Handbook of Solvents - George Wypych - ChemTech - Ventech!

7.3 Drying of coated film 405
However, in a multiple zone dryer the solvent concentration of coating at the end of
each zone could be found by analyzing the dryer exit gas with measured airflow. This experimental
method provides concentration profile of each solvent with drying as well as the total
drying rate of coating. It gives precise measurement value at the early stages of drying in
which the concentration of solvent in the dryer exit gas is high, and the length of each zone
is long enough to ensure negligible intermixing of air between adjacent zones.
The solvent concentrations of the exit gas are measured by portable gas chromatography
(GC), and the gas samples are taken at the exhausted air duct of each zone. From these
concentration data and the airflow rate of each zone, the evaporation rate of solvent at each
zone is calculated. (Figure 7.3.21)
Evaporation rate of solvent at zone k, ER k [kg/min]
= Solvent concentration, C k out [kg/m 3 ]×Airflow rate, Q k out [m 3 /min] [7.3.10]
The example of solvent concentration measurement and the accompanying results of
drying rate calculation are shown in Table 7.3.2., and the accompanying specification of
dryer and the formulation of coating solution is given in Table 7.3.3 and 7.3.4. The solvent
concentrations at the exhaust duct are measured by gas chromatography(MTI Analytical Instrument
200, Portable GC). The solvent concentrations were measured three times at the
same point, and the deviations from the average value were less than ±5%.
Table 7.3.2
Zone
Concentration, ppm
MEK Tol. Cyc. MEK
Evaporation rate, kg/h
Tol. Cyc. Total
1 1655 740 142 47.6 27.2 5.6 80.4
2 1150 988 359 40.5 44.4 17.2 102.0
3 485 1243 1866 14.0 46.0 73.5 133.6
4 308 157 2223 1.5 1.0 15.2 17.7
5, 6 269 99 278 6.6 3.1 9.4 19.2
Table 7.3.3
Operating conditions
Dryer specification
Drying air temperature, o C 50 ~ 120
Line speed, m/min 900
Total number of zones 6
Total dryer length, m 45
Dry coating thickness, μm 2.6
Dryer type Air floating dryer