How to improve the accuracy of power plant thermal control level measurement

Thermal control level measurement as an important signal in thermal control automatic control, automatic control of the power plant, some of the liquid level signal is a feedforward signal some level of three impulse control signal is as an important signal of logic control, as an important means of detecting signal outage of unit tripping, crisis, plays an extremely important role in automatic control of power plant, the liquid level measurement in power plant as an example to show how to improve the level of measurement accuracy, how to improve the accuracy of level measurement become the important topic in the installation. 1. Summary of installation in the thermal power installed, liquid level signal is generally installed in the condenser hot well, deaerator water tank, high-pressure heater and low pressure heater, steam drum, Steam separator) Many areas, such as, its signal as its equipment and the safe operation of the unit and its important parameters, if this parameter is more than the allowable values, may cause the unit tripping hazards. During the installation process, according to the requirement of the measurement accuracy is different, can choose single room balance container or double room balance container. ( 1) When choosing single room balance container, the positive pressure differential gauge head remain unchanged by the equilibrium constant water container, negative pressure head changes over the container liquid level, the error caused by the following reasons: (1) in the process of operation, when the container liquid level lower, due to the differential pressure increases, differential pressure meter table diaphragm or bellows to move from the positive pressure side suction side, so that the balance container water column temporarily reduce positive pressure side. (2) in the container, due to the saturated water in the container, the temperature of the steam and the container is different, have different heavy, caused the error of the meter reading. In the process of running, if the container for steam, such as the drum level, high level, as the change of the unit operation condition, the liquid level fluctuation is bigger, how to reading a few of the transmitter on the same container, and the correct response level H, as shown in figure: a positive pressure chamber pressure P1 カ : a negative pressure chamber pressure P2: P steam vapor pressure inside a container; H a measuring liquid level height; H1 zui low level to the transmitter height; The h2 zui high level to transmitter level; V1 measured level a severe; Lateral v2 a negative pressure level heavy: v3 a positive pressure side level heavy T a liquid level transmitter. Is negative pressure respectively: P1 = h1v3 + Hv1 P2 = h1v2 + P + P steam vapor pressure difference between pressure for: ⊿ P = P1 - The P2 = h1v3 HV1 steam + P - h1v2- P = Hv1 + h1v3 - steam H1v2 can be seen from the type on the v1 = v3 = v2, can reduce the level of error ( 2) When choosing double chamber balance container, because the balance of the container temperature is much lower than the temperature of the measured container, cause less than the water in the container, the surface of the negative pressure pipe cause measurement error. 2. Reduce the level measurement error factor ( 1) Eliminate installation factors, during the installation process, should fully combined with environmental factors, the positive pressure side and suction side of the environment, to eliminate the above formula in v3, severely affecting factors of the v2, v3 = v2, at the same time, during the installation process to fully guarantee the balance of the same container container installation are lateral pressure level elevation consistent ( The guaranteed h2 at run) In the installation, the valve and pipeline and the distance between the balance container, if the steam, to fully guarantee the balance before the container installed pipe diameter conform to or greater than the specification, make steam in the rapid cooling after the fluctuations in the container, and instrument piping installation environment eliminate level error is one of the factors. In the vacuum system level measurement, such as condenser hot well liquid level, fully guarantee the positive pressure side of the balance of the container liquid level is one of the important conditions for correct measurement, because in the process of hot well liquid level measurement ensures the vl = v2 = v3, so during the installation process balance containers with pipe diameter is not too big, when necessary in the case of ensure balance container to, can increase the elbow, prevent the balance level has been damaged by the vacuum container, fully guarantee the accuracy of the measurement of liquid level. ( 2) With temperature compensation, in a container, container water saturation, the temperature of the steam and container is different, have different severe, causing error of meter reading, if v1 v2 = = v3, instrument readings and container level is consistent, completely eliminate the reading error, due to the improvement of the computer, in the process of stress calculation, overcome container inside and outside temperature difference, will make the signal more accurately, therefore, can be installed on the container and pressure chamber a thermometer, temperature compensation in computer logic operation, severe difference basically eliminated, the instrument signal is more accurate. 3. Conclusion liquid level signal as one of the important parameters, automatic control in the power plant to improve the level measurement accuracy for safe and economic operation of hydropower station has a very important role, therefore, how to improve the accuracy of liquid level measurement is particularly important in the process of installation, the installation process of liquid level measurement equipment fully understand and take some measures to improve the accuracy of liquid level measurement, to ensure its safe, stable and efficient operation for a long period of time.

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