Environmental Engineering Reference
In-Depth Information
the chips are discharged. The drive wheels have a diameter of 80 cm, and they
rotate (clockwise) with a rate of 150 revolutions per minute. Friction forces as
well as air drag on the particles can be neglected. Calculate the driving power of
this belt.
3.10
Bio-oil flows through a duct with a radius of 2.5 cm at ambient temperature
with a velocity (v
1
)of10m
s
−1
; the duct is followed by a permeable wall
part with suction. At the end of this section (with the same radius), the
velocity (v
2
) has dropped to 8 m
s
−1
.If
p
1
= 140 kPa, estimate
p
2
for the case
that wall friction is negligible. What happens to
p
2
in the case of significant
friction?
3.11
An anaerobic digester (see Chapter 14 for this technology) produces biogas at
1.1 bar (absolute) and 25
C. This gas, composed of 60 vol.% CH
4
and 40 vol.
%CO
2
, is to be compressed to 25 bar (absolute) before delivery to its end use;
assume the compression to be isentropic and reversible. Calculate the temper-
ature after compression.
3.12
Dimethyl ether (DME) is combusted in a closed cylinder with 5 mol% excess
air. Assume the cylinder volume to remain constant during the (explosive)
combustion process. If no heat is exchanged with the environment, what is
the end temperature and pressure in the cylinder when the initial pressure is
1 atm. and the initial temperature is 25
C?
3.13
The enthalpy of formation of a bio-oil with the empirical composition formula
of CH
2.3
O
0.9
is estimated to be
mol
−1
at 20
C and 1 bar. Researchers
intend to convert this gas with a plasma torch into synthesis gas via the
reaction:
−
183.7 kJ
CH
2
:
3
O
0
:
9
+0
:
3H
2
Ol
ðÞ!
CO+ 1
:
25H
2
+0
:
2H
2
Og
ðÞ
What is the reaction enthalpy at 1100 K and 1 bar?
3.14
Determine the adiabatic, stoichiometric flame temperature at constant
pressure for n-butanol, an alternative biofuel, given that at standard conditions
(25 C, 1 atm) the enthalpy of combustion is
mol
−1
.
−
2670 kJ
PROJECTS
P3.1
Visit a local power plant that processes biomass or coal, identify the key
characteristics of this plant, and set up overall mass and energy balances for
the plant.
P3.2
Test the mechanical drying of biomass using a roller press (either manually or
electrically driven) of Example 8.1 (Chapter 8) yourself. Measure inlet and
outlet temperature accurately using, e.g., a K-type thermocouple.
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