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How do you design a controller for a static mixer?

  • 1.  How do you design a controller for a static mixer?

    Posted 07-10-2020 17:05
    I would like to have in my disposable examples or models for designing a PID controller for a static mixer. Any resource about this topic will be appreciated. I know how to start to design a PID controller for a batch reactor, but I am a little confused about how to do this task for a static mixer.

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    Rogelio Garcia
    Graduate Assistant
    University of Arkansas
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  • 2.  RE: How do you design a controller for a static mixer?

    Posted 07-11-2020 09:06
    An interesting question.

    A motionless mixer is a plug flow device. No smoothing. Pure dead time.

    Feedback control would be difficult. Emphasis would be on good feed control. 

    More details of what you want to achieve would help.

    Art Etchells DuPont Fellow emeritus






  • 3.  RE: How do you design a controller for a static mixer?

    Posted 30 days ago
    Thank you so much for reading my question @Arthur Etchells​, I appreciate your time.

    For this problem, the static mixer has two streams (1,2). The process variables are concentration and volumetric flow rate. The concentration of my material on stream 1 is fixed. However, the concentration of stream 2 is a disturbance. I want to be able to control the final concentration at the end of the static mixer, by regulating the volumetric flow on stream 1 (for this problem, I must not control the flow on stream 2). For stream have the same solvent, water. I would like to monitor the system via electroconductivity measurements.

    Thank you,
    Kind regards,

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    Rogelio Garcia
    Graduate Assistant
    University of Arkansas
    Batesville AR
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  • 4.  RE: How do you design a controller for a static mixer?

    Posted 30 days ago
    Rogelio

    I am an expert on mixing but over the years have worked with some good control engineers and they told me this is a tough system because of the pure time lag. 

    Typical time lag is a mixer length of 10 to 30 pipe diameters depending on the type of mixer.  

    I have seen them use ratio control on the two feeds with feed back from the  downstream detector to control the ratio.

    Does this make sense to you;?

    I understand the problem.  I hope these ideas help.  

    Cheers

    ART





  • 5.  RE: How do you design a controller for a static mixer?

    Posted 28 days ago
    Hello Rogelio Garcia,

    My comments:
    My experiences on similar types of applications.

    1. Blend ratio control & static mixer are used for different purposes & not the same. Your question therefore has two important objectives:
    a) How to design a blend ratio control.
    b) Why to use a static mixer.

    2. We used multi-blend ratio controller with property prediction & optimizer.
    a) Apply linear optimization model depending upon change of manipulated variables (volumetric flow) to optimize the quality under constraints as maximize quality but minimize the costs.
    b) Design & apply a ratio controller on a feed-forward mode.
    c) Design & integrate an inferential property models with the ratio controller & the optimizer. We used high speed FTNIR spectroscopic techniques.

    3. Static mixer was used downstream of the blend control valves to insure proper turbulent mixing. Turbulent mixing is desired to achieve proper mixing, unlike laminar mixing where stratification is a possibility. With stratification, improper blends will result.

    The use of static mixer is not linked to the control but to achieve a proper turbulent mix.
    Design of the process controller is linked to fast response time, in-line process analysis, optimize the quality control, and use a ratio controller for the manipulated variables (volumetric flows) against the control variables (the quality).

    Hope it helps for you to understand your question properly.

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    Eur Ing (FEANI) Santanu Talukdar CEng (UK) CSci (UK) MIChemE SMAIChE
    Chartered Chemical Engineer
    Independent industry consultant-
    Innovations Mgmt & Technology Transfers
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  • 6.  RE: How do you design a controller for a static mixer?

    Posted 27 days ago
    @Santanu Talukdar I appreciate your comments, they will be very helpful! ​Thank you so much for reading my question.

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    Rogelio Garcia
    Graduate Assistant
    University of Arkansas
    Fayetteville, AR
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  • 7.  RE: How do you design a controller for a static mixer?

    Posted 27 days ago

    Seems this situation is ideally suited for feed-forward control: measure the concentration in stream 2 upstream of the mixer and manipulate stream 1 flow rate.

     

    Vivek P. Utgikar, Ph.D., P.E.

    Professor, Department of Chemical and Biological Engineering

    University of Idaho

    875 Perimeter Drive, MS 1021

    Moscow ID 83844-1021

    vutgikar@uidaho.edu

    Phone: (208) 885-6970; Fax: (208) 885-7462

    Homepage: http://webpages.uidaho.edu/vutgikar/

     






  • 8.  RE: How do you design a controller for a static mixer?

    Posted 28 days ago
    Since there is so much pure delay in the response, consider using a dead time compensation control strategy like a smith predictor

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    Leon Levine
    Albuquerque NM
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