EP4130572B1

EP4130572B1 - Heat exchange bank

Info

Publication number: EP4130572B1
Application number: EP22180292.9A
Authority: EP
Inventors: Agostino CALCAGNO
Original assignee: Ruths SpA
Current assignee: Ruths SpA
Priority date: 2021-08-05
Filing date: 2022-06-22
Publication date: 2023-08-23
Anticipated expiration: 2042-06-22
Also published as: IT202100021287A1; EP4130572C0; EP4130572A1

Description

The present invention relates to a heat exchange bank suitable for realizing a heat exchange between at least two fluids at different temperatures. More specifically, the present invention relates to heat exchange banks as defined in the preamble of claim 1, and as illustrated in US 5 787 722 .
Exchange banks are typically used to transfer the energy possessed by a hot, i.e., higher temperature, gas flow, normally from an industrial process, to a cold, i.e., lower temperature, fluid circulating within heat exchange elements that make up the banks.
In particular, gases from industrial waste combustion plants are often used as the hot gas flow.
Usually in said plants, the cooling fluid contained within the elements is a subcooled liquid, a two-phase, saturated liquid-saturated steam mixture, or a superheated steam, in a pressure range generally between 10 and 80 bar and a temperature range between 120°C and 500°C.
Hot gases, on the other hand, usually range in temperature from about 100°C to 1200°C and, since they come from industrial combustion processes of municipal and/or industrial waste, they contain diffuse ash in their mass, typically between 0.5 gr/Nm3 and 20 gr/Nm3.
In heat exchange banks, it is known to obtain a tube bundle that is simultaneously traversed internally by a first, lower temperature fluid, called a cooling fluid, and lapped externally by a second, higher temperature fluid, typically a gas.
The ash contained in the hot gases, however, tends to foul the heat exchange surfaces of the heat exchange elements, i.e., the outer surfaces of the tubes in the tube bundle, undermining the heat exchange between the two fluids and irreparably compromising the performance of the banks.
For this reason, it is necessary to periodically shut down and clean the banks to restore them to optimal operation.
Cleaning operations involve cooling the bank, replacing replaceable parts by destructive cutting, and removing dust from heat exchange surfaces by mechanical abrasion or shaking.
Maintenance operations, however, result in technical downtime on the order of a few weeks, and significantly exacerbate plant operating costs when considering that on average such maintenance operations are performed about three times in a year.
Therefore, the need is felt for a heat exchange bank that enables an effective cleaning operation and is therefore capable of continuous operation for as long an interval as possible, thus reducing the time and frequency of maintenance operations.
In addition, there is a need to simplify cleaning operations of the bank in the event of a technical stoppage with the need for at least partial extraction thereof.
The object of the present invention is to make available a heat exchange bank capable of solving the problems mentioned in reference to the prior art.
Said object is satisfied by a heat exchange bank according to claim 1.
Further features and advantages of the heat exchange bank according to the present invention will be apparent from the description below of a non-limiting example of an embodiment of said bank, wherein:

Fig. 1 is a plan view of a heat exchange bank according to an embodiment of the invention;
Fig. 2 is a cross-sectional view of the heat exchange bank in Fig. 1, along the cross-sectional plane II-II indicated in Fig. 1;
Fig. 3 is a side view of the heat exchange bank in Fig. 1;
Fig. 4 is a cross-sectional view of the heat exchange bank in Fig. 1, along the cross-sectional plane IV-IV shown in Fig. 3;
Fig. 5 shows the enlarged detail V indicated in Fig. 4;
Fig. 6 shows side and plan views of heat exchange banks according to possible embodiments of the present invention;
Fig. 7 shows details of the tube bundle of a heat exchange bank according to a possible embodiment of the present invention;
Fig. 8 is a front view, partially in cross section, of a heat exchange bank according to a possible embodiment of the present invention;
Fig. 9 shows the enlarged detail IX indicated in Fig. 8;
Fig. 10 shows side and cross-sectional views of lower portions of heat exchange banks according to possible variant embodiments of the present invention;
Fig. 11 is a front view of a heat exchange bank according to a possible embodiment of the present invention.

With reference to the attached figures, 4' , 4' ' , 4' '' globally denote a heat exchange bank, suitable for realizing heat exchange between a first and second fluid at different temperatures.
Specifically, 4' denotes a vaporizer heat exchange bank, 4" a superheater heat exchange bank, and 4‴ an economizer heat exchange bank.
The definitions of vaporizer, superheater, and economizer heat exchange banks apply depending on whether the fluid flowing through the tube bundle is a two-phase, saturated liquid-saturated steam mixture, superheated steam, or subcooled liquid, respectively.
Elements or parts of elements common to the embodiments described hereinafter will be indicated with the same reference numerals.
The heat exchange bank 4 comprises a heat exchange apparatus 6 provided with a tube bundle 8 suitable to be traversed internally by said first fluid, support means 9 of the tube bundle 8 to the heat exchange apparatus 6, and containment means 10 of said second fluid suitable for accommodating said heat exchange apparatus 6 so that at least a portion of said tube bundle 8 is lapped externally by said second fluid.
The support means 9 are structurally distinct from said containment means 10, and an upper end 12 of said tube bundle 8 is operatively connected thereto.
Advantageously, the support means 9 comprise at least one chain 60 comprising a plurality of links 61 concatenated in series with each other, said chain extending parallel to the tubes of the tube bundle 8.
Preferably, said at least one chain 60 is provided with an anti-rotation device 62 configured so as to prevent or at least limit a rotation of the chain 60 and of the tube bundle 8 about an axis of rotation parallel to said tubes.
According to an embodiment, said at least one chain 60 is provided with at least one threaded tie rod 63, at least partially fixed on an upper cross member 64. Said threaded tie rod 63 allows an adjustment of the height of the various chains 60 in order to improve the flexibility characteristics of said heat exchange bank 4. It should be noted that said adjustment may advantageously be carried out externally to the flue gas loop. In other words, since the threaded tie rod 63 is external to the flue gas loop, an operator has free access to it from the outside.
According to a possible embodiment, said tube bundle 8 preferably extends along a prevailing direction Z.
Preferably, said prevailing direction Z is substantially perpendicular to a support plane A on which said bank rests.
In the examples shown in the figures, the support plane A is horizontal, and the prevailing direction Z is vertical.
With respect to a plane essentially perpendicular to the prevailing direction Z, and thus parallel to the support plane A, a direction X and a direction Y, perpendicular to each other, are defined.
The tube bundle 8 comprises a plurality of tubes parallel to each other, which, according to a possible embodiment, extend substantially in a vertical direction, i.e., perpendicular to said support plane A of the bank and parallel to said prevailing direction Z.
The tubes of the tube bundle 8 are suitable to be traversed internally by a first fluid such as a subcooled liquid (economizer bank) or a two-phase, saturated liquid-saturated steam mixture (vaporizer bank) or superheated steam (superheater bank), having a temperature between approximately 120°C and 500°C and a pressure between 10 bar and 80 bar in the normal operating ranges of heat banks.
Said tubes are preferably made of metallic materials, which are able to ensure mechanical and thermal resistance of the tubes under normal operating conditions, but also an adequate heat transfer coefficient, without, however, requiring excessive wall thicknesses of the tubes, so as not to overburden the structure of the bundle.
Advantageously, at an upper end 12 of the tube bundle 8, i.e., an end of the bundle facing away from the support plane A of the exchange bank 4 along said prevailing direction Z, said exchange apparatus 6 comprises at least one distribution manifold, fluidly connected to said tube bundle 8.
The at least one distribution manifold comprises an inlet suitable for receiving and conveying the first fluid within said manifold.
Each distribution manifold is fluidly connected to a plurality of tubes of the tube bundle so that a fluid in the tubes may be distributed through said inlets.
The fluid circulates within the tubes of the tube bundle 8 so that it enters through at least one inlet and exits through at least one outlet.
Advantageously, said at least one inlet and said at least one outlet are located on the same side of the tube bundle 8, that is, at said upper end 12.
In other words, the outlets and inlets of the tube bundle 8 are preferably located at the upper end 12 of the tube bundle 8.
According to a possible embodiment, the tubes of the bundle 8 extend in a coil along said prevailing direction Z.
For example, said tube bundle 8 extends at least in part along a broken line that forms a series of alternately protruding and receding angles.
Specifically, the tubes extend predominantly in a direction parallel to the prevailing direction Z and perpendicular to the support plane A of the bank, for example, in a vertical direction from the upper end 12 to the lower end 22 of the tube bundle and vice versa.
The tubes comprise straight segments, according to an embodiment directed along the prevailing direction Z, connected to each other by curves or sines or circumferential arcs extending along a direction substantially perpendicular to said prevailing direction Z.
In other words, the first fluid inside said coil, after traveling in one direction along a straight tube segment, having arrived at one end of the bundle, travels along a curved tube segment and reverses the motion, i.e., travels, in an opposite direction, along a subsequent straight segment of an adjacent tube, and so on.
According to an advantageous embodiment, each coil of said tube bundle, with respect to a plane perpendicular to said prevailing direction Z and thus substantially parallel to said support plane A, extends in turn according to a curve forming a series of alternately protruding and receding angles, or according to a curve forming a series of alternately concave and convex arcs.
In other words, with respect to a direction parallel to said direction X or Y, each tube of the tube bundle coil is offset with respect to the consecutive adjacent tube, in such a way, however, that the tubes are maintained in an aligned configuration.
Advantageously, by offsetting consecutive adjacent tubes by an amount not less than the diameter of said tubes, it follows that with respect to a direction X or Y, two consecutive adjacent tubes do not overlap.
According to a possible embodiment, said tube bundle 8 is structurally connected to a containment box 26 of the heat exchange apparatus 6.
Said containment box 26 is arranged at the upper end 12 of the tube bundle 8 operatively connected to the support means 9 and, according to a possible embodiment, is made according to a substantially box-like and hollow structure, so as to enclose and wrap around said upper end 12 of the heat exchange apparatus 6.
According to a possible embodiment, said containment box 26 encloses said support means 9.
According to a possible embodiment, the containment box 26 rests against said containment means 10.
The containment box 26 comprises a shell 28, which constitutes a side surface of the box, and a lid 30 that closes opposite ends of the shell 28.
Said lid 30 and said shell 28 are constrained to the frame 70 so as to form a closed box structure and extend substantially according to planes parallel to the support plane A and perpendicular to the prevailing direction Z of the tube bundle.
According to one embodiment, in the containment box 26, above the cooled canopy, insulating means and preferably panels of insulating material, such as ceramic material, are interposed.
Said cooled canopy is traversed by the tube bundle, and the interposition of the insulating means is such that gases are not able to leak into said canopy.
Thus, the tube bundle 8 is constrained to the heat exchange apparatus 6 exclusively at one end, i.e., outside of said end the bundle is not constrained to any structural element, i.e., the weight of said bundle rests entirely on the suspension systems present at an upper end 12 of the tube bundle 8.
In other words, the tube bundle is constrained at a single end so that it remains suspended, i.e., maintaining itself in a direction substantially parallel to the prevailing direction Z.
According to an embodiment, a frame 70 penetrated by cooling water is interposed between the containment box 26 and the tube bundle 8.
For example, said frame 70 may be attached to the convective chamber frame 73 by a C-shaped centering structure 71.
Advantageously, within said containment box 26, the heat exchange apparatus 26 further comprises shaking means 51, better described below, suitable for striking the tube bundle 8 to carry out tube bundle cleaning operations.
Preferably, said shaking means 51 are supported by the beams 64 by means of chains 60 and are associated with at least one shaking bar 52.
According to a possible embodiment, the sheet 53 is connected to the shell 28 and is mechanically independent of the shaking bar 52.
For example, the tubes of the tube bundle 8 are connected to the shaking bar 52 by means of cantilever connections 54 arranged near the upper ends 12 of the tube bundle 8.
For example, said cantilever connections 54 are welded to the tubes of the tube bundle 8 and to the shaking bar 52. In this way, the cantilever connections 54 are not affected by the elongation of the tubes of the tube bundle 8 due to the thermal stresses thereof.
Advantageously, the exchange apparatus 6 comprises coupling means 46 arranged at the end of the tube bundle 8 operatively connected to the support means 9.
According to a preferred embodiment, said coupling means 46 comprise at least one lifting lug 47, suitable for coupling with suitable lifting means, to enable the handling of the tube bundle 8.
The heat exchange bank 4 comprises containment means 10 suitable for accommodating within them the exchange apparatus 6 so that at least a portion of the tube bundle 8 is lapped externally by the second fluid.
Said containment means 10 preferably extend according to the prevailing direction Z of the tube bundle 8 so as to surround and contain said bundle.
The heat exchange apparatus 6 is advantageously supported on said containment means 10. The term "supported" means that the exchange apparatus 6 rests on a portion of the containment means by bearing thereon with its own weight, and thus is supported by them without further restraint.
According to a possible embodiment, advantageously said exchange apparatus 6 also comprises a cleaning system of the tube bundle 8.
Preferably said cleaning system is a shaking system, which realizes the cleaning of the surfaces of the tube bundle as a result of direct or indirect striking of said tube bundle.
Advantageously, said cleaning system is mounted near said upper end 12 of the tube bundle 8, preferably within said containment box 26, if provided.
In particular, placing the cleaning system outside the containment box, in an area not lapped by the hot, corrosive combustion gases, prolongs the life and reliability of said system.
Advantageously, the cleaning system comprises bars that are welded or otherwise made integral to the elements of the tube bundle.
Moreover, said shaking bars 52 are made integral with or connected to each other. A battery of shakers is suitable for striking said shaking bars 52 so as to vibrate the elements of the tube bundle 8.
According to an embodiment of the present invention, at least one hopper 56 is arranged at the lower end 22 of the tube bundle 8, said hopper being provided with at least one septum 57 configured to avoid preferential gas paths within the containment means 10 of the second fluid.
The heat exchanger banks described are used in any type of partial or total recovery plant, in other words, they are heat exchange devices, or heat exchangers or heat transformers, adapted to utilize the residual heat content of a fluid discharged from a plant of any type.
Advantageously, they are used in waste incineration plants, wherein the flue gas produced by the incinerator furnace constitutes the "hot" fluid, in other words, the second fluid having a residual heat content that is intended to be recovered, transferring it to the first fluid with a lower temperature, called the cooling fluid.
Combustion gases coming from thermo-destruction of waste are rich in toxic or polluting dust and therefore must be purified in order to be released into the atmosphere.
Normally, the purifier filters may not filter said gases at high temperatures, because at such temperatures the toxic substances contained in the gases are extremely corrosive to the point of rapidly deteriorating the filters themselves.
In said types of plants, the described banks are particularly advantageous.
In fact, in said incineration plants, the flue gases produced as a result of waste incineration are conveyed, according to a predetermined flue gas pathway, through the containment means, such as through properly insulated ducting systems to limit heat loss.
Advantageously, the heat exchange banks disclosed in the present invention are arranged along said path.
Preferably, the conveyor systems extend according to a horizontal direction, i.e., parallel to the support plane or base of the plant, while the exchange banks are developed according to a vertical direction, i.e., perpendicular to the direction horizontal to the support plane of the plant.
Said banks thus allow heat exchange between the flue gases and a cooling fluid that flows, through natural or forced circulation, within the tube bundles.
Advantageously, the first fluid or cooling fluid used is water in different physical states, and specifically in the form of a saturated liquid-saturated steam mixture, superheated steam, or subcooled liquid, depending on whether they are vaporizer banks 4', superheaters 4", or economizers 4‴, respectively.
The first fluid circulating within the tube bundle, as a result of the heat exchange, increases in temperature and may then be conveyed for a variety of uses, such as a motor fluid in steam turbine systems or to feed a thermal utility.
As may be appreciated from that which has been described, the heat exchange banks according to the invention make it possible to overcome the drawbacks presented in exchange banks of the prior art.
Unusually, the heat exchange banks described are removable with very simple operations, and the removal operation does not require any destructive cutting of sheets or pressure parts in general, but rather the removal of threaded connections on the supporting flanges of the bank with the heat exchange fluids.
The fact that destructive cutting operations are not carried out brings additional economic benefits, as well as a significant reduction in the technical downtime of the plant, as welded or replaced pressure parts must be retested and inspected.
An additional advantage relates to cleaning operations, as shaking systems of the prior art may be used with an amplified technical effect in heat exchange banks of the prior art.
In fact, in the known exchange banks, the tube bundle is constrained to the bank structure in a rigid manner so that, when subjected to a hammering action, the relevant tubes of the bundle vibrate modestly and the amount of dust removed is relatively little, for the same hammering action.
There is also the fact that the powders often contain residues that make them sticky or viscous, and said powders therefore tend almost to stick to the outer surfaces of the tubes of the bundle. Therefore, it is necessary for the hammering action to be vigorous and to induce large oscillations in the tubes so that the tubes may be adequately cleaned.
The disclosed tube bundle, due to the described constraint systems, possesses considerable elasticity in operation without any need to be disconnected from the exchange bank.
At the same time, in order to ensure elasticity of the tube bundle, preventing it from deforming excessively due to the thermal stresses caused by contact with hot gases, the arrangement of the tubes, which, with respect to a plane perpendicular to the preferential direction of the bundle, extend according to a curve that forms alternately protruding and receding angles, is particularly advantageous.
This configuration, while giving the tube bundle high flexibility and thus an effective and rapid cleaning of the tube bundle by the shaking systems, is able to ensure proper relative positioning between the tubes of the bundle during the operation of the exchange bank, so as not to affect the proper heat exchange between the tubes and the external fluid.
In fact, if the tubes of the bundle are excessively weak, there is a danger that due to thermal stresses the tubes will become excessively deformed and lose proper alignment with respect to the flow of hot gases, resulting in a reduction of the heat transfer surface area between the fluids.
Thus, the described tube bundle ensures high efficiency of the bank during all operating conditions, and enables rapid and accurate removal of the dust covering it, ensuring maximum cleaning efficiency.
Placing shaking systems in an area not lapped by hot, corrosive gases allows for a longer life of said shaking systems.
An additional advantage is that the support means between the tube bundle and the heat exchange bank are not hit by the flow of hot and corrosive gases. Thus, on the one hand, these support means are not subjected to any corrosive action that would compromise their durability, and on the other, they do not in turn constitute a receptacle for dust, which, as in the case of the banks of the prior art, inevitably tends to fall back on the tubes, thus contributing to the soiling of the bundle.
Obviously, a person skilled in the art, in order to meet contingent and specific needs, may make numerous modifications and variations to the heat exchange banks described above.
The scope of protection of the invention is defined by the following claims.

Claims

Heat exchange bank (4',4",4‴), suitable for realizing a heat exchange between a first and a second fluid at different temperatures, comprising an exchange apparatus (6) provided with a tube bundle (8), internally crossed by said first fluid, containment means (10) of said second fluid, suitable to accommodate said exchange apparatus (6) so that at least a portion of said tube bundle (8) is externally lapped by said second fluid,
- wherein said exchange apparatus (6) comprises support means (9) structurally distinct from said containment means (10) and to which an upper end (12) of said tube bundle (8) is operatively connected,

- wherein the support means (9) comprise at least one chain (60) comprising a plurality of links (61) concatenated in series with each other, said chain (60) extending parallel to the tubes of the tube bundle (8),

- wherein said at least one chain (60) is provided with an anti-rotation device (62), configured to prevent or at least limit a rotation of the chain (60) and the tube bundle (8) around a rotation axis parallel to said tubes, wherein said heat exchange apparatus (6) comprises a containment box (26) positioned at the end of the tube bundle (8) operatively connected to the support means (9),
the heat exchange bank being characterized by a frame (70) crossed, in use, by cooling water, the frame being interposed between the containment box (26) and the tube bundle (8).
The heat exchange bank (4',4",4‴) according to claim 1, wherein said at least one chain (60) is provided with at least one threaded tie rod (63) at least partially fixed on an upper cross member (64) of the heat exchange bank (4',4",4‴).
The heat exchange bank (4',4",4‴) according to claim 1 or 2, wherein said containment box (26) encloses said support means (9).
The heat exchange bank (4',4",4‴) according to claim 1, 2 or 3, wherein said containment box (26) is laid on said containment means (10).
The heat exchange bank (4',4",4‴), according to any one of the claims from 1 to 4, wherein said heat exchange apparatus (6) is laid on said containment means (10) .
The heat exchange bank (4',4",4‴) according to any one of the claims from 1 to 5, wherein said frame (70) is fixed to a frame of the convective chamber (73) by means of a 'C' centring structure (71).
The heat exchange bank (4',4",4‴) according to any one of the claims from 1 to 6, wherein said exchange apparatus (6) comprises shaking means (51) of said tube bundle (8), said shaking means (51) being positioned at said support means (9) and being associated with at least one shaking bar (52).
The Heat exchange bank (4',4",4‴) according to claim 7, wherein the shaking bar (52) is connected to an intermediate element (53) mechanically independent of the containment box (26).
The heat exchange bank (4',4",4‴) according to any one of the claims from 7 to 8, wherein the tubes of the tube bundle (8) are connected to the shaking bar (52) by means of cantilever connections (54) positioned near upper ends (12) of the tube bundle (8).
The heat exchange bank (4',4 ",4" ') according to claim 9, wherein said cantilever connections (54) are welded to the tube bundle (8) and to the shaking bar (52) .
The heat exchange bank (4',4",4‴) according to any one of the claims from 1 to 10, wherein at the lower end (22) of the tube bundle (8) at least one hopper (56) is positioned, provided with at least one septum (57) configured to avoid preferential gas paths inside the containment means (10) of the second fluid.
Heat exchange bank (4',4",4‴) according to any one of the claims from 1 to 11, wherein said tube bundle (8) extends in a coil along a prevailing direction Z.
The heat exchange bank (4',4",4‴) according to claim 12, wherein with respect to a plane perpendicular to said prevailing direction Z, said tube bundle (8) extends at least partially according to a broken line forming a series of alternately protruding and receding angles.
A steam generating plant comprising a heat exchange bank (4',4",4‴) according to any one of the claims from 1 to 13.