Regarding the commissioning of process instrumentation
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In work, it is common to encounter situations where, for requests related to instrumentation, the normal values and maximum values indicate that no instrument exists that can meet the process requirements simultaneously. For example, the main flow rate of nitrogen is 30 m3/nh under normal conditions, but it can reach 1200 m3/nh at its maximum. How should this problem be resolved? Also, sometimes it’s not possible to determine very accurate values for certain quantities; in such cases, a wide range must be provided. For example, the amount of hydrogen used for cooling in certain hydrogenation reactions – the values given by research institutions are within a very wide range. How do experts handle this situation?
In the field of instrumentation, it is necessary to meet the requirements set by the process engineering team as much as possible; the best option should then be chosen based on actual circumstances. If the range is too large, multiple instruments can be used for control
I often encounter this situation in my design work; it can be quite frustrating, haha... These days I usually specify the operating conditions under normal circumstances, but if the range provided by the client is very wide, I still need to discuss it with them. Sometimes, some parameters related to the manufacturing process aren’t specified with precision. I usually ask the professionals in the downstream stages about the impact of these parameters on their design; if it’s significant, then there’s no need to say anything – those parameters must definitely be specified accurately ； If it’s not very important, then give them a range that they need to determine. Hehe... I was a bit lazy, haha……
This is a common issue; just like the maximum and minimum values for the small circulation pipes of the blower, as well as the pressures before and after the control valves of those circulation pipes. In my opinion, it would be appropriate to calculate theoretical values in the project start-up report, with the maximum and minimum values allowing for some flexibility.
Personally, I’ve also become a bit more lenient with values that have little impact. For the measuring elements selected for instruments, such as in flow measurement, is it common to choose a pipe diameter size that is a few sizes smaller than that required by the process? Sometimes the process specification specifies something like DN80, but then the instruments suppliers claim that an instrument with a DN25 size is sufficient in normal cases. I wonder if anyone has encountered such a situation?