JPH04278101A - Exhaust heat recovery boiler - Google Patents

Abstract

PURPOSE:To mitigate an abnormal rise of the steam pressure in a low pressure drum which is generated in the hot banking of an exhaust heat recovery boiler. CONSTITUTION:A condenser drain piping 26 and a drain tank drain piping 28 are provided between a condenser 26 and drain tank 27 from a low pressure main steam pipe 14, and one of a condenser drain valve and a drain tank drain valve 30 is opened or closed based on the difference between the pressure detection signal 32 and the pressure setting signal 34 from a pressure detection device 31 to make the steam from a low pressure drum 5 escape to the condenser 24 and drain tank 27.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixed pressure type waste heat recovery boiler, and more particularly to a waste heat recovery boiler that suppresses a rise in pressure within a low pressure drum when a gas turbine is stopped.

0002

[Prior Art] Large-capacity thermal power plants are being constructed to meet the rapidly increasing demand for electricity, but these boilers are required to operate at variable voltage in order to obtain high power generation efficiency even during partial load. ing. This is a feature of recent electricity demand, as nuclear power generation increases, the difference between maximum and minimum loads increases, and thermal power generation tends to shift from base load to load adjustment.

[0003] In other words, in thermal power generation, there are few cases in which the boiler load is always operated at full load;
% load, 25% load, increasing the load to 25% load, or stopping the operation. DSS operation allows the system to operate only during the day when there is a high demand for electricity, and shuts down at night to improve power generation efficiency.

[0004] For example, combined cycle power plants have recently attracted attention as a part of high-efficiency power generation. This combined power generation plant first generates electricity using a gas turbine, then recovers the exhaust heat in the exhaust gas discharged from the gas turbine using an exhaust heat recovery boiler, and uses the steam generated by the exhaust heat recovery boiler to generate electricity. It operates a steam turbine to generate electricity.

[0005] As described above, combined power generation plants have high power generation efficiency because they generate power using gas turbines and steam turbines, and they also have excellent load response, which is a characteristic of gas turbines, and are therefore able to cope with sudden demand for electricity. It can sufficiently handle rising and falling movements, has excellent load followability, and is convenient for DSS operation.

FIG. 3 is a schematic diagram of a conventional mixed pressure type waste heat recovery boiler. A low-pressure boiler consisting of a low-pressure economizer 3, a low-pressure evaporator 4, and a low-pressure drum 5, from the downstream side to the upstream side of the exhaust gas passage 2 discharged from the gas turbine 1, a high-pressure economizer 6, and a high-pressure evaporator 7. , a high-pressure boiler consisting of a high-pressure drum 8 and a superheater 9 is arranged.

On the other hand, feed water, which is a fluid to be heated, is supplied from a low-pressure water supply pump 10 to a low-pressure economizer 3 via a water supply pipe 11, and after being preheated to a predetermined temperature, it passes through a drum water supply pipe 12 to a low-pressure drum 5. is supplied to The water supplied to the low-pressure drum 5 is naturally or forcedly circulated in the low-pressure evaporator 4 and then the low-pressure drum 5 through the low-pressure downcomer pipe 13 of the low-pressure drum 5, and is heated during this time and becomes water and water in the low-pressure drum 5. After being separated into steam, the water is transferred again to the low pressure downcomer 13 and the low pressure evaporator 4.
The steam is then recirculated to the low pressure drum 5, while the steam is supplied to the steam turbine 15 from the low pressure main steam pipe 14.

On the other hand, a part of the feed water diverted at the outlet of the low-pressure economizer 3 is supplied to the high-pressure economizer 6 from the high-pressure water pump 16 via the high-pressure water supply pipe 17, and is preheated to a predetermined temperature. The water is supplied to the high pressure drum 8 through a drum water supply pipe 18. The feed water supplied to the high pressure drum 8 is circulated in the order of the high pressure evaporator 7 and the high pressure drum 8 via the high pressure downcomer pipe 19 of the high pressure drum 8, similar to the low pressure boiler, and the steam separated in the high pressure drum 8 is drum steam. It is sent to the superheater 9 via the outlet pipe 20,
After being further heated here, the steam is supplied to the steam turbine 15 through the high-pressure main steam pipe 21.

On the other hand, the water separated in the high-pressure drum 8 is recycled to the high-pressure downcomer 19, the high-pressure evaporator 7, and the high-pressure drum 8. In addition, 22 and 23 in the figure are the high pressure main steam pipe 21,
High pressure and low pressure regulating valves of the low pressure main steam pipe 14, 24 a condenser,
25 is an exhaust gas damper. On the other hand, during hot banking of the exhaust heat recovery boiler, the exhaust gas damper 25 is closed, so the exhaust gas passage 2 is filled with exhaust gas G.
This accumulated exhaust gas G heats the feed water of the low pressure boiler, and the steam pressure in the low pressure drum 5 increases abnormally.

0010

[Problem to be Solved by the Invention] During hot banking of a conventional waste heat recovery boiler, heat transfer from high temperature exhaust gas staying in the boiler exhaust gas passage causes
The enthalpy of the feed water held in the low-pressure drum system increases,
As a result, there was a drawback that the steam pressure in the low-pressure drum increased over time.

FIG. 4 shows changes in the steam pressure of the low-pressure drum, and is a characteristic curve diagram in which the vertical axis shows the steam pressure of the low-pressure drum and the horizontal axis shows time. That is, the exhaust gas G is trapped in the exhaust gas passage 2 because the exhaust gas damper 25 shown in FIG. 3 is closed to enter hot banking. Therefore, the low pressure boiler side is warmed by the exhaust gas G, and the curve A in Fig. 4
As shown, the steam pressure in the low pressure drum 5 increases even after the gas turbine 1 is stopped. Therefore, in an exhaust heat recovery boiler that performs DSS operation, it is necessary to take into account the pressure increase during hot banking and design the design pressure to a high value as shown by straight line B, which is uneconomical.

The present invention aims to eliminate the drawbacks of the prior art, and its purpose is to alleviate the abnormal rise in steam pressure that occurs during hot banking of an exhaust heat recovery boiler, and to The aim is to lower the design pressure of the boiler.

[0013]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a condenser drain pipe and a drain tank drain valve having a condenser drain valve from a low pressure main steam pipe to a condenser and a drain tank. A pressure detector is installed on the low-pressure drum, and a calculator is installed to compare the pressure detection signal from the pressure detector with the pressure setting signal. At least one of the condenser drain valve and the drain tank drain valve is opened and closed.

[0014]

[Operation] When the enthalpy in the low-pressure drum system increases due to heat transfer from the high-temperature gas under hot banking conditions in the exhaust heat recovery boiler, and the steam pressure in the low-pressure drum increases, the drain valve is opened to condense water. This is accomplished by exhausting the steam in the low-pressure drum from the container drain piping and the drain tank drain piping.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic system diagram of an exhaust heat recovery boiler according to an embodiment of the present invention, and FIG. 2 is a flowchart of a computing unit. Figure 1
And in FIG. 2, numerals 1 to 25 indicate the same parts as the conventional one. 26 is a condenser drain pipe, 27 is a drain tank, 28 is a drain tank drain pipe, 29 and 30 are a condenser drain valve and a drain tank drain valve, 31 is a pressure detector, 32 is a pressure detection signal, and 33 is a calculation 34 is a pressure setting signal, and 35 is a control signal.

In this structure, the difference from the conventional waste heat recovery boiler shown in FIG. A held tank drain pipe 28 is provided so that an increase in steam pressure generated during hot banking is released from the condenser drain pipe 26 and the drain tank drain pipe 28 to the condenser 24 and the drain tank 27.

That is, as shown in FIG. 1, the steam pressure in the low-pressure drum 5 of the waste heat recovery boiler is detected by a pressure detector 31 as a pressure detection signal 32, and is input to a computing unit 33. This pressure detection signal 32 is compared with the pressure setting signal 34 in a calculator 33, and as a result of the comparison, the pressure detection signal 32 is the pressure setting signal 34.
If the temperature is higher than
4. Steam is released to the drain tank 27.

FIG. 2 shows a flow chart of the arithmetic unit 33. The pressure increase in the low pressure drum 5 during hot banking is detected by the pressure detector 31, and if it is judged in the calculator 33 that it exceeds the pressure setting signal, if the vacuum in the condenser 24 is established, An open signal is sent to the condenser drain valve 29 of the condenser drain pipe 26 to release steam from the condenser drain pipe 26. Further, if the vacuum in the condenser 24 is broken, the drain pipe drain valve 30 of the drain tank drain pipe 28 is opened to release steam to the drain tank 27.

By the above steam release operation, the low pressure drum 5
When the pressure reaches the lower limit of the pressure setting signal 34, the calculator 33 sends a signal to the condenser drain valve 29 and the drain tank drain valve 30 to close the valves. In this way, if a vacuum in the condenser 24 is established corresponding to the degree of vacuum in the condenser 24, steam will flow into the condenser 24 from the condenser drain pipe 26; If the drain tank drain piping 28 is broken, steam is released from the drain tank drain pipe 28 to the drain tank 27.

[0020] When the gas turbine 1 is stopped, the vacuum in the condenser 24 is usually destroyed in order to reduce the internal power, and in this case, the condenser 24 is filled with atmospheric air and O2 dissolved oxygen (D) up to 10,000 ppb.
O2 ) concentration increases, and DO2 concentration is 10 at restart
This is because it is necessary to degas to ppb.

By releasing the steam during hot banking to the condenser 24 and drain tank 27 in this way, the steam pressure in the low pressure drum 5 is lowered as shown by curve C in FIG. 4, and the design pressure is also lowered. As shown by straight line D in Figure 4, the design pressure is 1
．． It is economical because it can be reduced to about 1 times.

[0022]

According to the present invention, it is possible to alleviate the abnormal rise in steam generated during hotbanking of the exhaust heat recovery boiler, and it is possible to lower the design pressure of the exhaust heat recovery boiler.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram of an exhaust heat recovery boiler according to an embodiment of the present invention.

FIG. 2 is a flowchart of an arithmetic unit.

FIG. 3 is a schematic system diagram of a conventional exhaust heat recovery boiler.

FIG. 4 is a characteristic curve diagram in which the vertical axis shows the steam pressure of the low-pressure drum and the horizontal axis shows time.

[Explanation of symbols]

1 Gas turbine 4 Low pressure evaporator 5 Low pressure drum 8 High pressure drum 14 Low pressure main steam pipe 15 Steam turbine 21 High pressure main steam pipe 22 High pressure regulating valve 23 Low pressure regulating valve 24 Condenser 26 Condenser drain piping 27 Drain tank 28 Drain tank drain piping 29 Condenser drain valve 30 Drain tank drain valve 31 Pressure detector 32 Pressure detection signal 33 Arithmetic unit 34 Pressure setting signal

Claims (1)

[Claims] 1. A high-pressure, low-pressure drum that generates steam using exhaust gas from a gas turbine, and a high-pressure, low-pressure evaporator that heats water supplied to the high-pressure, low-pressure drum using the exhaust gas.
In an exhaust heat recovery boiler equipped with high-pressure and low-pressure main steam pipes having high-pressure and low-pressure regulating valves for supplying generated steam to a steam turbine, the low-pressure main steam pipe is connected to a condenser and a drain tank, and a condenser. A calculation in which a condenser drain pipe having a drain valve and a drain tank drain pipe having a drain tank drain valve are provided, a pressure detector is provided in the low pressure drum, and a pressure detection signal from the pressure detector is compared with a pressure setting signal. An exhaust heat recovery boiler characterized in that at least one of a condenser drain valve and a drain tank drain valve is opened or closed depending on a deviation between a pressure detection signal and a pressure setting signal during hot banking. .