Coil heat exchanger

Abstract

The invention belongs to the field of thermal engineering and can be utilized in the production of liquefied natural gas at the industrial gas plants. A coil heat exchanger comprising: a shell, a first bundle, a core, a multitude of tubes, a first and second group of tube sheets, a multitude of valves, refrigerant distributors, tube bundle supports, tube spacers, as well as coil tubes of tube bundles of multitude of heat exchanger zones of equal diameter; at the same time, the flows of liquid medium and refrigerant entering at different temperatures are later withdrawn from the multitude of bundle tubes at equal temperatures. The invention enables one to develop a coil heat exchanger providing equal heat transfer surface for all coils to equalize the heat transfer across the layers of tube bundle coils.

Description

[0001] COIL HEAT EXCHANGER

[0002] PERTINENT ART

[0003] Coil heat exchanger is designed to facilitate heat exchange between several flows under the conditions of a wide area of heat exchange with an aim to reduce the minimal temperature difference between the hot and the cold flows thereby decreasing the energy cost of liquefaction, enabling its potential utilization for liquefied natural gas production at gas chemical plants.

[0004] PRIOR ART

[0005] Rigid shell and tube heat exchangers of various types and modifications comprised of a shell with input and output chambers of the first flow passing through a straight tube bundle and the second flow passing through the annular space of the shell have seen wide adaptation throughout various branches of industry (Shell and tube heat exchangers with fixed tube sheets and shell and tube heat exchangers with shell temperature compensator. Catalog. M.: OAO “VNIINEFTEMASH” - 2003. - 71 pages). The general disadvantage of these devices is that the annular space accounts for a significant share of volume inside the shell, which keeps the velocity of the second flow low and, accordingly, the heat transfer coefficient from the second flow to the pipe walls also remains low, which leads to a decrease in the heat transfer coefficient values in the heat exchanger apparatus as a whole. It is important to note that these heat exchangers demonstrate a significant temperature difference between the hot and the cold flows, with minimal difference usually amounting to more than 10 °C. In case with cryogenic technologies, attempts are usually made to reduce this temperature difference as much as possible to keep energy consumption down.

[0006] There is a known heat exchanger design which is comprised of a shell with coil tubes, wound around its core, accommodated in coaxial rows with spacers distributed between the adjacent ones along helical lines with altemance in adjacent rows of the right and left windings (USSR inventor’s certificate SU 561070, IPC F28D 1 / 02, pending 05.07.1971, published 05.06.1977). The downside of this invention lies in varying hydraulic resistance of the flow’s local jets passing through the coil tubes of different diameters: the larger the diameter of the coils and, correspondingly, the overall length of the coil assembly, the lower the velocity of the local flow passing through the assembly and the lower the heat transfer coefficient, resulting in reduced heat transfer with each subsequent coil turn.

[0007] There is another type of heat exchanger known for its use in the field of cryogenic technology, specifically for liquefied natural gas production. This main heat exchanger liquefies the pipe-side flow by utilizing the warm and cold ends and comprises the following elements: a wall which constitutes a side of the housing, within which resides a bundle of tubes wound onto a spiral and arranged around the central mandrel; the first nozzle is designed to supply a first mass flow from the pipe side to the pipes of a first zone of the separate pipes in the above-mentioned bundle at the warm end of the said first zone of the separate pipes; the second nozzle is designed to supply a second mass flow of the said flow from the said pipe side to the pipes of a second zone of separate pipes in the said bundle at the warm end of the said second zone of individual pipes, with the second zone of individual pipes being offset from the first by a radius extending from said central mandrel to the said wall of the main heat exchanger; a distributor for refrigerant flow supplying on the said housing side designed for the cooling of the first and second mass flows with formation of vaporized refrigerant steam; line for vaporized refrigerant flow removal from the warm end of the said main heat exchanger; the first temperature transmitter which generates a first signal to indicate the temperature of the first mass flow; the second temperature transmitter which generates a second signal to indicate the temperature of the second mass flow; and a controller for equalizing the temperature of the first mass flow from the pipe side at the first axial location with the temperature of the second mass flow from the pipe side at the said first axial location through the comparison of the first signal indicating the temperature of the first mass flow with a second signal indicating the temperature of the second mass flow, followed by the adjustment of the first mass flow from the pipe side supplied by the said first nozzle relative to the second mass flow from the pipe side flow side supplied by the second said nozzle to equalize the first signal with the second signal (patent US 9982951 B2, F25J 1 / 00, F25J 1 / 02, F28F 9 / 00, F28D 7 / 00, F28D 7 / 02, F28F 27 / 02, pending 31.03.2011, published 21.03.2013). Among the disadvantages of this invention are the different lengths of the three twisted heat-exchange coils placed in the single shell of the heat-exchange apparatus, with one of the coils serving the function of hydrocarbon gas liquefaction, while the remaining two are used to support the operation of the circulation system for the light (LMR) and heavy (HMR) fractions of the refrigerant, which significantly complicates the regulation and control of the heat exchanger apparatus, be it adjustment of the unit’s LNG production rate or changes to the temperature of air supplied to the air cooling unit and the air cooling unit located between the first and the second refrigerant compressors.

[0008] There is yet another type of coil heat exchanger, which is closest, design- wise, to the claimed invention. It comprises the following elements: a shell, tube bundle containing a first bundle end and a second bundle end placed distal to the first bundle end; a core located centrally within the first bundle, with the space within the first bundle shroud extending from the first bundle end to the second bundle end and going from the first bundle core to its shroud; a multitude of tubes arranged within the shroud of the first bundle, with each of the tubes having a first tube end located at the first end of the bundle, and a second tube end located at the second end of the bundle, with a multitude of tubes being coiled around the core to form a multitude of twisted layers, with the multitude of twisted layers being divided into a multitude of zones that are concentrically arranged within the shroud of the first bundle, with the multitude of tubes containing a multitude of sets of tubes, with each of the multitude of sets of tubes located in another of the multitude of zones; a first group of tube sheets arranged at a first end of the bundle, with each of the first group of tube sheets connected, by fluid flow, with one of the multitude of sets of tubes at the first end of the tube; a multitude of valves, with each of the multitude of valves connected, via fluid flow, with each of the first group of tube sheets and located at the first end of the bundle; and a second group of tube sheets arranged at the second end of the bundle, with at least one of the second group of tube sheets connected, via fluid flow, with more than one of the multitude of sets of tubes at the second end of the tube (patent RU 2765593 Cl, IPC F28D 7 / 02, F28F 27 / 02, F28J 1 / 00, pending 29.04.2021, published 01.02.2022).

[0009] DISCLOSURE OF INVENTION

[0010] It was attempted, during the course of development of the claimed invention, to identify ways to improve the design of the wound heat exchanger with an aim to equalize the heat transfer between the layers of the tube bundles’ coils and achieve equal heat transfer surface for all the coils.

[0011] The posed problem is solved through implementation of a coil wound heat exchanger comprised of the following elements: a shell; a multitude of bundles containing the first bundle end and a second bundle end placed distal against the fist bundle end; a core located in the center within the first bundle, with the space inside the shroud of the first bundle extending from the first bundle end to the second bundle end and from the core of the fist bundle up to its shroud; a multitude of tubes arranged within a space of the first bundle’s shroud, with each of the multitude of tubes having a first end of the tube placed at the first end of the bundle, and the second end of the tube placed at the second end of the bundle, with the multitude of tubes being wound around the core to form a multitude of twisted layers, with the multitude of twisted layers being divided into a multitude of zones that are concentrically arranged in the space within the first bundle shroud, with the multitude of tubes containing a multitude of sets of tubes, with each of the multitude of sets of tubes located in located in another of the multitude of zones; the first group of tube sheets located at the first end of the bundle, with each of the tube sheets from the first group connected, via a fluid medium flow, with one of the multitude of sets of tubes at the first end of the tube; a multitude of valves, with each of the multitude of valves connected, via a fluid medium flow, with each of the first group of tube sheets and located at the first end of the bundle; and the second group of tube sheets located at the second end of the bundle, where at least one of the second group of tube sheets is connected, via a fluid medium flow, with more than one of the multitude of sets of tubes at the second end of the tube; refrigerant distributors located inside the apparatus shell for the uniform distribution of refrigerant supply over the diameter of the apparatus; tube bundle supports affixed on the core; pipe spacers mounted on the tube bundle supports and located between the layers of coils, with all the coiled tubes of tube bundles of a multitude of heat exchanger zones sharing the same diameter, fluid medium and refrigerant flows, entering at different temperatures, are discharged from the multitude of tubes of the tube bundle at the same temperature.

[0012] In that case all the coils of the heat exchanger shall have the same heat exchange surface and provide equal heat transfer conditions for the multitude of tube bundles of any of the multitude of zones, while the fluid medium and refrigerant flows entering the respective tube bundles of the coil wound heat exchanger in the liquid phase and at different temperatures shall leave the multitude of tubes of the tube bundle at the same temperature since during the transition of the flow of cooled liquid refrigerant from the tube bundle into the annular space, throttling with subsequent evaporation of liquid refrigerant in the annular space shall be applied at a constant temperature with absorption of evaporation heat taken from the cooled fluid medium and refrigerant flows in the tubular space.

[0013] It is therefore expedient to wind the coils of the first tube on the rod tightly to one another, which will allow one to calculate the length of the first tube of the multitude of tubes of the tube bundle of the multitude of zones in advance using the following equation:

[0014] Where “ITP ” stands for the length of the tube,

[0015] L - length of the rod,

[0016] D - diameter of the rod, d - outside tube diameter, then the length of any tube of a multitude of tubes of a tube bundle of a multitude of zones can be calculated using the following equation: where “z ” stands for a tube coil number, k - distance between the tube coils.

[0017] When tight coiling of the first tube on the rod is utilized k=0, z=l, and equation (2) turns into an identity, the validity of the derived equations is confirmed.

[0018] The claimed invention offers one flexibility when choosing a design arrangement: the equations provided can be used to calculate both the gaps between the coils for a given length of tubes, and the length of tubes when specified coil gaps are available.

[0019] LIST OF DRAWINGS

[0020] Figures 1 and 2 demonstrate prior art configuration, which matches prototype RU 2765593 Cl for the case of dividing the cooled flow into three sub-flows utilizing the following designations:

[0021] 306 - gas flow;

[0022] 312 - warm bundle;

[0023] 344, 346, 348 - sub-flows of the cooled flow;

[0024] 356, 358, 360 - sub-flows of the liquefied gas flow;

[0025] 326, 328, 333 - warm end tube sheet;

[0026] 329a-b — process pipelines;

[0027] 330 - core;

[0028] 332, 334, 335 - cold end tube sheet;

[0029] 350 - inner zone;

[0030] 352 - middle zone;

[0031] 354 - outer zone;

[0032] 362, 364, 366 - valves;

[0033] 316 - liquefied gas flow;

[0034] 374 - warm end of warm bundle 312;

[0035] 376 - cold end of warm bundle 312. Figure 3 demonstrates a schematic diagram of one of the possible implementation variants of the claimed coil heat exchanger utilizing the following designations:

[0036] 31 - shell;

[0037] 32 - core;

[0038] 33-35 - tubes of the tube bundles;

[0039] 36 - tube sheets of the upper distribution chambers;

[0040] 37 - tube sheets of the lower distribution chambers;

[0041] 38 - refrigerants’ cooling loop.

[0042] Figure 4 demonstrates a fragment of the heat exchanger with a coiled first row of tubes utilizing the following designations:

[0043] 41 - first coil of the spiral tube bundle;

[0044] 42 — core.

[0045] BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The pre-cooled feed gas flow 306 is divided into three sub-flows 346, 348 and 344, with each delivering to the tube sheet of the warm end 333, 328, 326 respectively. The warm end 374 and cold end 376 of the warm bundle 312 are divided into concentric heat exchange zones - the inner zone 350, middle zone 352 and outer zone 354. All the process pipes connected with each of the warm tube sheets 326, 328, 333 are located within a single zone. For example, all the 329a-b process pipes of the tube sheet of the warm end 326 are directed towards the outer zone 354. All the process tubes connected with each of the cold end tube sheets 332, 334, 335 are also directed towards the same zone. For example, all the 329a-b process tubes that end in the cold end tube sheet 334 are led out of the outer zone 354. To simplify the figures, only the 329a-b process tubes tied with the warm end tube sheet 326 and cold end tube sheet 334 are identified via references in figures 1 and 2. The indicated configuration leads to the fluid medium remaining separated throughout the whole duration of the method. For example, all fluid medium, which enters the warm bundle 312 by means of sub-flow 344, exits the warm bundle through sub-flow 356. In other words, each of the warm end tube sheets - 326, 328, 333 - is connected, via fluid flow, with only one of the cold end tube sheets 334, 332, 335. Configuration shown in figures 1 and 2 is designed to reduce non-uniform radial distribution, which denotes non-uniform cooling of the fluid media in different zones of the warm bundle. For this purpose, the heat exchanger is outfitted with valves 362, 366, 364 downstream from each of the warm end tube sheets 326, 328, 333 respectively to even out the temperature of the sub-flows 356, 360 n 358 exiting the cold end tube sheets 334, 332, 335 and coming together as a single liquefied gas stream 316.

[0047] The limitation of the invention lies in the non-uniformity of heat transfer among different rows of twisted tube bundles due to the differing hydraulic resistance of the local flow jets passing through the tube coils of varying diameters: the larger the diameter of coils and, accordingly, the coil length, the lower the local flow in the coil and the lower the heat transfer coefficient, or, in other words, passing of each subsequent coil translates into the heat transfer value decrease. This significantly complicates any attempts to control the operation of the heat exchanger as a whole when process flows’ parameters are adjusted (performance, temperature, pressure, composition) due to the plant’s transition, using a coil heat exchanger, from one mode of operation to another.

[0048] In figure 3, the coil heat exchanger consists of shell 31 with core 32 around which the tubes of the tube bundles 33, 34 and 35 are spirally wound, and which are used to transport feed natural gas with flows 1 and 2 to the lower ends of the tube bundles 33, 34 and 35 secured in the tube shells of the lower distribution chambers 37. Upper ends of the tubes of the tube bundles 33, 34 and 35 are secured in the tube sheets of the upper distribution chambers 36, from which a respectively cooled natural gas is supplied with flows 3 and 4, while light and heavy refrigerants - with flows 5 and 6. Each wound tube of each tube bundle includes the same surface area, which enables one to easily form the required heat transfer surface for each of the three tube bundles depending on the amount of heat transferred and the heat transfer coefficient of each separate flow. Moving via flow 7, the refrigerant enters the refrigerant cooling loop 38 and then, via flows 8 and 9, it returns to the coil heat exchanger.

[0049] In figure 4, the first coil of the spiral tube bundle 41 for cooled natural gas is tightly wound around the core 42.

[0050] In figure 5, one of the coil heat exchanger’s tube bundle configuration variants is shown. According to this configuration, the natural gas, via flow 51 , is fed to the bottom of the heat exchanger into the tubes of the tube bundle coiled around the core, it then flows upward, passing successively through the lower and upper cooling zones created by heavy and light refrigerants, and, via flow 52, liquefied natural gas is then discharged. Heavy refrigerant is fed, via flow 56, into the lower part of the heat exchanger into the tubes of the tube bundle, passes the lower cooling zone, and is then discharged from the middle part of the heat exchanger via flow 58, which is located above the lower cooling zone, and is then throttled and fed into the annular space of the lower cooling zone via flow 57, thereby cooling the light refrigerant flow, heavy refrigerant flow and the natural gas flow. Light refrigerant, via flow 53, is fed into the lower part of the heat exchanger into the tubes of the tube bundle, passes the upper cooling zone, and is then discharged, via flow 55, from the upper part of the heat exchanger located above the upper cooling zone, and is then throttled and fed, via flow 54, into the annular space of the upper cooling zone, thereby cooling the oncoming flows of light refrigerant and natural gas moving through the tube bundles’ tubes. When in the annular space, the light refrigerant moves from top to bottom and is eventually discharged, via flow 59, through the bottom nozzle into the refrigerant cooling loop.

[0051] Thus, the invention enables one to develop a coil heat exchanger that offers equal heat transfer surface for all the coils.

Claims

FORMULA OF INVENTION1 Coil heat exchanger comprising: a shell; a multitude of bundles comprising a first bundle end and a second bundle end placed distal to the first bundle end; a core located along the centerline inside the first bundle, with the space within the first bundle shroud extending from the first bundle end to the second bundle and, and from the first bundle core to the shroud of thereof; a multitude of tubes arranged in a space within the first tube bundle shroud, with each of the multitude of tubes having a first end of the tube placed at the first end of the bundle and a second end of the tube - at the second end of the bundle, while the multitude of tubes are being wound around a core to form a multitude of twisted layers, with the multitude of twisted layers being divided into a multitude of zones that are concentrically placed in the space found within the first bundle shroud, while a multitude of tubes is foreseen which contains a multitude of sets of tubes, wherein each of the multitude of sets of tubes is placed in a different zone out of the multitude of zones; a first group of tube sheets placed at the first end of the bundle, with each of the first group of the tube sheets connected, via a fluid medium flow, with one of the multitude of sets of tubes located at the first end of the tube; a multitude of valves, with each of the multitude of valves connected, via a fluid medium flow, with each of the first group of the tube sheets and placed at the first end of the bundle; and a second group of tube sheets located at the second end of the bundle, with at least one of the second group of tube sheets connected, via a fluid medium flow, with more than one of the multitude of sets of tubes at the second end of the tube; refrigerant distributors located inside the body of the apparatus for uniform distribution of refrigerant supply over the apparatus diameter; tube bundle supports affixed on the core; pipe spacers, affixed on the tube bundle supports and located between the layers of coils, characterized by the fact that all coiled pipes of the pipe bundles of the multiple heat exchanger zones share the same diameter, with liquid medium and refrigerant flows entering at different temperatures are later withdrawn from the multitude of tubes of the tube bundle at the same temperature.2 Coil heat exchanger as described in item 1 differentiated by the fact that the coils of the first tube on the rod are coiled tightly together.3 2 Coil heat exchanger as described in item 1 differentiated by the fact that the length of the first tube of the multitude of tubes of the bundle of tubes of the multitude of zones is calculated according to the following equation:where ITP stands for pipe length,L - rod length,D - rod diameter, d - outer pipe diameter.4 Coil heat exchanger as described in item 1 differentiated by the fact that the length of any tube of the plurality of tubes of the tube bundle of the multitude of zones is calculated according to the following equation:where z stands for the number of the tube coil, k — distance between the tube coils.

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