Page 103 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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surface area, and gas- and liquid-side controlled mass transfer coefficients is
presented in Fig. 2.
The gas (air) from the ventilator (1) is measured by the diaphragm (2),
connected to the differential manometer (4). The gas enters the column (7)
through the gas distributor (6), The air is mixed at about 3 m before the
diaphragm with the absorbed gas. In case of measurement of the effective
surface area, the gas (CO2) is coming from the gasholder (31) connected to the
water tank (30). The flow rate of the absorbed gas is measured by the rotameter
(29) and is regulated by the valve (28), respectively (33). The absorbed CO2 is
fed from gas bottles (27) to the gasholders (31). To prevent formation of ice in
the rotameter (29) the gas is heated preliminarily by means of a regulated
electrical heater (37). The device (32) is used to keep the pressure in the
gasholder constant. In case of investigation of gas-side controlled mass transfer
the absorbed gas, SO2 or NH3 is fed from the gas bottles (27) (filled with the
respective gas) through the valve (33).
There are two principle types of possibilities to prepare the absorbent,
respectively the saturated liquid, in case of investigation of desorption. The first
of them is to prepare it in a large tank in quantity enough for a given
experiment, as it is made in the installation presented in Fig. 1. Because in some
cases the liquid superficial velocity is very great, the volume of the tank has to
be very great too. To avoid throwing out of a large amount of polluted water
and mounting of very big tanks in the installation presented in Fig. 2, it is
accepted to recireulate the absorbent, eventually adding concentrated solution,
to maintain the concentration within the necessary limits. The disadvantage of
this method is that in some cases more analyses of the initial concentration of
the liquid phase are necessary. Its great additional advantage is that the liquid
flow rate is not changing because the quantity of the liquid in the tank is kept
constant. That is why it is easier and cheaper to work with recirculation.
The absorbent is pumped (22) from the column bottom towards the
liquid phase distributor (8) through the valves (19) and rotameters (18) and
irrigates the packing.
The temperatures of the two phases at the apparatus inlet and outlet are
measured with ordinary thermometers (t) having a precision of 0.1°C.
There are 3 points for taking samples from the liquid phase for analysis
(AL) and 2 points for the gas phase (A©).
The level of the liquid phase at the column bottom is observed through
a Plexiglas tube (12).