Posted Tue, 26 May 2020 16:33:54 GMT by Mirko Trionfini
I everyone, I have to admit I'm kind of a newbie in WEST.
I'm testing an activated sludge plant with a membrane separation, instead of the classic secondary clarifier.
I'm struggling with the fact that the parameters of the membrane set a constant Qout.
I'm using the ideal membrane (without fouling)
I tried to use a control to set a constant concentration in the SST of the concentrate, but it gave me an error (system error: Model contains one or more algebraic loops)
I have put a loopbreaker and this happens only if the PI_control is present.
If I don't put the control, though, I struggle with the fact that the membrane works in the opposite way of a clarifier (you set the Qout instead of the underflow).
If anyone could help me I'd find it very useful, thank you.
Posted Wed, 27 May 2020 15:19:29 GMT by Enrico Remigi WEST Product Owner
Hi Mirko,
there are a couple of things in your post ...
[list type=decimal]
[li][b]Loop-breaker[/b]: indeed, it may happen that an algebraic loop be detected due to a controller, i.e. the controlled variable is directly dependent on the measured variable.
Unfortunately, there is no such thing as a loop breaker block for signals (red lines); and the only way to solve the issue is to place a normal loop breaker on a blue connection (flux) in a position such that the data loop is also broken[/li]
[li][b]flow through the membrane[/b]: it's not entirely correct that Qout is constant. The outflow is regulated by the flux through the membrane (J12) which is a manipulated variable, i.e. can be controlled[/li]
If you need / prefer to directly control Qout, the only way is to re-write the model somehow in reverse, so that it exposes directly Qout (as an input) and e.g. the flux as an output.

You must be signed in to post in this forum.