Environmental Engineering Reference
In-Depth Information
If a process is built on a site with existing utility and waste processing systems of
sufficient capacity, the generation of an oxygen carrier can be kept outside the
process boundary. However, the costs of using utilities and having the waste
processed show up at the negative side of the process economics. For a process
design on a new (
) site, the generation of utilities specific for this
process must fall within the process boundary.
“
greenfield
”
d.
Analysis
One can set up mass and energy balances over the process input
output dia-
gram, covering all feed, product, and waste streams. From these balances,
one can see what fraction of a property (e.g., atoms, energy) present in the feeds
ends up in the products and what fraction goes to waste. Equation 7.2 presents
balance equations for a general property with an associated efficiency factor per
property. These efficiency factors play a role in the evaluation of a design:
-
Balance equation for property
p
:
n
o
+
X
n
o
X
L
feed
l
=1
φ
X
N
s
N
s
feeð Þ
l
x
feeð Þ
R
generation
ð
Þ
IN
:
:
X
p
,
i
:
X
p
,
i
=
:
l
,
i
i
i
=1
i
=1
n
o
+
X
n
o
X
L
prod
l
=1
φ
X
L
waste
l
=1
φ
X
N
s
N
s
ð Þ
l
prod
x
proð Þ
ð Þ
l
waste
x
wastð Þ
OUT
:
:
:
X
p
,
i
:
:
X
p
,
i
l
,
i
l
,
i
i
=1
i
=1
Feed-to-product efficiency factor
η
for property
p
:
"
#,
X
"
#
n
o
n
o
η
p
=
X
L
prod
l
=1
φ
X
N
s
L
feed
l
=1
φ
X
N
s
proð Þ
l
x
proð Þ
feeð Þ
l
x
feeð Þ
:
:
X
p
,
i
:
:
X
p
,
i
l
,
i
l
,
i
i
=1
i
=1
ð
Eq
:
7
:
2
Þ
ð
feed
=
prod
=
waste
Þ
φ
molar flow rate of a feed
=
product
=
waste stream
l
,
:
l
,
L
feeð Þ
=
proð Þ
=
wastð Þ
l
=1,
…
x
feed
=
prod
=
waste
ð
Þ
molar fraction of species
i
in a feed
=
product
=
waste stream
l
,
:
l
,
i
,
L
feeð Þ
=
proð Þ
=
wastð Þ
l
=1,
…
R
generation
ð
Þ
rate of generation of kmol of species
i
inside process
:
i
X
p
,
i
intensive property
p
of chemical species
i
>0
ðÞ
,
i
=1,
…
,
N
S
:
Species efficiency
X
p
,
i
=1
p
=
m
, kmol per kmol of species
i
ð
Þ
:
Atomefficiency
X
p
,
i
=
n
E
,
i
p
=
E
, number of atoms of element
ð
E
per molecule of species
i
:
Þ
X
p
,
i
=
h
i
Enthalpy efficiency
ð
i
at reference conditions
p
=
h
, enthalpy per kmol of species
:
Þ
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