JP2019065811A - Power generation plant and method for operating the same - Google Patents

Abstract

To provide a power generation plant comprising a boiler feedwater heating boiler capable of improving power generation efficiency.SOLUTION: A power generation plant comprises a boiler 3 comprising an economizer 18 and a superheater 13, a steam turbine 5 to be driven by steam generated by the boiler 3, a power generator 37 to be driven by the steam turbine 5, a feedwater heating boiler 7 for heating feedwater to be supplied to the boiler 3, and a control unit 30 for controlling an amount of heat to be applied to the feedwater by the feedwater heating boiler 7. The control unit 30 controls the amount of heat so that an outlet water temperature of the economizer 18 is less than a saturation temperature, and a temperature of exhaust gas to be supplied to an exhaust gas treatment device is less than an upper limit temperature of an operation temperature of the exhaust gas treatment device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power plant including a feed water heating boiler for heating boiler feed water, and an operation method thereof.

  In a power plant that supplies steam generated by a boiler using fossil fuel such as coal or oil to a steam turbine to rotationally drive a steam turbine, and generates power with a generator by this rotary drive, improvement of power generation efficiency and fossil There is a need to reduce fuel consumption and further reduce environmental impact. Further reductions in environmental impacts include the reduction of carbon dioxide emissions that are being addressed worldwide. For example, Patent Document 1 discloses that power generation efficiency is improved by heating boiler feed water using steam or hot water obtained in a large incinerator.

Patent No. 3611327 gazette

  However, in Patent Document 1, the boiler feed water is heated by steam or hot water obtained in a large incinerator to improve the power generation efficiency, but there are operational restrictions associated with each device specification of the power plant, The effective utilization of the heat of the whole power plant has not been carried out, and further power generation efficiency improvement techniques are desired.

  On the other hand, biomass-derived biomass fuels such as wood-based, agricultural-based, and sludge-based take carbon dioxide in the growth process of biomass, and are therefore carbon neutral which does not emit carbon dioxide that is a global warming gas. Various uses are considered. For example, a power plant which performs co-firing in a boiler using fossil fuel and biomass fuel is being considered.

  However, good biomass fuels are expensive, and there is a problem in cost competitiveness with fossil fuels. In addition, since inexpensive biomass fuels contain a large amount of corrosive components, in actuality, only small amounts can be mixedly burned in the boiler. Furthermore, there is an upper limit to the combined combustion rate due to the technical constraints of the boiler fuel supply facility and the environmental device, and when the output of the boiler is low, the input amount of biomass fuel can not but be reduced.

This invention is made in view of such a situation, Comprising: It aims at providing the power generation plant provided with the boiler for boiler feed water heating which can improve power generation efficiency, and its operating method.
Further, according to the present invention, in the case of using carbon-neutral biomass fuel because of reduction of environmental impact, it is possible to increase consumption of biomass fuel to reduce consumption of fossil fuel and reduce carbon dioxide emissions. It aims at providing a power plant and its operation method.

In order to solve the above-mentioned subject, the power plant of the present invention and its operation method adopt the following means.
That is, a power plant according to the present invention comprises a boiler having an economizer and a superheater, a steam turbine driven by steam generated by the boiler, a generator driven by the steam turbine, and a discharge from the boiler An exhaust gas processing apparatus for treating the exhaust gas, a feed water heating boiler for heating the feed water supplied to the boiler, and a control unit for controlling a heating amount of the feed water by the feed water heating boiler; The control unit controls the heating amount such that the outlet water temperature of the economizer is less than the saturation temperature and the exhaust gas supplied to the exhaust gas treatment device is less than the upper limit temperature of the operating temperature of the exhaust gas treatment device. It features.

  By heating the feed water supplied to the boiler by the feed water heating boiler, the enthalpy (heat amount per unit flow rate) of the feed water supplied to the boiler is increased, the turbine efficiency is improved, and the power generation efficiency for fossil fuel energy ( Hereinafter, the power generation efficiency can be simply improved. Furthermore, since the heating amount of the feed water heating boiler is controlled so that the outlet water temperature of the economizer is less than the saturation temperature at which steaming does not occur, the feed water can be heated as much as possible. Here, it is preferable that the outlet water temperature of the economizer be a temperature close to the saturation temperature, that is, a temperature that is about several degrees Celsius (for example, 2 degrees Celsius) lower than the saturation temperature by about 10 degrees Celsius. As a result, the enthalpy of the water supply can be increased as much as possible so as not to vaporize the outlet water temperature of the economizer, the turbine efficiency can be improved and the power generation efficiency can be improved, and the fossil fuel input to the boiler can be reduced. It is possible to reduce the amount of carbon dioxide that is not carbon neutral.

  Furthermore, the power generation plant according to the present invention includes an exhaust gas treatment device for treating the exhaust gas discharged from the boiler, and the control unit is less than the upper limit temperature of the exhaust gas supplied to the exhaust gas treatment device and close to the upper limit temperature. The heating amount is controlled to be a temperature.

  In the exhaust gas processing apparatus such as the denitrification apparatus, the upper limit temperature of the supplied exhaust gas is defined. The heating amount of the feed water heating boiler can be controlled to be increased so that the exhaust gas temperature is lower than the upper limit temperature and close to the upper limit temperature. Here, the exhaust gas temperature less than the upper limit temperature and close to the upper limit temperature is, for example, several ° C (for example, 2 ° C.) to several tens of degrees over the upper limit temperature of the equipment installed downstream of the exhaust gas flow It is a temperature as low as about ° C. Since the temperature is lower than the upper limit temperature of the exhaust gas, the feed water can be heated as much as possible. Thereby, the enthalpy of the water supply can be increased, the turbine efficiency can be improved, and the power generation efficiency can be improved.

  Furthermore, in the power generation plant of the present invention, a feed water heater for extracting steam from the steam turbine to heat the feed water is provided, and the control unit reduces the amount of steam to be supplied to the feed water heater. It is characterized by

Since the feed water is heated by the feed water heating boiler, the amount of steam extracted from the steam turbine is reduced to increase the steam flow rate of the steam turbine within the specified range of mechanical limits of the steam turbine and increase the turbine output. Do. In addition, when the total amount of steam supplied from the boiler to the steam turbine is adjusted so as to obtain the same turbine output in comparing before and after reducing the amount of extracted steam, the amount of extracted air can be reduced by As the total steam flow can be reduced, turbine efficiency can be improved.
In particular, if the boiler is partially loaded, the amount of extracted steam should be zero, because even if the amount of steam flowing to the steam turbine is increased, it is sufficiently within the specified range of mechanical strength of the steam turbine. Can further improve the turbine efficiency.

  Furthermore, in the power generation plant according to the present invention, the control unit reduces the amount of extracted steam supplied to the feedwater heater when the feedwater inlet temperature of the economizer is higher than the economizer inlet feedwater set temperature by a predetermined value or more. It is characterized by

  Furthermore, the power generation plant according to the present invention includes at least two feed water heaters for extracting and supplying each steam from different positions of the steam turbine, and the control unit is configured to load the boiler and the feed water heating boiler. The present invention is characterized in that the timings at which the respective steams change the amount of extracted air supplied to the respective feed water heaters are made different based on the amount of heating the feed water.

  Furthermore, in the power plant of the present invention, the control unit controls the amount of extracted steam based on the strength of the turbine blade of the steam turbine.

  The specified range of mechanical strength of the steam turbine is the strength of the turbine blade. The strength of the turbine blade is designed to be resistant to the differential pressure applied to the front and back of the turbine blade, which is determined by the flow and pressure balance of the steam flowing inside the steam turbine. The pressure changes according to the amount of steam extracted. Therefore, the amount of steam extraction is controlled in consideration of the strength of the turbine blade. As a result, it is possible to reduce the amount of extracted air as much as possible in consideration of the strength of the turbine blade to reduce the total steam flow rate flowing to the steam turbine, thereby further improving the turbine efficiency.

  Furthermore, in the power generation plant of the present invention, the control unit controls the amount of heating of the feedwater by the steam generated in the feedwater heating boiler, the feedwater heating boiler includes a steam dump valve, and the feedwater heating When the pressure of the steam generated in the boiler is higher than a predetermined pressure, the steam dump valve discharges the excess steam.

  Furthermore, the power plant of the present invention includes a superheater spray that controls the temperature of the superheated steam supplied from the superheater, and the control unit controls the spray amount of the superheater spray based on the change amount of the heating amount. To control.

There is a possibility that the temperature of the overheated steam supplied from the superheater may fluctuate due to the change of the heating amount or the extraction amount of the feed water heating boiler. The temperature of the superheated steam is set within a specified value that is equal to or lower than the design temperature of a metal material (such as steam piping and turbine blades) used under high temperature and high pressure. By rapidly suppressing the temperature fluctuation of the superheated steam by the superheater spray, it is possible to suppress the deterioration and damage of the steam piping and the turbine blade.
In addition, when a boiler is provided with the reheater, it is preferable to control collectively the flow volume of the reheater spray which controls the temperature of the reheat steam supplied from a reheater.

  Furthermore, in the power generation plant of the present invention, a heat exchanger for feed water heating which exchanges heat between the steam generated in the feed water heating boiler and the feed water supplied to the boiler, and a feed water bypassing the feed water heating heat exchanger A bypass pipe and a feed water bypass valve provided in the feed water bypass pipe, the control unit controlling the temperature of the steam generated by the feed water heating boiler to the temperature of the feed water at the inlet of the feed water heat exchanger When the value is higher than the predetermined value, the feed water bypass valve is closed, and the feed water is heated by the steam generated in the feed water heating boiler.

  Further, in the power plant of the present invention, the feed water heating boiler is characterized by being a biomass boiler using biomass fuel as a main fuel.

  By setting the boiler for feed water heating as a biomass boiler using biomass fuel as a main fuel, it is possible to burn off the biomass fuel in the feed water heating boiler without mixing the biomass fuel in the boiler. Therefore, the use ratio of biomass fuel to fossil fuel burned in the boiler can be increased. In addition, inexpensive biomass fuel containing a corrosive component can be used without affecting combustion in the boiler main body, the amount of fossil fuel used can be reduced, and highly efficient power generation can be performed.

  Further, according to the power plant operation method of the present invention, a boiler having an economizer and a superheater, a steam turbine driven by steam generated by the boiler, a generator driven by the steam turbine, and the boiler An operating method of a power generation plant comprising an exhaust gas processing apparatus for treating exhaust gas discharged from a boiler, and a feed water heating boiler for heating feed water supplied to the boiler, wherein the outlet water temperature of the economizer is a saturation temperature The heating amount is controlled such that the amount of exhaust gas supplied to the exhaust gas processing device is less than the upper limit temperature of the operating temperature of the exhaust gas processing device.

  Furthermore, the method is characterized in that the amount of extraction of steam supplied to a feed water heater for heating the feed water is reduced by extracting steam from the steam turbine.

Since the feed water is heated to a temperature as high as possible using the feed water heating boiler, the turbine efficiency can be improved, and the amount of fossil fuel input to the boiler into which fossil fuel is input can be reduced. It is possible to reduce the amount of carbon dioxide that is not neutral.
Further, by setting the boiler for feed water heating as the biomass boiler, the biomass fuel is burned exclusively by the feed water heating boiler without co-firing the biomass fuel in the boiler, so that the use ratio of the biomass fuel can be increased.

FIG. 1 is a schematic configuration view showing a power generation plant according to an embodiment of the present invention. It is the figure which showed the temperature change by superheater spray. It is the figure which showed the opening degree of the high pressure extraction valve. It is the flowchart which showed starting control of the biomass boiler. It is a flowchart showing separation control of a biomass boiler. It is the graph which showed the amount of heating before and behind applying a biomass boiler. It is the graph which showed the power generation efficiency to fossil fuel energy before and behind applying a biomass boiler. It is the graph which showed the breakdown of the energy before and behind applying a biomass boiler.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
A power plant 1 according to an embodiment is shown in FIG. The power plant 1 includes a boiler 3, a steam turbine 5, and a biomass boiler (a boiler for feed water heating) 7.

  The boiler 3 is equipped with the burner 11 which forms a flame using fossil fuels, such as coal and oil, in the furnace 10 of the boiler main body 3a. The furnace wall forming the furnace 10 is a water-cooled wall 12 constituted by heat transfer tubes and fins, and the water heated by the water-cooled wall 12 is led to the steam drum 15. A water drum 14 is provided vertically below the water cooling wall 12. The water in the steam drum 15 is led to the water drum 14 by the circulation pump 20, and the water is supplied to the water cooling wall 12. In addition, although the subcritical pressure boiler which has a drum is made into an example in this embodiment, it is applicable also to the supercritical pressure boiler which does not have a drum.

  The flue gas generated by the flame of the burner 11 flows vertically upward of the furnace 10 and is led to the superheater 13. The reheater 17 and the economizer 18 are provided in this order on the downstream side of the flue gas flow of the superheater 13.

  Between the economizer 18 and the steam drum 15, an economizer outlet pipe 22 through which water after being heated by the economizer 18 flows is connected. The economizer outlet pipe 22 is provided with an economizer outlet temperature sensor 22T and an economizer outlet pressure sensor 22P. The measured values of the sensors 22T and 22P are sent to the control unit 30.

  A water supply pipe 24 for supplying water (water) is connected to the economizer 18. The feed water passing through the feed water pipe 24 is supplied to the economizer 18 after being heated by the steam generated by the biomass boiler 7 as described later. The water supply pipe 24 on the inlet side of the economizer 18 is provided with a temperature sensor 58T. The measured value of the temperature sensor 58T is sent to the control unit 30.

  A flue gas temperature sensor 25T for measuring the temperature of the flue gas after passing through the economizer 18 is provided on the downstream side of the flue gas flow downstream of the economizer 18. The measured value of the combustion exhaust gas temperature sensor 25T is sent to the control unit 30. The combustion exhaust gas after passing through the combustion exhaust gas temperature sensor 25T is conducted to a denitration device (not shown) provided at an intermediate position of the exhaust gas duct connected to the boiler main body 3a for removing NOx in the combustion gas. It is eaten.

  The denitration apparatus is a selective catalytic reduction denitration apparatus using ammonia, and the upper limit temperature (for example, about 400 ° C. to about 420 ° C.) is determined in relation to the catalytic reaction temperature. Therefore, based on the temperature of the combustion exhaust gas temperature sensor 25T, the temperature of the combustion exhaust gas is controlled by adjusting the amount of heat exchange in the boiler 3 by the control unit 30 so as not to exceed the upper limit temperature of the NOx removal device. The flue gas passing through the denitrification apparatus is, for example, a dust processing apparatus, induction fan not shown on the downstream side after SOx and the like are removed by a desulfurization apparatus (not shown) to remove SOx in combustion gas. Are provided as needed, and are discharged to the atmosphere from a chimney at the downstream end of the exhaust gas duct.

  The heater 13 is provided with a heater spray 27. By injecting water or steam from the superheater spray 27, the superheated steam flowing in the superheater 13 is quickly cooled and controlled to a predetermined temperature range. The water used in the superheater spray 27 is, for example, a part of the outlet water of the economizer 18. The water injection amount and injection timing of the superheater spray 27 are controlled by the control unit 30.

  Although the installation position of the superheater spray 27 is schematically shown in FIG. 1, a more specific installation position will be described with reference to FIG. As for what was shown by FIG. 2, the superheater 13 is provided with the primary superheater 13a, the secondary superheater 13b, and the tertiary superheater 13c, for example. The superheater sprays 27 are provided between the primary superheater 13a and the secondary superheater 13b and between the secondary superheater 13b and the tertiary superheater 13c, respectively, and water is introduced at these positions. It is injected to lower the superheated steam temperature stepwise. That is, water is sprayed at the outlet of the primary superheater 13a so as to reach the primary superheater outlet set temperature, and water is sprayed at the outlet of the secondary superheater 13b so as to reach the secondary superheater outlet set temperature. Thus, by performing water spraying and controlling steam temperature, each superheater outlet preset temperature is adjusted, and it is controlled so that the temperature of the main steam supplied to steam turbine 5 turns into a temperature of a predetermined range.

  Further, although not shown, a reheater spray may be provided for the reheater 17 as well. The control unit 30 also controls the water injection amount and the injection timing of the reheater spray.

  The superheated steam leaving the superheater 13 is led to the steam turbine 5 through the main steam piping 32 as shown in FIG. In the present embodiment, the steam turbine 5 includes, for example, a high pressure turbine 34, an intermediate pressure turbine 35, and a low pressure turbine 36. The generator 37 is rotationally driven by the rotational power generated by the turbines 34, 35, 36, and power generation is performed.

  The main steam pipe 32 is connected to the inlet of the high pressure turbine 34. A high pressure turbine outlet pipe 38 is connected to the exhaust side of the high pressure turbine 34. The downstream end of the high pressure turbine outlet pipe 38 is connected to the reheater 17 so that the steam which has performed a predetermined expansion in the high pressure turbine 34 to rotationally drive the turbine is introduced to the reheater 17. It has become.

  Between the steam outlet side of the reheater 17 and the intermediate pressure turbine 35, a reheated steam supply pipe 40 for supplying reheated steam to the intermediate pressure turbine 35 is provided.

  An intermediate pressure turbine outlet pipe 42 is connected to the exhaust side of the intermediate pressure turbine 35. The downstream end of the intermediate pressure turbine outlet pipe 42 is connected to the inlet of the low pressure turbine 36, and the steam which has performed predetermined expansion in the intermediate pressure turbine 35 and rotationally drives the turbine is guided to the low pressure turbine 36 It is supposed to be.

  A low pressure turbine outlet pipe 44 is connected to the exhaust side of the low pressure turbine 36. The downstream end of the low pressure turbine outlet pipe 44 is connected to a condenser 46. In the condenser 46, the steam is cooled to a vacuum and condensed and liquefied by a cooling water (not shown). The condensed water liquefied by the condenser 46 becomes feed water and is led to the low pressure feed water heater 50 by the condensate pump 48.

  In the present embodiment, for example, in the low pressure feed water heater 50, the low pressure steam introduced from the low pressure turbine 36 heats the feed water from the condensed water. The feedwater heated by the low pressure feedwater heater 50 is led to the first medium pressure feedwater heater 52a and the second medium pressure feedwater heater 52b through the feedwater pump 51, and the medium pressure extracted from the medium pressure turbine 35 It is heated by steam. The feedwater heated by each of the medium pressure feedwater heaters 52a and 52b is led to the first high pressure feedwater heater 54a and the second high pressure feedwater heater 54b.

The high pressure steam led to the first high pressure feed water heater 54a is led via the first high pressure extraction pipe 55a. The first high pressure extraction pipe 55 a is provided with a first high pressure extraction valve 56 a whose opening degree is controlled by the control unit 30.
The high pressure steam led to the second high pressure feed water heater 54b is led via the second high pressure extraction pipe 55b. The second high pressure extraction pipe 55 b is provided with a second high pressure extraction valve 56 b whose opening degree is controlled by the control unit 30.
In the present embodiment, as an example, since the first high pressure extraction pipe 55a is connected to the upstream side (high pressure side) of the high pressure turbine 34 than the second high pressure extraction pipe 55b, the first high pressure extraction pipe 55a The pressure of the high pressure steam to be discharged is higher than the pressure of the high pressure steam led by the second high pressure extraction pipe 55b.

  The opening degree of each high pressure extraction valve 56a, 56b with respect to the load of the boiler 3 is shown by FIG. 3 as an example of this embodiment. The map (load program) shown in FIG. 3 is stored in the storage unit of the control unit 30, and has a valve opening degree set in advance according to the load. As shown in the figure, when the load on the boiler 3 is 100%, both high pressure extraction valves 56a and 56b are fully closed. When the load is smaller than the predetermined value, both high pressure extraction valves 56a and 56b are fully opened. However, in the present embodiment, the controllability of heating of the water supply is improved by setting the load region for switching between full closing and full opening to be different for the first high pressure extraction valve 56a and the second high pressure extraction valve 56b. There is. Specifically, the first high pressure extraction valve 56a operates on the higher load side than the second high pressure extraction valve 56b. Thus, the bleed flow rate of high-pressure steam can be changed by the first high-pressure extraction valve 56a, and the shortage can be arbitrarily controlled in a wide range by changing the shortage by the second high-pressure extraction valve 56b. As described later, when the biomass boiler 7 is turned on, the high pressure extraction valves 56a and 56b are controlled to be closed regardless of the load of the boiler 3, instead of the map shown in FIG.

  The steam after heating the feed water by each feed water heater 50, 52a, 52b, 54a, 54b is, as shown by a broken line arrow in FIG. 1, sequentially the feed water heaters 50, 52a, 52b, 54a, It is sent to 54 b and finally recovered by the condenser 46.

  The feed water heated by the high-pressure feed water heaters 54 a and 54 b passes through the feed water pipe 24 and is led to the feed water heating heat exchanger 60. In the feed water heating heat exchanger 60, the feed water is heated by the steam led from the biomass boiler 7 to the heating heat transfer pipe 61. Between the biomass boiler 7 and the feed water heating heat exchanger 60, after passing through the heating steam supply pipe 62 for supplying steam to the heating heat transfer tube 61 and the heating heat transfer tube 61, it was drained A return pipe 64 for returning drain water to the biomass boiler 7 and a return pump 65 are provided.

  The heating steam supply pipe 62 includes a heating steam temperature sensor 62T for measuring the temperature of the heating steam, a heating steam pressure sensor 62P for measuring the pressure of the heating steam, and a heating for measuring the flow rate of the heating steam. Steam flow sensor 62F is provided. The measured values of the sensors 62T, 62P, 62F are sent to the control unit 30.

  A return pump 65 is provided in the middle of the return pipe 64 so that drain water is sent to the biomass boiler 7 by the return pump 65 and circulated between the biomass boiler 7 and the heat exchanger 60 for feed water heating. It has become.

  A feed water bypass pipe 67 is provided to bypass the feed water heating heat exchanger 60. The water supply bypass pipe 67 is provided with a water supply bypass valve 68 whose opening and closing is controlled by the control unit 30. The feed water bypass valve 68 is fully closed when the feed water heating heat exchanger 60 is used, and is fully opened when the feed water heating heat exchanger 60 is not used. The water supply pipe 24 on the upstream side of the water supply bypass pipe 67 is provided with a temperature sensor 57T that measures the temperature of the heat exchanger inlet for water supply heating. The measured value of the temperature sensor 57T is sent to the control unit 30.

  The biomass boiler 7 burns biomass fuel to generate steam. The output of the biomass boiler 7 is controlled by the control unit 30. Specifically, the control unit 30 controls the supply amount of biomass fuel, the flow rate of combustion air, the supply amount of generated steam, and the like to be input to the biomass boiler 7. Thus, by controlling the output of the biomass boiler 7 by the control unit 30, the heating amount of the feed water in the feed water heating heat exchanger 60 is controlled.

  The biomass boiler 7 is provided with a steam dump valve 72 whose opening degree is controlled by the control unit 30. When the pressure of the steam generated by the biomass boiler 7 becomes excessive, excess steam is discharged to the condenser 46 via the steam dump valve 72. However, the discharge destination of the steam is not limited to the condenser 46, and may be another cooling device or atmospheric discharge, for example. When steam and drain water circulating in the biomass boiler 7 run short, even if part of the condensate in the condenser 46 is supplied via a water supply line (not shown) upstream of the return pump 65 of the return pipe 64 good.

  The control unit 30 includes, for example, a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a computer readable storage medium, and the like. Then, a series of processes for realizing various functions are stored in the form of a program, for example, in a storage medium or the like in the form of a program, and the CPU reads this program into a RAM or the like to execute information processing and arithmetic processing. Thus, various functions are realized. The program may be installed in advance in a ROM or other storage medium, may be provided as stored in a computer-readable storage medium, or may be distributed via wired or wireless communication means Etc. may be applied. The computer readable storage medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory or the like.

The power plant 1 configured as described above operates as follows.
The superheated steam generated in the superheater 13 of the boiler 3 is led to the high pressure turbine 34 of the steam turbine 5 and is led to the reheater 17 after rotationally driving the high pressure turbine 34. The steam led to the reheater 17 is reheated by the boiler 3 and led to the medium pressure turbine 35 as reheated steam. The reheated steam is led to the low pressure turbine 36 to rotationally drive the low pressure turbine 36 after the intermediate pressure turbine 35 is rotationally driven. The generator 37 is rotationally driven by the rotational power thus obtained, and power generation is performed.

  The steam that has completed the work of rotationally driving the turbine by performing predetermined expansion in the low-pressure turbine 36 is condensed in the condenser 46, and sequentially passes through the feed water heaters 50, 52a, 52b, 54a, 54b as water supply. It is heated by doing. Thereafter, the feed water is further heated by the feed water heating heat exchanger 60 and is supplied to the economizer 18 of the boiler 3.

  The heating amount of the feed water in the feed water heating heat exchanger 60 is adjusted by controlling the output of the biomass boiler 7 by the control unit 30. Specifically, it is as follows.

<Control based on economizer outlet temperature>
It controls so that the outlet temperature of water after heating by the economizer 18 does not vaporize exceeding the saturation temperature. This achieves the highest possible feed water temperature while preventing the water at the outlet of the economizer 18 from becoming steam.
The control unit 30 obtains a saturation temperature T1 from the pressure measured by the economizer outlet pressure sensor 22P and the temperature measured by the temperature sensor 22T. Then, a temperature below the saturation temperature T1 within a predetermined value (for example, 2 ° C. to 10 ° C.) is set as the economizer outlet temperature set value T1 set, and the control unit 30 controls the biomass boiler 7 so that the economizer outlet temperature set value T1 set. Feedback control of the output of Thereby, the temperature of the water supply is made as high as possible so that the outlet water temperature of the economizer 18 is not vaporized, and the enthalpy of the water supply is increased as much as possible.

<Control based on combustion exhaust gas temperature>
In consideration of the upper limit temperature of the device installed on the downstream side of the combustion exhaust gas, in the present embodiment, control is performed so as not to exceed the upper limit temperature T2 determined from the catalytic reaction temperature of the NOx removal apparatus. Thereby, the highest possible feed water temperature is realized while maintaining the catalytic reaction of the NOx removal system.
The control unit 30 obtains a measured temperature of the combustion exhaust gas temperature sensor 25T and sets a temperature below the upper limit temperature T2 within a predetermined value (for example, 5 ° C. to several 10 ° C. (for example 50 ° C.)) as the combustion exhaust gas temperature set value T2 set. The control unit 30 performs feedback control of the output of the biomass boiler 7 so that the combustion exhaust gas temperature set value T2set is obtained. Thereby, the temperature of the water supply is made as high as possible so that the combustion exhaust gas passing through the economizer 18 does not exceed the upper limit temperature, and the enthalpy of the water supply is increased as much as possible.

  The control unit 30 controls the amount of heating (for example, the amount of steam, pressure, temperature, and heat output) from the biomass boiler 7 so as to satisfy both the control based on the economizer outlet temperature and the control based on the combustion exhaust gas temperature.

<Control of high pressure bleed valve>
As described above, while controlling the heating amount of the biomass boiler 7, the high pressure extraction valves 56a and 56b are further controlled to control the extraction amount of high pressure steam. Specifically, the control unit 30 controls the high pressure extraction valves 56a and 56b as follows.
When the biomass boiler 7 is not inserted, that is, when the feed water is not heated by the feed water heating heat exchanger 60, the high pressure extraction valve is applied according to the load of the boiler 3 according to the load program in the map shown in FIG. Control the opening degree of 56a, 56b.

  When the biomass boiler 7 is turned on, the high pressure extraction valves 56a and 56b are controlled to close, that is, to reduce the amount of high pressure steam extracted. Specifically, when the feed water is heated by the heat exchanger 60 for feed water heating by the biomass boiler 7, the amount of high pressure steam extracted corresponding to the amount of heat corresponding to the amount of heating is reduced. The heating amount from the biomass boiler 7 is controlled based on the above-mentioned economizer outlet temperature and control based on the flue gas temperature from the heating steam temperature sensor 62T, the heating steam pressure sensor 62P, and the heating steam flow rate sensor 62F. The control unit 30 calculates so as to satisfy both.

  When the heating amount by the biomass boiler 7 exceeds the extraction amount of high pressure steam, the high pressure extraction valves 56a and 56b are fully closed, and the extraction amount of high pressure steam is made zero. It is preferable to perform the timing which fully closes high-pressure extraction valve 56a, 56b at this time based on the control map which determined the relationship with the heating amount from the biomass boiler 7 beforehand.

  By reducing the amount of high pressure steam extracted from the high pressure turbine 34, the steam flow rate flowing to the high pressure turbine 34 can be increased within the specified range of mechanical strength to improve turbine efficiency. Here, when controlling the amount of high pressure steam supplied to the first high pressure feed water heater 54a and the second high pressure feed water heater 54b in the closing direction of the high pressure steam extraction valves 56a and 56b, the specified value range of mechanical strength is used. The strength of the turbine blades of the high pressure turbine 34 is taken into account. That is, the strength of the turbine blade is designed to be durable against the differential pressure applied to the front and back of the turbine blade. Since this differential pressure is determined by the flow-pressure balance of the high pressure steam passing through the high pressure turbine 34, the high pressure extraction valve 56a is taken into consideration of the load of the boiler 3 so that the differential pressure does not exceed the allowable value of the strength of the turbine blade. , 56b, that is, the amount of reduction of the amount of high pressure steam extracted is determined. For example, when the high pressure extraction valves 56a and 56b are fully closed, the turbine strength at the MCR point (the boiler maximum continuous evaporation amount) is taken into consideration. When the turbine strength is sufficient even if the high pressure extraction valves 56a and 56b are fully closed at the MCR point, the high pressure extraction valves 56a and 56b can be fully closed even when the load is 100%. When there is no margin in the turbine strength, the amount of decrease in the amount of high pressure steam extracted is determined in consideration of the turbine strength at 100% load, and the degree of opening of the high pressure extraction valves 56a, 56b is set.

<Control of superheater spray>
The control unit 30 controls the superheater spray 27 when the amount of heating of the biomass boiler 7 changes or when the amount of high pressure steam extracted by the high pressure extraction valves 56a and 56b changes. If the heating amount of the biomass boiler 7 changes (for example, the emergency stop of the biomass boiler 7 or the calorific value change of the biomass fuel), the temperature of the main steam leaving the superheater 13 may change. Quickly control the main steam temperature to the appropriate range. In addition, if the amount of high-pressure steam supplied to the first high-pressure water heater 54a and the second high-pressure water heater 54b changes, the balance between the superheater 13 and the reheater 17 may change. 27 to quickly control the main steam temperature and the reheat steam temperature to the appropriate value range. Where a reheater spray is provided, it is preferable to control in conjunction with the superheater spray 27. Therefore, when the feed water is heated by the biomass boiler 7, a large amount of cooling heat is required as compared to the case where the feed water is not heated by the biomass boiler 7, and the control range of the injection amount of the superheater spray 27 and the reheater spray It is more preferable that a heater spray 27 or a reheater spray having a control range of the injection amount corresponding thereto be adopted.

<Biomass boiler start control>
Next, start-up control of the biomass boiler 7 will be described using FIG. 4.
First, as shown in step S1, when the load on the boiler 3 is above a certain level, the biomass boiler 7 is stopped, and high-pressure bleed air is supplied to the first high-pressure feedwater heater 54a and the second high-pressure feedwater heater 54b. When the valves 56a and 56b are open and the water supply bypass valve 68 is open, the biomass boiler 7 is started as shown in step S2. Thereby, biomass fuel is supplied to the biomass boiler 7 to generate steam.

  Then, in step S3, the biomass boiler outlet steam temperature measured by the heating steam temperature sensor 62T provided in the heating steam supply pipe 62 flows into the water heating system heat exchanger 60 measured by the temperature sensor 57T. It is judged whether it is more than predetermined value alpha than feed water temperature to make. If the condition of step S3 is satisfied, the process proceeds to step S4. If the condition is not satisfied, step S3 is repeated and the start of the biomass boiler 7 is continued. The predetermined value α is determined by the heat transfer characteristics of the feed water heating heat exchanger 60. In order to reduce the predetermined value α, it is necessary to increase the heat transfer area of the feed water heating heat exchanger 60. Turn For example, the predetermined value α is set to 2 ° C. to 10 ° C., more preferably 2 ° C. to 5 ° C.

  In step S4, the feed water bypass valve 68 is closed to lead the feed water to the feed water heating heat exchanger 60. At this time, the high pressure bleed valves 56a and 56b remain open.

  The water supply pipe 24 is provided with a temperature sensor 58T that measures the water supply inlet temperature of the economizer 18. The measured value of the temperature sensor 58T is sent to the control unit 30. In step S5, it is determined whether the water inlet temperature of the economizer 18 measured by the temperature sensor 58T is equal to or higher than the set temperature by a predetermined value β. If the condition of step S5 is satisfied, the process proceeds to step S6. If the condition is not satisfied, step S5 is repeated to wait for the water inlet temperature of the economizer 18 to rise. The predetermined value β is such that the opening of the high pressure extraction valves 56a and 56b can be adjusted to be closed by the fact that the water supply inlet temperature of the economizer 18 exceeds the set temperature. When unstable fluctuation occurs in the heat exchange amount of the exchanger 60, it affects the opening degree control of the high pressure extraction valves 56a and 56b. For example, the predetermined value β is set at 2 ° C. to 5 ° C.

  In step S6, the high pressure extraction valves 56a and 56b are controlled to close. This reduces the amount of high pressure steam extraction and increases the steam flow of the steam turbine within the specified range of mechanical limits to increase turbine output. In addition, when the total amount of steam supplied from the boiler to the steam turbine is adjusted so as to obtain the same turbine output in comparing before and after reducing the amount of extracted steam, the amount of extracted air can be reduced by As the total steam flow can be reduced, turbine efficiency can be improved. By improving the turbine efficiency, the power generation efficiency with respect to the load of the boiler 3 is improved. Under the condition that the power generation output after heating to the water supply by the biomass boiler 7 does not change, the amount of fossil fuel input to the boiler 3 can be reduced, and the emission amount of carbon dioxide which is not carbon neutral can be reduced. As described above, the input of the biomass boiler 7 is completed, and the start control ends (step S7).

When the start-up control is completed, as described above, the heating amount of the biomass boiler 7, the amount of high pressure steam supplied to the first high pressure feed water heater 54a and the second high pressure feed water heater 54b, and The temperature of the steam is controlled to operate the boiler 3, the biomass boiler 7 and the steam turbine 5 appropriate for the load of the power plant 1.
The heating amount of the biomass boiler 7 is both control based on the economizer outlet temperature 22T and control based on the combustion exhaust gas temperature 25T from the heating steam temperature sensor 62T, the heating steam pressure sensor 62P, and the heating steam flow rate sensor 62F. Is controlled by the control unit 30 so as to satisfy
Also, the extraction of high pressure steam supplied to the first high pressure feed water heater 54a and the second high pressure feed water heater 54b is high pressure so that the differential pressure applied to the front and back of the turbine blade does not exceed the allowable value on the strength of the turbine blade. The bleed valves 56a and 56b are controlled in the closing direction by setting the opening degree.
Furthermore, when the heating amount of the biomass boiler 7 and the amount of high pressure steam extracted by the high pressure extraction valves 56a and 56b change, the temperature of the main steam is quickly controlled by the superheater spray 27 to a range of appropriate values.

<Biomass boiler separation control>
Next, separation control for separating the feedwater heating by the biomass boiler 7 will be described with reference to FIG.
First, as shown in step S11, when the load on the boiler 3 is above a certain level, the biomass boiler 7 is activated, the high pressure extraction valves 56a and 56b are closed, and the water supply bypass valve 68 is closed. When the biomass boiler 7 is stopped as shown in step S12.

  Then, in step S13, it is determined whether the water supply inlet temperature of the economizer 18 measured by the temperature sensor 58T is lower than a value obtained by adding a predetermined value β to the set temperature. If the condition of step S13 is satisfied, the process proceeds to step S14. If the condition is not satisfied, step S13 is repeated. The predetermined value β is such that the opening of the high pressure extraction valves 56a and 56b can be adjusted to open when the feed water inlet temperature of the economizer 18 exceeds the set temperature, and if the predetermined value β is decreased, the heat for feedwater heating When unstable fluctuation occurs in the heat exchange amount of the exchanger 60, it affects the opening degree control of the high pressure extraction valves 56a and 56b. For example, the predetermined value β is set at 2 ° C. to 5 ° C.

  In step S14, the high pressure extraction valves 56a and 56b are opened while the water supply bypass valve 68 is closed.

  In step S15, the biomass boiler outlet steam temperature measured by the heating steam temperature sensor 62T provided in the heating steam supply pipe 62 flows into the feed water heating heat exchanger 60 measured by the temperature sensor 57T. It is determined whether it is lower than a value obtained by adding a predetermined value α to If the condition of step S15 is satisfied, the process proceeds to step S16. If the condition is not satisfied, step S15 is repeated. The predetermined value α is determined by the heat transfer characteristics of the feed water heating heat exchanger 60. In order to reduce the predetermined value α, it is necessary to increase the heat transfer area of the feed water heating heat exchanger 60. Turn For example, the predetermined value α is set to 2 ° C. to 10 ° C., more preferably 2 ° C. to 5 ° C.

  In step S16, the feed water bypass valve 68 is opened with the high pressure extraction valves 56a and 56b kept open. Thus, the feed water bypasses the feed water heating heat exchanger 60 and stops the feed water heating by the biomass boiler 7. By the above, separation control of the biomass boiler 7 is completed (step S17).

  In FIG. 6 and FIG. 7, when feed water heating is performed by the biomass boiler 7 as in the present embodiment (after addition of the biomass boiler) and when feed water heating is not performed by the biomass boiler 7 as a comparative example (biomass boiler addition) An example of the effect with the above will be described.

  In FIG. 6, the horizontal axis represents the load of the boiler 3, and the vertical axis represents the heating amount provided to the water supply from the biomass boiler 7. As shown in FIG. 6, heat is supplied to the feed water by feed water heating by the biomass boiler 7. In the figure, the amount of heat given to the feed water when the boiler load is 100% is represented as a relative value with 1.0.

In FIG. 7, the horizontal axis represents the output of the power generation plant, and the power generation efficiency, which is the vertical axis, represents the power generation efficiency for fossil fuel energy input to the power generation plant. In the figure, the power generation efficiency before the addition of the biomass boiler at an output of 100% is represented as a relative value with 1.0. As can be seen from the figure, even if the boiler load changes, it can be seen that the power generation efficiency is higher after the addition of the biomass boiler than before the addition of the biomass boiler. In particular, when the boiler load is low, the rate of increase in the power generation efficiency is large. In this case, the turbine efficiency of the steam turbine decreases when the power generation output is small, but the effect of heating the feed water and the effect of reducing the amount of high-pressure steam extraction contribute significantly to the improvement of the turbine efficiency as the power generation output decreases. Because
The power generation efficiency in FIG. 7 is defined as (obtained electric energy) エ ネ ル ギ (energy of fossil fuel to be introduced). Also, turbine efficiency is defined as (obtained electrical energy) ÷ [(energy of steam flowing into the turbine) − (energy of steam flowing out of the turbine)].

  FIG. 8 shows the relationship between the electrical energy obtained by the power generation of the power plant 1 and the fuel energy to be input to the power plant 1 (the boiler 3 and the biomass boiler 7) and the breakdown. Here, the case where the load is, for example, 50% of the middle is compared. 8 (a) shows the biomass boiler 7 before installation, and FIG. 8 (b) shows the biomass boiler 7 after installation. When the electric energy obtained by the power generation before and after the addition of the biomass boiler 7 is the same amount, as shown in FIG. 8 (b) (after the addition of the biomass boiler 7), after the addition of the biomass boiler As for fuel energy, fossil fuel input is reduced, and carbon dioxide emissions that do not become carbon neutral can be reduced.

  Specifically, the steam generated by the biomass boiler 7 is used to heat the feed water supplied to the boiler 3, the amount of steam extracted from the steam turbine 5 is reduced (the amount of extracted steam reduced), and the steam is further supplied to the boiler 3 The fossil fuel to be input to the boiler 3 can be further reduced according to the energy change amount by heating the feed water to a temperature lower than the saturation temperature in a predetermined range (increase the feed water enthalpy), and carbon dioxide which does not become carbon neutral Emissions can be further reduced.

According to the embodiment described above, the following effects can be obtained.
By heating the feed water supplied to the boiler 3 by the biomass boiler 7, the enthalpy of the feed water supplied to the boiler 3 can be increased, the turbine efficiency can be improved, and the power generation efficiency can be improved. Furthermore, since the heating amount of the biomass boiler 7 is controlled so that the outlet water temperature of the economizer 18 is a temperature less than and close to the saturation temperature so as not to be vaporized, the water supply is heated as much as possible Can. Thereby, the enthalpy of the water supply can be increased, the turbine efficiency can be improved, and the power generation efficiency can be improved. As a result, when generating power equivalent to the amount of power generation before the improvement of the power generation efficiency, the fossil fuel to be input to the boiler 3 can be reduced, and the emission amount of carbon dioxide that is not carbon neutral can be reduced.

  Since the heating amount of the biomass boiler 7 is controlled so that the exhaust gas temperature is less than the upper limit temperature of the NOx removal apparatus and close to the upper limit temperature, the feed water can be heated as much as possible. Thereby, the enthalpy of the water supply can be increased, the turbine efficiency can be improved, and the power generation efficiency can be improved.

  Since the feed water is heated by the biomass boiler 7, the amount of steam extracted from the steam turbine 5 can be reduced. By comparing the amount of extracted air before and after reducing the amount of extracted air as the same power generation output, by reducing the amount of extracted air, the total flow rate of steam flowing to the steam turbine 5 is reduced within the specified range of mechanical strength, and the turbine efficiency is reduced. It can be improved. In particular, when the boiler 3 is partially loaded, even if the amount of steam flowing to the steam turbine is increased, the mechanical strength is sufficiently within the specified value range, so the amount of high pressure steam extracted is made zero. Thus, the turbine efficiency can be further improved.

  The strength of the turbine blade as a specified range of mechanical strength of the steam turbine 5 is designed to have durability against the differential pressure applied to the front and back of the turbine blade, and this differential pressure flows to the steam turbine 5 It depends on the flow rate and pressure balance of the steam, and this differential pressure changes according to the amount of extraction. Therefore, the amount of steam extraction is controlled in consideration of the strength of the turbine blade. As a result, it is possible to reduce the amount of extracted air as much as possible in consideration of the strength of the turbine blade to reduce the total steam flow rate flowing to the steam turbine 5, and to further improve the turbine efficiency.

  There is a possibility that the temperature of the superheated steam supplied from the superheater 13 may fluctuate due to the change of the heating amount of the biomass boiler 7 and the extraction amount of steam of the steam turbine 5. By suppressing the temperature fluctuation of the superheated steam by the superheater spray 27, it is possible to quickly set the temperature of the steam pipe and the turbine blade used under high temperature and high pressure within a specified value, and to suppress deterioration and damage. Can. In addition, since the flow rate of the reheater spray for controlling the temperature of the reheat steam supplied from the reheater 17 is also controlled, the temperature of the reheat steam can be easily controlled to a desired value. .

  By using the biomass boiler 7 using biomass fuel as a main fuel as an additional boiler for heating feed water, it is possible to burn the biomass fuel in the biomass boiler 7 without mixing the biomass fuel in the boiler 3. Therefore, the ratio of use of biomass fuel to fossil fuel burned by the boiler 3 can be increased, and the amount of carbon dioxide that is not carbon neutral can be reduced. In addition, inexpensive biomass fuel containing a corrosive component can be used without affecting the combustion of the boiler 3 main body, and highly efficient power generation can be performed at low fuel cost.

In the embodiment described above, the heating amount of the biomass boiler 7 is controlled based on the outlet temperature 22T of the economizer 18, but instead of the outlet temperature 22T of the economizer 18, the inlet temperature 58T of the economizer 18 is used Also good.
In addition, although the biomass boiler 7 is used as an additional steam generating device for heating feed water, it is not always necessary to use biomass as fuel. As the fuel, for example, refuse or combustible waste can be used.
Further, although the feed water heating heat exchanger 60 is disposed in series with the feed water heaters 50, 52a, 52b, 54a, 54b, at least one of the feed water heaters 50, 52a, 52b, 54a, 54b It may be arranged in parallel to the object.

1 power generation plant 3 boiler 3a boiler main body 5 steam turbine 7 biomass boiler (boiler for feed water heating)
DESCRIPTION OF SYMBOLS 10 Fire furnace 11 Burner 12 Water-cooled wall 13 Superheater 15 Steam drum 17 Reheater 18 Economizer 20 Circulation pump 22 Economizer outlet piping 22T Economizer outlet temperature sensor 22P Economizer outlet pressure sensor 24 Water supply piping 25T Combustion exhaust gas temperature sensor 27 Superheater spray 30 control Part 32 Main steam piping 34 High pressure turbine 35 Medium pressure turbine 36 Low pressure turbine 37 Generator 38 High pressure turbine outlet piping 40 Reheated steam supply piping 42 Medium pressure turbine outlet piping 44 Low pressure turbine outlet piping 46 Condenser 48 Condensing water pump 50 Low pressure Water supply heater 51 Water supply pump 52a 1st medium pressure water supply heater 52b 2nd medium pressure water supply heater 54a 1st high pressure water supply heater 54b 2nd high pressure water heater 55a 1st high pressure extraction piping 55b 2nd high pressure extraction piping 56a 2nd 1High pressure bleed valve 56b Second high pressure bleed Valve 57T Temperature sensor 58T Temperature sensor 60 Heat exchanger for water supply heating 61 Heat transfer pipe 62 Heating steam supply piping 62T Heating steam temperature sensor 62P Heating steam pressure sensor 62F Heating steam flow rate sensor 64 Return piping 65 Return pump 67 Water supply bypass piping 68 Water supply bypass valve 72 Steam dump valve

Claims (11)

A boiler with an economizer and a superheater,
A steam turbine driven by steam generated by the boiler;
A generator driven by the steam turbine;
An exhaust gas treatment device for treating an exhaust gas discharged from the boiler,
A feed water heating boiler for heating feed water supplied to the boiler;
A control unit that controls a heating amount of the feed water by the feed water heating boiler;
Equipped with
The control unit controls the heating amount such that the outlet water temperature of the economizer is less than a saturation temperature and the exhaust gas supplied to the exhaust gas treatment device is less than the upper limit temperature of the operating temperature of the exhaust gas treatment device. A power plant characterized by A feed water heater configured to extract steam from the steam turbine to heat the feed water;
The power generation plant according to claim 1, wherein the control unit reduces an amount of extraction of steam supplied to the feed water heater.   The said control part reduces the amount of extraction of the steam supplied to the said feed water heater, when the feed water inlet temperature of the said economizer is higher than predetermined value by the inlet temperature of the economizer inlet water supply temperature, Power plant. At least two of the feedwater heaters for extracting and supplying each steam from different positions of the steam turbine;
The control unit is characterized in that the timing at which the amount of extraction of each steam supplied to the feedwater heaters is changed based on the load of the boiler and the amount of heating of the feedwater by the feedwater heating boiler. The power plant according to claim 1.   The power generation plant according to any one of claims 2 to 4, wherein the control unit controls an amount of extraction of the steam based on a strength of a turbine blade of the steam turbine. The control unit controls the heating amount of the feed water by the steam generated in the feed water heating boiler,
The feed water heating boiler includes a steam dump valve,
The power plant according to any one of claims 1 to 5, wherein when the pressure of steam generated in the feed water heating boiler is larger than a predetermined pressure, excess steam is discharged by the steam dump valve. A superheater spray for controlling the temperature of the superheated steam supplied from the superheater;
The power generation plant according to any one of claims 1 to 6, wherein the control unit controls a spray amount of the superheater spray based on a change amount of the heating amount. A heat exchanger for feedwater heating which exchanges heat between the steam generated by the feedwater heating boiler and the feedwater supplied to the boiler;
A feed water bypass pipe bypassing the feed water heating heat exchanger;
A feed water bypass valve provided in the feed water bypass pipe;
Equipped with
The control unit closes the feed water bypass valve when the temperature of steam generated in the feed water heating boiler is higher than the temperature of the feed water at the inlet of the feed water heating heat exchanger by a predetermined value or more, and the feed water heating is performed. The power supply plant according to any one of claims 1 to 6, wherein the feed water is heated by steam generated in a boiler.   The power plant according to any one of claims 1 to 7, wherein the feed water heating boiler is a biomass boiler using biomass fuel as a main fuel. A boiler with an economizer and a superheater,
A steam turbine driven by steam generated by the boiler;
A generator driven by the steam turbine;
An exhaust gas treatment device for treating an exhaust gas discharged from the boiler,
A feed water heating boiler for heating feed water supplied to the boiler;
A method of operating a power plant comprising
A power generation plant characterized by controlling a heating amount such that an outlet water temperature of the economizer is less than a saturation temperature and an exhaust gas supplied to the exhaust gas treatment device is less than an upper limit temperature of an operation temperature of the exhaust gas treatment device. How to drive.   The method of operating a power plant according to claim 10, wherein the amount of extraction of steam supplied to a feed water heater for heating the feed water is reduced by extracting steam from the steam turbine.

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