Abstract:
A method for cleaning tubes and heat exchangers provides an oscillating pump/valve mechanism to provide a periodic waveform of shocks to fouled tubes. Preferably, a pair of pneumatic control valves operates an actuator to oscillate a valve within a valve block, and isolation of a fluid within a manifold in the block creates a pumping action from the valve, to create an intense fluid shock wave to clean interior surfaces tubes.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the field of devices for cleaning clogged heat exchanger tubes and, more particularly to a system for cleaning tubes within a vessel using a pump valve mechanism for mechanically applying variable pressure to material clogging the tubes. 
   BACKGROUND OF THE INVENTION 
   A heat exchanger is normally formed of a plurality of tubes oriented generally parallel to one another. In normal operation, a fluid to be heated or cooled is delivered through the inside of the tubes of such a heat exchanger. The outside surface of the tubes are contacted with a fluid which adds heat or removes heat as required. The plurality of generally parallel tubes forms a bundle. A set of end plates, known as heads, commonly support the bundle of tubes at each end. 
   Heat exchangers usually operate in a continuous fashion, often for months at a time. However, such continuous operation may be periodically interrupted to clean the tubes. The cleaning process is necessary to remove residue which collects on the inside surface of the tubes which reduces their heat transfer capability. The tubes are normally formed of metal which has a relatively high thermal conductivity. The material which may coat the interior of the tubes, however, has a much lower thermal efficiency for heat transfer. Therefore, the coating formed on the interior of the tubes is detrimental to the efficiency of the operation of the heat exchanger. 
   As residue builds up on the inside surface of a heat exchanger tube, the tube becomes less and less efficient. One way to counteract this effect is to raise the temperature differential across the tube. However, there are limits to this solution. For instance, the metal used in the tubes of the heat exchanger has a limited capacity for heat as a result of metallurgical considerations. Exceeding the design temperature differential across through the tubes increases fatigue and therefore reduces the useful lifetime of the heat exchanger. 
   In a well known U-tube design, the bundle of tubes takes a 180° bend or elbow at more or less the mid-point of the respective tubes. Fluid enters an inlet box which is separated by a divider plate from an outlet box. The fluid then flows through the head, through the tubes in first one direction then the reverse direction, back through the head and finally into the outlet box on the other side of the divider plate. Cleaning the tubes involves removing the accumulated coating material on the inside of the tubes and the difficulty of cleaning the inside surfaces of the tubes is exacerbated by the bend in the tubes. Also, as exchanger designs have improved, the effective length of the tubes has increased. This makes the task of cleaning the tubes more difficult because the long and relatively narrow tubes do not permit easy access to the tubes. 
   One way that the tubes can be cleaned is by pumping water or perhaps chemically active solvents into the tubes. That is successful but it has limitations. Moreover, since a typical heat exchanger includes a large number of tubes, it is necessary to undertake the cleaning in a repetitive fashion so that a large number of tubes can be cleaned. 
   In my U.S. Pat. No. 5,423,917, I described a system and a method for cleaning heat exchanger tubes. The system described therein has proven very successful. However, the system includes a control panel with a ganged set of valves to set up a shock wave to be injected into a tube. For particularly stubborn and tenacious fowling, especially involving hundreds of tubes, this manual alignment of the control panel valves can become tiresome and tedious. Therefore, there remains a need for a system like that described in the &#39;917 patent but that mechanizes the shock wave generation process. The present invention is directed to solving this need in the art. 
   SUMMARY OF THE INVENTION 
   The present invention solves this need in the art by providing a pump/valve mechanism for directing a shock wave to a tube that is to be cleaned. A pump takes a suction from a sump and the pump discharges to an output and then through a valve which is switched to deliver water under pressure through a controllable orifice. The orifice delivers the water under pressure to the pump/valve mechanism which alternately directs pressurized water to the tube and to an overflow discharge. 
   In a preferred embodiment, the pump/valve mechanism is actuated pneumatically by regulated air pressure. However, any convenient and appropriate actuation means may be used. 
   In the rest of the tube cleaning system, a lance is provided to deliver pressurized water and the shock wave to the tubes. The lance is positioned by a ram, which cooperates with the lance to align the lance with individual tubes. The lance is directed in an X and Y pattern by a control mechanism to align with selected tubes. The lance is able to travel forwardly in the Z direction. It is constructed on a piston and cylinder mechanism which enables hydraulic control of lance insertion and retraction. 
   When the lance is inserted, the tip of the lance is placed in the particular tube to be cleaned. Hydraulic control enables rapid indexing of the lance to the left and right to align with the proper tube and to insert into that tube once alignment has been accomplished. The tip of the lance is profiled so that it forms a fairly quick seal with the end of the tube. The lance is hollow to deliver liquid through the end of the lance into the tube. A pressurized air supply provides air to the pump/valve mechanism to purge the tube to be cleaned to set the tube up for a water hammer action when the lance is pressurized with water or cleaning solution. 
   A pressure surge is set up by timed operation of the pump in cooperation with the orifice. Moreover, this delivers a flow of water into the tube. By appropriate shock wave creation with a mix of air and water injected violently into the tube, the corrosion materials collected on the inside of the tube are fractured and break away. There is a rapid flow of multiphase fluid through the tube. This rapid flow agitates the corrosion residue with sufficient shock tremors that the corrosion residue is broken and will flake off the wall. The loosened material is then flushed out of the tube by the continued flow of fluid from the lance. 
   These and other features of the present invention will be readily apparent to those skilled in the art from a review of the following description with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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 the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  is a schematic flow diagram of the system wherein the pump valve mechanism of the present invention finds application; 
       FIG. 2  is a section view of the pump/valve mechanism of this invention; 
       FIG. 3  is a side view of a lance mounting mechanism showing a lance which extends to seat against a tube to enable tube cleaning; 
       FIG. 4  is a sectional view along the line  3 - 3  of  FIG. 3  and shows details of construction of the mechanism which aligns the lance with a particular tube for cleaning; and 
       FIG. 5  is a sectional view along the line  4 - 4  of  FIG. 3  showing details of construction of the lance insertion mechanism. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Attention is now directed to  FIG. 1  of the drawings which illustrates a schematic of a system  10  for cleaning tubes and the like. The system includes a pump  11  driven by a suitable motor  12  of substantial power. The pump  11  takes a suction through a feed line  13  from a water sump or reservoir  14 . Water level is maintained in the sump by occasional replenishment. Moreover, the water is typically pure but it can be used with additives. For instance, certain types of acids or bases can be added to accomplish chemical attack on the material to be removed. 
   The pump  11  has a pump output  15  which is provided to a control valve  16 . The control valve  16  is a two position valve. In the illustrated position, water under pressure is delivered from the pump through an adjustable orifice  18 . Alternatively, the valve  16  connects with a line  17  which provides a return to the sump. The orifice  18  provides a control signal to manifold  20  of a pump valve mechanism represented in phantom in  FIG. 1  and described in greater detail below. 
   The manifold operates in conjunction with an air pressure manifold  21 . Pressurized air is provided on an air line  22  into a regulator valve  23  in the air pressure manifold. The regulator valve  23  provides a regulated air pressure output through a pair of control valves  24 . The control valves  24  are each of the same construction and connect in parallel at the output of the regulator  23 . The manifold  21  may be replaced with other actuation means, including a hydraulic actuator, an oscillating electric switch, a gas pilot valve, or other means to control a pump/valve mechanism in the manifold  20 . 
   The control valves  24  in the manifold are input to the manifold  10  which includes the pump/valve mechanism. Specifically, the control valves  24  provide air inlet lines  25  and  25 ′, respectively, to either side of an actuator  26 .  FIG. 2  provides greater detail of the pump/valve mechanism. As previously stated, the pump valve mechanism may be operated by any appropriate and convenient actuation means, but the pneumatic actuator is the preferred means and is illustrated. 
   As shown in  FIG. 2 , the air inlet lines  25  and  25 ′ provide air pressure into the actuator  26 . In the preferred embodiment, the actuator comprises a piston  70  within a cylinder  72 . Air pressure ported to the air inlet line  25  moves the piston to the right as seen in  FIG. 2 , and air pressure ported to the air inlet line  25 ′ moves the piston to the left. The piston  72  is coupled to a piston rod  74  which terminates at a linkage  76 . The linkage  76  pivots about a fulcrum  78  and links to a valve rod  80 . The valve rod  80  is mounted for movement within a pump/valve block  82 . Together, the actuator  26 , the block  82  and the parts associated therewith form the pump/valve mechanism of the invention. 
   A packing  84  seals around the valve rod  80  where it then enters a manifold  86 . The valve rod  80  terminates in a valve disc  88  which is configured to seat against a valve seat  90 . When the disc  88  is off the seat  90 , fluid under pressure from the manifold  86  is free to flow out an outlet fitting  92 . 
   Referring again to  FIG. 1 , the pump  11  provides fluid under pressure through the orifice  18  to the block  82  where it pressurizes the manifold  86 . Depending on the position of the valve rod  80 , fluid flows from the block  82  to the outlet fitting  92  or a waste discharge  94 . 
   The pump/valve mechanism has appropriate fittings on it to enable connection of a lance feed line  32 . The line  32  extends some distance, typically from 10 to 50 feet. Preferably the length of the line is kept relatively short so that pressure surges are not damped in the flow line. 
   The line  32  feeds fluid, including shock waves, to a lance  36 . The lance  36  is coaxial with an elongate cylinder  37  which encloses a piston  38 . The piston  38  is moved under hydraulic pressure in a double acting construction. This enables positive insertion and retraction of the lance. The hydraulic system preferably uses air from a suitable air pressure source delivered through a control valve  39  which connects to an air pressure regulator  40 . The air pressure is regulated and provided to an air motor  41 . The motor in turn is driven by the air to operate a hydraulic pump  42 . 
   An inlet line  43  connects to hydraulic oil sump  44 . Hydraulic oil is delivered to a control valve  45  to control the movement of the lance. 
   Specifically, the lance is extended when the valve is in the illustrated position. The lance is retracted when the valve moves to the opposite position. A return line  46  returns the low pressure oil to the sump. The valve is connected so that power is applied for extension of the lance and for retraction of the lance on operation of the valve. There is also additional equipment for positioning of the cylinder  37  as described below. 
   As shown in  FIG. 1 , the lance has an elongate rod portion which terminates at a tip  48 . The lance tip is sized to nest in the end of a tube  50 . A seal is made when the tube and tip make contact. The seal enables fluid to be introduced under pressure into the tube  50 . 
   An air inlet line  51  introduces pressurized air into the block  82  and into the manifold  86 . This permits the system to blow air through a tube to be cleaned prior the introduction of a shock wave of fluid from the system, thereby providing a water hammer to enhance the clearing effect of particularly stubborn blockages in tubes. 
   The lance  50  is moved with respect to a set of tubes in a fashion shown in  FIGS. 3 ,  4 , and  5 .  FIG. 3  shows the lance  36  which is supported and aligned by cylinder  37 . It is mounted so that it travels on a pair of parallel rails  52  and  53  shown in  FIG. 4  of the drawings. These permit movement in the X direction. The rails are parallel steel beams supported on rollers. A bracket is comprised of left and right frame members  54  and  55  which move as a unit. They enable vertical movement of the cylinder  37 . 
   More specifically, the frame members  54  and  55  define a gap where the lance extends through the gap. The cylinder  37  is anchored to the spaced plates  56  and  57  which capture the cylinder. The cylinder extends into a pair of guide surfaces and is supported against these guide services for controlled movement. The guide surfaces are formed along the edges of the frame members  54  and  55  and thus define the channel  58  shown in  FIG. 5  of the drawings. Rollers at  60  are located in this channel. There are typically four rollers, two at each corner as shown in  FIG. 5 , and a corresponding duplicate pair on the opposite side. 
   The several rollers guide the cylinder  37  for movement as illustrated. When it moves up or down, it is guided by the rollers  60  which clamp on the outside of the parallel frame members  54  and  55 . As previously mentioned, the frame members are able to move as a unit to the left or right as viewed in  FIG. 4 . While this provides one dimension of movement, the movement in the vertical direction in  FIG. 4  is the second dimension of movement. When the cylinder  37  is extended, the lance is moved in the Z direction toward the tubes  50 . 
   Attention is now directed to  FIG. 3  of the drawings where it shows the nozzle  48  at a particular tube  50 . The tube  50  is one of many. In fact, hundreds of tubes can be constructed in the heat exchanger. The heat exchanger is defined by a head  64  better shown in  FIG. 4  of the drawings. The extendible lance is forced against one of the tubes. The heat exchanger tube  50  is temporarily plugged by a plug  66  shown in  FIG. 1  to perform the method of this invention. 
   In the practice of this method, the first step is to temporarily plug the tube  50  with the plug. The plug can leak somewhat. It is not important that it maintain a perfect seal; in fact, it is desirable that it provides some leakage so that the plug restricts flow but does not totally block fluid flow. The plug serves as a liquid flow barrier. Preferably it has a length equal to the diameter of the tube plus a friction of an inch greater length. If it were longer, it would work equally well, but it would also cause more frictional drag while the plug moves along the tube  50 . In cleaning the tubes, the plug  66  is first placed in a tube and the lance is moved in an X and Y coordinate system until it is aligned with that particular tube. Then, the lance is extended and seats against the tube that has been plugged and the lance seats against the tube with a water-tight seal. As previously described, the tube is then blown free with pressurized air using air from the line  51 . 
   The next step is to fill the tube with water. This is accomplished by pressurizing the manifold  86  from the pump  11  and holding the disc  88  off the seat  90 . Fluid then flows through the lance to fill up the selected tube  50 . At this point, the system is set up to deliver a series of repeated shock waves from oscillating action of the pump/valve mechanism. Movement of the actuator piston  70  back and forth moves the valve rod back and forth at the same rate. In the action, the disk and rod act as a pump, forcing flid under pressure with a pressure surge out through the lance. This has the form of a fluid shock which is administered through the solid column of water. When that occurs, there is a tube impact which jars the coating materials on the inside of the tube. 
   When this shock loading is formed in the tube, the plug  66  may leak or may be forced downstream. No particular problem arises from that because water is always being added through the pump output. The incorporation of the orifice  18  coupled with the standing column of water downstream assures that the system transmits into the dirty tube the cleaning shock wave. The shock wave has the form of a change in pressure propagated through the standing column of water. This forms a shock wave which is experienced in the tube but it is not a pressure wave which is built up behind the plug  66 . In fact, it is not normal to use a plug to hold against high pump pressure. The plug is only a sufficient retardant to prevent complete escape of the water. The plug  66  will chatter and skid, moving finally to the far end of the tube  50 . The system utilizes a positive displacement pump  11  which enables the system to provide a relatively constant fluid output. As the pressure buildup is formed and is switched by the pumping action of the pump/valve mechanism, the water in the tube serves to break up the coating of material on the inside of the tube. 
   As a generalization, a representative pressure at the discharge of the pump  11  may exceed 10,000 psi. The pressure at the tip of the lance  48  is preferably also in that range. 
   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.