Storage tank level control
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This month, the company’s tank farm was subject to a special inspection conducted by a third-party company commissioned by the local emergency management agency. Parameters of one of the company’s storage tanks: designed height of 11,650 mm, installation height of the internal floating disk at 1,630 mm; it is also equipped with a nitrogen sealing system and an exhaust gas recovery system. DCS setting: Low-low alarm at 2000 mm ； Underestimated by 2100mm ； Overstated at 9100mm ； The reported level is 10,000 mm, while the actual liquid level is currently 9,200 mm. The inspection team proposed corrective actions in accordance with clause 4.8.9.3 of the \"Guidelines for Identifying and Addressing Safety Risks and Hazards in Hazardous Chemical Enterprises\": storage tanks should not operate at an excessively high liquid level ； The process control parameters for the storage tank level should not exceed the limits specified in the process sheet ； Changes to process parameters should follow the change management procedure ； In my opinion, the underreporting and overreporting of tank levels are used to provide alerts for DCS operators; whereas the occurrence of extremely low or extremely high levels that trigger interlock conditions constitutes an abnormality in safety production. Why do experts believe that the operation cannot be underreported or overreported? I’d like to hear how various professionals view this issue
If the readings are continuously overreported, the DCS will keep issuing alarms. When an overreporting condition occurs, is there any difference between the alarm signal for overreporting and the alarm signal for severe overreporting? If operators become careless and mistake the alarm signal for severe overreporting for a normal overreporting alarm, it could lead to serious production accidents. Even if your alarm signals differ, operating within the upper and lower limits ensures quick adjustment.
Overreporting or underreporting is also a form of deviation from the specified limits, serving as a reminder for operators to make adjustments as soon as possible so that the process parameters return to the normal range. If normal operations are continued while in an alarm state and the situation is ignored, it is a dangerous behavior.
Running consistently above the upper limit essentially means treating any overreporting as non-existent, right?
Each storage tank has a filling coefficient (based on the properties of the material contained within it). The maximum filling level is determined using this filling coefficient, and the value that should not be exceeded is calculated based on it. It is acceptable to reach high values on normal occasions, but they should not remain at high levels for a long time.
Reasonable suggestion: normal operation shouldn’t keep triggering alarms……