JP3764576B2 - Gas turbine intake cooling system - Google Patents

Description

【００２７】
この表１では、各熱交換器１６ａ〜１６ｄにおける冷水流量の値を、計画点に対する百分率で示してある。計画点においては、冷熱源１７から供給される冷水流量は均等に各々１００％であることを示している。また表１のカッコ内の値は、各熱交換器１６ａ〜１６ｄに最大限通水可能な流量割合を示す。つまり、本実施形態では、各熱交換器１６ａ〜１６ｄへ通水することができる最大流量の半分が計画点として定めてある。
【００２８】
そして、表１に示したように、運用例１は、例えば１つの熱交換器１６ａの冷水流量の要求値がゼロ、すなわち運用を停止した場合についてのものである。この場合には、残りの空気冷却器１６ｂ，１６ｃ，１６ｄへ通水する冷水流量はそれらの空気冷却器１６ｂ，１６ｃ，１６ｄの出口側に設けた流量調整弁２２ｂ，２２ｃ，２２ｄによって制御され、均等に分配される。つまり、残りの空気冷却器１６ｂ，１６ｃ，１６ｄへの冷水流量値は１３３％で同一である。
【００２９】
また、運用例２は、例えば１つの熱交換器１６ａの冷水流量の要求値が計画点よりも大きい値を示した場合についてのものである。この例では熱交換器１６ａの冷水流量の要求値が１６０％であり、この場合には、残りの熱交換器１６ｂ，１６ｃ，１６ｄへ通水する冷水流量は、それらの熱交換器１６ｂ，１６ｃ，１６ｄの各出口側にに設けた流量調整弁２２ｂ，２２ｃ，２２ｄによって制御され、均等に分配される。つまり、残りの空気冷却器１６ｂ，１６ｃ，１６ｄへの冷水流量値は８０％で同一である。
【００３０】
さらに運用例３は、例えば２つの熱交換器１６ａおよび６ｂの冷水流量の要求値が計画点よりも大きい値を示した場合についてのものである。すなわち、これらの熱交換器１６ａおよび６ｂへ通水する冷水流量が例えば１２０％の場合には、残りの熱交換器１６ｃ，１６ｄへ通水する冷水流量は、それらの熱交換器１６ｃ，１６ｄの出口にある流量調整弁２２ｃ，２２ｄによって制御され、均等に分配される。つまり、残りの空気冷却器１６ｃ，１６ｄの冷水流量値は８０％で同一である。
【００３１】
このように、本実施形態のガスタービン吸気冷却システムによれば、熱交換器１６ａ〜１６ｄの任意の１台以上からの冷水流量要求値が変化した運用においても、供給する冷水流量はその全量を一定に保ったまま、残りの熱交換器１６ａ〜１６ｄへ流量を均等にして通水することができる。したがって、１つの冷熱源１７を各軸の圧縮器１２ａ〜１２ｄの空気導入部１２ａ１〜１２ｄ１に効率よく導いて常に効率よく空気冷却することが可能となり、従来のように１対１で吸気冷却システムを各軸の熱交換器に対応させた場合に比して、多軸型のガスタービン発電プラントへの吸気冷却について、冷却媒体および熱源を効率よく運用することができる。
【００３２】
しかも、本実施形態では、計画点の流量（１００％）を各熱交換器１６ａ〜１６ｄに流通し得る冷却媒体の最大流量（２００％）の範囲内としてあり、また運転時において増減する流量割合は最大流量（２００％）の範囲内で均等な分配とするので、冷水の流量増大の要請に対してもエロージョンなどの可能性が生じることなく対応することができ、常に的確な冷却機能が発揮できるものとなる。
【００３３】
さらに、本実施形態では、空気導入部１２ａ１〜１２ｄ１がフィルタ２３の下流側に吸込み空気ａを素通しできる第１流路２４と、吸込み空気ａの熱交換を行う第２流路２５とを並列配置で備え、かつ第１流路２４および第２流路２５を通過する空気の量を、熱交換要求量に応じてダンパ２６によって調整できるようにしたので、季節あるいは時間に応じて熱交換要求量が変化する場合に、各流路２４，２５への空気流量を変化させて熱交換器１６ａ〜１６ｄと空気との接触量を調整することができる。例えば、流量抵抗を伴う第２流路２５での流量を低減させ、第１流路２４による空気流量を相対的に多くすることで、運転効率を向上させることも可能である。
【００３４】
なお、以上の実施形態では冷却媒体として冷水を用いたが、これに限らず、他の液体、気体等の種々の冷却媒体を適用できることは勿論である。また、４軸構成のガスタービンプラントへの適用例について説明したが、３以下または５以上の多軸構成のものについても適宜実施することができる。さらに、計画点等についても種々の設定変更が可能である。
【００３５】
また、共通な冷熱源を１つとしたが、２以上についても適用できる。
【００３６】
【発明の効果】
以上で詳述したように、本発明に係るガスタービン吸気冷却システムによれば、多軸型のガスタービン発電プラントへの吸気冷却についても、冷却媒体および熱源を効率よく運用することができるとともに、冷却媒体の流量増大の要請に対してもエロージョンなどの可能性が生じることなく対応することができ、常に的確な冷却機能が発揮できる等の優れた効果が奏される。
【図面の簡単な説明】
【図１】本発明に係るガスタービン吸気冷却システムの一実施形態を示す系統図。
【図２】図１に示した圧縮機の空気導入部の構成を詳細に示す構成図。
【図３】従来のガスタービン発電プラントの概略構成図。
【図４】ガスタービン回転トルクと大気空気温度との関係を示すグラフ。
【図５】夏季などのある１日の時刻と、大気温度、電力需要の関係を示すグラフ。
【符号の説明】
１ 回転軸
２ 圧縮機
４ ガスタービン
５ 発電機
３ 燃焼器
１０ａ，１０ｂ，１０ｃ，１０ｄ ガスタービンプラント
１１ａ，１１ｂ，１１ｃ，１１ｄ 回転軸
１２ａ，１２ｂ，１２ｃ，１２ｄ 圧縮機
１２ａ１，１２ｂ１，１２ｃ１，１２ｄ１ 空気導入部
１３ａ，１３ｂ，１３ｃ，１３ｄ 燃焼器
１４ａ，１４ｂ，１４ｃ，１４ｄ ガスタービン
１５ａ，１５ｂ，１５ｃ，１５ｄ 発電機
１５ａ，１５ｂ，１５ｃ，１５ｄ 発電機
１６ａ，１６ｂ，１６ｃ，１６ｄ 空気冷却器
１７ 冷熱源
１８ 冷凍機
１９ 供給配管
１９ａ 母管部分
２０ 戻し配管
２０ａ 統合配管部分
２０ｂ 枝管部分
２１ 冷水循環ポンプ
２２ａ，２２ｂ，２２ｃ，２２ｄ 流量調整弁
２３ フィルタ
２４ 第１流路
２５ 第２流路
２６ ダンパ
ａ 吸込み空気[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an intake air cooling system applied to a gas turbine plant, and more particularly to a gas turbine intake air cooling system that can efficiently operate a cold heat source when applied to a multi-shaft gas turbine plant.
[0002]
[Prior art]
For example, as shown in FIG. 3, a gas turbine power plant has a configuration in which a compressor 2, a gas turbine 4, and a generator 5 are connected to a common rotating shaft 1, and a plurality of combustors 3 are provided around the rotating shaft 1. It is said that.
[0003]
In the compressor 2, atmospheric air is sucked into high-pressure air, the high-pressure air is sent to the combustor 3 to burn the fuel, and the generated combustion gas is supplied to the gas turbine 4 as a high-temperature working gas. . In the gas turbine 4, the energy of the high-temperature working gas is replaced with rotational torque, and the generator 5 is rotationally driven based on the rotational torque to generate an electrical output. The high-temperature working gas supplied to the gas turbine 4 is sent to the atmosphere again as exhaust after changing energy to rotational torque.
[0004]
Since such a gas turbine power plant is easy to start and stop quickly, it can exhibit great convenience against load fluctuations, and its application has increased in recent years.
[0005]
By the way, it is known that the output of a gas turbine power plant is greatly affected by the difference in intake air temperature. That is, as shown in FIG. 4, the air temperature in the atmosphere and the gas turbine output are in an inversely proportional relationship. For example, when the gas turbine output when the air temperature is 15 ° C. is designed as 100%, the winter season Thus, the output is improved when the air temperature is 10 ° C., and conversely, the output is decreased when the air temperature is 30 ° C. as in summer.
[0006]
In addition, when the relationship between the atmospheric temperature and the power demand is observed by taking the summer day as an example, the power demand is relatively low in the time period from midnight to morning as shown in FIG. In the meantime, it has doubled the demand for electricity at midnight. Therefore, it is desirable to cool the intake air to the compressor 2 and keep the gas turbine output high at high temperatures such as in the summer when electric power demand doubles.
[0007]
In response to these demands, various studies on gas turbine intake cooling systems have been conducted so far. For example, a heat exchanger is provided in the air introduction part of the compressor, and the intake air is cooled and compressed by this heat exchanger. Techniques for feeding to a machine have been proposed (Japanese Patent Laid-Open No. 6-307258, Japanese Utility Model Laid-Open No. 6-87639, etc.).
[0008]
[Problems to be solved by the invention]
A gas turbine plant that is commonly used is a multi-shaft gas turbine plant in which a plurality of gas turbines are provided on different axes. In the conventional proposals in which the above-described gas turbine intake air cooling system is applied to such a multi-shaft gas turbine plant, a plurality of heat exchangers provided in the air introduction portion of the compressor of each shaft are provided in correspondence with each other. A cooling heat source is provided, a cooling medium is supplied from each cooling heat source to each heat exchanger, and cooling control is individually performed for each air introducing portion of the compressor of each shaft. That is, it is set as the structure which incorporated the gas turbine intake-air cooling system for every compressor of each axis | shaft.
[0009]
However, in a multi-shaft gas turbine plant, at least a single-shaft gas turbine is usually stopped for maintenance such as periodic inspection. Therefore, in the configuration in which the gas turbine intake cooling system is incorporated for each compressor of each shaft, the heat exchange medium supplied to the heat exchanger provided on the inlet side of the compressor and its cold heat source perform the intake air cooling operation. When it is not performed, it is left without being used elsewhere, and there is a problem that operational efficiency decreases.
[0010]
In addition, when observing the cooling medium supplied to the heat exchanger, such as chilled water, in general, in gas turbine plants, the flow rate of chilled water into the heat transfer tubes has been maximized in order to reduce the heat transfer area from the compact orientation of the equipment. I am designing. Increasing the cold water flow rate beyond this design value involves the possibility of erosion and the like. Therefore, conventionally, when it is necessary to increase the cooling operation in the heat exchanger for some reason, for example, it is necessary to stop the gas turbine of one or more shafts and perform the high output operation with the gas turbines of the other shafts. Even in this case, it is impossible to increase the flow rate of chilled water flowing through the heat exchanger in order to enhance the cooling operation of the intake air cooling system. Improvement was requested.
[0011]
The present invention has been made in view of such circumstances, and for cooling the intake air into a multi-shaft gas turbine power plant, the cooling medium and the heat source can be efficiently operated, and the flow rate of the cooling medium can be increased. It is an object of the present invention to provide a gas turbine intake air cooling system that can respond to a request without causing a possibility of erosion or the like and can always exhibit an accurate cooling function.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a heat exchanger is applied to a multi-shaft gas turbine plant including a plurality of gas turbines, and an air introduction portion of a compressor provided on each shaft is provided. An intake air cooling system for a gas turbine that cools intake air by each heat exchanger and sends it to each compressor, and supplies one or more common cooling heats for supplying a cooling medium to each heat exchanger The cooling medium is distributed from the cold heat source to the cooling medium inlet of each of the heat exchangers via a branched supply pipe, and the cooling medium after heat exchange from the cooling medium outlet of each of the heat exchangers Are combined with each other via an integrated return pipe and returned to the cold heat source.
[0013]
According to a second aspect of the present invention, in the gas turbine intake air cooling system according to the first aspect, the distribution amount when the entire amount of the cooling medium supplied from the cold heat source is evenly distributed to all the heat exchangers is used as the heat exchange. The flow rate at this planned point is set within the range of the maximum flow rate of the cooling medium that can be circulated through each heat exchanger, and during operation, each heat exchanger has a fixed rate from the flow rate at the planned point. A gas turbine intake air cooling system is provided that supplies a cooling medium with a flow rate that is increased or decreased.
[0014]
According to a third aspect of the present invention, in the gas turbine intake air cooling system according to the second aspect, when the required value of the coolant flow rate from one or more heat exchangers changes, the total supply amount from the cold heat source is kept constant. Provided is a gas turbine intake air cooling system in which the remaining supply amount is evenly distributed to other heat exchangers while being held.
[0015]
According to a fourth aspect of the present invention, in the gas turbine intake air cooling system according to any one of the first to third aspects, the air introduction part of each compressor has a first flow path through which the intake air can pass and a heat of the intake air. A gas turbine intake air cooling system comprising a second flow path for exchanging in parallel arrangement, and adjusting an amount of air passing through the first flow path and the second flow path in accordance with a required heat exchange amount Provide a system.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a gas turbine intake air cooling system according to the present invention will be described with reference to FIGS. 1 and 2. In addition, this embodiment shows the example of application to the gas turbine power plant of 4 axis | shaft structure. FIG. 1 is a system diagram showing the system configuration, and FIG. 2 is a configuration diagram showing in detail the configuration of the air introduction section of the compressor shown in FIG.
[0017]
As shown in FIG. 1, in this embodiment, compressors 12a to 12d, gas turbines 14a to 14d, and generators 15a to 15d are provided on the respective rotary shafts 11a to 11d in the four-shaft gas turbine plants 10a to 10d. The combustors 13a to 13d are connected around the rotary shafts 1a to 11d, respectively.
[0018]
The atmospheric air sucked by the compressors 12a to 12d becomes high-pressure air, and is sent to the combustors 13a to 13d to be used for fuel combustion. The generated combustion gas is used as a high-temperature working gas in the gas turbine 4. To be supplied. Each of the gas turbines 14a to 14d replaces the energy of the high-temperature working gas with the rotational torque, and rotationally drives the generators 15a to 15d based on the rotational torque, thereby generating an electrical output.
[0019]
In this, air coolers 16a to 16d are respectively installed in the air introduction portions 12a1 to 12d1 of the compressors 12a to 12d, and a common cold heat source 17 is provided for the air coolers 16a to 16d. ing. That is, the cold heat source 17 is configured as a tank that keeps cold water below the freezing point temperature by, for example, heat exchange with the refrigerator 18 that operates during or after the intake air cooling operation, thereby obtaining cold heat.
[0020]
And this one cold heat source 17 is each connected with the cooling medium inlet of the heat exchangers 16a-16d of each axis | shaft via the branch type supply piping 19, and cold water as a cooling medium is connected to each heat exchanger 16a-16d. Are to be distributed. The cooling medium outlets of the heat exchangers 16 a to 16 d are connected to the cooling heat source 17 via the integrated return pipe 20, and the chilled water after heat exchange in the heat exchangers 16 a to 16 d is returned to the return pipe 20. After flowing from the branch pipe part 20 b into the integrated pipe part 20 a and joining together, it returns to the cold heat source 17. A cold water circulation pump 21 is provided in the mother pipe portion 19 a of the supply pipe 19, and flow rate adjusting valves 22 a to 22 d are provided in the branch pipe portions 20 b of the return pipe 20, respectively.
[0021]
The air introduction portions 12a1 to 12d1 of the compressors 12a to 12d provided with such heat exchangers 16a to 16d are, as shown in FIG. 24 and a second flow path 25 for exchanging heat of the intake air a are arranged in parallel, and the amount of air passing through the first flow path 24 and the second flow path 25 is determined according to the heat exchange request amount. The damper 26 can be adjusted.
[0022]
Next, the operation will be described.
[0023]
In this embodiment, each distribution amount when the entire amount of cold water supplied from the cold heat source 17 is evenly distributed to all the heat exchangers 16a to 16d is determined as a planned point of flow rate in each of the heat exchangers 16a to 16d. is there. The flow rate at this planned point is within the range of the maximum flow rate of the cooling medium that can flow through each of the heat exchangers 16a to 16d. At the time of operation, it is possible to supply a cooling medium having a flow rate that is increased or decreased by a fixed rate from the flow rate at the planned point in accordance with the demands of the heat exchangers 16a to 16d.
[0024]
More specifically, when the required value of the coolant flow rate from one or more of the heat exchangers 16a to 16d changes, the remaining supply amount with the total supply amount from the cold heat source 17 held constant. Are evenly distributed to the other heat exchangers 16a to 16d.
[0025]
Table 1 shows a specific example of this operation.
[0026]
[Table 1]

[0027]
In Table 1, the value of the chilled water flow rate in each of the heat exchangers 16a to 16d is shown as a percentage of the planned point. In the plan point, it has shown that the flow volume of the cold water supplied from the cold-heat source 17 is each 100% equally. Moreover, the value in the parenthesis of Table 1 shows the flow rate ratio at which water can flow through the heat exchangers 16a to 16d as much as possible. That is, in this embodiment, half of the maximum flow rate that can be passed to each of the heat exchangers 16a to 16d is determined as a planned point.
[0028]
And as shown in Table 1, the example 1 of operation is a thing about the case where the required value of the cold water flow rate of one heat exchanger 16a is zero, ie, operation is stopped, for example. In this case, the flow rate of chilled water passing through the remaining air coolers 16b, 16c, and 16d is controlled by the flow rate adjusting valves 22b, 22c, and 22d provided on the outlet sides of the air coolers 16b, 16c, and 16d, Evenly distributed. That is, the cold water flow rate values to the remaining air coolers 16b, 16c, and 16d are the same at 133%.
[0029]
Moreover, the operation example 2 is for a case where the required value of the cold water flow rate of one heat exchanger 16a shows a value larger than the planned point, for example. In this example, the required value of the chilled water flow rate of the heat exchanger 16a is 160%. In this case, the chilled water flow rate to flow through the remaining heat exchangers 16b, 16c, 16d is the heat exchangers 16b, 16c. , 16d are controlled by flow control valves 22b, 22c, 22d provided on the respective outlet sides, and are evenly distributed. That is, the chilled water flow rate values to the remaining air coolers 16b, 16c, and 16d are the same at 80%.
[0030]
Furthermore, the operation example 3 is a case where the required value of the cold water flow rate of the two heat exchangers 16a and 6b shows a value larger than the planned point, for example. That is, when the flow rate of chilled water flowing to these heat exchangers 16a and 6b is 120%, for example, the flow rate of chilled water flowing to the remaining heat exchangers 16c and 16d is the same as that of the heat exchangers 16c and 16d. It is controlled by the flow rate adjusting valves 22c and 22d at the outlet and is evenly distributed. That is, the chilled water flow rate values of the remaining air coolers 16c and 16d are the same at 80%.
[0031]
As described above, according to the gas turbine intake air cooling system of the present embodiment, even in an operation in which the required value of the chilled water flow rate from any one or more of the heat exchangers 16a to 16d has changed, While keeping constant, water can be passed through the remaining heat exchangers 16a to 16d with equal flow rates. Accordingly, it is possible to efficiently guide one cooling heat source 17 to the air introducing portions 12a1 to 12d1 of the compressors 12a to 12d of the respective shafts so that the air cooling is always performed efficiently. As compared with the case where the heat exchanger of each axis is used, the cooling medium and the heat source can be efficiently operated for the intake air cooling to the multi-shaft type gas turbine power plant.
[0032]
Moreover, in the present embodiment, the flow rate (100%) at the planned point is within the range of the maximum flow rate (200%) of the cooling medium that can flow through each of the heat exchangers 16a to 16d, and the flow rate ratio that increases or decreases during operation Can be evenly distributed within the range of the maximum flow rate (200%), so it is possible to respond to the demand for increased flow rate of chilled water without the possibility of erosion, etc., and always exhibit an accurate cooling function. It will be possible.
[0033]
Furthermore, in this embodiment, the air introduction parts 12a1 to 12d1 are arranged in parallel with the first flow path 24 through which the suction air a can pass through the downstream side of the filter 23 and the second flow path 25 that performs heat exchange of the suction air a. The amount of air passing through the first flow path 24 and the second flow path 25 can be adjusted by the damper 26 according to the heat exchange request amount, so that the heat exchange request amount according to the season or time Can change the amount of contact between the heat exchangers 16a to 16d and the air by changing the air flow rate to the flow paths 24 and 25. For example, it is possible to improve the operation efficiency by reducing the flow rate in the second flow path 25 with flow resistance and relatively increasing the air flow rate in the first flow path 24.
[0034]
In the above embodiment, cold water is used as the cooling medium. However, the present invention is not limited to this, and various cooling media such as liquid and gas can be applied. Moreover, although the application example to the gas turbine plant of 4 axis | shaft structure was demonstrated, it can implement suitably also about the thing of 3 or less or 5 or more multi-shaft structure. Furthermore, various setting changes can be made for the planned points and the like.
[0035]
Moreover, although the common cold-heat source was made into one, it can apply also about two or more.
[0036]
【The invention's effect】
As described in detail above, according to the gas turbine intake cooling system according to the present invention, the cooling medium and the heat source can be efficiently operated for intake air cooling to the multi-shaft gas turbine power plant, It is possible to respond to a request for an increase in the flow rate of the cooling medium without causing the possibility of erosion and the like, and an excellent effect such as that an accurate cooling function can always be exhibited.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of a gas turbine intake cooling system according to the present invention.
FIG. 2 is a configuration diagram showing in detail a configuration of an air introduction unit of the compressor shown in FIG. 1;
FIG. 3 is a schematic configuration diagram of a conventional gas turbine power plant.
FIG. 4 is a graph showing the relationship between gas turbine rotational torque and atmospheric air temperature.
FIG. 5 is a graph showing the relationship between the time of a certain day such as summer, the atmospheric temperature, and power demand.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotating shaft 2 Compressor 4 Gas turbine 5 Generator 3 Combustors 10a, 10b, 10c, 10d Gas turbine plants 11a, 11b, 11c, 11d Rotating shafts 12a, 12b, 12c, 12d Compressors 12a1, 12b1, 12c1, 12d1 Air introduction part 13a, 13b, 13c, 13d Combustor 14a, 14b, 14c, 14d Gas turbine 15a, 15b, 15c, 15d Generator 15a, 15b, 15c, 15d Generator 16a, 16b, 16c, 16d Air cooler 17 Cold source 18 Refrigerator 19 Supply pipe 19a Main pipe part 20 Return pipe 20a Integrated pipe part 20b Branch pipe part 21 Chilled water circulation pumps 22a, 22b, 22c, 22d Flow rate adjusting valve 23 Filter 24 First flow path 25 Second flow path 26 Damper a Suction air

Claims (4)

It is applied to a multi-shaft gas turbine plant including a plurality of gas turbines, each of which includes a heat exchanger in an air introduction portion of a compressor provided on each shaft, and the intake air is cooled by each heat exchanger to An intake air cooling system for a gas turbine that is respectively sent to a compressor, comprising one or a plurality of common cooling heat sources for supplying a cooling medium to each of the heat exchangers, from which the cooling medium of each of the heat exchangers While distributing the cooling medium to the inlets through the branch type supply pipes, the cooling medium after the heat exchange from the cooling medium outlets of the heat exchangers is joined through the integrated return pipe to the cooling heat source. A gas turbine intake air cooling system characterized by returning. 2. The gas turbine intake air cooling system according to claim 1, wherein each distribution amount in a case where the entire amount of the cooling medium supplied from the cold heat source is evenly distributed to all the heat exchangers is used as a plan point of the flow rate in each of the heat exchangers. The flow rate at the planned point is within the range of the maximum flow rate of the cooling medium that can be circulated through the heat exchangers, and the cooling medium has a flow rate that is increased or decreased by a certain percentage from the flow rate at the planned points in the heat exchangers during operation A gas turbine intake air cooling system characterized by supplying 3. The gas turbine intake air cooling system according to claim 2, wherein when the required value of the coolant flow rate from one or more heat exchangers changes, the remaining supply amount from the cold heat source is kept constant, A gas turbine intake air cooling system characterized in that a supply amount is evenly distributed to other heat exchangers. 4. The gas turbine intake air cooling system according to claim 1, wherein the air introduction portion of each compressor has a first flow path through which the intake air can pass and a second flow path that performs heat exchange of the intake air. Are arranged in parallel, and the amount of air passing through the first flow path and the second flow path is adjusted according to the amount of heat exchange required.

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