4 replies to this topic

[deltaChe]

Ths loop (P-065) is to control the vacuum level in the reactor by breaking vacuum
by nitrogen injection.The vacuum level is controlled by the PID controller PIC-065 which measured
vacuum level by means the pressure transmitter PIT-065 and control valve PV-065

The other loops (P-075) is to control the reactor pressure through nitrogen injection.
The controller PIC-075 measures and controls the reactor pressure by means of the process value of
the pressure controller PIC-001D that read pressure transmitter PIT-001D at the reactor top
and the control valve PV-075.

My question is following.

N1. In this graph, PT-065 send signal to PIC-065, and then send to interlock. But in other project,
someone draw PT-065 send sinal to interlock first, then PIC-065. Could anyone please explain me about
this in detail.

N2. How can we cotrol/calculate the vacuum level and why we have to break this vacuum level?

These are my question. sorry to bother you professional a lot, and thank you very much.

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[ankur2061]

hswang2,

I have seen many posts from you & to which some members have tried to answer sincerely.

However, I have not seen any response from you to the members answers whether you have applied or understood the members answer or answers.

Is it that you are trying to run up a score on the number of posts?

I believe that you have been posting just for the sake of it.

Have you tried to analyze yourself the questions that you raise? I also doubt that based on some of the questions you have raised.

I would feel awkward asking some of the mundane questions that you have raised.

My advise to you would be to post judiciously so that the reader takes interest in your post & tries to answer it. Otherwise you will find that your posts remain unanswered & just take up precious forum space & your efforts to write go wasted.

Regards,
Ankur.

Edited by ankur2061, 23 June 2010 - 12:52 PM.

[deltaChe]

Thank you for your recommendation. I understand this forum is for everyone chemical/I&C professional to communacate
not just get answer. I will try to analyze my post carefully next time.

[riven]

Somebody review this I could be talking out my hat here



Let me describe the system.

System 1 (circled on the left ).
PT sends a signal to the interlock which then sends a signal to PIC which then controls the valve.

System 2 (circled on the right).
PT sends a signal to PIC; the PIC also receives a signal from the interlock and then PIC acts on the valve.

What is the purpose of the interlock: it is to prevent an undesired state.
What is the function of the PIC: to react and adjust a valve depending on the input it recieves.

My opinion
In system 1 the valve is always at a particular value unless the interlock says to change. In other words the pressure is allowed to change while the valve stays open or closed or other.
e.g. Interlock is set to send a signal when the pressure is 4 bar or more. If the pressure is less no signal is sent. If the pressure is more a signal is sent and the PIC reacts. This could be used to ensure that there is always a minimum amount of a substances flowing (or pressure) into the system (e.g. inert gas) but more importantly to keep the process constant.

In system 2 the PIC can directly change the valve as long as it is within the boundary set by the interlock. So perhaps the interlock says that the valve cannot be open more than 80% and not lees than 20% open. This allows the PIC to vary valve opening until this point is reached. This could be used to ensure that a maximum of component flowing and a minimum (or pressure) into the system.

Consider this under what happens in system with the diagram.
If we have too much flow of product then the load on the ejector becomes too high and the vacuum level drops so we reduce the nitrogen flow.
If we have too little product flow we are only sending nitrogen through the system. We can reduce the nitrogen flow.
If we have st up a min max interlock we can always keep our vacuum level at a certain value despite varying product flows.

Seems complex but the reaction may be production multiple 'stages' or products or regimes etc.

[deltaChe]

Thank you very much for your kindly help.

I would like to make some comment, but I am not sure if it is right or not:

In system 1, the sensor sends a signal first to the interlock and then to the PIC or TIC controller; the controller then sends a siganl to the valve to control a pressure or temperature increase/decrease. So, it seems to me that system 1 interlock is a saftey interlock because it got high priority.