JPS6228395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat exchanger diagnostic device for early detecting and diagnosing an abnormality in a heat exchanger in a power generation plant or other plant configured with a thermal cycle.

The present invention will be explained below by taking a thermal power plant as an example.

Traditionally, turbines, boilers,
For generators and various auxiliary equipment, plant state variables such as temperature, pressure, flow rate, water level, voltage, current, etc. are constantly monitored to see if they are within the limit values allowed for the equipment, and to check for deviations from the limit values. When this occurs, an immediate alarm is issued to warn of the abnormality, but this alarm limit value is intended to prevent equipment damage.
A considerable margin is given to the limit value itself, so even if an alarm is issued, it does not necessarily mean that the device is abnormal.

In this way, conventional alarm monitoring focuses on approaching an abnormal state, which makes it difficult to accurately catch an abnormality, and lacks the ability to analyze the cause of an abnormality. Therefore, there was a possibility that unnecessary plant operations could be performed. For example, if we look at high-pressure feed water heaters and low-pressure water heaters, which are examples of heat exchangers, only alarms are provided for high (or low) water levels in the vessel, and monitoring is performed to check for leaks or performance deterioration in the heater tube. It has not been.

The purpose of the present invention is to apply the second law of thermodynamics (it is impossible to continuously convert heat from one heat source into work without a drop in temperature or any other change). It is an object of the present invention to provide a diagnostic device for a heat exchanger, which is characterized in that it calculates the heat loss of each part of the heat exchanger and diagnoses an abnormality from the distribution of the heat loss.

The heat exchanger diagnostic device of the present invention is illustrated in FIG. 10, but before explaining this, the skeleton of a thermal power plant will be explained using FIG. 1.
In FIG. 1, steam generated in a boiler 1 passes through a main steam pipe 18 and enters a high-pressure turbine 2, where a portion of the thermal energy of the steam is converted into rotary mechanical energy for turning a generator 4. The steam that has done work in the high-pressure turbine 2 passes through a low-temperature reheat steam pipe 19, is heated again in a reheater 16, is led to a reheat turbine 3 through a high-temperature reheat steam pipe 20, and does work again. The steam that has done work in the reheat turbine 3 enters the condenser 5 as exhaust gas, is cooled by cooling water (not shown) such as seawater, and is returned to water. This condensate is pumped up by a condensate pump 6, passes through each heat exchanger of a condensate heat exchanger 7, an air extractor 8, and a gland condenser 9, and recovers heat. Raise the temperature of the condensate with
The feed water whose pressure has been increased by the boiler feed water pump 12 is further raised in temperature by the high pressure feed water heater 13 and is then supplied to the boiler 1 through the main water supply pipe 21. High pressure feed water heater 13, deaerator 11 and low pressure feed water heater 10
Both are heated by the extraction of the turbine and are also heat exchangers. Further, in the boiler, fuel controlled by a fuel regulating valve 17 passes through a fuel burner 14 and is burned in a furnace. The feed water receives heat from this combustion and becomes steam, which is superheated in the superheater 15 and sent to the turbine 2. FIG. 2 shows the state quantities of each part in such a plant when the plant is operating under normal conditions. In FIG. 2, some parts omitted in FIG. 1 are also shown. For example, 3' and 3'' are an intermediate pressure turbine and a low pressure turbine, respectively, 21 is a drain cooler, and 2
2 is a drain pump, 23 is a booster pump, 24
2 is a water pump turbine, 25 is a heavy oil heater, 2
6 is an air heater, and 27 is an SSR (steam seal regulator). Figure 2 shows the normal state of a plant generating 500 MW, and shows the temperature ( 1
°: °C), pressure (P: Kg/cm ² ), flow rate (G: Kg/
Hr) and enthalpy (H: Kcal/Kg) are shown. The state quantities shown here can be easily measured apart from enthalpy. The concept of the present invention when diagnosing the final stage high-pressure feed water heater 13 shown in the heat balance diagram of FIG. 2 as a typical example of a heat exchanger in a thermal power plant as described above will be explained below.

In FIG. 10, which shows an embodiment of the present invention, a block 101 represents energy loss (△
This circuit calculates Q), and the concept of calculating ΔQ will be explained below.

First, FIG. 3 shows the state quantities around the high-pressure feed water heater 13 at the final stage in FIG. 2.
That is, in the feed water heater 13 shown in Fig. 3, the pressure of the heating steam of the heater is 73.2 Kg/cm ² and the temperature is 363.5.
℃, and the enthalpy of this steam is calculated from the steam table using the temperature and pressure detected above.
It becomes 728.8Kcal/Kg. The pressure of the heated steam drain is approximately the same as the pressure inside the heaters, 69.6 Kg/cm ² , and the temperature is 260.6°C, and the enthalpy of this drain is found to be 271.6 Kcal/Kg from the steam table. The temperature of the water supplied to the heater is 255.0℃ and the pressure is pushed out from the water supply pump outlet, so here it is 289.9Kg/
^cm2 . The temperature of the heater outlet water supply is 285.2°C, and the pressure is approximately equal to the inlet water supply pressure. The water enthylpi at the place is 265.3Kcal/each from the steam table.
Kg, 299.7Kcal/Kg. Pressure inside the heaters
Since the temperature is 69.6Kg/cm ² and the interior is saturated water, the temperature can be found from the steam table and is 284.1℃.

In this way, the enthalpy (or temperature) can be easily determined from the steam table from the pressure and temperature measured at each point in Figure 3, so it can be easily calculated using the following formula based on the separately measured water supply flow rate of 1612676 Kg/Hr. The flow rate Gs of heating steam is determined.

Heating steam flow rate Gs = Feed water flow rate x (Outlet feed water enthalpy - Inlet feed water enthalpy) / (Heating steam enthalpy - Drain enthalpy) = 1612676 x (299.7 - 265.3) / (728.8 - 271.6) = 121339 Kg /Hr
...(1) Equation (1) is a known balance equation. Figure 4 is the third
This is a diagram showing the state of temperature change in the feed water heater shown in the figure.The numbers in the figure correspond to those in Figure 3, and the temperature distribution of water and steam in the feed water heater can be clearly understood.

On the other hand, FIG. 5 shows a different view of the state around the feed water heater 13 in FIG. 3. In other words, the entropy obtained from the steam table from the same pressure and temperature as measured in Figure 3 is shown in Figure 5.
It is shown in parentheses in the figure. The present invention is based on the second law of thermodynamics, which allows heat from a single heat source to be
In addition, it is impossible to continuously convert movement into work without causing any other changes.) From another perspective, this focuses on the fact that heat exchange without causing any other changes is impossible. That is impossible. Therefore, even in the heat exchange using the feed water heater shown in FIG. 5, heat exchange cannot be performed without energy loss.

The energy loss ΔQ in heat exchange of the feed water heater 13, which is the output of block 101 in FIG. 10, can be determined by the following formula.

Energy loss △Q={(Gs×Ts−Gw×Tw)}×(to+273.16)/K ^W (Kcal/K ^W H
)…(2) Here, Gs: Heating steam flow rate (Kg/Hr) Gw: Feed water flow rate (Kg/Hr) Ts: Heating fluid entropy (Kcal/Hr)
Kg〓) Tw: Entropy of feed water (Kcal/〓) ^KW : Generator output ( ^KW ) to: Base temperature (in Fig. 2, the condenser outlet feed water temperature is 33.1°C) Based on equation (2) The energy loss (ΔQ) due to heat exchange in the feed water heater 13 in FIG. 5 is calculated as follows.

△Q={121339×(0.68898-1.5001) ⁺ 1612676×(0.72837-0.6650)} Q=2.31Kcal/K
Even if the ^feed water heater 13 is in a normal state,
This is the energy loss that occurs during heat exchange operations.

Block 101 in Figure 10 shows each load (water supply flow rate)
It outputs the energy loss ΔQ when . The output of block 100 serves as a reference for energy loss, and if the actual energy loss differs from this, it can be determined that some abnormality has occurred. Among these abnormalities, there is a hole in the water supply pipe;
Figure 7 shows how the temperature characteristics at the inlet and outlet of the feed water heater change compared to normal conditions when a leak of feed water occurs from the water supply side (high pressure) to the steam or drain side (low pressure).

Figure 7a shows a case where a leak occurs in the water supply pipe on the inlet side of the feed water heater, Figure 7b shows a case in which a leak occurs in an intermediate water supply pipe, and Figure 7c shows a case in which a leak occurs in an outlet side water supply pipe. In each case, the change from the normal state (solid line) is indicated by a dotted line.

Here, taking the case of FIG. 7c as an example, the energy loss (ΔQ) during heat exchange will be determined. In the state shown in Figure 3, at the outlet of the feed water heater
If a leak of 20000Kg/Hr occurs, the drain temperature will rise to approximately 264.1℃, but the pre-temperature is 260.6℃.
℃, making detection by temperature difficult.

(121339×260.6+20000×285.2
/(121339+20000)≒264.1°C) The state values at this time are as shown in FIG. Here, enthalpy and entropy are obtained from the steam table and have the values shown in parentheses. Assuming that it is known that the leakage water from the water supply pipe on the outlet side of the feedwater heater is 20000Kg/Hr under the condition shown in Figure 8, the energy loss during heat exchange (△Q _LEA
When _K ) is calculated based on Figure 8 and using equations (2) and (3), the result is as follows.

△Q _LEAK = {(1592676×0.72837−1612676×0.6650+(141339×0.69678 −121339×1.5001)}×(33.1+273.1
6)/500000 ≒2.50 (Kcal/K ^W H) …(4) This △Q _LEAK is the energy loss △Q (=2.31Kcal/
This is relatively large compared to K ^W H), and this is due to an increase in the loss due to leakage from the water supply pipes, and the abnormal trend can be clearly seen.

However, the ΔQ _LEAK shown here is calculated theoretically, and as a practical matter, it is difficult to directly detect the leakage amount of 20,000 Kg/Hr from the water supply pipe in the feed water heater externally. By the way,
Since 20,000Kg/Hr corresponds to only 1.24% of the water supply amount, it is hidden by measurement errors and is difficult to detect with measuring instruments. As a result, leakage amounted to 20,000Kg/
Even if Hr exists, the calculated state quantities around the feed water heater will be as shown in Figure 9.

In the present invention, although the amount of leakage cannot be detected, the drain flow rate G _D can be detected, and attention has been paid to the fact that this is information that includes the amount of leakage. Drain flow rate G
_D can be measured, but in addition to that, the feedwater heater drain is regulated by the flow rate regulating valve 100 in Fig. 9, so the opening degree (Vp) of this flow rate regulating valve, the differential pressure across the front and back (△P ), the drain flow rate (G _D ) passing through the regulating valve can also be determined by the following formula.

G _D =f(Vp, △P)...(5) Here, the opening degree (Vp) of the flow rate adjustment valve and the differential pressure △P across the valve can be easily measured.

In Figure 9, the drain flow rate is calculated from equation (5) above.
If 125000Kg/Hr is detected (actually 121339 + 20000Kg/Hr as shown in Figure 8), the energy loss during heat exchange (△Q _LEAK ″) at this time is calculated as △Q _LEAK ″ = {1612676× (0.72837−0.6650) +125000×(0.69678−1.5001)} ×(33.1+273.16/50000
0) ≒1.90 (Kcal/K ^W H) ...(6) However, since the leakage amount is unknown in equation (6), the feed water flow rate at the outlet of the feed water heater is assumed to be the same as the inlet.

In Figure 9, the drain flow rate is actually 121339 + 20000 = 141339 Kg/H, but even if the flow rate calculated from the flow rate adjustment valve opening is detected as low as 125000 Kg/H due to a detection error, the feed water heater is functioning properly. Compared to the _energy loss △Q (= 2.31 (Kcal/K ^W H)) when If the drain flow rate is 141339Kg/Hr, the difference between △Q and △Q _LEAK ″ becomes larger.In other words, the method for calculating energy loss using equations (5) and (6) is (5).
Even if there is a fairly large error in the flow rate determined by the equation, slight fluctuations in flow rate can be easily determined, and furthermore, it is possible to determine whether the drain flow rate has increased or decreased in relation to the normal drain flow rate as shown below.

When △Q>△Q _LEAK '', a leak occurs (drain flow rate increases).

When △Q<△Q _LEAK '', the drain flow rate decreases. Here, the absolute value of energy loss has no particular meaning. Note that the drain flow rate may be measured using a flowmeter.

In Example 102 of FIG. 10, the obtained energy loss △Q _LEAK ″ is compared with that in the normal state (△Q), the presence or absence of leakage from the water supply pipe is determined based on the deviation, and a drain is connected to the signal line l ₁ . Outputs that the flow rate has increased and that leakage has occurred. If △Q-△Q _LEAK ″<α, outputs to signal line _l3 that some abnormality other than leakage has occurred, and |△Q-△Q _LEAK ″|≦ -α, a message indicating normality is output to the signal line _l2.The output of the signal line _l1 is used to notify the occurrence of leakage via the timer 103.

Since leakage from feed water heaters usually expands rapidly, △Q _LE obtained from equations (5) and (6)
Detection can also be made faster by determining the rate of change in _AK '' and adding a determination based on d/dt( _ΔQLEAK '')<-α' as an OR condition to the leakage detection logic shown in FIG.

Although the occurrence of leakage is detected by the above-mentioned circuit shown in FIG. 10, the present invention also detects other abnormalities or performance deterioration which is a factor of abnormality occurrence based on the following idea.

First, the performance of the feed water heater taken as an example of the present invention is represented by TD (terminal temperature difference) and DC (drain temperature difference). Therefore, this TD, DC
is significantly worse than that under normal conditions (TD,
(DC is larger than the normal value), performance deterioration may occur. Performance deterioration means that the heat exchange performance has deteriorated due to scale adhesion to the tube, etc. At this time, it appears in the form of increased TD, increased DC, or both increased TD and DC. Can be detected separately from abnormalities. Figure 6 shows the temperature characteristics of the feed water heater under normal conditions. In Figure 6a, TD represents the terminal temperature difference and DC represents the drain outlet temperature difference, but their characteristics are related to the feedwater flow rate (load) of the feedwater heater as shown in Figures 6b and c. There is. Therefore, these relationships can be expressed as blocks 104 and 104 in FIG.
107 and use them as reference values, and on the other hand, these actual values TDa and DCa are actually measured and respectively stored in block 1.
05, 108, the magnitude relationship is compared. Then, when the signal line _l4 or _l7 has an output, the OR circuit 1
Detector abnormality is output via 06. When there is an output on the signal line _l6 or _l9 , a performance degradation signal is outputted via the OR circuit 110.

Furthermore, since the opening degree of the drain regulating valve 100 shown in FIG.
Prepare the block 112 and check the difference with the actual opening VPa.
Find it with In this case, when the AND circuit 115 detects that there is an output on both signal lines _l3 and _l10 , and confirms that this state continues at time 113, it is determined that the drain regulating valve 100 is abnormal. When the timer 114 confirms that the AND circuit 116 detects that there is an output on the signal lines _l1 and _l12 , the drain flow rate detector is abnormal, and this fact is output. In addition, the signal lines l ₂ , l ₅ ,
The outputs of l ₈ and l ₁₁ are normal, and OR circuit 1
09 to notify that it is normal. In the embodiment of FIG. 10, the OR circuit 106 or the timer 11
Timer 103 when there is an output of 4 detector abnormality.
It is preferable to block the output of the timer 103 when a leak is being detected.

Figure 10 shows a comprehensive diagnosis around the feed water heater, where α, β, γ, and δ are margins for judgment that take into account detection errors, etc., and depend on the operating status of the feed water heater. It may be made variable. Of course, it is also possible to diagnose only some of these.
Of course, this diagnostic function can be incorporated into a computer.

The present invention is not limited to feed water heaters, but can be similarly applied to heat exchangers having thermal cycles as shown in FIGS. 4, 6, and 7.

Furthermore, when carrying out the present invention, if there is a large error in the measurement of the water supply flow rate, the diagnosis will be affected accordingly, but the judgment values α, β, γ, and δ in FIG. This can be handled by For even larger measurement errors, a separate reasonable check (determining the extent of the error based on the correlation with the generator output, the relationship with the main steam flow rate, etc.) is performed, and if there is an error that is more than necessary, it is treated as a measurement abnormality. It is better to interrupt the diagnostic process. Of course, if the diagnostic circuit becomes abnormal, the present invention becomes useless, so it is preferable to provide a self-diagnosis function and interrupt the diagnostic function of the present invention when it is determined that there is an abnormality.

Furthermore, the performance of the feed water heater taken up as an example of the present invention is represented by TD (terminal temperature difference) and DC (drain temperature difference). Therefore, this TD and DC are significantly worse than those under normal conditions (TD, DC
(becomes larger than the normal value), performance may be degraded. Performance deterioration means that heat exchange performance has decreased due to scale adhesion to the tube, etc.
At this time, it appears as TD becoming larger, DC increasing, or both TD and DC increasing, so it can be detected separately from other abnormalities.

[Brief explanation of the drawing]

Figure 1 is a skeleton diagram showing the functions of a thermal power plant, Figure 2 is a thermal balance diagram of a thermal power plant, Figures 3, 5, 8, and 9 are state diagrams showing state values around the feed water heater, and Figure 4 is a diagram showing the state values around the feed water heater. The figure is a temperature distribution diagram inside the feed water heater, Figures 6 and 7 are characteristic diagrams of the feed water heater, and Figure 10 is a temperature distribution diagram of the feed water heater.
The figure is a flow diagram showing the diagnostic algorithm of the abnormality diagnostic device. 1... Boiler, 2... High pressure turbine, 3... Reheat turbine, 4... Generator, 5... Condenser, 6... Condensate pump, 7... Condensate heat exchanger, 8... Air extractor, 9... Grand condenser , 10...Low pressure feed water heater, 11
... deaerator, 12 ... boiler feed water pump, 13 ... high pressure feed water heater, 14 ... fuel burner, 15 ... superheater,
16... Reheater, 17... Fuel adjustment valve, 18... Exhaust steam pipe, 19... Low temperature reheat steam pipe, 20... High temperature reheat steam pipe, 21... Main water pipe.

Claims (1)

[Scope of Claims] 1. A heat exchanger diagnostic device for diagnosing an abnormality in a heat exchanger that performs heat exchange through indirect contact between a heating material and a heated material, comprising: a first means for determining the energy loss occurring in the heat exchanger during heat exchange; a second means for detecting the flow rate of the heating material discharged from the heat exchanger; an output of the second means; , the entropy possessed by each of the heating material and the heated material at a predetermined point is derived using the state quantities of the heating material and the heated material, and the heat exchange from the heating material to the heated material is performed via the entropy. and a fourth means for detecting an abnormality in the heat exchanger by comparing the output of the third means and the output of the first means. Features of heat exchanger diagnostic equipment. 2 In the heat exchanger diagnostic device described in paragraph 1,
The second means is a diagnosis of a heat exchanger characterized in that the flow rate of the heating material discharged from the heat exchanger is determined by using the opening degree of a regulating valve and the differential pressure before and after the regulating valve. Device.