This application relates generally to a design for a cold box, and more particularly, to a cold box having a design that enhances core replacement.
Hydrocarbon gases such as natural gas are liquefied by cryogenic processes to reduce their volume for easier transportation and storage. Brazed aluminum plate fin heat exchangers have been utilized in the cryogenic processing of natural gas and liquefied natural gas (LNG) for many years. Compared to conventional shell & tube exchangers, they offer many advantages, including smaller size and weight, and hence less cost.
The maximum size of a heat exchanger that can be fabricated is limited by the size of the manufacturer's brazing furnace. For large capacity facilities, multiple sections of heat exchanger units, referred to as “cores,” are fabricated and interconnected to form the complete heat exchanger. Where several of these cores are required, a cold box configuration is utilized, with the exchanger assembled within a structural steel framework (the box), with an insulation such as perlite filling the voids within the box for heat conservation. With such cold boxes, maintenance can often be an issue, requiring extended shutdown periods to accomplish the necessary repairs required. When the repair or replacement of a core is necessary, the current practice of interconnecting the cores within the cold box impedes maintenance.
The oil & gas industry is now considering offshore floating LNG (FLNG) production units. U.S. Pat. No. 6,250,244 describes a floatable natural gas liquefaction system using a series of heat exchangers. The heat exchangers can be arranged in a cold box.
Another example of an offshore production unit is shown in U.S. Pat. No. 6,889,522, issued May 10, 2005 to Prible et al., the disclosure of which is incorporated herein by reference in its entirety. U.S. Pat. No. 6,889,522 describes two nautical vessels to produce store and unload liquefied petroleum gas (LPG) and LNG. The first vessel is a LPG/FPSO (liquified petroleum gas/floating production, storage and offloading) vessel. The second is a LNG/FPSO vessel. Certain technology that has applicability for FLNG applications utilize units which operate at cryogenic temperatures and which will utilize cold boxes with cores of brazed aluminum heat exchangers. Examples of such technology include the processes shown and disclosed in U.S. Pat. No. 5,755,114, issued May 26, 1998 to Foglietta and U.S. Pat. No. 6,412,302, issued Jul. 2, 2002 to Foglietta. The disclosure of both these patents is incorporated herein by reference in its entirety.
One of the concerns with current designs of FLNG units is the high repair cost for cold boxes used therein. The space around the cold boxes is congested and access to the cold boxes is more difficult.
Another concern with current designs of cold boxes such as those configured for use in FLNG units is the cost associated with downtime. In a typical onshore installation of a LNG unit, the economic consequences of taking a unit off-line are relatively modest. Sometimes the feed gas can be diverted around the plant, minimizing impact to the customer. In contrast, the cost of downtime on an FLNG unit containing the cores in a cold box would be high. A typical FLNG unit will be designed to remain offshore for a period of 20+ years, without the need for dry-docking, meaning that any repair must be made onsite. Costs will include those incurred in moving components to and from the offshore unit, and in paying personnel to safely service the offshore unit. It is likely that FLNG units will be installed at remote locations, with no easy access by vendors/suppliers and repair staff.
It is thus desirable that a cold box be designed such that the cost of core repairs, and the amount of downtime required to complete the core repairs, is minimized.
According to one embodiment there is provided a cold box including a housing providing an enclosed structure and at least one set of a plurality of cores within the housing, each core having a front, back, top, bottom and side surface. The cores in each set are positioned in a row in front-to-back relationship along an axis, the cores having a plurality of manifolds on their front and back sides. A plurality of headers are provided within the housing and are configured to be connected to conduits outside of the housing The headers extend parallel to the axis of the row of cores. The headers are positioned to the top, bottom and/or rear of the heat exchange units with the space between one side of all the cores and the housing being free from the headers. Feed lines connect each of the headers to a respective manifold.
According to a further embodiment there is provided a cold box including a housing providing an enclosed structure including a front, back, two sides, a top and a bottom. A plurality of cores having front, top, bottom and two spaced side surfaces are within the housing positioned in a row in front-to-back relationship. A plurality of manifolds are provided on the front and back surfaces of each core. A plurality of headers are provided within the housing adapted to be connected to conduits outside of the housing. The headers extend parallel to the axis of the row of cores. The headers are positioned to the top, bottom and rear of the cores with the space between the one side of the cores and the front of the housing being free from the headers. Feed lines connect each of the headers to a respective manifold on the cores.
According to yet another embodiment, a cold box is provided including a housing providing an enclosed structure including a front, back, two sides, a top and a bottom. A plurality of cores having front, top, bottom and two spaced side surfaces are provided within the housing, the cores being positioned in two rows with the cores in each row being in front-to-back relationship. A plurality of manifolds are provided on the front and back surfaces of each core. A plurality of headers are provided within the housing adapted to be connected to conduits outside of the housing. The headers extend parallel to the axis of the row of cores. The headers are positioned to the top, bottom and between the rows of cores heat exchange units with the space between one side of each of the cores and the housing being free from the headers. Feed lines connect each of the headers to a respective manifold on the cores.
Another embodiment is a method of making a cold box, comprising obtaining a housing providing an enclosed structure with a removable side wall and disposing at least one set of a plurality of cores within the housing, each core having a front, back, top, bottom and side surface, the cores in each set positioned in a row in front-to-back relationship along an axis, the cores having a plurality of manifolds on their front and back sides. The method also includes disposing a plurality of headers within the housing, the headers being configured to be connected to conduits outside of the housing, the headers extending parallel to the axis of the row of cores, the headers being positioned to the top, bottom and/or rear of the cores with the space between one side of all the cores and the housing being free from the headers, and connecting each of the headers to a respective core using a feed line.
The embodiments disclosed herein provide a new design for a cold box that has significantly lower maintenance and repair costs than a conventional cold box. In the embodiments described herein, the headers disposed in the cold box that lead to the cores are configured to permit easy removal of an individual core if repair or replacement becomes necessary with the cold box remaining in place. By facilitating repair and replacement, downtime is also reduced, providing additional advantages.
The goal of one who designs a floating heat exchange unit is to make the heat exchanger as small and lightweight as possible in order to minimize the footprint and buoyancy requirements of the floatation device that supports the unit. Along these lines, it has been an objective of various research and design projects to reduce the size and weight of equipment used on offshore platforms (see, for example, Offshore Engineer, December 2010, “Lighter topsides: the what, why and how” and Boyd, N. G. “Topsides Weight Reduction Design Techniques for Offshore Platforms,” Offshore Technology Conference, 5-8 May, 1986, Houston, Tex.). In contrast, the cold box design described herein moves in an opposite direction. More specifically, the new cold box is larger and/or heavier than units according to the previous design having the same capacity. Such a configuration clearly was not apparent to others at the time this new design was developed.
In some embodiments of the cold box, a new core is installed in the cold box and the cold box is put back on-line while a removed core is being repaired. This eliminates the need to have the manufacturer or supplier keep the unit off-line while the repair is being completed.
Referring to the drawings,
As shown in
Five cores 18 are positioned within the housing 4 in side-by-side relationship. These cores may be heat exchanger units. In the processing of natural gas and LNG, such heat exchanger units may be brazed aluminum plate fin heat exchangers.
As shown in
The exact number and placement of the manifolds 32 on the front 20, back 22, top 24 and bottom 26 surfaces depend upon the particular cryogenic process being used and the particular design of the interior of the heat exchanger unit. The manifolds 32 provide a fluid path to the interior of the core at various interior locations of the core depending upon the particular design and purpose of the core.
Headers 34 are provided that extend parallel to the axis of the row of cores 18, with each header 34 extending in a plane parallel to the front 6 and back 8 of the housing 4, and parallel to the manifolds 32. These headers 34 extend through the sides 10, 12 of the cold box housing 4 and are adapted to be connected to conduits (not shown) provided on the outside of the cold box housing 4. For this purpose, the headers 34 may be provided with companion flanges 35 (not all have reference numerals) at their open ends for connection to a similar flange provided on a conduit outside of the cold box.
As shown in
The exact number of headers 34 depends upon the particular design and purpose of the cores. Individual feed lines 36 (only some of which are numbered), which are linear in shape, extend between each of the headers 34 and its respective manifold 32 on each of the individual heat exchangers to provide a connection for flow from the header 34 to the manifold 32. As an example, the headers 34 may be used to convey such liquids and gases to and from the heat exchanger units 18 as warm feed gas (natural gas+methane refrigerant recycle), feed gas going to high pressure LNG, warm high pressure N2 refrigerant, boiloff gas being recirculated, cold low pressure N2 refrigerant and cold low pressure methane refrigerant. The particular liquid or gas being conveyed by the headers depends upon the particular cryogenic process. The interior of the cold box housing 4 may be filled with an insulation material such as perlite (not shown).
Within the housing are positioned six cores 118. As in the design of
Headers 134 are provided that extend parallel to the axis of the row of cores 118 and the manifolds 132, as well as the front 106 and the back 108 of the housing 104. These headers 134 extend through the sides 110, 112 of the cold box housing 104 and are adapted to be connected to conduits (not shown) provided on the outside of the cold box housing 104. For this purpose, the headers 134 may be provided with companion flanges 135 at their open ends for connection to a similar flange provided on a conduit outside of the cold box.
As shown in
Individual feed lines 136 (only some of which are numbered) extend between each of the headers 134 and its respective manifold 132 on each of the individual cores 118 to provide a connection for flow from the header 134 to the manifold 132. The feed lines 136 have a linear shape, are L-shaped, or have two straight sections 137, 139 joined to one another at an obtuse angle. The headers 134 may be provided with companion flanges at their open ends for connection to a companion flange provided on a conduit outside of the cold box. The interior of the cold box may be filled with an insulation material such as perlite.
In both the designs of
There are five cores 218 mounted in the housing 204. The cores 218 may be individual heat exchanger units, a non-limiting example of which is brazed aluminum plate fin heat exchangers. The cores 218 are substantially rectangular in cross section, and include, for reference purposes, a front surface 220, back surface 222, top surface 224, bottom surface 226 and spaced side surfaces 228 and 230. The five cores 218 are mounted in the housing 204 in a front-to-back relationship forming a single row along an axis extending from side to side in the housing 2. In the embodiment shown in
The front surface 220, back surface 222, top surface 224 and bottom surface 226 of each core in the design of
Headers 234 are provided that extend parallel to the axis of the row of cores 218 with each extending in a plane parallel to the front 206 and back 208 of the housing 204. The headers 234 extend perpendicular to the manifolds 232. The headers 234 extend through the sides 210, 212 of the cold box housing 204 and are adapted to be connected to conduits (not shown) provided on the outside of the cold box housing 204. For this purpose, the headers 234 may be provided with companion flanges 235 at their open ends for connection to a similar flange provided on a conduit outside of the cold box.
As shown particularly in
Individual feed lines 236 (only some of which are numbered) extend between each of the headers 234 and its respective manifold 232 on each of the individual heat exchangers to provide a connection for flow from the header 234 to the manifold 232. In the embodiment shown in
As mentioned previously, the headers 234 may be used to convey such liquids and gases to and from the heat exchanger units 218 as warm feed gas (natural gas+methane refrigerant recycle), feed gas going to high pressure LNG, warm high pressure N2 refrigerant, boiloff gas being recirculated, cold low pressure N2 refrigerant and cold low pressure methane refrigerant. The particular liquid or gas being conveyed by the headers depends upon the particular cryogenic process. When the cold box is in use, the free volume within the cold box may be filled with an insulation material such as perlite.
As described above, in the arrangement as shown in
There are six cores 318 mounted in the housing 2. The cores 318 may be individual heat exchanger units, such as brazed aluminum plate fin heat exchangers. As in the previous designs, the cores 318 in
As with the cores 218 shown in
Headers 334 are provided that extend parallel to the axis of the row of cores 318 with each extending in a plane parallel to the front 306 and back 308 of the housing 304. The headers 334 extend perpendicular to the manifolds 332. These headers 334 extend through the cold box housing 304 and are adapted to be connected to conduits (not shown) provided on the outside of the cold box housing 304. For this purpose, the headers 334 may be provided with companion flanges 335 at their open ends for connection to a similar flange provided on a conduit outside of the cold box.
As shown particularly in
With the arrangement shown in
In the embodiment shown in
There are ten cores 418 mounted in the housing 402. The cores 418 may be individual heat exchanger units, such as brazed aluminum plate fin heat exchangers. As in the previous designs, the cores 418 in
The front surface 420, back surface 422, top surface 424 and bottom surface 426 of each core 418 in the design of
Headers 434 are provided that extend parallel to the axis of the row of cores 418 with each extending in a plane parallel to the front 406 and back 408 of the housing 404. The headers 434 extend perpendicular to the manifolds 432. The headers 434 extend through the side walls 410, 412 of the cold box housing 404 and are adapted to be connected to conduits (not shown) provided on the outside of the cold box housing 404. For this purpose, the headers 434 may be provided with companion flanges 435 at their open ends for connection to a similar flange provided on a conduit outside of the cold box.
As shown in
With the arrangement shown in
The heat exchange units comprising the cold boxes described herein are typically configured to operate in the pressure range of 1300 psig or more, usually about 1300 to about 1400 psig. The units typically have a minimum design operating temperature of −320° F. or less, or −300° F.
The new cold boxes described herein have a variety of uses, and, as mentioned above, are particularly well-suited for inclusion in natural gas heat exchanger units, including LNG and FLNG units. The units can be maintained efficiently due to the ease of removal and replacement of cores needing repair.
As indicated above, in embodiments, the size and/or weight of the cold box is increased as compared to the size and/or weight of a conventional system having generally the same capacity. In a typical cold box according to certain embodiments disclosed herein, the space between the cores will increase by about 10-50%, or about 25-50% as compared to a conventional system having the same capacity, resulting in certain circumstances in an overall increase in volume of the cold box of about 10-30%, or about 20-30%. In some cases, the configuration within the cold box will employ additional pipe fittings that may increase the weight of the cold box by about 5-20%, or about 10-20% as compared to a conventional cold box having the same capacity.
While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.