PROCESSES: BASICS OF PROCESS DESIGN - Biomass as a Sustainable Energy Source for the Future - page 226

impact on the economic and ecological performance indicators. Give a list of
these design variables and explain why these have a high impact on the eco-
nomic performance indicators.

7.6 Explain the differences between the hierarchical design levels and the generic
engineering design steps in the Conceptual Design Matrix.
How will the specification of a reactor product yield at the process network
level set targets for design at the process unit (i.e., reactor equipment) level?

PROBLEMS

7.1 Pareto Trade-Off between Economy and Ecology in Design
Biomass (B) is converted to a hydrocarbon fuel product (P) and carbon dioxide
(CO 2 ) in a well-mixed continuous-flow reactor, operating at steady state. The nom-
inal chemical composition of B = [

] n .The
corresponding mass-based reaction stoichiometry is (in close approximation)

− C 1 O 0.6 H 1.4 − ] n and that of P = [ − C 1 H 2 −

s −1

k

575 kgCO 2 with k = 10 −3 1kgB ! 0 : 425 kg P + 0 :

This reaction is the first order in the biomass amount; the symbol k represents
the associated first-order reaction rate coefficient. The biomass is only partially
converted as full conversion would require a reactor of infinite size and cost. The
degree of conversion of the biomass ( X ) is defined as

X = F iðÞ

F ouðÞ
B
F iðÞ
B

−

B

with 0 ≤ X <1

The biomass intake rate ( F iðÞ
B

) and the volume flow ( φ V ) are kept constant:

;

F iðÞ
B

s −1 0×10 −3 m 3 s −1

=1 kg φ V =4 :

The degree of conversion is an independent design variable. The dependent
process variables are

F ouðÞ
B

F iðÞ
B

s −1

Outflowof B kg ð Þ : =1 ð Þ − X

F ouð P =0 425 XF iðÞ

B

s −1

Outflowof P kg ð Þ : :

F ouðÞ 575 XF iðÞ

B

Outflowof CO 2 kg ð s −1 Þ :

CO 2 =0

:

V R = φ V X
k 1

Reactor volume m 3

ðÞ :

ð Þ − X