JP5251311B2 - Power generation system - Google Patents

Description

  The present invention relates to a power generation system having a constant pressure once-through boiler that operates while maintaining a furnace outlet steam pressure at a predetermined reference pressure.

  Generally, there are a constant pressure operation method and a transformer operation method as an operation method of a boiler which is a steam generation source of a thermal power plant. The constant pressure operation method is an operation method in which, for example, a constant pressure once-through boiler is used to keep the main steam pressure of the boiler constant, and the steam flow rate is adjusted by opening and closing the steam control valve at the turbine inlet (for example, Patent Document 1). . On the other hand, the transformer operation method is a method of controlling the output by adjusting the amount of steam entering the turbine by changing the main steam pressure generated in the boiler, for example, using a transformer once-through boiler, keeping the opening of the steam control valve constant. (For example, Patent Document 2).

  In recent years, thermal power plants have been in charge of peak loads and middle loads, and high-efficiency operation with fluctuating loads has been demanded. With this, thermal power plants with constant pressure operation using a constant pressure once-through boiler are required. However, it is required to be able to cope with variable loads with high efficiency.

  FIG. 4 is a graph showing the relationship between the steam turbine load and the steam pressure in the constant pressure operation method. The steam turbine load (generator output) on the horizontal axis is shown as a percentage of the rated load (rated output). When the steam turbine load is 0%, the generator connected to the steam turbine is inserted into the power system, and the steam turbine (generator) is rotating in synchronization with the power system in a no-load state. is there. In this state, the furnace outlet steam pressure PW of the boiler is already maintained at the reference pressure PW0, and the superheater outlet steam pressure PT is also maintained at the predetermined pressure PT1. The reference pressure PW0 of the furnace outlet steam pressure PW is, for example, a supercritical pressure of 24.1 [MPa].

  In the start-up region A1 where the steam turbine load is 0% to 25%, the opening of the steam control valve (CV) is opened to start loading, and the boiler throttle valve bypass (BTB) valve and boiler throttle (BT) valve are turned on. An opening operation is performed, and finally, the superheater outlet steam pressure PT is increased to its reference pressure PT0 as being fully opened. The reference pressure PT0 of the superheater outlet steam pressure PT is equal to or slightly lower than 24.1 [MPa] of the reference pressure PW0 of the furnace outlet steam pressure PW, for example.

  In the constant pressure region A2 where the steam turbine load is 25% to 100% or more, both the furnace outlet steam pressure PW and the superheater outlet steam pressure PT of the boiler are held at a constant pressure (reference pressures PW0 and PT0). Open the opening of the steam control valve (CV) to increase or decrease the load.

  Thus, the pressure of the steam supplied to the steam turbine (superheater outlet steam pressure PT) is kept constant at the reference pressure PT0 (substantially supercritical pressure), and the power generation amount of the generator connected to the steam turbine is Because it is approximately proportional to the product of the pressure of the steam flowing into the steam turbine and the opening of the steam control valve, the steam control valve must be opened when the load required by the steam turbine (the amount of power generated by the generator) is low. It is necessary to narrow down the degree greatly. As a result, the efficiency of the steam turbine decreases due to the pressure loss of the steam on the downstream side of the steam control valve as the opening of the steam control valve is reduced.

  In addition, since the influence of adiabatic expansion appears significantly as the throttle width of the opening of the steam control valve increases, the temperature difference of the steam flowing into the steam turbine also increases. Therefore, it is necessary to restrict the rate of change of the steam temperature due to the temperature difference. In this case, the rate of change of the opening of the steam control valve is also restricted. As a result, it may not be possible to follow the load required by the steam turbine.

  Therefore, the applicant uses a constant pressure once-through boiler to maintain the boiler outlet steam pressure PW at the reference value PW0 and to prevent the steam turbine efficiency from being lowered when the opening of the steam control valve is adjusted. A power generation system employing a superheater transformer operation system with variable pressure was developed and filed as Japanese Patent Application No. 2007-91784.

  FIG. 5 is a graph showing the relationship between the steam turbine load and the steam pressure in the superheater transformer operation system in which the superheater outlet steam pressure is variable in Japanese Patent Application No. 2007-91784. The steam turbine load (generator output) on the horizontal axis is shown as a percentage of the rated load (rated output). The difference from the case of the constant pressure operation method shown in FIG. 4 is that a transformation region A3 is provided between the start region A1 and the constant pressure region A2, and the superheater outlet steam pressure PT changes according to the steam turbine load in the transformation region A3. It is made to let you. The transformation region A3 is a predetermined low load region (15% to 75%) in which the steam turbine load is less than the rated load.

  The start-up region A1 is set to a steam turbine load of 0% to 15%, and is narrower than a conventional steam turbine load of 0% to 25%. In the transformation region A3, the boiler throttle valve bypass (BTB) valve and the boiler throttle (BT) valve are opened to change the superheater outlet steam pressure PT according to the load in the range of 15% to 75% of the steam turbine load. Let In the constant pressure region A2 where the steam turbine load is 75% to 100% or more, both the furnace outlet steam pressure PW and the superheater outlet steam pressure PT are maintained at a constant pressure (reference pressures PW0 and PT0), and the steam control valve is used. Increase the load by opening the opening of (CV).

As described above, in Japanese Patent Application No. 2007-91784, while the opening degree of the boiler throttle bypass valve and the boiler throttle valve is adjusted in accordance with the steam turbine load in the transformation region A3, the furnace outlet steam pressure PW is maintained. The superheater outlet steam pressure PT is changed so as to decrease when the steam turbine load is small, thereby reducing the operation width of the steam control valve. Thereby, the pressure loss of the steam on the downstream side of the steam control valve is reduced, and the efficiency of the steam turbine is improved. In addition, the operating range of the steam control valve is reduced, the temperature change of the steam flowing into the steam turbine is reduced, and the life of the steam turbine is extended. Furthermore, the restriction of the operation width of the steam control valve is eliminated, the flow rate of the steam flowing into the steam turbine can be freely adjusted, and the followability to the required power generation amount of the steam turbine is improved.
JP 9-320504 A Japanese Patent Laid-Open No. 5-87303

  In Japanese Patent Application No. 2007-91784, the efficiency of the steam turbine can be improved, the life of the steam turbine can be extended, and the followability to the required power generation amount of the steam turbine can also be improved. However, there is still room for improvement in improving plant efficiency. That is, in the transformation region A3, the furnace outlet steam pressure PW is maintained at the reference value PW0 because the boiler is a constant pressure once-through boiler, but when the steam turbine load is small, the superheater outlet steam pressure PT is reduced. Therefore, when the steam turbine load is small, it is not necessary to maintain the furnace outlet steam pressure PW at the reference value PW0. Thus, since the furnace outlet steam pressure PW is maintained at the reference value PW0 even when the turbine load is small, there is still room for improvement in terms of improving the plant efficiency.

  An object of the present invention is to provide a power generation system that can further improve plant efficiency when a superheater outlet steam pressure is transformed using a constant pressure once-through boiler.

A power generation system according to the invention of claim 1 includes a furnace of a constant pressure once-through boiler that is supplied with fuel, water, and air and burns the fuel to generate steam, a superheater that superheats steam generated in the furnace, and the furnace A boiler throttle valve for adjusting steam supplied to the superheater provided in a main steam pipe between the superheater, a boiler throttle valve bypass valve provided by bypassing the boiler throttle valve, and the superheater A steam turbine that drives a generator connected to the steam that is superheated by the steam generator, and a steam flow that is provided in a main steam pipe between the superheater and the steam turbine, and that controls the flow rate of steam supplied to the steam turbine. a steam control valve, the load of the steam turbine is sliding pressure outlet steam pressure of the superheater according to the load of the steam turbine in a low load region determined in advance under the rated load, the steam turbine A superheater outlet steam pressure controller for constant pressure operation constant pressure to the rated load a predetermined outlet steam pressure of the superheater from a state in which the load exceeds the low-load region of the superheater outlet steam pressure controller When performing transformer operation, adjust the opening of the boiler throttle valve and the boiler throttle valve bypass valve to reduce the steam pressure at the furnace outlet to a reduced pressure reference pressure within an allowable range less than the reference pressure of the constant pressure once- through boiler. A furnace outlet steam pressure control device for controlling the furnace outlet steam pressure to a reference pressure of the constant pressure once-through boiler when the superheater outlet steam pressure control device performs a constant pressure operation of the outlet steam pressure of the superheater; It is provided with.

The power generation system according to a second aspect of the present invention is the power generation system according to the first aspect, wherein the furnace outlet steam pressure control device controls the furnace outlet steam pressure to the constant pressure once-through boiler when the furnace outlet steam pressure is controlled to be reduced. The pressure reduction control is performed so that the pressure is between the reference pressure and the low pressure alarm value.

  According to the present invention, when the transformer outlet steam pressure is reduced so that the superheater outlet steam pressure is reduced, the furnace outlet steam pressure is controlled to be reduced to a reduced pressure reference pressure within an allowable range less than the reference pressure of the constant pressure once-through boiler. The flow rate of water supplied to the furnace can be reduced. Therefore, the shaft power of the boiler feed water pump that supplies the feed water flow rate can be reduced, and the plant efficiency can be improved.

  In addition, the pressure reduction control of the furnace outlet steam pressure is controlled so that the furnace outlet steam pressure is a pressure between the reference pressure of the constant pressure once-through boiler and the low pressure alarm value. Is possible.

  FIG. 1 is a configuration diagram of a power generation system according to an embodiment of the present invention. Fuel, water, and air are supplied to the furnace 11 of the constant pressure once-through boiler, and the furnace 11 burns the fuel to evaporate the water in the water pipe and generate steam. The fuel is a gaseous fuel such as LNG or LPG, a solid fuel such as coal or biofuel, or a liquid fuel such as petroleum, and is burned by the burner of the furnace 11. Moreover, the condensed water condensed by the condenser mentioned later is supplied to the water pipe in the furnace 11 by a boiler feed pump, and the water pipe in the furnace 11 is circulated by the boiler circulation pump 12.

  The steam generated in the furnace 11 is led to the first superheater 15a and the second superheater 15b via the boiler throttle valve (BT valve) 13 or the boiler throttle valve bypass valve (BTB valve) 14. A temperature reducer 16 is provided between the first superheater 15a and the second superheater 15b, and the superheated steam superheated by the first superheater 15a is cooled by the temperature reducer 16. The superheated steam whose temperature is adjusted by the second superheater 15 b is guided to the high-pressure steam turbine 17 a of the steam turbine 17 through the main steam stop valve (MSV) 35 and the steam control valve (CV) 36. The steam that has finished work in the high-pressure steam turbine 17a is re-superheated by the reheater 18 and guided to the intermediate-pressure steam turbine 17b, and the steam that has finished work in the medium-pressure steam turbine 17b is guided to the low-pressure steam turbine 17c. . The high-pressure steam turbine 17 a, the intermediate-pressure steam turbine 17 b, and the low-pressure steam turbine 17 c drive the generator 19. The steam that has finished work in the low-pressure steam turbine 17c is condensed in the condenser 20 and returned to water.

  The water condensed in the condenser 20 is supplied to the low pressure feed water heater 22 and the deaerator 23 by the condensate pump 21, and the feed water deaerated by the deaerator 23 is supplied to the high pressure feed water heater by the boiler feed pump 24. 25. The feed water heated by the high-pressure feed water heater 25 is pumped to the temperature reducer 16 via the superheater spray pressure control valve (ISPR valve) 26 and the superheater spray control valve 27. The temperature reducer 16 controls the temperature of the superheated steam by injecting water into the superheated steam. However, in order to inject water, it is necessary to make the feed water pressure higher than the steam pressure. Therefore, by opening and closing the movable nozzle 28, the pressure of the water supplied to the temperature reducer 16 is maintained higher than the superheated steam pressure. Further, the water pumped to the economizer 29 through the movable nozzle 28 is guided to the furnace 11 by the boiler circulation pump 12 and is used again as steam.

  Next, the boiler starting extraction valve (BE valve) 30 and the boiler starting extraction valve bypass valve (BEB valve) 31 are used in the process of starting the boiler. When the boiler is started, the boiler throttle valve 13, the boiler throttle valve bypass valve 14, the boiler starting bleed valve 30, and the boiler starting bleed valve bypass valve 31 are all closed. First, after the burner of the furnace 11 of the boiler is ignited, the boiler starting extraction valve bypass valve 31 is opened, and the steam temperature from the furnace 11 is raised while supplying steam from the furnace 11 to the steam separator (WS) 32. In this case, the water separated by the steam / water separator 32 is discharged to the condenser 20 through the water drain valve (WD valve), and the pressure control of the steam / water separator 32 by the control valve (SP valve) 34. I do. When the furnace outlet steam temperature reaches a predetermined temperature (for example, 250 ° C.), the boiler start bleed valve bypass valve 31 is closed and the boiler start bleed valve 30 is opened to switch the valves. Further, when the furnace outlet steam temperature reaches a predetermined temperature (for example, 400 ° C.), the boiler starting bleed valve 30 is closed and the boiler throttle valve bypass valve 14 is opened.

  Next, the furnace outlet steam pressure control device 37 adjusts the furnace outlet steam pressure PW by adjusting the opening degree of the boiler throttle valve 13 and the boiler throttle valve bypass valve 14. On the other hand, the superheater outlet steam pressure controller 38 adjusts the superheater outlet steam pressure PT by adjusting the fuel flow rate, feed water flow rate, and air flow rate supplied to the boiler furnace 11. The fuel flow rate and the air flow rate are adjusted by adjusting the fuel flow rate and the air flow rate supplied to the burner of the furnace 11. The feed water flow rate is adjusted by controlling the rotation speed of the boiler feed water pump 24.

  The superheater outlet steam pressure control device 38 performs a transformation operation that changes the outlet steam pressure PT of the superheater 15 in a predetermined low load region where the load of the steam turbine 17 is less than the rated load. Further, from the state where the load of the steam turbine 17 exceeds the low load range to the rated load, constant pressure operation is performed at a constant pressure (reference pressure PT0) at which the outlet steam pressure PT of the superheater is determined in advance.

  Then, when the superheater outlet steam pressure control device 38 performs the transformation operation, the furnace outlet steam pressure control device 37 sets the furnace outlet steam pressure PW to a reduced pressure reference pressure within an allowable range less than the reference pressure PW0 of the constant pressure once-through boiler. Reduce pressure. Further, when the superheater outlet steam pressure control device 38 performs the constant pressure operation of the superheater outlet steam pressure PT, the furnace outlet steam pressure PW is controlled to the reference pressure PW0 of the constant pressure once-through boiler.

  FIG. 2 is a graph showing the relationship between the steam turbine load and the steam pressure in the power generation system according to the embodiment of the present invention. The steam turbine load (generator output) on the horizontal axis is shown as a percentage of the rated load (rated output). The difference from the superheater transformer operation method shown in FIG. 5 is that in the start-up region A1 and the transform region A3, the furnace outlet steam pressure PW is changed to a decompression reference pressure PW1 within an allowable range less than the reference pressure PW0 of the constant pressure once-through boiler. The decompression control is performed.

  In the start-up region A1 where the steam turbine load is 0% to 15%, the furnace outlet steam pressure PW is maintained at the reduced pressure reference pressure PW1. The decompression reference pressure PW1 is a pressure within an allowable range less than the reference pressure PW0 of the constant pressure once-through boiler, as will be described later. In a state where the steam turbine load is 0%, the generator 18 connected to the steam turbine 17 is inserted into the power system, and the steam turbine (generator) rotates in synchronization with the power system in a no-load state. State.

  In the state where the steam turbine load is 0%, the boiler throttle valve 13 and the boiler throttle valve bypass valve 14 are fully closed, the boiler starting bleed valve 30 is open, and the control valve 34 is connected to the steam separator 32. The pressure is controlled. As a result, the superheater outlet steam pressure PT is maintained at the predetermined pressure PT1.

  In this starting area A1, the opening of the steam control valve 36 is opened to start taking a load, and when the steam turbine load becomes about 5%, the boiler starting bleed valve 30 and the control valve 34 are closed. When the boiler starting bleed valve 30 and the control valve 34 are closed, the furnace outlet steam pressure control device 37 opens the boiler throttle valve bypass valve 14 to maintain the furnace outlet steam pressure PW at the decompression reference pressure PW1 while the furnace 11 Is supplied to the superheater 15. On the other hand, the superheater outlet steam pressure control device 38 adjusts the fuel flow rate, feed water flow rate, and air flow rate supplied to the boiler furnace 11 to increase the superheater outlet steam pressure PT. This also increases the turbine load.

  When the turbine load becomes 15% or more and the transformation region A3 is 15% to 75% of the steam turbine load, the furnace outlet steam pressure control device 37 does not fully open the boiler throttle valve bypass valve 14, and the superheater outlet The steam pressure PT is maintained at an opening degree (for example, 50%) that does not increase rapidly. At this time, the opening degree of the boiler throttle valve bypass valve 14 is set so that the differential pressure between the pressure reduction reference pressure PW1 of the furnace outlet steam pressure PW and the superheater outlet steam pressure PT is within the allowable differential pressure of the boiler throttle valve 13. Adjust.

  By maintaining the opening of the boiler throttle valve bypass valve 14 at a constant opening (for example, 50%), the superheater outlet steam pressure PT gradually increases. Thereafter, when the turbine load increases to some extent, the furnace outlet steam pressure control device 37 starts to open the boiler throttle valve 13 while maintaining the furnace outlet steam pressure PW at the decompression reference pressure PW1.

  In this way, in the transformation region A3, the boiler outlet steam pressure control device 37 opens the boiler throttle valve bypass valve 14 and the boiler throttle valve 13 while the boiler outlet steam pressure PW is maintained at the pressure-reducing reference pressure PW1. In operation, the superheater outlet steam pressure control device 38 performs a transformation operation for changing the superheater outlet steam pressure PT in accordance with the steam turbine load in a range of 15% to 75% of the steam turbine load.

  Next, in the constant pressure region A2 where the steam turbine load is 75% to 100% or more, the furnace outlet steam pressure PW of the boiler is increased from the reduced pressure reference pressure PW1 to the reference pressure PW0, and the furnace outlet steam pressure PW is changed to the reference pressure PW0. While being held, the superheater outlet steam pressure PT is also held at the reference pressure PT0, and the operation proceeds to a constant pressure operation.

  When the turbine load approaches 75%, for example, when the turbine load becomes about 70%, the furnace outlet steam pressure control device 37 is configured to bypass the boiler throttle valve so that the boiler outlet steam pressure PW becomes the reference value PW0. The valve 14 and the boiler throttle valve 13 are opened and finally fully opened, and a constant pressure operation is performed in which the furnace outlet steam pressure PW becomes the reference value PW0 when the turbine load is 75% to 100%. Further, when the turbine load approaches 75%, the superheater outlet steam pressure control device 38 adjusts the fuel flow rate, the feed water flow rate, and the air flow rate to the furnace 11 to set the superheater outlet steam pressure PT to the reference pressure PT0. When the turbine load is 75% to 100%, constant pressure operation is performed in which the superheater outlet steam pressure PT becomes the reference pressure PT0.

  Next, FIG. 3 is an explanatory diagram of the reference value PW0 of the furnace outlet steam pressure PW, the decompression reference pressure PW1, the low pressure alarm value ANN, and the trip value TRIP due to the decrease in the furnace outlet steam pressure PW. For example, the constant pressure once-through boiler in which the reference value PW0 of the furnace outlet steam pressure PW is 24.1 [MPa], which is a supercritical pressure, has a low pressure alarm value ANN of 23.0 [MPa], and the furnace outlet The trip value TRIP due to the decrease in the steam pressure PW is 22.1 [MPa]. In order to operate the constant pressure once-through boiler in compliance with the low pressure alarm value ANN (23.0 [MPa]) and the trip value TRIP (22.1 [MPa]), the furnace outlet steam pressure PW is set to the low pressure alarm value ANN. It is sufficient to operate so as not to be less than (23.0 [MPa]). The allowable range ΔPW of the decompression control operation in this case is a range from the reference value PW0 (24.1 [MPa]) to the low pressure alarm value ANN (23.0 [MPa]).

  Therefore, in the embodiment of the present invention, when performing the pressure reduction operation of the superheater outlet steam pressure PT in the transformation region A3, the furnace outlet steam pressure PW is reduced to the low pressure alarm value ANN. The depressurization control is performed at the depressurization reference pressure PW1 within the allowable range ΔPW which is not less than (23.0 [MPa]). As the reduced pressure reference pressure PW1, for example, 23.6 [MPa] satisfying the reference value PW0 (24.1 [MPa]) to the low pressure alarm value ANN (23.0 [MPa]) is employed.

  According to the embodiment of the present invention, when the superheater outlet steam pressure PT is being transformed so that the superheater outlet steam pressure PT is small when the steam turbine load is small, the furnace outlet steam pressure PW is Since the pressure reduction control is performed at the pressure reduction reference pressure PW1 within the allowable range ΔPW that does not become the pressure low alarm value ANN (23.0 [MPa]) or less, the water supply supplied to the furnace 11 when the reduced furnace outlet steam pressure PW is covered. The flow rate can be reduced. That is, since the shaft power of the boiler feed water pump 24 that supplies the feed water flow rate can be reduced, plant efficiency can be improved as a whole.

  Further, the pressure reduction control of the furnace outlet steam pressure PW is controlled so that the furnace outlet steam pressure PW becomes a pressure between the reference pressure PW0 of the constant pressure once-through boiler and the low pressure alarm value ANN, so that the operation of the constant pressure once-through boiler is performed. Operation within the allowable range is possible.

The block diagram of the electric power generation system concerning embodiment of this invention. The graph which shows the relationship between the steam turbine load and steam pressure in the electric power generation system concerning embodiment of this invention. Explanatory drawing of the reference value PW0 of the furnace exit steam pressure PW, the pressure-reduction reference pressure PW1, the pressure low alarm value ANN, and the trip value TRIP in the electric power generation system concerning embodiment of this invention. The graph which shows the relationship between the steam turbine load and steam pressure in the constant pressure operation system of a constant pressure once-through boiler. The graph which shows the relationship between the steam turbine load and steam pressure in the superheater transformation operation system which made variable the superheater exit steam pressure of a constant pressure once-through boiler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Furnace, 12 ... Boiler circulation pump, 13 ... Boiler throttle valve, 14 ... Boiler throttle valve bypass valve, 15 ... Superheater, 16 ... Temperature reducer, 17 ... Steam turbine, 18 ... Reheater, 19 ... Generator 20 ... Condenser, 21 ... Condensate pump, 22 ... Low pressure feed water heater, 23 ... Deaerator, 24 ... Boiler feed pump, 25 ... High pressure feed water heater, 26 ... Superheater spray pressure control valve, 27 ... Superheater spray control valve, 28 ... movable nozzle, 29 ... economizer, 30 ... boiler start bleed valve, 31 ... boiler start bleed valve bypass valve, 32 ... steam separator, 33 ... water drain valve, 34 ... Control valve, 35 ... main steam stop valve, 36 ... steam control valve, 37 ... furnace outlet steam pressure control device, 38 ... superheater outlet steam pressure control device

Claims (2)

A furnace of a constant pressure once-through boiler that is supplied with fuel, water, and air to burn the fuel and generate steam;
A superheater that superheats steam generated in the furnace;
A boiler throttle valve that is provided in a main steam pipe between the furnace and the superheater and adjusts steam supplied to the superheater;
A boiler throttle valve bypass valve provided to bypass the boiler throttle valve;
A steam turbine for driving a generator connected to the steam superheated by the superheater; and
A steam control valve that is provided in a main steam pipe between the superheater and the steam turbine and controls a flow rate of steam supplied to the steam turbine;
In a predetermined low load region where the load of the steam turbine is less than the rated load, the outlet steam pressure of the superheater is transformed according to the load of the steam turbine, and the load of the steam turbine exceeds the low load region. From the state to the rated load, the superheater outlet steam pressure control device that performs constant pressure operation at a constant pressure that determines the outlet steam pressure of the superheater in advance,
When the superheater outlet steam pressure control device performs a transformer operation, the opening degree of the boiler throttle valve and the boiler throttle valve bypass valve is adjusted to allow the furnace outlet steam pressure to be less than the reference pressure of the constant pressure once-through boiler. When the superheater outlet steam pressure control device performs a constant pressure operation of the outlet steam pressure of the superheater, the furnace outlet steam pressure is controlled to the reference pressure of the constant pressure once-through boiler. And a furnace outlet steam pressure control device. When the furnace outlet steam pressure control is performed to reduce the furnace outlet steam pressure, the furnace outlet steam pressure is reduced so that the furnace outlet steam pressure is a pressure between a reference pressure of the constant pressure once-through boiler and a low pressure alarm value. The power generation system according to claim 1, wherein the power generation system is controlled.

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