GB2585500A

GB2585500A - Tube cleaning Robot

Info

Publication number: GB2585500A
Application number: GB2009738.2A
Authority: GB
Inventors: Stephenson Adam; Sumsion Derek
Original assignee: Tube Tech International Ltd
Current assignee: Tube Tech International Ltd
Priority date: 2019-06-27
Filing date: 2020-06-25
Publication date: 2021-01-13
Anticipated expiration: 2040-06-25
Also published as: GB2585500B; GB201909265D0; GB202009738D0

Abstract

A robot for cleaning exterior tubes of a heat exchanger comprises a carriage 10 and motorised traction assemblies 12 engaging the tubes and advancing the carriage along the tubes. A lance 14 supported on a motorised mount 24, 26, 28, 30 on the carriage and positions the lance to direct a jet of fluid into spaces between the tubes. The mount permits the lance to pivot about two axes (24, 26). An obstruction detection system detects an obstruction(s) and resistance to forward movement of the lance. A sensor (MEMS – micro electro mechanical sensor) determines at least one of pitch, roll and yaw of the carriage so that the mount is controlled in dependence upon an output signal of the sensor to maintain the attitude of the lance constant during movement or the robot despite any possible pitching, rolling or yawing of the carriage. Obstructions may be sensed by current consumption of the driver motors, a strain gauge sensing deflection of the lance or a proximity sensor. The lance is guided around the obstruction(s) and the robot is reversed to clear the obstruction(s), and lance position in the heat exchanger where an obstruction is detected is recorded and maps found blockages.

Description

Tube cleaning robot

FIELD OF THE INVENTION

The invention relates to a robot for cleaning the exterior of tubes of a heat exchanger, in particular of a heat exchanger directly heated in a furnace.

BACKGROUND

In many industrial plants, such as refineries, a fluid is heated by flowing through a heat exchanger, also referred to as a convection bank, comprising a bundle of tubes over which pass the flue gases of a furnace. In some cases, the tubes are bare radiant tubes having smooth outer surfaces, while in others each tube is a finned convection tube having closely spaced fins projecting from its outer surface to increase the surface area of the tube and thereby improve the heat transfer.

Because of incomplete combustion of the fuel burned in the furnace, a deposit of soot and other combustion by-products can form on the tubes or between the fins, which, if allowed to build up, causes a serious deterioration in efficiency. To maintain good performance, it is therefore necessary to clean the outer surfaces of tube bundles periodically.

There are several known technologies for cleaning the tubes including: chemical spraying, using soot blower technology which utilises high pressure air, and fireball zs technology which injects an abrasive blast and chemical media into the upward draft of a flame.

EP 2691726, which is believed to represent the closest prior art to the present invention, describes a robot for cleaning the exterior of a furnace heat exchanger that includes a bundle of tubes heated by the flue gases of a heater furnace. The robot comprises a motorised carriage which is guided for movement along the outer surface of the bundle in a direction parallel to the tubes. A holder is attached to the carriage for -2 -holding a lance in a position relative to the carriage that permits the lance to penetrate between the tubes of the bundle and the lance is advanced along the heat exchanger by the carriage while remaining in the latter position.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a robot for cleaning the exterior of tubes of a heat exchanger, the robot comprising a carriage, traction assemblies for engaging the tubes to enable the carriage to be advanced along the tubes, at least one drive motor for driving the traction assemblies, a lance for directing a jet of fluid into spaces between the tubes, a motorised mount for supporting the lance on the carriage and positioning the lance relative to the carriage, and an obstacle detection system for detecting an obstruction to forward movement of the lance, wherein the mount permits the lance to be pivoted about two axes axis lying in a plane normal to the direction of travel of the robot, and a sensor is provided to determine at least one of the pitch, roll and yaw of the robot carriage, the mount being controlled in dependence upon an output signal of the latter sensor to maintain the attitude of the lance constant during movement of the robot, despite any possible pitching, rolling or yawing of the carriage.

As the surface of the convection bank on which the robot is advanced may not be perfectly flat, the attitude of the lance would change as the robot tilts up and down or from side to side. In the invention, a sensor is provided to determine at least one of the pitch, roll and yaw of the robot carriage and the mount is controlled in dependence upon an output signal of the latter sensor to maintain the attitude of the lance constant during movement of the robot, despite any possible pitching, rolling or yawing of the carriage.

The obstacle detection system may comprise a sensor for sensing current consumption the motor driving the traction assemblies to determine when the load on the motor exceeds a predetermined value, a strain gauge sensing deflection of the lance on encountering an obstruction, or a proximity sensor mounted on the lance to sense the presence of an obstacle in the projected path of travel of the lance. -3 -

If the robot of EP 2691726, met with an obstruction, it had to be removed from the furnace and the lance had to be repositioned to penetrate less deeply into the convection bank. The provision of an obstacle detecting system on board the robot enables the position of the lance to be adjusted dynamically, i.e. while the robot is traversing the length of the convection bank, to pass around obstacles. Once a lance has succeeded in passing around an obstacle, it can be returned to its original position and for this reason an obstruction at any given position in the convection bank need not limit the depth to which the bank can be cleaned over the remainder of its length.

As the point on the carriage of the robot at which the lance penetrates into the tube bank may not be the same for all furnaces, the mount may additionally be capable of translation relative to the carriage in a direction transverse to the direction of travel of the robot.

An important advantage of the invention is that it permits a record to be retained of all positions in the heat exchanger where an obstacle is detected. Thus a report may be generated to indicate locations in the convection bank where cleaning has not been fully successfully, for example on account of bending of the tubes or a build of deposit that the fluid emitted from the lance could not fully dislodge.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view showing a general configuration of a robot, and Figure 2 is a flow diagram illustrating a method of cleaning tubes according to the invention. -4 -

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows the general configuration of a robot for cleaning the exterior of tubes in a heat exchanger or convention bank of a furnace. The robot comprises a carriage 10, traction assemblies 12, a lance 14, and a mount 24, 26 and 28 for supporting, translating and pivoting the lance 14.

The carriage 10 is a flat plate onto which other components of the robot are mounted. The carriage 10 is generally rectangular, and features multiple holes for accepting screws, bolts and nuts. Components attached to the carriage 10 may include covers, batteries and motors. The carriage 10 also supports sub-assemblies of the robot, including a lance mount and traction assemblies.

Each traction assembly comprises continuous a track 12, also known as a caterpillar track. The tracks 12 rest on tubes of the heat exchanger and provide drive to move the robot along the tubes in order to clean the full length of the heat exchanger. Caterpillar tracks 12 are preferred belt to aid traction and to allow them to conform to the shape of the tubes but it is alternatively possible to use wheels.

The tracks are guided around a frame 16, within which is a drive motor (not shown) for driving the tracks 12. A separate drive motor within the 16 of each traction assembly allows for the robot to be steered along any bent tubes by driving each track 12 at a different speed or even in a different direction. A possible alternative is to use two motors mounted to the carriage 10 with shafts extending to the traction assemblies. In an embodiment where steering is not required or is accomplished in another way, a single motor may drive both tracks 12.

Each frame 16 contains an access hatch 18 through which the motor can be accessed. Screws 20 hold the hatch 18 in place. The frame 16 may include a vent 22 to reject heat produced by the motor to prevent overheating. Brackets 42 attach the traction assembly to the carriage 10. -s -

The motorised mount sewing to position the lance 14 provides three degrees of motion, each represented by a double-headed arrow in Figure 1. The mount comprises a first housing 28 guided by a block 34 to move along a track 32 that is attached to the carriage 10 and extends transversely to the direct of travel of the robot. The first housing 28 is movable along the track 32 by a motor 30 mounted on the carriage 10 and driving a shaft in screw-threaded engagement with the mounting block 34 by way of a chain transmission 40. This achieves the first degree of movement of the lance, which allows the lateral position of the base of the lance to be set correctly between the tubes over which the robot is advanced.

The first housing 28 rotatably supports a second housing 26 and contains a motor for rotating the second housing 26 about an axis parallel to the direction of movement of robot. This achieves the second degree of motion of the lance and allows its attitude in a vertical plane normal to the direction of movement of the robot to be set to suit the configuration of the tubes of the convection bank. For example, if the tubes are in a square array the lance my need to be vertical to pass between the tubes, whereas other configurations may require the lance to be introduced at an angle between the tubes.

The second housing 26 in turn rotatably supports a lance holder 24 and contains a motor to rotate the lance holder about an axis lying in the plane normal to the direction of movement of the robot. If the lance is vertical, the lance would be pivoted about a horizontal axis in this plane but if it is inclined to the vertical then is would pivot about an axis perpendicular to its plane of inclination. In each case, pivoting of the holder 24 by the motor in the second housing 26 achieves the third degree of motion, which sets the extent of penetration of the lance between the tubes of the convection bank.

The robot in the present invention further comprises an obstacle detection system for detecting obstacles in the path of the lance 14. In one embodiment, a sensor monitors the current supplied to the motors for driving the tracks 12. When the robot encounters resistance in its forward movement, the current delivered to the drive motor will increase on account of the increased load. If the current delivered is higher than a threshold value, it indicates that the lance has met an obstacle. Alternative ways of detecting an obstacle -6 -would be a strain gauge or a proximity sensor mounted on the lance, the former sensing deflection of the lance and the latter sensing an obstacle in the path of the lance. A still further possibility would be to sense torque on the shaft rotating the holder 24 or to sense the load current of the motor mounted in the second housing 26 to rotate the holder 24.

Figure 2 is a flow chart for an obstacle avoidance system as would be implemented in software, the flow chart describing the steps taken by the robot to cope with obstacles in the path of the lance 14. The flow chart assumes that obstacle detection relies on measuring the current load of the motor(s) advancing the robot but can readily to be adapted to suit other ways of detecting an obstacle or obstruction in the path the lance After initiating the process loop in step SI, the drive current of the motor(s) advancing the robot along the convection bank is measured in step S2. In step S3, the measured current value is compared with a threshold value. The process returns to step S2 if the current is within acceptable limits but if the threshold in step S3 is exceeded, then an obstacle is deemed to be present and action is taken to avoid it.

The first action taken in step S4 is for the control system to reduce the pressure of the fluid supplied to the lance 14, as cleaning of the convection bank cannot take place until the robot has passed the obstacle.

In step S5 the robot is reversed a short set distance and in step S6 the lance 14 is pivoted by a small amount with the intention of clearing the obstacle. The reversing of the robot is to ensure that the obstacle will not interfere with the pivoting of the lance.

In step S7, the robot is advanced by a distance greater than the set reversing distance of step S6 after the lance has been moved to clear the obstacle. While being advanced, the drive current of the motors is again monitored (step S8) and compared (step S9) with the threshold value. If the threshold value in step S9 is exceeded, it indicates that the lance 14 has not been raised sufficiently to clear the obstacle and -7 -therefore steps S5 to S9 are repeated until the robot succeeds in advancing the distance set in step S7 without exceeding the threshold value.

Once the robot has successfully advanced the distance set in step 57, the lance 14 is pivoted in order to return it to its original position (step S10). In step S11, the position of the lance 14 is compared with its original position. If the lance 14 is prevented from returning to its original position by the obstacle, steps S6 to S 11 are repeated. In place of step Sll, one could determine if the motor pivoting the lance encounters an excessive load and use that indication to return to step S7.

Once the lance 14 has successfully returned to its original position, the obstacle is deemed to have been cleared and cleaning of the convection bank can be resumed. In step S12, the pressure of the fluid supplied to the lance 14 is increased to working pressure. Step S13 returns the process to the start (step 51), where process loop is again initiated and step S2 continues to monitor the drive current of the motors.

A record of the position of any obstacles may be maintained so that a report may be produced to indicate the regions where cleaning has not been fully successful. The report of the obstacles may take the form of a map of the blockages found within the heat exchanger bundle.

To clean the convection bank efficiently, the jet of fluid emitted from the lance should be aimed consistently in relation to the tubes which it is cleaning. This should remain so even when the tubes along which the robot is advancing are not straight and may be bent in 3 dimensions. For example, if there is a dip in the tubes over which the robot is advanced, the robot will pitch downwards and, in the absence of measures to prevent it, the attitude of the lance would change, causing it to penetrate deeper into the convection bank.

To maintain the position of the lance 14 constant, its attitude relative to the carriage must be adjusted to compensate for the pitch of the robot. It will be appreciated -8 -that although the above example refers only to pitching, roll and yaw of the robot would also affect the position of the tip of the lance.

In the described embodiment of the present invention, a MEMS (micro-electro-mechanical sensor) sensor, acting in the same way as a gyroscope, is provided to determine the attitude of the carriage. The motorised mount is controlled in dependence upon the output signal of the MENIS sensor to compensate for pitch, roll and yaw of the robot and maintain the tip of the lance in its desired position. The task is analogous to that used in a military tank, where the aim of the gun barrel at a specific target is maintained while the tank moves over rough terrain.

The person skilled in the art will appreciate that various modifications may be made to the embodiments described without departing from the scope of the claims. For example, alternative forms of manipulator may be used to position the lance, alternative sensors, such strain gauges and proximity sensors, may be used to detect obstacles and alternative strategies may be adopted to enable cleaning to continue after an obstacle has been encountered.

Claims

-9 -CLAIMS 1. A robot for cleaning the exterior of tubes of a heat exchanger, the robot comprising a carriage (10), traction assemblies (12) for engaging the tubes to enable the carriage (10) to be advanced along the tubes, at least one drive motor for driving the traction assemblies, a lance (14) for directing a jet of fluid into spaces between the tubes, a motorised mount for supporting the lance (14) on the carriage and positioning the lance relative to the carriage, and an obstacle detection system for detecting an obstruction to forward movement of the lance, wherein the mount permits the lance to be pivoted about two axes axis lying in a plane normal to the direction of travel of the robot, and wherein a sensor is provided to determine at least one of the pitch, roll and yaw of the robot carriage, the mount being controlled in dependence upon an output signal of the latter sensor to maintain the attitude of the lance constant during movement of the robot, despite any possible pitching, rolling or yawing of the carriage.
2. A robot as claimed claim 1, wherein the mount is capable of translation relative to the carriage in a direction transverse to the direction of travel of the robot.
3. A robot as claimed in claim 1 or 2, wherein the obstacle detection system comprises a sensor for sensing current consumption of the motor driving the traction assemblies to determine when the load on the motor exceeds a predetermined value.
4. A robot as claimed in claim 1 or 2, wherein the obstacle detection system comprises a strain gauge sensing deflection of the lance on encountering an obstruction.
-10 - 5. A robot as claimed in claim 1 or 2, wherein the obstacle detection system comprises a proximity sensor mounted on the lance to sense the presence of an obstacle in the projected path of travel of the lance.
6. A robot as claimed in any preceding claim, further comprising a control system for controlling at least one of the motor driving the traction assemblies and the motorised mount in order to guide the lance around obstacles not dislodged by the fluid jet emitted by the lance.
7. A robot as claimed in claim 6, wherein, in response to detection of an obstacle in the path of the lance, the control system serves to cause the robot to reverse a short distance, to change the position of the lance to clear the obstacle and to return the robot to move in a forward direction.
8. A robot as claimed in claim 7, wherein after the lance has passed around a detected obstacle, the control system acts to return the lance to the position at which the obstacle was encountered.