A spray-drying operation similar to that described in Problem 5.23 is used by the pharmaceutical industry. Acetaminophen is an active pharmaceutical ingredient (API) that can be produced in powdered form by spray drying. A mixture of the API containing 75 wt% water is fed to an atomizer in a dryer where it is brought into contact with hot air that enters the dryer at 220°C and 6.0 bar. All of the water is evaporated. The outlet gas contains 8.1 mole% water and leaves the dryer chamber at 80°C and 1.0 atm absolute with a flow rate of 513:6 m3 /h. Calculate the production rate of powdered API and the volumetric flow rate of inlet air. 

Problem 5.23

Spray drying is a process in which a liquid containing dissolved or suspended solids is injected into a chamber through a spray nozzle or centrifugal disk atomizer. The resulting mist is contacted with hot air, which evaporates most or all of the liquid, leaving the dried solids to fall to a conveyor belt at the bottom of the chamber. 

Powdered milk is produced in a spray dryer 6 m in diameter by 6 m high. Air enters at 167°C and -40 cm H₂O. The milk fed to the atomizer contains 70% water by mass, all of which evaporates. The outlet gas contains 12 mole% water and leaves the chamber at 83°C and 1 atm (absolute) at a rate of 311 m³/min. 

Milk (70% H,O) Wet air 311 m'/min @ 83C, 1 atm Dried milk Inlet air 167C, -40 cm H,0