Chemical Engineering Question Help
Homework Assignment 3
Reading: F&R Chapter 4.4 and 4.5
1. In studio this week, we examined the batch crystallization. Let’s take a look at an analogous process that is performed continuously to produce large quantities of the crystalline product. The figure below depicts a continuous crystallization process for the production of solid sodium bicarbonate (NaHCO3) (baking soda). 8000 kg/h of an 8.00 wt% solution of NaHCO3 is combined with the recycle stream from the crystallizer and fed to an evaporator where water is removed to produce a 14.0 wt% solution. The resulting NaHCO3 solution is fed to the crystallizer where a solid cake is separated from the remaining solution (filtrate). The resulting cake is 95% NaHCO3 crystals and 5% solution (water + NaHCO3) and the filtrate consists of 10.0 wt% NaHCO3.
Crystallizer and Filter
a) Redraw and completely label the process diagram including values and units for the known quantities and assigning variables to the unknown quantities.
b) Perform a degree of freedom analysis on each of the following subsystems: evaporator, crystallizer/filter; mixing point; and the overall system. For each, list the number of unknowns, the number of independent material balance equations, the number of other equations, and calculate the degrees of freedom.
c) Write in an efficient the equations you would use to determine all unknown stream variables, circling the variables for which you would solve (don’t do any calculations).
d) Calculate the flow rate of water removed by the evaporator, the flow rate of the recycle stream, and the yield of NaHCO3 solids per kg of solution fed to the process.
e) Assuming the same feed rate as above, re-assess the yield of NaHCO3 solids per kg of solution fed if you learn that the filtrate is actually not recycled, but the evaporator still produces a 14 wt% NaHCO3 solution and the filter a 95% cake with 10% NaHCO3 in the filtrate.
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