Ex ¼ Ex
ph
þ Ex
ch
ð2Þ
Physical exergy is defined as:
Ex
ph
¼
X
i
n i ex
ph
i
ð3Þ
ex
ph
i ¼ h j À h o
À
Á À T o s j À s o
À
Á
ð4Þ
The differences h j À h o
À
Á
and s j À s o
À
Á
can be calculated from Eqs. 5 and 6:
h j À h o
À
Á ¼
Z
T j
T o
CpdT
ð5Þ
s j À s o
À
Á ¼
Z
T j
T o
Cp
T
dT À RLn
P
P o
ð6Þ
The chemical exergy is calculated to take into account the standard exergy of
each component (ex
ch
i )
Ex
ch
¼
X
i
n i ex
ch
i þ RT o Ln
n i
P
n i
ð7Þ
For the equipment which presents the need to supply power from an external
source, it considered another source of exergy to analyze. This is calculated by
Eq. 8.
Ex ¼
Z
T 2
T 1
1 À
T o
T
dQ
ð8Þ
7 Study Case: Biodiesel from Microalgae: Chlorella
Protothecoides Case
7.1 Process Design
7.1.1 Culture of Microalgae
In this work, it was considered a feed flow of 100,000 kg/h as calculation basis. The
microalgae culture was considered (for simulation purpose) using the conditions
reported by Yoo et al. (2014). The substrate employed was glucose at a
190
D. L. Restrepo-Serna et al.