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Encyclopedia of Physical Science and Technology EN014A-654 July 28, 2001 16:35

38 Reactors in Process Engineering

A. Autoclave C. Bubble Column
1. Description 1. Description
The autoclave reactor is a small cylindrical reactor, built The bubble column is a tower containing primarily liquid
to withstand high pressures, used to evaluate the kinet- (>90%) that has a gas or a lighter liquid sparged into the
ics of high-temperature, high-pressure reactions and the bottom, allowing bubbles to rise through the column. The
production of small quantities of specialty chemicals. column may contain staging, which enhances the mass
The reactor is typically packed with a supported catalyst, transfer characteristics of the reactor. In countercurrent
and reactant is added by injection. Pressure in the system operation the reactor is particularly attractive for slightly
is elevated by increasing the temperature of the autoclave. soluble gases and liquid–liquid systems. With cocurrent
Additional pressure, if needed, can be obtained with the flow and a highly baffled column, the reactor has mass
injection of additional gaseous reactant or an inert. transfer characteristics similar to those of a static mixer.
The reactor may sometimes contain a solid suspended in
2. Classification the liquid phase.
The autoclave is usually a heterogeneous batch reactor
mainly used for high-pressure kinetic studies. The au- 2. Classification
toclave is typically a solid catalyzed gas–liquid reaction The bubble column is a typical gas–liquid heterogeneous
system. reactor with the design also applicable to liquid–liquid
systems. The bubbles rise through the liquid in plug flow.
3. Applications
The liquid is well mixed by the bubbling gas and seldom
This reactor allows easy data collection for high- follows plug flow assumptions.
temperature, high-pressure reaction systems that have dif-
ficult flow properties. This includes reactants that are solid 3. Applications
at room temperature or mixtures of solids and liquids. Typ-
The bubble column can withstand high gas velocities and
ical reactions performed in autoclaves are coal liquefac-
still maintain high mass transfer coefficients. This column
tion, petroleum residuals and coal liquids upgrading, and
is particularly attractive for reactions that do not require
high molecular weight hydrogenation experiments.
large amounts of gas absorption or require well-mixed
liquids.
B. Blast Furnace There are numerous applications for bubble columns,
1. Description for example, gas–liquid columns include the absorption
of isobutylene in sulfuric acid, and liquid–liquid columns
The blast furnace, a vertical shaft kiln, is the oldest in- are used for nitration of aromatic hydrocarbons.
dustrial furnace. Reactant enters in the top of the shaft
and falls down through a preheating section, a calcinating
D. Chemostat–Turbidostat
section, past oil, gas, or pulverized coal burners, through
a cooling section, with the product ash falling through a 1. Description
discharge gate.
The chemostat is a biological CSTR where the substrate
concentration in the tank is maintained constant. The tur-
2. Classification
bidostat is similar to the chemostat except that the cell
The blast furnace operates continuously although the in- mass in the reactor is kept constant. The primary distinc-
dividual particles see a batch mode of reaction. The actual tion between the two reactors is the control mechanism
reaction conditions must be based on the batch reactor used to maintain continuous operation. A unique feature
sequence for the particles since complete conversion is of a biological CSTR is the washout point. When the flow
desired. This requires control of the mass throughput in rate is increased so that the microbes can no longer repro-
the furnace, but primarily it requires accurate temperature duce fast enough to maintain a population, the microbes
control. Control of the solids is maintained at the bottom wash out of the tank, and the reaction ceases. This washout
discharge port. Gas flow rate is controlled by blowers or point represents the limits of maximum flow rate for
by a stack discharge fan. operation.

3. Applications 2. Classification
Blast furnaces are used for the production of iron from ore The chemostat is a biological heterogeneous CSTR. The
and phosphorus from phosphate rock. microbes are considered a solid phase, and for aerobic