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Enhanced Ethanol Reactor Operation Through Periodic Forcing of the Feed Rate

  • Research Article - Chemical Engineering
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Abstract

This paper investigates the dynamic performance of bioethanol production process. The process is simulated by an experimentally validated model in the literature. The analysis of the open loop system revealed that the maximum productivity occurred at a moderate ethanol production and substrate consumption. Improvement of the process productivity beyond the maximum value is sought through periodic input forcing. Rectangular pulses were used to simulate the periodic input function because they are suitable for discrete control systems. The parameters of the rectangular pulse such as period, amplitude and central value were designed using numerical optimization. Forcing the optimized cycling input into the process revealed substantial increment of the ethanol production and substrate consumption. However, the obtained enhancement of productivity is considered marginal when compared to the existing maximum productivity. On the other hand, enrichment of productivity is considered reasonable when compared to that obtained when the process operates at steady state using the average value for the input periodic function.

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Abbreviations

D, D i :

Dilution rate and its initial value (1/h)

F :

Flow rate (l/h)

k :

Sampling instant

K 1, K 2 :

Saturation constants (g/l)

k c , k i :

PI controller settings, i.e. gain and gain divided by integral time

k c0 :

Initial value for controller gain

k p , k p0 :

Process gain, initial process gain

m p :

Maintenance factor of ethanol (1/h), 2.6

m s :

Maintenance factor for substrate (1/h)

npa:

Negative pulse amplitude

ppa:

Positive pulse amplitude

P c :

Limiting ethanol concentration for viable cells (g/l)

P′ c :

Limiting ethanol concentration for non-viable cells (g/l)

P r :

Productivity of ethanol (g/l h)

P w :

Pulse width

S, S 0 :

Substrate, feed substrate concentration (g/l)

u :

Input variable

V :

Reactor volume (l)

t :

Time

w i :

Weighting factor in the optimization problem

x :

State vector

X v :

Viable cell concentration (g/l)

X nv :

Non-viable cell concentration (g/l)

X d :

Dead cells (g/l)

Y :

Process output

Y x/p :

Yield coefficient in conversion from biomass to ethanol (–)

Y x/s :

Yield coefficient in conversion from biomass to substrate (–)

μ d :

Growth rate of dead cells (1/h)

μ max :

Maximum growth rate of viable cells (1/h)

μ′ max :

Maximum growth rate of non-viable cells (1/h)

μ nv :

Growth rate for non-viable cells (1/h)

μ V :

Growth rate of dead cells (1/h)

L:

Lower value

U:

Upper value

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Authors and Affiliations

  1. Chemical Engineering Department, King Saud University, PO Box 800, Riyadh, 11421, Saudi Arabia

    Emad Ali, A. Ajbar & K. AlHumaizi

Authors
  1. Emad Ali
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  2. A. Ajbar
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  3. K. AlHumaizi
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Correspondence to Emad Ali.

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Ali, E., Ajbar, A. & AlHumaizi, K. Enhanced Ethanol Reactor Operation Through Periodic Forcing of the Feed Rate. Arab J Sci Eng 38, 741–750 (2013). https://doi.org/10.1007/s13369-012-0526-5

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  • DOI: https://doi.org/10.1007/s13369-012-0526-5

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