JPH049502A - Drain water level controller of feed water heater - Google Patents

Abstract

PURPOSE:To carry out a stable operation of an electric power plant by mutually relating the conditions of drain water recovery to a low pressure feed water heater, first high pressure feed water heater, and deaerator and carrying out the most suitable and most favorable heat recovery by the process conditions. CONSTITUTION:A calculator 26 incorporates a calculation section 33 for the conditions of change-over and inputs the pressures of a first high pressure feed water heater 6, second high pressure feed water heater 7, and deaerator 1 by pressure sensors 27, 28, and 29, and at the same time comparison sections 34a and 34b compare and calculate the pressure differences between a second high pressure feed water heater 7 - deaerator 1 and those between the first high pressure feed water heater 6 - deaerator 1, and at the time of in-service for each feed water heater drain is recovered in the order of the second high pressure feed water heater, first high pressure feed water heater, low pressure feed water heater, and when load rises, drain is recovered in the order of the second high pressure feed water heater, deaerator and in the order of the first high pressure feed water heater, low pressure feed water heater, and further when the load rises, drain is recovered in the order of second high pressure feed water heater, first high pressure feed water, and deaerator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a feed water heater drain water level control device for a heat exchanger in a power generation plant or the like.

(Prior Art) Generally, in a power generation plant, a plurality of feed water heaters are arranged in a cascade in a heat exchanger in order to improve the thermal efficiency of a turbine plant as much as possible.

These feed water heaters introduce steam such as extracted air from a steam turbine or the like to preheat and raise the temperature of the feed water to be supplied to a steam generator such as a boiler. Furthermore, the steam that has exchanged heat with the feed water in the feed water heater condenses and becomes drain, which is drained in a cascade system from the feed water heater with high internal pressure to the feed water heater with low internal pressure in order, and the condensate system etc. It is designed to be collected at That is,
When a power generation plant, etc. is under normal rated load, drain from the high-pressure feed water heater is collected by the deaerator from the final stage of the high-pressure feed water heater, and drain from the low-pressure feed water heater is condensed by the drain pump. recovered into the system. On the other hand, the load on power plants, etc. has decreased, and the feed water heater in the final stage of the high-pressure system (
When the internal pressure of the first high-pressure feed water heater (first high-pressure feed water heater) decreases and it becomes impossible to collect condensate to the deaerator installed several tens of meters higher than this, the low-pressure system feed water heater hedrain is recovered. .

In such a feed water heater, so-called water induction (water induction), which prevents the heat exchange coefficient of the heat exchange system from decreasing and causes the steam turbine hedren to flow back through the bleed pipe, is used.
In order to prevent this, the water level in the feed water heater is controlled to be constant. In addition, in order to improve the heat exchange efficiency of the heat exchange system, the piping that collects condensate from the high-pressure feed water heater to the deaerator was installed not only in the final stage of the high-pressure feed water heater, but also in other high-pressure feed water heaters. In some cases, it may also be connected to a container to collect the drain. Furthermore, as a heating source for these feedwater heaters, in addition to the oil air from the main steam turbine, back-drawn boiler feedwater pump turbines (BFP-T
In some cases, bleed air and back air from (abbreviated as) are used.

Here, a control method of a conventional feed water heater drain water level control device will be explained with reference to FIG.

First, the water stored in the deaerator 1 is supplied to the water supply pump 2.
The water is preheated and heated through the water supply pipe 3 through the first high-pressure water heater 6 and the second high-pressure water heater 7, and then sent to a boiler (not shown).

The high-pressure feed water heaters 6 and 7 exchange heat with the feed water to preheat and heat it.
In order to raise the temperature, bleed steam is supplied from bleed steam pipes 8 and 9, and drain from a high-pressure feed water heater placed upstream of these pipes is supplied through drain pipes 30 and 31. The condensate that has undergone heat recovery in the high-pressure feed water heater 6.7 is discharged to predetermined equipment via flow rate control valves 10.11.12 and 13.14, respectively. That is, the drain from the second high-pressure feed water heater 7 is discharged through the drain pipes 31, 31a and the flow rate control valve 13, through the deaerator 1 and the flow rate control valve 14, to the first high-pressure feed water heater S6, and, The drain from the high pressure water heater 6 is drain pipe 32, 32a.
The water is discharged through the flow ffi control valve 10 to the deaerator 1, low-pressure feed water heater 4, and condenser 5, respectively. in this way,
If there are multiple drainage destinations, distribute them as follows.

That is, in the first high-pressure feed water heater 6, the water level signal from the water level detector 15 attached thereto and the water level controllers 17, 18 disposed in the respective drain pipes 32.32g, 32b are detected.
．． Distribution is performed based on the deviation from the target set value of No. 19. In addition, in the N2 high-pressure feed water heater 7, the flow control valve 13 disposed in the drain pipe 31.31a is operated by the water level controller 35 which receives a water level signal from the water level detector 16 attached thereto and adjusts the water level to 317 rJ. .14 with stop f#q control,
Distribution is performed using a solenoid valve 34 or a manual switch that operates depending on load conditions. In other words, in the first high-pressure feed water heater 6, each water level setting value is set to the standard water level so that the condensate is first collected in the deaerator 1, then in the low-pressure feed water heater 4, and then in the condenser 5. (NWL), NWL
+α, NWL +β, and their values are NWL<
It is a cascade of NWL+α<NWL+β.

Therefore, under high load conditions, the drain system has sufficient pressure to discharge the head of the deaerator 1, which is installed several tens of meters higher than the first high-pressure feed water heater 6. Therefore, the flow rate is 1k1 to reach the standard water level (NWL).
Drain is discharged by adjusting the opening degree of the 8Wr valve 1o. On the other hand, when the load decreases and the pressure in the first high-pressure feed water heater 6 decreases, the deaerator 1 head can no longer be recovered, and the water level in the first high-pressure feed water heater 6 rises and NWL+a
(>NWL). Therefore, the water level controller 18 is operated to adjust the valve opening of the flow jl control valve 11 and the low pressure feed water heater 4 is activated.
Drain the hedren. In this case, the connection to the condenser 5 is usually
Do not drain the drain. When a large level fluctuation (more than NWL+α) occurs in the water level in the M1 high-pressure feedwater heater 6, drain is discharged to the condenser 5 as a backup.

In addition, in the second high-pressure feed water heater 7, the conditions for drain recovery from the first high-pressure feed water heater 6 to the deaerator 1 are determined by understanding the load from the heat balance and actual operation results (usually,
(approximately 50% load). Then, this load is used as a threshold value, and this is used as the timing for switching, and switching is performed using the electromagnetic valve 34 or a manual switch. That is, during high load, since drain is recovered from the first high-pressure feed water heater 6 to the deaerator 1, the output of the water level controller 35 is switched to the switch 34.
The flow is switched to the flow control valve 14 side, and the first high-pressure feed water heater 6 head drain is recovered. At this time, the flow rate control valve 13 is fully closed. On the other hand, when the load is low, the reverse operation is performed.

By the way, in such a water supply/drain system, due to boiler variable pressure operation and changes in the BFP-T operation mode, the extraction pressure, which is the heating source for the feed water, may drop significantly compared to when operating at the specified pressure for the load. . For this reason,
The drain from the first high-pressure feed water heater 6 is not recovered to the deaerator 1, but continues to be recovered to the low-pressure feed water heater 4.

However, the third and fourth high-pressure feedwater heaters (not shown) located before the second high-pressure feedwater heater 7 have high bleed air pressure and use the bleed back air of the back-bleed type BFP-T. Due to the fact that the drain amount and pressure are
This is almost the same as when operating at the specified pressure. In a power generation plant that operates a boiler at variable pressure and uses bleed back air, this recovery state continues until the load approaches 80% to 90%. For this reason, the second high pressure water heater 7
When the drain from the second high-pressure feed water heater 7 is switched at about 50% load as described above using the solenoid valve 34 or the manual switch, the entire amount of drain from the second high-pressure feed water heater 7 is transferred to the first high-pressure feed water heater 6.
will be collected. However, since there is no pressure to recover the drain from the first high pressure feed water heater 6 to the deaerator 1, the drain is recovered to the low pressure feed water heater 4. Note that the low-pressure feedwater heater series is normally designed so that high-pressure drain does not flow in when the load is 50% or more.

(Problem to be Solved by the Invention) However, in such a conventional feed water heater drain water level control device, as described above, the drain switching conditions for the second high pressure feed water heater are based on the load and the first high pressure feed water heater. - The pressure difference between the deaerators is determined in advance, and switching is performed based on this value. Normally, this switching timing is between 50% and 75%.
% load, but it may deviate to 80% to 90% load due to boiler voltage transformer operation or BFP@T operation mode changes.

For this reason, even after the drain from the second high-pressure feed water heater is switched to the first high-pressure feed water heater, the deaerator hedrum cannot be recovered from this high-pressure feed water heater, and as a result, the entire amount of drain is transferred to the low-pressure feed water heater. It will be collected into a heater. However, as mentioned above, low pressure feed water heaters typically
% load (based on the specified pressure), the design prevents drain from the high-pressure feed water heater from flowing in.
The low-pressure feedwater heater and the '1s1 high-pressure feedwater heater will frequently issue alarms to notify of high or extremely high drain ice levels. Such a situation is unfavorable in terms of operation of the power plant.

The present invention has been made in view of the above points, and it measures the internal pressures of the high-pressure feed water heater and the deaerator, calculates the internal pressure difference between the two based on these internal pressures, and drains the water. An object of the present invention is to provide a drain water level control device for a feed water heater that calculates recovery conditions for a second high pressure feed water heater and determines whether to recover drain from a second high pressure feed water heater to a deaerator or a first high pressure feed water heater. .

[Structure of the invention]

(Means for Solving the Problems) The present invention has drain piping from a first high-pressure feed water heater and a second high-pressure feed water heater to a deaerator, and uses bleed air and bleed back air as a feed water heating source. In the feed water heater, there is provided a means for detecting the internal pressures of the high pressure feed water heater and the deaerator, and a means for calculating the internal pressure difference between the first high pressure feed water heater and the deaerator based on the internal pressures of the first high pressure feed water heater and the deaerator. means for calculating the condensate recovery conditions between the second high-pressure feed water heater and the deaerator based on the vessel internal pressure, and calculating the condensate recovery conditions between the two; and means for determining whether drain from the second high-pressure feed water heater should be recovered to the deaerator or the first high-pressure feed water heater based on recovery conditions.

(Function) In the feed water heater drain water level control device configured as above, the internal pressure of the high pressure feed water heater and deaerator is constantly detected, and the internal pressure of each high pressure feed water heater and deaerator is detected. The difference is calculated, and when each feedwater heater is in service, drain is collected in the order of the second high-pressure feedwater heater -> the first high-pressure feedwater heater - the low-pressure feedwater heater. Next, when the load of the plant increases, drain is recovered in the order of the second high-pressure feedwater heater-deaerator and first high-pressure feedwater heater-low-pressure feedwater heater. Furthermore, when the load of the plant increases, drain is recovered in the order of the second high-pressure feedwater heater, the node 1 high-pressure feedwater heater, and the aerator.

(Embodiment) An embodiment of the feed water heater drain water level control device of the present invention will be described below with reference to FIGS. 1 and 2. Note that parts common to the conventional feed water heater drain water level control device shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted here.

In the system diagram of the feed water heater drain water level control device shown in FIG. The first high-pressure feed water heater 6 (the high-pressure feed water heater in the final stage), the second high-pressure feed water heater 7 (the high-pressure feed water heater in the previous stage of the final stage), and the third and fourth high-pressure water supplies in the previous stage After being preheated and heated through a heater (not shown), the water is sent to a steam generator. In addition, steam from the bleed back air of the main turbine or BFP-T is supplied to each high pressure feed water heater, for example, the first and second high pressure feed water heaters 6.
At the same time, drain from the high-pressure feedwater heater in the previous stage flows in through drain pipes 30 and 31. Using these extracted steam and drain as energy sources, the high-pressure feed water heater exchanges heat to preheat and raise the temperature of the feed water.

On the other hand, drain piping 30, 31, 31a, 3232a
32b is connected to a high-pressure feedwater heater, such as a second and first high-pressure feedwater heater 7, 6, a deaerator l, a low-pressure feedwater heater 4, and a condenser 5 to discharge condensate, respectively. Also,
As shown in FIG. 1, the drain piping 3131a, 32.
゜14 is arranged. These flow rate control valves】011
．． 12, 13. 14 are deaerator 1, low pressure feed water heater 4,
PI (proportional, integral) water level controllers 17.1 attached to the condenser 5, first and second high-pressure feed water heaters 6, 7, respectively
It is activated by operation signals from 8, 19, 20, and 21.

In addition, the P1 water level controllers 17, 18, 19, 20, 21 are provided with a separately installed computing unit 2 that calculates the target water level setting values.
Set value switcher 22.232 that switches depending on the signal from 6.
4.25 is attached. This arithmetic unit 26 includes a first
A pressure detector 27 attached to each of the high-pressure feed water heater 6, the second high-pressure feed water heater 7, and the deaerator 1 internal pressure.
28.29 is detected and input. In addition to these internal pressures, the e4 calculator 26 also records various conditions (losses) such as drain/cooling zone loss of each high-pressure feed water heater, drain piping loss, and difference in position of flow ffi control valve installation. has been entered in advance. Based on these human power conditions, the computing unit 26 calculates the
Calculate drain recovery conditions between the deaerator and the first high-pressure feedwater heater.

In the feed water heater drain water level control device configured in this way, boiler variable pressure operation and BFP
Calculations for preventing instability of the water level in the feed water heater caused by differences in the operating modes of -T are performed by a computing unit 26 having the following configuration. That is, the second
As shown in the figure, the arithmetic unit 26 includes a switching condition arithmetic unit 33
As mentioned above, the internal pressures of the first high-pressure feed water heater 6, the second high-pressure feed water heater 7, and the deaerator 1 are detected by the pressure detectors 27, 28, and 29, and the arithmetic unit 26, various conditions (losses) such as heater drain cooling zone loss, piping loss, flow rate adjustment installation position difference, etc. are input in advance. Based on these input conditions, the comparators 34a and 34b of the calculator 26 compare and calculate the pressure difference between the second high-pressure heating water supply device 7 to deaerator 1 and the first high-pressure heating water supply device 6 to deaerator 1. and make the following judgments. Condition setting■ Second high pressure feed water heater internal pressure (P2) - Various losses (P
, )<pressure inside the deaerator (P,), and pressure inside the first high-pressure feed water heater (Pl) - various losses (PI)<pressure inside the deaerator (P,)...Condition A shall be.

■ P2-P, > Pd, and P, -P, <P, . . . Condition B is set.

■　Pl-PII>P, . . . Condition C is set.

By setting these conditions, the setting value switch 22゜23.2
4. The setting value switching command signal to 25 is sent to the switching condition calculation unit 33.
Output from In addition, these set value switchers 22 and 23
, 24, and 25 are configured to take set values appropriate to the process conditions at the time by these switching command signals.

More specifically, these switching conditions are illustrated as follows.

According to the embodiment of the present invention, by taking these relationships into consideration, each condensate recovery condition is correlated with the other, and the optimal and best heat recovery is performed depending on the process conditions at the time, and the drain water level of each feedwater heater is adjusted to a high level.・It is possible to control the feed water heater drain water level stably by suppressing extremely high levels.

That is, in the feedwater heater drain water level control device configured as described above, the internal pressures of the high-pressure feedwater heater and deaerator are constantly detected, and the internal pressure difference between each high-pressure feedwater heater and deaerator is detected. calculate. When each feedwater heater is in service, drain is collected in the order of the second high-pressure feedwater heater, first high-pressure feedwater heater, and low-pressure feedwater heater. Next, when the load of the plant increases, drain is recovered in the order of the second high-pressure feedwater heater-deaerator and first high-pressure feedwater heater-low-pressure feedwater heater. Furthermore, when the load on the plant increases, the second
Collect the drain in the order of high-pressure feed water heater - Section 1 high-pressure feed water heater - aerator.

Further, other embodiments of the feed water heater drain water level control device of the present invention will be described.

In another embodiment, when calculating the drain recovery conditions, instead of inputting the drain flow rate in the above-mentioned embodiment in advance, Calculate the drain flow rate from the opening command signal. Further, in the above-described embodiment, the pressure input to the computing unit is detected based on the internal pressure of the feed water heater and the deaerator, but it may also be based on the extraction pressure of the turbine or BFPφT. Furthermore, in the embodiment described above, the set value of the water level controller of the first high-pressure feed water heater was made variable, but check valves were provided in the drain pipes 32, 32a between the first high-pressure feed water heater and the deaerator. Therefore, the same effect can be obtained by keeping the set value constant, without making the set value variable. In this case, each water level setting value is NWL in the water level controller 17, and NWL+α in the water level controller 18.

〔Effect of the invention〕

According to the present invention, the conditions for drain recovery to the low-pressure feed water heater, the first high-pressure feed water heater, and the deaerator are correlated with each other, so that optimal and best heat recovery can be performed depending on the process conditions at the time. In addition, since the drain water level of each feed water heater can be suppressed from high or extremely high and stable drain water level control can be performed, extremely stable operation of the power generation plant is possible without frequent alarms.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an embodiment of the feed water heater drain water level control device of the present invention, Fig. 2 is a configuration diagram of a computing unit used in this drain water level control device, and Fig. 3 is a conventional feed water heater drain water level control system. It is a system diagram of a device. 1... Deaerator, 2... Water supply pump, 3... Water supply piping, 4... Low pressure feed water heater, 5... Condenser, 6, 7
...High pressure water heater, 26...Arithmetic unit, 30-32...Drain piping.

Claims (1)

[Scope of Claims] A feedwater heater having drain piping from a first high-pressure feedwater heater and a second high-pressure feedwater heater to a deaerator, and using bleed air and bleed back air as a feedwater heating source, the high pressure means for detecting the internal pressures of the feedwater heater and the deaerator; and a means for calculating the internal pressure difference between the first high-pressure feedwater heater and the deaerator based on the internal pressures, and determining drain recovery conditions between the two. means for calculating the internal pressure difference between the second high-pressure feed water heater and the deaerator based on the internal pressure of the vessel, and calculating drain recovery conditions between the two; and the calculated recovery conditions. and means for determining whether drain from the second high-pressure feed water heater should be recovered to the deaerator or the first high-pressure feed water heater.