×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Precision Temperature Control

Precision Temperature Control

Precision Temperature Control

(OP)
We have a 25,000 gal. tank with an aqueous solution that will be recirculated through a heat exchanger (not yet installed). Would it be feasible to control the temperature of the solution to +/- 0.5 deg F in the tank? Can anyone suggest literature that would confirm or disprove this feasibility?

Thanks

RE: Precision Temperature Control

Should be fairly easy to control at that temperature unless you adding or removing substantial heat in batch processes.  Overall heat balance will give you your answer.

RE: Precision Temperature Control

brent,

Perry's used to have a good process control chapter in the 5th and 6th edition, which was changed for the worse (in my opinion) starting in the 7th edition. The old chapter rightly defined a control design procedure which concentrated on defining the nature and magnitude of disturbances (and deadtime) expected. It will be very possible to control to +/-0.5F with the right instrumentation and design if the process is not subject to excessive disturbances- I think this is along the lines of ash's comment. For example, if you are trying to control temp using steam that varies unpredictably in pressure or quality then you are unlikely to be successful regardless of how much cost and effort is spent on design and instrumentation.

Once the disturbances are quantified, you will be in a better position to assess ability to meet your objective. You can also gain significant advantages using calculated variables (like duty control) and feed forward action in addition to conventional PID cascades.

More detail of your process and design proposal could help in getting an opinion from the forum.

best wishes,
sshep

RE: Precision Temperature Control

disturbances are part of it, for the most part you have to decide how uniform you want the temperature to be. That is not a function of control accuracy, but of the degree of mixing, tank insulation, etc.

for a continuously stirred tank and with more sensors than it would be worth, +/- 0.5 F is no problem.


RE: Precision Temperature Control

This is not a large tank but hacksaw makes great comments. I calc approx 8ftDx8ftH should do it- but check my calcs. The control objective determines both the equipment and control design. For example a disturbance of 1MMBTU/hr is calculated to change the pv by 5F/hr. The exchanger needs to be bigger than the disturbance, but not too big to control. Will you need to heat and cool? A bit more about the system would be helpful.

A well mixed tank would be essentual, and insulation will reduce the disturbance of ambient loss/gain. I envisoned that a pumparound system will control the temp on the pump suction using the recycle flow and exchanger outlet temp. The heat input can be reasonably calculated and controlled by such a system, but the he tightness of control is ultimately reflected in the cost. Hacksaw is also right to question the worth of setting a +/-0.5F objective.

best wishes,
sshep

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources