JP2008075996A - Exhaust heat recovery boiler and its steam pressure control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust heat recovery boiler and its steam pressure control method capable of preventing an increase in low pressure side steam pressure, only by adjusting opening of a high pressure side steam blowoff valve, when the low pressure side steam pressure increases to a preset value or more. <P>SOLUTION: Steam pipes 15 and 16 are arranged for respectively supplying steam of acquired respective pressures to respective steam turbines via respective steam drums 13 and 4, by generating two or more of steam pressures generated by an exhaust heat recovery boiler. The blowoff valve 17 is arranged for blowing off the steam from the higher pressure side steam drum 13 to the atmosphere only in the corresponding turbine steam pipe 15. The opening of the blowoff valve 17 is adjusted so that the steam pressure from the steam drum 13 does not become the preset value or more. When the low pressure side steam pressure increases to a specific value or more, the pressure preset value of the high pressure side steam blowoff valve 17 is reduced in response to its pressure increase quantity, and a high pressure side steam blowoff quantity is increased, and the opening of the blowoff valve 17 is adjusted so as to prevent an increase in the low pressure side steam pressure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust heat recovery boiler that uses exhaust heat from a gas turbine or the like and generates steam with a high-pressure steam drum and a low-pressure steam drum, and prevents an abnormal increase in low-pressure steam pressure without the need for a low-pressure steam atmosphere release valve. More particularly, the present invention relates to a control apparatus for an exhaust heat recovery boiler suitable for preventing the safety valve from operating and a method for operating the control apparatus.

FIG. 4 shows a waste heat recovery boiler system targeted by the present invention.
High-temperature exhaust gas from a gas turbine or the like flows through a flue 18, and a low-pressure economizer 2, a low-pressure evaporator 5, a high-pressure economizer 11, a high-pressure evaporator 14, and the like are installed in that order from the downstream side. ing.

The feed water supplied from the condensate pump 1 is adjusted in flow rate by the low-pressure feed water control valve 3, and then sequentially supplied to the low-pressure steam drum 4 and the low-pressure evaporator 5.
The low-pressure steam separated by the low-pressure steam drum 4 is sent to a low-pressure steam turbine (not shown) through a low-pressure steam pipe 6. It is to be noted that when the boiler is started, it consists of a system for releasing the generated steam to the atmosphere via the low-pressure steam atmosphere release valve 8 and a system for collecting it in the condenser 19 via the low-pressure steam turbine bypass valve 7.

  Further, the feed water passes through the connecting pipe 9 from the outlet of the low pressure economizer 2, is pressurized by the high pressure feed pump 10, passes through the high pressure economizer 11, and the flow rate is adjusted by the high pressure feed water control valve 12, and then the high pressure steam drum 13 And sequentially supplied to the high-pressure evaporator 14. The high-pressure steam separated by the high-pressure steam drum 13 is sent to the high-pressure steam turbine through the high-pressure steam pipe 15. At the time of start-up, the system consists of a system for releasing the generated steam to the atmosphere via the high-pressure steam atmosphere release valve 17 and a system for collecting it in the condenser 19 via the high-pressure steam turbine bypass valve 16.

A control method of the prior art exhaust heat recovery boiler will be described with reference to FIG.
The control of the high-pressure steam atmospheric release valve 17 (FIG. 4) shown in FIG. 3A subtracts the actual pressure signal from the high-pressure steam drum pressure transmitter 30 and the high-pressure steam pressure set value given by the signal generator 32. This is done by controlling the valve opening degree with a signal obtained by comparing the difference by the unit 31 and proportionally integrating the difference by the proportional integrator 33. The high-pressure steam pressure set value of the diffusion valve 17 given by the signal generator 32 is switched to the high-pressure steam turbine bypass valve 16 after the vacuum of the condenser 19 (FIG. 4) rises. The value is the same as the set value and is a fixed value.
The vacuum rise of the condenser 19 is completed by a vacuum pump provided in the condenser 19 before the boiler is started.

  The control of the low-pressure steam atmosphere release valve 8 shown in FIG. 3B is also given by the signal generator 40 and the actual pressure signal from the low-pressure steam drum pressure transmitter 34 as with the high-pressure steam atmosphere release valve 17. The low pressure steam pressure set value is compared by the subtractor 39, and the valve opening degree is controlled by a signal obtained by proportionally integrating the difference by the proportional integrator 41. Note that the set value given by the signal generator 40 is the same value as the pressure set value in order to switch to the low pressure steam turbine bypass valve 7 after the vacuum of the condenser 19 is increased, and is a fixed value.

  Japanese Patent Laid-Open No. 6-117279 discloses an invention relating to a method for controlling an exhaust heat recovery boiler in which a steam atmosphere diffusion valve is installed as in the present invention as shown in FIG. At the beginning, an invention related to throttle of fuel in a gas turbine is described, but there is no explanation about performing steam pressure control of a plurality of systems with a single steam atmosphere release valve.

  Furthermore, JP 2001-263004 A provides an air release valve that is normally closed to the main steam pipe that supplies the above to the turbine from the boiler, and when the turbine trips, the flow rate corresponding to the condensate amount of the turbine is set. A configuration is disclosed in which the opening degree of the atmospheric release valve is set so as to release from the main steam pipe.

  Japanese Patent Laid-Open No. 2001-108201 discloses a multi-pressure exhaust heat recovery boiler configured to merge a high pressure boiler and a low pressure drum with a high pressure boiler steam and a low pressure boiler steam. The structure which provided the pressure regulation valve or the bypass valve to the condenser in the exit piping of a low-pressure boiler so that an internal pressure may not be disclosed is disclosed.

Therefore, when the pressure fluctuation in the low-pressure drum is detected by joining the steam on the low-pressure boiler side with the steam on the high-pressure boiler side via the pressure regulating valve, the outlet pressure regulating valve of the low-pressure boiler is controlled to suppress the pressure fluctuation. It is disclosed that the opening degree of the bypass valve is controlled when the opening degree is controlled and a pressure fluctuation from the bypass valve to the condenser is detected. Further, it is described that the pressure is mainly maintained by a pressure regulating valve, and when the pressure in the low-pressure drum further increases, steam is discharged from the bypass to the condenser to keep the pressure constant.
JP-A-6-117279 JP 2001-263004 A JP 2001-108201 A

  In the prior art of Patent Document 1 above, a high-pressure steam atmospheric diffusion valve and a low-pressure steam atmospheric diffusion valve are provided. When the high-pressure steam pressure rises above the set value, the low-pressure steam pressure rises above the set value. At that time, the pressure control was performed by adjusting the opening of the low-pressure steam atmosphere release valve and releasing the steam to the atmosphere, so it was necessary to install two atmosphere release valves and it was an uneconomical design. .

  In the prior art of Patent Document 2 above, it is disclosed that when the turbine trips, the atmospheric discharge valve is opened to discharge a flow rate corresponding to the condensate amount of the turbine to the outside from the main steam pipe. Only a single brackish water separation drum is installed.

  In the prior art disclosed in Patent Document 3, the high pressure drum and the low pressure drum are optimally sized, and the purpose is to prevent pressure fluctuations in the low pressure drum due to fluctuations in the amount of steam on the high pressure drum side. Is a multi-pressure exhaust heat recovery boiler configured to join high-pressure steam and low-pressure steam, and originally has a high-pressure turbine steam supply system and a low-pressure turbine. It is an invention related to a boiler configuration that does not require the installation of an atmospheric release valve in each steam supply system.

  The object of the present invention is to control the steam pressure on the higher pressure side with the higher pressure side steam atmosphere release valve, and also when the steam pressure on the lower pressure side rises above the set value, Exhaust heat recovery boiler equipped with a steam pressure control device capable of preventing an increase in the steam pressure on the lower pressure side without adjusting the opening and installing a steam atmospheric diffusion valve on the lower pressure side, and its steam pressure control method And to provide a method for its operation.

The present invention employs the following means for solving the above problems.
According to the first aspect of the present invention, steam of three vapor pressures of high pressure, medium pressure and low pressure, or steam of two vapor pressures of high pressure and low pressure is generated in the exhaust gas flow path into which the exhaust gas from the gas turbine is introduced. A plurality of steam generation systems, each steam supply system supplying steam at each pressure generated in each steam generation system to each steam turbine via a steam drum, and steam at each pressure from each steam supply system Each of which is branched through a corresponding steam bypass valve, and then the steam after working in each of the steam turbines is bypassed to flow into a condenser for condensate supplied to the steam generation system. Steam that provides a steam bypass system and releases steam from the steam generation system to the atmosphere only in the steam drum or steam supply system corresponding to the higher pressure side steam generation system among the steam generation systems. An air release valve is provided, and the opening of the steam atmosphere release valve is adjusted so that the steam pressure of the steam drum corresponding to the steam generation system on the higher pressure side does not exceed the set value, and the steam pressure on the lower pressure side Is a waste heat recovery boiler provided with a steam pressure control device that lowers the pressure setting value of the higher-pressure side steam release valve when the pressure rises above a set value.

  In the invention according to claim 2, when the steam generation system comprises high pressure and low pressure, the steam atmosphere release valve is provided only in a high pressure steam supply system to a high pressure steam drum or a high pressure steam turbine, and the steam generation system Is composed of high-pressure, medium-pressure and low-pressure, the steam atmosphere release valve is a high-pressure steam supply system to the high-pressure steam drum or high-pressure steam turbine and / or high-pressure steam supply to the medium-pressure steam drum or medium-pressure steam turbine. It is an exhaust-heat recovery boiler of Claim 1 provided only in a system | strain.

The invention according to claim 3 is the steam pressure control method of the exhaust heat recovery boiler according to claim 1, wherein the output value obtained based on the deviation between the measured value and the set value of the steam pressure of the steam supply system on the higher pressure side, Compare the measured value of the steam pressure of the steam supply system on the lower pressure side with the output value obtained based on the deviation of the set value, and based on the higher output value, the opening degree of the higher pressure steam atmosphere release valve It is the steam pressure control method of the waste heat recovery boiler which adjusts.
The invention according to claim 4 is the steam pressure control method of the exhaust heat recovery boiler according to claim 3, which is operated when the exhaust heat recovery boiler is started.

(Function)
According to the inventions of claims 1 to 4, when the steam pressure from the lower pressure side steam drum is equal to or lower than the set value, only the steam pressure from the higher pressure side steam drum is equal to or lower than the set value. The opening of the higher-pressure side steam atmosphere release valve is adjusted, but only when the low-pressure steam pressure rises above the set value, the opening direction of the higher-pressure side steam atmosphere release valve is increased according to the pressure increase. Therefore, the amount of atmospheric emissions from turbine steam on the higher pressure side also increases. As a result, for example, the amount of heat exchange between the water supply and the exhaust gas in the high-pressure evaporator 14 and the high-pressure economizer 11 in the flue 18 shown in FIG. 4 increases, and the low-pressure evaporation installed downstream of the gas flow. Since the amount of heat exchange in the vessel 5 is reduced accordingly, the low-pressure steam pressure is lowered accordingly.

  As described above, the present invention adjusts the opening of the high-pressure side steam atmospheric diffusion valve so that the higher-pressure side steam pressure does not exceed the set value, and the lower-pressure side steam pressure rises above the specified value. In this case, lower the pressure setting value of the high-pressure side steam atmospheric diffusion valve according to the pressure increase, increase the high-pressure side vapor atmospheric emission amount, and prevent the low-pressure side steam pressure from increasing, This adjusts the opening of the steam atmosphere release valve.

  According to the present invention, for example, there is no auxiliary steam source for increasing the vacuum degree of the condenser at the time of starting the plant, and steam generated from the exhaust heat recovery boiler cannot be recovered to the condenser via the turbine bypass system, Even when the operation of dissipating to the atmosphere at the exhaust heat recovery boiler outlet is performed, it is possible to prevent both the higher-pressure-side turbine steam pressure and the lower-pressure-side turbine steam pressure from rising with one high-pressure steam-air diffusion valve. As a result, it is not necessary to install an atmospheric release valve in each of the high-pressure side turbine steam supply system and the low-pressure side turbine steam supply system as in the prior art, so that an economical design is possible.

An embodiment of the present invention will be described with reference to FIGS.
In the turbine steam system having the high-pressure turbine steam system and the low-pressure turbine steam system configured as shown in FIG. 1, the control of the high-pressure steam atmosphere release valve 17 is performed by generating an actual pressure signal and signal from the high-pressure steam pressure transmitter 30. The high pressure steam pressure set value given by the device 32 is compared by the subtractor 31, and the opening degree of the high pressure steam atmosphere diffusion valve 17 is adjusted by a signal obtained by proportionally integrating the difference by the proportional integrator 33.

  On the other hand, the actual pressure signal from the low pressure steam pressure transmitter 34 and the low pressure steam pressure set value given by the signal generator 36 are compared by the subtractor 35 and the difference is obtained by proportional integration by the proportional integrator 37. The high-pressure selector 38 compares the output signal from the proportional integrator 33 on the high-pressure steam pressure control side with the high-value selector 38, selects and outputs the higher one of these two output signals, and releases high-pressure steam to the atmosphere. The opening degree of the valve 17 is adjusted.

  Here, when the actual low-pressure steam pressure 34 is lower than the pressure set value 36, the high-value selector 38 selects the output signal of the proportional integrator 33 as the higher signal, so that the high-pressure steam atmosphere release valve 17 The degree of opening of the high-pressure steam atmosphere release valve 17 is adjusted by feedback control of only the steam pressure.

  When the actual low pressure steam pressure 34 exceeds the set value 36, the output signal of the proportional integrator 37 increases and becomes higher than the output on the proportional integrator 33 side, and is selected as a high value by the high value selector 38. The opening of the high-pressure steam atmospheric diffusion valve 17 is increased by an amount corresponding to the pressure increase, and as a result, the amount of high-pressure steam atmospheric emission increases.

  As described above, when the amount of high-pressure steam released from the atmosphere increases, the amount of heat exchange between the feed water passing through the high-pressure evaporator 14 and the high-pressure economizer 11 in the flue 18 shown in FIG. Increases, the exhaust gas temperature at the outlet of the high-pressure evaporator 14 decreases. Therefore, the exhaust gas temperature at the inlet of the low-pressure evaporator 5 installed downstream of the gas flow is also lowered, and the amount of heat exchange in the low-pressure evaporator 5 is reduced accordingly, so the low-pressure steam pressure is lowered accordingly.

The mechanism by which the low-pressure steam pressure decreases as the amount of high-pressure steam released to the atmosphere increases will be described with reference to FIG.
The horizontal axis of FIG. 5 shows the arrangement from the high-pressure evaporator 14 of FIG. 4 installed in the flue 18 to the low-pressure economizer 2 from the upstream side to the downstream side of the gas flow. Indicates temperature and fluid temperature.

  Here, the exhaust gas temperature and the fluid temperature indicated by solid lines indicate the case where the actual low pressure steam pressure is lower than the low pressure steam pressure set value. The exhaust gas from the gas turbine and the like is exchanged with the feed water (fluid) in each bank of the high-pressure evaporator 14, the high-pressure economizer 11, the low-pressure evaporator 5, and the low-pressure economizer 2, so that the exhaust gas becomes downstream of the gas flow. The temperature is decreasing gradually. On the other hand, the fluid temperature inside the high-pressure evaporator 14 and the low-pressure evaporator 5 is the temperature when the steam pressure is saturated, and the difference (ΔT) between the exhaust gas temperature and the fluid temperature becomes the heat absorption amount in each bank.

Dotted lines indicate the exhaust gas temperature and the fluid temperature when the high-pressure steam atmospheric emission increases.
When the opening of the high-pressure steam atmospheric diffusion valve 17 increases and the amount of atmospheric emission increases, the high-pressure steam pressure decreases, so that the internal fluid temperature of the high-pressure evaporator 14 also decreases to a temperature corresponding to the decrease in the high-pressure steam pressure. When the internal fluid temperature of the high-pressure evaporator 14 decreases, the heat exchange with the exhaust gas increases, so the decrease in the exhaust gas temperature that has passed through the high-pressure evaporator 14 increases, and the inlet of the low-pressure evaporator 5 installed downstream of the gas flow. As the exhaust gas temperature also decreases, the amount of heat exchange with the exhaust gas inside the low pressure evaporator 5 decreases, so the low pressure steam pressure also decreases accordingly.

  In the above embodiment, a double pressure exhaust heat recovery boiler composed of a high pressure steam drum 13 and a low pressure steam drum 4 has been described as an example, but also in a triple pressure exhaust heat recovery boiler composed of a high pressure, medium pressure, and low pressure steam drum. When the medium pressure or low pressure steam drum pressure abnormally rises above a specified value, it acts in the direction of increasing the opening of the high pressure steam atmosphere release valve 17 in accordance with the amount of the pressure rise in the same manner as the present invention. It is possible to prevent the high pressure, medium pressure, and low pressure steam pressure from rising abnormally with one of the steam atmosphere release valves 17. In other words, it becomes possible to make the intermediate pressure and low pressure atmospheric diffusion valves not installed. Further, depending on the capacity of the high-pressure atmospheric diffusion valve 17, an intermediate-pressure atmospheric diffusion valve can be provided.

  In the case of a triple-pressure turbine steam supply system, only the high-pressure atmospheric gas release valve 17 can be used, but in this case, the economic margin is high but the margin for control is small.

  In the case of a power plant, usually a plurality of exhaust heat recovery boilers are installed and an auxiliary boiler is provided. Therefore, when the plant is started, auxiliary steam can be supplied from the auxiliary boiler or other exhaust heat recovery boiler during operation. However, in order to reduce initial cost, there is a case where the startup of the plant is requested in a state where the auxiliary steam cannot be supplied at the time of startup of the plant due to reduction of the capacity of the auxiliary boiler. Yes, it has high industrial applicability.

It is a vapor | steam supply system figure of the waste heat recovery boiler of the Example of this invention. It is a figure which shows the waste heat recovery boiler steam pressure control apparatus of the Example of this invention. It is a figure which shows the waste heat recovery boiler control apparatus of a prior art. It is a vapor | steam supply system figure of the waste heat recovery boiler of a prior art. It is a figure which shows the change of the exhaust gas temperature and the fluid temperature in the flue of an exhaust heat recovery boiler.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Condensate pump 2 Low-pressure economizer 3 Low-pressure feed water control valve 4 Low-pressure steam drum 5 Low-pressure evaporator 6 Low-pressure steam pipe 7 Low-pressure steam turbine bypass valve 8 Low-pressure steam atmosphere release valve 9 Connecting pipe 10 High-pressure feed pump 11 High-pressure economizer 12 High Pressure Water Supply Control Valve 13 High Pressure Steam Drum 14 High Pressure Evaporator 15 High Pressure Steam Pipe 16 High Pressure Steam Turbine Bypass Valve 17 High Pressure Steam Atmospheric Emission Valve 18 Flue 19 Condenser 30 High Pressure Steam Pressure Transmitter 31, 35, 39 Subtractor 32 , 36, 40 Signal generator 33, 37, 41 Proportional integrator 34 Low pressure steam pressure transmitter 38 High value selector

Claims (4)

A plurality of steam generation systems for generating steam of three steam pressures of high pressure, medium pressure and low pressure, or steam of two steam pressures of high pressure and low pressure are provided in the exhaust gas flow path into which the exhaust gas from the gas turbine is introduced. ,
Each steam supply system for supplying steam at each pressure generated in each steam generation system to each steam turbine via a steam drum,
In order to convert the steam at each pressure from each steam supply system via a corresponding steam bypass valve into condensate for supplying the steam after working in each steam turbine to the steam generation system Each steam bypass system that bypasses and flows to the condenser
Of each of the steam generation systems, only a steam drum or a steam supply system corresponding to a higher pressure side steam generation system is provided with a steam atmosphere release valve that releases steam from the steam generation system to the atmosphere,
Adjust the opening of the steam release valve so that the steam pressure of the steam drum corresponding to the steam generation system on the higher pressure side does not exceed the set value, and the steam pressure on the lower pressure side increases to the set value or more. In this case, the exhaust heat recovery boiler is provided with a steam pressure control device that lowers the pressure setting value of the steam atmosphere discharge valve on the higher pressure side in accordance with the pressure increase. When the steam generation system consists of high pressure and low pressure, the steam atmosphere release valve is provided only in the high pressure steam supply system to the high pressure steam drum or the high pressure steam turbine,
When the steam generation system is composed of high pressure, medium pressure and low pressure, the steam atmospheric discharge valve is connected to the east pressure steam supply system to the high pressure steam drum or high pressure steam turbine and / or to the medium pressure steam drum or medium pressure steam turbine. The exhaust heat recovery boiler according to claim 1, wherein the exhaust heat recovery boiler is provided only in the high-pressure steam supply system. In the steam pressure control method of the exhaust heat recovery boiler according to claim 1,
Output value obtained based on deviation between measured value and set value of steam pressure in higher pressure side steam supply system, and output value obtained based on deviation between measured value and set value of steam pressure in lower pressure side steam supply system And adjusting the opening degree of the higher-pressure side steam release valve on the basis of the higher output value, the steam pressure control method for the exhaust heat recovery boiler, characterized in that   The steam pressure control method for an exhaust heat recovery boiler according to claim 3, wherein the exhaust pressure recovery boiler is operated when the exhaust heat recovery boiler is started.

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