PROCESSES WITH RECYCLE - Teach Yourself the Basics of Aspen Plus - page 53

TABLE 4.1 Process Performance Data
Fraction of Feed to Bottoms

Fraction of Feed
to Organic Phase:

Component Column 1 Column 2 Decanter

Ethanol 0.01 0.97 0.98

Water 0.97 0.0001 0.01

Cyclohexane 0.09 0.0001 0.99

Workshop 4.2 Increase the number of Wegstein iterations to 100. Reinitialize the
problem, and solve. What do you observe?

Workshop 4.3 Select C and F as the recycle streams. Provide initial values and
reinitialize.

a. Solve using Wegstein's method. What do you observe?
b. Solve using Newton's method. What do you observe?

Workshop 4.4 Figure 4.6 shows a continuous process for the recovery of solvents
from a mixture that includes a soluble solid. Upon concentration, the solid precipitates
and can be removed by filtration. You are to perform preliminary calculations without
energy balances using the process description given below.
The primary feed to the process, FD1, is composed of 100 lb/hr of ethanol (ETOH),
750 lb/hr of water (WATER), 100 lb/hr of toluene (TOL), and 50 lb/hr of soluble
solids (SOLIDS) at 14.696 psi. FD1 is sent to a column (CRUDSTL) along with a
second feed, FD2, composed of 250 lb/hr of saturated steam ( H 2 O ) at 30 psig. The still
produces two products: SOLVNTS and CRSOLIDS. 95% of the ethanol fed, 99% of
the toluene fed, and 50% of the water fed end up in the stream SOLVNTS, and all of
the solids end up in the stream CRSOLIDS. All of the solids in this stream precipitate
out of solution.
The stream CRSOLIDS is the feed to a filter that produces two streams: AQSLVNT
and SOLIDS. All of the solids fed, 1.0% of the ethanol fed, 1.0% of the toluene fed,
and 0.5% of the water fed end up in the stream SOLIDS.
The stream SOLVNTS is fed to a column (TOLSTILL) whose role is to sepa-
rate ethanol and toluene. The overheads (CRUDETOH) from this still are a stream
that is primarily ethanol and water which is purified in the azeotropic distillation
columns ESTILLHI and ESTILLLO. The bottoms (CRUDTOL) are sent to a decanter
(DECANT). The performance characteristics of TOLSTILL are as follows: 25% of the
ethanol fed, 45% of the water fed, and 99% of the toluene fed end up in the stream
CRUDTOL.
The decanter (DECANT) produces a relatively pure toluene product (TOL) and an
aqueous product (AQTOL), which is recycled to the column TOLSTILL. The perfor-
mance characteristics of the decanter are as follows: 50% of the ethanol fed, 99.9% of
the water fed, and 0.1% of the toluene fed end up in the stream AQTOL.
The stream CRUDETOH feeds the column ESTILLHI. The column produces two
products: ETAZH, whose composition is to be 88 mol % ethanol, and ETAQ, whose