On-site instrument failure analysis (one question per week): The answer for September 11 has been released
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This post was last edited by baodingzhai on 2009-9-18 at 11:01. Fault phenomenon: The level measuring instrument for the stripper tower in the sulfur unit is a float level gauge; a glass plate level gauge is installed at the same height. The process operators report that the DCS shows the liquid level at 100%, while when they go to the site to check, the glass gauge indicates 60%. The on-site display of the float level gauge also shows 100%. Try to analyze the reasons? Cause analysis: Upon on-site inspection by the process personnel, the glass panel indicated normal operation. The instrument technician opened the drain valve to discharge waste and found that debris was blocking it. The reason is that the dirt inside the cylinder trapped the float at 100%, causing the float indicator to show an inaccurate reading and remain unchanged. Fault resolution: The meter technician cleaned the dirt away and reinstalled the float, after which the readings returned to normal.
The bottom of the glass-like level gauge is blocked
1) Close the source valve of the float, and vent the medium inside the float. If the indicator returns to zero, then the float is in good condition; if the indicator does not show the correct value, the torque tube and hanging chain can be checked (provided that a torque tube is present). 2) If the float is fine, check the glass plate as well – close the source valve and clear any obstructions in the glass plate. This measurement should provide a better indication of the liquid level! Just to spark some discussion.
It’s easy to tell whether a glass plate is good or clogged. Sulfur units are prone to clogging, and it’s not certain that the float will get stuck either.
Possible failure symptoms include: 1. The float getting stuck to the wall, resulting in inaccurate readings. Inspection method: Calibrate the float using the water calibration method. 2. The glass level gauge is blocked; clean it out.
First, determine whether the on-site level gauge is stuck; if it’s not stuck, then check whether the float is stuck as well. It’s difficult to say anything without having actual data for comparison – in fact, it’s easy to identify the problem by looking at the DCS trend values on site.
It’s so frustrating – I finally finished writing the questions, only to find that the entire website has gone down. I think the first step is to check the trend chart of that liquid level in DCS to determine when it reached 100% and for how long. By considering this trend along with previous production conditions and whether the plant is currently in operation, it is possible to preliminarily assess whether there is a problem with the float ； 2. Go to the site, close the valve that connects the glass plate level to the equipment, and open the discharge valve for the glass plate to determine whether there is a problem with the glass plate. 3. If there is no problem with the glass plate, and considering point 1, it can be determined that there is a problem with the float. In most cases, issues with float level gauges arise from problems with the float itself, and in such situations on-site repair is required. 4. It’s also possible that the measurement range of the float is set incorrectly, but this situation occurs rarely
1# It’s possible that the glass plate level gauge is blocked. If that’s the case, opening the valve below and allowing fluid to flow through for a while should help resolve the issue. If the problem persists despite this, the float level gauge can be reset to zero; if it doesn’t return to zero, it means the float is stuck
The possible cause of the fault is an excessive amount of sulfur deposits on the inner wall of the float, which keeps the float at the 100% position； Or, due to a mechanical failure in the mechanical transmission part, the float is unable to move up and down with the liquid level.
1. Ammonia crystallization is the main cause of the failure; it may well be the primary reason. It is a common problem in sulfur plants, and I have encountered it as well. 2. Later, when some products were found to be substandard, measurement errors occurred due to a difference in density from the original design. In short, the specific situation needs to be analyzed collectively; I like the way moderators consolidate issues, as it allows for collective brainstorming~~