The discussion revolves around controlling the flow rates of three streams entering a vessel, where two streams depend on the flow rate of the third stream in a specific ratio. Participants explore how to configure control loops and represent them in a P&ID (Piping and Instrumentation Diagram).
Participants express varying opinions on the configuration of control loops and the number of flow transmitters required. There is no consensus on a single approach, as multiple configurations and considerations are discussed.
Limitations include the need for clarity on the specific ratios and dependencies between the streams, as well as the potential for operational issues in open loop configurations.
Engineers and technicians involved in process control, particularly those working with fluid dynamics and control systems in industrial applications.
Yes. "... and show it in my PID?" Not clear what you're asking here.princessme said:I have 3 streams entering my vessel and 2 of the streams are dependent on the 3rd stream's flow rate in a certain ratio. Is there a way to control the flow rate of the 2 dependent streams using the flow rate of the 3rd stream and show it in my P&ID?
What I meant was how should the configuration of the control loop be in my P&ID? I'm aware of how to show the control loop for 2 streams, but I'm having issues for 3 related streams to be controlled. Any references that I could refer to for this?Bystander said:Yes. "... and show it in my PID?" Not clear what you're asking here.
For instance, both the first and third stream are dependent on the flow rate of the first, both in different ratios. Does it mean that I need to have 2 control loops - one for streams 1 and 2, and another for streams 2 and 3?Bystander said:You've a couple possibilities: the third stream flow rate can be described as a function of the flow rate of either of the other two; pick one.
Yup. Third stream as fnn of first, or of second; of second is easier since it's a fixed ratio.princessme said:2 control loops
Noted. Thanks for the help.Bystander said:Yup. Third stream as fnn of first, or of second; of second is easier since it's a fixed ratio.
My plan was to put a control valve on stream 1 and 3, which are connected to a ratio station each. Each ratio station is connected to the FT on stream 2. Does that make sense?Bystander said:... and, when the third stream "runs away," how do you sense that upset condition?
Makes sense if you can be certain that which ever stream you leave as an "open loop" doesn't get plugged up, run dry, or otherwise fail.princessme said:Does that make sense?
So I should consider doing 2 closed control loops instead?Bystander said:Makes sense if you can be certain that which ever stream you leave as an "open loop" doesn't get plugged up, run dry, or otherwise fail.
Alright, thanks for the suggestion.Bystander said:FT on primary stream (set point) to "ratio" for two dependent streams, and FC plus FT sensing output for each dependent stream is the way I'd do it.
One does the trick --- two can have a nasty tendency to start calling each other liars.princessme said:1 be sufficient?