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Example 8 – Enclosed Drying System

Problem

A simple enclosed drying system with the following conditions for both the material and the drying gas

Material:

Feed Temperature = 20 ^oC

Feed Moisture Content (wet basis) = 0.08 kg/kg

Mass Flow Rate (wet basis) = 2000 kg/hr

Product Temperature = 50 ^oC

Product Moisture Content (wet basis) = 0.002 kg/kg

Drying Air

Pressure at Dryer Inlet = 102.4 kPa;

Temperature at Dryer Inlet = 120 ^oC

Mass Flow Rate (wet basis) at Dryer Inlet = 7200 kg/hr

Pressure drop of the dryer is 1.2 kPa. Dust entrained in dryer gas outlet is 0.2% of the total material the dryer handles. Dryer gas outlet stream goes through a fan to gain 1.2 kPa static pressure. Efficiency of the fan is 0.75. Exhaust air coming from the fan goes through a scrubber/condenser to collect the dusts and remove the moisture carried in the exhaust air. Temperature of the exhaust air from the scrubber/condenser is 30 ^oC. Air pressure drop in scrubber/condenser is 1.0 kPa. Collection efficiency of the scrubber/ condenser is 99%. The air coming out of the scrubber/condenser goes through a fan to gain some static pressure and then go through a heater to be heated to the required dryer inlet temperature (120 ^oC). Pressure drop of air in the heater is 0.6 kPa.

Solution:

The flowsheet is constructed and shown in Figure 8a. The result of the flowsheet is displayed in Figure 8b.

Figure 8a

Figure 8b