Environmental Engineering Reference
In-Depth Information
which the product is pumped through a duct of 10 cm diameter with a mass
flow rate of 25 t
h
−1
. The temperature at the pump suction side is 20
C. At this
temperature, the vapor pressure is 5.7 × 10
3
Pa. The density of ethanol is 789
kg
m
−3
. What is the background of cavitation? Does it occur in this situation?
Which assumption(s) have you made? When will there be a possibility for this
phenomenon to occur?
3.4
Present the time-dependent mass balance of a boiler drum in a steam
power plant.
s
−1
at 60 bar.
This stream still contains 2 wt% moisture. The feedwater from the economizer
(a heat exchanger) is fed to the drum at a mass flow rate of 62 kg
3.5
A steam boiler drum produces steam at a mass flow rate of 64 kg
s
−1
. It contains
3 ppm
w
solids. Makeup water, containing 50 ppm
w
solids, is also fed into the
drum at a mass flow rate of 2 kg
s
−1
. Steam production is such that the solid
content of the moisture leaving with the steam is 5 ppm
w
. Blowdown, which
is the release of hot liquid from the bottom of the drum, must keep the concen-
tration of solids in the drum to 1000 ppm
w
.
s
−1
.
b. Calculate the heat loss associated with blowdown in kW.
a. Calculate the blowdown requirement in kg
3.6
A steam boiler has a horizontal 1.5 m (inside diameter) drum that is 6.2 m long.
The normal water level is at the midplane. If the water level falls more than
30 cm below this point, serious dry running of some downcomers will be
the result. When the steaming rate is 12 kg
s
−1
and the pressure is 40 bar,
how long an interruption in the feedwater supply could be allowed?
3.7
A massive wood block with a mass of 1 kg falls from 15 m height in a proces-
sing building with an initial temperature of 20
C; it doesn
t jump up after
touching the ground. What is the end temperature when the heat capacity
can be considered to be constant: c
p
= 1000 J
'
kg
−1
K
−1
?
3.8
Power company
in the Netherlands operates a fluidized bed combus-
tion-based boiler with wood residues as fuel. The plant contains a simple
steam turbine. The steam conditions at the inlet of the turbine are 525
C
and 100 bar. Assume that condensation of the steam takes place at a
temperature of 20
C and that isentropic expansion of steam occurs in the
turbine.
“
E
”
kg
−1
) of the turbine expansion process?
b. If the power plant generates 25 MW
e
and water pump work can be
neglected, what is the mass flow rate of steam through the turbine?
c. What assumptions have you made for these calculations?
a. What is the specific power (kJ
Biomass chips from a hopper system are fed vertically (90
angle) onto a mov-
ing conveyer belt. The mass flow of the chips is 24 t
3.9
h
−1
. At the end of the belt,
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