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Finding thermal dryer capabilities. Chemical Engineering , December 12, 1983. David A Lee. When investigating the dryning requirements of a new or different material, an engineer must often determine whether the particular convection-type unit under consideration will be suitable. from a production standpoint. The information about the system shown schematically in the above figure is generally available, or can be easily be derived or estimated. Assuming that volumetric flowrate of the exhaust air Z, and its temperature, Tex, are know, whith X being the rate at which solvent is evaporated and Y the flow rate of the dry inlet air, and that any air leakage into or out the unit is negligible, the following mass balance is obtained. Assuming that the product is dried to bone dryness and that there is no significant heats of reaction and/or solution, the heat balance arround the dryer is presented above.

Replacing Y from thevolumetric balance , an equation to evaluate X is found and both equations could solve the thermal dryer capacity problem. The 1.05 factor icludes a 5% contingency for miscellaneous heat losses. Substituting Tex for Td and solving for Y, gives the equations in the next page.

Finding thermal dryer capabilities. David A. Lee, Chemical Engineering, December 10, 1985.

Z 3600 ft 3^min / * : 1.699 m 3^s / *

ρ.y 0.065 lb.m ft 3^/ * : 1.0412 kg m 3^/ *

T.ex 150 °F * : 338.7056 K *

V.f 70 :

H.g 11261055 0.454 / * J kg / * : 2.6166 106^* Gy *

H.l 281055 0.454 / * J kg / * : 65066.0793 Gy *

Cp.s 0.5 1055 0.454 / * 1.8 * J kg K * / * : 2091.4097 Gy K / *

Cp.g 0.25 1055 0.454 / 1.8 * J kg K * / * * :

ρ.x 0.0103 lb.m ft 3^/ * : 0.165 kg m 3^/ *

T.in 400 °F * : 477.5944 K *

T.f 60 °F * : 288.7056 K *

Find the X rate at which solvent is evaporated with Equation 5

X Z 1.05 ρ.y / (H.g H.l - (100 V.f - (V.f / Cp.s * T.ex T.f - (* + Cp.g T.in T.ex - (* / (* 1 ρ.x / + / : 0.0705 kg s / *

BTU 1055 J * :

lbm 0.4536 kg *

Δ°F 0.5556 K *

The amount of water that can be evaporated is X , which can be multiplied by the ratiiol 30 / 70 , in order to obtain the dried product. The Qr supplied to the Air heater must be compared with the Q found from the sensible heat equation.

Q.r 3106^* 10553600 / * W * : 8.7917 105^* W *

S X 3070 / * : 0.0302 kg s / *

To determine whether the air heater is adequate, the amount of air, Y, needed to dry the material is calculated . Then, the heat transferred from the hot air to the product could be also calculated. The Y value of equation 4, from the heat balance is the following:

Y 1.05 X * H.g H.l - (100 V.f - (V.f / Cp.s * T.ex T.in - (* + (Cp.g T.in T.ex - (* / * : 1.2376 kg s / *

Checked value of Y with equation 2.

Q Y Cp.g * T.in T.ex - (* : 1.7974 105^* W *

Y ρ.y Z X ρ.x / - (* : 1.3239 kg s / *

Z X ρ.x / Y ρ.y / + : 1.699 m 3^s / *

Value of Z checked from equation 1.

W X 3070 / * : 0.0302 kg s / *

The amount of dried product that could be obtained with the conditions presented .