6 replies to this topic

[Redbull010203]

Hi everyone,
has been a long time I've been reading interesting threads here sometimes but today I may need to start a new one! I have an interesting Assignment for school and my knowledge is quite restricted so I have to ask here for input, ideas or explanations from more experienced people..
The idea is to think about a chemical process ( can be a flash separation, a distillation column, an heater or whatever) that needs to have 2 inputs and 2 outputs. I thought about a cracking furnace. ( but take this in mind please, if you think about an easier process just tell me).Then I should draw a block diagram for this and until this point I can do it without big problems. Then, I should say if the system is linear, non linear or piecewise linear. How can I do that? If I don't find any transfer function for a cracking furnace in literature, how can I say if it's linear or not? And in case I find a transfer function,is just the nature of this function to say if the system is linear? Then also asks for dynamic and static characteristic, but I don't know what's meant by dynamic or static. Ok for dynamic I think when you change time constant but, again, without transfer function how can I say that?And, if I have a transfer function, is there anyway to relate it to the time constant and say without softwares the dynamic change?
I know are several doubts but I am also afraid I just thought at a more difficult process, indeed already to think about two manipulated and controlled variables for the cracking furnaces makes me think for hours and hours.. Any suggestion or further explanation for this are really welcome! Thanks, I'll also attache a file with the main doubts.

[Pilesar]

A cracking furnace is a very complex process equipment piece. I don't understand what the professor really wants, but I suggest you do the assignment with a simpler process if possible.

[Redbull010203]

A cracking furnace is a very complex process equipment piece. I don't understand what the professor really wants, but I suggest you do the assignment with a simpler process if possible.

Indeed, I changed and now I'm using a Distillation column where I can control the composition of methanol in top and bottom by manipulating stream of steam in the reboiler and of reflux ratio. In this case, the feed flow rate is a disturbance. I also found transfer function for this. But as you already said, no one can understand what the professor wants,and everyone is proceeding in a creative way. But I have lack of imagination and I'm stuck because I don't understand how to do the dynamic change part or step response/staircase experiments ( only theoretically no software...). 

[breizh]

Hi,

You may find pointers in the doc attached.

Good luck

Breizh

[Pilesar]

A stripper column (reboiler but no reflux) would be a bit simpler still. Inputs of flow rate, inlet temperature, column pressure, inlet composition and reboiler heat. Outputs of product stream flows, composition, temperatures.

[Redbull010203]

A stripper column (reboiler but no reflux) would be a bit simpler still. Inputs of flow rate, inlet temperature, column pressure, inlet composition and reboiler heat. Outputs of product stream flows, composition, temperatures.

In this case I would have 4 inlet and 4 outlet but I need the system to be 2x2. In case I choose 2x2 randomly from these 4, would the transfer function change? I mean, I don't understand from where the transfer functions come, if they depend on the nature of the input and output or if they depend on the process ( so for all distillation columns are the same)

[breizh]

Hi,

Consider your favorite search engine, key words Transfer function distillation column

https://dergipark.or...cle-file/126904

 

note : Youtube videos could be your ultimate resource

 

Breizh