Flexible assembly of recuperator for combustion turbine exhaust

The present invention is related to recuperators, and more particularly to heating pressurized air in a recuperator capable of recovering exhaust energy from a utility scale combustion turbine.

The exchange of heat from a hot gas at atmospheric pressure to pressurized air may be performed in a recuperator, of which many conventional designs are available. These commercial designs are limited in size and have a poor service history when applied to large heat recovery applications, such as recovery of waste heat from the exhaust gas stream of a utility size combustion turbine. Waste heat from a combustion turbine may be used to heat compressed air stored for power generation purposes in compressed air energy storage (CAES) plants, or other process requiring heated compressed air.

CAES systems store energy by means of compressed air in a cavern during off-peak periods. Electrical energy is produced on-peak by admitting compressed air from the cavern to one or several turbines via a recuperator. The power train comprises at least one combustion chamber heating the compressed air to an appropriate temperature. To cover energy demands on-peak a CAES unit might be started several times per week. To meet load demands, fast start-up capability of the power train is mandatory in order to meet requirements of the power supply market. However, fast load ramps during start-up impose thermal stresses on the power train by thermal transients. This can have an impact on the lifetime of the power trains in that lifetime consumption increases with increasing thermal transients. For these types of applications, the physical size of the heat exchanger and the large transient thermal stresses associated with rapid heating of the recuperator during startup have proven to be beyond the capability of conventional recuperator equipment.

Common to all heat recovery air recuperators (HRARs), the temperature of the exhaust-gas stream declines from the exhaust-gas inlet to the exhaust-gas outlet of the heat exchanger. The amount of heat transferred in each heat exchanger tube row over which the exhaust-gas flows is proportional to the temperature difference between the exhaust-gas and the fluid in the heat exchanger tubes. Therefore, for each successive row of heat exchanger tubes in the direction of exhaust-gas flow, a smaller amount of heat is transferred, and the heat flux from the exhaust-gas to the fluid (e.g., compressed air) inside the tube declines with each tube row from the inlet to the outlet of the heat exchanger section. Therefore, for each successive row of heat exchanger tubes in the direction of gas flow, the temperature of the tube metal is determined by both the amount of heat flux across the tube wall and the average temperature of the fluid inside the tube.

For example, in a conventional recuperator, the temperature of the heat exchanger tube metal is determined by both the amount of heat flux across the heat exchanger tube wall and the average temperature of the flow medium inside the heat exchanger tube. Since the heat flux declines from the inlet to the outlet of the recuperator section, the temperature of the heat exchanger tube metal is different for each row of heat exchanger tubes included in the recuperator section.

Each manifold (header) of a horizontal heat recovery air recuperator (HRAR) that runs perpendicular to the exhaust-gas flow acts as a collection point for multiple rows of tubes. These headers are of relatively large diameter and thickness to accommodate the multiple tube rows. FIGS. 1 a and 1 b are two views of such an assembly 100 , known as a multi-row header-and-tube assembly, utilized in typical heat exchanger arrangements. Included in the assembly 100 is a header 101 and multiple tube rows 105 A- 105 C. As shown in FIG. 1 a , each individual tube row 105 A- 105 C includes multiple tubes. In the interest of clarity of illustration, FIG. 1 b only shows a single tube in each tube row 105 A- 105 C. Since each of tube rows 105 A- 105 C is at a different temperature, the mechanical force due to thermal expansion is different for each tube row 105 A- 105 C. Such differential thermal expansion causes stress at tube bends and the attachment point of each individual tube to the header 101 . Further, also contributing to thermal stresses at the attachment point of each individual tube to the header 101 is a difference in thickness between the relatively thin-wall tubes as compared to the thick-wall header 101 . Under certain operating conditions, these stresses can cause failure of the attachment point, especially if the assembly 100 is subjected to many cycles of heating and cooling. Accordingly, a need exists for a flexible recuperator for large-scale utility plant applications that is capable of both rapid heating and cooling as well as a large number of start-stop cycles.

According to the aspects illustrated herein, there is provided a recuperator including a heating gas duct; an inlet manifold; a discharge manifold; and a once-through heating area disposed in the heating-gas duct through which a heating gas flow is conducted. The once-through heating area is formed from a plurality of first single-row header-and-tube assemblies and a plurality of second single-row header-and-tube assemblies. Each of the plurality of first single-row header-and-tube assemblies including a plurality of first heat exchanger generator tubes is connected in parallel for a through flow of a flow medium therethrough and further includes an inlet header connected to the inlet manifold. Each of the plurality of second single-row header-and-tube assemblies including a plurality of second heat exchanger generator tubes is connected in parallel for a through flow of the flow medium therethrough from respective first heat exchanger generator tubes, and further includes a discharge header connected to the discharge manifold. Each of the inlet headers is connected to the inlet manifold via a respective at least one of a plurality of first link pipes and each of the discharge headers is connected to the discharge manifold via a respective at least one of a plurality of second link pipes. Each of the heat exchanger tubes of each of the first and second single-row header-and-tube assemblies have an inside diameter that is less than an inside diameter of any of the plurality of first and second link pipes.

According to the other aspects illustrated herein, there is provided a compressed air energy storage system. The compressed air energy storage system includes a cavern for storing compressed air; a power train comprising a rotor and one or several expansion turbines; and a system providing the power train with the compressed air from the cavern that includes a recuperator for preheating the compressed air prior to admission to the one or several expansion turbines and a first valve arrangement that controls the flow of preheated air from the recuperator to the power train. The recuperator includes: a heating gas duct which receives heating gas flow in an opposite direction to a flow of the compressed air; an inlet manifold; a discharge manifold; and a once-through heating area disposed in the heating-gas duct through which said heating gas flow is conducted. The once-through heating area is formed from a plurality of first single-row header-and-tube assemblies and a plurality of second single-row header-and-tube assemblies. Each of the plurality of first single-row header-and-tube assemblies including a plurality of first heat exchanger generator tubes is connected in parallel for a through flow of a flow medium therethrough and further includes an inlet header connected to the inlet manifold. Each of the plurality of second single-row header-and-tube assemblies including a plurality of second heat exchanger generator tubes is connected in parallel for a through flow of the flow medium therethrough from respective first heat exchanger generator tubes, and further includes a discharge header connected to the discharge manifold. Each of the inlet headers is connected to the inlet manifold via a respective at least one of a plurality of first link pipes and each of the discharge headers is connected to the discharge manifold via a respective at least one of a plurality of second link pipes. Each of the heat exchanger tubes of each of the first and second single-row header-and-tube assemblies have an inside diameter that is less than an inside diameter of any of the plurality of first and second link pipes.

According to the still other aspects illustrated herein, there is provided an apparatus for heating pressurized air capable of recovering exhaust energy from a utility scale combustion turbine. The apparatus includes: a heating gas duct; an inlet manifold; a discharge manifold; and a once-through heating area disposed in the heating-gas duct through which a heating gas flow is conducted. The once-through heating area is formed from a plurality of single-row header-and-tube assemblies. Each of the plurality of single-row header-and-tube assemblies includes a plurality of heat exchanger generator tubes connected in parallel for a through flow of a flow medium therethrough and further includes an inlet header connected to the inlet manifold. Each of the plurality of single-row header-and-tube assemblies is connected to the discharge manifold. Each of the inlet headers is connected to the inlet manifold via a respective at least one of a plurality of link pipes. Each of the heat exchanger tubes of the single-row header-and-tube assemblies have an inside diameter that is less than an inside diameter of any of the plurality of link pipes.

The above described and other features are exemplified by the following figures and detailed description.

Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

FIG. 1 a is a perspective view of a multi-row header-and-tube assembly utilized in prior art heat recovery air recuperator;

FIG. 1 b is a front plan view of the multi-row header-and-tube assembly shown in FIG. 1 a;

FIG. 2 is a front perspective view of a stepped component thickness with single row header-and-tube assembly for a heat recovery air recuperator (HRAR) in accordance with an exemplary embodiment of the present invention;

FIG. 3 is a front plan view of FIG. 2 ;

FIG. 4 is a side plan view of FIG. 2 ;

FIG. 5 is front perspective view of a HRAR module in accordance with an exemplary embodiment of the present invention;

FIG. 6 is an enlarged perspective view of a top portion of the module of FIG. 5 ;

FIG. 7 is a side elevation view of an exemplary recuperator assembly having five HRAR modules of FIG. 5 assembled together and disposed in a heat gas duct in accordance with an exemplary embodiment of the present invention; and

FIG. 8 is a schematic view illustrating the recuperator assembly of FIG. 7 employed in a compressed air energy storage (CAES) system.

Referring to FIGS. 2-4 , a stepped component thickness with single row header-and-tube assembly 200 that is not subject to bend and attachment failure due to thermal stresses, discussed above, is provided for use in a once-through type horizontal HRAR. FIGS. 3 and 4 are front and side views of the perspective view of the stepped component thickness with single row header-and-tube assembly 200 of FIG. 2 . In the interest of clarity in the illustration, FIG. 2 only shows the outboard headers each having a single row of a plurality of tubes. However, the ellipsis illustrated in FIG. 2 indicates that each header includes a single row of tubes. More specifically, assembly 200 includes a first plurality of single tube rows 201 A- 201 F (e.g., “first tube rows”), each first tube row attached to a first common header (or inlet header) 205 A- 205 F, respectively. Thus, tube row 201 A is attached to common header 205 A, tube row 201 B (not shown) is attached to common header 205 B, and so on, through to tube row 201 F being attached to common header 205 F. Assembly 200 further includes a second plurality of single tube rows 201 G- 201 L (e.g., “second tube rows”), each second tube row attached to a second common header (or discharge header) 205 G- 205 L, respectively. Thus, tube row 201 G (not shown) is attached to common header 205 G, tube row 201 H (not shown) is attached to common header 205 H, and so on, through to tube row 201 L being attached to common header 205 H. Each common header 205 A- 205 L extends in a y-axis direction and each first tube row 201 A- 201 L extends in a z-axis direction, as illustrated. Such an arrangement as described above may be referred to as a stepped component single-row header-and-tube assembly discussed further hereinbelow.

Each header 205 A- 205 F is connected to at least one first collection manifold (or inlet manifold) 215 (two shown) via at least one first link pipe 220 A- 220 F (e.g., four first link pipes 220 A shown). Thus, header 205 A is connected to the collection manifold 215 via link pipe 220 A, header 205 B is connected to the collection manifold 215 via link pipe 220 B, and so on, through header 205 F being connected to the first collection manifold 215 via link pipe 220 F. Each collection manifold 215 extends in an x-axis direction, as illustrated.

In this construction, a single row of tubes 201 A- 201 F is attached to a relatively small diameter respective header 205 A- 205 F with a thinner wall than the large header 215 illustrated in FIGS. 2-4 . This arrangement may be described by the term “single-row header-and-tube assembly” for the tube-and-header assembly. The small headers 205 A- 205 F are, in turn, connected to at least one large collection manifold 215 , using pipes that may be described as links 220 A- 220 F. The combination of tubes 201 A- 201 F, small headers 205 A- 205 F, links 220 A- 220 F and large collection manifolds 215 may be described as a first stepped component thickness with single row header-and-tube assembly 230 .

In like manner, each header 205 G- 205 L is connected to at least one second collection manifold (or discharge manifold) 225 (two shown) via at least one second link pipe 220 G- 220 L (e.g., four second link pipes 220 G shown). Thus, header 205 G is connected to the second collection manifold 225 via link pipe 220 G, header 205 H is connected to the second collection manifold 225 via link pipe 220 H, and so on, through header 205 L being connected to the second collection manifold 225 via link pipe 220 L.

Each header 205 G- 205 L is connected to at least one second collection manifold 225 via at least one second link pipe 220 G- 220 L. Thus, header 205 G is connected to the second collection manifold 225 via second link pipe 220 G, and so on, through header 205 L being connected to the second collection manifold 225 via second link pipe 220 L. Likewise, the arrangement with respect to the second headers 205 G- 205 L and associated tubes 201 G- 201 L is referred to a second single-row-and-tube assembly. As described above with respect to the first stepped component thickness single-row header-and-tube assembly 230 , such an arrangement may be referred to as a second stepped component thickness single-row header-and-tube assembly 240 .

Each tube of each tube row 201 A- 201 L has a smaller diameter than each common header 205 A- 205 L and each link pipe 220 A- 220 L. Each common header 205 A- 205 L has a smaller diameter and thinner wall thickness than each collection manifold 215 .

As a result of this configuration, a high concentration of stresses during heating and cooling does not occur at bends and attachment points. More particularly, because the tubes of each tube row 201 A- 201 L do not have bends, no thermal stress associated with bends exists. Also, bending stress at the weld attachment of each tube to each header 205 A- 205 L does not occur because a bending moment imposed by tube bends during heating does not exist. Thus, the single-row assemblies 230 and 240 can withstand many more cycles of heating and cooling than the multi-row header-and-tube assembly 100 depicted in FIG. 1 , and discussed above.

FIG. 5 is front perspective view of a HRAR module (once-through heating area) 300 including the first stepped component thickness single-row header-and-tube assembly 230 and second single-row header-and-tube assembly 240 of FIGS. 2-4 in accordance with an exemplary embodiment of the present invention. The HRAR module 300 illustrates fluid communication of the first stepped component thickness single-row header-and-tube assembly 230 with the second single-row header-and-tube assembly 240 via a top portion 360 of module 300 .

Referring to FIG. 6 , the top portion 360 includes a plurality of third common headers 305 A- 305 L connected to a corresponding tube row 201 A- 201 L, and hence in fluid communication with a respective common header 205 A- 205 L via a corresponding tube row 201 A- 201 L. Furthermore, third common headers 305 A- 305 F are in fluid communication with corresponding third common headers 305 G- 305 L via a corresponding third link pipe 320 AL, 320 BK, 320 CJ, 320 DI, 320 EH and 320 FG, respectively.

For example and referring again to FIG. 5 , a fluid medium W (e.g., compressed air) flows into first common header 205 from an inlet 362 of first manifold 215 via first link pipe 220 A and flows through the first tube row 201 A in a first direction indicated by arrow 364 in FIGS. 5 and 6 . Fluid medium W then flows into corresponding third header 305 A and then into third header 305 L via third link pipe 320 AL. Fluid medium W then flows into corresponding second tube row 201 L in a second direction indicated by arrow 366 in FIGS. 5 and 6 . Second common header 205 L receives fluid medium W from corresponding second tube row 201 L and outputs fluid medium W from an outlet 368 of second manifold 225 via connection with second link 220 L. The HRAR module 300 is shown with the outlet 368 facing an exhaust gas flow 370 from a combustion turbine, for example, but is not limited thereto, and the inlet 362 downstream of the exhaust gas flow 370 . Referring to FIG. 4 , it will be recognized that the manifolds 215 and 225 each have a cap 372 on an opposite end thereof relative to inlet 362 and outlet 368 , respectively.

Referring now to FIG. 7 , there is shown one embodiment of a once-through type horizontal heat recovery air recuperator (HRAR) of the present invention incorporating fifteen (15) HRAR modules 300 (e.g., triple wide modules 300 in five sections, but not limited thereto), hereinafter generally designated as recuperator 400 . It can be seen that the recuperator 400 is disposed downstream of a gas turbine (not shown) on the exhaust-gas side thereof. The recuperator 400 has an enclosing wall 402 which forms a heating-gas duct 403 through which flow can occur in an approximately horizontal heating-gas direction indicated by the arrow 370 and which is intended to receive the exhaust-gas from the gas turbine. HRAR modules 300 are serially connected to each other and positioned in the heating-gas duct 403 . In the exemplary embodiment of FIG. 7 , five modules 300 are shown serially connected together, but one module 300 , or a larger number of modules 300 may also be provided without departing from the essence of the present invention.

The modules 300 , common to the respective embodiment illustrated in FIGS. 2 through 5 , contain a number of first tube rows 201 A- 201 F and second tube rows 201 G- 201 L, respectively, which are disposed one behind the other in the heating-gas direction. Each tube row of first tube rows 201 A- 201 F in turn is connected to a respective tube row of second tube rows 201 G- 201 L via a corresponding link 320 as described above with respect to FIGS. 5 and 6 and are disposed next to one another in the heating-gas direction. In FIG. 7 , only a single vertical heat exchanger tube 201 can be seen in each tube row 201 A- 201 L.

Heat exchanger tubes 201 of a respective common tube row 201 A- 201 F of the first tube row for each module 300 are each connected in parallel to a respective common first inlet header 205 A- 205 F, forming a first single-row header-and-tube inlet assembly, discussed above and shown in FIGS. 2 through 5 . Also, the heat exchanger tubes 201 of the first common tube rows 201 A- 201 F of each module 300 are each connected to a respective third common discharge header 305 A- 305 F, thus forming a single-row header-and-tube inlet assembly for each row 201 A- 201 F. Likewise, heat exchanger tubes 201 of second common tube rows 201 G- 201 L of a second once-through heating area are each connected in parallel to a respective common inlet third header 305 G- 305 L, forming a single-row header-and-tube discharge assembly for each row 201 G- 201 L, and are also each connected in parallel to a respective common discharge second header 205 G- 205 L, thus forming a second single-row header-and-tube discharge assembly for each row 201 G- 201 L. Each respective third common discharge header 305 A- 305 F is connected to a respective common inlet header 305 G- 305 L via a respective link pipe 320 .

Each first single-row header-and-tube inlet assembly of each module 300 is connected to an inlet manifold 215 via a first link pipe 220 A- 220 F, thus forming a first stepped component thickness with the single row header-and-tube inlet assembly 230 . Also, each second single-row header-and-tube discharge assembly of each module 300 is connected to a discharge manifold 225 via a second link pipe 220 G- 220 L, thus forming a second stepped component thickness with the single row header-and-tube discharge assembly 240 .

Each outlet 368 of a second manifold 225 of one module 300 is connected to an inlet 362 of a first manifold 215 of a successive module 300 via a coupler 374 , but for the first and last modules 300 connected in series. Flow medium W enters the first stepped component thickness with the single row header-and-tube inlet assembly 230 of a first module 300 , flows in parallel though the tube rows 201 A- 201 F, and exits the first stepped component thickness with the single row header-and-tube inlet assembly 230 of the first module through third link pipe 320 A- 320 L into the second stepped component thickness with the single row header-and-tube discharge assembly 240 of the first module 300 and exits via the discharge manifold 225 . Flow medium W then travels into an inlet 362 of a second module 300 connected to the outlet 368 of the first module 300 . The inlet 362 and outlet 368 are connected with coupler 374 .

A significant improvement in the flexibility of large recuperators can be achieved with an assembly of heat exchanger sections or modules 300 constructed using the configuration described above in FIG. 7 as a “stepped component thickness with single row header-and-tube assembly”. This new assembly uses single-row header-and-tube-assemblies throughout the recuperator to form the fluid circuits arranged in counter-flow required for a large recuperator 400 , as illustrated in FIG. 7 .

The large recuperator described with respect to FIG. 7 accommodates partial air flow during startup to minimize venting of stored air. The heat exchanger modules are completely drainable and ventable. Vents (not shown) may provided at every high point (e.g., using threaded plugs) for future maintenance purposes. Lower manifolds 215 , 225 may be fitted with drain piping and drain valves terminating outside the casing or heat gas duct 403 .

The heat exchanger modules 300 are completely shop-assembled with finned tubes, headers, roof casing, and top support beams. Heat exchanger modules 300 are installed from the top into the steel structure. Tube vibration is controlled by a system of tube restraints 380 , as best seen with reference to FIG. 5 , proven in large heat recovery steam generator (HRSG) service. Using the combination of these two concepts will allow the production of flexible recuperators for large-scale applications capable of rapid heating and cooling and a large number of start-stop cycles. For example, FIG. 8 is a schematic view illustrating the recuperator assembly of FIG. 7 employed in a compressed air energy storage (CAES) system having a capacity of around 150-300 MW.

A basic layout of a CAES power plant is shown in FIG. 8 . The plant comprises a cavern 1 for storing compressed air. The recuperator 400 as described with reference to FIG. 7 preheats the compressed air from the cavern 1 before it is admitted to an air turbine 3 . The recuperator 400 preheats the compressed air from cavern 1 via an exhaust gas flow flowing in an opposite direction, such as from a gas turbine 5 , for example. Following heat transfer to the cold compressed air from the cavern 1 , the flue gas leaves the system through the stack 7 . The airflow to the recuperator 400 and to the air turbine 3 is controlled by valve arrangements 8 and 9 , respectively.

While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.