Question

Chemical engineering question: an evaporation process has a goal of producing a syrup product (c) with 480 water to 100 sugar ratio. the feed is a dilute solution containing 20.7% sugar. if the total evaporate amounts to 2 tons of water,

a) draw the process diagram

b) what is the weight (tons) of the beginning feed and

c) how much syrup product (tons) was produced?

Answer 1

(a) Let the feed stream be represented by F, the steam evaporate be represented by E and the concentrated sugar syrup be by C. The block flow diagram for the process is:

(b) Let the mass and the weight fractions of sugar in the streams F, E and C be , , and , , respectively, i.e. m represents the mass and x be the concentrations. The mass is represented in tons.

It is given that there are 480 parts of water for 100 parts of sugar. Thus,

Concentration of syrup:

and the concentration of the feed is 20.7% that is 0.207 weight fraction.

It is not possible that with water being evaporated, the concentration of sugar in the product decreases. Hence there is an error in the problem statement and it must read as: 480 sugar to 100 water. Thus, the CORRECT concentration of the syrup is:

which seems logically more justified.

Also, it is given,

Feed concentration

Evaporate mass tons

And sugar, being non-volatile would not evaporate, and hence

Write the equations for overall mass balance and sugar component balance.

Overall Material Balance:                     -(1)

Sugar component balance:                 -(2)

Unknowns:

From (1), substitute in (2) with the given values. equation (2) becomes:

and substituting in equation (1),

Thus,

ANSWER (b): 2.6671 tons of dilute solution is being fed

ANSWER (c): 0.6671 tons of syrup product was formed

This answer was solved based on the logic presumption, and identifying the error in the question, since product cannot be less concentrated than the feed. In case the value for the product concentration is not exchanged and is some other value, appropriate change can be made in and the problem solution remains exactly same. Kindly let me know via comments if this is the case.

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