Handbook of Solvents - George Wypych - ChemTech - Ventech!

1522 Klaus-Dirk Henning
Regeneration step Basic principle Typical application
Steam desorption
Hot air desorption
Hot inert gas desorption
Pressure swing adsorption/vacuumregeneration
Reduced pressure and
low temperature steam
desorption
Increasing the bed temperature by direct
steaming and desorption of solvent. The
steam is condensed and solvent recovered.
Rotor adsorber are often desorbed by hot
air
Desorption by means of an hot inert gas
recirculation. Solvent recovery can be
achieved with refrigerated condenser
Atmospheric pressure adsorption and
heatless vacuum regeneration.
The revaporized and desorbed vapor is
transported from the adsorption bed via a
vacuum pump.
Steam desorption at low temperature and
reduced pressure.
Most widely used regeneration technique
for solvent recovery plants.
Concentration range from 1-50 g/m 3
Concentration by adsorption and incineration
of the high calorific value desorbate
Recovery of partly or completely water
soluble solvents.
Recovery of reactive solvents (ketones)
or solvents which react with hot steam
(chlorinated hydrocarbons)
Low-boiling and medium-boiling hydrocarbon
vapor mixes from highly concentrated
tank venting or displacement gases
in large tank farms.
Recovery of monomers in the polymer industry.
Recovery of reactive solvents of the
ketone-type.
Minimizing of side-reactions like oxidizing,
decomposing or polymerizing.
22.1.4.2.4 Safety requirements
Adsorption systems including all the auxiliary and ancillary equipment needed for their operation
are subject to the applicable safety legislation and the safety requirements of the
trade associations and have to be operated in accordance with the respective regulations. 2,19
Moreover, the manufacturer’s instructions have to be observed to minimize safety
risks. Activated carbon or its impurities catalyze the decomposition of some organics, such
as ketones, aldehydes and esters. These exothermic decomposition reactions 25,26 can generate
localized hot spots and/or bed fires within an adsorber if the heat is allowed to build up.
These hazards will crop up if the flow is low and the inlet concentrations are high, or if an
adsorber is left dormant without being completely regenerated. To reduce the hazard of bed
fires, the following procedures are usually recommended:
• Adsorption of readily oxidizing solvents (e.g., cyclohexanone) require increased
safety precautions. Instrumentation, including alarms, should be installed to
monitor the temperature change across the adsorber bed and the outlet CO/CO2 concentrations. The instrumentation should signal the first signs of decomposition,
so that any acceleration leading to a bed fire can be forestalled. Design parameters
should be set so as to avoid high inlet concentrations and low flow. A minimum gas
velocity of approximately 0.2 m/s should be maintained in the fixed-bed adsorber at
all times to ensure proper heat dissipation.
• A virgin bed should be steamed before the first adsorption cycle. Residual
condensate will remove heat.