Drying vapor, closed loop

The initial equipment costs and operating costs for the more conventional processes are higher than for supercritical carbon dioxide. The higher equipment costs are due to the additional parts needed for environmental treatments (i.e., scrubbers, vapor incinerators, etc.) The consumables costs are lower for the supercritical fluid processes due to the closed-loop recycle design of the supercritical fluid system, elimination of water for rinsing and the reduced electricity costs associated with not having to dry the parts. 

Hot air that is used to dry pharmaceuticals is recycled in a closed loop to prevent the contamination of the moist material from atmospheric impurities. In the first conditioning step for the air, 5000 k mol/hr at 105 kPa and 42 C with a 90% relative humidity are fed to a condenser to remove some of the water picked up previously in the dryer. The air exists the condenser at 17°C and 100 kPa containing 91 k mol/hr of water vapor. Next, the air is heated in a heat exchanger to 90°C, and then goes to the dryer. By the time the air enters the dryer, the pressure of the stream has dropped to 95 kPa and the temperature is 82 C. 

Drying of materials containing nonaqueous solvents is generally carried out in a closed-loop system so that the exhaust gas containing nonaqueous vapors is not discharged into the atmosphere to pollute the air. 

Enclosed system (cleaning) Cleaning, rinsing, and drying systems where the liquids are contained and the vapors are condensed and recycled. This reduces pollution generation. Examples Vapor cleaners spray cleaners vapor dryers. See also Closed-loop system. 

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