JPH0152641B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for early detecting and diagnosing abnormalities in equipment in a power generation plant or other plant configured with a thermal cycle.

The present invention will be explained below using 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 regularly monitored to see if they are within the limits allowed for the equipment, and to check for deviations from the limits. When an alarm occurs, an alarm is issued immediately to warn of an abnormality, but since the purpose of this alarm limit value is to prevent equipment damage, a considerable margin is set in the limit value itself, so even if an alarm is issued, This 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 risk of incorrect plant operation. In particular, for boilers, only alarms are provided for high boiler tube metal temperatures, and there is no monitoring for performance deterioration due to boiler tube leaks or dirt on heat transfer surfaces.

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). An object of the present invention is to provide an abnormality diagnosis method characterized by calculating reactive energy in each part of a boiler and diagnosing an abnormality from the distribution of the reactive energy.

Figure 1 is a skeleton diagram of a thermal power plant. 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 is transferred to the low-temperature reheat steam pipe 1.
9, is heated again in the reheater 16, and is led to the reheat turbine 3 through the high-temperature reheat steam pipe 20, where it 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 such as seawater, and is returned to water. This condensate is pumped up by a condensate pump 6, and heat is recovered through a condensate heat exchanger 7, an air extractor 8, and a ground condenser 9. The temperature of the condensate is raised by the boiler feed water pump 12, and the feed water whose pressure has been increased by the boiler feed water pump 12 is further raised by the high pressure feed water heater 13 and then sent to the main water supply pipe 21.
Water is supplied to boiler 1 through. The high-pressure feedwater heater 13, the deaerator 11, and the low-pressure feedwater heater 10 are all heated by extraction air from the turbine. Further, in the boiler, fuel controlled by a fuel control valve 17 passes through a fuel burner 14 and is burned in a furnace. The feed water receives radiant heat from this combustion and becomes steam, which is superheated in the superheater 15 and sent to the turbine. In such a plant, the state quantities of each part when the plant is operating under normal conditions, such as the boiler,
Temperature, pressure, flow rate, etc. in each part of the turbine, auxiliary equipment, etc. can be easily measured and can provide information as a diagnostic device.

An embodiment of the present invention will be described below with respect to a boiler.

Figures 3 and 2 show state quantities around the boiler (fluid side). That is, in the boiler shown in Figure 2, the pressure of the feed water at the boiler inlet is 282.2 ata and the temperature is 285.2°C, and the enthalpy of this feed water is found from the steam table to be 299.9 Kcal/Kg.
becomes. The main steam pressure at the boiler outlet is
254.9ata, the temperature is 543.0℃, and the enthalpy of this steam is found to be 791.6Kcal/Kg from the steam table. The boiler reheater inlet steam is the return of the high-pressure turbine exhaust, so it depends on the high-pressure turbine exhaust conditions.The pressure is 44.6ata and the temperature is 301.1℃.The enthalpy of this steam is calculated from the steam table.
It becomes 705.1Kcal/Kg. The steam at the outlet of the reheater is subject to flow resistance in the reheater, so the pressure is 42.8ata and the temperature is 541.0℃, and the enthalpy of this steam is 844.6Kcal/Kg when calculated from the steam table. The main steam flow rate through the superheater of the boiler is 1604655 Kg/H, and the reheat steam flow rate through the reheater is 1283576 Kg/H.

In this way, the enthalpy can be easily determined from the steam table from the pressure and temperature measured in Figure 2, so the main steam flow rate measured separately (sometimes calculated by flow balance from the feed water flow rate) and flow balance calculation The amount of heat generated in the boiler can be easily determined from the reheat steam flow rate determined from Equation (1) below.

Heat generated by boiler = main steam flow rate × (main steam enthalpy - feed water enthalpy) + Reheat steam flow rate × (reheater outlet steam enthalpy - reheater inlet steam enthalpy) =1604655×(791.6−299.9)+1283576 ×(844.6−705.1)=968067715.5Kcal/H……(1) Equation (1) is a calorific value calculation formula.

On the other hand, FIG. 3 shows a different view of the situation around the boiler in FIG. 2. That is, FIG. 3 shows the entropy (Kcal/Kg〓) determined from the steam table from the pressure and temperature measured in FIG. 2.

Another way to look at the second law of thermodynamics (which states that it is impossible for motion to continuously convert heat from one heat source into work without a drop in temperature or without any change in other sources) is that It can be said that it is impossible to exchange heat without causing any change in the Therefore, even in the heat exchange in the boiler shown in FIG. 3, heat exchange cannot be performed without energy loss.

Energy loss (reactive energy) due to heat exchange on the heat transfer surface of the boiler can be calculated using the following formula.

Energy loss = _o 〓 ⁱ⁼¹ (G _2i ×T _2i −G _1i ×T _1i ) × (t ₀ +273.16)/KW (Kcal/KWH) ……(2) where G: flow rate (Kg/H ) T: Fluid entropy (Kcal/Kg〓) KW: Generator output (KWH) t ₀ : Base condensate temperature (33.1°C in the example shown) Suffix i: Number of boiler heat transfer surfaces 2: Outlet side 1: Inlet side Based on equation (2), the energy loss (reactive energy, ΔQ) due to heat exchange in the boiler in Figure 3 is calculated as follows.

ΔQ={1604655×(1.4695−0.7288) +1283576×(1.7159−1.5072)} ×(33.1+273.16/500000)≒892.1Kcal/KWH Energy loss ΔQ calculated here=892.1(Kcal/
KWH) is the energy loss that occurs during heat exchange operations even when the boiler is in normal condition. The boiler shown in Fig. 3 actually has several heat transfer surfaces, the details of which are shown in Fig. 4. In FIG. 4, the feed water entering the boiler 1 exchanges heat with the boiler exhaust gas in the economizer 22, and then receives heat from the combustion furnace of fuel in the water wall, where water is converted to steam. Steam is superheater 2
4, it becomes superheated steam, and is further superheated to a predetermined temperature in a superheater 26. The desuperheater 25 is a temperature regulator for controlling the main steam temperature at the boiler outlet to a predetermined temperature, and the water at the inlet of the economizer is used as the detemperature water.

FIG. 5 shows the pressure and temperature characteristics of the fluid in this boiler 1 under normal conditions. In Figure 5, the entropy is determined from the steam table based on the pressure and temperature of the fluid, and from these the energy loss (ΔQ _N ) (calculated from equation (2)) at each heat transfer surface is calculated from ΔQ _N1 to ΔQ _N5 .
It was shown as

Now, in the boiler shown in Fig. 5, superheater 2
Figure 6 shows how the temperature characteristics of the entrance and exit of each heat transfer surface inside the boiler will change compared to the normal state if a leakage accident occurs in which the tube in No. 4 is punctured and steam is spouted into the furnace. It was shown to.

Figure 6 shows the case where a steam leak of 30,000 kg/H occurs from the superheater 24, and the heat input to the boiler (the energy of the fuel) is approximately constant (because the generator output is constant). Therefore, the fluid on the upstream side of the superheater 24 contains leaked steam (30,000
Kg/H) increases by a corresponding amount, so the pressure of the fluid,
Temperature changes. Figure 6 shows the state quantities and energy loss (ΔQ _L ) on each heat transfer surface at this time. In FIG. 6, the energy loss ΔQ _L30 for steam leakage of 30,000 kg/H is determined by equation (3).

ΔQ _L30 = Leakage steam flow rate × Steam entropy × (273.16 + Leakage steam temperature / Generator output) = 30000 × 1.2464 × (273.16 + 410.0 / 500000) ≒ 51.1Kcal / KWH ... (3) Calculation of other energy losses was calculated according to equation (2).

Comparing the energy loss in FIG. 6 with that in the normal state in FIG. 5, it can be seen that the energy loss in the superheater 24 with steam leakage has increased significantly.

However, since steam leakage cannot actually be measured, even if the leakage amount is 30,000 kg/H, it is assumed that all of it has flowed as the main steam flow rate as shown in Figure 7. Figure 7 shows the energy loss on the heat transfer surface. Comparing the energy loss in Figure 7 with that in the normal state in Figure 5, it is as follows: ΔQ _L3 ′ and ΔQ _L ′−ΔQ _N /ΔQ _N =741.6−728.0/728.0→ 1.9% ΔQ _L1 ′−ΔQ _N1 ／ΔQ _N1 =103.6−103.2／103.2→ 0.4% ΔQ _L2 ′−ΔQ _N2 ／ΔQ _N2 ＝372.8−368.1／368.1→ 1.3% ΔQ _L3 ′−ΔQ _N3 ／ΔQ _N3 ＝105.0−99.0／99.0 → 6.1% ΔQ _L4 ′−ΔQ _N4 ／ΔQ _N4 ＝1.0−1.5／1.5→ 33.3% ΔQ _L5 ′−ΔQ _N5 ／ΔQ _N5 ＝159.2−156.3／156.3→ 1.9% The energy loss of ΔQ _L4 ′ is the total energy loss. It can be seen that there is a large change compared to the change. In other words, since ΔQ _L3 ' has changed significantly, superheater 2
The fact that a loss has occurred in 4 and that ΔQ _L4 ' is changing in a decreasing direction indicates that the steam flow rate passing through the attemperator is estimated to be larger than the actual one. From this, it can be easily detected that steam leakage has occurred in the superheater 24.

Also, the reason why the energy loss around the desuperheater is a phenomenon that cannot occur in reality (the energy loss decreases despite steam leakage) is clearly because the main steam flow rate is higher than it actually is. (Similar results would also be obtained if the amount of deheated water was measured with a small amount, but the influence would be less in this case considering the measurement error). Therefore, if we calculate back how much the main steam flow rate is expected from this phenomenon, it will be as follows: +273.16/500000)=1.5x≒33551(Kg/H
) The x obtained here corresponds to the amount of steam leakage.

In this way, the energy loss indication (ΔQ _Li ) obtained from equation (2) is compared with that in normal conditions (ΔQ _Ni ), and the presence or absence of leakage of steam or feed water from inside the boiler is determined based on the amount of deviation. This is the point of the present invention. An example to which the present invention is applied is shown in FIGS. 8 and 9. Figure 8 shows the division of energy loss (obtained from equation (2)) on each heat transfer surface of the boiler (zone 1 to zone 5), and based on the ΔQ _Li obtained here, The diagnostic algorithm shown in FIG. 9 detects the occurrence of leakage based on the amount of deviation from normal ΔQ _Ni . In other words, in Fig. 9, for each zone of the boiler heat transfer surface, find the ratio of the deviation between the energy loss during normal operation (ΔQ _Ni ) and the energy loss found at the present time (ΔQ _Li ) (a/b), and then It checks whether the energy loss deviation ratio of each zone changes significantly compared to the total boiler energy loss deviation ratio, and if it changes significantly, it is diagnosed as leakage. The reason for comparing the total energy loss deviation rate of the boiler here is to eliminate the effects of boiler contamination and performance deterioration.The diagnosis is made by combining the deviation rate of each zone to detect abnormalities in the measuring instrument. This is to remove it.

Describing the operation of FIG. 9 in more detail, 28 is a signal generator provided for each zone;
For example, as shown in FIG. 10, a function generator may be used that stores the relationship between the normal energy loss ΔQ _N and the water supply flow rate, and when it is realized by a mathematical formula, it is sufficient to execute formula (2). The other input ΔQ _L of the subtractor 29 is also an energy loss, and is calculated using the same concept as ΔQ _N. However, in order to find the difference in energy loss (ΔQ _N −ΔQ _L ) according to No. 29, ΔQ _L is taken as the energy loss at that time, whereas ΔQ _N is taken as the energy loss at the past time. The output of this 29 is zero when the boiler is in a normal state, and output is only given in a leakage state. 30 is a divider,
Outputs ΔQ _N −ΔQ _L /ΔQ _N. This output of 30 is also called the leakage rate, and is determined for each zone in FIG. 31 is an adder which adds the output of 30-0 and the allowable value α. 32 is a subtracter, which outputs the output of the divider 30 for each zone in the divided boiler (leakage rate in each zone) and the adder 3
1 output (total boiler energy loss deviation ratio) is calculated, and when the former exceeds the latter, the output is output. Here, since the output of 31 is also an amount that increases due to leakage, when the increase rate of each part exceeds the increase rate of the boiler total, an output of 32 will be obtained, and by setting the allowable value α, This prevents malfunctions due to detection errors. As mentioned above, since there is no energy loss around the desuperheater, the output of the proportioner 30-4 provided for the zone regarding the desuperheater is added to the output of the adder 31 (boiler total energy loss deviation). It is meaningless to compare the percentages). If there is a leak in this part, the output of 30-4 will be a negative value, so the adder 33 adds it to the positive allowable value β, and when this becomes negative, it is determined that the leak is detected for the desuperheater. Leakage in each part discovered by 32 or 33 can be logically combined to achieve more reliable detection and identification of the leakage position. For example, when 32-1 outputs, the detection output of the detection part (output of subtractor 32-12) that monitors the area including zones 1 and 2 in FIG. High reliability can be obtained by calculating with circuit AND. still,
OR is an OR circuit that calculates a logical sum.

Note that leakage of steam and feed water from the boiler expands rapidly, so find the percentage deviation of the energy loss obtained from equation (2) from that under normal conditions, and then find the rate of change of that deviation percentage. In the leakage detection logic shown in Figure 10, if the deviation ratio is set to the change rate, abnormality detection can be made faster. Based on the diagnosis results, early detection and reliable detection can be achieved using the following logic.

Of course, this diagnostic function can be built into a computer and used for thermal equipment other than boilers.

[Brief explanation of drawings]

Figure 1 is a skeleton diagram showing the functions of a thermal power plant, Figures 2 to 8 are diagrams showing status values around the boiler, Figure 9 is the diagnostic algorithm of the abnormality diagnosis method of the present invention, and Figure 10 is the signal FIG. 3 is a diagram showing the characteristics of the generator. 28... Signal generator, 29, 32... Subtractor,
31, 33...adder, 30...divider.

Claims (1)

[Claims] 1. A plant abnormality characterized by determining the reactive energy due to heat exchange based on the entropy of the fluid at the entrance and exit of the plant that performs heat exchange with the fluid, and determining whether there is a fluid leak in the plant based on the change in reactive energy. Diagnostic method.