JPS629107A - Moisture separating heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to moisture separation heaters in steam turbine plants.

[Technical background of the invention and its problems]

Generally, in nuclear power plants using boiling water type or pressurized wood type light water reactors, the main steam led to the high pressure turpin is saturated steam, so it performs work in the high pressure turbine and becomes low temperature and low pressure. The high-pressure turbine exhaust steam (hereinafter referred to as cycle steam) is 14ata under rated load conditions.
, 196°C and humidity of 12-13%. Therefore, if this wet steam is directly introduced into the low-pressure turbine, it not only causes problems such as a decrease in the internal efficiency of the low-pressure steam turbine and erosion of the impeller, but also causes problems such as a decrease in the thermal efficiency of the plant.

Therefore, a moisture separation heater is installed between the high-pressure steam turbine and the low-pressure steam turbine, and the moisture in the cycle steam is removed and heated at the same time, in order to improve the internal efficiency of the low-pressure steam turbine. As the above-mentioned moisture separating heater, the one described in Japanese Patent Publication No. 1889/1989 is known.

FIG. 5 is a schematic system diagram of a steam turbine plant equipped with a moisture separation heater as described above.
Saturated steam of ~6 B ata is supplied via the main steam pipe 2 and performs work therein.

The steam that has completed its work in the high-pressure steam turbine 1 becomes steam with a rating of approximately 14 ata, 196° C., and a humidity of 12 to 13%, and is led to a moisture separation heater 4 through a conduit 3.

The moisture separation heater 4 usually has a horizontal cylindrical appearance,
It is a heat exchanger that houses a moisture separator 5 and a heater 6.7 inside, and has a one-stage heating method in which cycle steam is heated with a single-stage heater, and a two-stage heating method in which cycle steam is heated with a two-stage heater. There is a method.

Thus, the cycle steam discharged from the high-pressure cuben 1 is transferred to an inlet 8 provided at the lower part of the moisture separation heater 4.
When the steam flows into the moisture separating heater 4 and passes through the moisture separator 5, which has a large number of corrugated plates arranged in parallel, most of the moisture contained in the steam is removed and the moisture is It becomes steam with a concentration of about 1%. The moisture separated by the moisture separator 5 is sent to a feed water heater (not shown) via a drain discharge pipe 9 and used for heat recovery.

On the other hand, cycle steam with a moisture content of approximately 1% flows sequentially on the outside of each tube bundle of the first-stage heater 6 and the second-stage heater 7 in a direction perpendicular to the tube bundle, while flowing inside the tube. It is heated by exchanging heat with the flowing high-temperature heating steam, becomes hot air that is superheated by about 70 degrees Celsius under rated load conditions, flows out from the cycle steam outlet 10 provided in the upper part of the main body shell, and passes through the conduit 11 to low pressure. is supplied to the turbine 12.

The first and second stage heaters 6 and 7 are both composed of a large number of U-shaped heat exchanger tubes, and the heated steam header 13 of the first stage heater 6 receives oil from the high pressure turbine 1. Steam is supplied via conduit 14 and a portion of the main steam is supplied via conduit 16 to the heated steam header 15 of the second stage heater 7 .

However, the heaters 6 and 7, as shown in FIG.
It has a large number of U-shaped heat exchanger tubes 21 supported by support plates 20 arranged at appropriate intervals, and both ends of the U-shaped heat exchanger tubes 21 are fixed to the tube plate 23 of the heating steam header 22. There is. That is, one end of the U-shaped heat transfer tube 21 is opened to a heated steam inlet header 22a formed in a section in the heated steam header 22, and the other end is connected to a heated steam outlet header 22b.

Therefore, the heated steam consisting of extracted steam or main steam from the high pressure turbine enters the heated steam inlet header 22a and flows inside the U-shaped heat exchanger tube 21, while passing outside the tube orthogonally from the bottom to the top. It gradually condenses by exchanging heat with the low-temperature, low-pressure Nycle steam flowing in that direction, and then flows into the ladder 22b to the heated steam outlet and is roughly discharged from the drain discharge pipe 24.

However, when the condensate condensed in the heat transfer tube flows through the lower leg of the heat transfer tube, it may become supercooled to a temperature lower than the saturation temperature of the heated steam due to heat exchange with the low-temperature heated steam. At the outlet of the U-shaped heat transfer tube 21, the supercooled condensate and saturated steam flow out simultaneously or alternately, and the temperature changes between the saturation temperature and the supercooled condensate. Become. However, due to this temperature fluctuation, there is a problem that scratches due to thermal fatigue occur in the welded portion of the U-shaped heat exchanger tube 21 with the tube plate 23 on the outlet side.

Therefore, in order to prevent overcooling of the condensate drain, a vent steam exhaust pipe 25 is provided in the heated steam outlet header 22b as shown in FIG. 6, and a part of the heated steam is discharged from the vent steam exhaust pipe 25. There have also been proposals for extraction in an uncondensed state.

That is, by extracting a portion of the heated steam without condensing, the vent steam is transferred to the U-shaped heat exchanger tube 2.
When passing through the pipe of No. 1, the condensed condensate in the pipe is mixed,
Supercooling of the condensate drain is suppressed by contact with vent steam, which is saturated steam.

By the way, in order to obtain the effect of suppressing supercooling by this vent steam, it is necessary to ensure vent steam of 10% or more of the total heating steam flow rate not only during rated operation but also during low load. However, the flow rate of this vent steam is set by a fixed flow rate orifice provided in the middle of the vent steam exhaust pipe 25 that connects the heating steam outlet header 22b and the shell side of the feed water heater (not shown). The flow rate of steam is naturally determined by the pressure difference between the heated steam outlet header and the feed water heater on the shell side.

FIG. 7 shows the heated steam outlet header 22 of the first stage heater 6.
This is a graph in which the vertical axis is the pressure in b and the steam pressure on the shell side of the feed water heater, and the horizontal axis is the turbine load, and the pressure in the heating steam outlet header 22b is indicated by a-b in the figure. , is approximately 35 ata at rated load, and the pressure on the feed water heater side is represented by a-C in the figure, and is approximately 24 ata at rated load.
It is ata. Here, the pressure difference between the heating steam outlet header 22b and the feed water heater body side is represented by the difference between lines a-b and a-c in the figure, and is approximately 11 kg/cd during rated operation. The pressure difference decreases in the case of the first stage heater as the turbine load decreases. Therefore, the vent steam flow rate becomes smaller as the load decreases.

Figure 8 shows, on the vertical axis, the ratio of the heating steam flow rate and vent steam flow rate at each partial load to the heating steam flow rate and vent steam flow rate at the rated load in the first stage heater. The flow rate ratio is represented by the line a-de and the vent vapor flow m ratio is represented by the line a-c-b. In this way, both the heating steam flow rate ratio and the vent steam flow m ratio decrease as the turbine load decreases. However, when the vent steam is under 50% load, the discharge side of the vent steam is switched from the feedwater heater shell side to the condenser with lower pressure, so the decrease in the vent steam flow rate becomes gradual. Here, the ratio of the vent steam flow rate to the heating steam flow rate is set to 10% at rated load as described above, and even at partial load, the vent steam flow m ratio a-c-b is the heating steam flow rate ratio a -de above. In other words, even during partial load, the ratio of the vent steam flow m to the heating steam flow rate is always maintained at 10% or more.

However, when the turbine load is less than 50%, the vent steam of the first stage heater is discharged to the condenser, so it cannot be used at all for purposes such as heating feed water.

On the other hand, Figure 9 is a graph in which the vertical axis represents the steam pressure at the heated steam outlet header of the second stage heater and the first feed water heater shell side, and the horizontal axis represents the turbine load. The pressure is shown as a-b-c in the diagram, and is 50% from the rated load.
The load is about 67 ata, and after that it drops rapidly. Moreover, the pressure on the side for the first feed water heater is represented by de in the figure.

Figure 10 shows the heating steam flow rate at rated load and the heating steam flow rate ratio J3 and vent steam flow rate ratio at each partial load with respect to vent steam flow in the second stage heater on the vertical axis, and the turbine load on the horizontal axis. This is a graph with an axis. In the figure, the heating steam flow rate ratio is indicated by solid lines ae-b. It gradually decreases from the rated load to 50% load, and decreases somewhat suddenly below 50% load. On the other hand, the vent steam flow group is indicated by a-C-d in the figure, and from the rated load to 50% load, the vent steam flow rate ratio is 1.0, and the vent steam flow rate at the rated load is maintained. In other words, the steam pressure at the heated steam outlet header of the second stage heater is constant from the rated load to 50% load, and the pressure ratio before and after the vent steam orifice is in a critical state, and the vent natural air flow rate is constant. .

However, when the turbine load becomes 50% or less, the vent steam 1ffi suddenly decreases as shown by c-d in FIG. As shown in Figure 9 b-c, when the turbine load falls below 50%, the pressure at the heated steam outlet header of the second stage heater suddenly decreases, causing This is because the pressure difference decreases.

Here, the vent steam flow rate ratio c-d at a turbine load of 50% or less in FIG. In operation, the value is lower than the heating steam flow rate ratio.

However, when the vent steam flow ratio becomes lower than the heating steam flow rate ratio, the vent steam orifice is adjusted so that the vent steam flow rate is 10% of the heating steam flow rate at the rated load, as described above. Because of the design, the ratio of the vent steam flow rate to the heated steam flow rate is less than 10%, and the effect of suppressing the cooling that occurs in the heated steam condensation drain described above cannot be obtained, and the There are problems such as the possibility of damage due to thermal fatigue at the welded part with the plate.

[Purpose of the invention]

In view of these points, the present invention aims to improve the heat recovery of vent steam during low loads in the first stage heater of a moisture separation heater, and to improve the heat recovery of vent steam during low loads in the second stage heater. By supercooling the heated steam condensate drain due to the ratio of the vent steam flow rate to the flow rate being less than 10%, the welded part between the heat exchanger tube outlet and the tube plate is prevented from being damaged due to thermal fatigue, and the performance of the equipment is improved. The present invention also aims to provide a moisture separating heater that can improve reliability.

[Summary of the invention]

The present invention provides a method in which the ends of a large number of U-shaped heat exchanger tubes are connected to a heating steam inlet header and a heating steam outlet header, respectively.
In the moisture separation heater having a first stage heater and a second stage heater, a vent steam exhaust pipe is connected to the heated steam outlet header, and the vent steam exhaust pipe is connected to a vacuum orifice and a selectively It is connected to a high-pressure feed water heater and a condenser with different pressures through valves that are controlled to open and close. communicated with 5
% or more, it is communicated with a high-pressure feedwater heater, and in the second stage heater, when the turbine load is 40% or less, it is communicated with a condenser, and when it is 40% or more, it is communicated with a high-pressure feedwater heater. It is something.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

In FIG. 1, reference numeral 30a is the first stage heater of the moisture separation heater, 30b is the second stage heater, and both heaters 30
In both a and 30b, a large number of U-shaped heat exchanger tubes 31
One end of a, 31b is heated steam inlet header 32a, 32b
The other end is connected to the heating steam outlet header 33a, 33b.
It is connected to the.

By the way, the heating steam outlet header 33a.

33b has a vent steam exhaust pipe 34a, respectively.

34b is connected, and both vent hot air exhaust pipes 34
a, 34b are two lines 35a on the way.

36a, 35b, and 36b, and each system has a vacuum, orifice 37a, 37b, 37c, and 37
d, and gate valves 38a, 38b, 38c, and 38d are connected in series. One of the two systems 35a and 35b is led to the high-pressure feed water heater side 39, and the other system 36a and 36b is led to the condenser 40.

Thus, in both heaters 30a and 30b, the heating steam is supplied to the heating steam inlet header 32a, respectively.

32b, flows through U-shaped heat exchanger tubes 31a and 31b,
During that time, it condenses by exchanging heat with the low-temperature cycle steam flowing outside the tube, and most of it becomes a drain, which flows from the other end of the U-shaped heat exchanger tubes 31a and 31b to the heating steam inlet header 33a.
, 33b.

Therefore, the condensate condensed by the above heat exchange is led out of the container of the moisture valve 111 from a condensate drain outlet (not shown), and remains uncondensed through the heated steam inlet headers 33a, 3.
．． The vent steam that has flowed into the vent steam exhaust pipe 34
a, 34b, and vacuum orifices 37a, 3, respectively.
7b, 37c, 37d and gate valves 38a, 38b, 3
The water is discharged to the high pressure feed water heater 39 or condenser 40 via 8c and 38d.

By the way, in the first stage heater 30a, when the load is 5% or more, the gate valve 38a is opened and the gate valve 38b is opened.
is closed, and the vent steam is led out to the high-pressure feed water heater 39 through the pressure reducing orifice 37a and the gate valve 38a.On the other hand, in the no-load to 5% load range, the vacuum in the heating steam header and heat transfer tubes is For pulling, gate valve 3
8b is opened, and the other gate valve 38a is closed, and in this case, vent steam is led out to the condenser 40 via the gate valve 38b and the like.

In the above embodiment, even when the load is below 50%, the vent steam discharge pipe 34a is communicated with the shell side of the high pressure feed water heater 39 up to 5% load, so that the vent steam discharge pipe 34a is connected to the shell side of the high pressure feed water heater 39, so that the vent steam at partial load with respect to the rated load is Although the flow rate ratio changes as shown by a-c-f in FIG. 8, it becomes a threshold value rather than the heating steam flow rate ratio a-de. On the other hand, at the rated load, the decompression orifice 37a is set so that the ratio of the vent steam flow rate to the heating steam flow rate is 10%. Therefore, as mentioned above, since the vent steam flow rate ratio is larger than the heating steam flow rate ratio even in partial load, the ratio of the vent steam flow rate to the heating steam flow rate during partial load is also 10% or more, and the supercooling suppressing effect is obtained. Sufficient ventilation will be ensured.

On the other hand, in the second stage heater 30b, 5
Since the pressure of the heating steam is constant up to 0% load, the vent steam flow m is constant as shown in a-C in FIG. 10. However, when the turbine load becomes 50% or less, the pressure of the heating steam drops rapidly and the vent steam flow rate also begins to decrease. However, as mentioned above, even at partial load, it is necessary to maintain a ratio of 10% or more between the vent steam flow and the heating steam flow, but in the range e-d in the figure where the turbine load is about 35% or less, Vent steam flow northernmost e-d
However, the heating steam flow is below the ratio e-b, and in this range, the ratio of the vent steam flow rate to the heating steam flow rate is 10
less than %.

Therefore, in the present invention, the heating steam flow rate ratio a-e-b
When the turbine load is smaller than the point f where the turbine load is 40%, the load is slightly higher than the point e at 35% of the turbine load where the ratio a-c-d is equal. The valve 38c is closed and the gate valve 38d is opened. That is, when the turbine load is 40% or less,
The vent steam is switched from being supplied to the shell side of the high-pressure feedwater heater 39 to being introduced into the condenser 40 . Therefore, since the inside of the condenser 40 is almost vacuum, the pressure difference between the upstream side and the downstream side of the decompression orifice 37d in the vent steam system becomes large, and the amount of vent steam leakage increases. When this is shown in Figure 10 as a vent steam flow rate ratio, it is expressed as f-9, which exceeds the heating steam flow rate ratio ae-b, and the ratio of the vent steam flow claw to the heating steam flow rate is 1 even at low load.
0% or more, and it is possible to prevent damage to the welded portion at the outlet end of the heat exchanger tube due to supercooling of the heated steam condensate drain.

By the way, in the above embodiment, the vent steam exhaust pipes 34a and 34b are branched into two systems 35a and 36a.
, 35b-, and 36b are shown as having vacuum orifices, but as shown in FIG. 2, the vacuum orifices 37a, 37b may be provided.

Moreover, as shown in FIG. 3, each decompression orifice 37a,
37b, 37c, 37d to each gate valve 38a, 38b, 3
They may be provided on the downstream side of 8c and 38d, respectively.

Incidentally, the amount of vent steam is generally set so that the amount of heat exchanged in each heat exchanger tube at 100% load is calculated so that the required amount of steam flows through each heat exchanger tube. However, in such a device, during low-load operation, the differential pressure between the inlet and outlet is small, so the steam flow rate is small, and the lower part of the outer heat exchanger tube has a large amount of heat exchange, so the area near the heated steam outlet header becomes supercooled. Flow becomes unstable. That is, although sufficient steam flows through the inner circumferential heat exchanger tube, the steam flow rate is small in the lower part of the outer circumferential heat exchanger tube, and a supercooling phenomenon occurs in that section, causing condensate to accumulate.

Therefore, as this progresses, it becomes unbalanced with the inner heat exchanger tube, drain is discharged to the heated steam outlet header side, and the seal weld between the heat exchanger tube and tube sheet is damaged due to repeated supercooling and drain discharge. There are problems such as the occurrence of vibrations and vibrations.

FIG. 4 shows a system in which supercooling in the lower part of the outer heat exchanger tube is prevented based on the difference in heat exchange between the inner heat exchanger tube and the lower part of the outer heat exchanger tube as described above. The heated steam outlet header 33a is separated by a partition plate 41, and is connected to an inner heat exchanger tube outlet header 42a connected to an inner heat exchanger tube through which steam flows relatively easily, and an outer heat exchanger tube through which condensate is easily generated. Outlet header 42b for outer peripheral heat exchanger tube
is formed.

The outlet header 42a for the inner circumferential heat exchanger tubes and the header 42b for the outer circumferential heat exchanger tubes have vent steam exhaust pipes 43, respectively.
a, 43b are connected, and each vent steam exhaust pipe 43a, 4
3b is provided with an orifice 44a, 44b, respectively, and each orifice 44a.

Each pressure regulating valve 45a is in parallel with 44b.

45b is provided.

Further, pressure detectors 46a are provided at the inner heat exchanger tube outlet header 42a and the outer circumference heat exchanger tube outlet header 42b.

46b are provided, each "force detector 46a.

the signal detected at 46b and a pressure setting function generator 47a;
The deviation signal from 47b is pressure crab l! J set meter 488°48b
are inputted into the respective pressure regulators 48a,
Pressure regulating valve 45a by the output signal from 48b, ie the pressure in the outlet header.

The opening degree of 45b is controlled.

Therefore, at all times, the pressure regulating valve 45a.

45b is in a closed state, and the orifice 44a,
44b releases a constant amount of vent steam.

Therefore, when the drain is likely to accumulate in the lower part of the outer heat exchanger tube during low load operation of the turbine, the pressure regulating valve 45b is moved in the opening direction according to the difference between the pressure of the outer heat exchanger tube outlet header 42b and the set pressure. The pressure at the outlet header 42b for the outer heat exchanger tubes is controlled to be low, so that the flow of heated steam within the heat exchanger tubes is made smooth and supercooling is prevented.

Similarly, even when the inner circumferential heat exchanger tube becomes overcooled, overcooling of the heat exchanger tube is prevented by controlling the opening degree of the pressure regulating valve 45a, and the amount of venting is not unnecessarily reduced during high loads. It will not increase.

〔Effect of the invention〕

As explained above, in the present invention, both the vent steam discharge pipes of the first stage heater and the second stage heater in the moisture separation heater are selectively connected to the high pressure feed water heater and the condenser. In addition, in the first stage heater, the vent steam exhaust pipe is connected to the condenser only when the load is 5% or less, so the condenser is ineffective in terms of heat recovery. The outflow of vent steam to the tank is reduced and the heat recovery efficiency can be increased. Furthermore, in the second stage heater, the vent steam exhaust pipe is connected to the high pressure feed water heater when the load is 40% or higher, and the vent steam exhaust pipe is connected to the condenser when the load is lower than 40%. Even when Damage to the seal weld is reliably prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a moisture separating heater according to the present invention, FIGS. 2 to 4 are schematic diagrams showing other embodiments of the present invention, and FIG. 5 is a diagram showing a moisture separating heater provided with a moisture separating heater. Figure 6 is a longitudinal sectional view of the heater, Figure 7 is a schematic system diagram of a steam turbine plant.
The figure shows the relationship between the pressure in the heated steam outlet header in the first stage heater and the steam pressure on the shell side of the feedwater heater with respect to the turbine load. Figure 8 shows the ratio of heated steam ore to the turbine load in the first stage heater. FIG. 9 is a diagram showing the relationship between the pressure in the heating steam outlet header and the steam pressure on the shell side of the feedwater heater with respect to the turbine load in the second stage heater, and FIG. is the first
FIG. 2 is a diagram showing the relationship between the heating steam flow rate ratio and the vent steam flow rate ratio with respect to the turbine load in the stage heater. 30a... 1st stage heater, 30b... 2nd stage heater, 31 a, 31 'o/U-shaped heat exchanger tube, 32a, 3
2b...Heating steam inlet header, 33a, 33b...
Heating steam outlet header, 34a, 34b...Vent steam discharge pipe, 38a, 38b, 38c, 38d--Gate valve, 39...High-pressure feed water heater, 40... Condenser. Applicant's Representative Sato - Yutsuri Figure 2 Figure $ 5 Figure Turbine Load (2> Tsuru 7 Figure 0 25 50 75 f
qO turbine Kikuchi (X) Aoi 6 figure

Claims (1)

[Scope of Claims] 1. A moisture vaporizer having a first-stage heater and a second-stage heater, each of which connects the ends of a large number of U-shaped heat exchanger tubes to a heated steam inlet header and a heated steam outlet header, respectively. In the separation heater, a vent steam exhaust pipe is connected to the heated steam outlet header, and the vent steam exhaust pipe is connected to the high pressure feed water heater having different pressures from each other through a pressure reducing orifice and a valve that is selectively controlled to open and close. and a condenser, and the vent steam exhaust pipe is connected to the condenser in the first stage heater when the turbine load is 5% or less, and to the high pressure feedwater heater when the turbine load is 5% or more; In the second stage heater, when the turbine load is 40% or less, it is communicated with the condenser,
A moisture separation heater, characterized in that when the moisture content exceeds 40%, the moisture separation heater is connected to a high-pressure feed water heater. 2. A patent characterized in that the vent steam discharge pipe has branch pipes each connected to a high-pressure feed water heater or a condenser, and the branch pipes are provided with a pressure reducing orifice and an on-off valve. A moisture separating heater according to claim 1. 3. The heating steam outlet header is divided into two compartments that communicate with the inner peripheral side of the heat exchanger tube and the outer peripheral side of the heat exchanger tube, respectively, and the vent steam exhaust pipe connected to each compartment,
Moisture separation heater according to claim 1, characterized in that a vacuum orifice and a pressure-adjustable control valve are provided.