JPH11248101A - Natural circulation evaporator, waste heat recovery boiler and method of starting the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress a decrease in circulating force due to a gas-liquid two-phase flow in a vent pipe, to prevent backflow and unstable flow, and to complicate the structure in pipe routing. To avoid. SOLUTION: The natural circulation type evaporator includes a steam drum 1, a downcomer 2, a water seal tube 3, an inlet header 4, a heat transfer tube 5, a vent tube 6, a heat transfer tube 7, an outlet header 8, and a rising tube 9. . The heat transfer tube 5 receives one path of the in-tube fluid on the upstream side, and the heat transfer tube 7 receives two paths of the in-tube fluid on the downstream side. The intra-pipe fluid 1 path and the intra-pipe fluid 2 path are arranged in the same horizontal plane, and exchange heat with the extrapipe fluid in the same plane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention reduces the start-up time of an exhaust heat recovery boiler of a combined cycle power plant,
Natural circulation evaporator to obtain the desired starting characteristics,
The present invention relates to an exhaust heat recovery boiler and a method for starting the same.

[0002]

2. Description of the Related Art An exhaust heat recovery boiler is one of the key components of a combined cycle power plant that recovers heat of exhaust gas from a gas turbine and generates steam. This exhaust heat recovery boiler is provided with several heat exchangers composed of heat transfer tubes, which are called superheaters, evaporators, and economizers.

FIG. 16 shows a circulation circuit of a natural circulation type evaporator having horizontally disposed heat transfer tubes used in an exhaust heat recovery boiler. This is applied to a system in which the duct 15 of the exhaust heat recovery boiler has a vertical structure and the extra-tube fluid 10 is guided upward from below. The circulation circuit of this natural circulation type evaporator is composed of a steam drum 1, a downcomer 2, a water seal tube 3, an inlet header 4, a heat transfer tube 25, an outlet header 8, a riser 9, and a steam drum 1.

[0004] Water supplied to the steam drum 1 descends down the downcomer 2 to prevent a backflow.
Through the inlet header 4. The feedwater flowing into the inlet header 4 is guided to a horizontally arranged heat transfer tube 25, and evaporates while exchanging heat with the extra-tube fluid 10 to form a gas-liquid two-phase flow.
It flows into the exit header 8. The gas-liquid two-phase flow flowing into the outlet header 8 rises on the riser 9 and returns to the steam drum 1.

[0005] The circulation force of the natural circulation type evaporator is expressed by the following equation since the heat transfer pipe is disposed horizontally and the hydrostatic head of the fluid in the heat transfer pipe is zero.

(Circulating force) = (hydrostatic head of downcomer fluid) − (hydrostatic head of fluid in water seal pipe) − (hydrostatic head of fluid in riser pipe) (Equation 1) That is, the fluid in the riser pipe evaporates and becomes In the case of the liquid two-phase flow, the third term on the right side of (Equation 1) becomes small, and a natural circulation force is generated to circulate the fluid in the pipe.

In starting the exhaust heat recovery boiler having the natural circulation evaporator, in order to start circulation of the fluid in the pipe of the natural circulation evaporator, the fluid in the heat transfer pipe evaporates due to heat exchange with the extrapipe fluid 10. Then, the gas-liquid two-phase flow flows into the rising pipe 9 by utilizing the volume expansion due to the evaporation, and the circulation of the fluid in the pipe starts.

FIG. 17 shows a co-current two-pass natural circulation evaporator in which a heat transfer tube is turned vertically upward to pass the fluid in the tube in order to shorten the duct width of the waste heat recovery boiler and increase the amount of exchanged heat. Is shown. This is applied to a system in which the duct 15 of the exhaust heat recovery boiler has a vertical structure, and the extra-tube fluid 10 is guided upward from below, flows in from the heat transfer tube 5 and flows out to the heat transfer tube 7.

This method is called a co-current method because the high-temperature side of the extra-tube fluid 10 flows in from the low-temperature side of the in-tube fluid and the low-temperature side of the extra-tube fluid 10 flows out to the high-temperature side of the in-tube fluid. The circulation circuit of this natural circulation evaporator is as follows: steam drum 1 → downcomer 2 → water seal tube 3 → inlet header 4 → heat transfer tube 5 (1 path fluid in pipe) → vent pipe 6 → heat transfer pipe 7 (2 path fluid in pipe). →
It is composed of the outlet header 8 → the rising pipe 9 → the steam drum 1.

In the exhaust heat recovery boiler having the natural circulation type evaporator, at the time of start-up, heat exchange with the extrapipe fluid 10 first evaporates one path of the in-pipe fluid upstream of the extrapipe fluid 10 to evaporate. A liquid two-phase flow occurs. Next, the in-pipe fluid 2 path on the downstream side of the extrapipe fluid 10 evaporates to generate a gas-liquid two-phase flow,
The gas-liquid two-phase flow flows into the riser pipe 9 by utilizing the volume expansion due to the evaporation, and the natural circulation force is generated, so that the circulation of the fluid in the pipe starts.

That is, in the early stage of the operation of the exhaust heat recovery boiler, the amount of heat of the extrapipe fluid 10 is largely spent for heat exchange with the intrapipe fluid 1 path on the upstream side of the extrapipe fluid 10, so that some time does not elapse. Thus, evaporation does not occur in the in-pipe fluid 2 path downstream of the extrapipe fluid 10 near the riser pipe 9.

[0012] Therefore, since the gas-liquid two-phase flow flows into the riser pipe 9 and a natural circulation force is generated, the time until the circulation of the fluid in the pipe starts is longer than that of the above-mentioned natural circulation evaporator. Become.

Until the circulation of the fluid in the pipe of the natural circulation evaporator starts and steam is generated, the exhaust heat recovery boiler cannot increase the pressure, and if the time until the circulation of the fluid in the pipe becomes long, the exhaust heat The startup time of the recovery boiler also becomes longer.

Further, in a state where the circulation force cannot be obtained for a long time,
When the one-pass fluid in the pipe evaporates, the gas-liquid two-phase flow may flow backward toward the downcomer pipe 2 or the flow state may become unstable.

Further, if one passage of the fluid in the pipe evaporates in a state where the circulation force cannot be obtained for a long time, the void ratio of the gas-liquid two-phase flow in the pipe increases and dry-out occurs. Can be overheated and damaged.

[0016]

By the way, the following counter-flow natural circulation evaporator has been proposed to solve the above-mentioned difficulty of the co-current natural circulation evaporator. As shown in FIG. 18, the duct 15 of the exhaust heat recovery boiler has a vertical structure so that the extra-tube fluid 10 flows from below to the heat transfer tube 7 and further flows to the heat transfer tube 5. The term "counterflow method" is used because the extrapipe fluid 10 flows in from the high temperature side of the in-pipe fluid and flows out to the lower temperature side.

The circulation circuit of this natural circulation type evaporator is as follows: steam drum 1 → downcomer 2 → water seal tube 3 → inlet header 4 → heat transfer tube 5 (one-pass fluid in pipe) → vent pipe 6 → heat transfer pipe 7 (fluid in pipe) 2 passes) → exit header 8 → riser 9 → steam drum 1
It consists of.

In the exhaust heat recovery boiler having the natural circulation type evaporator, at the time of start-up, heat exchange with the extra-tube fluid 10 first evaporates two in-tube fluids on the upstream side of the extra-tube fluid 10 to elevate the rising pipe. The gas-liquid two-phase flow flows into 9 and the natural circulation force is generated, whereby the circulation of the fluid in the pipe starts. That is,
Compared with the co-current flow natural circulation evaporator, the two-path fluid in the pipe near the riser pipe 9 evaporates earlier than the one-fluid path in the pipe, so that the time during which the gas-liquid two-phase flow flows into the riser pipe 9 is shortened. The time until the circulation of the fluid in the pipe starts is shortened, and the startup time of the exhaust heat recovery boiler can be shortened.

Further, since the circulation force can be obtained in a short time, there is an advantage that damage to the heat transfer tube due to backflow and unstable flow or dryout is less likely to occur as compared with a co-current type natural circulation evaporator. .

However, this counterflow natural circulation evaporator has the following problems. That is, the circulation force of the natural circulation evaporator can be expressed by the following equation. (Circulation force) = (hydrostatic head of downcomer fluid)-(hydrostatic head of fluid in water seal pipe) + (hydrostatic head of vent pipe)-(hydrostatic head of fluid in riser pipe) ... (Equation 2) Fluid in vent pipe evaporates When the gas-liquid two-phase flow is established, the circulating force becomes smaller in the third term on the right side of (Equation 2) and acts as a force in the reverse flow direction, so that the circulating force is reduced. In general,
When the circulation force is small, the heat transfer tube is likely to be damaged due to unstable flow and dryout. In addition, vent pipe 6
The gas-liquid two-phase flow in the inside may obstruct the circulation of the fluid in the pipe, resulting in reverse flow or unstable flow.

Furthermore, when the pipes are routed, the riser pipe 9 and the heat transfer pipe 5, the water seal pipe 3, and the downcomer pipe 2 must be prevented from interfering with each other.

An object of the present invention is to suppress the circulation force from being reduced by the gas-liquid two-phase flow in the vent pipe, to prevent backflow and unstable flow, and to prevent the structure from becoming complicated when the piping is routed. An object of the present invention is to provide a natural circulation evaporator, an exhaust heat recovery boiler, and a startup method thereof that can be avoided.

[0023]

In order to achieve the above object, a first aspect of the present invention is a natural circulation type including a heat transfer tube for sequentially receiving one path of upstream pipe fluid and two paths of downstream pipe fluid. In the evaporator, the heat transfer tubes are arranged such that each path of the fluid in the tubes exchanges heat with the fluid outside the tubes in the same horizontal plane.

In the natural circulation type evaporator having the above-described structure, the circulation force does not become small even when the pipe fluid becomes a gas-liquid two-phase flow, and the flow of the pipe fluid is kept stable. This makes it difficult for backflow and unstable flow to occur. In addition, the structure can be simplified by laying out the piping.

Further, according to a second aspect of the present invention, the heat transfer tubes are arranged such that two paths of the in-tube fluid on the downstream side exchange heat with the extra-fluid fluid before one path of the on-tube fluid in the same horizontal plane. It is characterized by the following.

In the natural circulation evaporator having the above-described structure, since the two-pass fluid in the pipe evaporates before the one-pass fluid in the pipe, the startup time of the exhaust heat recovery boiler can be reduced. In addition, backflow and unstable flow are less likely to occur.

According to a third aspect of the present invention, the heat transfer pipe is located in a region where the extrapipe fluid flows in the horizontal direction, and the two downstream fluids in the same horizontal plane are the upstream fluid 1 in the pipe.
It is characterized in that it is arranged to exchange heat with the extravascular fluid before the path.

In the natural circulation type evaporator having the above-described structure, since the two-pass fluid in the pipe evaporates before the one-pass fluid in the pipe, the startup time of the exhaust heat recovery boiler can be reduced. In addition, backflow and unstable flow are less likely to occur.

Further, the invention according to claim 4 is the heat transfer tube in a region where the heat transfer tubes are separated from each other in which the extra-fluid fluid flows from below to above and further inverted and from above to below, and is located on the downstream side in the same horizontal plane. The two-pass fluid in the pipe is arranged to exchange heat with the extra-pipe fluid before the one-pass fluid in the pipe on the upstream side.

In the natural circulation evaporator having the above-described structure, the two-pass fluid in the pipe evaporates before the one-pass fluid in the pipe, so that the startup time of the exhaust heat recovery boiler can be reduced. In addition, backflow and unstable flow are less likely to occur.

According to a fifth aspect of the present invention, there is provided a heat transfer pipe in a partitioned area in which extra-fluid fluids having different state quantities or flow rates individually flow, and two pipe fluids on the downstream side in the same horizontal plane. It is characterized by being arranged so as to exchange heat with an extra-fluid fluid having a state quantity or a flow rate larger than that of the upstream intra-fluid one-pass side.

In the natural circulation type evaporator having the above-described structure, the amount of heat exchanged is adjusted by using a different amount of state or flow rate of the outside fluid in each region, so that two passes of the fluid in the pipe are performed before one pass of the fluid in the pipe. It evaporates and the startup time of the exhaust heat recovery boiler can be shortened. In addition, backflow and stable flow hardly occur.

Further, the invention according to claim 6 is provided with a natural circulation evaporator according to claim 1 in a duct.

In the natural circulation type evaporator having the above-described structure, the circulation force does not become small even when the pipe fluid becomes a gas-liquid two-phase flow, and the flow of the pipe fluid is kept stable. This makes it difficult for backflow and unstable flow to occur. In addition, the structure can be simplified by laying out the piping.

According to a seventh aspect of the present invention, there is provided a natural circulation evaporator according to the second aspect in a duct.

In the natural circulation type evaporator having the above-described structure, the two-passage fluid in the pipe evaporates before the one-passage fluid in the pipe, so that the startup time of the exhaust heat recovery boiler can be reduced. In addition, backflow and unstable flow are less likely to occur.

Further, the invention according to claim 8 is provided with a natural circulation evaporator according to claim 3 in a duct.

In the natural circulation type evaporator having the above-mentioned structure, since the two-passage fluid in the pipe evaporates before the one-passage fluid in the pipe, the startup time of the exhaust heat recovery boiler can be shortened. In addition, backflow and unstable flow are less likely to occur.

According to a ninth aspect of the present invention, there is provided a natural circulation evaporator according to the fourth aspect in a duct.

In the natural circulation evaporator having the above-described structure, since the two-pass fluid in the pipe evaporates before the one-pass fluid in the pipe, the startup time of the exhaust heat recovery boiler can be reduced. In addition, backflow and unstable flow are less likely to occur.

Further, the invention according to claim 10 is provided with a natural circulation evaporator according to claim 5 in a duct.

In the natural circulation type evaporator having the above-described structure, the amount of heat exchanged is adjusted by using a different amount of state or flow rate of external fluid in each region, so that two paths of fluid in the pipe are arranged before one path of fluid in the pipe. It evaporates and the startup time of the exhaust heat recovery boiler can be shortened. In addition, backflow and stable flow hardly occur.

The invention according to claim 11 has a plurality of zones arranged horizontally in a duct, and each zone is provided with a natural circulation evaporator according to claim 1.

In the natural circulation type evaporator having the above configuration, even when the pipe fluid becomes a gas-liquid two-phase flow in the evaporator of each zone, the circulation force is not reduced, and the flow of the pipe fluid is kept stable. It is. This makes it difficult for backflow and unstable flow to occur. Moreover, the structure can be simplified by routing inside the pipe.

Further, the invention according to claim 12 is a method for starting a waste heat recovery boiler having a natural circulation type evaporator provided with a heat transfer tube for sequentially receiving one path of upstream fluid in a pipe and two paths of downstream fluid in a pipe. The heat transfer tubes are arranged so that each path of the fluid in the tubes exchanges heat with the fluid outside the tubes in the same horizontal plane.
It is characterized in that the two-pass fluid in the pipe is started while maintaining a large amount of exchange heat compared to the one-pass fluid in the pipe.

In this starting method, since the starting is performed with a difference between the respective exchanged heat amounts, the two paths of fluid in the pipe evaporate before the one path of fluid in the pipe, so that the starting time of the exhaust heat recovery boiler can be shortened. . In addition, backflow and unstable flow are less likely to occur.

According to a thirteenth aspect of the present invention, there is provided a method of starting a waste heat recovery boiler having a natural circulation evaporator having a heat transfer tube for sequentially receiving one path of upstream fluid in a pipe and two paths of downstream fluid in a pipe. The heat transfer tubes are arranged such that each path of the fluid in the tube exchanges heat with the fluid outside the tube in the same horizontal plane, so that when starting the heat recovery steam generator, the two-pass fluid in the pipe is compared with the one-pass fluid in the pipe. In this case, the flow is started while the flow rate of the extra-fluid fluid is kept large.

In this start-up method, the start-up is performed with a difference in the flow rate of each of the extra-fluid fluids, so that the two-pass fluids evaporate before the one-pass fluid, and the start-up time of the exhaust heat recovery boiler is shortened. be able to. In addition, backflow and unstable flow are less likely to occur.

Further, the invention according to claim 14 is a method for starting a waste heat recovery boiler having a natural circulation type evaporator provided with a heat transfer tube which sequentially receives one path of upstream pipe fluid and two paths of downstream pipe fluid. The heat transfer tubes are arranged so that each path of the fluid in the tubes exchanges heat with the fluid outside the tubes in the same horizontal plane.
It is characterized in that the two-pass fluid inside the pipe is activated while keeping the temperature of the extra-fluid higher than the one-pass fluid inside the pipe.

In this start-up method, the start-up is performed with a difference in the temperature of each of the extra-fluid fluids, so that the two-pass fluid in the pipe evaporates before the one-pass fluid in the pipe, and the start-up time of the exhaust heat recovery boiler is shortened. be able to. In addition, backflow and unstable flow are less likely to occur.

According to a fifteenth aspect of the present invention, the heat transfer tube comprises a heat transfer tube with fins, and the heat transfer tube receiving the two fluid passages in the tube has a higher fin pitch than the heat transfer tube receiving one fluid passage in the tube. It is characterized by being performed.

In the natural circulation type evaporator having the above-described structure, the heat transfer tube for receiving the two fluids in the pipe has a larger heat transfer area than the heat transfer tube for receiving the one fluid in the pipe. It evaporates earlier than before, and the startup time of the exhaust heat recovery boiler can be shortened. In addition, backflow and unstable flow are less likely to occur.

Further, the invention according to claim 16 is characterized in that a heat transfer tube for receiving one path of fluid in the pipe and a heat transfer pipe for receiving two paths of fluid in the pipe are connected by a linear intermediate header for reversing the fluid in the pipe. It is assumed that.

In the natural circulation type evaporator having the above-described structure, the passage of the fluid in the pipe can be realized with a simple structure by using the linear intermediate header.

[0055]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention-first
Embodiment-will be described with reference to the drawings. In FIG. 1, the natural circulation evaporator includes a steam drum 1, a downcomer tube 2, a water seal tube 3, an inlet header 4, a heat transfer tube 5, a vent tube 6, a heat transfer tube 7, an outlet header 8, and a riser tube 9. I have. In this evaporator, the heat transfer tube 5 receives one path of fluid in the upstream pipe, and the heat transfer tube 7 receives two paths of fluid in the downstream pipe. Both the intra-pipe fluid 1 path and the intra-pipe fluid 2 path are arranged in the same horizontal plane, and are configured to exchange heat with the vertically flowing extra-pipe fluid in the same horizontal plane, for example.

In the present embodiment, the water supply supplied to the steam drum 1 goes down the downcomer 2 and flows into the inlet header 4 via the water seal tube 3. The feedwater that has flowed into the inlet header 4 is guided to the heat transfer pipes 5 arranged horizontally, and flows into the heat transfer pipes 7 placed on the same horizontal plane as the heat transfer pipes 5 via the vent pipes 6. During this time, the heat transfer tubes 5 and 7 exchange heat with the fluid inside the pipe and the fluid inside the pipe 2 to form a gas-liquid two-phase flow. Thereafter, the gas-liquid two-phase flow flows into the outlet header 8, rises on the riser 9, and returns to the steam drum 1.

Since the heat transfer pipes 5 and 7 and the vent pipe 6 are in the same horizontal plane, the circulating power of this natural circulation evaporator is such that the hydrostatic head of the fluid in the pipe at this point becomes zero, and is expressed by the following equation.

(Circulating force) = (Hydrostatic head of downcomer fluid) − (Hydrostatic head of fluid in water seal pipe) − (Hydrostatic head of fluid in ascending pipe) (Equation 3) That is, the fluid in the ascending pipe evaporates and air When the liquid has a two-phase flow, the third term on the right side of (Equation 3) is reduced, and a natural circulation force is generated to circulate the fluid in the pipe.

In this natural circulation type evaporator, since the vent pipe 6 is in the same horizontal plane, even if the fluid in the vent pipe evaporates to form a gas-liquid two-phase flow, the hydrostatic head in the vent pipe 6 remains at zero. This does not affect the circulating force of (Equation 3), and the circulating force does not decrease. In general, when the circulating force is small, the heat transfer tube is likely to be damaged due to the backflow and the unstable flow and further the dryout, but the natural circulation type evaporator of the present embodiment keeps the flow of the fluid in the tube stable, Unstable flow is unlikely to occur, and damage to the heat transfer tube due to dryout can be prevented.

Further, the riser pipe 9 and the heat transfer pipe 5, the water seal pipe 3, and the downcomer pipe 2 do not interfere with each other when the pipes are routed, so that the structure is larger than that of the conventional two-pass natural circulation evaporator of the counterflow type. Can be simplified.

Further, another embodiment of the present invention-a second embodiment-will be described. In FIG. 2, the natural circulation type evaporator includes a steam drum 1, a downcomer 2, a water seal tube 3, an inlet header 4, a heat transfer tube 5, a vent tube 6, a heat transfer tube 7, an outlet header 8, and a rising tube 9. I have. In this evaporator, the heat transfer tube 5 receives one path of fluid in the upstream pipe, and the heat transfer tube 7 receives two paths of fluid in the downstream pipe. Both the intra-pipe fluid 1 path and the intra-pipe fluid 2 path are arranged in the same horizontal plane, and are configured to exchange heat with the horizontally flowing extra-pipe fluid 10 in the same horizontal plane.

In the present embodiment, the water supply introduced to the steam drum 1 descends down the downcomer 2 and flows into the inlet header 4 via the water seal tube 3. The feedwater that has flowed into the inlet header 4 is guided to the heat transfer pipes 5 arranged horizontally, and flows into the heat transfer pipes 7 placed on the same horizontal plane as the heat transfer pipes 5 via the vent pipes 6. During this time, the heat transfer tubes 5 and 7 exchange heat with the fluid inside the pipe and the fluid inside the pipe 2 to form a gas-liquid two-phase flow. Thereafter, the gas-liquid two-phase flow flows into the outlet header 8, rises on the riser 9, and returns to the steam drum 1.

In this two-pass natural circulation evaporator in a counter flow system, when the exhaust heat recovery boiler is started, the two fluids in the pipe near the rising pipe 9 evaporate before the one fluid in the pipe. 9, the time for gas-liquid two-phase flow to flow hastened,
The time until the circulation of the fluid in the pipe is started is shortened, and the startup time of the exhaust heat recovery boiler can be shortened.

Further, since the circulation force can be obtained in a short time as in the above-described embodiment, the backflow and the unstable flow are less likely to occur, and it is possible to prevent the heat transfer tube from being damaged due to dryout. Will be possible.

Further, another embodiment of the present invention-a third embodiment-will be described. In FIG. 3, the natural circulation evaporator has the same configuration as that of the above embodiment (see FIG. 1). The intra-pipe fluid 1 path and the intra-pipe fluid 2 path are both arranged on the same horizontal plane, and exchange heat with the extra-pipe fluid that has been passed. That is, the downstream fluid 2 exchanges heat with the extra-fluid 1 path 11, and the upstream fluid 1 exchanges heat with the extra-fluid 2 path 12.

This embodiment has the above-described structure. When the exhaust heat recovery boiler is started, the heat transfer pipe 7 exchanges heat in the two-tube fluid with the extra-fluid 1 path 11, and the heat transfer pipe 5 performs the heat exchange in the first fluid 11.
The path exchanges heat with the extrapipe fluid 2 path 12 to form a gas-liquid two-phase flow. This gas-liquid two-phase flow flows into the outlet header 8 and rises
And the circulation of the fluid in the pipe is started.

In this start-up process, the two-path fluid in the pipe near the riser pipe 9 evaporates earlier than the one-passage in the pipe fluid, so that the time during which the gas-liquid two-phase flow flows into the riser pipe 9 is shortened, and the environment of the pipe fluid The time until the start of the heat recovery is shortened, and the startup time of the exhaust heat recovery boiler can be shortened.

Since the circulation force can be obtained in a short time as in the case of the above-described embodiment, backflow and unstable flow are less likely to occur, and damage to the heat transfer tube due to dryout can be prevented. it can.

Further, another embodiment of the present invention—a fourth embodiment—will be described. In FIG. 4, the natural circulation evaporator has the same configuration as that of the above embodiment (see FIG. 1). The intra-pipe fluid 1 path and the intra-pipe fluid 2 path are both arranged in the same horizontal plane, and are configured to exchange heat with the extra-pipe fluid flowing in the divided areas.
That is, one path of the fluid in the pipe exchanges heat with the fluid 13 flowing in one area, and the two path of fluid in the pipe exchanges heat with the fluid 14 flowing in the other area.

This embodiment has the above-mentioned structure. When the exhaust heat recovery boiler is started, one path of the fluid in the pipe exchanges heat with the extra-fluid 13 in the heat transfer pipe 5, and two paths of fluid in the pipe are changed by the heat transfer pipe 7. It exchanges heat with the external fluid 14 to form a gas-liquid two-phase flow. This gas-liquid two-phase flow flows into the outlet header 8, rises the rising pipe 9, and starts circulation of the fluid in the pipe.

In this start-up process, there is some difference in the state quantity between the extravascular fluid 13 and the extravascular fluid 14 separated by the region, and heat exchange occurs with the extravascular fluid 14 having a larger state quantity. Two pipe fluid paths evaporate before one pipe fluid path. As a result, the time during which the gas-liquid two-phase flow flows into the riser pipe 9 is shortened, the time until the circulation of the fluid in the pipe is started is shortened, and the startup time of the exhaust heat recovery boiler can be shortened.

Further, since the circulation force can be obtained in a short time as in the above-described embodiment, the backflow and the unstable flow are less likely to occur, and it is possible to prevent the heat transfer tube from being damaged due to dryout. it can.

Further, another embodiment of the present invention-a fifth embodiment-will be described. In FIG. 5, a waste heat recovery boiler is a natural circulation evaporator in which a heat transfer tube 5 for receiving one path of fluid in a pipe and a heat transfer pipe 7 for receiving two paths of fluid in a pipe are arranged in the same horizontal plane in a duct 15 having a vertical structure. (See FIG. 1). The one-pass fluid in the pipe and the two-pass fluid in the pipe are configured to exchange heat with the extra-fluid 10 flowing in the vertical direction in the same horizontal plane.

This embodiment has the above configuration.
By incorporating the natural circulation evaporator according to the present invention into the exhaust heat recovery boiler, the same effect as that of the above-described first embodiment can be obtained.

Further, another embodiment of the present invention, namely, a sixth embodiment will be described. In FIG. 6, a natural circulation type evaporator in which a heat transfer pipe 5 for receiving one path of fluid in a pipe and a heat transfer pipe 7 for receiving two paths of fluid in a pipe are arranged in a horizontal duct 15 in a duct 15 having a horizontal structure in a waste heat recovery boiler ( FIG. 2). The one-pass fluid in the pipe and the two-pass fluid in the pipe are configured to exchange heat with the horizontal fluid 10 in the same horizontal plane.

This embodiment has the above configuration.
By incorporating the natural circulation evaporator according to the present invention into the exhaust heat recovery boiler, the same effect as that of the above-described second embodiment can be obtained.

Further, another embodiment of the present invention, namely, a seventh embodiment will be described. In FIG. 7, a waste heat recovery boiler is a natural circulation evaporator in which a heat transfer tube 5 for receiving one path of fluid in a pipe and a heat transfer pipe 7 for receiving two paths of fluid in a pipe are arranged in the same horizontal plane in a duct 15 having a vertical structure. (See FIG. 3). The inside of the duct 15 is divided into a plurality of flow paths by a partition plate 16 for forming a path for the extra-fluid. The in-pipe fluid 1 path and the in-pipe fluid 2 path are placed in partitioned fluid flow paths, respectively, and exchange heat with the extrapipe fluid 12 and the extrapipe fluid 11, respectively.

This embodiment has the above configuration.
By incorporating the natural circulation evaporator according to the present invention into the exhaust heat recovery boiler, the same effect as that of the above-described third embodiment can be obtained.

Further, another embodiment of the present invention-an eighth embodiment-will be described. In FIG. 8, the exhaust heat recovery boiler is a natural circulation evaporator in which a heat transfer pipe 5 for receiving one path of fluid in the pipe and a heat transfer pipe 7 for receiving two paths of fluid in the pipe are arranged in the same horizontal plane in a duct 15 having a vertical structure. (See FIG. 4). In the duct 15, the flow paths are separated from each other by a partition plate 16 in order to allow the extra-volume fluid of different states to flow. The in-pipe fluid 1 path and the in-pipe fluid 2 path are placed in this partitioned fluid flow path,
3 and the extra-fluid 14 are each configured to exchange heat.

This embodiment has the above configuration.
By incorporating the natural circulation evaporator according to the present invention into the exhaust heat recovery boiler, the same effect as that of the above-described fourth embodiment can be obtained.

Further, another embodiment of the present invention—a ninth embodiment—will be described. 9, the exhaust heat recovery boiler is provided with a natural circulation evaporator (see FIG. 4) in which a pipe fluid 1 path and a pipe fluid 2 path are arranged in the same horizontal plane in a duct 15 having a vertical structure. The inside of the duct 15 is divided into a plurality of flow paths by a partition plate 16 which enlarges an extra-fluid flow channel inlet so that a large amount of extra-fluid fluid 14 flows on the two-fluid path side. The in-pipe fluid 1 path and the in-pipe fluid 2 path are placed in the partitioned extra-pipe fluid flow path, and exchange heat with the extra-pipe fluid 13 and the extra-pipe fluid 14, respectively.

This embodiment has the above-mentioned structure. When the exhaust heat recovery boiler is started, one path of the fluid in the pipe exchanges heat with the extra-fluid 13 in the heat transfer pipe 5, and two paths of fluid in the pipe exchange heat in the heat transfer pipe 7. The gas-liquid two-phase flow is exchanged. This gas-liquid two-phase flow flows into the outlet header 8, rises the rising pipe 9, and starts circulation of the fluid in the pipe.

In this start-up process, the extrapipe fluid 14 whose inlet is enlarged flows in a larger amount than the extrapipe fluid 13, so that two passes in the pipe near the riser pipe 9 evaporate before one pass in the pipe fluid. As a result, the time during which the gas-liquid two-phase flow flows into the rising pipe 9 is shortened, the time until the circulation of the fluid in the pipe is started is shortened, and the startup time of the exhaust heat recovery boiler can be shortened.

Further, since the circulating force is obtained within a short time, backflow and unstable flow are less likely to occur, and it is possible to prevent damage to the heat transfer tube due to dryout.

Next, another embodiment of the present invention will be described. In FIG. 10, the exhaust heat recovery boiler has a plurality of zones horizontally arranged in a duct 15 having a vertical structure, and each of the zones has one extra-fluid fluid and two extra-fluid fluids in the same horizontal plane.
A natural circulation evaporator (see FIG. 1) having a path is provided. All the one-pass fluid in the pipe and the two-pass fluid in the pipe of this evaporator are configured to exchange heat in the same horizontal plane with the extra-fluid fluid flowing in the vertical direction.

This embodiment has the above-described structure. When the exhaust heat recovery boiler is started, each heat transfer tube 5 exchanges heat with one tube fluid outside the tube 10 and each heat transfer tube 7 exchanges two passages of fluid inside the tube. Undergoes heat exchange to form a gas-liquid two-phase flow. This gas-liquid two-phase flow flows into the respective outlet headers 8 and further rises up the respective riser pipes 9 to start circulation of the fluid in the pipes.

The vent pipes 6 in each zone are in the same horizontal plane, and even when the pipe fluid becomes a gas-liquid two-phase flow, the circulating force is not reduced, and the flow of the pipe fluid is kept stable. As a result, backflow and unstable flow are less likely to occur, and damage to the heat transfer tubes due to dryout can be prevented.

Further, in the routing of the pipes, the riser pipe 9 does not interfere with the heat transfer pipe 5, the water seal pipe 3, and the downcomer pipe 2 in each zone, and the structure can be simplified.

Further, the exhaust heat recovery boiler of the above embodiment can be used most effectively by the following starting method.

The first starting method is a method in which the heat is exchanged on the heat transfer surface with a difference in the amount of heat exchanged. As shown in FIG. As a result, the exchange heat quantity on the side of the in-pipe fluid 2 path 18 is kept large.

Further, the second starting method is a method of starting with a difference in the flow rate of the extra-fluid fluid, which is compared with the intra-fluid 1 pass 19 side for a certain period of time as shown in FIG. The flow rate of the extravascular fluid on the two-pass 20 side is kept large. Incidentally, this starting method can be easily realized in the exhaust heat recovery boiler incorporating the evaporator according to the fourth embodiment already described.

The third starting method is a method of starting with a difference in the temperature of the fluid outside the pipe, which is compared with the fluid 1 inside the pipe 21 for a certain period of time as shown in FIG. The temperature of the extravascular fluid on the two-pass 22 side is kept high. This starting method can be realized by using the evaporator according to the second and third embodiments described above.
For example, a fuel may be separately charged to assist the extra-fluid fluid.

Further, another embodiment of the present invention will be described. In FIG. 14, the heat transfer tubes 5 and 7 have a difference in the heat exchange amount between the pitch L1 of the fins 23 of the heat transfer tube 5 that receives one path of fluid in the pipe and the pitch L2 of the fins 23 of the heat transfer pipe 7 that receives two paths of fluid in the pipe. Therefore, the pitch L2 of the heat transfer tubes 7 is formed at a higher density than the pitch L1 of the heat transfer tubes 5. The heat transfer tube 7 having a larger heat transfer area has better heat transfer characteristics than the heat transfer tube 5.

In the natural circulation type evaporator using the heat transfer tubes 5 and 7, two paths of fluid in the pipe near the riser pipe 9 evaporate before one pass of the fluid in the pipe. The time required for the heat to flow in is shortened, the time required for the circulation of the flow rate in the pipe to be started is shortened, and the startup time of the exhaust heat recovery boiler can be shortened. In addition, since the circulation force is obtained in a short time, the backflow and the unstable flow are less likely to occur, and it is possible to prevent the heat transfer tube from being damaged due to the dryout.

In this embodiment, instead of changing the pitch of the fins 23, it is possible to change the fin height, the fin shape and the fin material between the heat transfer tubes, or change the material of the heat transfer tubes themselves. You may do so.

Further, another embodiment of the present invention will be described. 15A and 15B, the heat transfer tube 5 has an inlet header 4 at the inlet thereof. The heat transfer tube 7 has an outlet header 8 at the outlet thereof. These heat transfer tubes 5, 7
Has a linear intermediate header 24 for reversing the fluid in the tube from one side to the other. When used in the evaporator according to the present invention, it is used so that the heat transfer tube 5 receives the upstream pipe fluid 1 path and the heat transfer tube 7 receives the downstream pipe fluid 2 path.

In this embodiment, the passage of the fluid in the pipe can be realized with a simple structure by using the linear intermediate header 24 instead of the vent pipe 6.

[0098]

As described above, according to the present invention, even when the fluid in the pipe has a two-phase gas-liquid flow, the flow of the fluid in the pipe is kept stable without reducing the circulating force. Therefore, according to the present invention, it is possible to prevent the backflow and the unstable flow from occurring, and it is possible to avoid the structure from being complicated in the routing of the piping.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a natural circulation evaporator according to the present invention.

FIG. 2 is a system diagram showing another embodiment of the present invention.

FIG. 3 is a system diagram showing another embodiment of the present invention.

FIG. 4 is a system diagram showing another embodiment of the present invention.

FIG. 5 is a configuration diagram showing an exhaust heat recovery boiler according to the present invention.

FIG. 6 is a configuration diagram showing another embodiment of the present invention.

FIG. 7 is a configuration diagram showing another embodiment of the present invention.

FIG. 8 is a configuration diagram showing another embodiment of the present invention.

FIG. 9 is a configuration diagram showing another embodiment of the present invention.

FIG. 10 is a configuration diagram showing another embodiment of the present invention.

FIG. 11 is a characteristic diagram showing a change in exchanged heat amount in the starting method of the present invention;

FIG. 12 is a characteristic diagram showing a transition of the flow rate of extrafluid fluid in the starting method of the present invention;

FIG. 13 is a characteristic diagram showing a transition of the temperature of the extrafluid fluid in the starting method of the present invention.

FIG. 14 is a configuration diagram showing another embodiment of the present invention.

FIG. 15 is a configuration diagram showing another embodiment of the present invention.

FIG. 16 is a system diagram showing a conventional natural circulation evaporator.

FIG. 17 is a system diagram showing a conventional co-flow two-pass natural circulation evaporator in a pipe.

FIG. 18 is a system diagram showing a conventional counter-flow two-pass natural circulation evaporator in a pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steam drum 2 Downcomer 3 Water seal pipe 4 Inlet header 5, 7 Heat transfer pipe 6 Vent pipe 8 Outlet header 9 Rise pipe 15 Duct 16 Partition plate

Claims (16)

[Claims] 1. A natural circulation evaporator comprising a heat transfer tube for sequentially receiving one path of an upstream pipe fluid and two paths of a downstream pipe fluid. Is disposed so as to exchange heat with an extravascular fluid. 2. The heat transfer tube according to claim 1, wherein the two fluid passages on the downstream side exchange heat with the extra-fluid fluid before the one fluid passage on the upstream side in the same horizontal plane. The natural circulation evaporator according to claim 1, wherein 3. The heat transfer tube is located in a region where the extra-fluid flows in the horizontal direction, and the two extra-fluid passages on the downstream side precede the one extra-fluid fluid on the upstream side in the same horizontal plane. The natural circulation evaporator according to claim 2, wherein the evaporator is arranged to exchange heat with the evaporator. 4. The heat transfer tube is located in a region where the heat transfer tubes are separated from each other in which the extra-fluid flows from below to above and further inverted and from above to below, and two downstream fluids in the same horizontal plane are upstream. 3. The natural circulation evaporator according to claim 2, wherein the evaporator is arranged so as to exchange heat with the extrapipe fluid before the one intrapipe fluid pass. 5. The heat transfer tube is located in an area separated from each other in which extra-fluid fluids having different state quantities or flow rates individually flow, and two downstream fluids in the same horizontal plane are connected to one fluid in the upstream fluid. The natural circulation evaporator according to claim 1, wherein the evaporator is arranged to exchange heat with a state quantity or flow rate of the extra-fluid fluid larger than that on the pass side. 6. An exhaust heat recovery boiler comprising a natural circulation evaporator according to claim 1 in a duct. 7. A heat recovery steam generator comprising a natural circulation evaporator according to claim 2 in a duct. 8. An exhaust heat recovery boiler comprising a natural circulation evaporator according to claim 3 in a duct. 9. A heat recovery steam generator comprising a natural circulation evaporator according to claim 4 in a duct. 10. An exhaust heat recovery boiler comprising a natural circulation evaporator according to claim 5 in a duct. 11. A waste heat recovery boiler having a plurality of zones arranged horizontally in a duct, each of which includes the natural circulation evaporator according to claim 1. 12. A method for starting a heat recovery steam generator having a natural circulation type evaporator provided with a heat transfer tube which sequentially receives one path of an upstream pipe fluid and two paths of a downstream pipe fluid, wherein the heat transfer pipes are arranged on the same horizontal plane. Inside the pipe, the paths of the pipe fluid exchange heat with the pipe extra fluid, so that when the exhaust heat recovery boiler is started, the pipe fluid 2
A starting method for an exhaust heat recovery boiler, wherein the path side is started while maintaining a large amount of exchanged heat as compared with the one-pass fluid side. 13. A method for starting a heat recovery steam generator having a natural circulation evaporator provided with a heat transfer tube for sequentially receiving one path of an in-pipe fluid and two paths of a downstream in-pipe fluid, wherein the heat transfer tubes are arranged on the same horizontal plane. Inside the pipe, the paths of the pipe fluid exchange heat with the pipe extra fluid, so that when the exhaust heat recovery boiler is started, the pipe fluid 2
A start-up method for an exhaust heat recovery boiler, wherein the path side is started while keeping the flow rate of the extra-tube fluid large as compared with the one-pass fluid in the pipe. 14. A method for starting an exhaust heat recovery boiler having a natural circulation evaporator provided with a heat transfer tube that sequentially receives one path of an upstream pipe fluid and two paths of a downstream pipe fluid. Inside the pipe, the paths of the pipe fluid exchange heat with the pipe extra fluid, so that when the exhaust heat recovery boiler is started, the pipe fluid 2
A method for activating a waste heat recovery boiler, wherein the path side is activated while keeping the temperature of the extra-pipe fluid higher than the one-pass fluid side. 15. The heat transfer tube comprises a finned heat transfer tube, and the fin pitch of the heat transfer tube for receiving the two fluids in the tube is formed at a higher density than that of the heat transfer tube for receiving the one fluid in the tube. The natural circulation evaporator according to any one of claims 1 to 5, characterized in that: 16. The heat transfer pipe for receiving the one-pass fluid in the pipe and the heat transfer pipe for receiving the two-pass fluid in the pipe are communicated by a linear intermediate header for reversing the fluid in the pipe. Item 6. The natural circulation evaporator according to any one of Items 1 to 5.