JP2019124436A - Water feed method of exhaust heat recovery boiler and exhaust heat recovery boiler - Google Patents

Abstract

To provide a water feed method of an exhaust heat recovery boiler capable of preventing heat exchanger tubes from corrosion by setting the feed water temperature appropriately even in a condition in which SOconcentration in flue gas changes without need for an external heat source such as a heat source in another system during operation of the exhaust heat recovery boiler.SOLUTION: A water feed method of an exhaust heat recovery boiler 1 comprises: a low-pressure economizer feed water process for supplying feed water to a low-pressure economizer 3; a low-pressure economizer discharge process for discharging the feed water supplied to the low-pressure economizer 3 from the low-pressure economizer 3; and a low-pressure economizer bypass process in which based on the measurement result of Sox concentration measuring means 61, setting the target feed water temperature of the feed water temperature supplied to the low-pressure economizer 3, and bypassing the feed water supplied to the low-pressure economizer 3 in the low-pressure economizer feed water process.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a water supply method for an exhaust heat recovery boiler and an exhaust heat recovery boiler.

  BACKGROUND ART Conventionally, a waste heat recovery boiler is used, for example, in a combined cycle power plant configured in combination with a gas turbine or the like. In a combined cycle power plant, a gas turbine rotationally drives a generator to generate electric power, and furthermore, steam is generated using exhaust heat of combustion exhaust gas discharged from the gas turbine. By supplying this steam to the steam turbine, it is possible to further utilize the rotational drive of the generator to add power generation by the steam turbine. Therefore, combined cycle power plants are attracting attention as highly efficient and environmentally friendly power plants.

  A heat recovery steam generator (HRSG: Heat Recovery Steam Generator) in such a combined cycle power plant is a steam using exhaust heat of combustion exhaust gas discharged from a device such as a gas turbine or a combustion device that generates and uses heat. Is known as a device that generates As an example of the exhaust heat recovery boiler, for example, those described in Patent Documents 1 and 2 below have been reported.

JP 2005-9792 A Patent No. 5613921 gazette

The exhaust heat recovery boiler recovers heat by heating the feed water / steam system with the thermal energy of the combustion exhaust gas discharged from a gas turbine or the like. The exhaust heat recovery boiler is provided with a plurality of heat exchangers that sequentially heat the feed water with the combustion exhaust gas when performing such heat recovery. In the heat exchanger (low pressure economizer) provided at the most downstream side in the flue gas flow of such an exhaust heat recovery boiler, when the temperature of the supplied water becomes equal to or lower than the acid dew point temperature, The moisture in the flue gas, which has been lowered to the temperature and exposed, may react with SO _x contained in the flue gas to produce H ₂ SO ₄ . In this case, the resulting H ₂ SO ₄ may corrode the heat transfer tube. Therefore, it is necessary to keep the temperature of the supplied water supplied above the acid dew point temperature.

In order to prevent such corrosion of the heat transfer tube, for example, in Patent Document 1, the feed water to the waste heat recovery boiler is heated using a heating source (a deaerator) in another system, and SO in the combustion exhaust gas ₍₂ ) The temperature control is performed so that the feed water temperature at the inlet of the low-pressure economizer (the downstream side where the combustion exhaust gas is at a low temperature) inlet temperature does not fall below the acid dew point temperature according to the concentration.

  On the other hand, in Patent Document 2, it is an object to prevent the corrosion of the heat transfer tube by preventing that the ammonium sulfate or the acid ammonium sulfate attached to the heat transfer tube absorbs the moisture and causes the corrosion while the gas turbine is stopped. And In order to solve this problem, Patent Document 2 discloses a circulation line in which the feed water heated by the low pressure economizer is again circulated to the inlet side of the low pressure economizer, and the feed water bypasses the low pressure economizer. A bypass line to the water supply system of the pressure / high pressure economizer is provided, and temperature control is performed so that the feed water temperature at the low pressure economizer inlet does not fall below the acid dew point temperature.

However, in patent document 1, the heating source which exists in another system | strain was required for heating of feed water temperature. In Patent Document 2, has an object of preventing corrosion of heat transfer tube in a period in which the gas turbine is stopped, the corrosion of the heat transfer tube in a condition of varying SO ₂ concentration in the combustion exhaust gas, such as during gas turbine operation Was not considered.

The present disclosure has been made in view of such circumstances, and does not require an external heat source such as a heating source in another system during operation of the exhaust heat recovery boiler, and the concentration of SO _{2 in} combustion exhaust gas It is an object of the present invention to provide an exhaust heat recovery boiler water supply method and an exhaust heat recovery boiler capable of preventing corrosion of a heat transfer pipe by setting the feed water temperature to an appropriate temperature even under the condition of changing.

In order to solve the above-mentioned subject, this indication adopts the following means.
In the water supply method for a waste heat recovery boiler according to some embodiments of the present disclosure, at least one economizer for heating feedwater with flue gas, and a position of the economizer where the flue gas is at the lowest temperature side And a SOx concentration measuring means for measuring the concentration of SOx in the flue gas passing through the low pressure economizer arranged in the low pressure economizer. The economizer feed water supply process, the low pressure economizer feed water discharge process for discharging the feed water supplied to the low pressure economizer from the low pressure economizer, and the low pressure based on the measurement result of the SOx concentration measuring means Setting a target feed water temperature of feed water temperature supplied to the economizer, and bypassing the water supply supplied to the low pressure economizer in the low pressure economizer water supply step; .

  In the water supply method for a waste heat recovery boiler according to some embodiments of the present disclosure, a target water supply temperature of the water supplied to the low pressure economizer is set based on the measurement result of the SOx concentration measurement unit, The low pressure economizer bypass step bypasses the feed water supplied to the low pressure economizer in the water supply process. By bypassing the feedwater supplied to the low pressure economizer, the low temperature feedwater supply flow rate to the low pressure economizer can be reduced. Thereby, the feed water temperature at the low pressure economizer inlet can be raised. Also, by setting the target feed water temperature of the feed water temperature supplied to the low pressure economizer based on the measurement result of the SOx concentration measurement means and performing water supply bypass, the low pressure economizer based on the SOx concentration in real time It is possible to change the inlet water temperature. Moreover, in the water supply method of the exhaust heat recovery boiler of the present disclosure, the water supply temperature at the inlet of the low pressure economizer can be raised simply by bypassing the water supplied to the low pressure economizer. Therefore, it is not necessary to apply heat such as steam from the outside to raise the feed water temperature, so it is possible to control the feed water temperature without providing new equipment.

  In the above embodiment, the low-pressure economizer bypass step is performed when adjusting the temperature of the feedwater supplied to the low-pressure economizer with respect to the target water supply temperature set based on the measurement result of the SOx concentration measurement unit. It is preferable to perform a low pressure economizer circulating step of returning the feed water discharged from the low pressure economizer to the low pressure economizer before.

  The low pressure economizer circulation process makes it possible to return the feed water discharged from the low pressure economizer to the low pressure economizer. Thus, the feed water temperature at the inlet of the low pressure economizer can be raised in adjusting the feed water temperature supplied to the low pressure economizer with respect to the set target water supply temperature. In addition, by performing the low pressure economizer circulation process before the low pressure economizer bypass process, even if the low pressure economizer circulation process is performed, if the feed water temperature at the low pressure economizer inlet does not rise, the low pressure economizer An operation of performing a bypass process is possible. That is, when the heat quantity is insufficient up to the target feed water temperature only in the low pressure economizer circulating process, the insufficient heat quantity can be compensated by the low pressure economizer bypass process.

  In the water supply method of the exhaust heat recovery boiler according to some embodiments of the present disclosure, the acid dew point temperature is set based on the measurement result of the SOx concentration measurement means, and the temperature of the water supply temperature supplied to the low pressure economizer The target feed water temperature is set by adding a predetermined margin temperature to the acid dew point temperature, and the low pressure economizer circulation step and / or the low pressure economizer bypass step is performed to achieve the target feed water temperature.

  Since the target feed water temperature is set by adding a temperature (margin temperature) having a margin from the dew point temperature, it is possible to set the feed water temperature to an appropriate temperature. That is, it is possible to calculate the current acid dew point temperature from the current SOx concentration, set a target water supply temperature having a margin from the acid dew point temperature, and control the water supply temperature based on the target water supply temperature. Become. As described above, it is possible to perform feedwater temperature control based on the current acid dew point temperature at the time of operation of the exhaust heat recovery boiler, so it is possible to set the feedwater temperature to an appropriate temperature. Thereby, the performance of the boiler can be improved as much as possible while preventing the corrosion of the heat transfer tubes.

  In the water supply method of the exhaust heat recovery boiler according to some embodiments of the present disclosure, the target water supply temperature is changed stepwise according to the SOx concentration in the combustion exhaust gas.

  As a result, it is possible to prevent the opening and closing from chattering (repeating the opening and closing of the valve at short time intervals) according to the opening degree command to each flow regulating valve, so that the control system of the entire system can be stabilized.

  The low pressure economizer is bypassed in the low pressure economizer bypass step according to the SOx concentration in the flue gas or the difference between the temperature of the feedwater supplied to the low pressure economizer and the target water supply temperature. Gradually increase the feed water bypass flow rate.

  As a result, it is possible to prevent the opening and closing from chattering (repeated opening and closing of the valve at short time intervals) by the opening degree command to the flow regulating valve that adjusts the bypass flow rate, and therefore it is possible to stabilize.

  In a waste heat recovery boiler according to some embodiments of the present disclosure, at least one economizer for heating feed water with flue gas, and the economizer among which the flue gas is at the lowest temperature side are disposed. And SOx concentration measuring means for measuring the concentration of SOx in the flue gas passing through the low pressure economizer, the low pressure economizer is supplied with the feed water to the low pressure economizer. A feed line, a low pressure economizer feed water discharge line for discharging the feed water supplied to the low pressure economizer from the low pressure economizer, a branch from the low pressure economizer feed water supply line, And a low pressure economizer bypass line for bypassing the water supply supplied to the low pressure economizer, the low pressure economizer being connected to the low pressure economizer based on the output of the SOx concentration measuring means. The eye of the water supply temperature supplied Set the water temperature, the control unit is provided for switching the use of the low pressure economizer bypass line.

  In a waste heat recovery boiler according to some embodiments of the present disclosure, adjustment of the temperature of the feedwater supplied to the low pressure economizer with respect to the target feedwater temperature set based on the output of the SOx concentration measurement means is a low pressure A controller is provided to switch the use of the economizer bypass line. By bypassing the feedwater supplied to the low pressure economizer, the low temperature feedwater supply flow rate to the low pressure economizer can be reduced. Thereby, the feed water temperature at the low pressure economizer inlet can be raised. In addition, the control unit sets the target feed water temperature of the feed water temperature supplied to the low pressure economizer based on the output of the SOx concentration measurement means, and bypasses the feed water, thereby reducing the low pressure coal charcoal based on the SOx concentration in real time. It is possible to change the feed water temperature at the inlet of the unit. Moreover, in the exhaust heat recovery boiler of the present disclosure, the feed water temperature at the low pressure economizer inlet can be increased simply by bypassing the feed water supplied to the low pressure economizer by the low pressure economizer bypass line. Therefore, it is not necessary to apply heat such as steam from the outside to raise the feed water temperature, so it is possible to control the feed water temperature without providing new equipment.

  In the above embodiment, a low pressure branch from the low pressure economizer feed water discharge line is connected to the low pressure economizer water supply feed line and returns the feed water discharged from the low pressure economizer to the low pressure economizer An economizer circulation line is further provided, and the control unit uses the low pressure economizer bypass line to adjust the temperature of the feed water supplied to the low pressure economizer based on the output of the SOx concentration measuring means. Before switching to bypass flow control, it is preferable to switch to circulation flow control using the low pressure economizer circulating line.

  The low pressure economizer circulation line enables the feed water discharged from the low pressure economizer to be returned to the low pressure economizer. Thereby, the feed water temperature at the low pressure economizer inlet can be raised. In addition, before adjusting the use of the low pressure economizer bypass line in adjusting the feed water temperature supplied to the low pressure economizer with respect to the set target water supply temperature, the circulation flow rate adjustment using the low pressure economizer circulation line If the feed water temperature at the low pressure economizer inlet does not rise even if the feed water discharged from the low pressure economizer is returned to the low pressure economizer by switching to the low pressure economizer, bypass flow adjustment using the low pressure economizer bypass line It is possible to operate to That is, when the amount of heat is insufficient up to the target feed water temperature only by the use of the low pressure economizer circulation line, the insufficient heat can be compensated by the use of the low pressure economizer bypass line. Thus, the feed water temperature can be set to an appropriate temperature, and the performance of the boiler can be improved as much as possible.

  According to the waste heat recovery boiler water supply method and the waste heat recovery boiler of the present disclosure, the feed water temperature can be set to an appropriate temperature without applying heat such as steam from the outside during operation of the waste heat recovery boiler . Thereby, the performance of the boiler can be improved as much as possible.

It is a schematic diagram showing the composition of the exhaust heat recovery boiler concerning one embodiment of this indication. BRIEF DESCRIPTION OF THE DRAWINGS It is a systematic diagram which shows the low-pressure economizer of the exhaust heat recovery boiler which concerns on one Embodiment of this indication, and the concrete structure of the vicinity. It is a flow chart which shows a water supply method of a waste heat recovery boiler concerning one embodiment of this indication. It is a graph showing the relation of acid dew point temperature, acid dew point temperature + margin temperature, and target feed water temperature. (A) The relationship between the inlet feed water temperature and time course of the low pressure economizer, (b) the relationship between the outlet temperature and time course of the low pressure economizer, and (c) the relationship between bypass flow rate and time course It is a graph.

  Hereinafter, an embodiment of a water supply method for a waste heat recovery boiler and a waste heat recovery boiler according to the present disclosure will be described with reference to the drawings. In addition, although the waste heat recovery boiler which applied the combustion exhaust gas from a gas turbine as combustion exhaust gas is demonstrated below as an example, it is not limited to this. That is, the combustion exhaust gas from a boiler or the like may be applied as the combustion exhaust gas.

[Waste heat recovery boiler]
Hereinafter, a waste heat recovery boiler according to an embodiment of the present disclosure will be described using FIGS. 1 and 2.
FIG. 1 is a schematic system diagram showing a configuration of a waste heat recovery boiler according to an embodiment of the present disclosure.

  A waste heat recovery boiler 1 as shown in FIG. 1 is provided in a flue gas passage into which flue gas (shown as a gas flow in the drawing) from a gas turbine (not shown) is introduced. The temperature of the flue gas near the inlet where the flue gas flows into the waste heat recovery boiler 1 is, for example, about 550 ° C. to 650 ° C. Although the flue gas passage in the exhaust heat recovery boiler 1 is described as a flue gas passage in which gas flows in the horizontal direction in the present specification, the flue gas passage may be directed in the vertical direction.

The combustion exhaust gas after heat recovery by the exhaust heat recovery boiler 1 is discharged to the atmosphere from the chimney 2 via the exhaust heat recovery boiler 1. At the inlet of the chimney 2, SOx concentration measurement means 61 for measuring the concentration of SOx in the combustion exhaust gas discharged from the exhaust heat recovery boiler 1 is provided. The SOx concentration measuring means 61 measures, for example, the concentration of SO ₂ in the combustion exhaust gas. If the SO _x yields a _H 2 SO ₄ reacts with water, SO _x becomes SO _3. Since it is known that conversion vary from SO ₂ to SO ₃ is generally about 5%, it is possible to grasp the concentration of indirectly SO ₃ by measuring the concentration of SO _2. The place where the SOx concentration measurement means 61 is provided is not limited to the entrance of the chimney 2 and is not limited as long as it can measure the SOx concentration of the combustion exhaust gas passing through the low pressure economizer 3 described later.

  The waste heat recovery boiler 1 is provided with a plurality of heat exchangers, and for example, a low pressure economizer 3, a low pressure evaporator 4, an intermediate pressure economizer 5, an intermediate pressure evaporator 6, a low pressure superheater 7, a high pressure economizing coal. And a high pressure primary superheater 12, a primary reheater 13, a secondary reheater 14, and a high pressure secondary superheater 15. These are sequentially disposed from the most downstream side to the most upstream side of the flue gas passage. A low pressure steam separation drum 16, a medium pressure steam separation drum 17, and a high pressure steam separation drum 18 are disposed vertically above the low pressure evaporator 4, the medium pressure evaporator 6, and the high pressure evaporator 11, respectively. Steam and water are separated from the brackish water mixture supplied from the low pressure evaporator 4, the medium pressure evaporator 6, and the high pressure evaporator 11 by the low pressure, medium pressure and high pressure steam separation drums 16, 17, 18.

  The low pressure economizer 3, the medium pressure economizer 5 and the high pressure economizer 8 have a low pressure feed flow control valve 21, a medium pressure feed flow control valve 22, and a high pressure feed flow control valve 23, respectively. Pressure and high pressure brackish water separation drum feed pipes 25, 26, 27 and so on are respectively disposed. Thus, the flow rate of the brackish water mixture is adjusted from the low pressure economizer 3, the medium pressure economizer 5 and the high pressure economizer 8 to the low pressure, medium pressure and high pressure brackish water separating drums 16, 17, 18 Ru.

  In addition, the low pressure economizer 3 is provided with a low pressure economizer feed water discharge line (high medium pressure water supply communication pipe) 42 for discharging the feed water supplied to the low pressure economizer 3 from the low pressure economizer 3, The low pressure economizer feed water discharge line 42 is connected to a high and medium pressure water feed pump 37. The low pressure steam water separation drum feed pipe 25 is connected midway of the low pressure economizer feed water discharge line 42 and is connected to the low pressure evaporator 4 via the low pressure steam separation drum water feed pipe 25. The high and medium pressure feed pump 37 is connected to the medium pressure economizer 5 via the medium pressure economizer inlet connection pipe 39 and is connected to the high pressure economizer 8 via the high pressure economizer feed water supply pipe 40. A water supply thermometer 53 is provided in the low pressure economizer feed water discharge line 42 on the upstream side of the installation portion of the high / medium pressure water supply pump 37.

  Steam used for power generation by converting steam energy into rotation of a generator (not shown) in a steam turbine is supplied to a condenser. The water condensed by the condenser 28 passes from the outlet of the condenser 28 through a condensate pump 29 provided in the water supply system 32. Thereafter, the low pressure economizer water supply line (low pressure economizer inlet water supply pipe) 46 is sequentially connected to the low pressure economizer 3 via the low pressure water supply pump 33 and the low pressure water supply stop valve 34 provided in the second half of the water supply system 32 sequentially. Introduced as water supply.

  During startup and operation, the feed water is heated by the combustion exhaust gas from the gas turbine in the low pressure economizer 3, and a part of the feed water is supplied via the low pressure steam water separation drum feed pipe 25 provided with the low pressure feed water flow control valve 21 It is supplied to the low pressure evaporator 4 from the steam separation drum 16. Further, the remaining feed water heated by the low pressure economizer 3 is sent to the high and medium pressure feed water pump 37 through the low pressure economizer feed water discharge line 42 and is pressurized by the high and medium pressure feed water pump 37. The feed water extracted from the middle stage of the high / medium pressure feed pump 37 is sent to the medium pressure economizer 5 from the medium pressure economizer inlet connection pipe 39 provided with the medium pressure feed water stop valve 38. Further, the feed water pressurized to a high pressure by the high / medium pressure feed pump 37 is supplied to the high pressure economizer 8 via the high pressure economizer feed water supply pipe 40 having the high pressure feed stop valve 41.

  In such a waste heat recovery boiler 1, the feed water heated by the low pressure evaporator 4 is separated by the low pressure steam water separation drum 16, the separated steam is sent to the low pressure superheater 7, and the separated water is again separated It is sent to the low pressure evaporator 4. The steam superheated by the low pressure superheater 7 is supplied to the steam turbine.

The feed water heated by the medium pressure economizer 5 is supplied from the medium pressure steam water separation drum 17 to the medium pressure evaporator 6 via the medium pressure steam water separation drum water supply pipe 26 provided with the medium pressure water supply flow control valve 22. Ru. The feed water heated by the medium pressure evaporator 6 is separated by steam by the medium pressure steam water separation drum 17, the steam is sent to the medium pressure superheater 9, and the water is sent again to the medium pressure evaporator 6. The steam superheated by the medium pressure superheater 9 is sequentially sent to the primary reheater 13 and the secondary reheater 14 and then supplied to the steam turbine. The high pressure feed water sent to the high pressure economizer 8 is supplied from the high pressure steam separation drum 18 to the high pressure evaporator 11 via the high pressure steam separation drum feed pipe 27 having the high pressure feed flow control valve 23. The feed water heated by the high-pressure evaporator 11 is separated by steam by the high-pressure steam separation drum 18, and the steam is sent to the high-pressure primary superheater 12 and the high-pressure secondary superheater 15 and is supplied to the steam turbine after being superheated. . The water separated by the high pressure brackish water separation drum 18 is sent to the high pressure evaporator 11 again.
Further, the denitration device 10 is disposed between the medium pressure superheater 9 and the high pressure evaporator 11, and ammonia is injected to the denitration device 10 from the upstream side of the gas flow during operation of the exhaust heat recovery boiler 1 .

  A flow meter 70 and a check valve 75 are provided in a portion between the high medium pressure water supply pump 37 and the high pressure water supply stop valve 41 in the high pressure economizer water supply pipe 40. Flow meters 71 and 72 are respectively provided in the low pressure brackish water separation drum feed pipe 25 and the medium pressure economizer inlet connection pipe 39. Further, check valves 76 and 78 are also provided in the medium pressure economizer inlet communication pipe 39 and the water supply system 32, respectively.

  Between the low pressure economizer feed water supply line 46 and the low pressure economizer feed water discharge line 42, a low pressure economizer bypass line 50 for bypassing the feed water supplied to the low pressure economizer 3, and the low pressure economizer 3 And a low pressure economizer circulation line 43 for returning the feed water discharged from the low pressure economizer 3 to the low pressure economizer 3.

Low temperature feed water from the condenser 28 can flow into the low pressure economizer bypass line 50. That is, the low pressure economizer bypass line 50 is connected to a water supply system 32 having a low pressure water supply stop valve 34 for supplying the water supply from the condenser 28. A bypass valve 51 is provided in the middle of the low pressure economizer bypass line 50.
Also, in the middle of the low pressure economizer circulation line 43, a low pressure economizer circulation pump 44 and a control valve 45 are provided.

  The exhaust heat recovery boiler 1 is provided with a control unit 60 that switches the use of the low pressure economizer bypass line 50 and the use of the low pressure economizer circulation line 43 based on the output of the SOx concentration measurement means 61. The bypass flow rate adjustment using the low pressure economizer bypass line 50 and switching to the circulation flow rate adjustment using the low pressure economizer circulation line 43 are performed by opening and closing control of the bypass valve 51 and the adjustment valve 45 and opening control . In addition to the output of the SOx concentration measuring means 61, the control unit 60 in FIG. 1 also receives the output of the water supply thermometer 53.

  The control unit 60 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 etc. 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 a 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.

Next, referring to FIG. 2, the low pressure economizer of the exhaust heat recovery boiler according to the present embodiment and the system in the vicinity thereof will be described in more detail.
FIG. 2 is a system diagram showing a specific configuration of the low pressure economizer of the exhaust heat recovery boiler according to the present embodiment and the vicinity thereof. In addition, about the component same as FIG. 1, the same code | symbol is attached | subjected and the duplicate description is abbreviate | omitted.

  The low-pressure economizer 3 is an economizer provided at a position where the flue gas passing through among the economizers provided in the exhaust heat recovery boiler 1 is at the lowest temperature side. In the waste heat recovery boiler 1, as shown in FIG. 2, the feed water branched from the low pressure economizer feed water supply line 46 is connected to the low pressure economizer feed water discharge line 42 and supplied to the low pressure economizer 3 A low pressure economizer bypass line 50 is provided to bypass the In addition, the low pressure economizer circulation which is branched from the low pressure economizer feed water discharge line 42 and connected to the low pressure economizer water supply feed line 46 and returns the feed water discharged from the low pressure economizer 3 to the low pressure economizer 3 A line 43 is further provided.

  As shown in FIG. 2, the branch point between the low pressure economizer feed water supply line 46 and the low pressure economizer bypass line 50 is at the junction of the low pressure economizer circulation line 43 to the low pressure economizer water supply line 46. On the other hand, it is located upstream of the low pressure economizer feed water supply line 46. In addition, the junction point of the low pressure economizer bypass line 50 to the low pressure economizer feed water discharge line 42 is the low pressure node relative to the junction of the low pressure economizer feed water discharge line 42 and the low pressure economizer circulation line 43. It is located downstream of the coal feeder water discharge line 42.

  Near the inlet to the low pressure economizer 3 of the low pressure economizer feed water supply line 46, a low pressure economizer inlet water supply thermometer 62 for measuring the temperature of the feed water supplied to the low pressure economizer 3 is provided . Further, a low pressure economizer outlet water supply thermometer 63 is provided in the vicinity of the outlet from the low pressure economizer 3 of the low pressure economizer water supply discharge line 42. Outputs of the low pressure economizer inlet water supply thermometer 62 and the low pressure economizer outlet water supply thermometer 63 are configured to be sent to the control unit 60. The control unit 60 controls the opening / closing and the opening degree of the low pressure water supply stop valve 34, the adjustment valve 45, and the bypass valve 51 based on the output of these thermometers in addition to the output of the SOx concentration measuring means 61. In the exhaust heat recovery boiler 1 according to the present embodiment, the temperature of the water supplied in the vicinity of the inlet of the low pressure economizer 3 is maintained at, for example, about 80 to 100 ° C. The temperature of the supplied water is maintained, for example, at about 140 to 160.degree.

The control unit 60 switches to adjustment of the circulation flow rate using the low pressure economizer bypass line 50 and the low pressure economizer circulation line 43 based on the output of the SOx concentration measurement means 61. When the control unit 60 adjusts the temperature of the feed water supplied to the low pressure economizer 3 based on the output of the SOx concentration measurement means 61, the control of the bypass flow rate using the low pressure economizer bypass line 50 Before switching, control is performed to switch to adjustment of the circulation flow rate using the low pressure economizer circulation line 43. Thereby, as described later, the feed water temperature of the low pressure economizer 3 can control the feed water temperature accurately by the heat balance in the low pressure economizer 3 through the low pressure economizer circulation line 43. Also, in order to change and control the feed water temperature with a large change range, the flow rate of the feed water flowing through the low pressure economizer 3 is reduced by the low pressure economizer bypass line 50 to reduce the amount of heat exchange with the combustion exhaust gas. The effect of raising the water supply temperature is enhanced. That is, the feed water temperature of the low pressure economizer 3 is first accurately controlled by the low pressure economizer circulation line 43, and when it is necessary to further raise the feed water temperature, the low pressure eco The stepwise control by the device bypass line 50 enables efficient control.
The details of the control by the control unit 60 will be described in the water supply method of the exhaust heat recovery boiler described later.

[Water supply method of waste heat recovery boiler]
Next, an example of the water supply method of the exhaust heat recovery boiler of the present disclosure will be described.
In the water supply method of a waste heat recovery boiler according to some embodiments of the present disclosure, at least one economizer for sequentially heating the water supply with the combustion exhaust gas, and the position where the combustion exhaust gas is at the lowest temperature among the economizers And SOx concentration measuring means for measuring the concentration of SOx in the flue gas passing through the low pressure economizer arranged in the above. Moreover, the water supply method of the exhaust heat recovery boiler according to some embodiments of the present disclosure includes a low pressure economizer feed water supply process, a low pressure economizer feed water discharge process, and a low pressure economizer bypass process. In the low pressure economizer feed water supply step, the water supply is supplied to the low pressure economizer provided at a position where the flue gas passing through is at the lowest temperature side among the at least one economizer. In the low pressure economizer feed water discharge step, the feed water supplied to the low pressure economizer is discharged from the low pressure economizer. In the low pressure economizer bypass step, the feed water supplied to the low pressure economizer is bypassed in the low pressure economizer water supply process based on the measurement result of the SOx concentration measurement means.

  In addition, although the case where the feed water method of the waste heat recovery boiler of this indication is applied is demonstrated to an example in the waste heat recovery boiler 1 shown in FIG. 2 below, it is not limited to this.

(Low pressure economizer feed water supply process)
In the low pressure economizer feed process, the low pressure economizer 3 is supplied with water. Specifically, by opening the low-pressure feed stop valve 34 provided in the feed system 32, feed water (for example, about 50 to 60 ° C.) flows from the feed system 32 into the low-pressure economizer feed water supply line 46, The coal vessel 3 is supplied.

(Low pressure economizer feed water discharge process)
In the low pressure economizer feed water discharge step, the feed water supplied to the low pressure economizer 3 in the low pressure economizer feed water supply step is discharged from the low pressure economizer 3. Discharge of the feed water is performed by flowing the feed water supplied to the low pressure economizer 3 to the low pressure economizer feed water discharge line 42.

(Low pressure economizer bypass process)
In the low pressure economizer bypass step, the low pressure economizer 3 is supplied in the low pressure economizer feed water supply process based on the measurement result of the SOx concentration measurement means 61 (while looking at the measurement result of the SOx concentration measurement means 61). Bypass the water supply. Specifically, based on the measurement results of the SOx concentration measurement means 61 and the low pressure economizer inlet water supply thermometer 62, the temperature of the water supplied to the low pressure economizer 3 is equal to or lower than the acid dew point temperature or the target water temperature to be described later If determined to be less than (TI ₀ ), the low pressure economizer bypass step is performed. In the low pressure economizer bypass step, a part of the water supplied from the water supply system 32 to the low pressure economizer 3 is bypassed to control the low pressure economizer feed water by opening the bypass valve 51 to control the opening degree. Send to discharge line 42. As a result, the flow rate of the feed water supplied to the low pressure economizer 3 decreases, and it becomes possible to raise the feed water temperature of the low pressure economizer 3 with respect to the heat exchange amount from the combustion exhaust gas.

(Low pressure economizer circulation process)
In addition, before performing the above-mentioned low pressure economizer bypass step, the low pressure economizer circulation which returns the feed water discharged from the low pressure economizer 3 to the low pressure economizer 3 based on the measurement result of the SOx concentration measuring means 61. A process is performed. Specifically, based on the measurement results of the SOx concentration measurement means 61 and the low pressure economizer inlet water supply thermometer 62, the temperature of the water supplied to the low pressure economizer 3 is equal to or lower than the acid dew point temperature or the target water temperature to be described later If it is judged that the value becomes (TI ₀ ) or less, the low pressure economizer circulating process is performed before the above-mentioned low pressure economizer bypass process. In the low pressure economizer circulating process, the feed water discharged from the low pressure economizer 3 is sent to the low pressure economizer circulating pump 44 by controlling the opening degree by opening the control valve 45, and the low pressure economizer circulating It flows into the line 43. The feed water flowing into the low pressure economizer circulation line 43 is sent to the low pressure economizer feed water supply line 46 and is again supplied to the low pressure economizer 3. As a result, the temperature-increased feed water discharged from the low pressure economizer 3 is mixed with the feed water supplied to the inlet of the low pressure economizer 3, so the feed water temperature of the low pressure economizer 3 can be raised. It becomes.

  Each process described above is performed under the control of the control unit 60.

  Here, the details of the low pressure economizer circulating process and the low pressure economizer bypass process will be more specifically described with reference to the flowchart of FIG. 3.

In step S1 shown in FIG. 3, the SO ₂ concentration measurement means 61 detects the concentration of SO ₂ contained in the flue gas from the outlet of the heat recovery steam generator (HRSG) 1 (ie, the inlet of the chimney 2). The SO ₂ concentration at this time is detected, for example, in the range of about 0.7 to 1.1 ppm in a normal operating state of a gas turbine (not shown) that causes the exhaust gas to flow through the exhaust heat recovery boiler 1.

In the next step S2, the acid dew point temperature (TA) is calculated from the SO ₂ concentration measured in step S1. The acid dew point temperature is calculated by the existing estimation formula. The acid dew point temperature at this time is calculated, for example, in the range of about 95 ° C. to 120 ° C.

In the next step S3, a target feed water temperature (TI ₀ ) is set from the acid dew point temperature (TA) calculated in step S2. The setting of the target feed water temperature is performed based on, for example, the equation TA + α. In this formula, α represents a temperature (margin temperature) having a margin from the acid dew point temperature. α is set, for example, in the range of 5 to 10 ° C. including the measurement error. The setting of the target feed water temperature (TI ₀ ) is not set as a linear function, but changes stepwise according to the concentration of SO ₂ in the combustion exhaust gas. I assume.

  In the next step S4, the feed water temperature (TI) is measured by the low pressure economizer inlet feed water thermometer 62.

In the next step S5, based on the target feed water temperature (TI ₀ ) and the feed water temperature (TI) obtained in the above step, the control valve 45 (feed water temperature control valve) is caused to flow to the low pressure economizer circulation line 43 Control the water flow rate. Specifically, flow control is performed so that the feed water temperature (TI) becomes equal to or higher than the target feed water temperature (TI ₀ ).

In the next step S6, as a result of performing step S5, it is determined whether the feed water temperature (TI) is less than the target feed water temperature (TI ₀ ). If the feed water temperature (TI) is equal to or higher than the target feed water temperature (TI ₀ ) (that is, the determination is No), the feed water temperature (TI) can be raised to the target feed water temperature (TI ₀ ) only by using the low pressure economizer circulation line 43 I understand. Therefore, the process returns to step S5, and the feed water temperature control is continuously performed only by using the low pressure economizer circulation line 43.

On the other hand, if the feed water temperature (TI) is less than the target feed water temperature (TI ₀ ) (that is, the determination is Yes), the feed water temperature (TI) is higher than the target feed water temperature (TI ₀ ) only by using the low pressure economizer circulation line 43 I understand that I can not Therefore, the low pressure economizer bypass line 50 is used in the next step S7.

  In the next step S7, the low pressure economizer bypass line 50 is used to increase the flow rate of the feed water flowing to the low pressure economizer bypass line 50. Flow control of the feed water flowing to the low pressure economizer bypass line 50 is performed by opening control of the bypass valve 51. The flow rate of the feed water flowing to the low pressure economizer bypass line 50 decreases the flow rate of the feed water supplied to the low pressure economizer 3 to increase the effect on the feed water temperature rise with respect to the heat exchange with the flue gas. This makes it possible to raise the feed water temperature (TI) of the low pressure economizer 3 with respect to the heat exchange amount from the combustion exhaust gas. This flow rate control may be performed stepwise so that the temperature settles and then changes to the next flow rate without rapid temperature change, in order to prevent and stabilize control hunting (chattering). That is, the flow rate of the feed water flowing to the low pressure economizer bypass line 50 may be increased stepwise by a small amount. Further, the flow rate of the feed water flowing to the low pressure economizer bypass line 50 may be increased as long as the chattering can be suppressed.

  In the next step S8, it is determined whether the flow rate of the feedwater (bypass line flow rate) flowing through the low pressure economizer bypass line 50 is equal to or more than the upper limit flow rate. If the bypass line flow rate is less than the upper limit flow rate (i.e., the determination is No), the process returns to step S4, and the feed water temperature (TI) is measured again. On the other hand, if the bypass line flow rate is equal to or higher than the upper limit flow rate (that is, YES determination), the process proceeds to the next step S9. The value of the upper limit flow rate of the bypass line flow rate is set from the controllability (CV value) of the opening degree of the bypass valve 51.

In the next step S9, the feed water temperature (TI) is to determine whether less than the target water temperature (TI _0), when the feed water temperature (TI) is less than the target water temperature (TI _0), the control unit 60 is alarm To notify the worker that the water supply temperature (TI) can not be adjusted to the target water supply temperature (TI ₀ ).

Here, a stepwise setting method of the target feed water temperature (TI ₀ ) in the step S3 will be described more specifically with reference to FIG.
FIG. 4 is a graph showing the relationship between the acid dew point temperature, the acid dew point temperature + the margin temperature, and the target feed water temperature, with a dashed dotted line and a solid line, respectively, and the SO ₂ concentration in the combustion exhaust gas.

As shown in FIG. 4, the higher the concentration of SO ₂ in the combustion exhaust gas, the higher the acid dew point temperature. Therefore, the temperature (acid dew point temperature + margin temperature) obtained by adding the margin temperature to the acid dew point temperature also increases as the SO ₂ concentration in the combustion exhaust gas increases.

The target feed water temperature is set stepwise so as to be a constant temperature in a specific SO ₂ concentration range based on the acid dew point temperature + the margin temperature. For example, as shown in FIG. 4, four stages of target feed water temperatures T1, T2, T3 and T4 may be set. The number of stages of the target feed water temperature is not particularly limited.

Next, the step-by-step control method of the bypass line flow rate in step S7 will be described more specifically with reference to FIG.
5 (a) shows the relationship between the inlet feed water temperature of the low pressure economizer and time course, FIG. 5 (b) shows the relationship between the outlet temperature of the low pressure economizer and time course, and FIG. 5 (c) shows the bypass flow rate and It is a graph showing the relation with time passage, respectively. Fig. 5 shows an example in which the bypass line flow rate is increased stepwise when the SO ₂ concentration is high and there is a difference between the feed water temperature (TI) and the target feed water temperature (TI ₀ ) or the SO ₂ concentration increases with time. It is.

If it is found that the feed water temperature (TI) can not be raised above the target feed water temperature (TI ₀ ) only by adjusting the circulation flow rate using the low pressure economizer circulation line 43, control to increase the bypass line flow (bypass flow) Do. At this time, first, as shown in FIG. 5C, when it is determined that the inlet feed water temperature (TI) of the low pressure economizer 3 needs to be increased with respect to the SO ₂ concentration (in step S7 of FIG. Correspondingly, the opening degree of the bypass valve 51 is gradually increased to increase the bypass flow rate. The increase control of the bypass flow rate is performed by gradually increasing the flow rate in a range that does not exceed the upper limit flow rate until the inlet feed water temperature (TI) of the low pressure economizer 3 reaches the target feed water temperature (TI ₀ ). It controls so that (It corresponds to FIG.3 S8). For example, as shown in FIG. 5C, control may be performed in which the bypass flow rate is changed in five stages. The number of stages of bypass flow control is not particularly limited, and the low pressure node may be selected according to the SOx concentration in the combustion exhaust gas or the temperature of the water supplied to the low pressure economizer 3 and the target water supply temperature (TI ₀ ). The flow rate of the feed water flowing to the charcoal box bypass line 50 may be controlled stepwise. The flow rate of the feedwater flowing to the low pressure economizer bypass line 50 is a range in which chattering can be suppressed when the SO ₂ concentration is low or the difference between the feedwater temperature (TI) and the target feedwater temperature (TI ₀ ) is small. It should be increased by When it is desired to increase the temperature increase rate of the feed water temperature (TI), the flow rate of the feed water flowing through the low pressure economizer bypass line 50 may be increased as long as chattering can be suppressed.

When the bypass flow rate flowing to the low pressure economizer bypass line 50 is increased, the supply of water supplied from the low temperature water supply system 32 supplied to the low pressure economizer 3 is reduced. For this reason, according to the flow rate of the feed water flowing to the low pressure economizer bypass line 50, the feed water temperature supplied to the low pressure economizer 3 and circulated is reduced to increase the feed water temperature relative to the heat exchange with the flue gas. The effect is greater. Thereby, it becomes possible to raise the inlet feed water temperature (TI) of the low pressure economizer 3 with respect to the heat exchange amount from the combustion exhaust gas. As shown in FIG. 5C, at the beginning of the passage of time, the bypass flow rate is not adjusted using the low pressure economizer bypass line 50, and the bypass flow rate is zero. In the region of the double arrow A in FIG. 5A, the feed water temperature (TI) is controlled by adjusting the circulation flow rate using the low pressure economizer circulation line 43. However, the feedwater temperature (TI) may not be able to reach the target feedwater temperature (TI ₀ ) only by adjusting the circulation flow rate using the low pressure economizer circulation line 43. At this time, it is necessary to compensate for the insufficient heat amount (the temperature difference shown by the double arrow B in FIG. 5A) by adjusting the bypass flow rate using the low pressure economizer bypass line 50.

  At this time, as shown in FIG. 5 (c), the bypass flow rate increases stepwise with the passage of time, as shown in FIG. The low pressure economizer bypass line 50 is used to make adjustments to increase the bypass flow. As a result, as shown in FIG. 5A, the feed water temperature (TI) at the inlet of the low pressure economizer 3 rises with the increase of the bypass flow rate, and the temperature rise rate also rises. That is, in order to change and control the feed water temperature with a large change range, the flow rate of the feed water flowing through the low pressure economizer 3 is decreased by the low pressure economizer bypass line 50 with respect to the heat exchange amount with the combustion exhaust gas. The effect of raising the feed water temperature is greater than the adjustment of the circulation flow rate using the low pressure economizer circulation line 43.

  As shown in FIGS. 5 (a) and 5 (b), the feed water temperature (TI) at the inlet of the low pressure economizer 3 and the feed water temperature (T0) at the outlet change in conjunction with each other. The reason for this is that if the bypass flow rate is increased, the amount of feed water flowing into the low pressure economizer 3 decreases, and the heat exchange amount with the flue gas in the low pressure economizer 3 does not change significantly. The outlet temperature (T0) of the economizer 3 rises. As a result, the temperature of the feedwater flowing through the low pressure economizer circulation line 43 rises, and the feedwater having the elevated temperature is returned to the low pressure economizer 3.

  The feed water temperature (TI) at the inlet of the low pressure economizer 3 and the feed water temperature (T0) at the outlet increase after a predetermined time delay from the timing when the bypass flow rate is increased. That is, immediately after the bypass flow rate is increased, the temperature of the feed water at the inlet and the outlet of the low pressure economizer 3 does not immediately rise, but there is a time delay. Therefore, control of the feed water temperature (TI) is performed in advance by adjusting the circulation flow rate using the low pressure economizer circulation line 43.

According to the configuration described above, according to the present embodiment, the following effects can be obtained.
As described above, in the exhaust heat recovery boiler 1 of the present embodiment, adjustment of the circulation flow rate using the low pressure economizer circulation line 43 based on the output of the SOx concentration measurement means 61, and the low pressure economizer bypass line A control unit 60 is provided to switch between the adjustment of the bypass flow rate using 50 and the like. The feed water temperature of the low pressure economizer 3 is mixed with the feed water supplied to the inlet of the low pressure economizer 3 with the temperature-increased feed water discharged from the low pressure economizer 3 by the low pressure economizer circulation line 43 Because of this, the heat balance in the low pressure economizer 3 makes it possible to control the temperature of the feed water to rise accurately. Moreover, in order to change and control the feed water temperature with a larger change range, the feed flow rate of the low temperature feed water to the low pressure economizer 3 is reduced by bypassing the feed water supplied to the low pressure economizer 3 It is possible to greatly increase the feed water temperature at the inlet of the low pressure economizer 3 with respect to the amount of heat exchange from the combustion exhaust gas, and to perform stable control by gradually increasing the bypass flow rate Become. That is, the feed water temperature of the low pressure economizer 3 is first accurately controlled by the low pressure economizer circulation line 43, and when it is necessary to further raise the feed water temperature, the low pressure eco The stepwise control by the device bypass line 50 enables efficient control.

  Further, the control unit 60 bypasses the water supply based on the output of the SOx concentration measuring means 61, so that it is possible to change the water supply temperature at the inlet of the low pressure economizer 3 based on the SOx concentration in real time. That is, it is possible to calculate the current acid dew point temperature from the current SOx concentration, set a target water supply temperature having a margin from the acid dew point temperature, and control the water supply temperature based on the target water supply temperature. Become. Thus, since it becomes possible to perform feedwater temperature control based on the current acid dew point temperature, it becomes possible to set the feedwater temperature to an appropriate temperature. Thereby, the corrosion of the heat transfer tube of the low pressure economizer 3 can be prevented, and the feed water temperature at that time can be made appropriate, so the performance of the boiler can be improved as much as possible.

  Further, in the exhaust heat recovery boiler 1 of the present disclosure, the feed water temperature at the inlet of the low pressure economizer 3 can be increased simply by bypassing the feed water supplied to the low pressure economizer 3 by the low pressure economizer bypass line 50. it can. Therefore, it is not necessary to increase the feed water temperature by adding a heat source such as steam from an external source such as a heat source in another system to raise the feed water temperature, so using the existing configuration near the low pressure economizer 3 without providing new equipment. The heat balance in the low pressure economizer 3 makes it possible to control the feed water temperature, and the performance of the boiler can be improved as much as possible. Therefore, the exhaust heat recovery boiler 1 of the present disclosure is excellent in control response because it is not affected by the response of the other system.

  Further, the low pressure economizer circulation line 43 enables the feed water discharged from the low pressure economizer 3 to be returned to the low pressure economizer 3. Thereby, the feed water temperature at the inlet of the low pressure economizer 3 can be raised. Moreover, before switching the use of the low pressure economizer bypass line 50, the use of the low pressure economizer circulation line 43 can be switched. Thereby, the operation of using the low pressure economizer bypass line 50 when the feed water temperature at the inlet of the low pressure economizer 3 does not rise even if the feed water discharged from the low pressure economizer 3 is returned to the low pressure economizer 3 Is possible. That is, when the heat quantity is insufficient up to the target feed water temperature only by the use of the low pressure economizer circulation line 43, the insufficient heat quantity can be compensated by the use of the low pressure economizer bypass line 50.

  Further, as described above, in the water supply method of the exhaust heat recovery boiler 1 of the present embodiment, the low pressure economizer circulation line 43 in the low pressure economizer feed water supply process based on the measurement result of the SOx concentration measurement means 61. In addition to the low pressure economizer circulating process using the above, the low pressure economizer bypass process bypassing the feed water supplied to the low pressure economizer 3 is characterized. By bypassing the feed water supplied to the low pressure economizer 3, the supply of low temperature feed water to the low pressure economizer 3 can be reduced. Thereby, the feed water temperature at the inlet of the low pressure economizer 3 can be raised.

  By bypassing the water supply based on the measurement result of the SOx concentration measurement means 61, it is possible to change the water supply temperature at the inlet of the low pressure economizer 3 based on the SOx concentration in real time. That is, it is possible to calculate the current acid dew point temperature from the current SOx concentration, set a target water supply temperature having a margin from the acid dew point temperature, and control the water supply temperature based on the target water supply temperature. Become. Thus, since it becomes possible to perform feedwater temperature control based on the current acid dew point temperature, it becomes possible to set the feedwater temperature to an appropriate temperature. Thereby, corrosion of the heat transfer tube of the low pressure economizer 3 can be prevented while improving the performance of the boiler as much as possible.

  In particular, by setting the target feed water temperature in stages, it is possible to prevent the opening degree command to each flow control valve from chattering opening and closing (repeated opening and closing of the valve at short time intervals), so the control system of the entire system Can be stabilized.

  In the water supply method of the exhaust heat recovery boiler 1 of the present disclosure, the water supply temperature at the inlet of the low pressure economizer 3 can be increased simply by bypassing the water supply supplied to the low pressure economizer 3. Therefore, it is not necessary to apply heat such as steam from the outside to raise the feed water temperature, so it is possible to control the feed water temperature without providing new equipment. Further, by controlling the bypass flow rate to increase stepwise, chattering can be suppressed as described above.

  In addition, the low pressure economizer circulating process makes it possible to return the feed water discharged from the low pressure economizer 3 to the low pressure economizer 3. Thereby, the feed water temperature at the inlet of the low pressure economizer 3 can be raised. In addition, by performing the low pressure economizer circulation process before the low pressure economizer bypass process, even if the low pressure economizer circulation process is performed, if the feed water temperature at the inlet of the low pressure economizer 3 does not rise, It is possible to operate the device bypass process. That is, when the heat quantity is insufficient up to the target feed water temperature only in the low pressure economizer circulating process, the insufficient heat quantity can be compensated by the low pressure economizer bypass process.

1 exhaust heat recovery boiler 2 chimney 3 low pressure economizer 4 low pressure evaporator 5 medium pressure economizer 6 medium pressure evaporator 7 low pressure superheater 8 high pressure economizer 9 medium pressure superheater 10 denitration device 11 high pressure evaporator 12 high pressure Primary superheater 13 Primary reheater 14 Secondary reheater 15 High pressure secondary superheater 16 Low pressure steam separation drum 17 Medium pressure steam separation drum 18 High pressure steam separation drum 21 Low pressure feed flow control valve 22 Medium pressure feed flow control valve 23 High pressure feed water flow control valve 25 Low pressure steam water separation drum feed pipe 26 Medium pressure steam water separation drum feed pipe 27 High pressure steam water separation drum feed pipe 28 Condenser 29 Condenser pump 32 Feed water system 33 Low pressure feed pump 34 Low pressure feed stop valve 37 High medium pressure Water supply pump 38 Medium pressure water supply stop valve 39 Medium pressure economizer inlet communication pipe 40 High pressure economizer coal supply water supply pipe 41 High pressure water supply stop valve 42 Low pressure economizer feed water discharge line (high medium pressure water supply communication pipe)
43 low pressure economizer circulation line 44 low pressure economizer circulation pump 45 control valve 46 low pressure economizer feed water supply line (low pressure economizer inlet water supply piping)
Reference Signs List 50 low pressure economizer bypass line 51 bypass valve 53 water supply thermometer 60 control unit 61 SOx concentration measurement means 62 low pressure economizer inlet water supply thermometer 63 low pressure economizer outlet water supply thermometer 70, 71, 72 flow meter 75, 76 , 78 Check valve

Claims (7)

Measurement of SOx concentration in the flue gas passing through at least one economizer which heats the feed water with flue gas, and a low pressure economizer arranged at a position where the flue gas is on the lowest temperature side of the economizer And a SOx concentration measuring means for
A low pressure economizer feed water supply process for supplying the water supply to the low pressure economizer;
A low pressure economizer feed water discharging step for discharging the feed water supplied to the low pressure economizer from the low pressure economizer;
The target feed water temperature of the feed water temperature supplied to the low pressure economizer is set based on the measurement result of the SOx concentration measurement means, and the water supplied to the low pressure economizer in the low pressure economizer water supply step. Low pressure economizer bypass process to bypass the
A water supply method for an exhaust heat recovery boiler, comprising:   When adjusting the temperature of the feed water supplied to the low pressure economizer with respect to the target feed water temperature set based on the measurement result of the SOx concentration measuring means, the low pressure before performing the low pressure economizer bypass step The low-pressure economizer circulating step of returning the feedwater discharged from the economizer to the low-pressure economizer is performed, the water supply method of the exhaust heat recovery boiler according to claim 1.   The acid dew point temperature is set based on the measurement result of the SOx concentration measurement means, and the target feed water temperature of the feed water temperature supplied to the low pressure economizer is set by adding a predetermined margin temperature to the acid dew point temperature, The water supply method for an exhaust heat recovery boiler according to claim 2, wherein the low pressure economizer circulation step and / or the low pressure economizer bypass step is performed to achieve the target feed water temperature.   The water supply method for an exhaust heat recovery boiler according to claim 3, wherein the target water supply temperature is changed stepwise in accordance with the SOx concentration in the combustion exhaust gas.   The low pressure economizer is bypassed in the low pressure economizer bypass step according to the SOx concentration in the flue gas or the difference between the temperature of the feedwater supplied to the low pressure economizer and the target water supply temperature. The feed water method of the exhaust heat recovery boiler according to any one of claims 1 to 4, wherein the bypass flow rate of the feed water is increased stepwise. At least one economizer which heats the feed water with the flue gas;
SOx concentration measurement means for measuring the concentration of SOx in the flue gas passing through a low pressure economizer placed at a position where the flue gas is on the lowest temperature side among the economizers;
Equipped with
In the low pressure economizer, a low pressure economizer feed water supply line for supplying the water supply to the low pressure economizer, and a low pressure junction for discharging the water supplied from the low pressure economizer from the low pressure economizer A low pressure economizer which branches from a coal feeder water discharge line and the low pressure economizer water supply line and is connected to the low pressure economizer water supply discharge line and bypasses the water supplied to the low pressure economizer And a bypass line is provided,
A target water supply temperature supplied to the low pressure economizer is set based on the output of the SOx concentration measurement means, and a control unit is provided to switch the use of the low pressure economizer bypass line. Waste heat recovery boiler. A low pressure economizer circulation line branched from the low pressure economizer feed water discharge line and connected to the low pressure economizer water supply feed line and returning the feed water discharged from the low pressure economizer to the low pressure economizer Is further provided,
The control unit uses the low pressure economizer bypass line to adjust the temperature of the water supply supplied to the low pressure economizer with respect to the target water supply temperature set based on the output of the SOx concentration measuring means. The exhaust heat recovery boiler according to claim 6, wherein the low-pressure economizer circulation line is switched to circulation flow adjustment before switching to bypass flow adjustment.

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