Patent Application
20210291206
This disclosure relates to air-cooled heat exchangers and particularly to methods and permanently installed apparatus for removing accumulated dust and debris from the external surfaces of the projecting fins and the heat exchange tubes of an air-cooled heat exchanger (ACHE).
Air-cooled heat exchangers are widely used in a variety of industrial facilities including large scale facilities for the production, treatment, storage and distribution of gas and liquid petroleum products. A typical ACHE of the prior art is illustrated in
In some installations, the ability to maintain continuous operation of the production units is dependent on the efficient operation of one or more ACHEs to reduce and control the temperature of process feedstreams within a prescribed temperature range in order to meet end product specifications and production goals. One measurable result of a reduction in the efficient heat transfer across the fins is an increase in power consumption associated with increasing the speed of the fans to accelerate the air flow through the ACHE in an effort to maintain the specified temperature reduction of the feed as it passes through the heat exchange tubes. This is particularly true in dry dusty environments where airborne dust and debris is introduced with the ambient air through the tube bundles and into contact with the surfaces of the cooling fins and accumulate within the tube-bundle which can quickly become coated with dust and collect dirt and debris that block the flow path and significantly reduces the rate of heat exchange compared to the original theoretical design specifications that generally specify a maximum outlet terminal temperature for the expected environmental conditions that is below the target temperature set by the process engineer. When the ACHE is fouled in a short period of time and its performance cannot be maintained by increasing the rate of air flow, more frequent and extensive cleaning is required.
A failure to properly maintain the efficient operation of ACHEs can lead to bottlenecks in production which can result in the interruption of downstream operations, the undesirable flaring of feedstreams, and significant financial losses. The above problems are multiplied when the ACHEs are in a desert or dusty environment as is often the case with natural gas and petroleum processing plants that are located in the vicinity of the sources of production.
Cleaning the outer surfaces and fins of the heat exchange tubes that make up the tube bundles of any type of ACHE presents a challenge because the majority of the rows of tubes forming the tube bundles are located beneath the upper and lowermost, or bottom rows, and because many tubes are packed into relatively compact configurations in order to minimize the overall space requirements for the installation of the units. Furthermore, the fins are necessarily thin to promote heat transfer efficiency and are susceptible to damage, e.g., if inadvertently impacted by manually directed cleaning equipment. For convenience, the term “tube bundle” as used in this description and claims will be understood to also include the plural form “tube bundles” when appropriate in the context of use.
One approach to the fouling problem of ACHE heat exchange tube fins is described in U.S. Pat. No. 8,974,607 in which a portable cleaning apparatus that is formed as a generally planar spray mat is positioned horizontally between the vertically spaced rows of heat exchange tubes and a pressurized cleaning fluid is distributed generally laterally through channels formed within the mat and is discharged outwardly away from the surface of the mat through spray nozzles onto the adjacent heat transfer fins. A second imperviously mat is positioned below the ACHE to collect and drain the used cleaning fluid for removal from the site. The system and method of the '607 patent requires personnel to position the mat between the rows of finned spray tubes which must be done with great care in order to avoid damaging the fins and the spray mat. The ACHE must be shut down during cleaning, which is another disadvantage of the method.
In U.S. Pat. No. 5,279,357, a permanently installed cleaning system is described that is positioned above and between the tube bundles and employs a series of horizontal stationary tubes fitted with nozzles or spray arms that rotate about a central axis to discharge the pressurized cleaning fluid through spray nozzles onto the adjacent fins. The ACHE must be especially designed and constructed with sufficient vertical spacing between the horizontal rows of tubes to accommodate the numerous pipes and nozzles and/or the rotating spray arms.
A temporary cleaning system is described in U.S. Pat. No. 4,141,754 for use with a specialized plate heat exchanger that is known as a rotary regenerative heat exchanger which is constructed with vertical plates mounted inside an exterior enclosure. The method of the '754 patent includes the disadvantages of having to shut down the heat exchanger, dismantle and remove the enclosure, and then install the temporary cleaning system. A pair of C-channels are positioned horizontally above the plates to form parallel tracks extending along a major axis, which cover only a portion of the width of the unit. A wheeled cleaning carriage is positioned to move along the length of the C-channels in response to a motor driven system via a pair of ropes attached to a take-up drum and the cleaning carriage. As illustrated, the cleaning fluid is delivered via a reciprocating conduit having discharge ports positioned in fluid communication with vertical conduits corresponding to the nozzles below the carriage surface. This system of the '754 patent thus suffers the disadvantages of (1) shutting down the operation of the heat exchange unit which necessitates the presence of a back-up unit operating in parallel, (2) the need to temporarily install the tracks, motor-driven cable system, and the cleaning fluid delivery conduits, and (3) the need to disassemble and move the apparatus in order to clean the entire area of the heat exchange plates.
Various types and configurations of portable spray cleaning apparatus that are temporarily put into position for the purpose of removing dirt and debris that has fouled and reduced the efficiency of an ACHE are known in the art. These various systems suffer from the disadvantages of (1) shutting down the operation of the ACHE in order to carry out the cleaning, (2) the need to temporarily install the elements of the cleaning system, and the cleaning fluid delivery conduits, and (3) the need to disassemble and move the apparatus once the cleaning operation has been completed.
A need exists for an automated online cleaning system for use with a wide variety of air-cooled heat exchangers that overcomes the following problems:
The above problems are addressed and other advantages are achieved in accordance with the present disclosure by an ACHE cleaning system and method in which a mobile frame-mounted cleaning apparatus is permanently positioned in spaced-apart relation above the uppermost tube bundle or below the lowermost tube bundle of an ACHE and configured for reciprocating movement on tracks secured to the ACHE side walls, or housing, that are parallel to the longitudinal axes of the tubes constituting the bundles.
The apparatus includes a transversely mounted spray head assembly comprised of a plurality of interchangeable fluid compartments that are securely positioned on, and carried by a reciprocating supporting frame that spans the width of the opening either above or below the tube bundles.
In an embodiment, each fluid compartment has an inlet for admitting a pressurized cleaning fluid, and the spray head assembly includes a fluid distribution manifold that is configured with a plurality of fluid discharge tubes or conduits with fluid-tight fittings that are in fluid communication with the inlets to the fluid compartments. The manifold receives pressurized cleaning fluid via a manifold inlet from an external source. The surface of each of the fluid compartments proximate the tube bundles is provided with at least one, but preferably a plurality of spray nozzles through which the pressurized cleaning fluid is discharged either downwardly in an embodiment in which the assembly travels above the tube bundles, or upwardly from below onto and between the finned heat exchange tubes in the embodiment in which the spray head assembly travels below the ACHE.
In a preferred embodiment, at least a portion of the spray nozzles are configured to discharge a generally elongated high-pressure spray pattern e.g., in the range of from 500 to 1500 psi, in order to maximize the amount of cleaning fluid impinging on the finned tubes while also avoiding any damage to the fins due to high pressure fluid impingement.
The individual fluid compartments are preferably dimensioned and configured to be of uniform height and depth, and of predetermined varied widths so that the total width of an assembly comprised of a plurality of fluid compartments can be varied within a predetermined range to span ACHE units of different widths. For example, if the width of an ACHE to be fitted with the cleaning system of this disclosure is 8.75 feet, the assembly can be configured with eight so-called standard width “W” compartments that are each one foot wide, one six-inch wide compartment, i.e., “½ W”, and one compartment that is three inches wide, or “¼ W”, to make up the total of 8.75 feet. Other intermediate widths can be employed as determined by the size and weight of the fluid compartments, and their transportability.
In an embodiment, the individual fluid compartments have side walls that are configured for engagement with adjacent compartments to form a rigid unitary structure that can be extended to span the width of the open area of the ACHE above the finned tubes. The opposite sides of each fluid compartment can include a surface that is provided with a plurality of projecting lugs and corresponding recesses that from matching patterns so that the designated right side surface of each compartment will mate with the left side surface of an adjacent compartment forming the assembly.
In an embodiment, the individual fluid compartments have side walls that are adapted to pass and/or receive pressurized cleaning fluid from at least one adjacent fluid compartment via a fluid passage that includes a resilient, compressible or otherwise movable fitting that is configured and dimensioned to engage in fluid-tight relation with a corresponding fitting in the side wall of an adjacent fluid compartment in which it is mounted. In an embodiment, the fluid passage is circular and the fitting is an annular member that is assembled in close-fitting fluid-tight relation with the side wall of the fluid compartment in which it is mounted. The annular member can be formed, e.g., by molding, from a durable resilient material such as neoprene in a generally cylindrical shape and provided with integrally molded flanges at either end, the longitudinal distance between the inside edges or faces of the flanges corresponding to the thickness of the compartment walls in which the annular member is to be mounted. The end of the annular seal that is inserted through the exterior wall of the fluid compartment is denominated the interior flange and is dimensioned and configured to undergo compression deformation to permit it to be press-fitted through the opening in the compartment side wall and rebound to its original shape in order to not only retain the annular seal securely in place, but also to provide a fluid-tight seal with the wall. The design, dimensioning and selection of materials of construction of the annular seals are within the skill of the art.
The end of the annular fitting opposite the interior flange has an outwardly facing surface that is configured to mate in fluid-tight sealing relation with the appropriately configured corresponding surface of an annular fitting secured in the side wall of an adjacent fluid compartment. The opposing surfaces of the facing sealing flanges are urged into sealing relation as a result of a predetermined lateral force applied to the plurality of aligned fluid compartments that form the assembly spanning the width of the ACHE opening above and adjacent the tube bundles, when the assembly is put in place on a transverse supporting frame that reciprocates on the tracks secured to the ACHE housing side walls that extend parallel to the longitudinal axes of the tubes.
In an embodiment, the supporting frame preferably includes vertical retaining end walls or other members at either end that are dimensioned and configured to maintain the fluid compartment assembly in place and prevent its lateral, or transverse movement. At least one of the vertical end wall retaining members can include a mechanism for adjustably applying a lateral force to the side wall of the adjacent fluid compartment in order to secure the entire assembly of fluid compartments in close-fitting relation. In the embodiment described above, the application of a lateral force brings the adjacent annular seal members into fluid-tight sealing relation so that a pressurized cleaning solution introduced into one fluid compartment via an inlet fitting, e.g., mounted into the top wall of the compartment will be transmitted to all adjacent compartments. The mechanism for adjustable applying a lateral force can be a lever-activated ratchet, either circular or linear, a manual or hydraulically actuated screw assembly, or a hydraulic ram or piston.
It will be understood that the manifold described above is not required where the fluid compartments comprising the assembly are in fluid communication with each other. Instead, a single conduit can be employed to introduce the pressurized fluid into an inlet of one compartment via a single fluid-tight fitting.
Each compartment is fitted with one or more cleaning spray nozzles the size and the spray characteristics of each are selected based on the tube bundle arrangement and configuration of a specific ACHE. Each of the fluid compartments has a fluid discharge wall that is provided with at least one, but preferably a plurality of nozzles for discharging the pressurized cleaning fluid in one or more predetermined spray patterns. The nozzles are spaced-apart transversely and, optionally, longitudinally. In an embodiment, the nozzles are aligned along a diagonal, and each nozzle is centrally aligned with the finned heat exchange tubes over which the spray head passes when the cleaning system is in operation.
In the description that follows, it will be understood that the term “nozzle” can refer to a point source nozzle where the cleaning and/or drying fluid is discharged from one orifice, or a slot nozzle in which the fluid discharge opening is elongated and relatively narrow as compared to its length.
The nozzles can be integrally formed in the fluid discharge wall or other surface of the compartment that moves proximate the heat exchange tubes by molding, cutting and/or drilling the openings. Alternatively, individual spray nozzles can be fitted to outlet openings in the bottom wall or lower portion of the compartments, e.g., by conventional threaded fittings, snap-fittings, frictional fittings, or the like.
The fluid compartments can be fabricated from metal sheets or rolls, and in a preferred embodiment are rotationally molded from polyethylene and/or other copolymers to provide a chemically resistant, highly durably container with high impact strength that can be worked with conventional tools to provide openings for mounting of fittings, nozzles, seals and the like, and is relatively lightweight to facilitate manual handling. The individual fluid compartments can be provided with integrally-molded handles and/or hand-holds for this purpose.
The mobile supporting frame is self-supporting and is comprised of securely assembled I-beams or L-beams, or channels, and is reinforced to form a rigid structure to withstand the dynamic loading of the filled fluid compartments during reciprocation. The support frame is dimensioned and configured to securely receive and retain a plurality of removable fluid compartments of varying widths and sizes.
Various arrangements of tracks, guide rails, pulleys, cables and electric motors can be utilized to move the mobile supporting frame from one end of the opening of the ACHE above or below the finned tube array. The cleaning system's mobile supporting frame and fluid compartments are preferably stored when not in use at one end of the ACHE under a protective cover that will shield the apparatus from contamination by the same dust and debris which must be cleaned from the finned tubes.
The embodiment in which the cleaning system is mounted below the tube bundles and the pressurized cleaning fluid is sprayed upwardly through the finned tubes has the advantage of providing a dual cleaning action as the pressurized fluid moves upwardly through the tubes and then drains downwardly under the effect of gravity.
Referring now to
In a preferred embodiment, the supporting frame (200) is provided with a plurality of fluid compartments (110), which are preferably of a uniform configuration and a width “W” to minimize inventory requirements. In order to accommodate ACHE units of different sizes and widths, e.g., that are not an even multiple of the fluid compartment, such as 10 times W, fluid compartments of ½ W (160) and ¼ W (170) are maintained in inventory to complete the spray head assembly and provide complete coverage of the tube bundles.
With continuing reference to
Positioned above the fluid compartments comprising the spray head assembly (100) is a fluid distribution manifold (180) that in the particular embodiment illustrated includes a manifold inlet (182) and a plurality of depending manifold discharge tubes (184), the free ends of which are each provided with fluid-tight fittings (186) that are configured and dimensioned to engage the inlet fittings (128) of the fluid compartments below. As illustrated, it will be understood that the manifold fittings that engage fluid compartments (160, 170) of narrower widths may be proportionally scaled to provide the required fluid-tight fitting when the pressurized fluid is introduced into manifold inlet (182) from an external source (not shown).
For the purposes of illustration, the manifold discharge tubes (182) appear as rigid conduits. However, it will be understood by those of ordinary skill in the art that the manifold discharge tubes can be configured as flexible hoses with appropriate fluid-tight fittings (186) attached, e.g., by clamps or other known means.
Any of various known types of fluid-tight fittings, such as quick-release hose fittings, can be used to couple the discharge manifold fittings (186) to the inlet fitting (128) of the fluid compartment to assure a fluid-tight coupling. The use of a flexible conduit for the manifold discharge tube (186) is desirable, since the manifold (180) will have to be attached and removed when the spray head assembly (100) and its supporting frame (200) are moved, e.g., initially placed for use on the ACHE and then removed for any eventual servicing of the unit. This manual task will be greatly facilitated by the use of quick-release couplings.
The fluid compartments (110) illustrated in
In a preferred embodiment of the system and apparatus, the close-fitting relationship and alignment of the compartments (110) on the frame is achieved by maintaining the dimensional tolerances during the manufacture of the compartments and of the assembly of the supporting frame (200) as described above. As is described in more detail below and in conjunction with
In an alternative embodiment shown in
Referring to an alternative embodiment illustratively depicted in
The patterns of the slot nozzles can be varied for a single compartment. The pattern and force of the spray discharged from the slot nozzles can also be varied by changing the pressure of the cleaning fluid supplied to the system. This variable can be determined by the operator based on experience, and can be dependent on a number of variable factors, such as the type and extent of fouling on the fins, the interval(s) between cleaning, the type and temperature of the cleaning fluid(s) and the like.
In the embodiment of
Referring now to
The slots can be of the same width and the nozzle exits can be of the same or of different configurations. For example, the opposing interior side walls of the slot nozzle can be parallel or slanted so that the discharge edge is either narrower than the compartment or intake side, or wider along the discharge edge to produce different spray patterns. Two or more different configurations can be used for the slots in a single compartment.
As will be understood by one of ordinary skill in the art that the number of slots can be greater, or less, than three, e.g., a total of four or five slots. Factors such as the availability, volume, pressure and temperature of the cleaning fluid discharged on the finned tubes, as well as the type and amount of accumulated dirt and debris on the finned tubes will effect the design criteria of the present system.
It will also be understood by one of ordinary skill in the art, the dimensions of the generally rectilinear compartments are not critical. In the interests of clarity and ease of description, the compartments shown in the attached drawings, with the exception of
An alternative embodiment, for example, is schematically illustrated in
Another embodiment of the spray head assembly (100) for use in the system of the present disclosure will be described with reference to
In an embodiment (not shown), the exterior side wall of the compartment (310) is recessed a predetermined amount to receive the exterior peripheral portion of the annular seal (330) during deformation to permit the facing exterior walls of the fluid compartments to be brought into touching relation. The interior flange of the annular seal is preferably dimensioned and configured to permit its deformation during insertion through the side wall passage (320) and then to return to its original configuration in order to provide the interior seal to retain the pressurized fluid.
The fluid compartment (310) is provided with a plurality of openings (124) in the bottom wall (322) adapted to receive nozzles as described above in connection with
Returning to
Referring now to the partially exploded view of the supporting frame (200), one embodiment of its construction is illustrated. It will be understood that the structural elements are fabricated from an appropriate gauge of steel or stainless steel to provide a sufficiently robust structure to support the fluid compartments which carry clean fluid to their capacity during the spray cleaning operation, and that the entire unit will be subject to additional stresses during reciprocating movement. The elements can be joined by welding, by threaded fasteners, rivets, either alone or in combination.
An embodiment illustrating the installation of a spray head assembly (100) in accordance with
A drive assembly positioned at an end of the ACHE that is preferably opposite the inlet and outlet headers includes an electric drive motor(560), a motor controller (562), a power supply (564) and a gear reducer (550). Drive shafts (552) extend from the gear reducer and are fitted with drive pulleys (540) that engage drive cables (530) attached to the transverse carriage member (502), or other suitable structural member of the carriage. The drive cables (530) can be of braided stainless steel construction or can take the form of a chain in which the pulleys are sprockets adapted to receive the chain in order to provide a more controlled movement and avoid any possible slipping of the pulley on a wet metal cable.
As shown in
As will be understood, the cleaning system could be used during operation of the ACHE where the air flow is downward through the tube bundles. In those plant installations where the cooling air fans are positioned below the elevated structure of the ACHE, the present cleaning system can be installed for operation in substantially the same configuration so that the cleaning fluid is passed from the cleaning nozzles upwardly in the same direction as the cooling air flow. Where the installation of the system is below the ACHE, the tracks will be supported on a separate assembly that is suspended from the ACHE structural members above. The manifold assembly is also positioned below the supporting frame (not shown).
In either of the downwardly or upwardly discharge configurations, the manifold carrying the pressurized fluid from the remote source is conveniently fed by a flexible conduit, e.g., a hose, at least a portion of which travels longitudinally over the tube bundles with the cleaning system. Supporting and transport systems are well known in the art for maintaining the hose in the desired position during movement of the cleaning assembly.
When the cleaning assembly is moved to the storage position, a protective cover (570) shown in phantom in both
As best shown in
While the invention has been described in conjunction with several embodiments, it is to be understood that many alternatives, modifications and variations will be apparent to those skilled in the art based on this description. Accordingly, the scope of the invention is to be determined by the claims that follow.
