Regarding the high liquid level interlock issue for oil tanks
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Currently, the design of finished oil tanks in our company generally assumes the use of high and low level switches for interlock purposes. Let’s discuss whether other chemical companies do the same thing. I personally don’t think this is very reasonable. The reasons are as follows: 1. According to requirement 6.1.1 of GB/T 50770-2013 \"Code for Design of Safety Instrumentation Systems in Petrochemical Industries\", analog measuring instruments should be used for safety instrumentation systems. 2. Digital instruments are difficult to detect once they fail, unless the fault signal is fed into the system. The explosion at the Bensfield oil depot in the UK illustrates this point: a failure in the level switch on one of the oil tanks went unnoticed, leading to a serious accident. 3. Level gauges, like radars and servos, currently include products with certifications of SIL2 or higher, making them highly reliable. Please discuss whether interlocks for oil tanks in China currently use 2OO3 or 1OO2 interlock systems. It is recommended to use a level gauge for interlocking the high and low liquid levels in oil tanks.
It’s not a matter of whether it exists or not; as long as such devices meet the explosion-proof requirements and are suitable for practical use in the field, they can be utilized, and indeed they are being used. Using transmitters is certainly better, but they are also more expensive. Once properly designed, they can function normally. The main advantage is that switch signals have a much lower cost of use compared to analog signals; this is why technicians should choose the appropriate option rather than necessarily the best one You’re right, right!
Dual protection can also be used; for example, in our case, level switches use combinations such as high-high-high, low-low-low, or for important tanks, level switches are used in conjunction with transmitters.
This post was last edited by shiwendong on 2017-10-23 at 13:36. The high-low level interlock for oil tanks is a reliable and essential safety device used to prevent oil leaks in oil depots, as well as other safety incidents such as oil spills, fires, and explosions. It plays a particularly important role in ensuring the safety of property and personnel. The explosion-proof emergency shut-off valve is interconnected with safety devices such as level gauges and combustible gas alarm lights; in the event of an accident at an oil depot or chemical plant, the shut-off valve closes rapidly upon receiving an alarm signal or as a result of an emergency power outage, thereby cutting off the flow of oil or chemical liquids and preventing the accident from escalating further.
Pure switch-type instruments are no longer used in interlocks, as they are not very reliable. Once installed, it is also not possible to perform calibration or adjustment. There is a fault that cannot be diagnosed or detected. For level gauges, there are currently products such as those based on radar or servo technology that have SIL2 or higher certifications; I think these are quite reliable. They can be used to drive relays based on set upper and lower level limits, serving as interlock conditions. But the investment is simply too large. In my opinion, for tank areas, it’s better to use radar or similar methods to accurately determine the liquid level – that’s far better than anything else. The larger the storage tank, the safer it is; it’s fine to wait for 5 minutes in such cases. The Bensfield oil depot explosion was entirely caused by an operator falling asleep. Under normal conditions, the amount pumped and the increase in the tank level per hour are both well-defined. It’s better than anything else as long as the liquid level is adjusted properly and the alarms for the static and dynamic tanks in the tank area are set up correctly.
This topic is great; it’s ideal for discussion and learning, and it would be best to have relevant laws and regulations available
It can be set on the DCS as a high liquid level interlock value; when this value is reached, the interlock condition is triggered, the material inlet valve is closed, and the pump is stopped.