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104 3. Heterogeneous Processes and Reactor Analysis

3.4.3 Slurry bubble column reactors

vironmen- Slurry bubble column reactors hae many applications in both industrial and en v
xample,
tal processes. For e they are used in the Fischer–Tropsch synthesis in industry or ,
aste
w in water treatment. The most important applications of these reactors are presented
in Table 3.8 (Shah et al. , 1982).
Typical operating conditions of these reactors are
• Length-to-diameter column in the range 2–30
• Diameter of solid particles belo w 50 m
• Operation temperatures in the range 20 °C—300 °C
• Operation pressures in the range 1–200 atm
• Gas velocities lower than 50 cm/s and much higher than the liquid v . elocity

3.4.4 Modelling of slurry bubble column reactors

In the common case, in slurry bubble column reactors, the catalyst phase remains in the
reactor while the liquid phase could remain in the reactor with a continuous flow of gas
(semibatch operation). Both gas and liquid could be in plug flow or could be well mix ed.
Regardless of the arrangement, the modeling procedure is to write mass balance equa-
tions for all reactants, for all reactions. If reactants exist in both gas and liquid phase, sep-
arate conservation equations are necessary for each phase. By using the global rate, model
equations will be expressed in terms of bulk concentrations, and thus the solution gives the
v
olume,
relation between the conersion of reactants and reactor v analogous to the results
for single-phase reaction systems (Smith, 1981).
Before analyzing the several forms of the material balances, the concept of limiting reac-
tant will be presented first as the sizing of the reactor is normally based on this reactant.
Limiting reactant in three-phase reacting systems
As it has been already mentioned, the limiting reactant is the reactant that will run out
first during the reaction, i.e. the reactant whose quantity is less than the one def ined by the

Table 3.8

The most important applications of slurry bubble column reactors
Industrial applications Environmental applications
action Coal liquef Adsorption of SO in an aqueous slurry of
2
magnesium oxide and calcium carbonate
Fischer–Tropsch synthesis SO or remoal from tail gas v
2
Synthesis of methanol Wet oxidation of waste sludge
Hydrogenation of oils Catalytic desulfurization of petroleum fractions
Alkylation of methanol and benzene Wastewater treatment
ins Polymerization of olef
Hydrogenation of coal oils, heavy oil fractions,
and unsaturated fatty acids