Improved tube-bundle

Abstract

Tube-bundle, part of a shell-and-tube process boiler apt to the indirect heat exchange between a tube-side high-temperature gas and a shell-side pressurized boiling water, provided at the exchanging tubes inlet with sets of ferrules of different length distributed at least in a portion of the bundle so as to increase the critical heat flux and the safety margin relative to the risk of steam blanketing. Tube-bundle wherein a shell-side baffle is installed in between the outlet ends of ferrules of different length.

Description

[0001] MNN007WO Giovanni Manenti

[0002] IMPROVED TUBE-BUNDLE

[0003] DESCRIPTION

[0004] Scope

[0005] The invention here disclosed refers to a tube-bundle with improved thermo-hydraulic and thermo-mechanical performance and applicable to heat exchangers and chemical reactors of the shell-and-tube type.

[0006] Specifically, this invention applies to process boilers located downstream of chemical reactors and designed to cool a process gas at high temperature and pressure by means of boiling pressurized water. More specifically, this invention applies to process boilers where the hot gas flows on tube-side.

[0007] Technical problem to be solved

[0008] The indirect heat exchange in shell-and-tube equipment between two fluids that contact each other at very different operating temperatures, at least in a portion of the bundle, results in high heat fluxes through the exchanging tube wall.

[0009] For example, in process boilers installed in methanol plants, the indirect heat exchange between the syngas discharged from an autothermal reactor at I000°C, flowing on tubeside, and the cooling pressurized boiling water at 320°C, flowing on shell-side, can result in heat fluxes of more than 350kW / m2through the exchanging tube wall.

[0010] For example, in vertical process boilers installed in nitric acid production plants, the heat exchange between the gas discharged from the ammonia oxidation reactor at 800°C, flowing on tube-side, and the cooling pressurized boiling water at 250°C, flowing on shellside, can result in heat fluxes of more than 15 OkW / m2through the exchanging tube wall.

[0011] Such large heat fluxes in process boilers, due to both the temperature differences between the fluids and the shell-side boiling regime, involve the risk of steam blanketing on the water-side surface of the exchanging tube.

[0012] Critical heat flux (CHF) and maximum heat flux (MHF) are key parameters for the thermo-hydraulic design of process boilers. The CHF represents the value of the heat flux, given the geometry and operating conditions of the tube-bundle, beyond which the phenomenon of steam blanketing occurs on the wetted surface of the exchanging tubes; the CHF is a parameter related to the tube-bundle. The MHF represents the maximum value of the heat flux, given the geometry and operating conditions of the tube-bundle, installed in the process boiler; the MHF occurs at tubes inlet, where the temperature difference between hot gas and boiling water is maximum. The MHF is a parameter related to the individual exchanging tube. MNN007WO Giovanni Manenti

[0013] The CHF and MHF installed in a process boiler must assure that CHF>MHF. Higher the CHF-to-MHF ratio, greater the safety margin installed in the boiler relative to the dangerous phenomenon of steam blanketing.

[0014] To prevent that MHF occurs at the tube-sheet and at the tube to tube-sheet welded joints where the hot process gas enters, in accordance with prior art, the exchanging tubes of process boilers operating with gas at high temperatures (>600°C) are normally provided, at the inlet, with ferrules inserted in the exchanging tube and extending into the shell. The ferrules are basically pipe butts usually externally lined with a thin layer of thermally insulating ceramic paper; the ferrules, therefore, thermally insulate the tube from hot gas and move the MHF away from the gas inlet tube-sheet, transferring the MHF to the ferrule outlet. Usually, the portion of ferrule inserted into the tube and extending into the shell has a length of about 100-200mm.

[0015] The ferrules installed at the inlet of tubes of a process boiler, according to conventional solutions, have the portion inside the exchanging tube and inside the shell substantially the same and have the sole purpose of transferring the MHF away from the gas inlet tube-sheet. Conventional ferrules are not designed to increase the CHF or to increase the CHF-to-MHF ratio of the tube-bundle. In other words, conventional ferrules do not improve the performance of the boiler relative to the CHF value and / or the CHF-to-MHF ratio. Therefore, conventional configurations of process boiler tube-bundles have a technological limitation.

[0016] Scope of the invention

[0017] The present invention is aimed at providing a tube-bundle for shell-and-tube type equipment, for the indirect heat exchange between two fluids, presenting an improved thermo-hydraulic and thermo-mechanical performance compared to the technological solutions available in prior-art. This is achieved by means of an innovative configuration of the tube-bundle, equipped with ferrules at the hot gas inlet, which eliminates the typical limit of conventional configurations.

[0018] In particular, the present invention provides for a tube-bundle for a shell-and-tube process boiler, with gas on tube-side, where the bundle CHF and CHF-to-MHF ratio are increased, keeping same bundle geometry and operating conditions, by adopting an innovative bundle configuration equipped with ferrules. Therefore, the invention here described allows increasing the thermo-hydraulic safety margins of the process boiler relative to the risky phenomenon of steam blanketing.

[0019] Alternatively, the present invention provides for a tube-bundle for a shell-and-tube process boiler, with gas on tube-side, where the bundle size, keeping same bundle operating MNN007WO Giovanni Manenti conditions and CHF, can be reduced. Therefore, the invention described here allows optimizing the process boiler from technical-commercial standpoint.

[0020] Brief description of the invention

[0021] The invention here disclosed consists in installing in the tube-bundle, at inlet of the exchanging tubes, ferrules of different lengths substantially uniformly distributed in the tube-bundle.

[0022] The present invention discloses a tube-bundle equipped with at least two sets of ferrules, placed at the inlet of the exchanging tubes, where the ferrules of each set have the same length and where the ferrules of different sets have different lengths from each other. The ferrules are substantially uniformly distributed in the tube-bundle, or at least in a portion thereof, so that an exchanging tube provided with a ferrule of length LI is directly surrounded by a group of exchanging tubes of which at least one is provided with a ferrule of length L2, where the length L2 is different from the length LI.

[0023] In this description, the heat exchanging tubes that directly surround a given heat exchanging tube correspond to the neighboring or closest tubes.

[0024] In this description, the inlet end or the inlet of the exchanging tubes refers to the end of the tubes from which the hot gas enters the tube. Similarly, the inlet end or the inlet of the ferrule refers to the end of the ferrule from which the hot gas enters the ferrule; the outlet end or the outlet of the ferrule refers to the end of the ferrule from which the hot gas exits the ferrule.

[0025] In this description, as it shall be better specified in next pages, the length of a ferrule refers to the portion of ferrule located inside the exchanging tube and extending into the equipment shell.

[0026] It is underlined that the ferrules object of the present invention are installed at the inlet of the exchanging tubes.

[0027] It is also emphasized that the CHF of a process boiler strongly depends on geometric parameters of the tube-bundle, such as the exchanging tubes pitch and number; in other words, the CHF is highly dependent on tubular density of the tube-bundle. Larger the tubes pitch, higher the CHF; smaller the tubes number, higher the CHF. Therefore, lower the tubular density of a boiler tube-bundle, i.e. smaller the number of tubes inscribed in a given boundary, higher the CHF relative to the boiler bundle. In general, higher the CHF and / or the CHF-to-MHF ratio of a boiler, greater the safety margin against the steam blanketing and more optimized the technical -economic design of the boiler. MNN007WO Giovanni Manenti

[0028] On the contrary, the MHF strongly depends on the operational and thermal parameters related to the individual exchanging tube (and indirectly on the intemal / extemal diameter of the tube) and does not depend on geometric parameters of the tube-bundle. In other words, the MHF relative to an exchanging tube is negligibly influenced by the tubes pitch or tubes number.

[0029] In a conventional tube-bundle, where the ferrules installed at tubes inlet have an identical length, the MHF relative to each exchanging tube is substantially released at the same longitudinal position for all the bundle tubes, i.e. at the outlet of the ferrules. This causes a decrease of CHF and CHF-to-MHF ratio for the tube-bundle: the MHF relative to all the exchanging tubes of a conventional bundle occurs at the same bundle cross-section, leading to high local steam fractions, and to the risk of steam engulfinent and steam blanketing on the outer surface of tubes.

[0030] On the contrary, the present invention teaches that, once geometry and operating conditions of the tube-bundle of a process boiler with gas on tube-side have been fixed, if sets of ferrules of different lengths LI, L2, L3, etc. are installed at inlet of the exchanging tubes and the distribution of ferrules of at least two sets is substantially uniform in the tubebundle or at least in a portion thereof, this is equivalent to space the exchanging tubes from one another from a thermo-hydraulic point of view. The distribution of ferrules of different lengths in the tube-bundle, or at least in a portion of the tube-bundle, is such that an exchanging tube with a ferrule of length LI is directly surrounded by a group of exchanging tubes of which at least one has a ferrule of different length L2, L3, etc. The MHF that is released at the outlet of the ferrule of length LI does not add-up to the MHF at the outlet of all the directly surrounding ferrules because at least one ferrule has a length L2, L3, etc., which is greater or less than the length LI. According to the present invention, the MHF occurring at exit of the ferrules of length LI, L2, L3, etc., he, respectively, on bundle crosssections longitudinally spaced from each other. In other words, the installation of ferrules of different lengths substantially uniformly distributed in the tube-bundle, or at least in a portion of the tube-bundle, is equivalent, from a thermo-hydraulic standpoint, to increase the tubes pitch, which leads to an increase of the bundle CHF and CHF-to-MHF ratio. The MHF remains unchanged as it essentially depends only on the heat transfer coefficient relative to the tube and the temperature difference between process gas and boiling water.

[0031] Once geometry and operating conditions of the tube-bundle of a process boiler are fixed, a major advantage obtained by implementing the configuration disclosed by the present invention is that the CHF and CHF-to-MHF ratio are increased. This means that the shell-and-tube equipment, i.e. the process boiler or the chemical reactor or the heat exchanger, works in milder and safer thermo-hydraulic and thermo-mechanical conditions, MNN007WO Giovanni Manenti leading to an extension of boiler operating life and / or to accept wider deviations from operating conditions, such as gas temperature or boiler water chemistry.

[0032] The present invention is also advantageous in case of revamping projects: by replacing at least a portion of ferrules of an existing process boiler, based on prior-art, with ferrules of different lengths substantially uniformly distributed in the bundle as per the present invention, the bundle CHF and CHF-to-MHF ratio are increased, and consequently a higher gas flow rate and / or temperature can flow across the existing boiler.

[0033] State-of-the-art

[0034] The concept of multiple ferrules in a tube-bundle of a process boiler with gas on tubeside was introduced at the AIChE Annual Meeting conference in 2003; the related publication is "L.Presciuttini and D.Lippolis, Facing the Demand of Reformed Gas Boilers of Big Capacity, Ammonia Technical Manual, AIChE Annual Meeting, Nov. 15-21, 2003".

[0035] The cited publication describes [p. 82] a horizontal tube-bundle having at tubes inlet two sets of ferrules of different lengths, where the longer ferrules are installed in the tube rows located in the highest portion of the tube-bundle, where the highest steam fraction occurs. Installation of longer ferrules in the highest portion of tube-bundle prevents generating additional steam where the steam fraction is already high. This publication also discloses the possibility of using more than two sets of ferrules of different lengths.

[0036] The above publication, therefore, describes a tube-bundle provided with two sets of ferrules where the ferrules of a given length belonging to the first set are concentrated in a portion of the tube-bundle, and the ferrules of different length belonging to the second set are concentrated in the remaining portion of the bundle. Therefore, the cited publication describes a tube-bundle divided into two portions each provided only with ferrules of identical length, i.e. two bundle portions where an exchanging tube with ferrule of length LI is directly surrounded by exchanging tubes only with ferrules of identical length LI. The configuration described in the cited publication implies that the tube-bundle areas with ferrules of equal length present low CHF and CHF-to-MHF ratios; this configuration therefore presents a limit relative to the increase of the bundle CHF and a limit relative to the technical-economic optimization of the process boiler. Moreover, the use of longer ferrules in the upper tube rows represents another downside relative to the configuration of the cited publication: the exchanging tubes of the upper rows do not produce steam and thus, from thermo-hydraulic standpoint, they do not contribute to the natural draft but they introduce a net resistance to the upward steam flow.

[0037] Patent document No. W02018215102A1 describes a process boiler having ferrules (or bypass tubes) placed inside the exchanging tubes and inside the shell; these ferrules can MNN007WO Giovanni Manenti be different from each other and / or have different dimensions [page 21, lines 23-29], However, this prior-art document teaches that the ferrules, differently from the present invention, are inserted at outlet end of the exchanging tubes and are not conceived for moving the MHF or increasing the bundle CHF and CHF-to-MHF ratio.

[0038] Patent documents No. US2015 / 0159956 and No. US8424591 disclose configurations of ferrules, apposite for process boilers, where the ferrules installed in the bundle have identical length.

[0039] Patent document No. US4294312 describes a tube-bundle with straight exchanging tubes where ferrules longer than the tubes are inserted inside the exchanging tubes so that the ends of the ferrules extend beyond the ends of the exchanging tubes and into the distribution chambers.

[0040] Patent document No. US4191246 describes a steam generator tube-bundle with "U" shaped heat exchanging tubes and ferrules of identical length.

[0041] Patent documents No. US4401153 and No. EP2482020B1 describe tube-bundles with "U" shaped heat exchanging tubes equipped with ferrules installed in a set of straight legs of the heat exchanging tubes. These documents do not disclose ferrules of different lengths substantially uniformly distributed in the bundle.

[0042] Numerous patent documents describe ferrule configurations for heat exchanging tubes; some patent documents are doc. No. US2445273, No. US3707186, No. US20010040024Al, No. W02009066260A1, No. US2008202732A1 and No. EP3724590. However, none of these documents describes a tube-bundle having ferrules of different lengths substantially uniformly distributed in the bundle.

[0043] Brief description of the figures

[0044] To support the detailed description given hereafter, the following figures are attached:

[0045] - Fig. l, where the inlet portion of a process boiler with gas on tube-side is schematically shown in longitudinal section according to the prior-art;

[0046] - Fig.2, where a detail of the inlet portion of a process boiler with gas on tube-side is schematically shown in longitudinal section according to the prior-art;

[0047] - Fig.3, where the inlet portion of a process boiler with gas on tube-side is schematically shown in longitudinal section according to a preferential configuration of the present invention;

[0048] - Figs.4, 5 and 6, where the tube-bundle of a process boiler with gas on tube-side is schematically shown in cross-section according to preferential configurations of the present invention; MNN007WO Giovanni Manenti

[0049] - Figs.7 and 8, where the inlet portion of a process boiler with gas on tube-side is schematically shown in longitudinal section according to preferential configurations of the present invention;

[0050] - Fig.9, where the tube-bundle of a process boiler with gas on tube-side is schematically shown in cross-section according to a preferential configuration of the present invention.

[0051] Detailed description of the invention

[0052] Fig. 1 schematically shows, in section, the longitudinal view of the gas inlet portion of a process boiler (1), according to the prior-art; the boiler (1) is of shell-and-tube type and of substantially cylindrical geometry with longitudinal axis (X). The boiler portion (1) includes a shell (2) that envelops the heat exchanging tubes (3) forming the tube-bundle, a transversal baffle (21) that supports the exchanging tubes (3), a tube-sheet (4) which the inlet ends of the exchanging tubes (3) are connected to, a distribution chamber (5) connected to the tube-sheet (4) on the opposite side relative to the shell (2), an inlet connection (6) located on the chamber (5) and inlet and outlet connections (8) located on the shell (2). The distribution chamber (5) is internally lined with refractory (7) which protects the metal walls from high temperatures; the refractory (7) also coats and protects the tube-sheet (4) on tube-side (TS).

[0053] According to Fig. 1, the process gas (G) at high temperature and pressure flows on the tube-side (TS) of the boiler (1). The gas (G) enters the chamber (5) from the inlet connection (6), distributes in the exchanging tubes (3) and indirectly exchanges heat with the cooling boiling water (W) that flows on the boiler shell-side (SS) through the relative inlet / outlet connections (8). The distribution chamber (5) is therefore in fluid communication with the exchanging tubes (3).

[0054] The gas inlet portion of the boiler (1) in Fig. 1 is equipped with ferrules at the inlet of the exchanging tubes (3).

[0055] Fig.2 schematically shows, in section, the longitudinal view of the inlet portion of an exchanging tube (3) equipped with ferrule (10), a portion of tube-sheet (4) of a portion of refractory (7), in accordance with the prior-art. Fig.2 corresponds to the detail (DET) relating to Fig. 1.

[0056] According to Fig.2, the exchanging tube (3) is connected to the tube-sheet (4) by means of a welded joint (9) of any type; more specifically, the inlet end of the exchanging tube (3) is welded to the tube-sheet (4). The tube-sheet (4), on tube-side (TS), is lined with refractory (7). The ferrule (10) is substantially tubular in shape; basically, the ferrule (10) corresponds to a pipe butt. The ferrule (10) is partially inserted in the exchanging tube (3) MNN007WO Giovanni Manenti coaxially relative to the tube longitudinal axis (Y). Therefore, the ferrule (10) has a smaller external diameter than the internal diameter of the exchanging tube (3) for at least a longitudinal portion of the ferrule. The ferrule (10) has an inlet end (11) placed in the distribution chamber and, specifically, in correspondence with the free surface (14) of the refractory (7), and an outlet end (12) placed inside the exchanging tube (3) and beyond the tube-sheet (4), in the direction of the gas flow (G), so that the ferrule (10) extends into the shell. The ferrule (10) is externally provided with a layer of thermally insulating ceramic paper (13) which, preferably, extends longitudinally for all, or almost all, of the ferrule (10). The layer of ceramic paper (13) fdls the gap formed between the tube (3) and ferrule (10).

[0057] According to the prior art, the ferrule (10) in Fig.2 can have a flared or conical inlet end (11) to reduce the pressure drops of the entering gas (G). Similarly, the outlet end (12) can be flared or conical to decrease the turbulence of the exiting gas (G). The ferrule (10) is partially embedded in the refractory (7); the ferrule (10) allows the passage of gas (G) through the refractory layer (7).

[0058] According to Fig.2, the hot process gas (G) flowing on tube-side (TS) in the distribution chamber enters the ferrule (10) from the inlet end (11), flows along the ferrule (10) and exits through the outlet end (12) into the exchanging tube (3). The ferrule (10), including the ceramic paper (13), is a barrier to heat exchange. The ferrule (10) protects the tube-sheet (4), the tube to tube-sheet welded joint (9) and the first portion of the exchanging tube (3) from high temperature. The indirect heat exchange between gas (G) and water (W) along the ferrule (10) is minor, and consequently the heat flux along the ferrule (10) is also minor.

[0059] As shown in Fig.2, the ferrule (10) protrudes from the wetted surface (15) of the tubesheet (4), located on shell-side (SS), by a protrusion length (L); in other words, the ferrule (10) extends into the shell, inside the exchanging tube (3), by a protrusion length (L). This length (L) allows the MHF to be transferred from the tube-sheet (4) to the outlet end of the ferrule (12). Thus, the strong indirect heat exchange between hot gas (G) and boiling water (W) and the consequent strong heat flux occur at the outlet end of the ferrule (12), while the indirect heat exchange between gas (G) and water (W) along the ferrule is minor.

[0060] Fig.3 schematically shows, in section, the longitudinal view of the gas inlet portion of a process boiler (100), in accordance with a preferential configuration of the present invention; the boiler (100) is of shell-and-tube type and substantially cylindrical in shape with a longitudinal axis (X). The boiler portion (100) shown in Fig.3 is similar to the one already described in Fig. 1; the numbering relative to Fig.3 corresponds to that of Fig. 1 for MNN007WO Giovanni Manenti some details and therefore the description of Fig.3 is partially omitted referring to the description of Fig. l. The ferrules in Fig.3 have a configuration similar to the ferrule described for Fig.2, and therefore the detailed description of the ferrules of Fig.3 is omitted referring to the description given for Fig.2. The hot gas (G) of Fig.3 flows as already described for Figs. 1 and 2.

[0061] According to Fig.3, ferrules of different lengths are installed at the inlet of the exchanging tubes (3). It is underlined that in this description the length of the ferrules, or the length of the protrusion of the ferrules, refers to the portion of the ferrule that protrudes in the shell (2) from the wetted surface (15) of the tube-sheet (4), as already described for Fig.2.

[0062] Fig.3 schematically shows two sets of ferrules installed in the bundle; the first set of ferrules has first ferrules (16) of length (LI) and the second set of ferrules has second ferrules (17) of length (L2). The first and second ferrules (16,17) are installed in the exchanging tubes (3) so to be substantially uniformly distributed in the tube-bundle. The lengths (LI) and (L2) are different and, precisely, the length (L2) is greater than the length (LI).

[0063] Each ferrule (16,17) in Fig.3 has an inlet end (11) and an outlet end (12) placed, respectively, in the distribution chamber (5) at the free surface (14) of the refractory (7) and in the shell (2) inside an exchanging tube (3), as already described for Fig.2. The outlet ends (12) of the first ferrules (16) and the outlet ends (12) of the second ferrules (17) are longitudinally spaced from each other due to the different protrusion length (L1,L2).

[0064] Fig.3 shows that a transversal baffle (21), apt to support the exchanging tubes, is installed on shell-side (SS) in a longitudinal position of the tube-bundle interposed between the outlet ends (12) of the first and second ferrules (16,17).

[0065] Figs.4, 5 and 6 schematically show transversal views of the tube-bundle of the boiler (100) of Fig.3, according to the Z-Z' cross-section of Fig.3, and according to preferential configurations of the present invention. The Z-Z' section of Fig.3 transversely cuts the tubebundle between the outlet ends of the first and second ferrules (16,17). For descriptive simplicity, the transversal baffle (21) is not shown in Figs. 4, 5 and 6.

[0066] Figs.4, 5 and 6 show the layout of the exchanging tubes (3) enveloped by the shell (2) and the layout of the first and second ferrules (16,17) inside the tubes. The exchanging tubes (3) with the second ferrules (17) of length (L2) are marked with a cross, whereas the exchanging tubes (3) with the first ferrules (16) of length (LI) are not marked with a cross. The exchanging tubes (3) in Fig.4 are arranged with a triangular pitch; the exchanging tubes (3) in Figs. 5 and 6 are arranged with a square pitch. MNN007WO Giovanni Manenti

[0067] According to Figs.4, 5 and 6, the first ferrules (16) of length (LI) and the second ferrules (17) of length (L2) are distributed in a substantially uniform way relative to the bundle cross-section. An exchanging tube (3) equipped with the first ferrule (16) is directly surrounded by a group of exchanging tubes (3) of which at least one is equipped with the second ferrule (17); in the same way, an exchanging tube (3) equipped with the second ferrule (17) is directly surrounded by a group of exchanging tubes (3) of which at least one is equipped with the first ferrule (16).

[0068] In Fig. 4, each exchanging tube (3) equipped with the second ferrule (17) is directly surrounded by a group of exchanging tubes (3) only equipped with the first ferrule (16).

[0069] In Fig.5, the first and second ferrules (16,17) are distributed alternately by rows of exchanging tubes (3) and so that a row of tubes has the same set of ferrules. The rows of heat exchanging tubes alternate in such a way that a row of heat exchanging tubes (3) provided with a first ferrule (16) is preceded and followed by a row of heat exchanging tubes (3) provided with a second ferrule (17).

[0070] Finally, in Fig.6, the layout of the first and second ferrules (16,17) substantially corresponds to a checkerboard layout.

[0071] As shown in Figs.4, 5 and 6, the exchanging tubes (3) have the first and second ferrules (16,17) preferably arranged so that the ferrules (16,17) are symmetrical relative to two transversal axes (H,V) perpendicular to each other and relative to the cross-section of the bundle.

[0072] Fig.7 schematically shows, in section, the longitudinal view of the gas inlet portion of a process boiler (101), in accordance with a preferential configuration of the present invention; the boiler (101) is of shell-and-tube type and substantially cylindrical in shape with a longitudinal axis (X). The portion of the boiler (101) shown in Fig.7 is similar to the one already described for Fig. 1 except for the lack of refractory, for the presence of an inner chamber (18) and for the presence of some exchanging tubes (3b) without ferrule; the numbering relative to Fig.7 corresponds to that of Fig. 1 for some details and therefore the description of Fig.7 is partially omitted referring to the description of Fig. 1. The ferrules in Fig.7 have a configuration similar to the ferrules described for Fig.2 except for the lack of refractory and for the presence of an inner chamber (18), and therefore the detailed description of the ferrules in Fig.7 is omitted referring to the description given for Fig.2.

[0073] The portion of the boiler (101) shown in Fig.7 does not have a protective refractory layer on tube-side (TS); the portion of the boiler shown in Fig.7 includes, inside the distribution chamber (5), an inner chamber (18) connected to an inner tube-sheet (19). The MNN007WO Giovanni Manenti inner chamber (18) and the inner tube-sheet (19) are spaced out from the distribution chamber (5) and the tube-sheet (4) to form a passage for the gas (G).

[0074] As shown in Fig.7, the tube-bundle comprises a first set of exchanging tubes (3a) equipped with ferrule (16,17) and a second set of exchanging tubes (3b) without ferrule; consequently, the tube-bundle of the boiler in Fig.7 is made of two sub-bundles where the first sub-bundle comprises the exchanging tubes (3a) with ferrule and the second subbundle comprises the exchanging tubes (3b) without ferrule. The end of the exchanging tubes (3a) with ferrule connected to the tube-sheet (4) corresponds to the gas (G) inlet end. The end of the exchanging tubes (3b) without ferrule connected to the tube-sheet (4) corresponds to the gas (G) outlet end.

[0075] Fig.7 schematically shows two sets of ferrules of different lengths installed in the first set of exchanging tubes (3a); the first set of ferrules has first ferrules (16) of length (LI) and the second set of ferrules has second ferrules (17) of length (L2). The first and second ferrules (16, 17) are installed at the tubes inlet of the first set of exchanging tubes (3a) so to be substantially uniformly distributed in the first sub-bundle. The lengths (LI) and (L2) are different and, precisely, the length (L2) is greater than the length (LI).

[0076] Each ferrule (16,17) in Fig.7 has an inlet end (11) and an outlet end (12) placed, respectively, in the distribution chamber (5) at the inner tube-sheet (19) and in the shell (2) inside an exchanging tube (3). In particular, the inlet end (11) is placed at the inner tubesheet (19) so that the ferrules (16,17) are in direct fluid communication with the inner chamber (18). The outlet ends ( 12) of the first and second ferrules ( 16, 17) are longitudinally spaced from each other due to the different length of protrusion (L1,L2).

[0077] Fig.7 shows that a transversal baffle (21), apt to support the exchanging tubes, is installed on shell-side (SS) in a longitudinal position of the tube-bundle interposed between the outlet ends (12) of the first and second ferrules (16,17).

[0078] According to Fig.7, the gas (G) entering the boiler first flows into the inner chamber (18), distributes and flows in the ferrules (16,17) and exits into the tubes of the first set of exchanging tubes (3a) where the gas indirectly exchanges heat with the shell-side fluid (SS). Then, the gas (G) flows into the tubes of the second set of exchanging tubes (3b) where it indirectly exchanges heat with the shell-side fluid (SS) and exits into the distribution chamber (5) on the outside of the inner chamber (18). Consequently, the distribution chamber (5) of the boiler of Fig.7 is equipped with at least one gas inlet connection (not shown in the figure) in direct fluid communication with the inner chamber (18), and at least one gas outlet connection (not shown in the figure). As an expert in the field can understand, the configuration of the distribution chamber (5) and related gas MNN007WO Giovanni Manenti inlet / outlet connections, of the inner chamber (18), of the inner tube-sheet (19) and of the ferrules (16,17) is conceived to segregate the hot gas flow (G) entering the boiler from the cold gas flow (G) leaving the boiler.

[0079] Fig.8 schematically shows, in section, the longitudinal view of the gas inlet portion of a process boiler (102), in accordance with a preferential configuration of the present invention; the boiler (102) is of shell-and-tube type and substantially cylindrical in shape with a longitudinal axis (X). The portion of the boiler (102) shown in Fig.8 is identical to the one already described for Fig.7 except for the lack of the inner tube-sheet; for a detailed description of the tube-bundle, therefore, reference is made to the previous description given for Fig.7. The ferrules in Fig.8 have a configuration similar to the ferrule described for Fig.2 except for the lack of the refractory, and therefore the detailed description of ferrules of Fig.8 is omitted, referring to the description given for Fig.2.

[0080] The configuration reported in Fig.8 is a variant of the configuration reported in Fig.7; the differences consist in the fact that, in Fig.8, the inner tube-sheet is absent, the inner chamber (18) is connected to the tube-sheet (4) in a connection zone (20), and the inlet end ( 11 ) of the ferrules ( 16, 17) is connected to the tube-sheet (4) and / or to the exchanging tubes (3a) of the first sub-bundle. Preferentially, the tube-side (TS) surface or portion of the tubesheet (4) where the ferrules (16,17) are connected is provided with a protective layer; preferentially, the protective layer corresponds to a weld deposit. The ferrules (16,17) are in direct fluid communication with the inner chamber (18). The connection zone (20) of the inner chamber (18) delimits the first sub-bundle, composed of exchanging tubes (3a) with ferrule, from the second sub-bundle, composed of exchanging tubes (3b) without ferrules.

[0081] Fig.8 schematically shows two sets of ferrules of different lengths (L1,L2) installed at the inlet of tubes of the first sub-bundle; the ferrules (16, 17) are distributed in the first subbundle in a substantially uniform way. The ends ( 12) of the first ferrules (16) and the second ferrules (17), located in the shell (2) inside the exchanging tubes, are longitudinally spaced from each other due to the different protrusion length (L1,L2).

[0082] Fig.8 shows that a transversal baffle (21), apt to support the exchanging tubes, is installed on shell-side (SS) in a longitudinal position of the tube-bundle interposed between the outlet ends (12) of the first and second ferrules (16,17).

[0083] The gas flow (G) related to the alternative configuration of Fig.8 substantially corresponds to the flow described for Fig.7. Consequently, the ferrules (16,17) are in direct fluid communication with the inner chamber (18); the distribution chamber (5) is equipped with at least one gas inlet connection (not shown in the figure) in direct fluid MNN007WO Giovanni Manenti communication with the inner chamber (18) and at least one gas outlet connection (not shown in the figure). As an expert in the field can understand, for Fig.8, the configuration of the distribution chamber (5) and relevant gas inlet / outlet connections, of the inner chamber (18) and of the ferrules (16,17) is conceived to segregate the hot gas flow (G) entering the boiler from the cold gas flow (G) leaving the boiler.

[0084] Fig.9 schematically shows the transversal view of the tube-bundle of the boilers (101,102) relative to Figs.7 and 8, according to the Z-Z' cross-sections of Figs.7 and 8, and according to a preferential configuration of the present invention. The Z-Z' section of Figs.7 and 8 cuts transversely the tube-bundle between the outlet ends of the first and second ferrules (16,17).

[0085] According to Fig. 9, the tube-bundle of the boiler (101,102) is divided into two substantially circular zones concentrically arranged relative to each other: a first central zone consisting of the first set of exchanging tubes (3a) equipped with ferrule (16,17) (corresponding to the first sub-bundle), and a second peripheral zone consisting of the second set of exchanging tubes (3b) without ferrule (corresponding to the second subbundle). The subdivision of the tube-bundle into the first and second sub-bundle is represented by a dotted circle (19,20) in Fig.9; this dotted circle may correspond to the inner tube-sheet (19) or to a portion of it (see Fig.7), or to the connection zone (20) (see Fig.8). The exchanging tubes (3a) with ferrules (17) belonging to the second set of ferrules are marked with a cross; the exchanging tubes (3a) with ferrules (16) belonging to the first set of ferrules are not marked with a cross.

[0086] According to Fig. 9, the first sub-bundle equipped with ferrules (16,17) has a substantially uniform distribution of ferrules (16,17) relative to the cross-section. In particular, an exchanging tube (3a) provided with a first ferrule (16) of length (LI) is directly surrounded by a group of exchanging tubes (3a) of which at least one is provided with a second ferrule (17) of length (L2); conversely, an exchanging tube (3 a) provided with a second ferrule (17) of length (L2) is directly surrounded by a group of exchanging tubes (3a) of which at least one is provided with a first ferrule (16) of length (LI). The first sub-bundle equipped with ferrules (16, 17) has an axis of symmetry (H) relative to the crosssection of the bundle; the ferrules (16,17) are arranged so to be substantially symmetrical relative to the transverse axis of symmetry (H) of the bundle.

[0087] With reference to Figs. 7-9, therefore, a preferred configuration of the present invention provides that at least two sets of ferrules are substantially uniformly distributed in a portion of the tube-bundle so that, in said tube-bundle portion, an exchanging tube provided with a ferrule of length (LI) belonging to a first set of ferrules is directly MNN007WO Giovanni Manenti surrounded by a group of exchanging tubes of which at least one is provided with a ferrule of length (L2) belonging to a second set of ferrules. Consequently, in accordance with the invention here disclosed, the ferrules of at least two sets can be substantially uniformly distributed either in the tube-bundle or at least in a portion thereof. In other words, as per the present invention, the configuration according to which an exchanging tube having a ferrule of length (LI) belonging to a first set of ferrules is directly surrounded by a group of exchanging tubes of which at least one having a ferrule of length (L2) belonging to a second set of ferrules can also be applied to one or more portions of the tube-bundle.

[0088] It is emphasized that with reference to Figs.7, 8 and 9, the exchanging tubes can be either straight or "U" curved. In the first case, the boiler (100,101,102) is equipped with a second tube-sheet and a second distribution chamber (not shown in the figures). In the second case, the first set of exchanging tubes (3a) and the second set of exchanging tubes (3b) correspond, respectively, to the first and second sets of straight legs of the "U" bundle. In both cases, the first and second sets of exchanging tubes (3a, 3b) correspond, respectively, to the first and second gas pass (G) on tube-side (TS).

[0089] Therefore, it is emphasized that according to the present invention the shell-and-tube equipment can include, at the gas inlet tube-sheet which the exchanging tubes are connected to, both exchanging tubes equipped with a ferrule (where the hot gas to be cooled enters) and both exchanging tubes not equipped with a ferrule (where the cooled gas exits).

[0090] According to a preferential configuration of the present invention, ferrules of a specific length, belonging to a set of ferrules, are installed in the tube-bundle so that they are symmetrical, or substantially symmetrical, relative to at least one transverse axis of symmetry of the bundle.

[0091] According to a preferential configuration of the present invention, the ferrules of a specific length, belonging to a set of ferrules, are installed in the tube-bundle so that they are symmetrical, or substantially symmetrical, relative to two bundle transverse axes of symmetry perpendicular to each other.

[0092] In this description, the terminology "substantially symmetrical" means that most of the ferrules contribute to the symmetry or, in other words, that a limited number of ferrules do not participate in symmetry. A limited number of ferrules corresponds preferentially to less than 10% of the ferrules, more preferably less than 5% of the ferrules and even more preferably to less than 3% of the ferrules.

[0093] Preferentially, according to the present invention, the difference between the protrusion lengths of two ferrules of different lengths is greater than 100mm, or greater than 250mm, or greater than 500mm. MNN007WO Giovanni Manenti

[0094] According to a preferential configuration of the present invention, a shell-side transversal baffle is installed between the ferrule outlet ends of one set and the ferrule outlet ends of another set. In other words, the tube-bundle here disclosed has preferentially an intermediate transversal baffle installed in a longitudinal position placed between the outlet ends of ferrules of length (LI) and the outlet ends of ferrules of length (L2). In a process boiler, such an intermediate transversal baffle allows segregating, at least partially, the heat release and the consequent shell-side steam production relative to adjacent exchanging tubes equipped with ferrules of different lengths. More specifically, the intermediate transversal baffle object of the present invention allows segregating the shell-side thermo- hydraulic effects of MHF occurring at outlet of ferrules of length (LI) from the shell-side thermo-hydraulic effects of MHF occurring at outlet of ferrules of length (L2). The intermediate transversal baffle object of this invention helps to improve the thermo- hydraulic performance of the bundle of a process boiler, consolidating the safety margins relative to the steam blanketing phenomenon.

[0095] The shell-and-tube equipment object of this invention preferably include a bundle with straight exchanging tubes, welded at the ends to a first tube-sheet and a second tube-sheet (not shown in the figures).

[0096] Alternatively, the shell-and-tube equipment object of this invention preferably include a bundle with U-shaped heat exchanging tubes, welded at the ends to one tube-sheet or two separate tube-sheets.

[0097] It is emphasized that the equipment object of this invention are preferentially equipped, in addition to the ferrules, with other elements designed to protect the metal walls from the high temperature of the hot gas (G) entering the equipment. For example, as already described for Figs. 1-3, the distribution chamber and / or the gas inlet tube-sheet are lined with refractory material on tube-side. Alternatively, the distribution chamber and / or the gas inlet tube-sheet can be coated on tube-side with a metallic layer obtained by weld deposit and / or a ceramic layer obtained by spray which material is resistant to high temperature, corrosion or erosion.

[0098] It is emphasized that according to the preferential configurations relating to Figs.7 and 8, the inner chamber and the inner tube-sheet are made of materials resistant to high temperatures; in any case, protective layers can also be installed or deposited on said inner chamber and tube-sheet.

[0099] The shell-and-tube equipment object of this invention preferably include exchanging tubes with an external diameter equal to or greater than 31.75mm, more preferably equal to or greater than 33.70mm and even more preferably equal to or greater than 38.05mm. MNN007WO Giovanni Manenti

[0100] In accordance with an alternative and preferential configuration of the present invention, the tube-bundle is composed of exchanging tubes of different external diameters. In accordance with a preferential configuration of the present invention, the exchanging tubes provided with ferrule at inlet have different external diameters.

[0101] In accordance with an alternative and preferential configuration of the present invention, ferrules of different lengths have a different external and / or internal diameter relative to at least one longitudinal portion of the ferrule. In accordance with a preferential configuration of the present invention, the longer ferrules have an internal diameter, at least for a longitudinal portion of the ferrule, that is greater than the internal diameter of the shorter ferrules. If the longer ferrules have a larger internal diameter, for at least a longitudinal portion of the ferrule, than the internal diameter of the shorter ferrules, the pressure drops of the gas flowing in the longer ferrules and of the gas flowing in the shorter ferrules can be substantially balanced. If the gas pressure drops are substantially balanced in ferrules of different lengths, the gas flow rate in the exchanging tubes equipped with different ferrules is substantially balanced. As per a preferential configuration of the present invention, the internal diameter of two ferrules of different lengths differs, for at least one longitudinal portion of the ferrule, by at least 0.5mm, or 1.0mm, or 1.5mm, or 2.0mm on diameter. It is underlined that as per the present invention, the difference in the internal diameter between two ferrules of different lengths can also refer to a very short longitudinal portion of ferrule; in other words, the ferrule can be internally provided with a profile or an element that forms a local narrowing or enlargement, even abrupt, such as an obstacle, apt to differentiate or modify the gas flow. It is underlined that, according to the present invention, the difference in the internal diameter or internal profile of the ferrule may also refer to a different shape and / or size of the inlet and / or outlet end of the ferrule.

[0102] The shell-and-tube equipment object of this invention can be arranged horizontally or vertically; if vertically arranged, the gas inlet tube-sheet at which the ferrules of different lengths are installed, can be placed at the top or bottom.

[0103] It is emphasized that the ferrules of different lengths object of this invention can be made of any material; the ferrules are preferably metallic or ceramic.

[0104] It is emphasized that the ferrules of different lengths object of this invention may include elements apt to improve the anchoring of ferrules in the refractory and / or to the tube-sheet or exchanging tube. For example, the portion of ferrule embedded in the refractory may have an external shape suitable for a strong anchoring of the ferrule.

[0105] It is emphasized that the outlet end of ferrules object of this invention is placed inside the exchanging tube, i.e. it is placed at a point between the ends of the exchanging tube. MNN007WO Giovanni Manenti

[0106] The tube-bundle object of the present invention, according to a preferred configuration, is provided with two sets of ferrules where the ferrules of each set have the same length, where the ferrules of one set have different length from the ferrules of the other set and where the ferrules of each set are uniformly or substantially uniformly distributed in the bundle or at least in a portion thereof. However, it is underlined that the bundle of the present invention can also comprise more than two sets of ferrules of different lengths, where the ferrules of one set have the same length, where the ferrules of one set have different length than the ferrules of another set and where the ferrules of at least two sets are uniformly or substantially uniformly distributed in the bundle or at least in a portion thereof.

[0107] Finally, according to a preferential configuration of the present invention, the number of ferrules of a given length does not differ from the number of ferrules of a different length by more than 30%, or by more than 20%, or by more than 10%, or by more than 5%. According to a preferential configuration of the present invention, sets of ferrules of different lengths count a number of ferrules differing from one set to another of not more than 50 ferrules, or not more than 25 ferrules, or not more than 10 ferrules, or not more than 5 ferrules. As per a preferential configuration of the present invention, sets of ferrules of different lengths count an identical or comparable number of ferrules.

[0108] The tube-bundle here disclosed, implemented in a process boiler where the tubular density is imposed, allows the bundle CHF to be increased by at least 2%, or by at least 5%, or by at least 10%, or by at least 15%.

[0109] The tube-bundle here disclosed, implemented in a process boiler where the critical heat flux CHF is imposed, allows the radial size of the bundle to be reduced by at least 2%, or at least 5%, or at least 10%.

[0110] From the above, the tube-bundle object of the present invention represents an improvement over a conventional bundle equipped with ferrules of identical length or ferrules of different length but not uniformly distributed in the bundle. The tube-bundle here disclosed, equipped with ferrules of different lengths substantially uniformly distributed in the bundle, or at least in a portion of the tube-bundle, and applied to a process boiler, advantageously allows increasing the boiler critical heat flux CHF, therefore improving boiler thermo-hydraulic safety margins, or advantageously allows reducing the boiler size, therefore optimizing the boiler technical -economic design.

[0111] The tube-bundle object of the present invention can be subjected to further modifications and variants, all attributable to the same inventive concept, as well as to MNN007WO Giovanni Manenti include details and / or construction materials different from those described above without departing from the inventive concepts.

[0112] The protection scope of the present invention is described in the attached claims.

Claims

MNN007WO Giovanni ManentiClaims1. Tube-bundle, part of a shell-and-tube equipment (100,101,102) essentially of cylindrical shape developed along a longitudinal axis (X) and apt for the indirect heat exchange between a high-temperature gas (G) flowing on tube-side (TS) and a cooling fluid (W) flowing on shell-side (SS), comprising exchanging tubes (3, 3a, 3b) enveloped by the shell (2) and connected at the ends to at least one tube-sheet (4) and in fluid communication with at least one distribution chamber (5) placed at said at least one tubesheet (4) on the opposite side relative to the shell (2) and provided with at least one gas inlet connection (6), and comprising at least two sets of ferrules (16,17) installed at said at least one tube-sheet (4) and at the inlet of at least one portion of said exchanging tubes (3,3a), where said ferrules (16,17) are substantially tubular in shape, each having an inlet end (11) placed in said at least one distribution chamber (5) and an outlet end (12) placed in the shell (2) inside an exchanging tube (3,3a), where the length (L1,L2) of the ferrule portion extending in the shell (2) inside the exchanging tube (3) is identical for ferrules belonging to a set and different for ferrules belonging to different sets so that the outlet ends (12) belonging to different sets of ferrules result longitudinally spaced each other, said tube-bundle being characterized in that the ferrules (16,17) of at least two sets are uniformly or substantially uniformly distributed in the tube-bundle or at least in a portion thereof so that an exchanging tube (3,3a) provided with a ferrule (16,17) belonging to a set is directly surrounded by exchanging tubes (3) of which at least one is provided with a ferrule (17,16) belonging to another set.

2. Tube-bundle as per claim 1, wherein the ferrules (16,17) of at least one set are installed in the tube-bundle so that they are symmetrical or substantially symmetrical relative to at least one transverse axis (H) of the bundle.

3. Tube-bundle as per claim 1, wherein the ferrules (16,17) of at least one set are installed in the tube-bundle so that they are symmetrical or substantially symmetrical relative to two transverse axes (H, V) of the bundle perpendicular to each other.

4. Tube-bundle as per any claim 1 to 3, wherein a transversal baffle (21), apt to at least partially segregate the shell-side effects of heat flux at outlet of ferrules of different length, is installed on shell-side (SS) between the outlet ends (12) of a set of ferrules (16) and the outlet ends (12) of another set of ferrules (17).MNN007WO Giovanni Manenti5. Tube-bundle as per any claim 1 to 4, wherein the length (LI) relative to the ferrules (16) of one set differs from the length (L2) relative to the ferrules of another set by at least 100mm.

6. Tube-bundle as per any claim 1 to 5, wherein ferrules (16,17) belonging to different sets have different internal diameters for at least a longitudinal portion of the ferrule or have a different internal profile apt to modify the gas flow (G).

7. Tube-bundle as per claim 6, wherein the ferrules (16,17) with greater length have a larger internal diameter.

8. Tube-bundle as per any claim 1 to 7, wherein said at least one tube-sheet (4) is lined on tube-side (TS) with refractory (7), and wherein said inlet end (11) is placed at the free surface (14) of refractory (7) so as to be in direct fluid communication with said at least one distribution chamber (5).

9. Tube-bundle as per any claim 1 to 7, wherein an inner chamber (18) and an inner tube-sheet (19) are installed within said at least one distribution chamber (5) and spaced from the distribution chamber (5) and said at least one tube-sheet (4) so as to create a passage for gas (G), wherein said inner chamber (18) is directly in fluid communication with said at least one gas inlet connection (6) and connected to said inner tube-sheet (19), and wherein said inlet end (11) is at said inner tube-sheet (19) so that said ferrule (16,17) is in direct fluid communication with the inner chamber (18).

10. Tube-bundle as per any claim 1 to 7, wherein an inner chamber (18) is installed inside said at least one distribution chamber (5) and connected (20) to said at least one tubesheet (4) and spaced from said distribution chamber (5) so as to create a passage for gas (G), wherein said inner chamber (18) is directly in fluid communication with said at least one gas inlet connection (6), and wherein said inlet end (11) is connected to said at least one tube-sheet (4) and / or to the related exchanging tube (3,3a) so that said ferrule (16, 17) is in direct fluid communication with the inner chamber (18).

11. Tube-bundle as per any claim 1 to 10, wherein said exchanging tubes (3, 3a, 3b) are straight or "U" shaped, and connected at the ends to two separate tube-sheets.

12. Tube-bundle as per claim 9 or 10, wherein said heat exchanging tubes (3a, 3b) are “U” shaped, and connected at the ends to said at least one tube-sheet (4).

13. Tube-bundle as per any claim 1 to 12, wherein said exchanging tubes (3,3a) provided with ferrule (16,17) have different external and / or internal diameters.

14. Tube-bundle as per any claim 1 to 13, wherein the number of ferrules of a given length does not differ from the number of ferrules of a different length by more than 30%.MNN007WO Giovanni Manenti15. Tube-bundle as per any claim 1 to 14, wherein said equipment (100,101,102) corresponds to a process boiler installed downstream of a chemical reactor, and wherein said cooling fluid (W) is pressurized boiling water.

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