In recent years, various thermal power plants have actively organized and implemented Article 25 Requirements for Preventing Serious Accidents in Power Production (hereinafter referred to as requirements), Item 8, Preventing Boiler Drum from Being Full of Water and Lack of Water, and Several Provisions on Configuration, Installation and Use of Boiler Drum Water Level Measurement System of State Power Company (hereinafter referred to as regulations). However, many problems have been encountered in the process of organization and implementation, which has led to the actual implementation of various power plants. These difficulties and differences are mainly caused by the backward technology, large measurement error and few independent measuring points of the existing drum water level measuring system.

At present, mica water level gauge, electric contact water level gauge, ray water level gauge, liquid level switch, single-chamber balancer and double-chamber balancing container are mostly used for drum water level. From the principle of primary sensing conversion, these water level meters can be summarized into two types, one is based on the principle of connector, and the other is based on the principle of differential pressure water level meter. As we all know, the current water level meters are designed and manufactured according to the above two principles, and the adopted process structure is simple, which can not overcome the measurement error caused by temperature change, and its error is large, which can not strictly meet the safe and economic operation of boilers.

First of all, the following two principles briefly explain the measurement error produced by the water level gauge:

(A) the principle of the connector

As shown in figure 1:

Equation (1) holds, regardless of the static pressure effect of saturated steam (δ H, r//, g).

Hr/g≈h×r×g - ( 1)

H≈h×r/ r/

δH = H-H≈(r/r/- 1)×H-(2)

acceleration of gravity

R: Measure the average density of water column in the cylinder.

R/: saturated water density in the drum

R//: saturated steam density

H: Measure the water level in the cylinder.

Δ h: the difference between the drum water level and the measuring cylinder water level.

It can be seen from formula (2) that Δ h is related to the density r/ of saturated water, the average density r of water column in the measuring cylinder and the water level height h (where r is always greater than or equal to r/, and Δ h exists when r≥r/ and r ≥ 1). When r = r/, Δ δh = 0, otherwise Δ h will always exist. The average density r of the water column in the measuring cylinder is related to the cylinder pressure, water level, the structure of the measuring cylinder, the temperature and wind direction of the environment in which the measuring cylinder is located, and the diameter of the sampling tube. And the influence is very great, so R has great uncertainty. The water level difference between the two measuring tubes of the same mica water level meter without blind area is 10-20mm near the zero water level. The higher the water level, the greater the error, and the lower the water level, the smaller the error. This error is only caused by the difference of environmental temperature and structure, so imagine that it is difficult to control the difference within 30 mm when sampling at different positions of the drum and connecting water level meters with different structures at the 0 water level of the drum. Because of this, no matter how good your mica water level gauge, bull's-eye water level gauge, electric contact water level gauge, X-ray water level gauge and liquid level switch are, the measurement results are also very inaccurate.

Through the tests of several power plants, the mica water level gauge is about 1 10mm lower than the actual water level when the 200MW unit is rated, and the subcritical boiler is about 150mm lower. In order to overcome this error, each power plant moves the zero point of electrical contact and the scale of mica water level meter downward by 50, 60, 80 (670 t/h) 65438. The result of downward movement can only reduce the measurement error of drum water level at zero water level, but the error increases at high and low water levels, especially near the shutdown value of low water level, and the water level display is on the high side. This interferes with the operator's judgment of the accident water level, which is not conducive to the effective control of the safe operation of the boiler by the operator. The error is large at low pressure, which is not conducive to boiler start-up and low load operation monitoring.

(2) Differential pressure water level gauge (single chamber balance container)

As shown in Figure 2, whether it is a textbook or a ministerial document, what is more serious is that the single-chamber balance container in practical application is also installed in this way.

Let's briefly analyze the measurement error of single-chamber balance container:

When p2 = 0, Formula (3) holds.

h =(r-r//)g . L-δp 1-(3)

g(r/ - r/)

Where Δ p1:the pressure difference between the reference water column and the drum water level measured by the transmitter (when p2 = 0).

L: reference water column height

R: average density of reference water column

Δ P2: Additional pressure difference between positive and negative pressure sides of instrument pipeline.

The density (r/, r/) of saturated steam and saturated water here is a single-valued nonlinear function of drum pressure P, which can be obtained by measuring the drum pressure. The uncertainty of the average density r of water in the reference water column is one of the main reasons for the measurement error.

As shown in Figure 2, the top of the single-chamber balance container is always saturated steam, and the water surface in contact with it is saturated water. In addition to heat dissipation, the single-chamber balance container will also conduct heat and heat down along the metal wall and water. The temperature distribution of the reference water column is shown in Figure 3:

The temperature distribution t=f(x) of the reference water column is an exponential function of the reference water column, and its functional relationship is related to the cylinder structure, the diameter of the surface pipeline, the ambient temperature, the wind direction, the heat preservation and other factors, which has great uncertainty. After the accident of "12. 16" in Qinhuangdao Thermal Power Plant, the conservative calculation error is+108mm by measuring the outer surface temperature of the balance vessel and tube of No.3 boiler. The range of the water level gauge in this factory is 400 mm, and the protection setting value is-384 mm. After the boiler dry pot bursts, the CRT still displays-327 mm. The measurement error is the main reason for the low water level protection of the drum. (The distance L of the sampling tube on the steam-water side is 850 mm)

Attachment: Special Analysis Report on Low Water Level Protection of No.4 Boiler Drum in Qinhuangdao Thermal Power Plant

According to the test records of # 3 boiler, the difference between heat preservation and non-heat preservation of reference water column surface tube (A-C) is at least 45mm, the maximum is 85 mm, and the average difference is 67 mm, while the difference with heat tracing and heat preservation (B-C) is at least 125 mm and the maximum is 172 mm. The average phase difference is142 mm. Although the surface tube (A) with heat insulation and no heat tracing is only 17℃ higher than the bare surface tube (C), the temperature of the surface tube at a considerable distance from the lower end of the equilibrium vessel is much higher than that of the surface tube without heat insulation.

Attachment: "Summary Table of Drum Water Level Gauge of 300MW Unit in Shi Heng Power Plant"

The experimental situation of Shi Heng Power Plant is the same as that of Qinhuangdao Thermal Power Plant, which shows that the installation method of single-chamber balance vessel shown in Figure 2 is not desirable and must be revised.

As we all know, the double-chamber balance vessel is a part of mechanical compensation, but the error is small within a certain pressure and measurement range, and the error is too large when the boiler starts, stops and has an accident, so it cannot be used. In the "Requirements" and "Regulations", the use is no longer advocated, so I will not repeat it here. At the same time, it is suggested to cancel the double corrugated differential pressure water level gauge.

To sum up, the random errors of the water level meters installed at present are very large, which can't meet the requirements of "Stop the boiler immediately when the deviation of each water level meter is greater than 30 mm" and "Do not start the boiler without water level protection", which is also the main reason why it is difficult for the power plant to implement the requirements and regulations.

As can be seen from the above, the main reasons for the measurement error are the water temperature (water density) in the measuring cylinder of the communicator and the water temperature (water density) in the reference water column of the balance container. Solving the water temperature problem also overcomes the large random error caused by the uncertainty of water temperature change.

Second, the working principles of several new drum water level meters are briefly introduced below, which successfully solves the problem of large measurement error caused by temperature and makes it possible to accurately measure the drum water level.

(1) Built-in single-chamber balance container

As shown in Figure 4:

h = L-δP/g(r/-r/)-(4)

(4) where L and G are constants, r/-r// is a single-valued function of drum pressure, and δ p is the differential pressure value measured by the transmitter, thus eliminating the influence of ambient temperature on the reference water column density, thus overcoming this error.

Figure 5 (with color map)

Fig. 5 is a set of data curves of Tongliao Power Plant # 1 boiler accident door after misoperation. 1.2.3 is the drum pressure, 4.5.6 is the water level curve of the original single-chamber balance container, and 7 is the water level curve of the built-in single-chamber balance container. As can be seen from the figure, the interference of the safety door action has little influence on the built-in balance container, and the measurable result is very different from the original single-chamber container.

(2)GJT high-precision sampling electrode measuring cylinder

As shown in fig. 6

GJT high-precision sampling electrode measuring cylinder adopts comprehensive technology to realize real sampling and high-reliability measurement and sensing in all working conditions.

2. 1 high precision sampling

Based on the principle of heat transfer, the average temperature of water sample is close to the saturated water temperature in the drum, and the sampling water column is close to the water level in the drum, so that the electrode can be detected as in the drum and the water level can be measured with high accuracy.

2. 1. 1 heating water sample

The measuring cylinder is equipped with a cage-type inner heater to heat the water sample with saturated steam. The heater consists of different heat transfer elements. Heating methods include internal heating and external heating. Internal heat includes both radial heat transfer units of water column and axial layered heat transfer units. The upper opening of the heater is opened, and saturated steam (a) from the steam side sampling tube enters the heater to heat the water column like a steam cage. The heat transfer mode and structural design are not only conducive to increasing the heating area (GJT design can make the heating area reach 1.4 times the cylinder cooling area), but also conducive to heat exchange.

Saturated steam (a) releases latent heat of vaporization in the heater, and its condensate is led to the downcomer by the hydrophobic pipeline, with the downcomer and the steam drum as one side and the hydrophobic pipeline and the heater as the other side, forming a communication device. The average water temperature in the exposed drainage pipe is lower than that in the sewer pipe, and the water level is lower than that on the sewer pipe side. The lower the elevation of the connection point, the higher the pressure and the greater the water level difference. In order to ensure that the water level on the drain side will not rise to the heating section and reduce the heating area, it is required that the connection point be selected at 15m below the center line of the steam drum. Thus, when the pressure is 6.0 MPa, the water level in the drainage pipe is 0.5 m below the heater, and when the pressure is lower than 1.0 MPa, the water level will approach the bottom of the heater, which will affect the heating, while the sampling error at 1.0 MPa is very small and can be ignored. Therefore, the heating system can adapt to the variable parameter operation of the boiler and ensure the real sampling under all working conditions.

2. 1.2 Increase the content of saturated water in water samples.

Setting the condenser makes the new measuring cylinder much higher than the ordinary measuring cylinder. Saturated steam from the sampling pipe on the steam side is condensed in the condenser, and a large amount of condensed water (B) (at saturated water temperature) is collected along the wall, and several drainage pipes arranged in saturated steam discharge water samples with different depths, and the low-temperature water samples are replaced out of the measuring cylinder. It can also be considered that the new condensed water increases the saturated water content in the water sample and increases the average temperature of the water sample. High-speed displacement can effectively increase the temperature of water column and make it evenly distributed up and down. The reason why the cage-type inner heater is used is to use the condensed water generated by the heat dissipation of the steam side cylinder to further reduce the sampling error and strengthen the self-optimization function of water quality.

The combination of the above two technologies makes the heat flow into the water sample much larger than that of the ordinary measuring cylinder, and the transition time of heat balance is shorter. When the pressure change causes the water level in the drum to change, the heat flux density

With the change, the temperature of water sample changes quickly, so the dynamic response of sampling to pressure change is also fast. The generation of a large amount of condensed water forms a continuous high-temperature water flow to the drum in the water-side sampling pipe. When the drum water level rises greatly, less water samples return to the measuring cylinder, and the difference between water temperature and saturation temperature is small, so the sampling dynamic error of drum water level rise is small. The cage inner heater occupies a considerable space in the measuring cylinder. Compared with the old measuring cylinder, the cross-sectional area of water column is much smaller, so it responds quickly to the change of drum water level.

There is a stable heat source in GJT measuring cylinder, so the installation requirements of sampling pipeline length, section and site layout of measuring cylinder are looser than those of old measuring cylinder.

2.2 High reliability measurement sensing

2.2. 1 Stability and reliability of accurate sampling

Using heater and condenser to eliminate the influence of drum pressure and ambient temperature in the first sampling process, its reliability and stability obviously exceed that of the old measuring cylinder.

2.2.2 Self-optimization of water quality

The condenser not only increases the temperature of water sample, but also realizes the self-optimization of sampling water quality. A large amount of pure water enters the water chamber, and the old water sample with poor water quality is pressed into the drum, forming an automatic purification replacement cycle, and the water sample is "living water". The design replacement rate can be as high as 20 times /h, and the water quality has strong self-optimization function. The unique advantage of GJT measuring cylinder is: (1) no pollution discharge. The water quality is good, and the pollution to the electrode is reduced. After the initial installation and thorough flushing, there is no need to discharge sewage during the maintenance period of 3 ~ 4a years, which not only reduces the maintenance amount, but also avoids the life loss of the hot sewage accelerating electrode and reduces the number of protection switches caused by it. (2) It can improve the resistivity of water samples, reduce the working current, slow down the electric corrosion of electrodes and prolong the service life. (3) The water quality is stable, and the upper and lower water resistance rates of the water sample are evenly distributed, which is beneficial to improve the stability of secondary instrument measurement, and it is not necessary to adjust the critical water resistance of the instrument frequently. (4) There is continuous high-temperature water flowing to the steam drum in the water side sampling pipe. When the water level of the steam drum fluctuates greatly, the thermal shock of the electrode is less, which reduces the thermal stress of the electrode and prolongs the service life of the electrode.

2.3 characteristics of electrode assembly

RDJ flexible self-sealing electrode assembly (as shown in Figure 7) is another important technical feature of GJT measuring tube. The mechanical seal for electrode installation utilizes the principle of valve packing. The pressure in the cylinder increases the sealing force, and the self-tightening force is proportional to the pressure. The higher the pressure, the greater the self-tightening force. Coupled with the pre-tightening force, there is enough force to ensure that the seal does not leak. The flexible sealing material can withstand the high temperature of 1000℃, and has high bearing capacity, good resilience and heat tightness. The electrode is provided with disassembly thread, which is convenient to disassemble and can be operated by ordinary female workers. However, the sealing force of electrode assemblies at home and abroad decreases with the increase of pressure, which requires a large pre-tightening force. In addition, mechanical sealing is adopted, which has low sealing reliability and poor heat sealing performance. The elevation angle of RDJ electrode is 2 ~ 3, which can prevent the electrode from hanging water and water stains.

As shown in Figure 7:

2.4 electrode sensor with large range and full working condition

GJT-2000B drum water level electrode sensor has large range and full working condition, which is an extension of GJT-2000A measuring cylinder performance. When the boiler stops due to water level accident, the measuring cylinder can monitor the specific water level accident value in the boiler drum for accident analysis and treatment. Reduce the transition time between furnace opening and shutdown.

Table 1 GJT-2000 High-precision sampling electrode sensor water sample temperature measurement data

Measurement sequence 1 234

+300 steam side temperature /℃ 352.8 353.4 30 1.4 296.7

0 water side temperature/℃

-300 water side temperature/℃

Average water temperature/℃ 351.0351.9 303.2 297.8

Drum pressure/MPa 17.50 17.64

Load/MW 270 303

Measurement time: when the load is reduced at 23: 00 17: 30 and when the load is reduced at 23: 00.

Table 1 is a set of data of No.2 1025t/h subcritical drum boiler of Shanxi Sunshine Power Generation Co., Ltd. (Yangquan No.2 Power Plant) in June 2002, 65438+/kloc-0+February 2002, and 65438+measured the steam temperature and water temperature in the electric contact drum with I K thermocouple. As can be seen from the table 1, the water temperature in the measuring cylinder is consistent with the steam temperature, indicating that the water in the measuring cylinder is indeed the same.

(3) WDP has no blind area and low deviation double color water level gauge.

As shown in fig. 8

WDP series double color water level gauge with no blind area and low deviation, this product uses saturated steam in the drum to heat the surface of the water level gauge to prevent the saturated water in the meter from transferring heat to the outside, and then uses saturated water condensed in the condenser to replace the water in the meter to accelerate the water circulation in the meter, so that the water temperature in the meter is close to the saturated water temperature, and the water level in the water level gauge is close to the real water level in the drum at any time and under any working conditions, thus achieving the purpose of correctly monitoring the water level in the drum. The saturated water condensed in the condenser is used to replace the water in the meter, which speeds up the circulation in the meter. Because the replaced fresh water is saturated water condensed by saturated steam, the salt content is low, which reduces the scaling of mica sheet and virtually prolongs the sewage discharge cycle of the instrument. Because the temperature change of the watch body is small, the thermal deformation of the watch body is reduced, the leakage of the watch body is reduced, the maintenance cycle of the watch body is prolonged, and the maintenance cost is reduced.

Advantages of WDP series double color water level gauge without blind area and low deviation;

The deviation is small (due to the addition of saturated steam tracing tube and saturated water replacement, the water temperature in the surface is close to that in the drum, so it can truly reflect the water level in the drum).

● No blind area (there are five-window mica with water level pipes on both sides, and the water level can be clearly seen as long as it is within the upper and lower boundaries of the five-window mica).

Long service life, low leakage rate and low maintenance cost.

Three new types of drum water level measuring instruments have solved the key technical problem of large measurement error of drum water level, making accurate measurement of drum water level a reality.

After three years of application of GJT measuring tube in Matou Power Plant, the difference between the zero position of measuring tube and the measured value of drum water level line center is 23 mm

Fig. 9 is the measured external surface temperature of 670t/h ultra-high pressure drum boiler in Tongliao Power Plant on 1 October 26th, 2003. As can be seen from this figure, the upper and lower temperatures of GJT measuring cylinder are the same, the lower end of WDP water level gauge is lower than the upper end, and Tongliao is not equipped with condenser, so the water condenses less, the lower part dissipates heat quickly, and the temperature is naturally low.

Table 3: Measured Record of Start-up and Safety Door Setting of Boiler 1 in Tongliao Power Plant

Due to the requirements of most power plant regulations, mica water level gauge shall prevail. In fact, when the water level gauge is "0", the actual water level is about 100 mm higher than that of the drum 0, and the steam quality is deteriorated due to long-term high water level operation. The No.3 boiler (670t/h) in Jiaozuo Power Plant was measured by Henan Electric Power Experimental Research Institute. The average value of saturated steam conductance was 65438 0.7 μ s at -75 mm and 5.5μS/ cm at+65438 000 mm, which solved the problem of large measurement error, not only improved the accuracy and reliability of drum water level monitoring, but also solved the reality of long-term high water level operation of drum.

Three, the drum water level measurement sampling point is insufficient

Article 3. 1 of the Code requires that "each water level measuring device shall have an independent sampling hole. It is not allowed to connect multiple water level measuring devices in parallel on the same sampling hole to avoid mutual influence and reduce the reliability of water level measurement. " But the number of measuring holes in many steam drums is small, especially in recent years, only four pairs of boilers have been produced. "Patent technology for multi-hole measurement of drum water level" uses the original hole measuring nozzle (mother tube) with larger inner hole of drum as the sampling channel, inserts the newly added sampling tube into the drum, and samples at a certain distance from the sampling port of the mother tube, thus increasing independent sampling holes without opening holes in the drum. Generally, 4 pairs of steam and water measuring holes can be added. The risk of reaming is small, the construction is convenient, the management is easy and the construction period is short. This technology can also move the measuring point in the middle of the drum to the head of the drum, providing high-quality sampling points for the monitoring main meter and protection instrument. The problem of insufficient water level measuring points was successfully solved, and the requirements of article 3. 1 of the regulation were met.

Four, steam drum water level protection

At present, there are great differences in the design of drum water level protection system among domestic power plants. Many ultra-high pressure boilers are unprotected, and many subcritical boilers only use differential pressure water level signals. A few power plants use water level switches or several water level gauges as protection logic. The reason is that the attention and technical understanding of various factories are inconsistent, and there is no better unified standard in the country. Let's talk about our views on the design of drum water level protection.

4. 1 The transmitter signal should not be used alone to protect the drum water level for five reasons.

First, the water level measurement signal is unstable, and there are too many influencing factors to be reliable. (as shown in Figure 2) Due to the thermal insulation and heat tracing of instrument pipes and the interference of other heat sources, there will be an additional pressure difference of Δ P2, which leads to a large measurement error and is easily overlooked.

Second, there are too many conversion links and fault points in water level measurement, which leads to unreliable measurement.

Thirdly, due to external interference, such as the disappearance of power supply, freezing of instrument pipes and transmitters, leakage of instrument pipes and valves, the measurement signal will be unreliable.

Fourthly, there is a Technical Code for Design of Thermal Power Plants DL5000-94 Thermal Protection Contacts.

The signal should come from an instrument. "

Fifth, "danger concentration", the Code only requires three differential pressure water level signals, which are used for adjustment, display and protection respectively, and the design principle is that "protection signals should be sampled independently".

One transmitter of a 1025t/h forced circulation boiler in a power plant in Anhui province was damaged and leaked, which caused two transmitters to indicate high and automatically reduce water supply, resulting in low drum water level and low water level protection refusing to operate. Then stop the machine manually to check the cavitation of boiler water circulating pump. The failure of low water level protection in the "12. 16" accident in Qinhuangdao thermal power plant fully proves that it is not advisable to use differential water level signal as protection alone.

4.2 It is suggested to use two electric contact water level gauges and three differential pressure selection signals for drum water level protection for five reasons.

First, it is required that Article 8. 1 mentions that "the configuration of water level gauge should adopt two or more working principles to ensure that the water level of boiler drum can be correctly monitored under any operating conditions." It shows that the water level signal measured by a principle is not reliable enough, so the signal used for protection is even more so.

Secondly, the previous electric contact water level gauge has a large measurement error and is easy to leak water, but GJT measuring cylinder has successfully solved these two problems. It was first installed in Huaiyin Power Plant at 1996. Up to now, more than a dozen sets of 100 have been installed in boilers of different capacities in more than a dozen power plants, and satisfactory results have been achieved.

Thirdly, it not only meets the requirements of Technical Code for Design of Thermal Power Plants, but also takes into account the requirements of the two documents, which is more scientific and reasonable.

Fourthly, the danger is dispersed and the reliability of protection is improved.

5. The steam drum water level protection is different from other thermal protection, and its control has four aspects: 1. Automatic adjustment. 2. Thermal signal alarm and interlock. 3. The accident evolution is a relatively slow process, which is monitored and adjusted by operators. 4. Finally check the water level protection system. So from the design point of view, it can be relatively "safe" to prevent and protect unnecessary misoperation.

4.3 It is not recommended to use water level switch for protection, because:

It is difficult to reach the protection action value in normal operation of steam drum, and there is no means of transmission experiment at ordinary times. If the water level switch is rusted and stuck, it is difficult to find out if it can't act, which will easily lead to the protection refusing to act, and there is a great accident hidden danger. A fault was found during the maintenance of Chaoyang Power Plant, and the water level switch protection is now cancelled.

Five, the problems in the process of measuring system conversion

5. 1 water side sampling problem

Case 1: In order to solve the problem of large deviation of water level measurement in a power plant, the water-side sampling tubes of four transmitters were led to the middle of the drum. Although the problem of deviation between water level meters is solved, it brings the problem of large error in water level measurement. After the boiler is started, the differential pressure water level is 80 ~ 1 10 mm lower than GJT electric contact water level gauge and WDP mica water level gauge. The sampling tube on the water side of a differential pressure water level gauge was replaced by mica water level gauge, which eliminated the error. The deviation between the three water level gauges is within 30mm.

Case 2: A Russian-made drum boiler with reduced distribution of double furnaces (765,438+0 downcomers) in a power plant. After the transformation of the measuring system, the deviation between water level meters meets the requirements when the unit load is below 180 MW, and the water level changes within 50mm when the load is above 180 MW.

Case 3: A Russian-made double-hearth (7 1 downcomer) drum boiler in a power plant is equipped with two GJT electric contact measuring cylinders. After the boiler is started, the measurement error is very large. After the measuring point was moved to the end of the drum, the problem was solved.

5.2 Instrument pipeline laying

Case 1: In the initial transformation of GJT electric contact water level gauge, the drainage pipe used the original double-chamber balance container, and the drainage pipe was arranged in parallel with the instrument pipeline, resulting in a measurement error of about140 mm. After rearrangement, the error was eliminated.

5.3 The sampling point on the steam side of GJT full-range electric contact water level gauge should not be on the steam collection pipeline.

Case 1: The steam side sampling point of GJT full-range electric contact water level gauge installed in power plant is selected on the steam header. Although the total pressure sampling method is adopted, the water level display is still about 500mm high. The total pressure in the steam collecting pipe is less than that in the steam drum. The reason is that the steam-water injection orifice in the drum causes pressure loss, so the display of the measuring electric contact tube is on the high side, and there is an opportunity to stop the machine and change the sampling point to the exhaust pipe. The problem can be solved.

5.4 The instrument valve stem must be installed horizontally.

Case 1: the signal deviation and fluctuation of differential pressure water level gauge in a power plant are large, which is found to be caused by the vertical installation of sampling valve rod. After correction, the problem was solved. The analysis shows that the valve is low and high, which is equivalent to the "convex" phenomenon in instrument management, which leads to the clear requirements of "steam plug" in the requirements and regulations.

Six, steam drum water level accident case

1958101October 3 1, the power supply of # 2, # 1 (230t/h) boilers in a factory was interrupted, and the indicators of steam, water flow, water level and other instruments were abnormal, resulting in misjudgment and misoperation of the stoker.

197610 June 18, the water level of boiler #3 in a factory failed, and the water level rose to full capacity. Although it was too late to open the emergency drain valve and superheater drain valve, four steam turbines (mother pipes) were forced to stop water supply.

1977 65438+1October 3rd, the No.6 boiler (430t/h made in Soviet Union) of a power station was started, and the DDZ differential pressure water level gauge failed, so the self-regulation could not be put into manual water level regulation. When the load is 70MW, the differential pressure water level gauge and mica water level gauge are basically the same, and the electric contact water level gauge is 50 ~ 100 mm high. When the load is 90MW, the boiler is seriously short of water, and the negative value of the electric contact water level gauge is the largest, and the differential pressure water level gauge is-270mm, which leads to the bursting of the water wall.

197765438+1October 12, the heating load of boiler No.2 (HG4 10t/h) in a factory is in the starting state, and the differential pressure water level gauge is inaccurate and ineffective. The operation is guided by the water level set by the driller. Due to inadequate measures, improper monitoring and operation errors, the boiler was seriously damaged by water shortage. Misjudgment and misoperation, boiler full of water.

1979165438+1October 8th, 9 boilers and 8 machines in a factory were put into operation. When 60% load of No.3 boiler was started after overhaul, the self-adjustment failed, and the water level was high, and the water level was ++ 160mm, which was changed to manual adjustment. When the emergency drain valve and drain valve were ready to open, the boiler was seriously full of water, causing the main steam header to overflow, resulting in the shutdown of 8 boilers and 7 units.

1980 On February 8th, when the load of # 2 boiler (HG670t/h) in a factory increased from 150MW to 160MW, the combustion was unstable, the water level fluctuated greatly, the operation monitoring was wrong, the judgment and operation were wrong, and the boiler was filled with water first and then the dry pan was seriously damaged. Six water wall tubes burst and nine others were damaged. The weld cracks between fins of water wall are more than 6 meters in the back wall and 20 meters in the front wall.

1July 25th, 982 # 2 boiler (670t/h made in Soviet Union) was overhauled, and the boiler load 1.2- 1.8MPa, differential pressure water level gauge and differential pressure water level gauge could not be put into operation. Due to the dirty water in the measuring cylinder as a reference, the water level gauge of the electric contact is abnormal. The mica water level gauge of the water supervisor is not skilled and cannot accurately report the water level. In addition, the small signal cut off the water flow meter without instructions, and the water supply adjustment operation was wrong, which led to the long-term water shortage of the boiler and burned 249 water wall tubes, which constituted a major damage accident.

198210/0 on October 4th, when the load of # 4 boiler (SG400t/h) in a factory suddenly increased from 40MW to 70MW, the water wall tube of 173 was burnt out due to improper operation of water supply regulation, so it was overhauled for 20 hours.

1On June 7th, 983, boiler # 7 (HG670t/h) of a factory was shut down due to economizer leakage. Due to the lack of a large number of water level meters to guide the operation of water replenishment and water supply, the operation was wrong, which led to the boiler being full of water and boosting the pressure, and it was not discovered until the boiler superheater safety door acted. Due to the lax electric main valve, feed water enters the steam turbine, resulting in a bending accident of the main shaft.

1990 65438+1On October 25th, the No.2 boiler of Xinxiang Power Plant in Henan Province was flooded. In the process of boiler recovery after fire extinguishing, the water supply control valve leaked greatly, which failed to effectively control the water level, the drum was full of water, the steam temperature dropped sharply, the static parts such as cylinders were deformed, the turbine shaft was bent and the shafting was broken.

1997 16 February 16 When the water stop, low water level protection and backup protection of No.4 boiler in Qinhuangdao Thermal Power Plant fail, the mica water level gauge has a small range, and the electric contact water level gauge incorrectly displays water, and the positive error of the differential pressure water level gauge is large, which leads to the boiler running in the water stop state for a long time, resulting in repeated water wall explosions and large-area overheating damage.

At the end of 2002, a forced circulation drum boiler (1025t/h) in a power plant in Anhui province was damaged and leaked by one transmitter, which caused two transmitters to indicate high water supply and automatically reduce water supply, resulting in low drum water level and low water level protection refusing to operate. After that, manually stop the boiler water circulating pump and check the cavitation.

In the process of transformation of various power plants, we know that many power plants have had accidents caused by the level of drum water in history, resulting in different degrees of consequences. To sum up, it is imperative to reform the drum water level measurement and protection system.