Environmental Engineering Reference
In-Depth Information
10.15
In a BFB gasifier, biomass fuel can be fed from the top or from the bottom part
(in-bed feeding); what are the implications of these different ways of feeding
for the gas composition?
10.16
Inwhichway are reaction and separation combined in the gasifiers dealt with in
this chapter? Can you think of further intensifications of these functions?
10.17
Explain the role of NaOH (aq.) addition in the SCW gasification process.
10.18
Which problems do you foresee when applying SCW gasification with
seaweed (macroalgae) as feedstock?
10.19
Which oxidizer(s) could be used to
in situ
generate heat in SCW gasification?
10.20
Name a few advantages and disadvantages of gas cleaning at high temperature
versus low (near ambient) temperature.
10.21
Often, a (multi)cyclone is positioned before a filter. Mention one advantage
and one disadvantage of such a particle cleaning constellation.
10.22
Identify a few compounds in the product gas of the fluidized bed gasifier that
are not shown in the gas composition of Example 10.1.
PROBLEMS
10.1
Repeat the chemical equilibrium calculation using a Gibbs energy minimiza-
tion routine for the case of dry biomass gasification (CH
1.4
O
0.6
) at 1300
C and
2.0 MPa. What are the main differences with the results obtained at 850
C (see-
Figs. 10.2 and 10.3)?
10.2
Have a look at Table 10.6. Perform chemical equilibrium calculations for the
given feedstock and process conditions. Which of the given compositions
approaches the obtained results better?
10.3
For Example 10.1, verify the elemental balances for C, H, and O. Do they close
to a reasonable extent?
10.4
Consider a perfectly stirred reactor to be used for dry wood gasification. The
composition of wood is given as overall molecular formula: CH
1.4
O
0.6
. The
reactor volume (V) is 4 m
3
, and the mass flow rate of wood is 2 kg
h
−1
. Primary
air consists of 23 wt% O
2
and is fed to the gasifier with a mass flow rate
ϕ
m,air.
Oxygen in the air reacts with biomass in an idealized way so as to form only CO
and H
2
. The reaction is given as CH
1
:
4
O
0
:
6
+
j
v
1
j
O
2
!
v
2
CO+ v
3
H
2
with
ν
i
being the stoichiometric coefficients. The rate of consumption of O
2
,
R
O2,1
, in [kmol
m
−3
s
−1
] is given by
R
O2,1
=k
1
Y
O2
exp(
−
T
a1
/T),
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