Environmental Engineering Reference
In-Depth Information
The process performance is evaluated by means of two different indicators. The
ecological indicator is the
carbon atom efficiency
. This efficiency is the
fraction of carbon atoms in biomass B ending up in product P; carbon left in
the unconverted biomass and in CO
2
is
ε
ðÞ
“
lost
”
:
ε
C
=
w
c
,
P
F
ouðÞ
12
12 + 2
12
P
w
c
,
B
F
iðÞ
with
w
c
,
P
=
1
;
w
c
,
B
=
ðÞ
:
:
12 + 0
6
16 + 1
4
1
B
The
economic performance
is expressed by means of a profit function (
P
). The
profit function is made up of earnings from product sales minus the costs of feed
and wastes and the capital charge (cost of capital investment per unit of time).
There are trade-offs in this design. A higher conversion increases product output
as well as reactor size and cost. The carbon efficiency benefits from a high con-
version. The company for which you design this reactor aims for a better balance
between ecological and economic performances.
The profit per hour is given by
3600
P
=
F
ouðÞ
P
F
iðÞ
B
F
ouðÞ
B
F
ouðÞ
C
cap
,
h
$h
−1
p
P
−
c
B
−
c
W
−
CO
2
c
CO
2
−
in which the capital charge,
C
cap,h
, is given by
C
cap
,
h
=
ccf
t
prod
I
cap
$h
−1
with the capital investment,
I
cap
, given by
q
V
V
0
I
cap
=
I
0
ðÞ
$
Data are given in Table 7.8.
TABLE 7.8 Data for the evaluation of the economic
performance
Value
Price of fuel product,
p
P
($ kg
−1
)
0.500
Price of biomass feed,
p
B
($ kg
−1
)
0.050
Cost of biomass waste,
c
W
($ kg
−1
)
0.010
Cost of CO
2
emissions,
c
CO
2
($ kg
−1
)
0.005
Capital charge factor (annual),
ccf
(−)
0.200
Production hours, t
prod
(hyear
−1
)
8000
Reference investment,
I
0
(M$)
6
Reference capacity (for
X
0
= 0.8),
V
0
,(m
3
)
16.0
Capacity (=volume) scaling factor,
q
(−)
0.600
Validity range of investment correlation (m
3
)
1 ≤
V
≤ 200
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