July 30, 2021: Pharmaceutical Interview Questions and Answers
#Drying #DryingOperatingPrinciples #EquipmentClassificationsForDrying
1. What is Drying?
The removal of a liquid from a solid by evaporation.
2. What are the Operating Principles of different equipment for Drying?
| Types of Drying principle | Details of Principles |
| Direct Heating, Static Solids Bed | Heat transfer is accomplished by direct contact between the wet solids and hot gases. The vaporized liquid is carried away by the drying gases. There is no relative motion among solid particles. The solids bed exists as a dense bed, with the particles resting upon one another. |
| Direct Heating, Moving Solids Bed | Heat transfer is accomplished by direct contact between the wet solids and hot gases. The vaporized liquid is carried away by the drying gases. Solids motion is achieved by either mechanical agitation or gravity force, which slightly expands the bed enough to flow one particle over another. |
| Direct Heating, Fluidized Solids Bed | Heat transfer is accomplished by direct contact between the wet solids and hot gases. The vaporized liquid is carried away by the drying gases. The solids are in an expanded condition, with the particles supported by drag forces caused by the gas phase. The solids and gases intermix and behave like a boiling liquid. This process commonly is referred to as fluid bed drying. |
| Direct Heating, Dilute Solids Bed, Spray Drying | Heat transfer is accomplished by direct contact between a highly dispersed liquid and hot gases. The feed liquid may be a solution, slurry, emulsion, gel or paste, provided it is pumpable and capable of being atomized. The fluid is dispersed as fine droplets into a moving stream of hot gases, where they evaporate rapidly before reaching the wall of the drying chamber. The vaporized liquid is carried away by the drying gases. The solids are fully expanded and so widely separated that they exert essentially no influence on one another. |
| Direct Heating, Dilute Solids Bed, Flash Drying | Heat transfer is accomplished by direct contact between wet solids and hot gases. The solid mass is suspended in a finely divided state in a high-velocity and high-temperature gas stream. The vaporized liquid is carried away by the drying gases. |
| Indirect Conduction, Moving Solids Bed | Heat transfer to the wet solid is through a retaining wall. The vaporized liquid is removed independently from the heating medium. Solids motion is achieved by either mechanical agitation or gravity force, which slightly expands the bed enough to flow one particle over another. |
| Indirect Conduction, Static Solids Bed | Heat transfer to the wet solid is through a retaining wall. The vaporized liquid is removed independently from the heating medium. There is no relative motion among solid particles. The solids bed exists as a dense bed, with the particles resting upon one another. |
| Indirect Conduction, Lyophilization | Drying in which the water vapor sublimes from the product after freezing. |
| Gas Stripping | Heat transfer is a combination of direct and indirect heating. The solids motion is achieved by agitation and the bed is partially fluidized. |
| Indirect Radiant, Moving Solids Bed | Heat transfer is accomplished with varying wavelengths of energy. Vaporized liquid is removed independently from the solids bed. The solids motion is achieved by mechanical agitation, which slightly expands the bed enough to flow one particle over one another. This process commonly is referred to as microwave drying. |
3. Equipment Classifications used for drying.
| Equipment type | Sub classification description | Sub classification |
| Direct Heating, Static Solids Bed | Static solids bed subclasses primarily are distinguished by the method of moving the solids into the dryer. | • Tray and Truck • Belt |
| Direct Heating, Moving Solids Bed | Moving solids bed subclasses primarily are distinguished by the method or technology for moving the solids bed. | • Rotating Tray • Horizontal Vibrating Conveyor |
| Direct Heating, Fluidized Solids Bed (Fluid Bed Dryer) | Although fluid bed dryers may differ from one another in geometry, operating pressures, and other conditions, no fluidized solids bed dryer subclasses have been identified. | No sub class |
| Direct Heating, Dilute Solids Bed, Spray Dryer | Although spray dryers may differ from one another in geometry, operating pressures, and other conditions, no spray dryer subclasses have been identified. | No sub class |
| Direct Heating, Dilute Solids Bed, Flash Dryer | Although flash dryers may differ from one another in geometry, operating pressures, and other conditions, no flash dryer subclasses have been identified. | No sub class |
| Indirect Conduction Heating, Moving Solids Bed | Moving solids bed subclasses primarily are distinguished by the method or technology for moving the solids bed. | • Paddle • Rotary (Tumble) • Agitation |
| Indirect Conduction Heating, Static Solids Beds | No indirect heating, static solids bed shelf dryer subclasses have been identified. | No sub class |
| Indirect Conduction, Lyophilization | No lyophilizer subclasses have been identified. | No sub class |
| Gas Stripping | Although gas stripping dryers may differ from one another in geometry, shape of agitator, and how fluidizing gas is moved through the bed, no gas stripping dryer subclasses have been identified. | No sub class |
| Indirect Radiant Heating, Moving Solids Bed (Microwave Dryer) | Although microwave dryers may differ from one another in vessel geometry and the way microwaves are directed into the solids, no indirect radiant heating, moving solids bed dryer subclasses have been identified. | No sub class |
Source: fda.gov
