RU2807843C1 - Twisted heat exchanger - Google Patents

Abstract

FIELD: heat engineering.

SUBSTANCE: used in the production of liquefied natural gas at gas industry enterprises. A coiled heat exchanger including: a shell, a first bundle, a core, a plurality of tubes, a first and a second group of tube sheets, a plurality of valves, refrigerant distributors, tube bundle supports, tube separators, and coiled tubes of tube bundles of multiple heat exchanger zones of the same diameter; wherein fluid and refrigerant streams entering at different temperatures exit the plurality of tubes of the tube bundle at the same temperature.

EFFECT: developing a twisted heat exchanger that provides an equal heat transfer surface for all turns to equalize heat transfer across the layers of turns of tube bundles.

4 cl, 5 dwg

Description

The twisted heat exchanger is designed for heat exchange between streams in conditions of a large heat exchange area to reduce the minimum temperature difference between hot and cold streams to reduce energy costs for liquefaction and can be used in the production of liquefied natural gas at gas industry enterprises.

Rigid shell-and-tube heat exchangers of various modifications have found wide application in various industries, containing a casing with input and output chambers for the first flow passing through a straight tube bundle, and the second flow passing through the intertube space of the casing (Shell-and-tube heat exchangers with fixed tube sheets and shell-and-tube heat exchangers with temperature compensator on the casing. Catalog. M.: OJSC "VNIINEFTEMASH". - 2003. - 71 p.). A common disadvantage of these designs is the large volume of the inter-tube space of the casing, due to which the speed of the second flow is low and, accordingly, the heat transfer coefficient from the second flow to the pipe walls is low, which leads to a decrease in the heat transfer coefficient in the heat exchange apparatus as a whole. It is very important that these heat exchangers have a large temperature difference between the hot and cold flow; usually the minimum difference in the apparatus is more than 10°C; in cryogenic technologies, in order to reduce energy costs, they try to reduce this temperature difference as much as possible.

A known heat exchanger contains a casing with coil tubes wound on a core, placed in coaxial rows, between adjacent rows of which spacers are installed, which are located along helical lines alternating in adjacent rows of right and left windings (USSR author's certificate SU 561070, MPK F28D 1 /02, application 07/05/1971, publ. 06/05/1977). The disadvantage of this invention is the different hydraulic resistance of local streams of flow passing through turns of coil tubes of different diameters: the larger the diameter of the turns and, accordingly, the length of the coil, the lower will be the speed of the local flow in the coil and the lower the heat transfer coefficient, that is, in each subsequent turn of the coil pipes, heat transfer decreases.

Known used in cryogenic technology, in particular for the production of liquefied natural gas, is a main heat exchanger for liquefying the flow from the pipe side, using a warm end and a cold end, wherein the main heat exchanger contains: a wall forming the side of the housing, inside which there is a bundle of pipes wound in a spiral , located around the central mandrel; a first nozzle for supplying a first pipe-side mass flow rate to pipes of a first zone of individual pipes in said tube bundle at the warm end of said first zone of individual pipes; a second nozzle for delivering a second mass flow rate of said pipe-side flow into pipes of a second discrete pipe zone in said tube bundle at the warm end of said second discrete pipe zone, the second discrete pipe zone being offset from the first discrete pipe zone along a radius extending from said central mandrel to said wall of said main heat exchanger; a distributor for supplying a refrigerant stream on said side of the housing to cool the first and second mass streams to form a vaporized refrigerant stream; a line for removing a stream of evaporated refrigerant from the warm end of said main heat exchanger; a first temperature sensor that generates a first signal indicating the temperature of the first mass flow rate; a second temperature sensor that generates a second signal indicative of the temperature of the second mass flow rate; and a controller for equalizing the temperature of the first pipe-side mass flow rate at the first axial location with the temperature of the second pipe-side mass flow rate at the first axial location by comparing the first signal indicating the temperature of the first mass flow rate with the second signal indicating the temperature of the second mass flow rate , and adjusting the first mass flow rate of the tube side flow supplied by said first nozzle relative to the second mass flow rate of the tube side flow supplied by said second nozzle to align the first signal with the second signal (US patent 9982951 B2, F25J 1/00, F25J 1/ 02, F28F 9/00, F28D 7/00, F28D 7/02, F28F 27/02, application 03/31/2011, publ. 03/21/2013). The disadvantage of this invention is the different lengths of three twisted heat exchange coils placed in a single body of the heat exchanger, while one of the coils serves to liquefy hydrocarbon gas, and the other two ensure the functioning of the circulation system of light (LMR) and heavy (HMR) fractions of the refrigerant, which is essential complicates the regulation of the operation of the heat exchanger as a whole when the productivity of the installation for the produced liquefied natural gas changes, as well as when the temperature of the air entering the air-cooling refrigerator and the air-cooling refrigerator between the first and second refrigerant compression compressors changes.

Also known is the twisted heat exchanger closest to the claimed invention, containing: a casing; a first bundle comprising a first bundle end and a second bundle end located distal to the first bundle end; a core located centrally within the first bundle, the space within the first bundle casing extending from the first end of the bundle to the second end of the bundle and extending from the core of the first bundle to its casing; a plurality of pipes disposed in a space within the casing of the first bundle, each of the plurality of pipes having a first pipe end located at a first end of the bundle and a second pipe end located at a second end of the bundle, the plurality of pipes being wound around a core to form a plurality of twisted layers, wherein the plurality of twisted layers is divided into a plurality of zones that are concentrically located in a space within the casing of the first bundle, the plurality of tubes comprising a plurality of sets of tubes with each of the plurality of sets of tubes located in another of the plurality of zones; a first group of tube sheets located at a first end of the bundle, each of the first group of tube sheets being in fluid flow communication with one of a plurality of sets of tubes at the first end of the tube; a plurality of valves, each of the plurality of valves being in fluid communication with each of the first group of tube sheets and located at a first end of the bundle; and a second group of tube sheets located at the second end of the bundle, wherein at least one of the second group of tube sheets is in fluid flow communication with more than one of the plurality of sets of tubes at the second end of the tube (patent RU 2765593 C1, IPC F28D 7/ 02, F28F 27/02, F28J 1/00, application 04/29/2021, publ. 02/01/2022). Figures 1 and 2 show the configuration from the prior art, shown in the prototype RU 2765593 C1 for the case of dividing the cooled flow into three subflows using the following notations:

306 - gas flow;

312 - warm bun;

344, 346, 348 - subflows of the cooled flow;

356, 358, 360 - subflows of liquefied gas flow;

326, 328, 333 - warm end tube sheet;

329a-b - process pipes;

330 - core;

332, 334, 335 - cold end tube sheet;

350 - internal zone;

352 - middle zone;

354 - external zone;

362, 364, 366 - valves;

316 - liquefied gas flow;

374 - warm end of warm bundle 312;

376 - cold end of warm beam 312.

The pre-cooled feed gas stream 306 is divided into three substreams 346, 348 and 344, each of which feeds a warm end tubesheet 333, 328, 326, respectively. The warm end 374 and the cold end 376 of the warm bundle 312 are divided into concentric heat exchange zones—an inner zone 350, a middle zone 352, and an outer zone 354. All process pipes associated with each of the warm tube sheets 326, 328, 333 are located in a single zone. For example, all process tubes 329a-b of warm end tube sheet 326 are directed to the outer zone 354. All process tubes associated with each of the cold end tube sheets 332, 334, 335 are also directed to one zone. For example, all process pipes 329a-b that terminate in the cold end tube sheet 334 are discharged from the outer zone 354. To simplify the figures, only the process pipes 329a-b associated with the warm end tube sheet 326 and the cold end tube sheet 334 are indicated in fig. 1 and 2 reference positions. This configuration results in the fluid remaining separated throughout the process. For example, all fluid entering the warm bundle 312 through subflow 344 exits the warm bundle through subflow 356.

In other words, each of the warm end tube sheets 326, 328, 333 is in fluid communication with only one of the cold end tube sheets 334, 332, 335. The configuration of FIG. 1 and 2 is designed to reduce uneven radial distribution, meaning uneven cooling of fluids in different zones of the warm beam. To this end, the heat exchanger includes valves 362, 366, 364 downstream of each of the warm end tube sheets 326, 328, 333, respectively, to equalize the temperature of the substreams 356, 360 and 358 exiting the cold end tube sheets 334, 332, 335 and connecting into a single liquefied gas stream 316.

The disadvantage of the invention is the unevenness of heat transfer in different rows of twisted bundles of pipes as a result of different hydraulic resistance of local streams of flow passing through the coils of coil tubes of different diameters: the larger the diameter of the coils and, accordingly, the length of the coil, the lower the speed of the local flow in the coil and the lower the coefficient heat transfer, that is, in each subsequent turn of the coil pipe, the heat transfer decreases. This significantly complicates the regulation of the operation of the heat exchanger as a whole when the parameters of process flows (capacity, temperature, pressure, composition) change when an installation using a twisted heat exchanger changes from one mode to another.

During the development of the claimed invention, the problem of structural improvement of a twisted heat exchanger was solved to level out the heat transfer across the layers of turns of tube bundles, ensuring an equal heat transfer surface for all turns.

The problem is solved due to the fact that a twisted heat exchanger, including: a casing; a plurality of bundles comprising a first bundle end and a second bundle end located distal to the first bundle end; a core located centrally within the first bundle, the space within the first bundle housing extending from the first end of the bundle to the second end of the bundle and from the core of the first bundle to its housing; a plurality of pipes disposed in a space within the casing of the first bundle, wherein each of the plurality of pipes has a first end of the pipe located at a first end of the bundle and a second end of the pipe at a second end of the bundle, the plurality of pipes being wound around a core to form a plurality of twisted layers, wherein a plurality of twisted layers are divided into a plurality of zones, which are concentrically located in a space within the casing of the first bundle, and a plurality of pipes are provided containing a plurality of sets of pipes, with each of the plurality of sets of pipes being located in another of the plurality of zones; a first group of tube sheets located at a first end of the bundle, each of the first group of tube sheets being in fluid flow communication with one of a plurality of sets of tubes at the first end of the tube; a plurality of valves, each of the plurality of valves communicating in fluid flow with each of the first group of tube sheets and located at a first end of the bundle; and a second group of tube sheets located at a second end of the bundle, wherein at least one of the second group of tube sheets is in fluid communication with more than one of a plurality of sets of tubes at the second end of the tube; refrigerant distributors located inside the device body to uniformly distribute the refrigerant supply across the diameter of the device; tube bundle supports fixed to the core; pipe separators mounted on the supports of the tube bundles and located between the winding layers, while all the twisted pipes of the tube bundles of the plurality of heat exchanger zones are of the same diameter, the fluid and refrigerant flows entering at different temperatures exit the plurality of pipes of the tube bundle at the same temperature.

In this case, all coiled heat exchanger tubes have the same heat exchange surface and provide equal heat transfer conditions for multiple tube bundles of any of the multiple zones, and fluid and refrigerant flows entering the corresponding coiled heat exchanger tube bundles in the liquid phase at different temperatures exit the plurality of tubes bundle of tubes at the same temperature, since when the flow of cooled liquid refrigerant passes from the tube bundle into the inter-tube space, it is throttled with subsequent evaporation of the liquid refrigerant in the inter-tube space at a constant temperature with the absorption of the heat of evaporation taken from the cooled flows of fluid and refrigerant in the tube space.

It is advisable to wind the turns of the first pipe on the rod tightly to each other, which will allow you to pre-calculate the length of the first pipe of many pipes of a bundle of pipes of many zones according to the equation:

where l _TP is the length of the pipe,

L - length of the rod,

D - diameter of the rod,

d is the outer diameter of the pipe,

then the length of any pipe of a set of pipes of a bundle of pipes of a set of zones is calculated by the equation:

where z is the number of the pipe turn,

k is the distance between the turns of the pipe.

When the first pipe is tightly wound onto the rod, k=0, z=1, and equation (2) turns into an identity, which confirms the validity of the resulting equations.

The claimed invention provides flexibility in the design solution: using the given equations, it is possible to calculate both the gaps between the turns for a given length of pipes, and the length of the pipes for a given value of the gaps between the turns.

Figure 3 shows a diagram of one of the possible implementation options for the claimed twisted heat exchanger using the following notation:

31 - body;

32 - core;

33-35 - pipes of tube bundles;

36 - tube sheets of the upper distribution chambers;

37 - tube sheets of the lower distribution chambers;

38 - refrigerant cooling circuit.

The twisted heat exchanger is a housing 31 with a core 32, on which pipes of tube bundles 33, 34 and 35 are spirally wound, through which the source natural gas is supplied via streams 1 and 2 to the lower ends of the pipes of tube bundles 33, 34 and 35, fixed in tube sheets lower distribution chambers 37. The upper ends of the pipes of the tube bundles 33, 34 and 35 are fixed in the tube sheets of the upper distribution chambers 36, from which respectively cooled natural gas is supplied through streams 3 and 4, light and heavy refrigerants through streams 5 and 6. Each twisted pipe Each tube bundle includes the same surface, which makes it easy to form the required heat transfer surface for each of the three tube bundles, depending on the transferred amount of heat and the heat transfer coefficient of each stream separately. Through stream 7, the refrigerant enters the refrigerant refrigeration circuit 38 and through streams 8 and 9 it returns to the twisted heat exchanger.

Figure 4 shows a fragment of a heat exchanger with a coiled first row of pipes using the following notation:

41 - first turn of the spiral tube bundle;

42 - core.

The first turn of the helical pipe bundle 41 for refrigerated natural gas is wound tightly around the core 42.

In fig. Figure 5 shows one of the options for assembling bundles in the volume of a twisted heat exchanger, in which natural gas through stream 51 is supplied to the lower part of the heat exchanger into the pipes of a tube bundle wound on the core and rises upward, passing successively the lower and upper cooling zones created by heavy and light refrigerants , and liquefied natural gas is discharged through stream 52. The heavy refrigerant is supplied via stream 56 to the lower part of the heat exchanger into the pipes of the tube bundle, passes through the lower cooling zone, is removed from the middle part of the heat exchanger via stream 58, located above the lower cooling zone, is throttled and supplied to the annular space of the lower cooling zone via stream 57, cooling the flow light refrigerant stream, heavy refrigerant stream and natural gas stream. Light refrigerant is supplied via stream 53 to the lower part of the heat exchanger into the pipes of the tube bundle, passes through the upper cooling zone, is removed from the upper part of the heat exchanger via stream 55, located above the upper cooling zone, is throttled and supplied to the annulus of the upper cooling zone via stream 54, while cooling counter flows of light refrigerant and natural gas moving through the pipes of the tube bundles. In the inter-tube space, light refrigerant moves from top to bottom and is discharged through the lower fitting into the refrigerant cooling circuit along flow 59.

Thus, the invention makes it possible to develop a twisted heat exchanger that provides an equal heat transfer surface for all turns.

Claims (12)

1. Twisted heat exchanger, including: casing; a plurality of bundles comprising a first bundle end and a second bundle end located distal to the first bundle end; a core located centrally within the first bundle, the space within the first bundle housing extending from the first end of the bundle to the second end of the bundle and from the core of the first bundle to its housing; a plurality of pipes disposed in a space within the casing of the first bundle, wherein each of the plurality of pipes has a first end of the pipe located at a first end of the bundle and a second end of the pipe at a second end of the bundle, the plurality of pipes being wound around a core to form a plurality of twisted layers, wherein a plurality of twisted layers are divided into a plurality of zones, which are concentrically located in a space within the casing of the first bundle, and a plurality of pipes are provided containing a plurality of sets of pipes, with each of the plurality of sets of pipes being located in another of the plurality of zones; a first group of tube sheets located at a first end of the bundle, each of the first group of tube sheets being in fluid flow communication with one of a plurality of sets of tubes at the first end of the tube; a plurality of valves, each of the plurality of valves communicating in fluid flow with each of the first group of tube sheets and located at a first end of the bundle; and a second group of tube sheets located at a second end of the bundle, wherein at least one of the second group of tube sheets is in fluid communication with more than one of a plurality of sets of tubes at the second end of the tube; refrigerant distributors located inside the device body to uniformly distribute the refrigerant supply across the diameter of the device; tube bundle supports fixed to the core; pipe separators mounted on the supports of the tube bundles and located between the layers of winding, characterized in that all the twisted pipes of the tube bundles of the plurality of heat exchanger zones are of the same diameter, the flows of fluid and refrigerant entering at different temperatures are discharged from the plurality of pipes of the tube bundle at the same temperature . 2. Twisted heat exchanger according to claim 1, characterized in that the turns of the first pipe on the rod are wound tightly to each other. 3. Twisted heat exchanger according to claim 1, characterized in that the length of the first pipe of a plurality of pipes of a bundle of pipes of a plurality of zones is calculated according to the equation: , where l _TP is the length of the pipe, L – rod length, D – diameter of the rod, d is the outer diameter of the pipe. 4. Twisted heat exchanger according to claim 1, characterized in that the length of any pipe of a plurality of pipes of a bundle of pipes of a plurality of zones is calculated according to the equation: where z is the number of the pipe turn, k is the distance between the turns of the pipe.