Self Assessment Quiz

Q5.1. A tank contains 100 cum of fresh water. Brine of concentration 1 kg/cum enters at a rate of 2 cum/min and leaves at 1 cum/min. what is the exit concentration of brine when tank contains 150 cum.

Q5.2. As a supervisor of a small  scale  CSTR  reactor  you have been continuously plagued with start up  problem that  result long times to reach steady state  so resulting  in shutting down your operations.  After each shut down, at much cost all vessels must be emptied and cleaned.  Your process involves irreversible first order liquid phase isomerization A => B which is carried out in a CSTR.

A new engineer on the job suggests that that approach to steady state would be eliminated if we would fill the tank with species A at an initial concentration of CAO / (1+ kτ). Justify if the suggestion is OK or not. Sourced from Fogler

Q5.3. The liquid phase reaction A+B = C+D is carried out in pot still connected to an overhead condenser. Product D is volatile and is removed as soon as it is formed. The reaction is second order and is irreversible.

(a) What is the time required to reach a conversion of 80%.

(b) What is the volume of liquid present in the pot at this instant of time.

Data: NAO = 1.0 kmol; NBO = 1 kmol ; CAO = 10 kmol/cum; k = 0.1 cum/ , mixture density 20 mol/L

Q5.4. A reactor is maintained at a constant temperature of 4000C and is fed with pure with gas at a steady rate of 1.0 gmol/min. The product gas stream is withdrawn from the container at a rate sufficient to keep the total pressure constant at 3 atm. The contents of the reactor are kept spatially uniform by agitation. A second order reaction  2A => B is taking place. The velocity constant at 4000C is 60 cum/kmol.min Sourced from Mickley Sherwood & Reed

Q5.4.1. It  is  desired  to  have  an  exit  conversion  of  0.5  what  is  the  volume  required?

Q5.4.2. If the exit pipe is closed and pressure maintained by controlling feed. How long would it take to reach 90 mol percent B?  

Q5.5. It was monsoon 1994.  Our 400 ton/d garbage processing project was one year old.  It was launched in May 1993 amidst much doubt and expectation. In the June 94 the phase I of the project spread over 4 hectares to process 200 ton/d was showing clear signs of progress with developing biology, well laid out paths, the project office and storage facilities etc. All this amidst the stench and filth of one of the largest dumping grounds in the world.

In August 94, due to an unforeseen civic strike the dumping ground management was not in place and about 3000 tons of waste was dumped indiscriminately at the site prepared for the process.So in August 94 our work was in shambles.  12 months of labour lay in ruins and added to this was the adverse press. Restoration was needed and urgently.  A strategic central area was available where waste could be assembled.  An L & T poclain could be engaged to collect the waste and deliver to the central area.  A human chain could then be deployed to distribute the waste over the 4 hectares site with necessary topping with culture.  This way the entire waste we thought could be processed and the site saved from embarrassment.

Estimates indicated that L &T Poclain could deliver waste at an initial rate of 100 ton/hr   but the rate would fall linearly with consumption of waste.  This fall in rate was due to the time required to collect the waste and bring to the central area.  The human chain could distribute the waste at rate of 10 ton/hr .It was decided that 98 percent of the waste would be handled as above and the rest would be handled manually at 10 ton /hr .We did manage to survive the crisis and the adverse press.  So did the developing ecology at site. What then is your estimate of the time required to clear the problem?