How is a false liquid level in a boiler formed?

Generally, important level gauges should use dual-level gauges. It can’t be that both of them fail at the same time, right? There are also references such as flow rate and temperature, along with alarms (it seems to be of the float-type). It might be due to poor instrument design or inadequate inspection, as well as a lack of responsibility on the part of the staff.

It can be indirectly observed and determined through the temperature entering the tower, the pressure of the waste heat exchanger used to control the valve opening, and the amount of water supplied; generally, it uses magnetic levitation, right?

The boiler operates in such a way that the lower part contains liquid, while the upper part is filled with steam. There is also a transitional zone in between where liquid and steam are mixed together. The liquid portion continuously boils due to heating, generating steam; at the same time, as the steam rises, it exerts a buoyant force on the liquid level. Taken all together, this situation can easily lead to an incorrect reading of the liquid level! Everyone is aware of the hazards associated with false liquid levels. So how can we avoid their occurrence? Our company uses \"three impulse\" control, which is a control system that includes three parameters: the drum level, steam flow rate, and feedwater flow rate. The liquid level is the primary parameter, the feedwater flow rate is the secondary parameter, while the steam flow rate is an important interfering parameter; it is a very complex control system. When the liquid level changes, the valve can be opened and closed directly. . . . Of course, during startup and shutdown, it remains under single impulse control; once the system is operating normally, it switches to three impulse control

This post was last edited by ZZJJAA70 on 2009-11-16 at 20:20. Cause of false water level: It refers to a temporarily inaccurate water level. 1. When the boiler pressure drops suddenly, the saturation temperature of the water in the boiler falls to that corresponding to the new pressure; as a result, a large amount of heat is released, causing the water to evaporate on its own. This increases the number of bubbles in the water, leading to an expansion in volume and an increase in the water level, thereby creating a false water level ； 2. When the boiler pressure rises suddenly, the corresponding saturated temperature increases. Part of the heat is used to heat the water in the boiler, which reduces the amount of evaporation, decreases the number of bubbles in the water, causes it to contract, and leads to a drop in the water level; this too results in an apparent water level ； 3. In winter, the weather is cold, especially in the northern regions, which causes instrument components to freeze and become blocked, resulting in incorrect readings or malfunctions, as well as transmission issues that prevent the actual values from being displayed on the computer. Methods for dealing with false water levels: 1. When a false water level occurs in the boiler, it is necessary to make an accurate assessment first; operators should regularly monitor changes in the boiler’s load and analyze each situation individually in order to take the right corrective actions ； 2. In the event that the load increases sharply and the water level rises suddenly, it should be clear ； 3. From the perspective of this equilibrium condition where the evaporation rate is greater than the water supply rate, the rise in water level is temporary and will soon decline. It is not advisable to reduce the water supply; instead, combustion should be intensified to restore steam pressure. Once the water level begins to drop, the water supply should be increased immediately to match the steam generation, thereby restoring the normal water level ； 4. If the increase in load is small, the resulting change in water level can still be significant; if this is not controlled, it may lead to the tank becoming full. In such cases, the water supply should be reduced appropriately to prevent overfilling, while at the same time the combustion should be intensified to restore atmospheric pressure ； As soon as the water level begins to drop, increase the water supply immediately; otherwise, the water level will become too low again. In various situations, it is necessary to use multiple methods for measurement, assessment, and comprehensive analysis; one should not conclude that there is an excessive amount of water in the furnace based solely on a high water level alarm. More sensors can be used to conduct measurements from different angles, and by comparing these results, a factual conclusion can be drawn!

What do you mean by \"load\" in your explanation??? Please explain in detail??? I would appreciate your guidance

Floor 4 is the same as ours: three impulse actions, and false level readings occur very rarely

During operation, call for water every two hours to prevent false level readings

Hello, if three impulse regulation is used. . Will the problem of false liquid levels not occur then? Is the reading shown on the computer the actual liquid level, or is it different under high pressure, for example? . The reduced level transmitted by the bubbles is fake. However, after a systematic analysis, no action was taken to increase the water supply volume. Another issue is whether the drum level measured by the level gauge represents the actual level of water or the level in that ambiguous zone between water and steam. Please advise

Abnormal boiler water level. I. Boiler overfilled with water: 1. Symptoms: ① The water level alarm goes off, and the high water level indicator light turns on； ②The indicator lights of the electric contact level gauge are fully on ； ③The drum water level is above the highest visible level ； ④The water supply flow is abnormally greater than the steam flow ； ⑤The salt content in the steam increases ； ⑥Decrease in superheated steam temperature ； ⑦In severe flooding conditions, water hammer occurs in the steam pipes, and steam emerges from the flanges. 2. Reasons: ① Automatic water supply failed, and the water supply control device malfunctioned. ②Incorrect readings from the water level gauge, steam flow meter, and feedwater flow meter lead to misjudgments by operators, resulting in improper operations. ③The water supply pressure suddenly increased. ④The operators were careless, failed to monitor the water level properly, made untimely adjustments, or performed incorrect operations. 3. Handling: ① When the boiler steam pressure is normal and the feedwater pressure is normal, and if the drum water level exceeds +75mm and it is confirmed that the drum is full of water, the cause should be identified immediately. ②If the water level is affected due to a failure of the automatic water supply system, immediately switch from automatic to manual mode and reduce the water supply by closing the control valve. If the water level continues to rise, open the emergency discharge valves to release water. ③If the drum water level continues to rise by more than +100 mm, reduce or close the feedwater valve (open the economizer recirculation valve when feeding water is stopped) and increase drainage. ④Depending on the decrease in steam temperature, reduce or close the desuperheating water valves; if necessary, open the superheater drain valves. ⑤If the drum water level exceeds the visible portion of the gauge, immediately shut down the boiler, close the main steam valve, and notify the electrical and turbine teams to increase the water discharge until the drum reaches its normal water level. When the water level rises due to abnormal feedwater pressure, contact the steam turbine immediately to restore normal conditions as soon as possible. ⑥Once the fault is resolved, resume the operation of the boiler unit as soon as possible. II. Boiler water shortage: 1. Symptoms: ① The water level alarm goes off, and the low water level indicator light turns on. ②All the negative value indicator lights of the electric contact level gauge are on. ③The drum water level is below the lowest visible level. ④The water supply flow is abnormally lower than the steam flow. ⑤The temperature of the superheated steam rises. 2. Reason: ① Automatic water supply failure. ②Incorrect readings from the water level gauge, steam flow meter, and feedwater flow meter lead to misjudgments by operators, resulting in improper operations. ③The boiler load dropped suddenly. ④A failure in the feed water pump causes a drop in feed water pressure. ⑤Leakage in the boiler blowdown pipe and valves, resulting in excessive blowdown volume. ⑥Rupture of the water wall or economizer tubes. ⑦The operators were careless, failed to monitor the water level properly, made untimely adjustments, or performed incorrect operations. 3. Handling: ① When the boiler steam pressure and feedwater pressure are normal but the drum water level is below –75 mm, verify the accuracy of the water level gauge; if automatic control fails, switch to manual mode and increase the feedwater supply appropriately. ②If the water level continues to drop below –100 mm, in addition to increasing the water supply volume, check whether the sewage valves and drain valves are properly closed, and reduce the load if necessary. ③If the drum water level continues to drop and disappears from the drum level gauge, the boiler must be shut down immediately, the main steam valve must be closed, and water must continue to be supplied to the boiler. ④If, due to the negligence of the operators, the water level disappears from the drum level gauge and the electric contact level gauge is unable to determine it, the boiler must be stopped immediately, and the main steam valve as well as the feedwater valve should be closed. After shutting down the boiler, perform a water call; if no water is detected, it is strictly prohibited to feed water into the boiler. Once water level appears on the gauge after the water call, water supply to the boiler can be increased, while making sure to restore the proper water level. ⑤If the water level drops due to low feedwater pressure, immediately notify the turbine to increase the feedwater pressure. III. Unclear water level: 1. When the water level cannot be seen in the drum level gauge, and it is also impossible to determine it using a electric contact level gauge, stop the boiler immediately and cease feeding water into it. 2. After shutting down the furnace, determine the water level using the following method: ① Slowly open the drain valve of the water level gauge; pay attention to when water appears in the gauge, as this indicates a slight level of water, and treat it accordingly. ②If the drop in water level is not visible, close the steam valve and the drain valve, and pay close attention to the water level. If the water level gauge shows a water level, it indicates mild water shortage, which should be handled as such. ③If the water level line is still not visible, close the water gate and then slowly open the drain gate. The appearance of a water level line in the gauge indicates severe overfilling, while the absence of such a line indicates severe underfilling; in either case, take action appropriate for severe overfilling or severe underfilling. IV. Damage to the drum level gauge: 1. When the drum level gauge is damaged, immediately isolate the faulty gauge, close the steam valve and water valve, open the drain valve, and use another level gauge to monitor the water level. 2. When all the drum level gauges are damaged, the boiler may continue to operate for 2 hours under the following conditions. ①Automatic water supply regulation is reliable ； ②The water level alarm is in good condition ； ③The two electric contact level gauges are indicating correctly, and they were calibrated with the drum level gauge within four hours. ④Take urgent measures to repair the drum level gauge as soon as possible. 3. Maintain stable boiler load. 4. If the automatic water supply is unreliable, in the event that all the drum level gauges are damaged, operation is permitted only for 30 minutes based on a reliable electric contact level gauge. V. Boiling of steam and water: 1. Phenomena: ① The water level gauge in the steam drum fluctuates violently; in severe cases, it becomes impossible to see the water level through the gauge. ②The temperature of the superheated steam drops sharply; in severe cases, water hammer occurs within the steam pipes, and steam escapes from the flanges. ③The salt content in steam and boiler water increases, leading to a rise in conductivity. 2. Reasons: ① The quality of the boiler water does not meet the standards; the salt content in the suspended solids is too high. ②Waste discharge was not carried out in accordance with regulations. ③The row spacing is too small or not set. ④The load increases significantly. ⑤The drum water level remains too high. 3. Treatment: ① Appropriately reduce the boiler’s evaporation rate and maintain stability. ②Operate the continuous sewage discharge at full capacity; if necessary, activate the emergency drain valves and regular discharge systems, increase water intake and discharge, and maintain the water level slightly below normal. ③Stop adding the chemical. ④Open the superheater drain valve and inform the turbine to increase drainage. ⑤Notify the laboratory staff to test the boiler water and take measures to improve its quality. ⑥The boiler load is not allowed to be increased until the quality of the boiler water improves. ⑦After the fault is resolved, the water level gauge must be flushed.

Reply to 9# Qi Lili: A three Impulse control system is a highly complex control system. The liquid level displayed on the main control panel is indeed accurate, as it has been corrected accordingly； It can definitely ensure accurate liquid level control; the three-pulse control system is a composite control system that combines feedforward and cascade control. In the three states, changes in liquid level, changes in steam flow rate, and changes in feedwater flow rate each cause changes in subsequent parameters, but ultimately all of these affect the opening degree of the feedwater valve