What are the factors that affect the measurement of the drum water level? What are the methods and measures to reduce the measurement error of the drum water level?
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The drum water level is one of the key monitoring parameters in power plants, and accurate measurement of it is essential for the safe operation of the boiler. Traditional measurement methods include: in-situ dual-color level gauges, electric contact level gauges, and differential pressure level gauges (with single-chamber or double-chamber balanced container compensation). The measurement errors of local level gauges and electric contact level gauges are affected by boiler pressure, heat dissipation conditions, installation method, and the actual water level, making it difficult to calculate them accurately. Therefore, in high-parameter and large-capacity units, various types of differential pressure level gauges are commonly used as the main instruments for measuring the drum level; however, the measurement error of such level gauges is also affected by many factors. What are the factors that affect the measurement of the drum water level? What are the methods and measures to reduce the measurement error of the drum water level?
The last edit to this post was made by zgj2405 on 2011-7-30 at 08:41. The main factors that affect water level measurement include the following: 1. The installation conditions, location, and environment of the drum water level gauge; the positioning error of such gauges is generally between 10 and 50 mm, and the environments in which each gauge is located vary, which affects heat dissipation； 2. The influence of the conditions under which the drum is installed: the levelness requirement when installing the drum should be ≤5 mm, but after several years of operation of the boiler, this value increases to 15–20 mm. The water level gauge is installed based on the centerline of the drum, which results in errors in its installation ； 3. Regarding the impact of water entering the steam drum from the feedwater and water wall, the feedwater temperature cannot remain constant due to the influence of various heating conditions, and it is lower than the saturated temperature at the corresponding pressure ； The water entering the water wall contains a large number of bubbles, which continue to evaporate; as a result, its density is lower than that of water at the corresponding temperature and pressure ； 4. The effect of the downcomer: During boiler operation, water in the drum continuously flows into the downcomer at high speed, resulting in the water level in the drum not being at an ideal level. Variations in this level occur depending on the position of the downcomer, with differences that can range from 40 to 60 mm ； 5. Inherent errors of the measuring instrument itself: although the instrument has high precision, measurement and installation errors still exist. Methods and measures to reduce measurement errors of the drum water level: 1. Choose a suitable sampling location that is above the set value for water level protection, with a certain margin ； 2. An appropriate diameter for the sampling pipeline, in order to reduce flow resistance and prevent delays in water level display ； 3. Try to shorten the length of the connecting pipes to reduce flow resistance and increase the temperature of the medium inside them. The horizontal section before the container should be long enough to facilitate the condensation of vapor ； 4. Install a connecting pipe between the soda water sampling pipes as a damper to mitigate the impact of large fluctuations in the water level of the drum on water level measurements ； 5. Each level gauge should have independent sampling holes, sampling pipelines, and balance containers to avoid interference between them ； 6. The steam-side sampling tube is inclined toward the drum to facilitate the return flow of condensed water, ensuring a constant water level in the balance vessel ； 7. Proper insulation of the pipelines ensures both the maintenance of the medium’s temperature and effective heat dissipation.