Dryers specifications

Between 1 s and 1 min specific contact time, conduction heat-transfer performance decreases theoretically as the 0.29 power of contact time. This is consistent with empirical data from several forms of indirect-heat dryers which show performance variation as the 0.4 power of rotational speed (21). In agitator-stirred and rotating indirect-heat dryers, specific contact time can be related to rotational speed provided that speed does not affect the physical properties of the material. To describe the mixing efficiency of various devices, the concept of a mixing parameter is employed. An ideal mixer has a parameter of 1. 

Amount of removed moisture Evaporational rate referred to the cross section of the dryer Specific energy consumption... 

Readers requiring basic description of the freeze drying process can obtain more information from the preceding chapter on freeze drying in Chapter 11 from the handbook. What follows are some additional considerations on top of the conventional operation of a freeze dryer specific to the freeze drying of protein-based pharmaceutics. 

The heat input to diyers is to a gas and as such takes place over a range of temperatures. Moreover, the gas is heated to a temperature higher than the boiling point of the liquid to be evaporated. The exhaust gases from the dryer will be at a lower temperature than the inlet, but again, the heat available in the exhaust will be available over a range of temperatures. The thermal characteristics of dryers tend to be design-specific and quite difierent in nature from both distillation and evaporation. 

Fractionation. Direct fractionation also can be used to remove dissolved water from LPG. The water-rich overhead vapor from the dryer fractionator is returned to the fractionator as reflux and the water phase is discarded. A dry LPG product that meets either propane or butane water specifications is produced as a ketde product from the fractionator. 

Sodium and Potassium Benzoate. These salts are available in grades meeting the specifications of the 25ationalVormulary (18) and the Vood Chemicals Codex (19) (Table 7). Sodium benzoate [532-32-1] is produced by the neutralization of benzoic acid with caustic soda and/or soda ash. The resulting solution is then treated to remove trace impurities as weU as color bodies and then dried in steam heated double dmm dryers. The product removed from the dryers is light and fluffy and in order to reduce shipping and storage space the sodium benzoate is normally compacted. It is then milled and classified into various product forms, the names of which often bear Httle relationship to the actual form of the product. 

Cg = humid heat for humidity H in units of kj / (kg-K) and = latent heat of vaporization at / in kj /kg. The slope of the constant-enthalpy adiabatic cooling line is —C j which is the relationship between temperature and humidity of gas passing through a totally adiabatic direct-heat dryer. The humid heat of a gas—vapor mixture per unit weight of dry gas includes the specific heat of the vapor... 

Udel is a slightly yellow but tianspaient engineering thermoplastic. It has low flammability and smoke emission and good electrical properties. It has excellent resistance to water, steam, and alkaline solutions. Specific uses for Udel iaclude microwave cookware, beverage dispensers, coffee brewers, cookware, hair dryers, com poppers, and steam table trays. Its steam resistance makes it particularly fit for a dishwasher environment. Properties of polysulfone resias ate given ia Table 11. 

Tests on plant-scale dryers are usually carried out to obtain design data for a specific material, to select a suitable diyer type, or to check present performance of an existing diyer with the objective of determining its capacity potential. In these tests overall performance data are obtained and the results used to make heat and material balances and to estimate overall drying rates or heat-transfer coefficients. 

The recycle requirements of products in different apphcations can vaiy substantially depending upon the scale of operation, the ease of diying, and the finished-product specification. The location of reintroduction of undried material back into the diying medium has a significant impact upon the dryer performance and final-product characteristics. 

P-type manifold—veiiical configuration. The P ring dryer (see Fig. 12-100) incorporates a single-stage classifier and was developed specifically for use with heat-sensitive materials. The undried material is reintroduced into a cool part of the dryer in which it recirculates until it is dry enough to leave the circuit. 

Design Methods The size of the agitated flash dryer is based on the evaporation rate required. The operating temperatures are product-specific. Once established, they determine the airflow requirements. The diyiug chamber is designed based on air velocity (approximately 3 m/s) and residence time (product-specific). 

Chemical dryers are materials which combine with or absorb moisture from air when brought into close contact. There are two general types. One, using deliquescent material in the form of pellets or beads, is reputed to obtain a dew point, with 700°F inlet air to the dryer, of between 35°F and 50°F depending on the specific type of deliquescent material. The material turns into a liquid as the water vapor is absorbed. This liquid must be drained off and the pellets or beads replaced periodically. Entering air above 900°F is not generally recommended. 

Dryer, feed 5 per cent water, product specification 0.5 per cent H20 Polymer losses in filter and dryer 1 per cent... 

Mode of operation Generic type Feed condition Specific dryer types Jack- eted Suitable for heat-sensitive materials Suitable for vacuum service Retention or cycle time Heat transfer method Capacity Typical evaporation capacity... 

Assuming that radiation losses amount to 20 kJ/kg of dry air used, determine the mass flow of dry air supplied to the dryer and the humidity of the outlet air. The latent heat of water vapour at 295 K = 2449 kJ/kg, the specific heat capacity of dried material = 0.88 kJ/kg K, the specific heat capacity of dry air = 1.00 kJ/kg K, and the specific heat capacity of water vapour = 2.01 kJ/kg K. 

A flow of 0.35 kg/s of a solid is to be dried from 15 per cent to 0.5 per cent moisture on a dry basis. The mean specific heat capacity of the solids is 2.2 kJ/kgdegK. It is proposed that a co-current adiabatic dryer should be used with the solids entering at 300 K and, because of the heat sensitive nature of the solids, leaving at 325 K. Hot air is available at 400 K with a humidity of 0.01 kg/kg dry air and the maximum allowable mass velocity of the air is 0.95 kg/m2s. What diameter and length should be specified for the proposed dryer ... 

An industrial dryer for granular material can be modeled (Becker et al 1984) with the total specific cost of drying C( /m3) being... 

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