JPS624604B2 - - Google Patents

Description

[Detailed Description of the Invention] Conventional combined circulation supercritical pressure boilers have a circulation pump installed at the outlet of the economizer, so they have many features such as stability at startup and partial load, and reduced startup loss. However, on the other hand, it had the disadvantage that it was not suitable for operation as a medium-load thermal power plant because it could not operate under reduced pressure at low loads. Figure 1 is a system diagram of an example of such a conventional combined circulation supercritical pressure boiler.
In the diagram, 01 is the water supply pump, 02 is the high pressure heater, and 03
is the water supply control valve, 04 is the energy saver, 05 is the mixing bulb, 0
6 is the circulation pump, 07 is the furnace, 08 is the superheater, 0
9 is a high pressure turbine, 010 is a recirculation pipe, 011
012 indicates a startup bypass valve, and 012 indicates a turbine bypass valve.

In the case of steady operation in such a device, the system is operated so that the pressure in the system from the water pump 01 outlet to the superheater 08 outlet is all above the critical pressure. The flow inside the heat exchanger that follows is all single-phase flow, and there is almost no difference in specific volume between hot water and steam, so the steam (or high-temperature hot water) at the furnace outlet ○D is recirculated ○ Mixing ball 0 with E' and high temperature hot water ○A at the outlet of the economizer
When mixing in the pump 06, no water hammer or the like occurs, and the flow of the high-temperature hot water in the pump 06 after mixing is stable, so there is no fear of cavitation or the like. (Even at partial load, no problem will occur as long as it is operated above the critical pressure.) However, as nuclear power plants have been constructed and operated as base-load power generation facilities in recent years, supercritical large-scale thermal power plants It also came to be operated as a medium-load thermal power plant and as a peak-load thermal power plant. However,
If a supercritical pressure large-scale boiler is used for such intermediate thermal power operation with frequent use of low intermediate loads, and if the low load operation is continued for a long time in a high pressure state, it will lead to an increase in turbine throttling loss and an increase in feed water pump power. Not only that, but it also requires a lot of maintenance, which is uneconomical. As a result, there became a desire for a high-output thermal power plant that could achieve maximum efficiency even when operating as an intermediate thermal power plant, and depressurized operation was considered as a specific measure for this purpose.

By the way, it is assumed that the conventional combined cycle system shown in FIG. 1 is operated under reduced pressure.
For example, superheater 08 outlet pressure during 100% load operation
Operating at 255Kg/cm ² g, 125 at 50% load
When operating under reduced pressure at Kg/cm ² g, hot water evaporates in the furnace 07, resulting in a so-called two-phase flow of steam and water mixture at point ○E at the furnace outlet. In this case, the evaporation is
This occurs at a constant temperature corresponding to the saturation temperature of 125 kg/cm ² g (approximately 325° C.), which is considerably lower than the temperature during evaporation of approximately 380° C. without pressure reduction. Therefore, the latent heat of vaporization is large, and it contains 25 to 30% saturated moisture at the furnace outlet.

In this state, the steam/water mixture flows in the superheater 08, and a part of the mixture is recirculated and guided to the mixing bulb 05. On the other hand, the hot water from the outlet of the high-pressure heater 02 is introduced into the economizer 04 (the temperature at point ○ is slightly lower than the steady state due to the reduced pressure operation), is further heated in the economizer 04, and enters the mixing bulb 05. . During depressurization, the temperature at point ○A at the exit of the economizer will be lower than normal, but the saturated state will also drop, so the condition at point ○A at the exit has the possibility of generating some steam, or the proportion of subcooling will decrease. will be extremely small. Therefore, mixed ball 05
Inside, a highly dry air-fuel mixture and hot water on the verge of evaporation mix, and the fluid, which undergoes a severe phase change of condensation of steam and evaporation of hot water, is sent to circulation pump 06. Cavitation is expected to occur inside the ball, and water hammer is expected to occur inside the mixed ball 05. Therefore, operation that brings the inside of the furnace 07 into a reduced pressure state is not possible.

The purpose of the present invention is to eliminate the above-mentioned problems and provide a flow system that allows reduced pressure operation in a combined circulation boiler. In pipes where fluid flows through a pipe and is heated sequentially,
A mixer is provided upstream or in the middle of the economizer pipe, a circulation booster pump is provided downstream of the mixer, and a gas-liquid separator is provided in the middle or downstream of the furnace pipe. This boiler device is characterized in that the liquid outlet and the liquid outlet are communicated with each other.

In this way, in the present invention, a gas-liquid separator is provided at the outlet of the furnace tube, and the mixing bulb is directly connected to the gas-liquid separator through a circulation pipe. In addition to returning the saturated water to the superheater to the mixing bulb, the mixing bulb was moved to the inlet side of the energy saver so that the subcooled state inside the mixing bulb was lower than the saturation point, thereby eliminating the cavitation phenomenon of the circulation pump. . In addition, in order to prevent the steaming phenomenon in the economizer, the economizer is divided into two stages, the low temperature economizer is the conventional method, and the high temperature economizer is equipped with a distribution header and orifice (if necessary) at the inlet. Even if teaming occurs, it will not be a problem.

The installation position of the gas-liquid separator in the furnace pipe system can be selected at an appropriate intermediate position by considering the partial load characteristics of the furnace pipe system. In this case, during depressurization operation,
Branch circulation will be performed from the outlet of the gas-liquid separator installed in the middle of the furnace.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a flow system diagram of an embodiment of the boiler of the present invention, FIG. 3 is a three-dimensional layout diagram, and FIG. 4 is a detailed diagram of a recirculation system. In these figures, 3 is a water supply control valve, 4a is a first economizer, 4b is a second economizer, 7a is a first furnace tube, 7b is a second furnace tube, and 7c
is a third furnace tube, 8a is a first superheater, 8b is a second superheater, 8c is a third superheater, and 8d is a fourth superheater. A mixer 5 is provided between the first economizer 4a and the second economizer 4b. Reference numeral 6 denotes a circulation booster pump, which is provided downstream of the mixer 5.

A gas-liquid separator 21 is provided downstream of the third furnace wall 7c.

The mixer 5 and the liquid outlet of the gas-liquid separator 21 communicate with each other through a circulation pipe 10. A total flow meter 22 is provided between the circulation booster pump 6 and the second economizer 4b. A separator outlet flow meter 23 is provided downstream of the gas-liquid separator 21. A differential pressure control valve 24 is provided downstream of the separator output flow meter 23. Reference numeral 25 denotes a level control valve, which is provided in the middle of the circulation pipe 10. 26 is a variable speed motor that drives the booster pump 6. Further, 27 is a differential pressure control controller, 28 is a level controller, and 29 is a flow controller. Note that 30 is the second superheater 8b.
A superheat reducer 31 provided between the third superheater 8c and the third superheater 8c is a spray valve.

In such boiler equipment, boiler water supply is
From the water supply control valve 3, it passes through the low-temperature first economizer 4a,
It is introduced into a mixer 5, where it is mixed with boiler circulating water, and then enters a circulation booster pump 6 where it is pressurized.
The boiler water passes through the total flow meter 22 and reaches the furnace tube from the high temperature second economizer 4b.

The furnace tubes are the first furnace tube 7a from the one with the highest heat load,
It is divided into a second furnace tube 7b and a third furnace tube 7c, which are connected by a connecting tube, and the boiler water sequentially passes through these furnace tubes and is heated to become steam.

A gas-liquid separator 21 is provided at the outlet of the furnace tube (or it can be placed in the middle), and saturated water in the brackish water mixture generated during low-load decompression operation is separated here. The steam exiting the gas-liquid separator 21 passes through a separator outlet flow meter 23, a differential pressure control valve 24, and is further transferred to a first superheater 8a and a second superheater 8 at low temperatures.
b, passes through the desuperheater 30, and passes through the high-temperature third superheater 8c and fourth superheater 8d, where it is successively heated and becomes high-temperature, high-pressure superheated steam that reaches a turbine (not shown). The steam that has done work in the turbine is cooled in a condenser (not shown) and returned to water, and then the condensate pump,
The high-temperature, high-pressure feed water passes through the feed water treatment device, low pressure heater, deaerator, feed water transfer pump, medium pressure feed water heater, boiler feed water pump, and high pressure feed water heater (all not shown), and then returns to the boiler from the feed water control 3. will be introduced in

On the other hand, the superheater outlet temperature is controlled by the spray valve 31.

Also, a startup drain valve is used as a turbine bypass during startup.

The flow rate in the furnace tube is controlled by a total flow meter 22 at the outlet of the circulation booster pump 6 and a flow meter 23 at the separator outlet, and by a float controller 29 and a variable speed motor 26 to maintain a predetermined flow rate.

At the outlet of the furnace tube, a differential pressure control valve 24 is provided to maintain the circulation amount in the system and stabilize the flow at low loads, and controls the differential pressure between the mixer 5 and the gas-liquid separator 21 to a predetermined value (e.g. The differential pressure controller 27 controls the pressure to maintain the pressure at 4 kg/cm ² ).

Circulating saturated water during low load decompression is passed through the gas-liquid separator 21
It passes through a circulation pipe 10 connecting the mixer 5 and the mixer 5 via a level control valve 25. The level is controlled by a level controller 28.

In the flow system between the furnace and the economizer, if the amount of water supplied = steam amount is Q _A and the amount of circulation is Q _B , the relationship of system flow Q _C = Q _A + Q _B holds. Figure 5 is a graph showing the relationship between these loads and the system flow. From low load to about 80% load, in addition to the water supply amount Q _A (throughflow flow), a circulation flow Q _B flows, and Q _C =Q _A +Q _B
is controlled to a nearly constant value regardless of the load. Point P indicates a dry point. At a load above this point (approximately 80%), the outlet of the furnace tube becomes completely dry steam, so at a load above point P, the circulation flow Q _B =
O, and only Q _A flows in a flow-through state. Therefore, the pump 6 only operates as a booster pump for the water supply pump.

Figure 6 shows the enthalpy pressure diagram, but the second
It represents the state of water to steam at each point and each load in Figure 5.

In a supercritical pressure boiler, the design pressure is in a state exceeding the critical point, so as long as the operating state is maintained above the critical point, the fluid in the furnace tube becomes a single-phase flow even under partial load. This is shown in FIG. 6, where the operating conditions are within the range of and' (indicated by dotted lines), which corresponds to the operation of a conventional combined circulation boiler.

However, frequent use of low load operation in such a high pressure state is uneconomical as mentioned above, so depressurized operation is desirable, but if such depressurized operation is performed, the load will be The pressure decreases accordingly, and the state of each part indicated by circles ○ to ○ in FIG. 2 changes as shown by circles to ○ in FIG. 6.

Particularly at the furnace tube outlet ○, the temperature of the steam gradually decreases, and as the pressure decreases after point P, the steam in the system becomes mixed with brackish water, and the proportion of saturated water increases. (○ indicates the case where there is no circulation flow.) In the case of the conventional combined circulation boiler shown in Figure 1, such a depressurized brackish water mixture enters mixer 05 as it is at intermediate or low load. As a result, the highly dry air-fuel mixture and the hot water at the exit of the economizer, which is about to evaporate, collide and mix, resulting in severe phase changes such as steam condensation and hot water evaporation.
6, cavitation inside the pump and water hammer phenomenon inside the mixer are unavoidable. Furthermore, since the air-fuel mixture containing moisture is sent to the superheater 08, there are concerns not only of changes in steam temperature characteristics but also of accidents due to scaling troubles and the like.

According to the present invention, a gas-liquid separator 21 is provided at the outlet of the furnace 7c (or it can be placed in the middle), where the steam-water mixture is separated, the steam is sent to the superheater 8a, and the separated saturated water is mixed. At the same time, the water at the outlet of the low-temperature economizer can be returned to a sufficiently subcooled state inside the mixer 5, and then introduced into the pump 6 in that state. It can be operated safely under any load conditions without any problems. Of course, sufficient circulation flow can be obtained at low loads, resulting in good flow stability and safe operation that is incomparable to ordinary once-through boilers. The industrial benefits are significant, such as reduced maintenance.

As explained in detail above, according to the present invention,
The present invention is industrially useful because a large-capacity combined circulation supercritical pressure boiler can be operated safely and economically even at low loads.

[Brief explanation of the drawing]

Fig. 1 is a flow system diagram of a conventional combined circulation type supercritical pressure boiler, Fig. 2 is a flow system diagram of an embodiment of the combined circulation type supercritical pressure boiler of the present invention, and Fig. 3 is a three-dimensional diagram of the same. Figure 4 is a detailed diagram of the recirculation system, Figure 5 is a diagram showing the relationship between the load and system flow of the boiler of the present invention, and Figure 6 is an enthalpy pressure diagram showing the state of each part of the boiler of the present invention at each load. It is. 4a...first economizer, 4b...second economizer, 5...mixer, 6...circulation pump, 7a, 7b, 7c...furnace tube, 8a, 8b, 8c...superheater, 10...circulation pipe line, 21... Gas-liquid separator, 22, 23... Flow meter, 24... Differential pressure control valve, 25... Level control valve, 2
6... variable speed motor, 27... differential pressure control controller,
28... Level controller, 29... Flow controller.

Claims (1)

[Claims] 1 In a system in which fluid flows through the pipe from the economizer pipe to the furnace pipe to the superheater pipe and is heated sequentially,
A mixer is provided upstream or in the middle of the economizer pipe, a circulation booster pump is provided downstream of the mixer, and a gas-liquid separator is provided in the middle or downstream of the furnace pipe. A boiler device characterized in that a liquid outlet and a liquid outlet are communicated with each other.