This project was funded by the National Plan for Science, Technology and Innovation (MAARIF AH)—King Abdulaziz City for Science and Technology—the Kingdom of Saudi Arabia, award number (10-WAT1397-04).
The present invention relates to an online cleaning system used to clean a tube and shell heat exchanger including a cleaning system comprising a positioner, a plunger, an umbilical cleaner, and a motor. The cleaning system uses a tube that contains both rotating and translating mechanical actions and cleans while the heat exchanger is in operation.
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
There are several types of heat exchangers used in various industries. A common type is known as a shell and tube type. Modern shell and tube exchangers are of several types, including: (1) a straight through version where the heat exchange tubes are generally straight, (2) a U-tube version where the heat exchange tubes are bent into a U so the inlets and outlets of the heat exchange tubes pass through the same tube sheet and open into compartments provided by a channel and (3) a floating head type where the inlets and outlets are at one end of the exchanger, the tubes are straight and open, at the opposite end of the exchanger, into a floating head or manifold that directs flow back toward the outlet. U-tube type heat exchangers have a cost advantage because only one set of inlet/outlet channels is required. Straight through heat exchangers are typically selected when the tube side fluid deposits materials in the tube or is corrosive because it is usually more difficult to clean the curve in a U-tube type.
Fixed-tube-sheet exchangers are used more often than any other type. The tube sheets are welded to the shell. Usually these extend beyond the shell and serve as flanges to which the tube-side headers are bolted. This construction requires that the shell and tube-sheet
There is no limitation on the number of tube-side passes. Shellside passes can be one or more, although shells with more than two shell-side passes are rarely used.
Tubes can completely fill the heat-exchanger shell. Clearance between the outermost tubes and the shell is only the minimum necessary for fabrication. Between the inside of the shell and the baffles some clearance must be provided so that baffles can slide into the shell. Fabrication tolerances then require some additional clearance between the outside of the baffles and the outermost tubes. The edge distance between the outer tube limit (O.T.L.) and the baffle diameter must be sufficient to prevent vibration of the tubes from breaking through the baffle holes. The outermost tube must be contained within the O.T.L. Another type of shell and tube heat exchanger is a U-tube heat exchanger. In a U-tube heat exchanger, the tube bundle consists of a stationary tube sheet, U-tubes (or hairpin tubes), baffles or support plates, and appropriate tie rods and spacers. The tube bundle can be removed from the heat-exchanger shell. A tube-side header (stationary head) and a shell with integral shell cover, which is welded to the shell, are provided. Each tube is free to expand or contract without any limitation being placed upon it by the other tubes.
The U-tube bundle has the advantage of providing the minimum clearance between the outer tube limit and the inside of the shell for any of the removable-tube-bundle constructions. Clearances are of the same magnitude as for fixed-tube-sheet heat exchangers.
The number of tube holes in a given shell is less than that for a fixed-tube-sheet exchanger because of the limitations on bending tubes of a very short radius.
The performance of shell and tube heat exchangers degrades over time by the deposition of solids from the tube side flow onto the inside wall of the heat exchanger tubes. This is commonly referred to as tube side fouling and can significantly impair the performance of heat exchangers. Fouling deposits act as an insulator and thereby reduce heat transfer across the walls of the tubes. This fouling can also cause increased pressure drops across the tubes thereby decreasing flow through the tubes. Under certain conditions, these deposits can also promote corrosion of the inside of the tube wall, a phenomenon known as under-deposit corrosion. This corrosion, if left unchecked, can produce leak paths through the tube wall allowing commingling of the heat exchange fluid and the process fluid. Even though tube side fouling is a persistent maintenance problem, it is much preferred to shell side fouling because it is much easier to clean and inspect the interior of the heat exchange tubes as compared to the outside. For this reason, in situations where one of the two fluids is more corrosive or more prone to produce deposits in the heat exchanger, this fluid may preferably be put through the tubes rather than through the shell.
Over time, heat exchangers tend to develop residue on the surfaces of the tubes, tube sheets, tube support plates and other internal structural parts. The residue can comprise adherent films, scales, sludge deposits, corrosion and/or other similar materials. Over time, this residue can have an adverse affect on the operational performance of the exchangers. The same problem can arise for all piping and tubing found in industrial facilities.
Various methods have been developed to clean the inside of heat exchanger tubes to remove deposits. These deposits are often relatively hard and therefore difficult to remove from the tube walls. To effectively clean tube side fouling, the heat exchanger is usually taken off-line and out of service to access and mechanically clean the inside of the tubes. These off-line methods of cleaning include high pressure water cleaning known as hydroblasting, mechanical cleaning using brushes, scrapers or projectiles, and blasting with abrasive media. Once the tubes are cleaned and while the heat exchanger is off-line, the tubes may be inspected to determine if corrosion has thinned or pitted the tube wall and a determination can be made to replace or retain the tube. In some circumstances, the tube may be replaced or simply plugged, i.e. a plug is placed in the tube to block flow through it.
Most inspection techniques require the heat exchanger to be out of service. Cleaning by circulation of abrasive media may conventionally be done while a heat exchanger is in operation by inserting media into the flow entering the tubes and then separating the media from flow out of the tubes. As currently practiced, heat exchangers must be out of service in order to plug a leaking or unserviceable tube. The cost of disassembling and then reassembling the heat exchanger to permit access to the tubes for cleaning and inspection can be significant. More significant in many situations is the lost production cost from taking the heat exchanger and its associated equipment out of service.
Other manual methods involve taking the heat exchanger off-line and out of service to manually clean the tubes. These manual methods of cleaning include: high pressure water cleaning to blast away the deposits, acid cleaning to loosen or dissolve the deposits, or the propulsion of a brush or scraping implement through the tube to scrape off the deposits.
Another common method involves the controlled application of high pressure water and/or chemical streams to the affected areas of the heat exchanger. This method can require the presence of one or more persons at or near the point of application of the high pressure stream to the exchanger during the cleaning process.
For example, an operator may stand in clear view of, and near the line-of-fire of, the high pressure stream to direct the stream to the affected areas of the exchanger. Another person may be needed to operate a control panel next to the exchanger to further control the direction and volume of stream flow. This type of work is extremely labor intensive and potentially hazardous. For example, it may be necessary for crews to manually reposition the device providing the high pressure stream for each cleaning stroke. Further, those persons in close proximity to the cleaning environment can be exposed to high pressure water, hazardous cleaning chemicals or other potentially toxic, poisonous or volatile materials.
All of these manual methods result in the loss of use of the heat exchanger during cleaning and incur the cost associated with the cleaning itself. Furthermore, after cleaning and during operation, the tubes begin to foul and continue fouling resulting in a reduction in heat transfer until the next cleaning. In the case of acid cleaning, pitting and corrosion of the tube may occur.
The costs associated with reduced capacity of heat exchanger tubes can also be substantial in situations where the throughput of process fluids has to be curtailed. In one oil refinery, the estimated lost production costs of reduced throughput from a catalytic cracker due to deteriorating heat exchange performance has been in the range of $500,000/year.
Other methods for cleaning the tubes without taking the heat exchanger out of service include devices which introduce a number of tube cleaners (e.g., balls or brushes) into the fluid which passes through the tubes. The tube cleaners are designed to fit tightly enough into the tube to contact the tube wall while still being pushed through the tube by the fluid pressure. At the outlet of the tube these tube cleaners are collected and recycled back to the tube inlet. In some systems the tube cleaners are propelled through the tube in a direction opposite the fluid flow by reversing the fluid flow temporarily. The number of tube cleaners used and the recycle rate may vary depending upon the cleaning effectiveness desired.
While these on-line systems avoid having to take the heat exchanger out of service, there is significant cost associated with the necessary piping and valving. Further, these methods are prone to plugging of the tube by debris that has been loosened by the tube cleaners. After the tubes have been cleaned the pressure drop across the tube and the heat transfer rate across the tube wall return to their nominal design points.
The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
In one embodiment of the present invention a cleaning system used to clean tube and shell heat exchangers (HEX).
In another embodiment, the system includes a positioner, a plunger, and an umbilical cleaner.
In another embodiment, the system cleans the HEX while the heat exchanger remains in operation.
In another embodiment, the system isolates and cleans a single tube at a time while the HEX remains in operation.
In another embodiment, the system further includes a diagnostic tool system to monitor the status of individual pipes in the HEX.
In another embodiment, the diagnostic tool system includes data collection.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.
The present invention relates to a cleaning system used to clean tube and shell heat exchangers. The cleaning system includes multiple mechanical systems. The cleaning system is an online cleaning system and cleans the tubes in the tube and shell heat exchanger while the heat exchanger remains in use. The system also isolates and cleans the tubes one at a time while the other tubes remain online for the heat exchanger to function.
In one embodiment of the invention, the cleaning system comprises a positioning system.
Rotational selection of 2-3 is implemented by attaching an annular rail 5-3 sliding on a fixed rail support. The angular selector 1-3 rotates the annular rail 5-3 to a specified rotational position so that the cleaning system may be inserted into a particular tube of the heat exchanger. The angular selector 1-3 is preferred to be installed at a fixed position. The motor may be electric or hydraulic. The positioner moves the cleaning system to a particular tube. The positioner attaches to the tube in a disk like attachment form. Tube selection moves the plunger to select a tube and then plunge the plunger to start the cleaning process of the tube. The position of any tube in 2D space could be described by selecting coordinates from a coordinate system (r, θ).
The positioner includes a motor 3-3 that may be electric or hydraulic. The motor moves along the straight rail that is positioned across the diameter of the heat exchanger. The straight rail may be singly or doubly formed. Preferably, the straight rail is singly formed.
The hydraulic fluid power motor may be run from the outside of the system and is easier to maintain and safer to operate compared to an electric motor that is immersed inside the fluid.
In another embodiment of the invention, a rectangular positioner 3-5 is illustrated in
In
In another embodiment of the invention, a sensory system is used to check and verify the angular and radial positions of the positioner so that the positioner inserts the plunger into the correct tube at the correct angle to allow for maximum cleaning of each particular tube of the heat exchanger.
In another embodiment of the invention, the plenums of the heat exchanger are slightly enlarged to facilitate the positioner to have easy access to peripheral tubes. The cleaning system may be an insert between the plenum and the tube-sheet/base-plate.
Once the positioner locates and isolates a single tube in the heat exchanger, a plunger system that is attached to the positioner attaches to the tube. The plunger is anchored around the tube. In one embodiment, the plunger may enter the tube slightly. In another embodiment, the plunger does not enter the tube but rather the plunger attaches itself to the outer perimeter of the tube. The plunger structure includes materials such as but not limited to a rubber shoed cylinder. The rubber material of the plunger allows for the plunger to be pushed around the tube in order to seal the plunger around the tube. The shoe is slightly larger than the tube but small enough not to cover the neighboring tubes. The cleaning elements enter the tube through the plunger. The cleaning elements are connected by a cable/umbilical cord.
In one embodiment of the invention, the cleaning system may include one plunger and one positioner in which the cleaning system enters one side of the tube of the heat exchanger.
In another embodiment, there are two positioners and two plungers in which the cleaning system enters both sides of a tube. A first positioner and a first plunger enter one side of the tube and a second positioner and a second plunger enter the other side of the tube. Only the first positioner and first plunger contain the motor that holds the cable of the cleaning element of the cleaning system. With two plungers, a special fluid circulation of different flow rate and possibly different fluid could be established. The cleaning debris could also be caught and cleaned out. With only one positioner and one plunger then the cleaning fluid mixes from the other side with the heat-exchanging medium. There is only a limited flow control.
The flow established in the tube through both plungers moves the brush. However, this motion is controlled because the allowed length is determined by the motor holding the rolled cable. The plunger is hollow to allow the flow of a fluid circulation and allow a cable-connected brush to go through the plunger as illustrated in
A plunger is connected to the positioner.
In another embodiment of the invention, a cable connected to a plunger is inserted into the tube of the heat exchanger once the plunger connects to the base of the heat exchanger and attaches and isolates a particular tube. The cable includes cleaning elements including but not limited to nozzles, wire brushes, and ultrasonic transducers.
The plunger connects the isolated tube to an external circulation system 10-19 that is part of the cleaning system. Isolating individual tubes with a controlled circulation enables effective cleaning. The external circulation system 10-19 filters out the debris that is accumulated from the cleaning system with a filter 11-19 once the cleaning system is activated in each particular tube. The functional unit of the external circulation system is located outside the heat exchanger while cleaning the tube. Circulation of the external system is controlled by flow rate, pressure and type of fluid, and may be monitored by a diagnostic tool fitted to the cleaning system 9-19.
When referring to flow rate of the external system, a specific forward flow helps make the tension in the cord of the cleaning system and moves the implement forward into the tube of the heat exchanger. A fast flow rate of the external system controls the rotational rate of the rotating brush. A slow or reversed flow eases retrieval of the cleaning element. The external cleaning system includes methods of cleaning the tubes but is not limited to protective chemicals or abrasive materials could be used to carry out the cleaning process. Such protective chemicals include but are not limited to organic and inorganic solvents, acids and bases such as strong acids or chlorine based liquids. Such abrasive materials include but are not limited to minerals. Also, a coating material may be applied to the tube in order to effectively clean the tube.
The plunger is comprised of a soft-ended tube. The diameter of the plunger is larger than a single tube but small enough not to include neighboring tubes in the circulation. This is illustrated in
With the positioner and the plunger in place, a cleaning element attached to a cord is allowed to flow in the tube. The cleaning element enters the tube by fluid flow pressure of the fluid in the heat exchanger pipes. The pressure against the plunger pulls the cleaning element into the tube. Once the cleaning element enters the tube, the pressure from the fluid flow keeps the cleaning element stable and prevents the cleaning element from exiting the tube prematurely. A balance of flow and the speed of cord release control the motion. The flow also is utilized to create a rotation action by a turbine as in turbo molecular pumps. The rotation revolves a brush in the tube to remove scaling or bio-matter that could have adhered to the tube internal surface. The flow rate, determined by the circulation through the tube and/or the heat exchanger, controls the rotational speed of the brush. Plunger width is defined as the width of the plunger from the heat exchanger pipe to the end of the plunger once attached to the heat exchanger pipe. Axial displacement occurs through compression when the plunger is retracted from the tube and also when is the plunger seals the tube.
Other methods of cleaning the tube include but are not limited to sending a non-rotating element 8-16 and utilization of ultrasonic resonator to shake off the tube clean. In this embodiment of the invention, the cleaning element includes a motor attached at the end of the cleaning element. The motor vibrates the cleaning element which initiates a sonicating movement of the cleaning element against the tubes. Vibration from the sonicating movement cleans the tubes.
In another embodiment of the invention, the cleaning system is used to clean other surfaces of the heat exchanger besides the internal tubes including the base plates at both ends of the heat exchanger and the annular and straight rail of the positioner of the cleaning system. The base plates on both ends must be maintained and kept clean in order to ensure that the plunger properly seals the individual tubes of the heat exchanger when the cleaning system is in operation. The annular rail and the straight rail surfaces must be maintained and kept clean in order for the positioner to function properly and to allow for optimal cleaning.
The base plate is cleaned by an attachment adjacent to the plunger mechanism. When the plunger is tilted away from the surface of the heat exchanger, the cleaning attachment is brought closer to the base plate and cleans the base plate. Cleaning of the base plate by the attachment includes two motions made by the attachment. The motions include angular and radial motions to swipe the baseplate clean. However, if the plenum (water box) is made wider there is no need for tilt mechanism.
The rails are cleaned by a separate attachment connected to the plunger mechanism. The ultrasound transducer cleans the sensitive toothed line in the rail. The separate attachment is only activated intermittently as need, as the rails do not need to be cleaned as often as the tubes of the heat exchanger.
Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, define, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.
The present application is a Continuation of Ser. No. 14/523,201, now allowed, having a filing date of Oct. 24, 2014.
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Number | Date | Country | |
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Parent | 14523201 | Oct 2014 | US |
Child | 15928822 | US |