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Bioprocess Engineering

, Volume 10, Issue 5–6, pp 217–223 | Cite as

Evaluation of sensors for the control of a continuous ethanol fermentation

  • M. Polakovic
  • C. F. Mandenius
Originals

Abstract

A method is presented for the evaluation of sensors used in the control of continuous fermentations. Simulations of open-loop response to input disturbance provided a starting point for the choice of sensor type. This was evaluated quantitatively through a sensitivity ratio. It was shown that in the case of ethanol fermentation, there existed three regions where different sensors could be used for the process control depending on the inlet sugar concentration. Sugar sensors were preferable above an inlet sugar concentration of 50 kg/m3, while ethanol sensors were preferable below 25 kg/m3. In the intermediate region, sugar and ethanol sensors demonstrated equally good performance. A controllability study of a continuous ethanol fermentation was also made. A single-stage continuous stirred-tank fermentor was simulated operating at a dilution rate of 0.1 1/h and inlet glucose concentration of 160 kg/m3. The outlet glucose concentration was controlled with a PI controller. Mean square error of the controller input signal during the first five hours after introducing input disturbance was taken as a measure of the controllability. This was studied in the relation to the two key sensor characteristics, sampling time and accuracy.

Keywords

Fermentation Glucose Concentration Dilution Rate Sensor Characteristic Ethanol Fermentation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of Symbols

cp kg/m3

ethanol concentration

cp kg/m3

fermentor ethanol concentration corresponding to c si and D

cs kg/m3

substrate (glucose) concentration

cs kg/m3

fermentor glucose concentration corresponding to c si and D

csi kg/m3

inlet substrate (glucose) concentration

csi kg/m3

inlet glucose concentration value used for sensitivity evaluation

csm kg/m3

glucose concentration — measured value

css kg/m3

glucose concentration setpoint value

cx kg/m3

biomass concentration

D 1/h

dilution rate

D 1/h

dilution rate value used for sensitivity evaluation

Di 1/h

dilution rate at ith sampling interval

D0 1/h

dilution rate at steady state

Kc m3/kgh

controller gain

Kp kg/m3

product inhibition constant

Ks kg/m3

Monod constant

n1, n2

random numbers

rp kg/m3 h

ethanol production rate

rs kg/m3 h

substrate (glucose) consumption rate

rx kg/m3 h

biomass growth rate

\(\vec \alpha \)

vector of independent variables

yi

ith dependent variable

Yps

ethanol yield

Yxs

biomass yield

\(\vec x\)

parameter vector

αj

jth parameter

βij

sensitivity of yi with respect to αj

βp

sensitivity of fermentor ethanol concentration

βs

sensitivity of fermentor glucose concentration

γ

sensitivity ratio

Δcp kg/m3

ethanol concentration difference corresponding to a change of c si by 5%

Δcs kg/m3

glucose concentration difference corresponding to a change of c si by 5%

Δcsi kg/m3

concentration difference added to c si

εi kg/m3

error at ith sampling interval

μ 1/h

specific growth rate

μm 1/h

maximum specific growth rate

σs kg/m3

standard deviation of monitored glucose concentration

τI h min kg/m3

integral time

τs min

sampling period

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Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • M. Polakovic
    • 1
  • C. F. Mandenius
    • 1
  1. 1.Department of Physics and Measurement Technology, Bioprocess Measurement Technology GroupLinköping Institute of TechnologyLinköpingSweden

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