JP2971597B2 - Waste heat recovery boiler - Google Patents

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 exhaust heat recovery boiler, and more particularly to an exhaust heat recovery boiler that suppresses a pressure increase in a low pressure drum when a gas turbine is stopped.

[0002]

2. Description of the Related Art Large-capacity thermal power plants are being constructed to meet the rapidly increasing demand for electric power. However, these boilers are required to perform a voltage-changing operation in order to obtain high power generation efficiency even at a partial load. ing. As a characteristic of recent power demand, the difference between the maximum and minimum loads increases with the increase in nuclear power generation, and thermal power generation tends to shift from base load use to load adjustment.

[0003] In other words, in the case of thermal power generation, there are few boiler loads that are always operated at full load.
The load is increased to 25% load, the load is reduced to 25%, the operation is stopped, or the operation is stopped. The so-called high-frequency start / stop (hereinafter simply referred to as DSS) operation is performed to carry the intermediate load. With DSS operation, operation is performed only in the daytime when power demand is high, and operation is stopped at night to improve power generation efficiency.

For example, as part of high-efficiency power generation, a combined cycle power plant has recently been receiving attention. This combined cycle power plant first generates power using a gas turbine, recovers waste heat in exhaust gas discharged from the gas turbine using a waste heat recovery boiler, and uses steam generated by the waste heat recovery boiler to recover heat. The steam turbine is operated to generate power.

[0005] As described above, the combined cycle power plant performs power generation by a gas turbine and power generation by a steam turbine, and thus has high power generation efficiency and excellent load response, which is a characteristic of the gas turbine. It can sufficiently cope with ascending and descending and has excellent load followability, which is convenient for performing DSS operation.

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

On the other hand, feed water as a fluid to be heated is supplied from a low-pressure feed pump 10 to a low-pressure economizer 3 through a feed pipe 11 and preheated to a predetermined temperature.
And supplied to the low-pressure drum 5. The feedwater supplied to the low-pressure drum 5 is naturally circulated or forcedly circulated in the order of the low-pressure evaporator 4 and the low-pressure drum 5 through the low-pressure downcomer 13 of the low-pressure drum 5, and is heated during this time to be mixed with water in the low-pressure drum 5. After being separated into steam, the water is again recycled to the low-pressure downcomer 13, the low-pressure evaporator 4, and the low-pressure drum 5, but 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 feedwater diverted at the outlet of the low-pressure economizer 3 is supplied from the high-pressure water pump 16 to the high-pressure economizer 6 through the high-pressure water supply pipe 17 and preheated to a predetermined temperature. It is supplied to the high-pressure drum 8 through the drum water supply pipe 18. The feed water supplied to the high-pressure drum 8 passes through the high-pressure down pipe 19 of the high-pressure drum 8 similarly to the low-pressure boiler, and the high-pressure evaporator 7,
The steam circulated in the order of the high-pressure drum 8 and separated in the high-pressure drum 8 is sent to the superheater 9 through the drum steam outlet pipe 20, where the temperature is further raised, and then the steam turbine 15 is sent from the high-pressure main steam pipe 21. Supplied to

On the other hand, the water separated by the high pressure drum 8 is recirculated to the high pressure downcomer 19, the high pressure evaporator 7, and the high pressure drum 8. 22 and 23 are high-pressure main steam pipes 21,
The high-pressure, low-pressure control valve of the low-pressure main steam pipe 14, a condenser 24,
25 is an exhaust gas damper. On the other hand, at the time of hot banking of the exhaust heat recovery boiler, since the exhaust gas damper 25 is closed, the exhaust gas passage 2 is filled with the exhaust gas G,
The staying exhaust gas G heats the feed water of the low-pressure boiler, and the steam pressure of the low-pressure drum 5 rises abnormally.

[0010]

During hot banking of a prior art waste heat recovery boiler, heat transfer from high temperature exhaust gas retained in a boiler exhaust gas passage is performed.
The enthalpy of feedwater held in the low-pressure drum system rises,
As a result, there is a disadvantage that the vapor pressure of the low-pressure drum increases with time.

FIG. 4 shows a change in the steam pressure of the low-pressure drum, 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 confined in the exhaust gas passage 2 to close the exhaust gas damper 25 of FIG. Therefore, the low-pressure boiler side is heated by the exhaust gas G, and the curve A in FIG.
As shown by, even after the gas turbine 1 is stopped, the steam pressure of the low-pressure drum 5 increases. Therefore, in the exhaust heat recovery boiler performing the DSS operation, it is necessary to design the design pressure to a high value as shown by a straight line B in consideration of the pressure increase during the hot banking, which is uneconomical.

An object of the present invention is to eliminate the drawbacks of the prior art, and it is an object of the present invention to mitigate an abnormal increase in steam pressure generated during hot banking of an exhaust heat recovery boiler, and to further reduce exhaust heat recovery. The purpose is to reduce the design pressure of the boiler.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a condenser drain pipe having a condenser drain valve from a low pressure main steam pipe to a condenser and a drain tank, and a drain tank drain valve. A pressure detector on the low-pressure drum, and a calculator for comparing the pressure detection signal from the pressure detector with the pressure setting signal. ,Previous
If the condenser vacuum is established, set the condenser drain
Open the valve to allow steam to escape to the condenser, and the condenser vacuum
If not, open the drain tank drain valve
To allow steam to escape to the drain tank.
It is characterized by the following.

[0014]

When the enthalpy of the low-pressure drum system rises due to heat transfer from the high-temperature gas under the hot banking conditions of the exhaust heat recovery boiler, and the steam pressure in the low-pressure drum rises, the drain valve is opened to condense water. This is achieved by evacuating the steam in the low pressure drum from the container drain pipe and the drain tank drain pipe.

[0015]

Embodiments of the present invention will be described below 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 shows a flow chart of a computing unit. FIG.
2 and FIG. 2, reference numerals 1 to 25 indicate the same components as those of the related art. 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 an operation , 34 is a pressure setting signal, and 35 is a control signal.

In such a structure, the point different from the conventional waste heat recovery boiler shown in FIG. 3 is that the condenser drain pipe 26 from the low pressure main steam pipe 14 to the condenser 24 and the drain tank 27 from the low pressure main steam pipe 14 A drain tank drain pipe 28 is provided so that a rise 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 of the low-pressure drum 5 of the exhaust heat recovery boiler is detected by a pressure detector 31 as a pressure detection signal 32 and input to a calculator 33. The pressure detection signal 32 is compared with a pressure setting signal 34 by a calculator 33, and as a result of the comparison, the pressure detection signal 32 is
If the pressure is higher than the above, the condenser drain valve 29 and the drain tank drain valve 30 are opened by the control signal 35, and the condenser 2 is connected to the condenser drain pipe 26 and the drain tank drain pipe 28.
4. The steam is allowed to escape to the drain tank 27.

FIG. 2 shows a flowchart in the arithmetic unit 33. The pressure detector 31 detects the pressure rise of the low-pressure drum 5 during hot banking, and when it is determined in the arithmetic unit 33 that the pressure exceeds the pressure setting signal, if the vacuum of 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. If the vacuum of 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-described vapor discharging operation, the low-pressure drum 5
When the pressure reaches the lower limit of the pressure setting signal 34, a signal for closing the valves is sent from the calculator 33 to the condenser drain valve 29 and the drain tank drain valve 30. If the vacuum of the condenser 24 is established in accordance with the degree of vacuum of the condenser 24 in this manner, steam flows into the condenser 24 from the condenser drain pipe 26, and if the condenser 24 Is destroyed, steam is discharged from the drain tank drain pipe 28 to the drain tank 27.

In general, when the gas turbine 1 is stopped, the vacuum of the condenser 24 is broken in order to reduce the power in the station. In this case, the condenser 24 is filled with the atmosphere and O is contained in the condensate. ₂ dissolved and dissolved oxygen up to 10,000 ppb (DO
₂ ) The concentration increases and the DO ₂ concentration is 10 ppb when restarting.
It is necessary to degas until.

By releasing the steam during the hot banking to the condenser 24 and the drain tank 27, the steam pressure in the low-pressure drum 5 becomes lower as shown by a curve C in FIG. As shown by the straight line D in FIG. 4, the design pressure can be reduced to about 1.1 times, which is economical.

[0022]

According to the present invention, the abnormal rise of steam generated during hot banking of the exhaust heat recovery boiler can be mitigated, and the design pressure of the exhaust heat recovery boiler can be reduced.

[Brief description of the drawings]

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 showing the steam pressure of the low-pressure drum on the vertical axis and time on the horizontal axis.

[Explanation of symbols]

 DESCRIPTION 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 control valve 23 Low pressure control valve 24 Condenser 26 Condenser drain pipe 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 Operation unit 34 Pressure setting signal

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kimiya Sakamoto 6-9 Takara-cho, Kure City, Hiroshima Prefecture Inside Babkotsk Hitachi Industrial Co., Ltd. (56) References JP-A-61-76802 (JP, A) JP-A-63 -243601 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) F22B 1/18

Claims (1)

(57) [Claims] 1. A high-pressure, low-pressure drum for generating steam by exhaust gas from a gas turbine, a high-pressure, low-pressure evaporator for heating water supplied to the high-pressure, low-pressure drum with the exhaust gas, and supplying the generated steam to the steam turbine. A high-pressure, low-pressure main steam pipe having a high-pressure, low-pressure control valve, and a condenser drain having a condenser drain valve from the low-pressure main steam pipe to a condenser and a drain tank. A pipe and a drain tank drain pipe having a drain tank drain valve are provided, a pressure detector is provided on the low-pressure drum, and an arithmetic unit for comparing a pressure detection signal from the pressure detector with a pressure setting signal is provided, and a hot-banking operation is performed. the deviation between the pressure detection signal and the pressure setting signal, if the vacuum of the condenser is established, condenser drain
Open the vent valve to allow steam to escape to the condenser, and if the condenser vacuum is not established, drain
Open the drain valve to allow steam to escape to the drain tank.
An exhaust heat recovery boiler characterized by being configured as described above .