Coulson Drying Flashcards
A granular material containing 40 per cent moisture is fed to a countercurrent rotary dryer at a
temperature of 295 K and is withdrawn at 305 K, containing 5 per cent moisture. The air supplied,
which contains 0.006 kg water vapour/kg dry air, enters at 385 K and leaves at 310 K. The dryer
handles 0.125 kg/s wet stock.
Assuming that radiation losses amount to 20 kJ/kg dry air used, determine the mass flowrate of
dry air supplied to the dryer and the humidity of the exit air.
The latent heat of water vapour at 295 K = 2449 kJ/kg, specific heat capacity of dried material =
0.88 kJ/kg K, the specific heat capacity of dry air = 1.00 kJ/kg K, and the specific heat capacity
of water vapour = 2.01 kJ/kg K.
- 07 kg/s
0. 0284 kg/kg dry air
0.126 kg/s of a solid product containing 4 per cent water is produced in a dryer from a wet feed containing 42 per cent water on a wet basis. Ambient air at 294 K and of 40 per cent relative humidity is heated to 366 K in a preheater before entering the dryer from which it leaves at 60 per cent relative humidity. Assuming that the dryer operates adiabatically, what must be the flowrate of air to the preheater and how much heat must be added to the preheater? How will these values be affected if the air enters the dryer at 340 K and sufficient heat is supplied within the dryer so that the air again leaves at 340 K with a relative humidity of 60 per cent?
Volume of air = 3.16 m3/s
Air requirement = 0.66 m3/s
Q = 31.0 kW
Qtotal = 242 kW
