Project Bonsai code sample demonstrating chemical process optimization in a continuous stirred tank reactor (CSTR). Efficient control of an exothermic, non-linear chemical reaction with a CSTR is a benchmark in which to compare PID, MPC and Bonsai brains.
For an overview of this sample, watch Chemical Reactor Optimization with Microsoft Project Bonsai.
The chemical process here considers a transition from low to high conversion rate (high to low residual concentration). Because the chemical reaction is exothermic (produces heat), the reactor temperature must be controlled to prevent a thermal runaway. The control task is complicated by the fact that the process dynamics are nonlinear and transition from stable to unstable and back to stable as the conversion rate increases. The reactor dynamics are modeled in Simulink. The controlled variables (states) are the residual concentration and the reactor temperature, and the manipulated variable (action) is the temperature of the coolant circulating in the reactor's cooling jacket.
This example shows how to use Project Bonsai's Machine Teaching strategies to learn a controller for a chemical reactor transitioning from low to high conversion rate. For background, see Seborg, D.E. et al., "Process Dynamics and Control", 2nd Ed., 2004, Wiley, pp. 34-36. This sample is largely adapted from the MathWorks': Gain scheduled control of a chemical reactor.
Bare minimum for the sim (all units are continuous):
| Action | Range | Units |
|---|---|---|
| dTc | [-20, 20] | [Kelvin] |
Final set for Bonsai training:
Note: Performance improved when making the brain learn the per-timestep adjustment to apply to previous dTc. Control is maintained with the addition of
dTc_adjust, and an accumulator was added on the simulator side.
| Action | Continuous Value | Units |
|---|---|---|
| dTc_adjust | [-5, 5]* | [Kelvin/min] |
Note: given an additional rule that requires keeping dTc changes at no more than 10 Kelvins/min, we forced dTc_adjust to be on the [-5, 5] range (for Ts=0.5min)
Which matches the set of Observable States used for bonsai training
| State | Continuous Value | Units |
|---|---|---|
| Cr | [0.1, 12] | [kmol/m3] |
| Tr | [10, 800] | [Kelvin] |
| Tc | [10, 800] | [Kelvin] |
| Cref | [0.1, 12] | [kmol/m3] |
Note, the .ink file defines ranges higher than the ones shown here. That is made on purpose since the brain will try to explore, and thus will hit extreme limits in doing so.
Tref was removed as observable state since brain to simplify brain
training. With Bonsai's solution, Tref is not needed to be able to drive
the concentration linearly between points.
Tc < 10degrees / minTr < 400to prevent thermal runaway
Please open the MATLAB livescript, Chemical_Process_Optimization.mlx,
for further descriptions and instructions for getting started with this
sample.
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