Page 279 - Chemical Process Equipment - Selection and Design

246 DRYERS AND COOLING TOWERS

TABLE 9.5. Specification Form for a Dryera
~ ~~
1. Operation mode batch/continuous
operating cycle -
h
2. Feed (a) material to be dried
(b) feed rate -
kg/h
(c) nature of feed solution/slurry/sludge/granuIar/
fibrous/sheet/bulky
(d) physical properties of solids:
initial moisture content - kg/kg
hygroscopic-moisture content - kg/kg
heat capacity - kJ/kg"C
bulk density, wet - kg/m3
particle size -
mm
(e) moisture to be removed:
chemical composition -
"C
boiling point at 1 bar -
heat of vaporization - MJ/kg
heat capacity - kJ/kg"C
(f) feed material is scaling/corrosive/toxic/abrasive/
explosive
(9) source of feed
3. Product (a) final moisture content - kg/kg
(b) equilibrium-moisture content at 60% r.h. - kg/kg
(c) bulky density - kg/m3
(d) physical characteristics granular/flaky/fibrous/powdery/
sheet/bul ky
"C
4. Design restraints (a) maximum temperature when wet -
"C
when dry -
(b) manner of degradation -
(c) material-handling problems,
when wet
when dry
(d) will flue-gases contaminate product?
(e) space limitations
5. Utilities (a) steam available at
maximum quantity
costing
Ib) other fuel
at
with heating value
costing
(c) electric power
frequency
phases
costing - $/kWh
6. Present method of drying
7. Rate-of-drying data under constant external conditions:
ordata from existing plant

8. Recommended materials of construction
(a) parts in contact with wet material
(b) parts in contact with vapors
a Questionnaires of several manufacturers are in Appendix C.
(Keey, 1972, p. 325).

is not as effective in this regard as the same increase in the amount becomes
of fresh air. Recycling is practiced, however, to reduce heat
consumption when the fresh air is cold and to minimize possible H, = 97.4(R + 1) + 1400(1.16 - W) (9.16)
undesirable effects from over-rapid drying with low humidity air. 7790(R + 1)
Parallel current operation also avoids overrapid drying near the
end. For parallel flow, the moisture balance of Example 9.4 and replaces line 30 of the computer program.