Recuperator with external manifolds for organic rankine cycle plants
Patent Information
- Application Number
- EP2023798515
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-19
- Filing Date
- 2023-10-13
- Publication Date
- 2025-08-27
- Estimated Expiration
- 2043-10-13
AI Technical Summary
In organic Rankine cycle plants, the existing recuperator designs with internal manifolds are difficult to maintain and repair due to the complexity of accessing and replacing finned batteries, especially when leaks or breakages occur, leading to high costs and inefficiencies in heat exchange efficiency.
A recuperator design with external manifolds for the supply and delivery of the liquid phase of the organic working fluid, allowing for easy identification and sealing of damaged tubes without disassembling the entire unit, enabling faster and safer maintenance.
Facilitates easy diagnosis and repair of internal damage, reduces maintenance costs, and improves operational efficiency by allowing external access for sealing broken tubes, thus enhancing the practicality and safety of recuperator maintenance.
Smart Images
Figure 1.1
Abstract
Description
[0001] RECUPERATOR WITH EXTERNAL MANIFOLDS FOR ORGANIC
[0002] RANKINE CYCLE PLANTS
[0003] DESCRIPTION
[0004] Technical sector of the invention
[0005] The present invention relates to a recuperator with external mani folds organic Rankine cycle plants . The solution adopted for the innovative recuperator with external mani folds is particularly suitable for organic Rankine cycle plants in which there is a notable di f ference between evaporation temperature and condensation temperature of the organic working fluid .
[0006] Background art
[0007] As is known, a thermodynamic cycle is defined as a finite success ion of thermodynamic trans formations ( for example isotherm, isochore , isobar or adiabatic ) at the end of which the system returns to its initial state .
[0008] Such cycle can be direct , for example a direct Rankine cycle , in which a thermal source is used for the production o f mechanical / electrical energy and heat at a temperature lower than that of the thermal source . In particular, an ideal Rankine cycle is a thermodynamic cycle composed of two adiabatic trans formations and two isobars . In the case of a direct cycle , its purpose is to trans form heat into work . This cycle is generally adopted especially in thermoelectric power plants for the production of electric energy and uses water as a driving fluid, both in liquid and in steam form, with the so-called steam turbine .
[0009] More speci fically, organic Rankine cycles ( ORC ) have been hypothesi zed and created which use high molecular mass organic fluids for the most diverse applications , in particular also for the exploitation of low-medium enthalpy thermal sources . As in other steam cycles , the plant for an ORC cycle includes one or more pumps for feeding the organic working fluid, at least one heat exchanger ( also called pre-heater or evaporator, depending on the function performed) to carry out the preheating, vapori zation and possible overheating or heating phases in supercritical conditions of the same working fluid, a steam turbine for the expansion of the fluid, mechanically connected to an electric generator, a condenser which returns the organic working fluid to the liquid state . It is also known that in ORC cycles the use of high molecular mass organic fluids very often involves the need to introduce a further heat exchanger called ' recuperator ' or ' recuperator ' downstream of the turbine and upstream of the condenser which recovers a good portion of the sensible heat of a low-pressure organic fluid vapor, a heat that is used to preheat the organic working fluid in the liquid phase downstream of the cycle feeding pump and upstream of the pre-heater .
[0010] It is in fact a characteristic of many fluids used in ORC cycles to have a saturation curve in the Temperature-Entropy diagram with the right branch having a trend opposite to the trend of the analogous right branch of the water vapor saturation curve , that is , with a slope comparable to that of the left branch .
[0011] The consequence of this is that , by expanding the steam of the organic working fluid in a turbine starting from a saturated steam condition, at the end of the expansion the steam is very overheated .
[0012] In order to exploit the exergetic value of this steam, before introducing it into the condenser which works at low temperature , it is advisable to recover its sensible heat . In a typical cycle used to produce energy in cogeneration, where Octamethyltriloxane is used as a working fluid and has an evaporation temperatures of approximately 270 ° C and a condensation temperature of approximately 80 ° C, it is calculated that the thermal power recovered in the recuperator is roughly equivalent to that introduced subsequently by the preheater and the evaporator at the expense of the external source : in other words , the presence of the recuperator allows the conversion ef ficiency of the cycle to be roughly doubled compared to a similar system without a recuperator in which the external source should al so make up for this share of thermal power which instead is available within the cycle itsel f .
[0013] The importance of installing an ef ficient and reliable recuperator, especially in ORC cycles where there is a notable di f ference between evaporation temperature and condensation temperature of the organic working fluid, is therefore evident .
[0014] It must also be said that the superheated vapor phase has much lower exchange coef ficients than the liquid phase present in the recuperator . In the example above , the steam pressure is approximately 0 . 1- 0 . 2 bar absolute , a value which involves the presence of a steam that is not very dense and has high volumetric flow rates and low exchange coef ficients .
[0015] In many applications the type of recuperator used is of the " finned batteries" type ( Tube Fin Heat Exchangers , also called " finned coil heatexchangers" ) , commonly used also in civil ian sphere for air heat pumps , for refrigerators or condensers in general , for giving-of f or absorbing heat from ambient air .
[0016] In patent EP1426565 Bl of the same applicant a typical arrangement of said type of recuperator is illustrated inside a casing which can contain either only the recuperator or also a condenser . It is in fact necessary to guarantee that the steam side , in contact with the large surface of the fins of the recuperator, is perfectly isolated from the external environment , i . e . is in contact only with the vapor of the organic fluid to be cooled . This type of recuperator is then inserted into a large diameter casing ( typically having a diameter between 1 m and 3 m and a variable length from 3 m to 10 m for turbogenerators approximately from 0 , 3 MW to 10 MW of electric power) . With reference to figure 1 which illustrates a known embodiment , the recuperator 1 includes at least one finned battery 2 and a casing 3 inside which the finned battery is contained . The figure also illustrates the IN entry and OUT exit of the vapor of the organic working fluid, as well as its path inside the casing 3 . The figure also illustrates the mani folds 4 , which collect the tubes containing the liquid phase of the organic working fluid, which tubes exchange heat inside the finned battery . The mani folds 4 are in their standard configuration, i . e . ins ide the casing 3 of the recuperator 1 and are placed on the side where the cylindrical vessel is closed by domed bottoms .
[0017] Also consider the following points :
[0018] - a recuperator module with dimensions x = 5000 mm, y = 1500 mm, z = 1000 mm is composed of approximately 5000 tubes ( containing the liquid phase ) and has approximately 10000 welds ,
[0019] - to avoid mounting flanges and gaskets on a large diameter casing, the container containing the finned battery is normal ly closed with a cover (with rounded bottom) which is welded to the casing so that any removal / replacement of a finned battery, once installed is quite di f ficult and expensive , provided that the installation site has suf ficient space to allow its removal ,
[0020] - it is not uncommon for one of the welds or a tube of the finned battery itsel f to have a leak or breakage : i f it is small , the leakage of liquid from one of the tubes towards the environment of the casing is not critical because the two fluids present are the same but in di f ferent phases ( liquid and vapor ) .
[0021] However, i f even a complete breakage of a tube occurs , the " internal" leakage is not tolerable and the finned battery will almost certainly have to be replaced as it is di f ficult to repair it inside the vessel . In these large casings there is often a "man' s pace" to be able to access the inside but the probability that the tube to be sealed is in an accessible position is very low and often zero . There is , therefore , a need for a recuperator design solution that solves or at least mitigates the above- mentioned drawbacks .
[0022] Summary of the invention
[0023] The solution of the technical problems referred to in the previous paragraph is obtained, according to the present invention, with a recuperator for ORC plants , comprising at least one finned battery and a containment casing of the finned battery, and in which the tubular manifolds for the supply and the delivery of the liquid phase of the organic working fluid are external to the casing . In this way, it is possible to identi fy any leakage linked to the breakage of one of its tubes containing the liquid phase of the organic working fluid and to seal the damaged tube with a relatively simple , fast and safe operation . According to one aspect of the present invention, a recuperator for an organic Rankine cycle plant is therefore described, having the characteristics set out in the independent product claim attached to the present description .
[0024] Further preferred and / or particularly advantageous ways of implementing the aforementioned system are described according to the characteristics set out in the attached dependent claims .
[0025] Brief description of the drawings
[0026] The invention wil l now be described with reference to the attached drawings , which illustrate some nonlimiting exemplary embodiments of a recuperator for ORC systems , in which :
[0027] - figure 1 schematically illustrates an example of a recuperator according to the known art , - figure 2 schematically illustrates a detail of a recuperator for ORC plants , according to a first embodiment of the present invention,
[0028] - figure 2a illustrates a containment casing of the recuperator according to the embodiment of figure 2 ,
[0029] - figure 2b illustrates the recuperator of figure 2 during a first assembly phase ,
[0030] - figure 2c illustrates the recuperator of figure 2 in a final assembly phase ,
[0031] - figure 3a illustrates a containment casing of the recuperator in a second embodiment of the present invention, and
[0032] - figure 3b illustrates the recuperator in an operational configuration .
[0033] Detailed description
[0034] The recuperator 20 , 30 according to the present invention includes a casing 21 , 31 inside which at least one finned battery 20a, 30a is located . The vapor of the organic working fluid laps the fins of the finned battery inside the casing, while the liquid phase of the organic working fluid flows inside a plurality of tubes 24 , 34 . The tubes 24 , 34 as well as being housed inside the finned battery 20a, 30a, include two end portions external to the finned battery: a first portion 24i, 34i has the function of adducting the liquid phase of the organic working fluid inside the finned battery; a second portion 24o, 34o has the function of delivering the liquid phase of the organic working fluid towards the other components of the ORC plant (for example, towards the pre-heaters) .
[0035] Throughout the present description, the suffix "i" (IN) will specify that the component in question is part of the adduction side of the liquid phase, while the suffix "o" (OUT) will specify that the component in question is part of the delivery (or outlet) side of the liquid phase. However, when both the suffixes "i" and "o" are missing, it will be understood that the component in question can belong indifferently to both the supply side and the delivery side. Furthermore, for ease of reading, a single finned battery will be described, keeping in mind that the recuperator according to the present invention may also include more than one finned battery.
[0036] With particular reference to figure 2, a first embodiment of the recuperator 20 according to the present invention provides that the supply tubes 24i to the finned battery 20a and the delivery tubes 24o from the finned battery are welded to a corresponding external mani fold 251 , 25o which includes a cover 27 i , 27o and a tube plate 26i , 26o which is preferably flat . The shape of the tube plates 26 is such as to reproduce a portion of the shell 22 of the casing 21 , so that once the tube plate 26 is inserted into the casing 21 it restores the integrity of the shell 22 .
[0037] In fact and with reference to figure 2a, in the shell 22 of the casing 21 there are openings 23i , 23o obtained by eliminating a part of the shell 22 which will then be "closed" by the corresponding tube plates 26i , 26o of the finned battery once the finned battery itsel f is inserted, as shown in figure 2c .
[0038] This first embodiment requires si zing the casing 21 so that there is suf ficient space to be able to carry out the assembly operation of the recuperator 20 inside the casing 21 .
[0039] In fact , in figure 2b a first assembly configuration is illustrated according to which the finned battery 20a must first be inserted inside the casing 21 according to the axial direction of the casing 21 , maintaining the mani folds 25 ( and the corresponding tube plates 26 ) inside the casing 21 itsel f .
[0040] Subsequently, in figure 2c, the finned battery 20a is translated according to a radial direction ( indicated by an arrow) , until the mani folds 25 protrude from the casing 21 in correspondence with the openings 23 and the tube plates 26 can restore , after welding, the integrity of the shell 22 .
[0041] Therefore , the casing 21 will require a volume V which also includes the " lost" volume intrinsic to this solution . Such extra volume is of considerable si ze but is essential to allow the transversal translation of the finned battery during assembly .
[0042] A second embodiment of the present invention, which does not need to si ze the casing taking into account the need for an extra volume necessary for mounting the recuperator, is illustrated in figures 3a and 3b .
[0043] Also in this second embodiment , the recuperator 30 according to the present invention provides that the adduction tubes 34 i and the delivery tubes 34o are welded to a corresponding external mani fold 35i , 35o which includes a cover 37 i , 37o and a preferably flat tube plate 36i , 36o . The shape of the tube plates 36 is such as to reproduce a portion of the shell 32 of the casing 31 , so that once the tube plate 36 is inserted into the casing 31 it restores , after welding, the integrity of the shell 32 . In fact and with reference to figure 3a, in the shell 32 of the casing 31 there are openings 33i, 33o obtained by eliminating a part of the shell 32 which will then be "closed" by the corresponding tube plates 36i, 36o of the finned battery. The difference compared to the previously described solution consists in the fact that, while the openings 23 of the solution in figure 2a are slotted according to a "closed" shape, the openings 33i, 33o of the solution in figure 3a are slotted according to an "open" shape, so being without of respective end edge 33 'i, 33 'o.
[0044] In this way the finned battery 30a can be mounted according to a single operation (figure 3b) , i.e. it will be installed inside the casing 31 by translating it according to the axial direction of the casing 31 only and, thanks to the absence of the end edges 33' of the openings 33, until the manifolds 35 protrude from the casing 31 in correspondence with the openings 33 and the tube plates 36 can restore, after welding, the integrity of the shell 32.
[0045] Therefore, according to this embodiment, the insertion of the finned battery 30a inside the casing 31 occurs without the need for a radial translation of the same and therefore without the need to provide an empty space inside the casing 31 to allow this translation, as in the previous solution. Therefore, given the same dimensions of the finned battery, according to this embodiment it is possible to use a casing with a smaller diameter and therefore less expensive .
[0046] According to the present invention, therefore, in the event of a leakage or breakage of a tube, action can be taken in this way:
[0047] - open the cover 27, 37 of the manifold 25, 35,
[0048] - identify the broken tube with a simple pressure test, at the casing side,
[0049] - seal both the inlet and outlet tubes, i.e. the two end portions of the broken tube, by inserting a forced or welded cap.
[0050] The present procedure is simple and effective, as well as being consolidated as is usually done in a 'shell&tube' exchanger in which the exchanger tubes are supported on a flat plate which constitutes the circular head of the exchanger.
[0051] It is possible to realize the manifold 25, 35 according to different all effective design solutions, which therefore fall within the scope of the present invention. For example, the cover 27, 37 can be bolted to the manifold 25, 35 after inserting a suitable pressed or welded sealing gasket; alternatively, the cover can be welded directly to the manifold.
[0052] Furthermore, the connection of the tubes 24, 34 to the tube plate 26, 36 can also be achieved in different variations, all included within the scope of the present invention. For example, the tubes can be directly expanded or welded to the tube stubs; alternatively the tubes can be expanded or welded to tube sections of different material and / or thickness. These stubs in turn can be pre-expanded or pre-welded to the tube plate.
[0053] Ultimately, the solution according to the invention has several advantages: first of all, an ease of diagnosis of any internal damage, on the tube side, to the finned battery of the recuperator: with this solution the identification of any damaged tube is done directly from the outside of the recuperator casing, by removing the cover of the manifold only, which is in an external position and, therefore, is easily accessible ; a relative ease and safety of the exclusion intervention of any damaged tube(s) , which will be sealed without the need to access the inside of the casing and extract the entire finned battery. The recuperator is not infrequently placed at high altitude or in places that are di f ficult to access . The advantage of being able to carry out an operation of this type without extracting the finned battery benefits practicality, safety and speed of intervention : sometimes the extraction itsel f would be impossible without dismantling part of the building containing the plant ; even in the case of welded covers 27 , 37 , the cutting / opening operation of said covers is far simpler, faster and less invasive than removing a rounded bottom of 1-3 m in diameter in order to extract the battery; with the traditional solution it is also very di f ficult ( i f not impossible ) to identify the broken tube ( s ) and to cap / replace them, so much so that it is often preferable to replace the entire battery rather than trying to repair it with the second embodiment of the invention ( figures 3 , 3a, 3b ) , lower cost of the recuperator component given by the smaller overall dimensions of the casing with the same useful surface area of the internal finned battery .
[0054] It is clear that the teachings of the present invention can also be applied to the solution referred to in patent EP 1426565 Bl , i . e . to the heat exchange group comprising a recuperator and a condenser housed in a single casing .
[0055] In addition to the ways of implementing the invention, as described above , it should be understood that numerous further variations exist . It must also be understood that said ways of implementation are only exemplary and do not limit neither the obj ect of the invention, nor its applications , nor its possible configurations . On the contrary, although the above description makes it possible for the skilled man to implement the present invention at least according to one of its exemplary configurations , it must be understood that numerous variations of the described components are conceivable , without thereby departing from the obj ect of the invention, as defined in the attached claims .
Claims
CLAIMS1. Recuperator (20, 30) for an organic Rankine cycle plant operated by an organic working fluid comprising : at least one finned battery (20a, 30a) a casing (21, 31) , delimited by a shell (22, 32) inside which the at least one finned battery (20a, 30a) is accommodated, so that a vapor phase of the organic working fluid flows outside the at least one finned battery (20a, 30a) and inside the casing (21, 31) , a plurality of tubes (24, 34) , inside which a liquid phase of the organic working fluid flows, partially allocated inside the at least one finned battery (20a, 30a) , so that between the vapor phase of the organic working fluid and the liquid phase of the organic working fluid a heat exchange is achieved, a first end portion (24i, 34i) of tubes of the plurality of tubes (24, 34) , abutting on a first manifold (25i, 35i) and external to the at least one finned battery (20a, 30a) with supply function of the liquid phase of the organic working fluid, a second end portion (24o, 34o) of tubes of the plurality of tubes (24, 34) , abutting on a second manifold (25o, 35o) and external to the at least onefinned battery (20a, 30a) with delivery function of the liquid phase of the organic working fluid, the recuperator (20, 30) being characterized by the fact that, in combination: first manifold (25i, 35i) and second manifold (25o, 35o) are external to the casing (21, 31) and are provided with corresponding first tube plate (26i, 36i) and second tube plate (26o, 36o) , respectively integral with the first end portion (24i, 34i) of tubes and with the second end portion (24o, 34o) of tubes, the shell (22, 32) of the casing (21, 32) is provided with a first opening (23i, 33i) and a second opening (23o, 33o) , the shape of the tube plates (26i, 36i, 26o, 36o) reproduces the shape of the openings (23i, 33i, 23o, 33o) , so that the tube plates (26i, 36i, 26o, 36o) close the corresponding openings (23i, 33i, 23o, 33o) .
2. Recuperator (20) according to claim 1, in which the openings (23i, 23o) of the shell (22) are closed shape slots.
3. Recuperator (30) according to claim 1, wherein the openings (33i, 33o) of the skirt (32) are open shape slots.
4. Recuperator (20, 30) according to any of the preceding claims, in which the tube plates (26i, 36i, 26o, 36o) are flat.
5. Recuperator (20, 30) according to any of the preceding claims, in which the first manifold (25i, 35i) and second manifold (25o, 35o) are provided with corresponding first covers (27i, 37i) and second covers (27o, 37o) removable in case of maintenance.
6. Recuperator (20, 30) according to claim 5, wherein the covers (27i, 37 i , 27o, 37o) are bolted to the corresponding manifolds (25i, 35i, 25o, 35o) and the manifolds (25i, 35i, 25o, 35o) are equipped with sealing gaskets.
7. Recuperator (20, 30) according to any of the preceding claims, in which the end portions (24i, 34i, 24o, 34o) of the tubes are expanded or welded to the corresponding tube plates (26i, 36i, 26o, 36o) .
8. Recuperator (20, 30) according to one of claims 1 to 6, wherein the end portions (24i, 34i, 24o, 34o) of the tubes are expanded or welded to pipe stubs, said stubs being in turn pre-expanded or prewelded to the corresponding tube plates.
9. Heat exchange unit comprising the recuperator (20, 30) according to any of the preceding claims and a condenser for an organic Rankine cycleplant, wherein the recuperator (20, 30) and the condenser are housed in a single casing.
10. Method for assembling a recuperator (20) according to claim 2 comprising the following steps: insert a finned battery (20a) inside a casing (21) , according to an axial direction, with manifolds (25) and corresponding tube plates (26) inside the casing (21) , translate the finned battery (20a) according to a radial direction until the manifolds (25) come out of the casing (21) at the openings (23) and the tube plates (26) restore, after welding, the integrity of a shell (22) of the casing (21) .
11. Method for assembling a recuperator (30) according to claim 3 comprising the following step: insert a finned battery (30a) inside a casing (31) , according to an axial direction, with manifolds (35) external to the casing (31) and corresponding tube plates (36) which restore, after welding, the integrity of a shell (32) of the casing (31) .
12. Method for maintaining a recuperator (20, 30) according to any of claims 1 to 8, wherein in the event of a tube leak or rupture, the method comprises the following steps:open a cover (27, 37) of a manifold (25,35) , identify the broken tube with a pressure test, on the casing side, - seal the first and second end portion of the broken tube by inserting a forced or welded plug.