Patent Description:
Heat exchangers are used in a variety of different industries. The heat exchangers concerned with the present invention are liquid to liquid heat exchangers rather than liquid to air heat exchangers. A typical liquid to liquid heat exchanger, comprises a shell and a core. The core has two end plates which define headers at the axial ends of the shell. A bundle of tubes is welded, expanded, or both expanded and then welded in holes in the two end plates to define fluid flow passages between the two headers. Baffle plates support the tubes along their length and maintain their spacing.

The shell is a tube of much larger diameter and encompasses the core. In use, a first fluid is pumped through the core tubes and a second fluid is pumped through the shell. The tubes are made of a good thermal conductor, so that a transfer of heat takes place between the two fluids during their passage through the heat exchanger.

The flow of fluids through the shell and the core can result in a build-up of deposits. This build-up leads to a reduction in the efficiency of the heat exchanger. It is therefore essential to clean the exterior of the tubes of the heat exchanger to remove such deposits.

The conventional method of removing deposits is to separate the shell from the core, and to then use a high-pressure jet of fluid (usually water) to dislodge the deposits by directing the tip of a lance between the tubes.

<CIT> discloses a lance which is used for high pressure jetting of a heat exchanger core, the lance being of a thickness sufficiently small to fit between the tubes of the core. Conventionally, such a lance is handheld and positioned manually to penetrate between the tubes of the heat exchanger core but it is has also been proposed for such a lance to be supported and guided by a mechanical arm. <CIT> discloses a system for cleaning a tube bundle of a heat exchanger core, the system comprising: a lance for directing a jet of fluid into spaces between the tubes of the bundle,a carriage for advancing the lance into the bundle,a mount movable relative to the carriage for holding the lance, and a sensor for detecting relative movement between the lance and the carriage, so as to detect when a reaction force acting on the lance upon encountering an obstruction in the tube bundle exceeds a predetermined limit.

With a view to providing a cleaning system capable of autonomous operation, the present invention provides, in accordance with a first aspect, a system for cleaning a tube bundle of a heat exchanger core as hereinafter set forth in Claim <NUM> of the appended claims.

The ability of the system to detect when the lance encounters an obstruction allows data to be collected about the condition of the tube bundle and allows actions to be taken autonomously based on such data.

The system also affords the advantage over the prior art of being able to penetrate the tube bundle without manual control from an operator. This is because if the system were not sensitive to the presence of an obstruction, there would be is a significant risk of damaging the lance or the tube bundle.

The relative movement between the carriage and the lance may be achieved using at least two fixed members with a shaft extending therebetween and connected for movement with the carriage, and at least one slidable member connected for movement with the lance and slidable on the shaft. The movement of the slidable member is biased forward by a spring with any reaction force on the lance acting against the spring. The spring stiffness may be chosen depending on multiple parameters to adjust the sensitivity of the system to a reaction force.

To prevent movement of the lance in a plane perpendicular to the lance, two flat stabilisers may be provided to straddle the lance, the stabilisers being capable of insertion between the tubes of the bundle to be cleaned.

The sensor used for detecting the reaction force may be a proximity sensor. The proximity sensor may be mounted to one of the slidable members and may sense its proximity to a rod extending down the centre of the spring, the rod being attached for movement with one of the fixed members.

In some embodiments, the cleaning system may further comprise a computer system for receiving data from the lance, which data may include at least one of pressure emitted from the lance, number of attempts at clearing the obstruction, and time since the lance stopped advancing.

According to a second aspect of the invention, there is provided a method of cleaning a tube bundle of a heat exchanger as hereinafter set forth in Claim <NUM> of the appended claims.

In some embodiments, the lance may be retracted a set distance after detecting an excessive reaction force to minimise damage to the lance. The lance may then be advanced to clear the obstruction. The advancing and retracting steps may be repeated a pre-set number of times.

With an aim of allowing a client to receive documentation regarding the cleaning of their heat exchanger, a report may be generated to show data relating to the severity of any obstructions in the bundle. To aid ease of understanding, the report may include a graphical representation of the obstructions in the bundle.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:.

<FIG> shows the general configuration of a heat exchanger cleaning apparatus <NUM>. The apparatus <NUM> comprises a platform <NUM> having ground engaging wheels <NUM> to enable the platform <NUM> to be positioned alongside a heat exchanger tube bundle that is to be cleaned. The bundle, which is not shown in the drawing, is supported on a stand with the tubes lying horizontally and the stand may allow the bundle to be rotated. Once the platform <NUM> has been positioned alongside side the bundle, it is held stationary in a horizontal attitude by adjustable ground engaging feet <NUM>.

The platform carries two jetting assemblies, generally designated <NUM> and <NUM>, respectively, and its function is to allow the height of both of these assemblies above the ground to be adjusted and also to allow them both to be translated horizontally parallel to the tubes of the bundle. The first jetting assembly <NUM> is a lance assembly having a fluid jet emitting lance to be inserted between the tubes of the bundle to clean between the tubes. The second jetting assembly <NUM>, referred to as a fan jet, has four nozzles <NUM> that rotate about a central axis and sprays jets of fluid onto the outer surface of the tube bundle.

The two jetting assemblies <NUM> and <NUM> are mounted for vertical sliding movement on opposite sides of a vertical column <NUM> and are moved in opposite directions by a toothed belt driven by a common motor. The column <NUM> is itself guided for horizontal movement relative to the platform <NUM> and it is moved by a motor driven pinion that engages with a rack on the platform <NUM>. In this way, the two jetting assemblies can be moved along as well as up and down relative to the tube bundle, thereby allowing the bundle to be cleaned over its entire length.

The two jetting assemblies <NUM>, <NUM> receive fluid (usually water) under high pressure from a pump via respective supply lines <NUM>, <NUM>. Cameras <NUM> mounted on the platform <NUM> allow the cleaning process to be monitored remotely and the supply lines <NUM>, <NUM> include safety valves to cut off the high-pressure supply if, for example, danger to personnel or equipment is detected.

The present invention is concerned in particular with the lance assembly <NUM>, the purpose of which is to clean automatically between the tubes of the bundle. To this end, the lance assembly is required to be able to determine the position of the outer surface of the bundle, to advance into the bundle when the region between the tubes has been cleaned and it is safe to do so, and to determine the degree of penetration of the lance into the bundle to ascertain when cleaning to a desired point has been achieved.

Forcing the lance forward when it is impeded can cause damage to the lance and possibly to the tube bundle. The lance should therefore not be advanced if the region of the tubes ahead of it has not been fully cleaned and still presents an obstruction.

With a view to fulfilling all these objectives, the lance assembly of <FIG> comprises a main chassis <NUM> that is secured to the column <NUM> by a gimbal mount <NUM>.

A carriage <NUM> that supports the lance <NUM> is itself slidable along the main chassis <NUM> to advance the lance <NUM> in the direction of the arrow <NUM> into the tube bundle.

A pair of jaws <NUM> straddling the lance <NUM> are mounted for movement with the carriage <NUM> and the lance <NUM> and serve as a means of sensing the position of the outer surface of the tube bundle. The jaws are mounted on the end of two arms which retract against a spring bias when they abut the tube bundle. The retraction activates a switch and movement of the lance after operation of the switch serves to indicate the degree of penetration of the lance between the tubes of the bundle.

The lance <NUM> is secured to the carriage <NUM> by means of the mount <NUM>, which is itself slidable relative to the carriage <NUM> and spring biased to urge the lance <NUM> forward. If the lance encounters an obstruction, the mount <NUM> moves backwards against the spring bias and in the process operates a switch, the signal from which is used to prevent forced advance of the lance.

The chassis <NUM> comprises a box section of sufficient rigidity to withstand the forces imparted on the lance <NUM> during use. The box section has an end cap on each end in order to allow access to fixings and also to prevent pooling of fluid therein.

Rails <NUM> are fixedly mounted to the chassis <NUM> and allow for the chassis <NUM>, and therefore the lance <NUM> to be slid relative to the gimbal mount <NUM> to a position ready for cleaning the tube bundle.

Both the attitude of the gimbal mount <NUM> and the position of the gimbal mount <NUM> relative to the chassis <NUM> are adjusted manually, and in combination with the vertical adjustment afforded by the vertical column <NUM>, the lance assembly <NUM> as a whole can be positioned optimally relative to the tube bundle to be cleaned and can be used on a variety of tube bundle configurations.

A motor <NUM> is mounted to the chassis <NUM> and, via a toothed belt, drives the carriage <NUM> along a further set of rails <NUM> located on the opposite side of the chassis <NUM>.

To prevent entanglement and damage of cables, a chain-linked cable guide <NUM> is provided on the top surface of the chassis and is mounted at one end to the carriage <NUM> via a bracket <NUM>.

The mount <NUM> is connected to the carriage <NUM> using a floating arrangement whereby bearing blocks <NUM> are fixed to the carriage <NUM> and transmit the forward drive of the carriage <NUM> to runners <NUM>. Fixedly attached for movement with the runners <NUM> are fixed members <NUM>, and a shaft <NUM> extending therebetween (see <FIG>). Two slidable members, designated 62a and 62b can be slid along the shaft <NUM> and may therefore move relative to the runners <NUM> and the carriage <NUM>. The mount <NUM> is coupled for movement with the slidable members 62a and 62b by means of machine screws (not shown).

The above described mounting system permits the carriage <NUM> to be advanced with the mount <NUM> in instances where no reaction force is applied by the lance <NUM> to the mount <NUM> exists but allows relative movement between the carriage <NUM> and the mount <NUM> when a reaction force is applied. Such relative movement is opposed by a spring <NUM> which serves to bias the mount <NUM> forwards.

The spring <NUM> is mounted between the front slidable member 62a and a spring stop <NUM> which is fixed to a rod <NUM>. The rod <NUM> extends through a hole in the front slidable member 62a to a fixed plate <NUM>. The fixed plate is attached to the end of shafts <NUM>.

The extent of the reaction force of the lance <NUM> is measured by a proximity sensor <NUM> (located under a cover <NUM>, shown in <FIG>, but removed in <FIG>) mounted to the rear slidable member 62b sensing the distance between itself and the rod <NUM>. As reaction force increases due to encountering an obstruction, the distance between the sensor <NUM> and the rod <NUM> increases. The spring stiffness is chosen based on the requirements of the client, the stubbornness of deposits on the tubes and the expected backpressure to be encountered.

Although the mounting system has been described with reference to a proximity sensor, it will be clear to the person skilled in the art that different types of sensors may be used, such as but not limited to, a contact switch, a pressure pad, a force sensitive resistor, a strain gauge, or a piezoelectric sensor.

The purpose of the jaws <NUM> is to abut the outer surface of the tube bundle so the cleaning apparatus <NUM> may clean a tube bundle autonomously with minimal operator input. The jaws <NUM> may move in two directions; vertically, and also in the direction of the major axis of the lance <NUM>.

First, they can move in the vertical direction by a small amount if the lance assembly is not in the exact required position or to allow for the bending of tubes in the bundle. To allow such a movement, the jaws <NUM> are connected to the arms <NUM> via fingers <NUM> (see <FIG>). The fingers <NUM> are pivotable about mounting bolts <NUM> against a spring biased mechanism <NUM>, partially hidden by cover <NUM>, and the deflection is measured using sensors.

The second direction of movement is parallel to the movement of the lance <NUM> when penetrating the tube bundle to clean between the tubes. The arms <NUM> are movable relative to the runners <NUM> using tracks on each of their inner surfaces that offer sliding or rolling engagement. The sliding or rolling engagement is similar to that commonly found in kitchen drawers.

The arms <NUM>, and therefore the jaws <NUM> are biased forward by linear springs <NUM> to force the jaws <NUM> to remain in contact with the tube bundle as the lance penetrates or retracts from said bundle. The term "linear spring" is used to relate to a spring constructed in manner similar to a steel tape measure, where the tape is wound back into its cylindrical housing with a nearly constant force independent of extension. The range of movement of the jaws <NUM> is from a fully extended state where the jaws <NUM> straddle the tip of the lance <NUM> as shown in the figures, to a fully retracted state where the jaws either touch or almost touch the mount <NUM>.

Upon retraction of the jaws <NUM>, a switch is activated which starts a measurement sensor, which may be in the form of a transducer, in order to determine the degree of penetration of the lance <NUM> into the tube bundle. Rather than activating a switch as soon as the jaws <NUM> begin retraction, the switch may instead be activated once a certain degree of penetration has occurred. This allows the output of the sensor to also be used to indicate that it is safe for fluid to be emitted from the lance <NUM>.

The lance <NUM> is a cylindrical tube as is known in the art and, more specifically, in <CIT>. The lance <NUM> contains one or more holes toward its tip for emitting a fluid, at high pressure to clean tubes of a heat exchanger core, which comprises a tube bundle. The fluid is generally water but may, for example, include an abrasive to improve the cleaning capabilities of the apparatus <NUM>.

The at least one hole may be positioned at the tip, or along the length of the lance <NUM>. If positioned along the length of the lance <NUM>, the holes may be orientated so as to emit fluid in any direction, i.e., projecting forwards towards the tip of the lance <NUM>, backwards away from the tip of the lance <NUM>, or in a direction orthogonal to the major axis of the lance <NUM>. Where more than one hole is provided, each hole may be orientated in either the same or different direction.

The lance <NUM> may be rotated about its major axis to aid cleaning, and this may be achieved using an electric motor <NUM> mounted on the top of the mount <NUM>. In the example shown in the figures, the motor <NUM> is mounted orthogonal to the major axis of the lance <NUM>. The motor <NUM> rotates a first bevel gear which drives a second bevel gear, the second bevel gear mounted for rotation with the lance <NUM>. The bevel gears are located within the mount <NUM> to protect them from debris and fluid.

It will be appreciated that whilst an electric motor is disclosed in the above paragraph, this is not limiting and is merely an example. It will be clear to the person skilled in the art that a pneumatic motor may be employed to achieve the desired outcome.

Due to the reaction forces of the fluid jets emitted from the lance <NUM> when cleaning stubborn material from the tube bundle, the lance <NUM> is prone to buckling or, as it is rotating, to precession. To prevent precession, the lance is straddled by two flat stabilisers <NUM> lying in a generally horizontal plane and sufficiently thin to be able to penetrate between the tubes of the bundle. The stabilisers <NUM> extend the majority of the length of the lance <NUM>. Movement of the tip lance <NUM> in a vertical plane is inhibited by the jaws <NUM> and once the tip of the lance has penetrated between the tubes of the bundle by the tubes that have been cleaned.

For the cleaning apparatus <NUM> to be able to run autonomously in a safe manner, at least one safety valve needs to be provided to cut off the high-pressure supply of fluid. In the present embodiment, there is an electronically controlled safety valve (not shown) linked to multiple sensors. The electronically controlled safety valve is activated by a foot pedal which is depressed by a 'foot' analogue which may be electronically, pneumatically or hydraulically controlled. The safety valve may be operated to cut-off the high-pressure supply in the following non-limiting scenarios:.

The above are merely examples and it will be clear that many other parameters may be monitored and linked to the safety valve to reduce the risk associated with the autonomous cleaning apparatus <NUM>.

A second safety valve may be employed to cut off the high-pressure supply of fluid to the lance <NUM>, the safety valve being operated using a user operated pedal (not shown). The configuration of the pedal is such that pressure may only be supplied to the lance <NUM> when the pedal is depressed, meaning that the cleaning system can only be operated when the apparatus operators are in a safe location, such as from within a control box or behind a safety barrier. If the operator notices anything unsafe such as a person walking towards the apparatus <NUM>, the pedal allows the operator to override the system and stop the supply of fluid. The configuration of the pedal allows the operator to simply take their foot off the pedal to stop the system.

The second safety valve, operated manually by the operator and situated in-line and upstream of the first valve, is the master switch. That is to say that no matter the status of the first valve, it is not possible for full working pressure to be achieved without the pedal operating the second valve being depressed.

Before fluid flow commences, the apparatus <NUM> must be set up. The apparatus is rolled to a position that platform <NUM> lies parallel to the tube bundle and then held in place and supported by the feet <NUM>. The lance assembly <NUM> is positioned at the height of the centre of the tube bundle, i.e., the height at which the most penetration is required during cleaning. The chassis <NUM> is then moved manually forward in the direction of the arrow <NUM> to a point before the end caps of the chassis <NUM> lie next to the outer surface of the tube bundle. The chassis <NUM> is clamped in place and the gimbal mount <NUM> adjusted for optimum cleaning.

The lance assembly <NUM> is then raised or lowered to a point just above or below the tube bundle. Using the motor <NUM>, the lance <NUM> is then advanced to a point past the centre of the bundle, this setting the desired maximum penetration into the bundle. There is no advantage to advancing the lance <NUM> further than this as the bundle can be rotated and cleaned from the other side. Furthermore, if the bundle is split in half longitudinally, passing the centre of the bundle will cause fluid emitted from the lance <NUM> to be sprayed at nearby equipment and operators, presenting a safety risk due to the very high pressure at which the lance <NUM> emits fluid.

The advancing distance is measured by a transducer and is logged into the cleaning system, and acts as a limit to which the lance <NUM> can advance. The lance is then fully retracted to its starting position.

Once the above setup steps have been complete, the lance assembly is lowered to the gap between the first rows of tubes where cleaning is to be commenced.

The carriage <NUM> and lance <NUM> are advanced towards the outer surface of the tube bundle. During this phase, the jaws <NUM> will contact the outer surface of the bundle and come to a stop. The switch displaced by the arms <NUM> will indicate that the tip of the lance <NUM> is about to commence penetrating between the tubes of the bundle and measurement of its advance is commenced.

As the carriage <NUM> is driven forward, the lance <NUM> will move relative to the arms <NUM> and penetrate the bundle, this penetration being measured by the penetration measuring transducer. Such a measuring device may be in the form of a rotary encoder and may, for example, be mounted to the shaft of the motor <NUM> which advances the lance <NUM>. Alternatively, a linear encoder or any other device capable of measuring the movement of the lance <NUM> relative to the arms <NUM> may be employed.

Upon a pre-set degree of penetration, a switch or sensor will output a signal allowing the first safety valve to permit high-pressure fluid to be emitted from the lance, providing that the second safety valve is also permitting passage of fluid.

The lance <NUM> continues to advance until it either reaches the limit point set in an earlier step, or the backpressure sensor <NUM> detects that excessive resistance if being encountered by lance <NUM>. If a large reaction force is applied by the lance <NUM> to the mount <NUM>, the sensor <NUM> prevents the motor <NUM> from advancing the carriage <NUM>. Depending on the settings, the lance <NUM> may be held still for a set period of time in the hope that the obstruction will be cleared, or it may move forwards and backwards a set number of times, known in the art as pecking, to try to clear the obstruction. Obstructions may be in the form of deposits or may be structural supports for the bundle. If re-programmed to do so, the electronically controlled safety valve can stop the flow of fluid after a set time or number of pecks to reduce damage to the lance <NUM> and allow the operator to investigate the problem further.

Once the lance <NUM> reaches the limit point, the lance may return to its initial position while still emitting fluid at full working pressure to clean the tubes further with a second pass.

As the lance is being retracted, the safety valve operating switch is again triggered and the electronically controlled safety valve reduces the pressure to the lance. The jaws <NUM> remain in contact with the outer surface of the tube bundle at this stage due to the forward biasing linear springs <NUM>.

The lance <NUM> is then fully retracted from the tube bundle to its starting position where the jaws <NUM> are no longer in contact the tube bundle and the tip of the lance <NUM> is clear of the tubes.

The lance assembly <NUM> is then moved horizontally along platform <NUM> a set amount to advance into the bundle once again. After the lance has traversed the full length of the tube bundle, the lance assembly is lowered on vertical column <NUM> to clean a different gap.

The cleaning apparatus <NUM> is connected to a computer system (not shown), the computer system being able to receive data from the lance <NUM> and the sensor <NUM>. The type of information that the computer system may receive includes; fluid pressure, reaction force measured by the sensor <NUM>, the number of attempts at clearing the current obstruction, and time passed since the lance <NUM> stopped advancing.

The computer system may use the received information to generate a report indicating the severity of some obstructions. Optionally, the report may include a diagram or three-dimensional representation of the bundle showing the obstructions in an easy to understand format such as a heat map.

It will be appreciated that the above description are merely embodiments of the invention, and that any minor adaptation to the embodiments described above are intended to fall within the scope of the claims.

For example, although foot operated pedals are used in the described embodiment for actuation of the safety valves, other methods of activation could be used such as a switch or pressure sensor in the system operator's seat or a button or lever.

Claim 1:
A system for cleaning a tube bundle of a heat exchanger core, the system comprising:
a lance (<NUM>) for directing a jet of fluid into spaces between the tubes of the bundle,
a carriage (<NUM>) for advancing the lance (<NUM>) to penetrate into the bundle,
a mount (<NUM>) movable relative to the carriage (<NUM>) for holding the lance,
a spring (<NUM>) acting on the mount (<NUM>) to urge the lance towards the tube bundle, any reaction force on the lance being opposed by said spring, and
a sensor (<NUM>) for detecting relative movement between the lance (<NUM>) and the carriage (<NUM>), so as to detect when a reaction force acting on the lance (<NUM>) upon encountering an obstruction in the tube bundle exceeds a predetermined limit.