JPH063286B2 - Steam generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steam generator (boiler), and by improving the can-keeping procedure when the boiler is stopped, the boiler start-up time is greatly shortened.
This is to reduce the lifespan consumption of the superheater outlet pipe and main steam pipe that accompany boiler startup, and to reduce the amount of fuel.

2. Related Art FIG. 4 shows an outline of a thermal power plant system.

In FIG. 4, the boiler feed water heated in the economizer 1 is mixed with the boiler circulating water in the steam drum 2, and is absorbed by the furnace water cooling wall 4 via the downcomer pipe 3 to become a saturated water / steam mixture. , Circulate in the steam drum 2. The saturated steam separated by the steam drum is superheated by the primary superheater 5, then temperature-controlled by the superheat reducer 6, and then superheated to a specified temperature by the secondary superheater 7, and then sent to the high-pressure turbine 8. Being sent.

In addition, 9 is a primary superheater outlet pipe, 10 is a primary superheater outlet communication pipe, 11 is a secondary superheater inlet communication pipe, 12 is a secondary superheater inlet pipe, 13 is a superheater outlet pipe, 14 is Main steam pipe, 15 turbine inlet main blocking valve, 16 and 17 primary and secondary superheater outlet blow control valves, 18 and 19
Indicates the attached pipes, respectively.

The exhaust gas from the high-pressure turbine 8 enters the reheater 21 via the low-temperature reheat steam pipe 20, is superheated to a specified temperature, and then reaches the intermediate-pressure turbine 24 via the communication pipe 22 and the reheat stop valve 23. Steam from this medium-pressure turbine is crossover pipe 25
To reach the low-pressure turbine 26. The exhaust gas of the low-pressure turbine is condensed in the condenser 27, boosted in pressure by the condensate pump 28, and reaches the deaerator 30 via the low-pressure feed water heater 29. Water supply is boosted from the deaerator by the boiler water supply pump 31, and is supplied to the boiler via the high-pressure water supply heater 32.

In addition, 33 is a superheat reducer spray control valve, 34 is a water supply pipe.

However, these thermal power plants are used for load changes as the number of base-load operated nuclear power generation facilities increases, and so-called two-shift operation in which each night is stopped / started in the early morning is required.

FIG. 5 shows an example of the unit stop activation characteristic curve of 8 hours stop, in this example, the unit is disconnected at 0 o'clock, the boiler enters the state of hot banking, 7 o'clock fire, 8 o'clock joint, 9 o'clock Full load has been reached.

The most basic functions required for such a two-shift operation unit are that it can be rapidly started (ignition to full load time is short), that the life of the equipment is small, and that start-up loss is small. is there. Also, in general,
For units that have a suitable start-up heat recovery device,
The shorter the startup time, the less the startup loss. Therefore, the rapid start is very important for the thermal power plant, but the limiting condition is the thermal stress caused by the temperature change of the equipment caused by the rapid start. The shorter the startup time, the greater the thermal stress generated in the conventional boiler, and the longer the life consumption.

In the boiler, however, it is the superheater outlet heading that maximizes the life consumption by starting and stopping. This is because, in the power generation boiler, the steam at the outlet of the superheater has a high pressure / high temperature, so that the pipe thickness is large and the temperature change is large. With regard to the former, high pressure and high temperature are advancing from the viewpoint of increasing plant efficiency, so even if some improvements can be made by using high-grade materials, they will be exposed to increasingly severe conditions. Therefore, an effective measure is to reduce the temperature change of the superheater outlet pipe offset. That is,
This is to suppress the temperature drop when the unit is stopped.

This temperature drop near the outlet of the superheater is mainly due to cooling of the heat transfer surface by boiler purging after extinguishing the boiler and cooling of the steam in the superheater / main steam pipe system due to heat dissipation. It may also be cooled by the low temperature steam generated at startup, which can be avoided by proper application of the superheater blow line or superheater bypass line.

Problems to be Solved by the Invention As described above, in the future thermal power plant, the unit capacity becomes large and the efficiency becomes high, so that the pressure becomes high and the temperature becomes high. Therefore, the boiler pressure resistant member, especially the superheater outlet pipe The displacement is a large-sized / thick-walled member, and the life consumption is large due to start / stop, but on the other hand, frequent and rapid start / stop or sea shift operation is required.

In view of such a situation, the present invention minimizes the lifespan consumption by minimizing the temperature change (fall) of the superheater outlet pipe heading accompanying the start-up / shutdown, and the rapid operation of the high-pressure / high-temperature boiler. The start-up is enabled, and at the same time, the start-up time is shortened, so that the fuel consumption for start-up is reduced and the economical start-up is enabled.

Means for solving the problems When the boiler is stopped, the superheater outlet heading and the main steam pipe cooling (temperature drop) are performed by the boiler purge (replacement of combustible gas in the boiler with cold air) and the boiler, especially the superheater / main steam pipe. Since this is a phenomenon caused by heat dissipation from the turbine and movement of steam in the system whose temperature is lowered, the present invention provides an auxiliary steam line in the main steam pipe near the turbine inlet main block valve in order to prevent this. Connected, at the time of stopping and starting the boiler, introducing auxiliary steam for heat insulation from the steam source other than the boiler into the main steam pipe through the auxiliary steam line, and flowing in the reverse direction to the superheater side, and the secondary superheater. The blow control valve installed in the blow line installed near the inlet pipe controls the system pressure to ensure the required amount of auxiliary steam, and thus the main steam pipe and And the outlet pipe of the superheater are kept at a high temperature.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a boiler system according to the present invention, and FIG. 2 schematically shows a boiler configuration.

In FIGS. 1 and 2, boiler feed water from a high-pressure feed water heater (not shown) passes through a water feed pipe 40 and a coal economizer inlet header 4
1, it is heated by the economizer 42 and reaches the steam drum 45 from the economizer outlet header 43 through the economizer outlet water supply pipe 44. This supply water reaches the water drum 45-2 in the downcomer 45-1 together with the boiler circulating water, absorbs heat in the furnace water cooling wall, becomes a brackish water mixture, and returns to the steam drum 45. The steam separated by the steam drum reaches the lower semi-annular gather 47 through the ceiling / rear flue rear wall (steam cooling wall) 46. From here, the steam enters the primary superheater inlet pipe 51 through the rear flue side wall 48, the outlet pipe 49, and the outlet communication pipe 50. The steam absorbs heat in the primary superheater 53, the temperature is controlled by the desuperheater 55 from the outlet pipe 54, enters the secondary superheater inlet pipe 56, and rises to a specified temperature in the secondary superheater 57. After being heated, it is sent to the turbine 60 from the secondary superheater outlet pipe 58 through the main steam pipe 59. A main stop valve 61 is installed at the inlet of this turbine.

In addition, 62 is a spray water supply pipe connected to the desuperheater 55, 63 is a spray water amount control valve, and controls so that the superheater outlet steam temperature becomes a predetermined value. Reference numerals 64, 65 and 66 respectively indicate a rear flue steam cooling wall drain line, a secondary superheater inlet blow line and a superheater outlet blow line, 67 indicates a turbine inlet main steam pipe blow line, and 68, 69 and 70 respectively. , 71 are control valves, respectively. These blow lines discharge the drain generated when the boiler is stopped when the boiler is started,
Used to treat low temperature steam generated at boiler startup (collected in condenser or released to atmosphere).

Although the configuration described above is the same as the conventional one, according to the present invention, the auxiliary steam line 72 for preventing the temperature drop of the superheater outlet pipe approaching temperature when the boiler is stopped has the main steam pipe 59 near the turbine inlet main blocking valve 61. The auxiliary steam is injected to maintain the metal temperature of the superheater outlet pipe head at a predetermined value.

Explaining this auxiliary steam line in detail, the auxiliary steam line 72 is connected to another boiler or an auxiliary boiler that is operating while the boiler is stopped, and supplies the auxiliary steam for heat retention while the boiler is stopped. It is a line. The auxiliary steam control valve 73 is provided so that the temperature of the metal temperature measuring thermocouple 75 installed in the superheater outlet pipe 58 becomes a predetermined temperature.
It is controlled by the temperature control 74. Reference numeral 76 indicates a check valve.

While the boiler is stopped, the main steam stop valve 61 installed at the turbine inlet is fully closed and the boiler is bored up. Therefore, it is not possible to secure the auxiliary steam flow necessary for maintaining the predetermined temperature only by installing the auxiliary steam line. In order to solve such a problem, the pressure detector 90 detects the system pressure, and the secondary superheater inlet blow control valve 69 is controlled by the pressure controller 77 so that the pressure becomes a predetermined pressure. Will ensure the required amount of auxiliary steam.

That is, the auxiliary steam control valve 73 controls the amount of auxiliary steam so that the metal temperature of the outlet superheater outlet pipe is a predetermined amount, and the secondary superheater inlet blow control valve 69 is controlled so that the system pressure becomes a predetermined pressure. Control system steam pressure.

Here, the temperature and pressure of the auxiliary steam are restricted in relation to the turbine ventilation steam conditions at the time of startup. The present invention is particularly directed to a plant that performs a night-time stop operation, but the turbine-side required steam condition at the time of aeration generally differs depending on the turbine type and the turbine metal temperature depending on the steam condition at the time of turbine stop, but 70 kg / It is around cm ² × 460 ° C. Therefore, when the turbine is ventilated, both the outlet pipe of the superheater and the main steam pipe are exposed to the steam of about 460 ° C., and the metal temperatures thereof are also about the same. Therefore, when the boiler is stopped, it is rational to maintain the temperature so that it does not drop below the vapor temperature during ventilation.

That is, the heating steam supplied from the auxiliary steam line 72 is
The steam temperature slightly higher than the steam conditions (pressure, temperature) at the time of ventilation is used, and the superheater outlet header metal temperature is monitored, so that the heating steam control valve 73 does not fall below the steam temperature at the time of ventilation.
The amount of steam is controlled at. Moreover, in order to introduce the heating steam into the main steam pipe system, the system internal pressure must be lower than the heating steam pressure, so even if the superheater outlet header metal temperature falls to the ventilation condition temperature, If the internal pressure is high,
The ventilating condition pressure is controlled by the secondary superheater inlet blow control valve 69. That is, the temperatures of the final superheater and the main steam pipe are maintained at substantially the same level as when the turbine is ventilated even when stopped.

Generally, in controlling ventilation conditions and pressure, there is no need to control the pressure with a blow control valve because of the pressure drop at the time of stop, but the blow system has a turbine gland seal, low pressure feed water heater seal, deaerator seal, etc. It can also be used effectively by connecting to an auxiliary steam system for traces such as heavy oil piping.

EFFECTS OF THE INVENTION As described above, according to the present invention, the superheater outlet header metal temperature decreases when the boiler is stopped, but the heating steam having a predetermined temperature (equal to or higher than the steam temperature during ventilation) is introduced into the main steam pipe. As a result, the temperature can be maintained above the predetermined temperature. That is, since the change in metal temperature due to stop-start can be suppressed to a minimum value or below an allowable value (see FIG. 3), start-up time can be shortened. Therefore, the generation of thermal stress associated with the stop-start of the boiler is reduced or becomes less than the allowable level, so that the life is extended and the reliability is improved. In addition, the shortening of the start-up time enables efficient start-up and reduces the amount of fuel used. That is, at the time of start-up, until the temperature of the generated steam reaches a sufficiently high temperature that does not cool the main steam pipe and superheater outlet pipe, which are high-temperature elements, the generated steam is kept in the main steam pipe and superheater outlet pipe. Since the main steam pipe and the superheater outlet pipe are kept at a high temperature and are not cooled by not introducing them into the heat pump, the high temperature steam necessary for starting the turbine can be quickly obtained, and therefore the quick start can be achieved. It becomes possible and the fuel required at the time of starting can be saved. If the reduction of thermal stress is explained in detail, the thermal stress generated at the outlet pipe of the superheater is caused by the temperature difference between the inner and outer surfaces caused by starting and stopping the boiler. The metal temperature is low on the inner side-high on the outer side when stopped, and high on the inner side-low on the outer side at startup.The larger the temperature change width and the faster the temperature change rate (quick start / stop), the difference between the inner and outer surface temperatures. Becomes larger and the generated thermal stress becomes larger. Therefore, the generation of thermal stress can be reduced by injecting the heating steam of a corresponding temperature into the system when the boiler is stopped to reduce the decrease in the metal temperature.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a steam generator according to the present invention, FIG. 2 is a schematic configuration diagram thereof, FIG. 3 is a diagram showing changes in metal temperature of a superheater outlet pipe, and FIG. 4 is a thermal power plant. FIG. 5 is a system diagram showing an example, and FIG. 5 is a diagram showing an example of boiler stop / start characteristics. 56..Secondary superheater inlet pipe, 59..main steam pipe, 6
0 ... Turbine, 61 ... Main blocking valve, 65 ... Secondary superheater inlet blow line, 69 ... Secondary superheater inlet blow control valve, 72 ... Auxiliary steam line

Claims (1)

[Claims] 1. An auxiliary steam line is connected to a main steam pipe in the vicinity of a turbine inlet main shut-off valve, and auxiliary steam for heat insulation is supplied from a steam source other than the boiler through the auxiliary steam line when the boiler is stopped or started. It is introduced into the steam pipe and flows in the opposite direction to the superheater side, and the system pressure is controlled by the blow control valve installed in the blow line installed near the secondary superheater inlet pipe to secure the necessary amount of auxiliary steam. A steam generator characterized in that