, require a long setup time, and are very heavy and expensive. Further, the time and expense required to program and debug the programmable controller is often longer and greater than the total cost of a satisfactory cleaning job without such a controller.  
         [0012]     Thus, there remains a need for a system for cleaning the interior surfaces of tanks which is flexible, effective, and efficient. The present invention is directed to filling this long felt need in the art.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention addresses these and other drawbacks in the art to improve high pressure water cleaning of inner surfaces of tanks or vessels. This improvement is achieved by the tool&#39;s ability to unfold and fold so that the tool easily fits through small access openings and at the same time allowing the water jets to be positioned at optimal distances relative to the vessel wall for superior cleaning results. The folding and unfolding process is powered only by the water jet force and water pressure supplied to the jets. The folding and unfolding process is speed controlled using dampening devices. In the present invention, no electric or electronic components are used.  
         [0014]     This invention synchronizes the transversal and rotational movements of water jets. While the jets are directed at a pre-adjusted distance to the vessel wall, they are moved in three dimensions. This movement results in a controlled spiral or helical cleaning track along the vessel walls. The travel speed of the water jets and the distance between adjacent cleaning tracks can be adjusted to match the cleaning needs. The entire inner surface of the vessel can be covered precisely. Once the cleaning tool has been moved from one end of the vessel to the other with the travel of the water jets controlled in that manner the vessel wall will have been thoroughly cleaned. The exact positioning of the water jets allows the removal of very hard deposits.  
         [0015]     The rotational movement is powered either by water or air flow. A pneumatic-hydraulic device is used to convert the rotational movement into the additional transversal movement.  
         [0016]     Thus, the present invention provides a vessel cleaning system for cleaning storage tanks, reactors, etc. in all industries. The system of this invention is directed to cleaning many different types of deposits, especially very hard deposits from vessel walls using high pressure water jets. A spray sub-system comprises a tool carrier with water jet nozzles attached thereto which unfolds by rotating and telescoping inside the vessel at the start of a cleaning cycle and folds up at the end of the cleaning cycle. The unfolding and folding procedure is required to get the tool carrier in and out of the tank through a relatively small access so that the cleaning system is still able to position water jets at a required distance to a vessel wall and therefore deposits to be removed from the vessel wall. The unfolding and folding procedure is speed controlled and simultaneously used to clean certain areas inside the vessel.  
         [0017]     The unfolding and folding operation is strictly a mechanic and/or hydraulic process initiated with the starting and stopping of and powered by the high pressure water flow only. A combined rotational and transverse movement of the tool carrier and the unfolding and folding movement is controlled in a way that results in a spiral movement of the water jets when cleaning two dimensional flat surfaces and in a helical movement of the water jets when cleaning cylinder walls. All movements are speed controlled: the travel speed of jets and the pitch of the spiral and the helix are adjusted depending on the cleaning requirements for the deposit to be removed from the vessel wall. Impact properties of water jets on deposited materials can be maintained constant throughout the cleaning operation.  
         [0018]     These and other features and advantages of this invention will be readily apparent to those skilled in the art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to embodiments thereof which are illustrated in the appended drawings.  
         [0020]      FIG. 1  is a side section view of a tank cleaning system of the present invention in use within a tank having horizontally disposed dividing plates with vertical channels through the plates.  
         [0021]      FIG. 2  is a side section view of the tank cleaning system within a tank with no internal dividing plates.  
         [0022]      FIG. 3A  is a side view of a tank cleaning sub-system.  
         [0023]      FIG. 3B  is a front view of the tank cleaning sub-system of  FIG. 3A .  
         [0024]      FIG. 3C  is a detail view of an alternative spray nozzle for use on the tank cleaning sub-system.  
         [0025]      FIG. 4  is a section view of a damping device for controlling the rate of rotation of a spray sub-system. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]      FIG. 1  illustrates a presently preferred embodiment of the tank cleaning system  10  of this invention in a tank  12  with dividing plates  14  and a center hole  16  in each dividing plate. It should be understood that only a portion of the tank  12  is illustrated, and it may extend a substantial distance above and/or below the portion illustrated in  FIG. 1 .  
         [0027]     The system  10  comprises a feed sub-system  20 , a support  22 , and a nozzle jet sub-system  24 . The feed sub-system  20  includes a prime mover  26  which imparts lateral movement to a feed tube  28  as shown by an arrow  30 . The prime mover  26  also imparts rotational movement to the feed tube  28 , as shown by an arrow  32 . The feed tube carries fluid, typically water, under high pressure for cleaning the interior of the tank  12  as described in greater detail below. The high pressure fluid is provided by a high pressure source, typically a compressor (not shown).  
         [0028]     The prime mover thus controls the lateral and rotational movement of the feed tube. The lateral movement of the tube is controlled at such a rate as to create a controlled helical movement of the spray from the nozzle jet sub-system  24  for complete and efficient cleaning, as described further below.  
         [0029]     The feed tube  28  passes through and is supported by a feed pedestal  34  which also serves to support a feed tube sheath  36 . The feed tube sheath is a flexible, non-rotating conduit through which the rotating feed tube passes. The other end of the feed tube sheath  36  is coupled to the support  22 , which is typically mounted to a structural member  38  in the vicinity of the tank  12 . The feed tube sheath  36  has an opening  40  through which the feed tube  28  passes. The feed tube  28  is then directed downwardly into the tank  12 , where it continues to rotate as shown by an arrow  42 . Also, movement back and forth of the prime mover  26  as shown by the arrow  30  results in lateral movement of the feed tube  28  as shown by an arrow  44 .  
         [0030]     The nozzle jet sub-system  24  is illustrated in  FIG. 1  already deployed within the tank  12 . While  FIG. 1  is not necessarily to scale, it should be recognized that the horizontal diameter of the tank is large compared to the horizontal diameter of the center hole  16 , so that the nozzle jet sub-system must be small enough in its own horizontal diameter to pass through the center hole  16 . Once through the center hole  16 , however, the nozzle jet sub-system must then direct high pressure fluid against the interior surfaces of the tank in order to adequately clean these surfaces. The present invention accomplishes this difficult task by providing two motions to the nozzle jet sub-system, to be described below in greater detail.  
         [0031]     The nozzle jet sub-system  24  comprises a centrally disposed swivel  50  with at least two arms  52  extending therefrom. While the nozzle jet sub-system is being deployed within the tank  12 , the arms  52  extend substantially vertically, i.e. parallel with the direction of travel of the system. Once the nozzle jet sub-system is properly positioned about midway between dividing plates  16 , the arms are rotated to a horizontal positioned, as shown in phantom in  FIG. 1 . Then, nozzle extensions  54  telescope out to a deployed position, carrying a nozzle jet  56  on the end of each nozzle extension  54  to a position adjacent an interior surface  58  of the tank  12 . It should be noted that the arms  54  may also be flexible to assist in drawing them through small access holes or center holes in dividing plates.  
         [0032]     To clean vessel walls  58 , the sub-system  24  must be properly positioned within the tank between divider plates. Once a portion of the tank is cleaned, the sub-system  24  is collapsed, repositioned through center hole  16 , and redeployed to clean the next portion of the tank. Thus, the distance between dividing plates within the tank must be greater than the length between nozzle jets before the extension arms are extended so that the sub-system  24  can freely rotate into position between divider plates. Further, once the sub-system  24  is horizontally deployed with the jets near the interior surface of the tank, the sub-system is then lifted until the extension arms, which are now parallel to the dividing plates, are as close as possible to the dividing plate immediately above the sub-system  24  so that the portion of the inside surface of the tank immediately beneath the divider plate will be properly cleaned.  
         [0033]     Once the sub-system  24  is properly positioned within the tank, the feed tube  28  is pressurized with fluid, typically water. The nozzle jets  56  are then activated and the telescopic extension arms  54  extend, thereby positioning the nozzle jets  56  close to the vessel wall  58 . No dampening of extension arm movement is applied. With the activation of the nozzle jets, the sub-system  24  is then rotated about the vertical axis of the tank to direct the jet spray around the interior surface of the tank, as controlled by the feed system  20 .  
         [0034]     With the start of the rotation of the sub-system  24 , the sub-system  24  is then lowered by feeding the high pressure feed hose  28  at a controlled feed rate. The feed rate is determined by a predetermined length of feed for each rotation of the sub-system  24  to provide some overlap for each track of the spray against the interior surface of the tank.  
         [0035]     Once sub-system has been lowered as much as possible, thereby cleaning the portion of the tank between the dividing plates, the nozzle jets are stopped and the telescopic arms are retracted. The sub-system  24  is then centered between the dividing plates and the extension arms are rotated into a vertical position. The tank cleaner can now be lowered in the next tank section between the next set of dividing plates.  
         [0036]     Note that the preceding detailed description was directed to cleaning the interior surfaces of the tank in between dividing plates. However, the dividing plates themselves must also be cleaned. To clean dividing plate surfaces, two jets per extension arm are installed with the jet direction vertically up and down parallel to vessel center axis when in operation. The sub-system  24  is positioned along the axis of the tank and then lowered into the individual tank sections with the extension arms in a vertical position as previously described. When the sub-system  24  is positioned in the center between two dividing plates, the extension arms are rotated into a horizontal position. The sub-system is then lifted until the extension arms, which are now parallel to the dividing plate, are as close as necessary to the upper dividing plate for proper cleaning results.  
         [0037]     The nozzle jets are then activated and the telescopic extension arms extend at a preset speed, determined by a dampening system. The system then operates as previously described, this time to spray a high pressure fluid against the bottom surface of the dividing plate above the sub-system  24  and the top surface of the dividing plate below the sub-system  24 . The rotational speed of the sub-system  24  is coordinated with the extension speed of the telescopic arms  54  so that the resulting movement of the water nozzle jets is a spiral pattern.  
         [0038]     We have found that the jets which face in a downward direction have less of a cleaning effect on the lower dividing plate than the upwardly directed jets. However, the downwardly direction jets must be active as a counter force to the jets facing up to provide a balanced force acting upon the ends of the extension arms.  
         [0039]     Once the extension arms have extended all the way to their full extent, water pressure through the feed tube  28  is stopped and the extension arms retract. The sub-system  24  is then lowered until the extension arms are as close as necessary to the lower dividing plate. The process is then repeated with the cleaning of the top surface of the lower dividing plate in a manner just described in respect of the dividing plate above the sub-system  24 . After cleaning both dividing plate surfaces, the system is centered between the dividing plates and the extension arms are rotated into a vertical position. The sub-system  24  is then lowered into the next tank section.  
         [0040]      FIG. 2  illustrates the application of the tank cleaning system  10  in an open tank  60  without dividing plates or internally installed moving parts. As previously described, the system  10  comprises the feed sub-system  20 , the support  22 , and the nozzle jet sub-system  24 . The feed sub-system  20  includes the prime mover  26  which imparts lateral movement to the feed tube  28  as shown by the arrow  30 . The prime mover  26  also imparts rotational movement to the feed tube  28 , as shown by the arrow  32 .  
         [0041]     The feed tube  28  passes through and is supported by the feed pedestal  34  which also serves to support the feed tube sheath  36 . The other end of the feed tube sheath  36  is coupled to the support  22 , which in the embodiment illustrated in  FIG. 2  is adapted to mate with an upper access port  62  of the tank  60 . The feed tube  28  is then directed downwardly into the tank  60 , where it continues to rotate as shown by the arrow  42 . Also, movement back and forth of the prime mover  26  as shown by the arrow  30  results in up and down movement of the feed tube  28  as shown by the arrow  44 .  
         [0042]     In the embodiment of  FIG. 2 , the cleaning apparatus is positioned along the center axis of the tank  60  near the top of the tank, with the distance of sub-system  24  to the top of the tank equal to the radius of the vertical part of vessel. The length from the center of the sub-system  24  to the water jet outlet nozzles equals the horizontal radius of the vessel minus the distance for an individual jet outlet to the vessel wall for best cleaning results. If the nozzle is too close to the vessel wall, the jet is too narrow, resulting in a pencil beam of water against the vessel wall and inadequate overlap from one track to the next. If the nozzle is too far from the vessel wall, the water spray has too little force to clean certain tenacious depots on the vessel wall.  
         [0043]     With the initial positioning of the sub-system  24 , the extension arms are vertical, one jet facing the top of the vessel and one jet facing the bottom. When activated, the lower jet will typically be too far from the bottom of the tank to have much of a cleaning effect. Once the water jets are activated, the extension arms will rotate to a horizontal position. Also, simultaneously with the activation of the jets, the sub-system  24  will begin to rotate about the vertical axis, beginning a cleaning action along the inside top surface of the tank. This additional rotation is provided by the prime mover  26  through rotation of the feed tube  28 . The rotational speed around the vertical axis is coordinated with extension arm rotational speed around the sub-system  24 , so that the resulting spiral pattern track of water jets on the vessel wall provides an overlap of one jet track to the next. The distance between tracks and traveling speed of the water jets may require some adjustment, depending on type of material that has to be removed from the tank walls.  
         [0044]     Once the extension arms have reached a horizontal position, the sub-system  24  is lowered into the tank with its rotation around the tank vertical axis maintained, thus creating a spiral cleaning track down the wall of the vessel. The cleaning apparatus is lowered by feeding the high pressure water feed tube at a controlled feed rate in relation to the rotational speed of the sub-system  24 . The prime mover  26  coordinates the rotation of the cleaning apparatus around the vertical tank axis and the downward movement of apparatus.  
         [0045]     The downward movement of the apparatus is stopped once the apparatus reaches a position in the center of the vessel with a distance of the sub-system  24  to the bottom of the vessel equal to the radius of the vertical part of the vessel, thus the distance of the jet outlet to the vessel wall required for best cleaning results will be reached. Now the extension arms will be rotated back into vertical position at the same rotational speed as they were rotated into horizontal position at the beginning of the cleaning process with the high pressure water pump continuing to run. With the tank cleaner rotation along the tank vertical axis maintained the jet moving towards the lower center of the tank will clean the bottom in a spiral pattern. Alternatively, the supply of pressurized water through the feed tube may be stopped, and the extension arms rotated into a vertical position and the same procedure as in the very beginning is repeated to clean the bottom of the tank by starting at a vertical position and moving in a controlled fashion to a horizontal position. However, at the end of the cleaning process, the arms are returned to a vertical position in order to pull the tank cleaner out of the tank.  
         [0046]      FIGS. 3A and 3B  depict a presently preferred embodiment of the sub-system  24 , which may be referred to herein as the “tank cleaner”.  FIG. 3C  depicts an alternative spray nozzle for use on the sub-system  24  for cleaning dividing plates within a tank as described above, in which spray outlets from the nozzle are directed in diametrically opposed directions.  
         [0047]     The sub-system  24  includes a frame  70  suspended by the rotating high pressure water hose or feed tube  72  in the center of the tank. A center plate  74  is held by the suspended frame and supported by a bearing  76  that allow the plate to rotate around an axis perpendicular to the vessel center axis. The two extension arms  54  are coupled to center plate, with one water jet insert  76  each at each extension arm tip. The extension arms may vary in length, depending on the specific cleaning job or application. The jet directions and extension arm length axes are in the same geometrical plane perpendicular to the rotational axis of the center plate, and jet forces of the two jets match each other and are directed in opposite directions with one jet presenting the counter force to the other jet.  
         [0048]     The jet and extension arm length axes are offset, thus, the jet reaction forces generate a torque with a direction perpendicular to the vertical tank center axis. This torque rotates the center plate with the extension arms. The rotational movement is dampened by a hydraulic cylinder  78  and restricted to 90° between vertical and horizontal extension arm positions. The damping can be adjusted with an adjustable orifice  80  in order to control the rotational speed of extension arms.  
         [0049]      FIG. 4  depicts a schematic view illustrating the damping feature of the spray sub-system  24 . As previously described, the sub-system  24  is fed with high pressure fluid from a tube  28 , which is coupled into the swivel  50 . Fluid pressure is directed through the arms  52  and the extensions  54 , creating a moment to rotate the swivel as shown by the arrows in  FIG. 4 . Rotation of the swivel  50  rotates a pinion gear  92  which meshes with a rack  94 . The rack  94  is joined to a piston  96  within a cylinder  98 . Moving the rack to the right pushes hydraulic fluid from the cylinder to the right out through the adjustable orifice  80  to the other side of the piston  96 . Thus, the rate of rotation of the swivel is controlled by the setting on the orifice  80 .  
         [0050]     Preferably, the orifice  80  is an adjustable throttle check valve. The spray sub-system  24  is shown in  FIG. 4  at the full horizontal position. Once the spray process with the spray sub-system in the horizontal position is complete, the arm extensions retract and the swivel rotates to place the arms in a vertical position. A weight  90  provides a biasing means to pull the arms to a vertical position. To aid in this movement, the orifice includes a check valve which permits unrestricted flow from left to right as seen in  FIG. 4  to more quickly move the arms to a vertical position. The arm extensions  54  also include a biasing means to assist in retracting the arm extensions when the high pressure fluid is no longer being supplied to the spray nozzles  56 .  
         [0051]     The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.

Technology Category: 7