On the issue of the shutdown time for special valves in large catalytic units
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This post was last edited by wyxboy86 on 2015-6-16 at 12:39. Today I talked with an experienced instrument technician from an installation company about the butterfly valves at the exhaust fan inlet. I said that both cut-off butterfly valves at the exhaust fan should be able to close within 1 second, as that’s what the logic and relevant documentation specify; however, the experienced technician thought it was completely impossible! Because these two butterfly valves are larger than 60 inches. This valve is from German ADAMS. Since I have not actually encountered a situation in which both valves closed or the unit had to be shut down urgently during operation, I have no insight into the actual performance of such large valves that are controlled hydraulically. I would like to ask those experienced technicians or experts in special valves who have dealt with large butterfly valves that can close quickly, whether via pneumatic or hydraulic means, whether such valves can respond promptly And is it completely turned off? Can the cut-off butterfly valves from Tyco or ADAMS, or the anti-surge valves used in Fisher’s units of 20 inches and larger, truly achieve full opening in 3 seconds?
Theoretically, there is no problem. Generally, during the self-protection test before startup, the time taken for the self-protection action should be recorded to meet the design requirements. In actual operation, the time taken for the self-protection action should be longer; however, exactly how long it is can be determined by observing the valve position trend of that valve after the self-protection action occurs.
Records on a millisecond level should be available for lookup
Is the actuator of the smoke exhaust valve of a dual-cylinder type? For Tyco control butterfly valves, I recall that there is a assist-close spring located above the actuator. The required closing times for the two butterfly valves in your system are different; what was the reason for choosing valves from two different manufacturers during the selection process? In my experience, it’s usual to choose valves from just one manufacturer
The two butterfly valves were not fully closed, which led to damage to the smoke extractor blades. I would like to share the details of what happened; from my understanding, failure to close the butterfly valves in time can cause the unit to overspeed.
All parameters related to the interlock system should be recorded on a millisecond basis; therefore, your DCS cannot retrieve this information. You should ask the instruments for the records of ESD activation! Additionally, the operation of special valves places great emphasis on the timing of switching! For the valves in the catalytic cracking unit, every time we start up and test the interlocks, we must ensure that these valves are closed within a certain time frame – and that’s on a second-by-second basis! Just as you mentioned, for the two valves at the inlet of the smoke extractor, the pneumatic operation takes roughly 1.5 seconds, while the hydraulic operation also takes about 2 seconds. There’s no room for carelessness here; otherwise, the consequences can be severe! As for that experienced technician you mentioned, his understanding still remains at the level of traditional instrumentation; he could use some time to update his knowledge!
Some things should be left at that, without pressing too hard! ;P
I’m interested in smoke extractors with a split shaft design. Could you tell me which company you represent?
There are likely two sets of split-shaft units in operation in Yanshan at present, one set in Jingmen, and one set in Shijiazhuang. Back then, three sets of GHG smoke extractors were imported; they were of the horizontal three-stage type, but they were all modified later on.