New model to control DO in aerobic tank

Hi all,

I am new on this forum. I have a problem: I would need to set up a control (PI controller) on the aerobic tank that return as output DO imposing constant Kla and constant flow air. I currently have a control that, fixed setpoint DO, it calculate Kla such that it has setpoint DO; I noticed that on the link tank-control control you can choose several variables to y_M, while on the link control-tank only parameter u to Kla.

Essentially I would check that you have consumption of DO in the tank when the biodegradable load changes in input plant, with constant Kla and constant flow air. At present imposing a set point of DO, when I increase the input load, having to maintain set point DO, the model returns me an increase of Aeration Energy and so of flow air. I suppose I should create a new model in the library. but how?!

Thanks

This is not clear to me: [b]maybe you can elaborate further?[/b]

[quote author=iacopod link=topic=2452.msg5652#msg5652 date=1431081913]
.. imposing constant Kla and constant flow air ..
Essentially I would check that you have consumption of DO in the tank when the biodegradable load changes in input plant ..
[/quote]
[list]
[li]if kLa (and/or the air flow rate) is constant, you're not controlling anything, right?[/li]
[li]you could quantify the effect of the variation of the organic load by comparing the (steady-state) DO levels perhaps?[/li]
[/list]
In either case, you don't need a controller but rather work with the existing state variables of the AS tank.

Alternatively, you may want to control DO (e.g. by a PI controller). You're right: the DO will be maintained around the set-point. So you could quantify the effect of the organic load by comparing the kLa's generated by the controller, or the air flow rate required, to maintain the DO.

Either way, I don't see the need to modify a base model (or create a new model).

Looking more carefully I saw that there is a controller Aerator (that on Model Editor is called irvine_carbon_footprint). I think it might be useful to me. In a few words, given Q_air returns O2_tank, right? Could you tell me please more about how to use this block? Which variables I have to select on the links?

Thanks

If you select the Block, in the WEST layout, and [b]press the F1 key[/b], the Model Guide will start up, showing the description of that specific model.

Anyhow, "given" the actual DO in the tank, the tank volume and the sludge age (all are to be given as input signals to the aerator), it will return the kLa.
The aerator is [u]not a control model[/u]: it is a simple aerator. Thus it needs to be integrated in a 'control loop' with e.g. a PI control model.
The PI controller will receive the DO measurement as input; and return (output signal 'u') the necessary 'Q_Air' (so it is to be linked to the manipulated variable 'Q_Air' of the aerator).
The aerator will receive the SRT from a calculator (or you could use a constant value, if SRT is relatively constant); it will also receive DO and V_ASU from the tank, as input; and it will return the kLa.

Sorry,

I don't understand the sequence of the blocks. The cycle is: the aerator receive DO, V_ASU, SRT from the tank and return the kLa at the tank, right? How does PI controller receive DO measurement as input? From aerator or tank? And return (output signal 'u') Q_Air? What connects the output of controller?

Thank you for your availability

See image attached

Thank you very much