Hi, I have the numerical answers but not the intermediate steps. Q1 a) A continu

Question

Hi, I have the numerical answers but not the intermediate steps.

Q1 a) A continuous mult-stage tower for distilling air has one feed (with nitrogen mole fraction 0.79), one top product (with nitrogen mole fraction 0.9), and one bottom product. The column internal pressure is 1 atm. Feed enters the column as saturated vapour with a flow rate of 50 mol s-1 and the recovery is 95% The column has a total condenser and the reflux ratio R is 1.5 The air is binary mixture of oxygen and nitrogen and all liquids and vapours in the tower have molar enthalpies of -3.65 kJ mol and 2.25 kJ mol respectively An x-y diagram for the binary mixture of oxygen and nitrogen at 1 atm is provided in Figure 1. i) Calculate q (the quality' of the feed to the column) and the slope of ANSWER: q-0, slope 0 10 marks ii Calculate the molar flowrate of the distillate, the molar flowrate of the bottom product, and the mole fraction of nitrogen in the bottom ANSWER: D-41.7 mol s-1, W-8.3 mol s-1, xw-0.237 ili) By drawing a McCabe-Thiele construction on Figure 1, determine the number of ideal stages in this tower and specify at which ideal stage the feed should enter the column. [You must attach Figure 1 to your script] ANsWER: 2 ideal plates plus reboiler; feed may be on stage 1 or 2 depending on diagram drawn iv) Use your McCabe-Thiele diagram (Figure 1) to estimate the composition of the liquid leaving each of the ideal stages. You should provide a justification of your answer 10 marks ANSWER: x2-0.69, x1+:0.46 v) Perform material and enthalpy balances to find an expression for the vapour flowrate in the stripping section of the column and thus calculate the reboiler duty 25 marks ANSWER: 320 kw vi) State at least three important assumptions that form the basis for the above analysis of a distillation column and explain the meaning of each one 20 marks 90 30 20 10 10 20 30 50 60 70 80 90 100 MOL PER CENT NITROGEN IN UQUID CONSTANT PRESSURE LIQUID VAPOUR EQUILIBRIUM DIAGRAM for NITROGEN OXYGEN PRESSURE 760mm Hg

Explanation / Answer

Answer to question (i)

q is defined as the heat required to raise the feed to the saturated vapor state to the latent heat of vaporization of saturated liquid

Since the feed is already a saturated vapor, no additional heat is required to raise the feed to saturated vapor

Hence, q = 0

Now the slope of q- line is given by q/q-1 = 0/0-1 = 0

Hence, q = 0 and slope of q line =0

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