Question

Wet leather containing 55% water by mass enters a continuous tunnel dryer and leaves at a rate of 400 lbm/h containing 12 wt% water. Dry air containing no water vapor enters the dryer at 160°F and the exit air stream leaves the dryer at 120°F containing 8 mole % of water vapor. Calculate the rate at which wet leather enters the dryer and the molar flow rate of the inlet air.

Answer 1

wet leather contain 55% water by wt initially

& 12% water by wt finally

leaving rate of leather = 400lb/h

as it contain 12% water it will contain 88% solid matter

so wt of solid = 0.88*400 =352 lb/hr

feed contain 45% solid matter

so taking material balance for solid

solid in feed= solid in leaving stream

0.45F=352

F=782.22lb/hr ....ans .   (rate at which leather enters)

to calculate molar flow rate of inlet air

water removed = 782.22-400=382.22lb

moles of water removed = 9173.37kg/hr)/(18g/mol)=9.63166kmol/hr

rate of water vaporised=rate of water vapor carried with air

9.63166=0.08G

G=120.39kmol/hr

dry air = (1-0.08)120.39 =110.76kmol/hr (dry air)

therefore the molar flow rate of air with which it enters =110.76kmol/hr