JP2000205501A - Exhaust heat recovery boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure maintenance of inner pressure of a fuel economizer at a level not greater than design pressure without frequently permitting a relief valve to open even if the inner pressure of the fuel economizer is blocked when operation is suspended. SOLUTION: A boiler has such an arrangement in which an upstream portion of a feed water regulating valve 18 of a connecting tube 13 and a blow down tank 22 are connected by a drain tube 22 having an on-off valve 21, and a pressure detector 23 is arranged at an upper entrance header 8 of a fuel economizer 5 so as to detect inner pressure of the fuel economizer 5. A command signal 24 is outputted from the pressure detector 23 to the on-off valve 21 in order to open the on-off valve 21 when the detected pressure reaches a predetermined upper limit value and close the on-off valve 21 when reaching a predetermined lower limit value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust heat recovery boiler.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional waste heat recovery boiler. In FIG. 3, reference numeral 1 denotes an exhaust gas from a gas turbine (not shown) driven by using natural gas, heavy oil, or the like as a fuel; FIG. 2 shows an exhaust gas channel that flows from the left side to the right side in the figure. In the exhaust gas channel 2, a superheater 3, an evaporator 4, and a economizer 5 are sequentially arranged in the flow direction of the exhaust gas 1. The steam is generated by heating water by a heat exchanging section including the superheater 3, the evaporator 4, and the economizer 5.

[0003] The steam generated in the heat exchanging section comprising the superheater 3, the evaporator 4, and the economizer 5 is used as a driving steam for a steam turbine or a heat source for an air conditioner.
Further, the exhaust gas 1 whose exhaust heat has been recovered and cooled to a low temperature is subjected to an appropriate gas treatment and then discharged to the atmosphere from a chimney (not shown) on the downstream side.

Here, the economizer 5 is constituted by a plurality of heat transfer tubes 6 formed so as to go back in the exhaust gas flow path 2 to the upstream side while twisting up and down in a vertical manner. The water introduced into the inlet header 8 is heated while being exposed to the high-temperature exhaust gas 1 while flowing through each heat transfer tube 6, and is collected as high-temperature water in the upper outlet header 9.

The structure of each heat transfer tube 6 will be described in more detail. The bent portion at the upper end of each heat transfer tube 6 is formed by an inverted U-shaped bend portion 10, and the bent portion at the lower end of each heat transfer tube 6 is formed. Are formed by common lower headers 11, and the temperature of the water is gradually raised while the heating unevenness is leveled at each lower header 11.

The evaporator 4 is provided with a steam drum 12 for separating water and steam at an upper portion thereof. The steam drum 12 has hot water collected at an upper outlet header 9 of the economizer 5. Is guided through the communication pipe 13.

Then, the hot water flowing down from the lower portion of the steam drum 12 to the lower header 15 via the downcomer 14 is heated while ascending the heat transfer tube 16 and is returned to the steam drum 12 as steam. It has become.

Further, the superheater 3 is constituted by a plurality of heat transfer tubes 17 formed so as to go back in the exhaust gas flow path 2 to the upstream side while twisting up and down.
The steam is introduced from the upper part of the steam drum 12 of the evaporator 4 to the inlet end located at the most downstream side of
7, and is supplied to the destination as superheated steam.

In such an exhaust heat recovery boiler, when its operation is stopped (stop on the gas turbine side), the economizer 5
Feed control valve 18 provided in a connecting pipe 13 connecting between the upper outlet header 9 of the evaporator 4 and the steam drum 12 of the evaporator 4.
Is fully closed to seal the internal pressure of the economizer 5.

That is, if the water supply control valve 18 is kept open and the internal pressure of the economizer 5 is released when the operation is stopped, the temperature of the hot water in the economizer 5 drops and the restart time is reduced. It takes a long time to start up, and furthermore, the hot water tends to boil due to the pressure drop, and a large amount of steam accumulates in the bend portion 10 at the upper part of the economizer 5. In order to avoid these concerns, the water supply control valve 18 is fully closed to seal the internal pressure of the economizer 5, and the operation is stopped. The temperature of the hot water in the economizer 5 is maintained so as not to drop so much, and a steam pool is prevented from being formed as much as possible in the bend portion 10 above the heat transfer tube 6 of the economizer 5.

[0011]

However, even if the operation of the exhaust heat recovery boiler is stopped, since the superheater 3 and the reinforcing members of various devices have a relatively large amount of retained heat, the exhaust gas Since the high-temperature exhaust gas 1 remains in the flow path 2 and the high-temperature exhaust gas 1 flows to the lower temperature side, the economizer 5 which is supposed to receive a low gas temperature in the normal operation is operated when the operation is stopped. Rather, it is exposed to a high gas temperature and is heated remarkably. If the internal pressure of the economizer 5 is kept closed, an excessive pressure rise exceeding the design pressure may occur.

Of course, in the connecting pipe 13 connecting between the upper outlet header 9 of the economizer 5 and the steam drum 12 of the evaporator 4, the supply pressure of hot water from the economizer 5 rises above the design pressure. Conventionally, a relief valve 19 is provided for the purpose of protecting the various devices by avoiding such a situation. However, generally, this type of relief valve 19 is opened small by an amount exceeding a predetermined set pressure. When the pressure is released to the outside of the system, it immediately closes, so that the internal pressure of the economizer 5 repeatedly increases and decreases within a relatively narrow pressure fluctuation range near the set pressure of the relief valve 19, and the relief valve 19 is operated for a long time. Frequent opening over many times, the internal valve disc is worn out (erosion) in a short time,
The problem that the maintenance work requires a great deal of work is inevitable.

That is, when the relief valve 19 is opened, the economizer 5
When the high-temperature water from the side passes outside the system at a high differential pressure, the high-temperature water rapidly decompresses and changes into steam containing water droplets at a stretch, so that the steam containing the water droplets flows at high speed. The impact on the valve disc is extremely large,
The valve disc of the relief valve 19 is relatively easily worn.

The present invention has been made in view of the above-mentioned circumstances, and even if the internal pressure of the economizer is shut down when the operation is stopped, the internal pressure of the economizer is reduced to the design pressure without frequently opening the relief valve. The purpose is to be able to reliably hold the following.

[0015]

According to the present invention, a superheater, an evaporator, and a economizer are connected in the exhaust gas flow direction in an exhaust gas flow path, and a hot water heated by the economizer is supplied to a water supply control valve. In the exhaust heat recovery boiler, which leads to the steam drum above the evaporator through the connecting pipe provided and guides the steam generated in the steam drum to the superheater, a portion of the connecting pipe on the upstream side of the water supply control valve blows. A drain pipe having an open / close valve is connected between the tank and the down tank, and a pressure detector for detecting the internal pressure of the economizer is provided at an appropriate position of the economizer. A command signal for opening the on-off valve when reaching an upper limit value and for closing the on-off valve when reaching a predetermined lower limit value is output from the pressure detector.

In this way, even if the water supply control valve is fully closed when the operation is stopped and the internal pressure of the economizer is closed, the rise in the internal pressure of the economizer is monitored by the pressure detector, and the pressure detection is performed. The open / close valve is opened by the command signal at the upper limit set in the heater, and a portion of the warm water in the economizer is safely released to the blowdown tank through the drain pipe, thereby releasing the internal pressure of the economizer. Therefore, it is reliably prevented that the internal pressure of the economizer rises excessively beyond the set pressure.

Further, when a certain amount of hot water is withdrawn from the economizer and the internal pressure of the economizer drops, and the internal pressure of the economizer reaches the lower limit set in the pressure detector, The on-off valve closes again and seals the internal pressure of the economizer, so unnecessary pressure drops are avoided and the internal pressure of the economizer can be maintained high without any problem. Becomes

In this case, a reverse angle valve or the like suitable for use at a high differential pressure can be appropriately used as the on-off valve, and the pressure is controlled by a pressure range having an upper limit value and a lower limit value. Since the frequency of the opening operation can be reduced as much as possible by performing an intermittent opening operation with a large interval, when used as a countermeasure for pressure increase of the economizer when the operation is stopped, erosion occurs in a short time. It is possible to avoid the risk of occurrence.

The relief valve will not be opened in the normal operation stop state unless a failure occurs in the on-off valve, the pressure detector, and the like. It will be operated for the purpose of avoiding danger.

Further, in the present invention, a downward branch pipe provided with a closing valve may be provided at a portion downstream of the on-off valve of the drainage pipe so as to appropriately close the flow path.

In this way, the control by the pressure detector is released to open the on-off valve of the drain pipe and the closing valve of the branch pipe is opened by manual operation or the like, so that a part of the drain pipe and the branch pipe are connected. It becomes possible to use it as a vent pipe, so that when the economizer drained and emptied for maintenance etc. is filled with water again, it is possible to satisfactorily extract the air accumulated at the top at the end In addition, the present invention can be easily implemented simply by replacing the drain pipe with the place where the conventional vent pipe is arranged.

As described above, when the drain pipe is used as a countermeasure for increasing the pressure of the economizer when the operation is stopped, the shut-off valve may be fully closed to block the flow path of the branch pipe.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an embodiment of the present invention, in which the same reference numerals as in FIG. 3 denote the same parts.

As shown in FIG. 1, in the exhaust heat recovery boiler of the present embodiment, an opening / closing valve 21 is provided between a portion of the connecting pipe 13 upstream of the water supply control valve 18 and the blowdown tank 20.
And a pressure detector 23 is installed at the upper inlet header 8 of the economizer 5 so that the internal pressure of the economizer 5 can be detected, and the detected pressure reaches a predetermined upper limit. A command signal 24 for opening the on-off valve 21 when it has reached and for closing the on-off valve 21 when it has reached a predetermined lower limit is output from the pressure detector 23 to the on-off valve 21.

Here, the blowdown tank 20
This tank is used to store the extracted water when the evaporator 4 and the economizer 5 are emptied for boiler water blow-up and maintenance at the time of start-up. It is.

In this embodiment, in particular, the drain pipe 2
A downstream branch pipe 26 having a closing valve 25 is provided at a portion downstream of the on-off valve 21 so as to appropriately close the flow path. A funnel receiver 27 is provided for visually confirming that the air discharged from the branch pipe 26 no longer contains air.

Thus, even if the water supply control valve 18 is fully closed to shut down the internal pressure of the economizer 5 when the operation is stopped, the rise in the internal pressure of the economizer 5 is not detected by the pressure detector. The on / off valve 21 is opened by the command signal 24 at the upper limit value set in the pressure detector 23, and a part of the warm water in the economizer 5 is discharged through the drain pipe 22 to the blowdown tank 2.
Since the pressure is safely released to zero and the internal pressure of the economizer 5 is released, the internal pressure of the economizer 5 is reliably prevented from excessively increasing beyond the set pressure. You.

Also, a certain amount of hot water is extracted from the economizer 5 and the internal pressure of the economizer 5 is reduced.
When the internal pressure reaches the lower limit value set in the pressure detector 23, the on-off valve 21 is closed again and the internal pressure of the economizer 5 is sealed, so that unnecessary unnecessary pressure drop is avoided. , And the internal pressure of the economizer 5 can be kept high within a range that does not cause any trouble.

Here, a reverse angle valve or the like suitable for use at a high differential pressure can be appropriately used as the on-off valve 21, and a pressure control having a range between an upper limit value and a lower limit value. In this case, the frequency of the opening operation can be reduced as much as possible by performing an intermittent opening operation with a large interval, so that when used as a countermeasure for the pressure increase of the economizer 5 when the operation is stopped, the erosion occurs in a short time. It is possible to avoid the danger of doing so.

The relief valve 19 will not be opened in the normal operation stop state unless the on-off valve 21, the pressure detector 23 and the like fail, so that the emergency valve according to the original design concept can be used. It will be operated for the purpose of temporary danger avoidance.

In particular, in the present embodiment, the control by the pressure detector 23 is released to open the on-off valve 21 of the drain pipe 22 and the closing valve 25 of the branch pipe 26 is opened by manual operation or the like, so that one of the drain pipes 22 is opened. The part and the branch pipe 26 can be used as a vent pipe, and when the economizer 5 that has been drained and emptied for maintenance or the like is filled with water again, the air that has finally accumulated upwards is good. Can be easily carried out simply by replacing the drain pipe 22 at the place where the conventional vent pipe is arranged.

That is, although not shown in FIG. 3 showing the above-described conventional example, a vent pipe for venting air is conventionally provided at a portion of the connecting pipe 13 upstream of the water supply control valve 18. Therefore, assuming that the vent pipe is also provided with the function as the vent pipe as in the present embodiment, it is only necessary to replace the drain pipe 22 at the place where the conventional vent pipe is arranged.

As described above, when the drain pipe 22 is used as a countermeasure against the pressure increase of the economizer 5 when the operation is stopped, the shutoff valve 25 may be fully closed and the flow path of the branch pipe 26 may be closed. .

FIG. 2 is a graph showing the transition of the pressure detected by the pressure detector 23, which also shows the opening operation of the on-off valve 21. For example, the upper limit set for the pressure detector 23 is about 3.0 MPa. When the lower limit is set to about 1.5 MPa, when the detected pressure reaches the upper limit of about 3.0 MPa after the operation is stopped, the on-off valve 21 opens with a sufficiently large opening degree. When the pressure detected by the pressure detector 23 rapidly decreases and reaches the lower limit of about 1.5 MPa, the operation of returning the opening of the on-off valve 21 to the fully closed state of 0% is intermittently repeated.

Here, as is clear from this graph, at the beginning of the operation stoppage, a relatively large amount of retained heat remains in the superheater 3 in the exhaust gas passage 2 and the reinforcing material of various devices. Even if the internal pressure of the economizer 5 is released by opening the on-off valve 21, the internal pressure rises relatively quickly, but the interval of the opening operation gradually increases as the exhaust gas passage 2 cools down with the passage of time. In other words, the frequency of the opening operation as a whole can be reduced so as to be incomparable to the case where the conventional relief valve 19 is used.

It should be noted that the relief valve 19 will not be opened in the normal operation stop state unless the on-off valve 21 and the pressure detector 23 and the like fail, so that the emergency valve according to the original design concept can be used. It will be operated for the purpose of temporary danger avoidance.

Therefore, according to the above-described embodiment, even if the internal pressure of the economizer 5 is shut off when the operation is stopped, the internal pressure of the economizer 5 can be kept below the design pressure without frequently opening the relief valve 19. Can be held.

Further, since a part of the drain pipe 22 and the branch pipe 26 can be used as a vent pipe, the present invention can be easily carried out simply by replacing the drain pipe 22 at the place where the conventional vent pipe is arranged. Can be.

Incidentally, the exhaust heat recovery boiler of the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the gist of the present invention.

[0041]

According to the exhaust heat recovery boiler of the present invention described above, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, even if the internal pressure of the economizer is closed when the operation is stopped, the internal pressure of the economizer is maintained without frequently opening the relief valve. Can be reliably maintained below the design pressure.

(II) According to the second aspect of the present invention, since a part of the drain pipe and the branch pipe can be used as a vent pipe, the place where the conventional vent pipe is disposed It can be easily implemented simply by replacing the drain pipe.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a graph showing a change in pressure detected by a pressure detector.

FIG. 3 is a schematic view showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Exhaust gas flow path 3 Superheater 4 Evaporator 5 Energy saving device 12 Steam drum 13 Communication pipe 18 Water supply control valve 20 Blowdown tank 21 Open / close valve 22 Drainage pipe 23 Pressure detector 24 Command signal 25 Closing valve 26 Branch pipe

Claims (2)

[Claims] 1. A superheater, an evaporator, and a economizer are connected in the exhaust gas flow direction in an exhaust gas flow direction, and hot water heated by the ecommerer is connected to an evaporator via a communication pipe provided with a water supply control valve. In an exhaust heat recovery boiler that leads to an upper steam drum and guides steam generated by the steam drum to a superheater, an on-off valve is provided between a blow-down tank and a portion of the connecting pipe upstream of a water supply control valve. A pressure detector for detecting the internal pressure of the economizer is provided at an appropriate position of the economizer, and the opening and closing is performed when the pressure detected by the pressure detector reaches a predetermined upper limit. An exhaust heat recovery boiler, wherein a command signal for opening the valve and closing the on-off valve when the predetermined lower limit is reached is output from the pressure detector. 2. The drainage pipe according to claim 1, wherein a downward branch pipe provided with a shutoff valve is provided at a position downstream of the on-off valve of the drainage pipe so as to appropriately close the flow passage. Waste heat recovery boiler.