Environmental Engineering Reference
In-Depth Information
Problem 5.6
The collection efficiency
η
of particles in an electrostatic precipitator is given by the Deutsch
equation
η
=
1
−
exp
(
−
A
w/
Q
)
w
=
where
A
is the area of collection plates,
is the drift velocity (
0.05
d
p
m/s, where
d
p
is the
µ
particle diameter in
m), and
Q
is the volumetric flow rate. (a) Calculate the collection efficiency
for
d
p
=
500 m
2
and
Q
from Problem 5.3. Tabulate and plot
these results. (b) Calculate the plate area necessary for 99% removal efficiency of 1-
0
.
1, 0.3, 1, and 3
µ
m, using
A
=
75
,
µ
m-diameter
particles.
Problem 5.7
The plant with the parameters given in Problem 5.1 has an electrostatic precipitator with the removal
efficiencies and weight distribution in the given size ranges (shown in Table P5.7). Determine the
rate of fly-ash emission (g/s).
TABLE P5.7
Particle size,
µ
m
0-5
5-10
10-20
20-40
≥
40
Removal efficiency, %
70
92.5
96
99
100
Weight, %
14
17
21
23
25
Problem 5.8
A
coal
has
a
heating
value
of
12,000
Btu/lb
and
the
following
molecular
composition:
C
100
H
100
S
1
N
0
.
5
. It is burnt in air, without excess oxygen.
(a) Calculate the emission rate of SO
2
and NO
2
in lb/MBtu. Once more assume that the total
emission rate of NO
2
is twice the emission rate of fuel NO
2
. Compare this with the 1970
U.S. emission standards for large coal-fired boilers.
(b) Calculate the mole fraction and volume fraction (ppmV) of SO
2
and NO
2
in the flue gas.
Problem 5.9
The flue gas of the plant in Problem 5.8 is to be treated with flue gas desulfurization (FGD) using a
limestone (CaCO
3
) wet scrubber to remove the SO
2
. Assume that 2 moles of CaCO
3
are necessary
for every mole of SO
2
. How much limestone is consumed per ton of coal?
Problem 5.10
The flue gas of the plant in Problem 5.8 is to be treated with flue gas denitrification (FGN) using
urea (CO(NH
2
)
2
) injection directly into the boiler. Assume that a molar ratio NO
2
:CO(NH
2
)
2
=
1:1
is necessary. How much urea is consumed per ton of coal?
