Indian Institute of Technology Kharagpur (IIT-K) 2007 M.Tech Chemical engineering Engineering aspects of aration and transport processes-2 - Question Paper
INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR
Date of Examination: 24/04/2007 (FN) Full Marks: 80
End Autumn Semester 2007 Time: 3 hrs.
Subject Name: EASTP - II Subject No.: CH33006
Students: 3rd year BTech & Int. MTech in Chemical Engg.
Question No. 1 is compulsory. Answer any three questions from Q2, Q3, Q4 & Q5.
Make realistic assumptions with justification as necessary after stating its
justification..
Ql. Answer any 10 from following (10 > 2 = 20 marks)
a. In a continuous distillation column, when is the piping arrangement to recycle the column bottom product to the plant feed line used?
b. Whats a breakthrough curve?
c. Whats the significance of Langlier index?
Jid. Why shock dosing of chlorine is done in cooling water lines leaving the cooling tower basin?
e. When will a designer provide a water boot?
f. A flash dram must have a liquid level in it for efficient operation. Why?
g. How do you decide if the solvent should be introduced from the top or from the bottom of a counter-current extractor column?
h. What consideration will you use for deciding the cooling water basin capacity?
i. Why do large natural draft cooling towers have hyperbolic section?
j. What are the three major sections in an extraction plant?
k. When does a designer opt for a multipass tray?
1. ' Why pump around reflux is provided in some distillation columns?
m. What is a pressure swing adsorption process?
n. In some extraction columns part of the material is taken out, cooled/heated and returned to the column. When is this type of arrangement made?
Q2. A feed stream (100 moles / hr, 40% benzene, 60% toluene) is to be fractionated into a stream of 88% benzene and a toluene rich stream containing not more than 6% benzene. The continuous distillation column shall operate at 0.5 Kg/cm2(g). Preliminary estimate of the reflux ratio is 3.9. You are required to design the distillation plant with total condenser and reboiler. Storage tanks are not included in design scope.
Battery limit conditions for design are : (i) Feed is available at about atmospheric pressure (free flowing from feed tank by gravity), 35 deg C., (ii) Product streams are to leave after heat recovery / cooling to 40 deg C, minimum 4 Kg/cm2(g) pressure. Adequate cooling water @ 35 deg C, 4 Kg/cm2(g) and steam @ 5 Kg/cm2(g), 20 deg C superheat is available.
Antoine equation describes the dependence of vapor pressure of a pure chemical species i on temperature. logio(P*i) = Aj- Bj/(T+Cj); A, B, and C for a benzene & toluene are tabulated below. P is expressed in mmHg, and TC.
Formula species ID A B C
C6H6 benzene 6.90565 1211.033 220.790
C7H8 toluene 6.95464 1344.800 219.482
Estimate (a) column top and bottom temperatures, (b) vapor load on the top tray in m3/hr at top tray condition. <2x3+4=10 marks>
Suggest your P&JD for the distillation plant including all piping, pumps, heat exchangers, safety devices, column pressure, temperature and level controls that you feel are needed for safe and convenient operation, start up and shutdown. Use only standard flowsheeting symbols and provide a very brief description of your plant arrangement. <P&ID: 10 marks >
Q3a. Detail the layout of a draw-off tray with draw-off box for a distillation column with a properly labeled sketch. Mention the considerations for arriving at all dimensions of chimneys and draw off box. <5+5 -10 marks>
Q3b. Draw the general arrangement of i\ compartment tray drier that uses a single blower for sucking fresh air as well as re-circulating moist air. The drier should operate at about 15 mm water column above atmospheric. The drier should have independent adjustments for re-circulation flow as well as the fresh air intake. Specifically show the location of the vent with justification for choosing its location. < 8+2=10 marks>
Q4a. A process in a rubber processing plant that uses toluene as solvent generates
continuously vents around 12 m3/hr air saturated with toluene vapor at 30 deg C. (1) Suggest a scheme for recycling the solvent to the extent possible. The exit air must be free of toluene smell. (2) Estimate the maximum toluene recovery possible. <5+3=8 marks>
Q4b. What is common method of pulling vacuum for large / industrial-scale vacuum crystallizers? Explain the working of the vacuum pulling system with a detailed diagram showing the complete system . < 4 marks>
Q4c. When will you suggest freeze-drying an item? Show on a phase diagram sketch how will you decide the operating temperature / pressure for freeze drying ? < 1+4=5 marks>
Q4d. Is blowdown from a cooling water system essential ? Estimate blowdown rate for a circulation rate of 6ooo m3/hr cooling water system with water temperatures 35/47 deg c. assume realistic values for any other data you may require. <l+2=3marks>
Q5. A continuous 3 m3/hr dilute ethanol stream (2% v/v in water) is available. Ethanol is also miscible in hydrocarbons boiling in the gasoline range (70 -140 deg C). This ethanol can be extracted at room temperature with gasoline.The blend can be sold as gasohol. A set of equilibrium experiments were conducted to evaluate worth of the above proposal.
Assume that the results of the investigation shows a favorable equilibrium distribution of ethanol between water and hydrocarbon phases and the extraction will be done with 6:1 hydrocarbon to aqueous phase ratio (v/v) to recover 88% of ethanol from feed and produce gasohol containing 10% ethanol. Provide a preliminary proposal for the plant that includes (i) type of extraction equipment and justification for selecting it, (ii) rough sizing of major equipment with basis of sizing / calculation, (iii) Brief description and P&ID of the complete plant with all facilities that you feel may be necessary for safe operation, start up and shutdown. <2+8+10=20 marks>
3A
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