KR102514159B1 - Heat exchanger for a molten salt steam generator in a concentrated solar power plant (iii) - Google Patents

Abstract

As heat exchanger (1), a bundle of parallel U-bent tubes (2) distributes the first fluid to the tubes (2) of the first straight section (9) through which the first hemispherical bonnet (16) connects. connected to a first end of which the second hemispherical bonnet 16 collects the first fluid from the tubes 2 of the second straight section 10, each of which connects to an intershell space ( 5) made of tubesheets (11, 12) designed to withstand the difference between the second fluid low pressure inside and the first fluid high pressure inside the individual bonnet 16, the tubesheets being circular plates 12 having a central circular orifice; ), wherein the tube sheet further comprises a hemispherical shell (11) positioned above the orifice and rigidly connected to the circular plate (12) for physically separating the first fluid and the second fluid ( One).

Description

HEAT EXCHANGER FOR A MOLTEN SALT STEAM GENERATOR IN A CONCENTRATED SOLAR POWER PLANT (III)}

The present invention relates to the field of heat exchangers, such as evaporators, superheaters, reheaters and economizers intended for use in heat exchangers, in particular in thermal fluid steam generators such as molten salt steam generators (MSSG) in concentrating solar power plants (CSP). will be.

It is known that CSP tower installations generally include one or more solar receivers located at the apex of a central tower. These solar receivers are heated by the focused incident solar rays and produce a hot fluid that is further used to produce high-pressure steam that can drive a turbine and produce electricity.

More specifically, a CSP tower installation has at least a heliostat solar field, a solar receiver installed on the top of the tower, a steam generator, a steam turbine and a storage system as major components. In molten salt technology, molten salt is typically heated to 565° C. in a solar receiver and stored in a hot storage tank. When electricity production is required, hot salt flows from a hot tank to a molten salt steam generator (MSSG), generating steam to be injected into a steam turbine.

1 schematically shows the components of a typical so-called heat exchanger train for an MSSG. Hot molten salt flows from inlet 100 through reheater 101 (or preheater with or without reheater) and superheater 104 to enter evaporator 102. The hot salt then flows from the outlet of the evaporator 102 to the economizer 103 and to the outlet 105 .

The so-called "shell and tube" heat exchanger refers in the prior art to a heat exchanger design suitable for high pressure applications. This type of heat exchanger consists of a large pressure vessel called a "shell" having inside a set of tubes called a "bundle". For the purpose of transferring heat from the second fluid to the first fluid and vice versa (the first and second fluids have different temperatures), the first fluid flows through the tube while the second fluid flows inside the shell above the tube. flow in

Many variations exist in shell and tube designs. As an example, Fig. 2 schematically shows a straight tube heat exchanger (two-pass tube-side). The ends of each tube 21 are connected to water boxes or plenums 29 through holes provided in the separator plate called 'tube sheets' 27 . The tubes 21 may be straight as shown in FIG. 2 or bent in a “U” shape (U-tube).

To provide improved heat exchange between the two fluids, the flow path of the second fluid is often determined by an intermediate baffle 28 forming a separate passage, so that the second fluid flow moves in that direction as it proceeds from one passage to the next. this changes The baffle is usually in the form of a partial circular segment or annular ring and disk installed perpendicular to the longitudinal axis of the shell 22 to provide a zigzag flow of the secondary fluid.

A prior art alternative of this design, shown in Figure 3, is a horizontal hairpin heat exchanger. The hairpin heat exchanger 1 has two shells 22 comprising straight sections of U-tubes. The head of the hairpin includes a 180° U-bent portion of the tube. The advantages of this hairpin design are:

- no joint expansion system is required, as thermal expansion is essentially managed by the hairpin design;

- Draining and venting of the heat exchanger is easier due to the straight tubes and the horizontal position of the exchanger.

Other concepts of steam generators are already known. A synthesis of these different concepts is reported in Sandia report 93-7084 "Investigation of Heat Storage and Steam Generator Issues, Bechtel Corporation", which lists the advantages and disadvantages of existing steam generators.

It has been known since the 1920's that in order to improve the heat transfer efficiency of a heat exchanger, shell-mounted baffles may have a specific shape for guiding the fluid in a helical path. Moreover, in the case of a continuous spiral baffle, the heat transfer rate increases by about 10% compared to a conventional segmented baffle for the same shell-side pressure drop (J. Heat Transfer (2007), Vol. 129(10), 1425-1431). This pattern reduces the leakage stream from the segmented baffle and allows for a significant increase in the heat transfer coefficient (J. Heat Transfer (2010), Vol. 132(10), 101801). In addition, fluid stratification and stagnant zones are avoided (according to calculations), allowing full drainage and reducing fouling susceptibility (lower fouling resistance and lower heat transfer area).

Document WO 2009/148822 discloses a shell-mounted baffle for guiding a fluid in a helical flow pattern with different helix angles when the baffle is proximal to the inlet and outlet, respectively. Documents US 2,384,714, US 2,693,942, US 3,400,758, US 4,493,368 and WO 2005/019758 each disclose a different kind of baffle, each with the same objective of providing a helical flow pattern of a fluid. Document US 1,782,409 discloses a continuous spiral baffle.

Document GB 2 020 793 A discloses a counter flow heat exchanger, in particular a steam generator, having two stationary tube plates, an upper tube plate and a lower tube plate, the tube plates arranged opposite each other in parallel coaxial relation and with different mean A nest of tubes extends between the upper and lower tube plates, the tubes being connected to the tube plates and distributed in a substantially polar symmetrical arrangement and having an S shape at one end. Having a bent portion, the straight portion of the tube nest substantially includes a heat transfer zone surrounded by a substantially uniform distribution within an annular space defined between the inner jacket and the outer shroud attached to the tube plates. In use, a heating fluid, such as liquid sodium, passes through the annular space to heat the fluid flowing in the tube.

Current solutions are unsatisfactory in terms of e.g. thermal gradient flexibility, efficiency (pressure drop, heat transfer coefficient), drainage, natural circulation, absence of corrosion and leaks, etc., a newly designed steam generator and/or its individual heat exchanger is Must meet technical requirements such as:

- improved thermal efficiency by reducing internal leakage and bypass stream;

- improved pressure drop by reducing localized stream obstruction;

- improved ramp-up capability;

- improved reliability;

- Improved fouling behavior, etc.

Also, fast start-up generally results in leaks, particularly at the joints between the tubes and the tubesheet.

The present invention aims to overcome the disadvantages of prior art heat exchangers for steam generators.

In particular, the present invention provides lower pressure drop, lower internal leakage (bypass), improved heat transfer coefficient, lower fouling tendency, easily drainable molten salt, natural circulation (i.e. no circulation pump), long life and The aim is to obtain a heat exchanger of reduced size that exhibits high flexibility in terms of the heat gradient as well as improved efficiency thanks to an optimized hydrodynamic salt flow resulting in a competitive cost.

A first aspect of the present invention is a heat exchanger having a first straight section, a second straight section, and a bent section or elbow linking the first and second straight sections, each straight section comprising an inner cylindrical shell and portions of an outer cylindrical shell of the heat exchanger, wherein both cylindrical shells have first and second straight portions respectively located within the first straight section and the second straight section of the heat exchanger, and located within a vent section or elbow of the heat exchanger. working in concert to form an intershell space surrounding a bundle of parallel U-Bent tubes, each having a 180°-bent section, so that, in use, a first fluid to be heated and evaporated flows within the U-Bent tubes. The outer cylindrical shell has an inlet at one end and an outlet at the other end for a second fluid, which is a high-temperature thermal fluid, so that when in use, the second fluid flows along an annular flow path within the intershell space and forms a U-vent Cooled by exchanging heat with a first fluid flowing in the tubes, the intershell space also surrounds baffles that guide the second fluid, and a bundle of parallel U-vent tubes, a first hemispherical bonnet to receive the first fluid. At a first end distributing to tubes of a first straight section, and a second hemispherical bonnet collects a first fluid in the form of a liquid, vapor, or liquid/vapor mixture from the tubes of a second straight section. Connected to the second end through joints, each joint being made of a tube sheet designed to withstand the difference between the second fluid low pressure inside the intershell space and the first fluid high pressure inside the individual bonnet, the tube sheet being a central circular A heat exchanger comprising a circular plate having an orifice, wherein the tube sheet further comprises a hemispherical shell positioned over the orifice and rigidly connected to the circular plate for physically separating a first fluid from a second fluid.

According to a preferred embodiment of the present invention, the hairpin heat exchanger also includes one or a suitable combination of the following features:

- the thickness of the circular plate is greater than that recommended by ASME standards to withstand the same pressure differential;

- the interface between the bonnet and the tube sheet circular plate is essentially flat, the hemispherical shell being oriented towards the inside of the heat exchanger and located inside the inner cylindrical shell;

- the thickness of the hemispherical shell is between 20% and 40% of the thickness of the tube sheet plate;

- said first straight section and said second straight section consist of separate enclosures linked by said elbow, forming a hairpin heat exchanger shell;

- the first straight section, the second straight section and the bent section or elbow consist of one single enclosure or shell enclosing a bundle of parallel U-bent tubes, the first hemispherical bonnet and the second hemispherical bonnet coincident do;

- the heat exchanger is of a horizontal type, in which the flow of the second fluid relative to the flow of the first fluid is co-current or countercurrent;

- the first fluid is feedwater or a fluid comprising supercritical carbon dioxide;

- the second fluid is molten salt or a mixture of molten salts, thermal oil or liquid sodium;

- the baffles are in the form of continuous spiral baffles;

- the baffles are assembled, preferably welded or bolted, to the inner cylindrical shell;

- sealing means are provided between the outer cylindrical shell and the baffles;

- the heat exchanger is provided with a distribution jacket for uniformly supplying the second fluid from the thermal fluid inlet to the heat exchanger;

- the distribution jacket has a plurality of apertures distributed 360° over its inner surface, the apertures preferably supplying the second fluid to the first turn of the spiral baffle.

A second aspect of the present invention relates to an evaporator made of the heat exchanger as described above.

A third aspect of the present invention relates to a superheater made of the heat exchanger as described above.

A fourth aspect of the invention relates to a reheater and/or economizer and/or preheater made of the heat exchanger as described above.

A fifth aspect of the invention relates to a molten salt steam generator (MSSG) comprising at least one heat exchanger train made of an evaporator, superheater, reheater and/or economizer and/or preheater as described above. Advantageously, the superheater, reheater and/or economizer and/or preheater are operated counter-flow while the evaporator is operated co-current.

Still within the scope of the present invention, the molten salt steam generator is a once-through or forced circulation steam generator.

1 schematically shows the components of a typical heat exchanger train for a molten salt steam generator.
Figure 2 schematically shows an embodiment of a "shell-and-tube" straight tube heat exchanger according to the prior art.
3 is a perspective view of a prior art horizontal hairpin generator;
4a and 4b are plan and front views, respectively, of a first preferred embodiment of a heat exchanger according to the present invention.
5A and 5B are corresponding sectional views of a heat exchanger according to the embodiment of FIG. 4, respectively.
6a and 6b are views corresponding to FIG. 5 each with a support system of the heat exchanger.
7 is a longitudinal cross-sectional detail view of one exchanger end according to the present invention, with focus on a particular tube sheet.
8A and 8B are perspective and sectional views, respectively, of the particular tube sheet described above.
9 is a cutaway 3D view of a second embodiment of the present invention showing an evaporator having a U-tube design.
10A and 10B show respective thermography simulation data for a tube sheet (A) according to the prior art and a specific tube sheet (B) of the present invention.

A first preferred embodiment of the present invention relates to a novel design for a horizontal hairpin heat exchanger 1, as shown in FIGS. 4 to 9 .

The heat exchanger has reciprocating motion between the two fluids. A first fluid, generally a mixture of water and steam, is passed through a first bundle of parallel horizontal straight tube sections 2 located at a first straight part of the hairpin and at a second straight part of the hairpin. Circulates through a second bundle of straight tube sections (2). The tubes 2 of the first bundle are connected to the tubes 2 of the second bundle by a 180° bent tube section located at the head of an elbow 32 or hairpin, forming U-bent tube sections.

Supercritical carbon dioxide is an example of an alternative first fluid that can be used in the present invention.

According to this embodiment, a bundle of tubes 2 in each straight section is located between the inner cylindrical shell 3 and the outer cylindrical shell 4, as shown in FIGS. 5 and 6 .

The inner space 5 defined by the two shells 3, 4 makes it possible to keep a heat source, preferably a second fluid, within the annular flow path. This second fluid is a thermal fluid, for example molten salt(s) heated by a solar receiver at the apex of a CSP tower installation. The thermal fluid will flow in contact with the bundle(s) of tubes (2), thereby transferring heat to the parallel-flowing first fluid flowing through the tubes (2). The first fluid and the second fluid may be co-current or counter-current without departing from the scope of the present invention. Similarly, the heat source or second fluid may be any thermal fluid such as water, thermal oil, liquid sodium, fluidized bed, or the like.

As shown in FIG. 4, the first distribution jacket 30 is provided with an inlet nozzle 6, respectively, an outlet nozzle 6 at one end of the heat exchanger 1, through which the thermal fluid flows into the heat exchanger 1 ) enters or exits the heat exchanger. Similarly, an outlet nozzle 7, respectively an inlet nozzle 7, is provided in the second distribution jacket 30 at the other end of the heat exchanger 1 to discharge the cooled thermic fluid or to receive the hot fluid.

Advantageously, the thermal fluid is evenly distributed over the shell over 360° (inlet, circulation, fluid temperature) thanks to the distribution jacket 30 located at the inlet nozzle of the heat exchanger.

In order to improve the efficiency of heat transfer, as shown in Figs. 5 and 6, the space 5 is equipped with a closed continuous spiral baffle 8 capable of guiding the flow of thermal fluid to the straight part of the hairpin exchanger. . The thermal fluid then flows spirally between the inner shell and the outer shell according to an annular flow path in a heat exchanger, for example an evaporator operating under natural circulation. The continuous helical baffle configuration ensures a gentle flow of the secondary fluid, avoiding sudden direction changes or dead zones, such as in exchangers with baffles perpendicular to the flow. In this way, the heat transfer rate is greatly increased and the pressure drop is greatly lowered compared to exchangers with conventional segmented baffles (see above).

According to one embodiment, the inner cylindrical shell 3 and the baffles 8 can be welded or bolted together. Sealing means may also be provided between the outer shell 4 and the baffles 8 to prevent parasitic streams.

Advantageously the spiral baffle is designed using an innovative solution (sealing device and manufacturing, not shown) to have the smallest possible clearance between the baffle and the tube. This can suppress or at least strongly reduce the bypass between the baffles and through the tubes.

Continuing according to the present invention, as shown in FIG. 7 , at each outer end of the straight section of the hairpin exchanger, an annular bundle of parallel straight tubes 2 is passed through a particular tube sheet 11 , 12 to a high pressure fluid It is connected to the (half) spherical bonnet 16 containing (steam/steam). Certain tube sheets 11, 12 have the following characteristics:

- the tube sheet plate 12 itself is hollow in its center, with orifices machined therein and corresponding to the extension of the straight section of the heat exchanger without the tubes 2;

- physically rigid separation (see rectangular frame) between the molten salt low pressure zone (13) and the high pressure water/steam bonnet zone (15) of the straight part of the heat exchanger welded or rigidly connected to the tube sheet plate (12) above the orifice secured by the spherical head 11;

- The tube sheet plate 12 is thicker than in common designs in the prior art according to the recommendations of the ASME (American Society of Mechanical Engineers) code.

According to the above features, the heat exchanger components work cooperatively so that the heat exchanger operates as follows:

- the spherical bonnet 16 distributes the first fluid (water/steam etc.) towards the tubesheet 12; The spherical shape of the bonnet makes it possible to design a thinner bonnet;

- the tube sheet 12 distributes the first fluid towards the tube bundle 2 at the inlet of the heat exchanger and from the tube bundle at the outlet of the heat exchanger;

- the annular salt flow down (of the second fluid) is improved by continuous spiral baffles (8) of shell-and-tube configuration, and the U-tube design (14) reduces the differential thermal expansion of the tube allow you to manage

As in the classic shell-and-tube configuration, the first fluid, usually water, is under high pressure in a quasi-spherical vessel or plenum. On the other side of the tube sheet, the salt flowing around the tube bundle is kept under a much lower pressure, requiring a very thick tube sheet to withstand the pressure difference.

It is an unexpected effect or advantage of the present invention to suggest a tube sheet much thicker than specified in the prior art. Oversizing the tube sheet plate 12 helps reduce its bending stress and reduces creep. In addition, certain machining of the tube sheet and/or bonnet can reduce the amount of waste metal.

yes

The present invention is flexible and adapts to a series of heat exchanger designs used in MSSG technology, such as reheaters, superheaters, economizers, preheaters and evaporator devices, in which all common components are manufactured according to the comprehensive heat exchanger design of the present invention. it is intended

As described above (FIG. 1), the hot molten salt of decreasing temperature, for example first flows in parallel through a reheater and a superheater, recombines and enters the evaporator and sequentially into the preheater/economizer.

In this embodiment, hot molten salt entering the system at high temperature, e.g., 563° C. (and certainly below the degradation temperature for normal molten salt, 650° C.) flows in parallel through a superheater and a reheater, combine, It passes continuously through the evaporator and preheater. The cold salt typically leaves the preheater at a temperature of 290-300 °C, preferably at a temperature of about 293 °C, or above a minimum temperature which is the solidification temperature of the heat transfer fluid (as low as 90 °C for molten salts such as sodium derivatives). . Alternatively, any thermal fluid, such as thermal oil, may be used in place of the molten salt in the operating temperature range, in this case for example in the operating temperature range of 80 °C (condensation and/or crystallization temperature) to 380 °C (example of degradation temperature). .

It is also within the scope of the present invention that the thermal fluid can have a temperature of up to 700 °C. All metal parts are advantageously made of noble metal or stainless steel capable of withstanding temperatures of up to 600 °C and higher.

More specifically, according to one embodiment, the molten salt from the reheater and superheater enters the evaporator through an inlet nozzle and, as described above, within the evaporator in a natural circulation manner in an annular space located between the inner pipe and the outer shroud. flows in a spiral Saturated water flows from the vapor drum (spherical or horizontal) of the evaporator through a downcomer (not shown) and from the hemispherical bonnet to a U-tube inside the heat exchanger for steam generation. In this design, high-pressure water flows in a tube that does not come into contact with the shell. Preferably, all heat exchangers are horizontal.

Although the design of the heat exchanger according to the invention is optimized for natural circulation running, it can also be used with once-through or forced circulation steam generators.

According to an alternative embodiment of the present invention shown in figure 9, the straight tube sections of the first tube bundle and the second tube bundle are one single U-unit located within a single enclosure or shell (not forming a hairpin shell). Forming a tube bundle, the elbow 32 of the U-tubes 2 is on one side of the exchanger and the inlet/outlet of a single U-tube bundle located on the other side is a tube sheet 11, 12 according to the present invention. ) through which it is connected to the spherical bonnet 16.

The present invention provides a particularly high flexibility in terms of thermal gradients thanks to the following features:

- the tube sheet is hollow in the center to avoid detrimental thermal gradients inside the tube sheet; This improves the thermal behavior of this component during start-up, resulting in a longer lifetime of this component (see Fig. 10b, lower thermal gradient of the tube sheet in the present invention compared to the prior art in Fig. 10a);

- between the tube sheet 12 and the inner pipe 3, certain machining may be foreseen in order to avoid peak stresses and to improve the life of this latter component;

- certain machining between the tube sheet 12 and the spherical bonnet 16 (without flanges) may also be foreseen;

- the spherical bonnet 16 was chosen as a header or end part to avoid any cold areas during the start of installation;

- the high-pressure water flows within the tube or pipe (2) rather than the shell side (4), which allows its thinner thickness and consequently a higher heat gradient capability;

- the traditional straight baffle is replaced by a spiral baffle (8), so that the salt flows in a spiral while the water is restricted to flow in the tubes (2);

- The continuous spiral baffle (8) allows smooth flow direction changes. At equivalent ΔP, the continuous spiral baffle (8) ensures higher velocity flow, higher exchange surface and smaller heat exchanger design compared to conventional baffles. Moreover, since there is no dead zone with such a baffle design, the risk of fouling is lower.

Furthermore, according to the present invention, the special connection of tubes and tubesheets, such as the internal bore wilding (IBW) known per se in the art, provides a corrosion-free and leak-free solution (no risk of crevice corrosion, leakage or loosening). (no risk of relaxation) can also be provided.

1 hairpin heat exchanger
2 straight tubes (sections)
3 inner cylindrical shell
4 outer cylindrical shell
5 intershell space
6 thermal fluid inlet
7 thermal fluid outlet
8 spiral baffle
9 first straight section
10 second straight section
11 The spherical head of the tube sheet
12 thick tube sheet
13 2nd low pressure fluid (molten salt)
14 U-bent tube
15 high pressure fluids (water/steam)
16 bonnet (entry or exit)
17 tube passage
18 front closure
19 rear closure
20 support
21 straight tube
22 shell
23 Shell-side fluid inlet
24 Tube side fluid inlet
25 Tube side fluid leakage
26 Shell-side fluid leakage
27 tube seat
28 straight baffle
29 water box or plenum or bonnet
30 distribution jacket
32 elbow
33 separation plate
Molten salt inlet of 100 MSSG
101 MSSG reheater
Evaporator of 102 MSSG
103 MSSG economizer
Superheater of 104 MSSG
Molten salt outlet of 105 MSSG

Claims (22)

A heat exchanger (1) having a first straight section (9), a second straight section (10) and a bent section or elbow (32) linking the first straight section and the second straight section,
Each straight section (9, 10) comprises an inner cylindrical shell (3) and part of an outer cylindrical shell (4),
Both cylindrical shells have first and second straight sections respectively located within the first and second straight sections 9 and 10 of the heat exchanger, and the vent section or elbow 32 of the heat exchanger. working in concert to form an intershell space (5) surrounding a bundle of parallel U-vent tubes (2) each having a 180°-bent portion located within the first fluid to be heated and vaporized in use. flows within the U-bent tubes (2),
The outer cylindrical shell (4) has an inlet (6) at one end and an outlet (7) at the other end, respectively, for a second fluid, which is a high-temperature thermal fluid, so that, when in use, the second fluid passes through the intershell space. cooled by exchanging heat with the first fluid flowing along the annular flow path in (5) and flowing in the U-vent tubes (2);
the intershell space (5) also surrounds the baffles (8) guiding the second fluid;
A bundle of parallel U-bent tubes (2), at a first end from which a first hemispherical bonnet (16) distributes the first fluid to the tubes (2) of the first straight section (9), and A connection at the second end where a second hemispherical bonnet 16 collects the first fluid in the form of a liquid, vapor, or liquid/vapor mixture from the tubes 2 of the second straight section 10 connected through
Each said connection is a tube designed to withstand the difference between the second fluid low pressure inside the intershell space 5 and the first fluid high pressure inside the first hemispherical bonnet 16 and the second hemispherical bonnet 16 made of sheets 11, 12;
The tube sheet comprises a circular plate (12) with a central circular orifice;
the tube sheet further comprises a hemispherical shell (11) positioned above the orifice and rigidly connected to the circular plate (12) for physically separating the first fluid and the second fluid;
The heat exchanger (1), wherein each said hemispherical shell (11) is oriented towards the inside of said heat exchanger (1) and located inside said inner cylindrical shell (3). According to claim 1,
Heat exchanger (1), characterized in that the thickness of the circular plate (12) is thicker than the thickness recommended by the ASME standard to withstand the same pressure difference. According to claim 1,
Heat exchange, characterized in that the interface between the first hemispherical bonnet (16) and the circular plate (12) of the tube sheet and the interface between the second hemispherical bonnet (16) and the circular plate (12) of the tube sheet are essentially flat. Ki (1). According to claim 1,
Heat exchanger (1), characterized in that the thickness of the hemispherical shell (11) is 20% to 40% of the thickness of the circular plate (12) of the tube sheet. According to claim 1,
Heat exchanger (1), characterized in that the first straight section (9) and the second straight section (10) consist of separate enclosures linked by the elbow (32) to form a hairpin heat exchanger shell. According to claim 1,
the first straight section (9), the second straight section (10) and the bent section or elbow (32) consist of one single enclosure or shell enclosing a bundle of parallel U-bent tubes (2); , Heat exchanger (1), characterized in that the first hemispherical bonnet (16) and the second hemispherical bonnet (16) coincide. According to claim 1,
The heat exchanger (1), characterized in that the heat exchanger is of a horizontal type and the flow of the second fluid relative to the flow of the first fluid therein is co-current or countercurrent. According to claim 1,
The heat exchanger (1), characterized in that the first fluid is feedwater or a fluid containing supercritical carbon dioxide. According to claim 1,
Heat exchanger (1), characterized in that the second fluid is molten salt or a mixture of molten salts, thermal oil or liquid sodium. According to claim 1,
Heat exchanger (1), characterized in that the baffles (8) are in the form of continuous spiral baffles. According to claim 1,
The heat exchanger (1), characterized in that the baffles (8) are assembled, welded or bolted to the inner cylindrical shell (3). According to claim 1,
Heat exchanger (1), characterized in that sealing means are provided between the outer cylindrical shell (4) and the baffles (8). According to claim 1,
Heat exchanger (1), characterized in that the heat exchanger has a distribution jacket (30) for uniformly supplying the second fluid to the heat exchanger from the thermal fluid inlets (6, 7). According to claim 13,
The heat exchanger (1), characterized in that the distribution jacket (30) has a plurality of openings distributed over 360° over its inner surface, said openings supplying the second fluid to the first turn of the spiral baffle (8) ). An evaporator made with the heat exchanger according to claim 1. A superheater manufactured with the heat exchanger according to claim 1. A reheater made of the heat exchanger according to claim 1. An economizer manufactured with the heat exchanger according to claim 1 . A preheater manufactured with the heat exchanger according to claim 1. an evaporator according to claim 15; a superheater according to claim 16; and a molten salt steam generator (MSSG) comprising at least one heat exchanger train made of at least one of a reheater according to claim 17 , an economizer according to claim 18 and a preheater according to claim 19 . 21. The method of claim 20,
wherein said superheater, said reheater, said economizer and said preheater are operated in counter flow while said evaporator is operated in co-current. 21. The method of claim 20,
The molten salt steam generator (MSSG), characterized in that the molten salt steam generator is a once-through or forced circulation steam generator.

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