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

The three major assumptions that forms the basis of the method used above are as follows

1. The molar heat of feed components are equal

2. For every mol of liquid vaporized , every mol of vapor is condesed

3. Other heat effects such as heat of solution, hea transfer from distillation column to surrounding are neglected.

If 1st assumptioons is not made it will requried vaporization data of each component and also lot of statistical data and analysis to find the vaporization at the desired temperature and pressure

If 2nd assumption is not made it means some kind of chemical reaction is involved which is providing some addition activation energy in the column. As the temperature varies along the length of the column. This would have to be calculated again and again at every point in the column

If heat of solution is incorporated, that would required heat of solution charts which are not ready available which is consume lot of time to overcome this approximation. In cases where ther=y are not available one would require to simulate the system and obatin those charts.

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