Environmental Engineering Reference
In-Depth Information
SHORT-ANSWER QUESTIONS
17.1
What are the advantages of liquid transportation fuels based on biomass over
other sustainable energy solutions for transportation purposes?
17.2
Compare the different fuels treated in this chapter: give their advantages and
disadvantages.
17.3
What are the hurdles when trying to make a
“
fair
”
comparison between the
different fuels?
17.4
In multitubular FTS reactors, typically particles of 1 or a few mm are used.
Decreasing the particle size would increase the catalyst effectiveness. For what
reason(s) is the particle size not reduced?
17.5
The reaction equation for Fischer
-
Tropsch synthesis (RX. 17.1) shows that for
longer hydrocarbons, the Fischer
Tropsch reaction needs H
2
/CO in a ratio of
about 2:1. However, in practice, often, a lower syngas ratio is used. What are
the advantages of using a lower syngas ratio? What are the disadvantages?
-
17.6
Compare (RX. 17.1) and (RX. 17.3). What agreement and what difference do
you observe?
17.7
Why is it currently more attractive to convert methanol to olefins (MTO) than
to gasoline (MTG)?
PROBLEMS
17.1
In Example 17.1, we have calculated the reaction rate for Fischer
Tropsch
synthesis as a function of the temperature. Assume a fixed bed reactor in
which the catalyst, with a density of 2500 kg
-
m
−3
, fills 60% of the reactor
volume (porosity is 0.40). The catalyst effectiveness may be assumed to be
1 (note that is a simplification; typically, it is <1 in fixed beds). The reactor
is cooled with cooling water of 465 K. The heat
transfer coefficient
is
K
−1
, and the reactor contains 100 m
2
of heat exchange surface
per m
3
of reactor volume.
m
−2
600 W
a. What is the rate of heat generation per m
3
of reactor volume? Plot this as a
function of the temperature for the range 470
530 K.
b. What is the rate of heat removal of the heat exchange surface at 470, 500,
and 530 K? Plot this for the same temperature range.
c. What do you conclude from comparing the results of a and b?
-
17.2
Suppose the Fischer
Tropsch reactions take place in identical spherical
catalyst particles suspended in a homogeneous fluid phase. The reactants
-
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