712 Fermentation and Biochemical Engineering Handbook The first step refers to the choice of continuous versus batch drying and depends on the nature of the equipment preceding and following the dryer as well as on the production capacity required. In general, only batch dryers will be considered in the following Batch dryers include Fluidized-bed dryers. These may be used when the average particle diameter is s0. 1 mm. (The equipment required to handle smaller particles may be too large to be feasible. Inert gas may be used if there is the possibility of explosion of either the vapor or dust in the air It is easy to carry out tests in a small fluid-bed dryer. Shelf dryers. Theys are usually employed ofr small capacities and when the solvent doesn t present particular problems Vacuum dryers. These are the most-used batch dryers Vacuum dryers are usually considered when Low solids temperature(<40C)must be maintained to prevent heat causing damage to the product or changing its When toxic or valuable solvent recovery is required When air combines with the product, during heating, causing Before starting work on selecting a dryer, it is good practice to collect all the data outlined in Table 1 In vacuum drying, the objective is to create a temperature difference or driving force"between the heated jacket and the material to be dried. To accomplish this with a low jacket temperature, it becomes necessary toreduce the internal pressure of the dryer to remove the liquid/ solvent at a lowervapor pressure. Decreasing the pressure creates large vapor volumes. Economic considerations arising from concems of leakage, ability to condense the solvent, size of vapor line and vacuum pump, affect the selection of the operating pressure. Materials handled in vacuum dryers may range from slurries to solid shapes and from granular, crystalline product to fibrous solids. The characteristics of each type of vacuum dryer is discussed below to help make a proper choice Vertical Vacuum Pan Dryers. The agitated vertical dryer(Fig 3 has been designed for drying many different products which may come from centrifuges or filters. Generally, the body is formed by a vertical cylindrical casing with aflat bottom flanged to the top cover head. The unit is fully heated by an outside half-pipe jacket welded on the cylindrical wall, the bottom and the top head712 Fermentation and Biochemical Engineering Handbook The first step refers to the choice of continuous versus batch drying and depends on the nature of the equipment preceding and following the dryer as well as on the production capacity required. In general, only batch dryers will be considered in the following. Batch dryers include: Fluidized-bed dryers. These may be used when the average particle diameter is I 0.1 mm. (The equipment required to handle smaller particles may be too large to be feasible.) Inert gas may be used if there is the possibility of explosion of either the vapor or dust in the air. It is easy to carry out tests in a small fluid-bed dryer. Shelf dryers. Theys are usually employed of? small capacities and when the solvent doesn’t present particular problems. Vacuum dryers. These are the most-used batch dryers. Vacuum dryers are usually considered when: Low solids temperature (< 40°C) must be maintained to prevent heat causing damage to the product or changing its nature When toxic or valuable solvent recovery is required When air combines with the product, during heating, causing Before starting work on selecting a dryer, it is good practice to collect all the data outlined in Table 1. In vacuum drying, the objective is to create a temperature difference or “driving force” between the heated jacket and the material to be dried. To accomplish this with a lowjacket temperature, it becomes necessary to reduce the internal pressure of the dryer to remove the liquidsolvent at a lower vapor pressure. Decreasing the pressure creates large vapor volumes, Economic considerations arising from concerns of leakage, ability to condense the solvent, size of vapor line and vacuum pump, affect the selection of the operating pressure. Materials handled in vacuum dryers may range from slurries to solid shapes and from granular, crystalline product to fibrous solids. The characteristics of each type of vacuum dryer is discussed below to help make a proper choice. Vertical Vacuum Pan Dryers. The agitated vertical dryer (Fig. 3.) has been designed for drying many different products which may come from centrifuges or filters. Generally, the body is formed by a vertical cylindrical casing with a flat bottom flanged to the top cover head. The unit is fully heated by an outside half-pipe jacket welded on the cylindrical wall, the bottom and the top head. oxidation or an explosive condition