ChE 250

Spring 2000                                                                             Problem Set #4

Due Thursday, February 24

 

Reminder: Exam I is Thursday, Feb. 24 at 7:15 pm
in room 1227, Engineering Hall

 

Review Felder and Rousseau from beginning through Section 4.5, read Sections 11.1-2. 

 

1.   In paper manufacture, a slurry containing 2 wt% cellulose fiber (remainder water) is first deposited on a moving belt made of screen.  After sufficient water drains out, the raw paper sheet (40 wt% fiber) can support its own weight and is taken through a drier.  At the drier exit, the paper is only 5 wt% moisture, and is collected on a roll for storage.  Amazingly, this process occurs at 60 mph in many paper mills!

a)   Show a flowsheet, labeling all operations and known streams.

b)   A particular paper line produces 800 lb/min of rolled paper.  Determine the water removal rate in each step.  What is the rate of fiber slurry flowing onto the belt at the start of the process?

c)   A paper mill producing 500 tons/day of paper cannot release the associated millions of gallons/day of wastewater.  How is water consumption reduced in a paper mill?

 

2.   A petrochemical plant has a reactor waste stream containing hydrogen (20 mole%) in methane. The engineers wish to recover the valuable hydrogen before sending the methane to the steam plant for fuel.  They have no single process that can accomplish the separation cleanly, but do know of individual strategies capable of purifying one component and rejecting a mixed stream.  A membrane unit can extract 20% of the hydrogen entering it, and produces a H₂ stream with 99% purity.  An adsorption cycle unit can remove 50% of the methane fed to it, and allow only 0.5% hydrogen in its effluent.  It is proposed to use these two processes together to separate the reactor waste stream as shown below:

 

 

a)   The reactor waste flow rate is 10 mole/s.  Determine the flow rates of the hydrogen-rich and methane-rich product streams.  What % of the incoming hydrogen is recovered for use elsewhere?

b)   To order the equipment, capacities must be specified.  Calculate the flow rate into each separation unit.  Compare these results with the feed rate into the whole process, and comment.

 

3.   Do F&R problem 11.5 - gas storage tank

 

4.   Do F&R problem 11.11 - tracer study