At the beginning of the advent of radar level gauges, they were installed and used under a positive pressure environment. Normally, the liquid level measurement of open liquid media, such as water and sewage, is basically something that is neither sticky nor Ordinary liquid that does not crystallize. With the continuous development of industry, the improvement of production process requirements, and the advancement of production technology, radar level gauges have gradually begun to be used under the conditions of viscosity and negative pressure, although the magnetic flap is now measured at negative pressure. This piece, but due to the complexity of various comprehensive factors involved in the negative pressure state, inadvertent attention will affect the normal measurement,
The measured medium of the radar liquid level gauge is isolated from the indicator, sealed, leak-proof, and suitable for the measurement of liquid level under corrosive conditions. Vibration, simple structure, easy installation and low maintenance cost are now available in power, petroleum, chemical, metallurgy, Environmental protection, shipbuilding, construction, food and other industries.
In order to prevent scaling, the seawater needs to reach the boiling point under low temperature, and the inside of the seawater device is required to be in a negative pressure state, which is about -0.093MPa during normal operation. This is the process requirement that the user must use to achieve the radar level gauge. It is the typical failure analysis of pipeline leakage under the negative pressure state.
1. Description of fault phenomenon
The main body of the desalination unit U3 concentrated salt water level gauge began to fluctuate from 30 to 70. Check that there is no abnormality in the level gauge body. After closing the upper and lower valves of the level gauge, the level measurement fluctuations are reduced, but the failure phenomenon has not disappear. Use the blast furnace cooling opportunity to reduce the main load of seawater U3 and find the cause of the failure. Fully close the upper and lower valves of the liquid level gauge and remove the lower wire plug. Open the sewage valve for exhaust and sewage treatment. Detect the magnetic float and find no abnormality. Fluctuations exist after commissioning. After the replacement of the concentrated salt water level gauge, it was put into trial operation again, and it was found that the liquid level gauge showed greater fluctuation and more frequent. After investigation, it was found that there was a leak at the pipe connected to the liquid level measurement container. After the radar liquid level gauge blocked the leak, the liquid level measurement showed that it returned to stable and the production in the load state returned to normal.
Second, analyze the cause of the failure
From the actual situation, when the fault occurs, the actual liquid level of the concentrated brine does not fluctuate, but the floating ball inside the radar level gauge does float up and down, thus showing the illusion of liquid level fluctuation. After closing the valve on the radar level gauge, the fluctuation stops, and it can be judged that the floating of the floating ball is due to the interaction between the gas-water mixture and the negative pressure environment. That is, the gas enters from the bottom of the radar level gauge and drives the float upward. The upper part of the radar level gauge communicates with the negative pressure environment. When the gas inside the level gauge penetrates the water surface and is sucked into the negative pressure environment, the float becomes smaller due to the smaller volume The fall back, so repeated, caused the illusion of liquid level fluctuation.
3. Propose a solution
(1) During inspection, not only the body of radar level gauge but also all connecting pipes and flanges should be inspected. Considering the corrosiveness of concentrated brine, the pipeline connected to the liquid level gauge should be replaced regularly.
(2) When the radar level gauge under negative pressure has a fluctuation in the liquid level display, the following steps can be used to analyze and solve it.
â‘ First check the display of the magnetic flap of the liquid level gauge. If the magnetic flap shows stable, it means that there is a problem with the liquid level transmission unit or signal transmission part. Continue to measure the current signal output by the liquid level transmitter. Whether the output current signal and circuit of the electrical isolator are normal, so as to detect the fault point.
â‘¡If the display of the level gauge magnetic flap is consistent with the upper display, when the fluctuation is not severe, first close the connection valve of the level gauge and the measuring container, open the sewage valve to discharge sewage, and continue to check whether there is a problem with the float of the level gauge itself If there is no problem, check the upper and lower screw plugs of the liquid level gauge and whether there is leakage at the sewage valve and the connecting flange. At the same time, observe the fluctuation of the liquid level gauge by changing the opening of the upper and lower valves of the liquid level gauge.
â‘¢ The radar liquid level gauge checks the leak point of the liquid level measuring container and the connecting pipe.
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