Page 64 - Chemical Process Equipment - Selection and Design

36 APPENDIX 2.1
another water cooler, then another “flomix“ (leaving at 150”F), and ethane as an impurity. It is throttled to 50psig and recycled to the
then through a centrifuge and into the sulfonic acid surge tank. reactor. In two subsequent towers, ethylene is separated from light
Fresh water is also fed to each of the ‘‘flomixers.” Wash acid is and heavy impurities. Those separations may be taken as complete.
rejected by the centrifuge and is sent to the sulfuric acid system. Construct a flow diagram of this plant. Show such auxiliary
The “flomix” is a small vertical vessel which has two compartments equipment as drums, heat exchangers, pumps, and compressors.
and an agitator with a separate impeller for each compartment. Show operating conditions and flow quantities where calculable with
the given data.
NEUTRALIZATION
9. TALL OIL DISTILLATION
Neutralization of the sulfonic acid and building up with sodium
sulfate and tetrasodium pyrophosphate (TSPP) is accomplished in Tall oil is a byproduct obtained from the manufacture of paper pulp
two batch reactors (5 hr cycle) operated alternately. The sodium from pine trees. It is separated by vacuum distiaation (50mmHg)
sulfate is pumped in solution with its transfer pump from the in the presence of steam into four primary products. In the order of
sodium sulfate system (which can be represented by a block). The decreasing volatility these are unsaponifiables (US), fatty acid (FA),
TSPP is supplied as a solid and is fed by means of a Redler rosin acids (RA), and pitch (P). Heat exchangers and reboilers are
conveyor which discharges into a weigh hopper running on a track heated with Dowtherm condensing vapors. Some coolers operate
above the two reactors. Each reactor is agitated with a propeller with water and others generate steam. Live steam is charged to the
and a turbine blade in a single shaft. inlet of every reboiler along with the process material. Trays are
Sodium hydroxide of 50% and 1% concentrations is used for numbered from the bottom of each tower.
neutralization. The 50% solution discharges by gravity into the Tall oil is pumped from storage through a preheater onto tray
reactor; the 1% solution is injected gradually into the suction side 10 of the pitch stripper T-1. Liquid is withdrawn from tray 7 and
of the reactor slurry circulating pump. As the caustic is added to the pumped through a reboiler where partial vaporization occurs in the
reactor, the contents are recirculated through a water-cooled presence of steam. The bottom 6 trays are smaller in diameter and
external heat exchanger (exit at 160°F), which is common to both serve as stripping trays. Steam is fed below tray 1. Pitch is pumped
reactors. When the reaction is completed in one vessel, the product from the bottom through steam generator and to storage. Overhead
is fed gradually by means of a slurry transfer pump to two double vapors are condensed in two units E-1 and E-2. From the
drum dryers which are steam-heated and are supplied with accumulator, condensate is pumped partly as reflux to tray 15 and
individual vapor hoods. The dry material is carried away from the partly through condenser E-1 where it is preheated on its way as
dryers on a belt conveyor and is taken to a flaker equipped with an feed to the next tower T-2. Steam is not condensed in E-2. It flows
air classifier. The fines are returned to the trough between the dryer from the accumulator to a barometric condenser that is connected
drums. From the classifier, the material is taken with another belt to a steam jet ejector.
conveyor to four storage bins. These storage bins in turn discharge Feed enters T-2 at tray 5. There is a pump-through reboiler.
onto a belt feeder which discharges into drums which are weighed Another pump withdraws material from the bottom and sends it to
automatically on a live portion of a roller conveyor. The roller tower T-3. Liquid is pumped from tray 18 thrbugh a cooler and
conveyor takes the drums to storage and shipping. returned in part to the top tray 20 for temperature and reflux
Notes: All water cooled exchangers operate with water in at control. A portion of this pumparound is withdrawn after cooling as
75°F and out at 100°F. All pumps are centrifugal except the complex unsaps product. Steam leaves the top of the tower and is condensed
transfer, and the sulfonation reactor feed, which are both piston in the barometric.
type; the neutralization reactor recirculation pump and the transfer Tray 5 of T-3 is the feed position. This tower has two reboilers.
pumps are gear pumps. One of them is a pumparound from the bottom, and the other is
Show all storage tanks mentioned in the text. gravity feed from the bottom tray. Another pump withdraws
material from the bottom, and then sends it through a steam
8. NATURAL GAS ABSORPTION generator and to storage as rosin acid product. A slop cut is
withdrawn from tray 20 and pumped through a cooler to storage.
A gas mixture has the composition by volume: Fatty acid product is pumped from tray 40 through a cooler to
storage. Another stream is pumped around from tray 48 to the top
Component N* CH, C2He C,H, tray 50 through a cooler. A portion of the cooled pumparound is
Mol fraction 0.05 0.65 0.20 0.10
sent to storage as another unsaps product. A portion of the
overhead steam proceeds to the barometric condenser. The rest of
It is fed to an absorber where 75% of the propane is recovered. The
total amount absorbed is 50mol/hr. The absorber has four it is boosted in pressure with high pressure steam in a jet
theoretical plates and operates at 135psig and 100°F. All of the compressor. The boosted steam is fed to the inlets of the two
absorbed material is recovered in a steam stripper that has a large reboilers associated with T-3 and also directly into the column
number of plates and operates at 25 psig and 230°F. below the bottom tray.
Water is condensed out of the stripped gas at 100°F. After The vapors leaving the primary barometric condenser proceed
compression to 50 psig, that gas is combined with a recycle stream. to a steam ejector that is followed by another barometric. Pressures
at the tops of the towers are maintained at 50mmHg absolute.
The mixture is diluted with an equal volume of steam and charged Pressure drop is 2mmHg per tray. Bottom temperatures of the
to a reactor where pyrolysis of the propane occurs at a temperature
of 1300°F. For present purposes the reaction may be assumed to be three towers are 450, 500, and 540”F, respectively. Tower overhead
simply C3H8+ &H4 + CH, with a specific rate k = 0.28/sec. temperatures are 200°F. Pitch and rosin go to storage at 350°F and
Conversion of propane is 60%. Pressure drop in the reactor is the other products at 125°F. The steam generated in the pitch and
20 psi. rosin coolers is at 20 psig. Process steam is at 150 psig.
Reactor effluent is cooled to remove the steam, compressed to
285 psig, passed through an activated alumina drying system to 10. RECOVERY OF ISOPRENE
remove further amounts of water, and then fed to the first Draw carefully a flowsheet for the recovery of isoprene from a
fractionator. In that vessel, 95% of the unconverted propane is mixture of C, hydrocarbons by extractive distillation with aqueous
recovered as a bottoms product. This stream also contains 3% acetonitrile according to the following description.