Author Topic: How to control Ammonia (NH4) with a set of controllers?  (Read 495 times)

Delia

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How to control Ammonia (NH4) with a set of controllers?
« on: December 26, 2018, 08:39:30 am »
Hello,
In my Project I would like to control NH4 in my aerobic tank, so as not to exceed the limit waste. That control consist in carry out the reduction of ammonia with an on/off controller with Ymax=5mg/L and Ymin=3mg/L instructions. Moreover, when Ymax exceeds the value, a pump starts, supplying 1250m3/h of air flow, also after 2 min an other pump starts to work in the same way to the first one. That happens only while Ymax>5mg/L, when it’s Ymax<5mg/L both pumps go off at the same time, furthermore when Ymin<3mg/L,  umin it’s 0.

My main problem is that, I don’t know exactly how to arrange the controller interface. I tried the disposition below, changing the DO variable for the NH4, and adding a control timer (located in the empty pin in the On/Off controller with T1=0 and T=2min as a variables). Also, as I told I put an on/off, instead of PI, moreover I don’t need the Avg and SRT calc elements (or I think so).

Could you help me in order to find the correct control arrangement in that layout?
Thanks in advance.
Delia.

Enrico Remigi

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Re: How to control Ammonia (NH4) with a set of controllers?
« Reply #1 on: December 29, 2018, 10:22:05 am »
Hi,
I don't see the OnOff controller in your image - only the PI, unless the name / model don't match.
Most importantly, I don't see the ammonia controller - which I assume is on the effluent (or directly on the tank, which may however cause an algebraic loop ...).
How would you implement the 1st and 2nd pump? Two separate aerators? I don't quite understand ...
In any case, I would suggest you consider implementing your control algorithm as a new model, as I am not sure you will be able to realise it by just assembling existing, base control models (that are essentially limited by only 1 input and 1 output).
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)

Delia

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Re: How to control NH4 with a set of controllers?
« Reply #2 on: December 30, 2018, 06:31:21 pm »
Hi,

The main idea in the previous post is how can I model in my west project, the real controller of the wastewater plant. That real controller is based on the NH4 .It’s composed of an on/off controller with Ymax=5mg/L and Ymin=3mg/L instructions. When NH4 exceeds 5mg/L a blower starts to supply 1250 m3/h of air flow, also after 2 min another blower starts to work in the same way to the first one (I want to simulate those blowers with an Aerator controller).



There is only one variable to control and it is NH4, the previous image it’s only an example of Layout, but in my case, I would like to change the DO variable with the NH4, because dissolved oxygen has nothing to do with my project.


Maybe the two blowers can be modelled as a blower with the aerator control. But the main problem is how to connect the control blocks with the corresponding variables.

Enrico Remigi

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Re: How to control Ammonia (NH4) with a set of controllers?
« Reply #3 on: January 04, 2019, 08:25:24 am »
Setting up the On-Off should be straight-forward:
  • it takes the NH concentration in the effluent as input signal (y_M) - you may need a probe block
  • it returns 'some kind' of Q_Air as output signal (u)
  • u_Min, y_Min: 0, 3
  • u_Max, y_Max: 1250, 5
The reason why I say 'some kind' of Q_Air, is that it all really depends on what the on-off controller controls: it may be connected to an aeration model (Irvine), in which case yes, it connects to Q_Air; or it may be connected to a PI controller (simpler solution), in which case it should probably connects to u_Max, i.e. max kLa ...
In any case, what you cannot realise by using the standard, base control models in the library is the 2 min delay by which a second (identical?) on-off model would be triggered. For this, you need to write your own code.
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)