JPH10185104A - Steam drum corrosion preventive device of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam drum corrosion preventive device of a boiler capable of preventing corrosion in a steam drum easily and economically during boiler shutdown. SOLUTION: There are provided a nitrogen primary valve V1 and a nitrogen secondary blow valve V2, which are mounted on a nitrogen supply pipe L1, a boiler operating state detection signal output member which outputs an operating state detection signal s3 of a boiler B, a pressure sensor S1 which outputs a pressure detection signal s1 of a steam drum D and a control unit C where the pressure detection signal s1 and the operating state detection signal s3 are input. The control unit C opens the nitrogen primary valve V1 when the boiler B is in a shutdown state and the pressure value of the steam drum D fails to exceed a reference value and introduces nitrogen gas into the steam drum D by closing the nitrogen secondary blow valve V2, and closes the nitrogen primary valve V1 and opens the nitrogen secondary blow valve V2 to stop the supply of nitrogen gas when the boiler is in an operating state or the pressure value of the steam drum exceeds the reference pressure value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for preventing the inside of a steam drum from being corroded when the operation of a boiler is stopped.

[0002]

Generally, in a boiler, when the operation of the boiler is stopped, an air vent valve attached to a steam drum of the boiler is opened to allow outside air to enter the steam drum. Is performed. This is because, when the operation of the boiler is stopped, the pressure in the steam drum decreases as the temperature of the steam drum decreases, thereby preventing the inside of the steam drum from becoming in a vacuum state.

However, if the air vent valve is opened and air enters the boiler when the operation of the boiler is stopped as described above, the oxygen contained in the entered air oxidizes and corrodes the inner wall surface of the steam drum. The problem arises.

Conventionally, in order to prevent such corrosion in the steam boiler when the operation of the boiler is stopped, a method of injecting a deoxidizer into the boiler before stopping the operation of the boiler has been adopted. There is a problem that the work is troublesome and the cost is high. In addition, when the pressure in the steam drum is reduced while the boiler is stopped, the can bottom blowing operation (sludge in the boiler water settled at the bottom of the boiler during the stop of the boiler (so-called sludge) It is difficult to discharge the mud from the boiler), and the sludge remaining in the boiler may increase corrosion.

The present invention has been made to solve the above-described problem of corrosion when the operation of the conventional boiler is stopped.
That is, the present invention can prevent the inside of the steam drum from being corroded when the operation of the boiler is stopped, and can easily and economically prevent the corrosion, and furthermore, the steam drum before the operation of the boiler is started. It is an object of the present invention to provide a steam drum corrosion prevention device for a boiler that can easily blow a can bottom.

[0006]

To achieve the above object, a boiler steam drum corrosion prevention apparatus according to a first aspect of the present invention includes a nitrogen gas supply source connected to a boiler steam drum through a nitrogen supply pipe. An electromagnetic on-off valve attached to a nitrogen supply pipe connecting the nitrogen gas supply source and the steam drum to communicate and shut off the nitrogen gas supply source and the steam drum, and a nitrogen supply pipe downstream of the electromagnetic on-off valve An electromagnetic blow valve connected to the boiler, a boiler operation state detection signal output member that outputs a boiler operation state detection signal indicating the operation state of the boiler, and a pressure in the steam drum that is attached to the steam drum and detects the pressure in the steam drum. A drum pressure detection member that outputs a detection signal, and a drum pressure detection signal output from the drum pressure detection member and a boiler operation state detection signal output member. When the boiler operation state detection signal to be input is input, the boiler operation state detection signal indicates the boiler operation stop state, and the drum pressure value indicated by the drum pressure detection signal is equal to or less than a preset reference pressure value. A valve opening signal for opening the solenoid valve is output to the solenoid valve, and a valve closing signal for closing the solenoid valve is output to the solenoid valve, and the boiler operating state detection signal indicates the operating state of the boiler. When the drum pressure value indicated or indicated by the drum pressure detection signal is equal to or higher than a predetermined reference pressure value, a valve closing signal for closing the electromagnetic on / off valve is output to the electromagnetic on / off valve, and the electromagnetic blow valve is supplied with the electromagnetic blow valve. And a control member for outputting a valve opening signal for opening the blow valve.

In the apparatus for preventing corrosion of a steam drum of a boiler according to the first invention, a control member monitors the operation state of the boiler and the drum pressure of the steam drum, and the control member receives a signal from a boiler operation state detection signal output member. A determination is made as to whether the boiler is in an operation state or in an operation stop state based on the input boiler operation state detection signal, and further determined in advance based on a drum pressure detection signal input from a drum pressure detection member. It is determined whether the drum pressure of the steam drum is higher or lower than the reference pressure value.
When the boiler is in an operation stop state and the drum pressure value of the steam drum is smaller than the reference pressure value, the control member outputs a valve opening signal to the solenoid on-off valve to open the solenoid on-off valve and By closing the electromagnetic blow valve by outputting a valve closing signal to the blow valve, the nitrogen gas supply source communicates with the steam drum to introduce nitrogen gas into the steam drum. Further, when the boiler is in operation and the drum pressure value of the steam drum is larger than the reference pressure value, a valve close signal is output to the electromagnetic on / off valve to close the electromagnetic on / off valve, and a valve open signal is transmitted to the electromagnetic blow valve. Is output to open the electromagnetic blow valve, thereby shutting off the communication between the nitrogen gas supply source and the steam drum and stopping the supply of the nitrogen gas.

As described above, according to the first aspect,
Since the nitrogen gas is automatically introduced into the steam drum when the boiler is stopped, it is easy to prevent the inside of the steam drum from corroding due to the entry of air due to the decrease in the internal pressure of the steam drum due to the stop of the boiler. be able to.
Further, in order to prevent the corrosion of the steam drum, it is not necessary to inject a large amount of a deoxidizing agent as in the prior art, and the number of steps is unnecessary, which is economical. Furthermore, since the inside of the steam drum is always pressurized even when the operation of the boiler is stopped,
Blowing of the bottom of the steam drum before the operation of the boiler can be easily performed.

In order to achieve the above object, a steam drum corrosion prevention device for a boiler according to a second aspect of the present invention, in addition to the configuration of the first aspect, outputs a valve closing signal to an electromagnetic on-off valve in a control member, and further comprises an electromagnetic valve. The reference pressure value when outputting the valve opening signal to the blow valve is set to a value higher than the reference pressure value when outputting the valve opening signal to the solenoid on-off valve and outputting the valve closing signal to the solenoid blow valve. It is characterized by:

In the boiler steam drum corrosion prevention apparatus according to the second aspect of the invention, the control member outputs the valve closing signal to the electromagnetic on / off valve and the output of the valve opening signal to the electromagnetic blow valve to the electromagnetic on / off valve. This is performed at a pressure value higher than the drum pressure value of the steam drum when outputting a signal and outputting a valve closing signal to the electromagnetic blow valve. As described above, since the reference pressure values for opening and closing the electromagnetic on-off valve and the electromagnetic blow valve are different, the standard for outputting the valve open signal to the electromagnetic on-off valve and outputting the valve close signal to the electromagnetic blow valve is different. Hunting of the drum pressure of the steam drum before and after the pressure value (fluctuation in pressure)
In such a case, the electromagnetic on-off valve and the electromagnetic blow valve do not cause chattering (fluttering of the valve), and the nitrogen gas can be smoothly introduced into the steam drum, thereby ensuring the corrosion of the steam drum. Can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a preferred embodiment of a steam drum corrosion preventing apparatus for a boiler according to the present invention. A steam generator D of a boiler B has a nitrogen generator or a nitrogen gas cylinder not shown. A nitrogen supply source is connected via a comanche (source plug) V0, a pressure reducing valve Vd, and a nitrogen primary valve V1. In the nitrogen supply pipe L1 for supplying nitrogen from the nitrogen supply source to the steam drum D, a nitrogen secondary blow valve V2 is connected downstream of a connection portion of the nitrogen primary valve V1.

Each of the nitrogen primary valve V1 and the nitrogen secondary blow valve V2 is an electromagnetic valve, and is controlled to open and close by a valve opening and closing signal from the control unit C as described later.

Note that M connected to the nitrogen supply pipe L1
1 and M2 are pressure gauges. The superheater 1 and the high-pressure header 2 are further connected to the steam drum D by a steam pipe L2.

The combustion gas of the boiler B is supplied to a gas turbine 4 connected to a generator 3 via a superheater 1 by a gas pipe L3. A pressure sensor S1 is attached to the steam drum D, and a pressure sensor S2 is attached to the high-pressure header 2. These pressure sensors S1 and S2 are connected to a control unit C, respectively, and detect the detected drum pressure. And a pressure detection signal s2 indicating the high-pressure head pressure to the control unit C. The control unit C further includes:
An operation state detection signal s3 indicating the operation state of the boiler B and an operation state detection signal s4 indicating the operation state of the gas turbine 4
Is entered.

The operation state detection signal s3 and the operation state detection signal s4 are, for example, ON / OFF signals of the power supply of the boiler B and the gas turbine 4,
Is detected from the power switch or the like.

The control unit C
As described later, the pressure detection signals s1 and s2 input from the pressure sensors S1 and S2, respectively, and the boiler B
And a valve opening / closing signal v1 to the nitrogen primary valve V1 and a valve opening / closing signal v2 to the nitrogen secondary blow valve V2 based on the operating state detection signals s3 and s4 input from the gas turbine 4, respectively. Primary valve V1 and nitrogen 2
Open / close control of the next blow valve V2 is performed.

Next, the opening and closing control of the nitrogen primary valve V1 and the nitrogen secondary blow valve V2 by the control unit C is as follows:
This will be described based on the flowchart shown in FIG. 2, the control unit C monitors the operation state of the boiler B and the gas turbine 4 based on the operation state detection signals s3 and s4 input from the boiler B and the gas turbine 4.

That is, the control unit C determines whether or not the boiler B is in the operating state based on the operating state detection signal s3 (step a) and determines whether or not the boiler B is in the reheating operation (step a). Step b) is performed, and when it is determined that the boiler B is in the operating state or in the reheating operation in the determinations in steps a and b, a valve opening / closing signal v1 is output to the nitrogen primary valve V1. The primary nitrogen valve V1 is closed (step c), and a valve opening / closing signal v2 is output to the secondary nitrogen blow valve V2 to open the secondary nitrogen blow valve V2 (step d).

By controlling the opening and closing of the nitrogen primary valve V1 and the nitrogen secondary blow valve V2, when the stopped boiler B resumes its operation or starts the reheating operation, as described later, the boiler B Supply pipe L to steam drum D
The supply of nitrogen gas via 1 is shut off.

In the determinations in steps a and b, even if it is determined that the boiler B is not in the operating state or in the reheating operation, that is, in the stopped state, the control unit C further controls the gas turbine 4
Of whether or not the gas turbine 4 is in the operating state based on the operating state detection signal s4 input from step (e).
When it is determined that the gas turbine 4 is in the operating state, the process proceeds to steps c and d as described above,
By outputting the valve opening / closing signal v1 and the valve opening / closing signal v2, the nitrogen primary valve V1 is closed and the nitrogen 2
Next blow valve V2 is opened.

The control unit C further monitors the drum pressure in the steam drum D and the high-pressure header pressure of the high-pressure header 2 based on the pressure detection signals s1 and s2 input from the pressure sensors S1 and S2, respectively.

That is, the control unit C determines that the high-pressure header pressure in the high-pressure header 2 is 3.0 kg / cm based on the pressure detection signal s2 input from the pressure sensor S2.
It is determined whether or not the pressure is equal to or more than 2 (step f). If it is determined in step f that the high-pressure header pressure is less than 3.0 kg / cm ² , the high-pressure header pressure is further increased to 2. It is determined whether it is 5 kg / cm ² or less (step g). And the high pressure header pressure is 2.5 kg / cm
If it is determined to be less than or equal to ² , even if the boiler B and the gas turbine 4 are stopped, step c
The process proceeds to steps d and d to output the valve opening / closing signal v1 and the valve opening / closing signal v2, thereby closing the nitrogen primary valve V1 and opening the nitrogen secondary blow valve V2.

As described above, whether the high-pressure header pressure of the high-pressure header 2 is equal to or higher than the predetermined pressure (3.0 kg / cm ² ) is determined by the steam drum corrosion preventing apparatus in this embodiment. It is assumed that a plurality of boilers are connected to the high-pressure header 2. When any one of the plurality of boilers connected to the high-pressure header 2 is operated, the operated boiler is operated. Therefore, even if nitrogen gas is introduced into the steam drum D of the boiler whose operation has been stopped as described later, this nitrogen gas passes through the high pressure header 2 There is no danger that the nitrogen will flow out to the various places where the feed is supplied. However, if all the boilers are stopped and the internal pressure of the high-pressure header 2 is reduced, the nitrogen is immediately added to the steam drum D by stopping the operation of the boiler. Guide gas Then, the nitrogen gas may flow out to various places where the steam is supplied through the high-pressure header 2 to cause an oxygen-deficient state, so that the nitrogen gas is introduced into the steam drum D before the introduction of the nitrogen gas. This is to determine whether or not 2 has an internal pressure sufficient to prevent the outflow of nitrogen gas.

If it is determined only in step f that the internal pressure of the high-pressure header 2 is to be determined again in step g after the determination in step f,
If the internal pressure of the hunting is around 3.0 kg / cm ² , it is because the nitrogen primary valve V1 and the nitrogen secondary blow valve V2 cause chattering. In order to prevent the chattering from occurring, In the state where nitrogen gas is introduced into the steam drum D, even if the pressure of the high-pressure header 2 drops to less than 3.0 kg / cm ² in step f, the process does not immediately proceed to steps c and d. , The pressure of the high-pressure header 2 is lower than the reference pressure of step f.
It is determined that the process proceeds to steps c and d only when the pressure drops to kg / cm ² or less.

When the control unit C determines in step f that the internal pressure of the high-pressure header 2 is equal to or higher than 3.0 kg / cm ² , the control unit C further determines the internal pressure based on the pressure detection signal s1 input from the pressure sensor S1. It is determined whether or not the drum pressure in the steam drum D is 1.5 kg / cm ² or less (step h). In this step h, when the drum pressure of the steam drum D is 1.5 kg / cm ² or more, If it is determined that there is, a determination is further made as to whether or not the drum pressure of the steam drum D is 2.0 kg / cm ² or more (step i). When it is determined that the drum pressure of the steam drum D is 2.0 kg / cm ² or more, the process proceeds to steps c and d even when the boiler B and the gas turbine 4 are stopped. And the valve open / close signal v
1 and the valve opening / closing signal v2, the nitrogen primary valve V1 is closed and the nitrogen secondary blow valve V2 is opened.

In step h, the determination of the drum pressure of the steam drum D is performed when the drum pressure of the steam drum D is higher than a predetermined value (1.5 kg / cm ² ). This is because there is no possibility that the air enters and the steam drum D is corroded, and it is not necessary to introduce nitrogen gas.

Further, if the determination of the drum pressure of the steam drum D is repeated in step i after the determination of step h, the determination of the drum pressure of the steam drum D is performed in the same manner as described above. Is about 1.5 kg / cm ^2, the primary nitrogen valve V1 and the secondary nitrogen blow valve V2 cause chattering. In order to prevent the chattering from occurring, the nitrogen is added to the steam drum D. In the state where the gas is introduced, even if the pressure of the high-pressure header 2 increases to 1.5 kg / cm ² or more in step h, the process does not immediately proceed to steps c and d, and the steam drum D Only when the drum pressure has risen to 2.0 kg / cm ² or more, which is higher than the reference pressure in step h, the process proceeds to steps c and d.

In steps a, b, e, f, and h above, it is determined that both the boiler B and the gas turbine 4 are in an operation stop state, and the internal pressure of the high-pressure header 2 becomes 3.
0 kg / cm ² or more and the drum pressure of the steam drum D is 1,
When the pressure is 5 kg / cm ² or less, the nitrogen primary valve V1 is opened (step j), and the nitrogen secondary blow valve V2 is closed (step k).

When the nitrogen primary valve V1 is opened and the nitrogen secondary blow valve V2 is closed, nitrogen gas is supplied into the steam drum D via the nitrogen supply pipe L1, and the steam drum D is filled. This prevents the air from entering the steam drum D when the operation of the boiler B is stopped, thereby preventing the inside of the steam drum D from being corroded.

In the above example, a plurality of boilers are connected to the high-pressure header 2, and when any one of the plurality of boilers is stopped, the high-pressure header 2 is operated by another operating boiler. Is supplied to the steam drum D on the premise that the internal pressure of the steam drum D is maintained at a predetermined value or more. However, when only one boiler is connected to the high-pressure header 2, By connecting an electromagnetic on-off valve to the pipe L2 and controlling the control unit C to open the nitrogen primary valve V1 and close the electromagnetic on-off valve connected to the steam pipe L2 at the same time, the boiler B Even if the internal pressure of the high-pressure header 2 drops below a predetermined value due to the stop of the operation, the introduction of the nitrogen gas into the steam drum D can be enabled.

In this case, it is not necessary to determine the internal pressure of the high-pressure header 2 in steps f and g in FIG. FIG. 3 shows another example of the preferred embodiment of the steam drum corrosion prevention device for a boiler according to the present invention, in which the example of FIG. 1 is an example of a boiler connected to a gas turbine. On the other hand, an example is shown for a boiler that is not connected to a gas turbine.

In FIG. 3, similarly to the example of FIG. 1, a steam supply D (not shown) such as a nitrogen generator or a nitrogen gas cylinder is provided on a steam drum D 'of a boiler B' with a comanche (main plug) V0 '. , Pressure reducing valve Vd 'and nitrogen primary valve V
1 '. Then, a nitrogen supply pipe L for supplying nitrogen from the nitrogen supply source to the steam drum D '
At 1 ', a nitrogen secondary blow valve V2' is connected downstream of the connection of the nitrogen primary valve V1 '.

The nitrogen primary valve V1 'and the nitrogen secondary blow valve V2' are both electromagnetic valves, and are controlled to open and close by an open / close signal from a control unit C ', as described later. I have.

The high pressure header 2 'is further connected to the steam drum D' by a steam pipe L2 '.
In FIG. 3, Va ′ is a drum air vent valve,
M1 'and M2' connected to a nitrogen supply pipe L1 '
Is a pressure gauge.

The steam drum D 'has a pressure sensor S1'
A pressure sensor S2 'is attached to the high-pressure header 2'. The pressure sensors S1 'and S2' are connected to the control unit C ', respectively. Signal s
1 'and a pressure detection signal s2' indicating the high pressure head pressure are output to the control unit C '. An operation state detection signal s3 'such as a power on / off signal indicating the operation state of the boiler B' is input to the control unit C '.

The control unit C '
Is based on pressure detection signals s1 'and s2' input from pressure sensors S1 'and S2' and an operation state detection signal s3 'input from boiler B, respectively, as described later. The valve open / close signal v1 '
And a valve open / close signal v to the nitrogen secondary blow valve V2 '.
2 ′ is output to control the opening and closing of the nitrogen primary valve V1 ′ and the nitrogen secondary blow valve V2 ′.

Next, control of opening and closing of the nitrogen primary valve V1 'and the nitrogen secondary blow valve V2' by the control unit C 'will be described with reference to the flowchart shown in FIG.
In FIG. 4, the control unit C ′ determines whether or not the boiler B ′ is in an operation state based on the operation state detection signal s3 ′ input from the boiler B ′ (step 1). When it is determined that the boiler B 'is in the operating state, a valve opening / closing signal v1' is output to the nitrogen primary valve V1 'to output the nitrogen primary valve V1'.
Is closed (step m) and the nitrogen secondary blow valve V
A valve opening / closing signal v2 'is output to 2' to open this nitrogen secondary blow valve V2 '(step n).

By controlling the opening and closing of the nitrogen primary valve V1 'and the nitrogen secondary blow valve V2', when the boiler B 'whose operation has been stopped resumes its operation, as described later, the steam drum of the boiler B' The supply of nitrogen gas to D 'through the nitrogen supply pipe L1' is shut off.

In the determination in step 1 above, even if it is determined that the boiler B 'is not in operation, that is, it is stopped, the control unit C'
Further, the internal pressure of the high-pressure header 2 'is set to 3. based on the pressure detection signal s2' input from the pressure sensor S2 '.
It is determined whether or not the pressure is 0 kg / cm ² or more (step o). If it is determined in step o that the internal pressure of the high-pressure header 2 is less than 3.0 kg / cm ² , It is determined whether or not the internal pressure of the high-pressure header 2 is 2.5 kg / cm2 or less (step p). When it is determined that the internal pressure of the high-pressure header 2 is 2.5 kg / cm ² or less, the process proceeds to steps m and n even if the boiler B ′ is stopped. By outputting the open / close signal v1 'and the valve open / close signal v2', the nitrogen primary valve V1 'is closed and the nitrogen secondary blow valve V2' is opened.

The determination of steps o and p is made for the same reason as in the examples of FIGS.
When the control unit C ′ determines in step o that the internal pressure of the high-pressure header 2 ′ is equal to or more than 3.0 kg / cm ² , the control unit C ′ further outputs a pressure detection signal s1 ′ input from the pressure sensor S1 ′. It is determined whether or not the drum pressure in the steam drum D ′ is 1.5 kg / cm ² or less (step q) based on this. In this step q, the drum pressure of the steam drum D ′ is 1.5 kg / cm 2. ^When it is determined that the pressure is ² or more, it is further determined whether or not the drum pressure of the steam drum D ′ is 2.0 kg / cm ² or more (step r). When it is determined that the drum pressure of the steam drum D ′ is 2.0 kg / cm ² or more, the process proceeds to steps c and d even when the boiler B ′ is stopped. By outputting the valve opening / closing signal v1 'and the valve opening / closing signal v2', the nitrogen primary valve V1 '
Is closed and the nitrogen secondary blow valve V2 'is opened.

The determinations in steps q and r are made for the same reason as in the examples shown in FIGS.
In the above steps l, o and q, it is determined that the boiler B 'is in the operation stop state, the internal pressure of the high pressure header 2' is 3.0 kg / cm ² or more, and the drum pressure of the steam drum D 'is 1, In case of 5 kg / cm ² or less, nitrogen primary valve V1 '
Is opened (step s), and the nitrogen secondary blow valve V2 'is closed (step t).

This nitrogen primary valve V1 'is opened and nitrogen 2
By closing the next blow valve V2 ', nitrogen gas is supplied into the steam drum D' via the nitrogen supply pipe L1 ',
It is filled in the steam drum D '. This prevents air from entering the steam drum D 'when the operation of the boiler B' is stopped, and prevents the inside of the steam drum D 'from being corroded.

This example is also for the case where a plurality of boilers are connected to the high-pressure header 2 '. However, as in the examples of FIGS. In one case, an electromagnetic on-off valve is connected to the steam pipe L2 'so that the control unit C' opens the nitrogen primary valve V1 'and at the same time closes the electromagnetic on-off valve connected to the steam pipe L2'. Even if the internal pressure of the high-pressure header 2 'drops below a predetermined value due to the shutdown of the boiler B', it is possible to introduce nitrogen gas into the steam drum D '. be able to.

In this case, it is not necessary to determine the internal pressure of the high-pressure header 2 'in steps o and p in FIG.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of the best mode of the present invention.

FIG. 2 is a flowchart showing a control process in the control unit of the example.

FIG. 3 is a circuit diagram showing another example of the best mode of the present invention.

FIG. 4 is a flowchart showing a control process in the control unit of the same example.

[Explanation of symbols]

B, B '... Boiler D, D' ... Steam drum V1, V1 '... Nitrogen primary valve (electromagnetic on-off valve) V2, V2' ... Nitrogen secondary blow valve (electromagnetic blow valve) L1, L1 '... Nitrogen supply pipe S1, S1 '... pressure sensor (drum pressure detection member) s1, s1' ... pressure detection signal (drum pressure detection signal) s3, s3 '... operation state detection signal (boiler operation state detection signal) v1, v1' ... valve opening / closing Signal (valve open signal, valve close signal) v2, v2 '... valve open / close signal (valve open signal, valve close signal)

Claims (2)

[Claims] A nitrogen gas supply source connected to a steam drum of a boiler via a nitrogen supply pipe; a nitrogen gas supply source attached to the nitrogen supply pipe connecting the nitrogen gas supply source and the steam drum; An electromagnetic on-off valve for communicating and shutting off the drum, an electromagnetic blow valve connected to a nitrogen supply pipe downstream of the electromagnetic on-off valve, and a boiler operation for outputting a boiler operation state detection signal indicating an operation state of the boiler A state detection signal output member, a drum pressure detection member attached to the steam drum for detecting a pressure in the steam drum and outputting a drum pressure detection signal, and a drum pressure detection signal output from the drum pressure detection member And a boiler operation state detection signal output from the boiler operation state detection signal output member, and the boiler operation state detection signal Outputting a valve opening signal for opening the electromagnetic on-off valve to the electromagnetic on-off valve when the drum pressure value indicated by the drum pressure detection signal indicates an operation stop state and is equal to or less than a preset reference pressure value. A valve closing signal for closing the electromagnetic blow valve is output to the electromagnetic blow valve, and the boiler operation state detection signal indicates the operation state of the boiler or the drum pressure value indicated by the drum pressure detection signal indicates a preset reference pressure. A control member that outputs a valve closing signal for closing the electromagnetic on-off valve to the electromagnetic on-off valve when the value is equal to or more than a value and outputs a valve opening signal for opening the electromagnetic blow-on valve to the electromagnetic blow valve. An apparatus for preventing corrosion of a steam drum of a boiler. 2. The control member outputs a valve closing signal to an electromagnetic on / off valve and outputs a valve opening signal to the electromagnetic on / off valve and outputs a valve opening signal to the electromagnetic on / off valve. The apparatus for preventing corrosion of a steam drum of a boiler according to claim 1, wherein the value is set to a value higher than a reference pressure value when a valve closing signal is output to the boiler.