Process Description
The process is a continuous solvent recovery process. The
equipment consists of Rectification Towers and a Heat Exchanger
Group which is used for pre heating of the inlet low concentration
acid and the cooling of the take-off acid and the vapour from
the top of the tower (containing 0.2% nitric acid)
Three towers are installed in parallel and operate on a pressure/vacuum
system. Any combination of one, two, or three towers can be
operated at any one time. The normal operation has been two
in operation and one spare.
The in feed is at the middle of the tower. The product is drawn
out in a vapour state from the tower bottom, and indirect heating
is applied by high-pressure steam (15 bar) into a reboiler.
The vapour from the top of the tower is condensed fed into a
distributor and re-circulated to the tower top at a specified
reflux ratio. The excess is discharged to waste.
The inlet acid is at 10°C and is preheated through a heat exchanger
with the take - off acid to 50°C again it goes to a second preheating
this time exchanging with steam condensate to 110°C and is fed
to the tower in a partially vaporized state.
The take-off acid from the bottom of the tower is in a vaporized
state passes through a mist separator exchanger heat with industrial
water in a condenser and is converted to liquid at 120°C, exchanges
heat with the incoming acid and is cooled to 40°C and is stored.
Because of the particular manufacturing process of acrylic fiber
the feed in acid contains organic polymer of low molecular weight
and various salts used as catalyst. A continuous bleed off this
residue takes place to a storage tank and is treated in a separate
process to recover the acid content and discharge the solids.
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