Air separation oxygen production area: [Weekly Topic] Week 11 of 2011——Emergency shutdown, what if the instrument air supply is not available?
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Since our instrument air is supplied after passing through molecular sieves, in the event of an emergency shutdown it is essential to ensure a steady supply of instrument air. But what if the backup system for instrument air fails to function at such times? I’m not sure how various plants ensure a continuous supply of instrument air; what are some good solutions in case the supply of instrument air is disrupted during an emergency shutdown?
Connect all the instrument air in the plant together. I’ve heard that some facilities have specialized equipment for supplying instrument air, in order to ensure a stable supply of gas. It is best to have a backup gas source, such as a nitrogen tank. For reference only.
Reply to 1# gader Backup instrument system: 1, Storage tank； 2. Instrument compressors – are there any other styles besides these two? I used to work on a 3000 capacity air separation unit that didn’t have a backup instrument system; there were instances of overpressure in the tower, which led to the safety valves activating! Large air separation units must be handled with great care; without them or if they fail to function properly, who knows what serious consequences could arise! It’s a good topic; let’s all discuss it!
Reply to 3# you*n*nyou: I have experienced two incidents of loss of instrument air. The first time, it was mainly related to dealing with the sealing air for air shut-off valves and cryopumps; the second time was much worse
The handwheel is pressed down; other specific situations need to be analyzed individually
Reply to 4# gader: Please explain in detail so that we can learn as well and know how to avoid it! ! ! Thank you! ! ! !
Reply to 6# you*n*nyou: It’s a long story, but I hope it won’t be necessary to use it. Personally, I think having two circuits of instrument air isn’t safe enough; three circuits would be better. The reason is simple: the backup instrument air system is not used for long periods of time, and if it fails to function properly in an emergency, it can cause serious problems. To give a real example, due to low temperatures, a malfunction occurred in one of the pipelines of the air separation system, forcing an emergency shutdown. At that moment, the pressure regulating valve of the backup instrument air system could not open properly because it had not been used for a long time, putting the air separation system at risk of running out of air
This item should be included in the accident plan. This should be handled accordingly based on one’s own situation! Our equipment should be constantly encountering problems and being improved accordingly!
An instrument air compressor station is an essential independent system for chemical enterprises! Even if a separate instrument air compressor station is not installed, there is a compressor driven by an electric motor in the production unit that supplies instrument air to the entire plant’s instrument control system in emergency situations; otherwise, even the initial commissioning and purging processes cannot be carried out.
Here in my plant, there are two metering units, each with a capacity of 10 cubic meters per minute, one in use and one as a backup. I have encountered two instances of a drop in instrument air pressure; once it was due to an increase in the number of usage points, resulting in insufficient flow for both units and thus a decrease in instrument air pressure. Another time, the machine that was in use stopped working, and the backup one couldn’t be started either. Now we connect the nitrogen tank to the instrument air tank; when neither of the two instrument air supplies is available, nitrogen is used as the source of instrument air~~
It is recommended to add a 300-cubic-foot instrument gas compressor as a spare; this won’t cost much. It’s okay even without a heat-free drying system. If the air supply is limited, I heard that bottled gas or gas cylinders can be used.