Print pageChemical Processing Mini Puzzler
Tank rupture puzzler
A new tank ruptured while being filled. A flammable, toxic liquid is stored in the tank. The high level alarm went off and shortly before the tank cracked. What caused the problem and how would you fix it after the tank is repaired?
A. The liquid was siphoned out of the tank The pressure relief valve was useless because the tank was damaged because of vacuum. Put the high level switch on the side of the tank, replace the relief valve with breather vent. Run the breather vent to a the seal pot (if the flow to the knock-out is sized to match the fill).
B. The overflow line is plugged. The pressure relief valve malfunctioned. Look into causes of the overflow being plugged. Confirm that the relief valve is set correctly.
C. The liquid was siphoned out of the tank. The pressure relief valve was useless because the tank was damaged because of vacuum. Replace the relief valve with a pressure/vacuum rupture disc. The best solution is to move the high level switch to the side of the tank, install a block valve in the feed line to shut off when the high level switch alarms.
D. The liquid was siphoned out of the tank. The problem is where the overflow is located so move it lower — on the side of the tank and relocate the seal pot so that it is not so low. Replace the relief valve with a pressure/vacuum rupture disc. Relocate the high pressure switch to lower in the exit line tree.
Reduce hazardous chemical inventory puzzler
You must reduce inventory of a hazardous chemical used at your plant. You use about 500 gallons per week (20%), 200 gallons per week (average), 0 for 10% of time. You must maintain a one-week supply for emergencies. What is the best way to cut inventory?
A. Hire a tote contractor but keep 3,500 gallons in storage.
B. Buy a small tank with 1,400 gallons as a minimum.
C. Keep a warehouse off plant grounds; keep at least 3,500 gallons in storage.
D. Find a safer alternative chemical or method but keep 3,500 gallons for now as a minimum.
Equipment rental deal puzzler
A salesman offers you a deal on equipment costing $2,300. You may rent it for $331/month for a year, then pay a book value of $1,959. 10% annual interest and a 5-year life are assumed. Is this a good deal?
A. Yes
B. No
Distillation column reboiler puzzler
A high-pressure reboiler on a distillation column operates with a vertical thermosiphon. A small ΔT is used to distill a multi-component mixture. Start-up is a frequent problem lately. Twice in the past year, the column was shutdown and the reboiler required cleaning. What is cause of the problem and the best solution?
A. The temperature differential is too low; raise the temperature.
B. Boil-off of lighter components is leaving tar. The column level is too high during start-up; lower the level.
C. Boil-off; install a valve and throttle flow from the reboiler.
D. Boil-off; inject a lift gas in the outlet of the reboiler.
Fastener arrangement puzzler
Which is the correct fastener arrangement and why? (Click on Show Diagram)
A. Hard nut with a soft bolt because there is more threading on a bolt.
B. Hard nut with a soft bolt because bolts soft material will harden.
C. Soft nut with hard bolt because it will be easier to re-tap.
D. Soft nut with hard bolt because nuts are easier to replace.
Ammonia refrigeration cascade puzzler
A 10-ton cascade refrigeration cycle uses ammonia and water. Water is available at 90ºF and the cool room is maintained at 40ºF. The minimum approach for the intercooler is 15ºF. If compressor efficiency is 70%, what is the horsepower of the compressor?
A. 99-hp
B. 12-hp
C. 8-hp
D. 7-hp
Level control valve puzzler
A level control valve that was recently inspected is operating outside of its normal range and the tank level is dropping slowly. What is the most likely cause?
A. The orifice plate has worn out (enlarged).
B. The level control valve is plugged.
C. The air supply to the control valve may have dropped.
D. The orifice plate is plugged.
Pressure switch alarm puzzler
A pressure switch in corrosive service is bugging your operators. It is a normally-open (NO) switch. (See the diagram). It seems to alarm periodically. An inspection of the marshalling panel shows that the N2 purge line has not worked for sometime. Plant air continually seeps into the box, which is badly corroded. What is the likely cause of the problem?
A. The contacts are corroded.
B. The switch is faulty.
C. The termination in the PLC is bad.
D. A ground-fault error.
Contaminated fermentation batch puzzler
A fermentation batch is contaminated. In fact, this particular fermenter has failed to reach production for several weeks. A plot of performance shows a steady progression, and it is getting worse. The inoculation seems sterile and tests show that there must be something wrong with the fermenter. Other fermenters using the same air line, mash line and CIP system are operating fine with few contamination problems. Each fermenter is an open vessel with a vent (a spray ball inside). What is the likely cause of the problem?
A. The mash (sugar) feed line is contaminated.
B. The CIP system is not working effectively.
C. The air line is contaminated.
D. Contaminants are dripping in from the vent.
Pump pressure puzzler
A pump pressure gauge on a new pump is reading lower than expected. It is a centrifugal pump. The ratio of NPSHA over NPSHR is about 2 so there is plenty of suction head. A current reading shows that the pump is drawing the correct horsepower, based on a flow measurement downstream. What could be the problem?
A. The pump impeller is undersized.
B. The specific gravity of the fluid is higher than expected.
C. The gauge is located too close to the discharge.
D. There is an obstruction somewhere in the discharge line.
Blower problem puzzler
A blower used in pneumatic conveying has been in service for several years. Suddenly, it stops drawing air. Production has stopped completely. There have been no re-occurring problems with this system. No recent maintenance was performed. What is the likely cause?
A. The line after the pick-up point has become plugged.
B. The feeder screw conveyor has plugged off.
C. There is a hole in the discharge line.
D. A lobe is broken in the blower.
Curing issue puzzler
A urethane polymer is produced in batch. It takes several batches to fill the product container. After several weeks of running smoothly, the product cures in-place. What went wrong?
A. The bonding agent or crosslinker aged.
B. The formulation contains impurities that caused an autocatalysis.
C. The lubricant used in the product mandrel and mold failed in some way.
D. Operator error.
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