JPH0658161B2 - Waste heat recovery boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a waste heat recovery boiler, and is particularly configured to prevent abnormal pressurization due to temperature rise of incompressible feed water in a closed loop economizer at startup. Regarding the waste heat recovery boiler.

<Conventional technology and its problems> As a part of high-efficiency power generation, a combined cycle power plant has recently been drawing attention. In this plant, power is generated by a gas turbine, heat in exhaust gas discharged from the gas turbine is recovered by a waste heat recovery boiler, and steam generated in the boiler drives a steam turbine to generate power.
In addition to high-efficiency power generation, this plant can be said to be the optimum plant for intermediate load operation in line with recent power demand patterns due to the features of gas turbines such as the ease of rapid startup and high load response.

Example 1 FIG. 1 shows an example of the present invention. The concept of the system of the combined power generation plant including the gau turbine 1, the waste heat recovery boiler 5, and the steam turbine 3 to which the present invention is applied will be first described with reference to this figure.

In the figure, this device is composed of a low pressure drum 9 and a low pressure economizer 7.
And a low-pressure boiler system including a low-pressure evaporator 8, a high-pressure boiler system including a high-pressure drum 13, a high-pressure economizer 11, a high-pressure evaporator 12, and a high-pressure superheater 14, and a low-pressure water supply pump 6 to a low-pressure pump 6. A low-pressure water supply system for supplying water to the low-pressure drum 9 via the economizer 7, the low-pressure flow rate control valve 15,
A part of the water supply is taken out, the pressure is raised by the high-pressure water supply pump 10, and the water is supplied to the high-pressure drum 13 through the high-pressure economizer 11 and the high-pressure flow rate adjusting valve 16, and the high-pressure water supply pump 10 and the high-pressure water supply pump 10. The high-pressure economizer 12 is mainly configured by a recirculation flow passage 19 that takes out a part of the high-pressure feed water from the midway of the high-pressure economizer 12 and recirculates it to the flow passage between the low-pressure feed pump 6 and the low-pressure economizer 7.

In the apparatus having the above structure, the feed water deaerated by the condenser 4 is sent into the low pressure drum 9 by the low pressure feed pump 6 through the economizer 7 and the flow control valve 15, and the economizer 7 is also used.
A part of the supplied water is further pressurized by the high-pressure water supply pump 10 and sent to the high-pressure drum 13 via the high-pressure economizer 12 and the flow rate control valve 16.

As described above, a part of the high temperature feed water at the inlet of the high pressure economizer 12 is recirculated to the inlet side of the low pressure economizer 7, and the temperature of the inlet feed water of the low pressure economizer 7 is set to a temperature at which low temperature corrosion does not occur. By heating up to 0, it is possible to prevent corrosion of the economizer and its peripheral equipment due to acidic components in the exhaust gas.

The waste heat recovery boiler 5 is composed of a plurality of high and low pressure drum type boilers as indicated by reference numerals 12 and 8 in order to recover the exhaust heat from the gas turbine 1 to the maximum extent. It has a characteristic that an evaporation phenomenon occurs in the heat transfer tube group portion having a low inflow gas temperature to the boiler and a relatively low temperature, that is, in the low pressure economizer 7 and the high pressure economizer 11. If a mixed fluid of steam and water is present in the economizer, the control system becomes unstable, making it difficult to continue the operation. In addition, water hammer causes various inconvenient problems such as equipment damage.

For this reason, unlike the conventional thermal power boiler, the feed water flow rate control valves 15 and 16 are installed at the outlets of the high and low pressure economizers to adjust the water levels of the drums 9 and 13 within a predetermined range, and the low pressure feed pump 6 and high pressure The discharge fluid pressure of the water supply pump 10 keeps the internal fluid pressure of the heat transfer tubes of the economizers 7 and 12 at a required pressure, and maintains the fluid temperature in the economizers 7 and 11 at a temperature equal to or lower than the saturation temperature at the pressure. Then, it is devised so as to prevent evaporation in the relevant part.

The above is the outline of the conventional technique.

In the present invention, when the plant is stopped at night, the high- and low-pressure recirculation lines 17a and 17b are used for the purpose of preventing self-evaporation in the economizers 7 and 11 based on the pressure drop, and prevent the harmful effects caused by the steam-water mixture. It is configured to do.

That is, if self-evaporation occurs in the economizer 7 or 11, the specific gravity of the steam-water mixture at that portion becomes lighter, so the boiler drums 9 and 13 are recirculated through the recirculation lines 17a and 17b.
The can water in the inside circulates and expels the steam part of the economizer into the drum.

Although the above configuration enables prevention of steam generation in the economizer, on the other hand, the following problems have been pointed out and their improvement is desired.

That is, at the time of start-up, the economizer circulation systems 17a and 17b are closed, the low-pressure water supply pump 6 and the high-pressure water supply pump 10 are started, and the drum level control of the high- and low-pressure drums 13 and 9 becomes possible. Although the exhaust gas from No. 1 is introduced, the can water in the evaporators 8 and 12 expands due to the temperature rise, and the drum water level tends to rise. Therefore, the flow rate control valves 15 and 16 are set to 10 at the initial stage of activation so that the drum water level does not exceed a predetermined value.
It is controlled to continue the closing operation for about 30 minutes. Therefore, the water in the economizers 7 and 11 is heated in the closed pipe, and the fluid volume increases by 5 to 6%. Therefore, it usually expands by about 1 m ³ in each economizer system, although it depends on the capacity of the economizer. Water is an incompressible fluid, so it is made of steel pipes, tubes,
Pipes will be subjected to severe loads, and unless consideration is given to releasing the volume expansion of the internal fluid to the outside of the system,
It is clear that it will lead to serious accidents such as destruction or blast.

For this reason, a safety valve is provided for such a closed system so that the safety valve can be dealt with, and it is obligatory to install the safety valve according to the regulations. However, the installation of the safety valve has the following problems, and it is not sufficient as a fundamental solution to the problem, which causes a new danger and also has an economical problem. That is, when high-pressure water or high-temperature water that boils due to reduced pressure is ejected from the safety valve, it is certain that the valve body will be damaged by erosion, and the possibility of an external leak accident is extremely high. In particular, in the above-mentioned device, the safety valve is activated every time it is started, and it cannot withstand practical operation. In addition, the expensive boiler water that has been subjected to impurity removal and dissolved oxygen removal treatment is discharged out of the system, and economic disadvantages cannot be ignored.

<Object of the Invention> The present invention is configured in view of the above-mentioned problems, and is capable of minimizing the amount of boiler water discharged to the outside of the system at the time of startup and increasing the amount of heat recovery, a waste heat recovery boiler. The purpose is to provide.

<Summary of the Invention> In short, the present invention is a waste heat recovery boiler in which a pipeline configured to automatically return the pressurized fluid in the economizer to a condenser or the like is arranged.

Example 1 Hereinafter, a first example of the present invention will be described. In FIG. 1, reference numeral 19 is a recirculation pipeline connected to the low pressure economizer outlet line 25. Reference numeral 18 is a check valve provided in the outlet line 25, and 21 is a control valve for the recirculation pipeline 19. This recirculation line 19 is also connected to the inlet line 26 of the high pressure economizer 11, the lines 25 and 26 are connected in the conventional device, and at least a part of the feed water of the low pressure economizer 7 is connected to the high pressure economizer. It is configured to flow into the charcoal vessel 11. A water supply supply line 27 is connected to the downstream side of the recirculation pipeline 19.

In the above apparatus, for example, when the power demand decreases at night, the condenser 4 breaks the vacuum at night stop and performs the supplementary stop operation. For this reason, the feed water comes into contact with the atmosphere in the condenser 4, and O ₂ is dissolved in the feed water.
Dissolved oxygen of about ppb is included in the condensate. Therefore, before the start-up, the condensate is circulated by the system 20 to remove the dissolved oxygen in the condensate, and the dissolved oxygen amount is the specified value (10 pp.
When it reaches (b or less), the gas turbine 1 is started and the plant starts.

When the water supply reaches the specified dissolved oxygen concentration, the system 20
It can be closed by the control valve 22, but from the aspect of safety and equipment protection, it is confirmed that the feed water flow meter 23 continuously feeds water, or an open signal of the turbine bypass valve 24. It is controlled not to be fully closed until is transmitted. On the other hand, the feed water in each economizer 7 and 11 is also increased in pressure by the passage of the exhaust gas, but the feed water from the low-pressure economizer 7 is passed through the line 25 and the check valve 18 to the recirculation pipeline 19. In addition, in the case of the high-pressure coal economizer 11, it flows into the recirculation pipeline 19 via the line 26, and the excess water is returned to the condenser 4 via the low-pressure water supply line 27 and the condensate circulation line 20. Hold the pressure inside the economizer at a specified value,
The startup operation is completed and the rated operation is started. Here, the control valve 21
It is preferable to set the minimum flow rate opening even after the rated value is entered so that it will not be fully closed, and it is possible to cope with abnormal pressure rise during rated operation. In the figure, reference numeral 2 is a generator, 3 is a steam turbine, and 14 is a superheater.

<Embodiment 2> FIG. 2 shows a second embodiment. In the first embodiment described above, the recirculation pipeline 19 is branched from the connecting portion between the high pressure economizer 11 side and the low pressure economizer 7 side, and the low pressure economizer inlet line 28 and this recirculation. It was in communication with the conduit 19. While this configuration simplifies the pipeline configuration, when the pressure on the high pressure economizer side is considerably high and the opening degree of the valve 22 is erroneously adjusted, part of the water supply that has exited the recirculation pipeline 19 will become a line. 28
There may be a situation in which the gas flows back to the low-pressure economizer side after passing through.

The second embodiment can be constructed so as to more effectively take measures against this point. That is, the recirculation pipe 19 is branched from the upstream side of the check valve 18 of the low pressure economizer outlet line 25 to prevent the feed water from flowing into the recirculation pipe 19 from the high pressure economizer 11. A pressure relief line dedicated to the low-pressure economizer is provided, and a pressure relief line 29 dedicated to the high-pressure economizer is branched from the high-pressure economizer inlet line 26 on the high-pressure economizer 11 side. In this case, if the pressure detector 30 is arranged in the line 26 and the valve 31 is controlled based on the detection result of the detector 30, the pressure of the high pressure economizer can be automatically adjusted.

<Effect> Since the present invention is configured as described above, it is not necessary to eject the high-pressure fluid through the safety valve, so it is possible to prevent the plant from being stopped due to valve damage, and to improve the operating efficiency of the entire plant. Can be significantly improved.

In addition, since all the amount of expanded water can be collected in the system, expensive water supply can be effectively used in this device, which is frequently started and stopped, and economic efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram of a combined cycle power plant showing a first embodiment of the present invention, and FIG. 2 is a plant system partial view showing a second embodiment. 7 ... Low-pressure economizer 11 ... High-pressure economizer 19 ... Recirculation pipe 25 ... Low-pressure economizer outlet line 26 ... High-pressure economizer inlet line 18 ... Check valve

Claims (2)

[Claims] 1. A high-pressure drum and a low-pressure drum connected to a high-pressure evaporator and a low-pressure evaporator, respectively, and a low-pressure water supply for replenishing makeup water to the low-pressure drum via a low-pressure economizer and a flow control valve provided at its outlet. The low-pressure water supply system including the pump and the front of the low-pressure coal economizer outlet flow rate control valve are branched to pass through the high-pressure water supply pump, the high-pressure economizer, and the high-pressure economizer outlet flow control valve in this order, and make-up water is supplied to the high-pressure drum. The high-pressure water supply system for replenishing and a recirculation pipeline for recirculating a part of the water supply at the inlet of the high-pressure economizer to the low-pressure water supply system upstream of the low-pressure economizer via the high-pressure water supply pump. And a pipeline for treating an excessive boiler can water amount are branched from the recirculation pipeline, the low pressure water supply system, and the outlet side pipeline of the low pressure water supply pump of the low pressure water supply system and connected to the turbine condenser. Consists of condensate circulation line Waste heat recovery boiler, wherein the door. 2. The waste heat recovery boiler according to claim 1, characterized in that an excess can water treatment line dedicated to the high pressure side, which branches from the water supply pipe line at the inlet of the high pressure economizer, is provided. The waste heat recovery boiler according to claim 1.