Patent Application
20140112759
The subject matter disclosed herein relates to thermal control of gas turbine casings and, more particularly, to flow control devices and systems for preferentially heating or cooling gas turbine casings.
In gas turbines, maintaining a desired radial clearance between the tips of the rotating blades of the turbine (sometimes called “buckets”) and the facing interior surfaces of the casing is important to performance of the turbine and endurance of the parts. The radial clearance can vary, for example, during transient operation such as start up or stoppage when rotational speed is changing. Also, temperature differences can have an effect on the clearance, not only during such transient operation as individual components are experiencing temperature change, but also during steady state operation as substantial heat is transferred to the turbine section casing internally by hot gas flowing from the combustor section. Casings are commonly constructed from multiple, somewhat non-uniform, arcuate portions arranged circumferentially around the turbine section and attached together, for example, at flanged edges. Accordingly, the circumferentially non-uniform configuration leads to an uneven thermal response around the casing, and non-roundness and local stress concentration can occur as the temperature of the casing changes.
Various strategies have been used be used to control the tip/casing clearance. For example, in some gas turbines, air impingement cooling is used on the outside of the turbine casing to remove heat from the casing, thereby maintaining a more uniform temperature distribution. In such systems an external blower supplies ambient air to manifolds distributed around the casing. Use of such systems incurs capital and operational costs, and also impacts net turbine efficiency.
Achieving a relatively uniform and suitably high heat transfer coefficient across the large, non-uniform, non-standard casing surfaces can be a challenge using such external air impingement. Accordingly, adjustable mounts have been proposed for fine tuning the distance between the casing outer surface and the opposing manifold plate. U.S. Pat. No. 8,123,406 discloses such an adjustable manifold system.
To achieve high heat transfer rates, some gas turbines use manifold plates facing the casing with many small air outlet holes and short nozzle to surface distances. Use of such relatively small impingement cooling holes correspondingly dictates a relatively high differential pressure drop across the holes, thereby requiring cooling air supplied at a higher pressure. Consequently, a higher pressure blower may be needed adding further capital and operational cost, and further negative impact on gas turbine net efficiency. Also, external blowers of the types above can only provide air to the casing at or near room temperature, whereas heating (rather than cooling) of the casing might be desired during some operation conditions. For example, during start up as the mass of the casing is cool and the buckets begin rotating in the hot combustor flow, the tip clearance may be smaller than desired, or the tips may even undesirably contact the inner casing or a shroud element on the inner casing.
In some systems, gas is extracted from the compressor section to cool portions of the turbine section. U.S. Pat. No. 7,690,885 discloses a gas turbine with such compressor gas extraction. Extracted cooling gas passes through plenums and baffles attached to a shroud support, arranged radially outward of a shroud that surrounds the rotating blades or the turbine, to cool the shroud's outer surface. The gas then follows different paths through the shroud to form a film cooling layer along the shroud's inner surface. However, further improvements in thermal management of turbine casings could still be made.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
According to certain aspects of the disclosure, a device for directing gas impingement to an inner casing of a gas turbine may include a plate configured for attachment to the outer surface of the inner casing. The plate has a first surface opposing the inner casing when the plate is attached to an area of the inner casing and a second surface opposite the first surface. The plate defines a plurality of holes through the plate from the first surface to the second surface. The holes are arranged with a predetermined non-uniform distribution in the plate corresponding to a desired preferential impingement pattern for providing non-uniform heat transfer from the area during operation of the gas turbine so as to control temperature of the inner casing across the area. Various options and modifications are possible.
According to certain other aspects of the disclosure, a gas turbine casing assembly may include an inner casing arranged around a central axis, the inner casing defining an opening therethrough in communication with an interior of the gas turbine, an outer casing arranged around the inner casing, and at least one plate attached to an outer surface of the inner casing. The plate has a first surface opposing the inner casing and having a second surface opposite the first surface. The plate defines a plurality of holes through the plate from the first surface to the second surface. The holes are arranged with a predetermined non-uniform distribution in the plate corresponding to a desired preferential impingement pattern for providing non-uniform heat transfer from the area during operation of the gas turbine so as to control temperature of the inner casing across the area. The plate and inner casing defines a thermal control gas flow path from radially outside of the plate through the holes in the plate and then through the inner casing into the interior of the gas turbine. As above, various options and modifications are possible.
According to other aspects of the disclosure, a gas turbine includes a compressor section, a combustion section downstream from the compressor section, and a turbine section downstream from the combustion section. The turbine section includes an inner casing arranged around a central axis, the inner casing defining an opening therethrough in communication with an interior of the turbine section, an outer casing arranged around the inner casing, and at least one plate attached to an outer surface of the inner casing. The plate has a first surface opposing the inner casing and a second surface opposite the first surface. The plate defines a plurality of holes through the plate from the first surface to the second surface. The holes are arranged with a predetermined non-uniform distribution in the plate corresponding to a desired preferential impingement pattern for providing non-uniform heat transfer from the area during operation of the gas turbine so as to control temperature of the inner casing across the area. The plate and inner casing define a thermal control gas flow path from radially outside of the plate through the holes in the plate and then through the inner casing into the interior of the turbine section. As noted above, various options and modifications are possible.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
The compressor section 112 may include an axial flow compressor in which a working fluid 100, such as ambient air, enters the compressor from the inlet section 111 and passes through alternating stages 113 of stationary vanes and rotating blades (shown schematically in
The combustion section 114 may include any type of combustor known in the art. A combustor casing 115 may circumferentially surround some or all of the combustion section 114 to direct the compressed working fluid 100 from the compressor section 112 to a combustion chamber 119. Fuel 101 is also supplied to the combustion chamber 119. Possible fuels include, for example, one or more of blast furnace gas, coke oven gas, natural gas, vaporized liquefied natural gas (LNG), hydrogen, and propane. The compressed working fluid 100 mixes with fuel 101 in the combustion chamber 119 where it ignites to generate combustion gases having a high temperature and pressure. The combustion gases then enter the turbine section 116.
In turbine section 116, sets of rotating blades (buckets) 124 are attached to shaft (rotor) 122, and sets of stationary blades (vanes) 126 are attached to the turbine section casing 120. As the combustion gases pass over the first stage of rotating blades 124, the combustion gases expand, causing the rotating blades 124 and shaft 122 to rotate. The combustion gases then flow to the next stage of stationary blades 126 which redirect the combustion gases to the next stage of rotating buckets 124, and the process repeats for the following stages until the combustion gases exit turbine section 116 via exhaust section 117.
Gas turbine 110 as schematically illustrated is a single shaft, single cycle turbine. However, it should be understood that such illustration is for convenience only; the present disclosure can be employed with two shaft turbines, combined cycle turbines, etc. Therefore, no limitation of the invention is intended by the turbine illustrated schematically in
Referring to
A contributor to the efficiency of gas turbines is the amount of air/exhaust gas leakage through the blade tip to casing shroud clearance 134. Due to the different thermal growth characteristics of turbine blades 124 and turbine casing 120, and forces created by rotation of the blades, clearances 134 can significantly change as the turbine transitions through transients from ignition to a base-load steady state condition.
As illustrated in
In the exemplary embodiment of
If desired, edges 150 of plates 140 may be partially or entirely sealed at an interface 156 with inner casing 121 so that air flow from the area 152 between the plates and the casing can only escape via holes 154 into the turbine interior, rather than by flowing around edges 150 of the plates. In such case, a sealing interface 156 may extend partially or entirely around plates 140. Such sealing interface 156 may have various forms, such as an interlocking flange 157 within a slot 159 in turbine inner casing, with or without a separate seal member, etc. Use of a sealing interface 156 can assist in controlling the thermal management of inner casing 121 so that it occurs substantially or completely via flow through holes 144 and 154 and/or occurs substantially via impingement.
Holes 144 may be positioned in an array. In an exemplary embodiment, the holes 144 may be spaced from each other in the range from about 0.1 to 2.0 inches, and individual holes 144 may be sized between about 0.025 and 0.250 inches. Thus a variety of hole sizes and densities is possible between plates or within a given plates. As shown in
The gap 164 between each plate 140 and inner casing 121 affects the heat transfer coefficient. In one embodiment, gap 164 is such that heat transfer occurs substantially via impingement cooling (perpendicular flow onto the surface of inner casing 121, rather than ducting across the surface). Too large of a gap can result in an undesirably low heat transfer coefficient where the heat transfer is substantially via ducting. Too little of a gap can result in both an undesirable and a non-uniform heat transfer coefficient. In an exemplary embodiment, a gap 164 of between about 0.1 and 2.0 inches provides a suitable heat transfer coefficient. However, gap 164 is not limited to this range and may be any distance that provides a suitable heat transfer coefficient. Also, it should be understood that gap 164 need not be uniform across the entire plate 140 or from plate to plate. Gap 164 can accordingly vary to match the casing shape, mass, temperature distribution, etc., as desired.
By maintaining gap 164 in the desired range, with the pressures experienced by a gas turbines and using gas extracted from compressor 112, impingement cooling can be achieved through substantially perpendicular flow through holes 144 in plates 140 onto the outer surface of inner casing 121. (See flow path 190 from space 125 through plate 140 into space 152, and through inner casing 121 into (and eventually out of) blades 126). By placement of holes 144 in desired locations and densities, with desired dimensions, a preferentially located heating or cooling of inner casing 121 can be achieved. In other words, inner casing 121 can have heat transferred to or from it in a non-uniform fashion, as dictated by the plate and hole designs. This arrangement can vary in different turbines, in different plates within the same turbine, in different installation locations of the same turbine, or in other ways. Thus, the hole arrangement can be made to accommodate a variety of desired heat transfer coefficients on the outer surface of the casing, in view of particular applications and functions in a given turbine. The design and the use of plates 140 are therefore flexible, providing benefits in many applications.
During start-up the extracted compressor gases will actually be warmer than inner casing 121. Therefore, during wind up until a steady state is achieved, the preferential thermal control achieved would be substantially the heating of the impinged areas of casing 121 opposing holes 144. At some point during wind-up and/or once steady state is achieved the extracted compressor gas will function to cool the impinged area. Accordingly, plates 140 can be considered preferential thermal control devices, operating at least substantially according to impingement rather than ducting, to heat or cool impinged areas of inner casing 121.
Referring to
Mount 142 may comprise an assembly of various components that include a threaded bore 166 in inner casing 121, a helicoil 168 in the bore, and a threaded member such as a screw 170 in the helicoil. A busing 172 is located around helicoil 168, and held in place by a pin 174. Bushing 172 fits within a circular flange 176 in plate 140 alignable with bore 166. Belleville springs 178 are held between two washers 180. This arrangement beneficially allows for some float between plate 140 and inner casing 121 during use of the turbine. However, other mounting structures could be used or substituted.
Mount assembly 142 therefore provides for improved plate 140 to inner casing 121 gap distance control and reduces the installation time when the plates are mounted to the casing, both during the initial fit-up and during subsequent re-installations. Relatively improved and tighter tolerances during the re-installations may also be maintained by the mounts 142. Spacers 182 may be provided on plate bottom surfaces 146 to assist in maintaining the desired gap 164. Spacers may contact indentations 184 on inner casing if desired, to ensure proper location.
The present disclosure is also directed to a related method of thermal control of a turbine casing that may include supplying compressor-extracted gas to a space outside a turbine inner casing and transferring the gas through holes in a plate attached to the outer casing. The holes are arranged with a predetermined non-uniform distribution to achieve a desired heat transfer via impingement on the inner casing surface. The method can be used to heat or cool the inner casing, and can be used during start-up or steady state operation. The plate and the hole distribution can also be considered at least a part of a means for providing preferential heat transfer with reference to the outer casing.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
