Dryer

To recover liquid in order of preference of settlers, Section 5.8, thickeners. Section 5.10 and sedimentation centrifuges. Section 5.12 clarifier, settler, washing tray thickener, reactor larifier, hydrocyclone, batch tubular bowl centrifuge, batch automatic (horizontal or vertical bowl, disc with intermittent nozzle discharge) continuous disc bowl centrifuge with nozzle discharge. 

To recover liquid and solids in order of preference of filters expellers and presses. Section 5.17. 

If the cake is compressible use low pressure 200 kPa or vacuum rotary drum. 

For dry soUds consider the following filtering centrifuges. Section 5.13 basket, basket automatic constant speed vertical, basket automatic variable speed horizontal continuous conical with scroll conveyor, oscillating conical screen cylindrical screen with pusher conveyor or horizontal solid-screen scroll conveyor. 

Before considering drying as a method of removing solvent from a solid material or selecting specific drying equipment, the material should be tested sufficiently to determine whether it can be dried safely. The tests should measure 

The provision of thermal energy to a dryer is a separate consideration. Heating may be indirect, for example by steam or by the use of waste heat from another processing step. It may also be by direct firing, in which case proper handling of the feed and design of the combustion system are essential. 

There are many references and design codes dealing with combustion safeguards. Factory Mutual s Loss Prevention Data Book Service publishes data sheets that describe safeguards against fires and the prevention of fuel explosions. Examples are number 6-9, Industrial Ovens and Dryers, and numbers 6-17/13-20, Rotary Kilns and Dryers. The NFPA also has a series of 

In summary, energy supply systems must be built with regard to their safe operation while exposed to an inherent fire hazard. Prime considerations include  

Fuel or vapor explosion hazards require installation of explosion vents. These can be blowout panels that also provide some insulating value and structural strength. A frequent practice is to provide a vent ratio of one square foot of surface to every fifteen cubic feet of dryer volume. This is illustrative only, and may serve as a first estimate. Venting systems must conform to NFPA68. 

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Four of the more common types of thermal dryers used in the process industries are illustrated in Fig. 3.15. 

Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing. 

Drum dryers are shown in Fig. 3.15c. his consists of a heated metal roll. As the roll rotates, a layer of liquid or slurry is dried. The final dry solid is scraped off the roll. The product comes ofiF in flaked form. Drum dryers are suitable for handling slurries or pastes of solids in fine suspension and are limited to low and moderate throughput. 

Spray dryers are shown in Fig. 3.15d. Here, a liquid or slurry... 

Another important class of dryer is the fluidized-bed dryers. Some designs combine spray and fluidized-bed dryers. Choice between dryers is usually based on practicalities such as the materials handling characteristics, product decomposition, product physical form (e.g., if a porous granular material is required), etc. Also, dryer efficiency can be used to compare the performance of different dryer designs. This is usually defined as follows -. 

If the total heat consumed is from an external utility (e.g., mains steam), then a high efficiency is desirable, even perhaps at the expense of a high capital cost. However, if the heat consumed is by recovery from elsewhere in the process, as is discussed in Chap. 15, then comparison on the basis of dryer efficiency becomes less meaningful. 

As with distillation and absorption, when evaporators and dryers are chosen, no attempt should be made to carry out any optimization at this stage in the design. 

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. 

Evolving Dryer Design to Improve Heat Integration... 

It was noted earlier that dryers are quite difierent in character from both distillation and evaporation. However, heat is still taken in at a high temperature to be rejected in the dryer exhaust. The appropriate placement principle as applied to distillation columns and evaporators also applies to dryers. The plus/minus principle from Chap. 12 provides a general tool that can be used to understand the integration of dryers in the overall process context. If the designer has the freedom to manipulate drying temperature and gas flow rates, then these can be changed in accordance with the plus/minus principle in order to reduce overall utility costs. 

Like distillation, the appropriate placement of evaporators and dryers is that they should be above the pinch, below the pinch, but not across the pinch. The grand composite curve can be used to assess appropriate placement quantitatively. 

Dryers are different in characteristic from distillation columns and evaporators in that the heat is added and rejected over a large range of temperature. Changes to dryer design can be directed by the plus/minus principle. 

Distillation columns, evaporators, and dryers should be above the... 

Mueller M A, Yetter R A and Dryer F L 1999 Flow reactor studies and kinetic modelling of the... 

A fume hood is constructed in the manner shown in figure 6. Strike drew the frame as being made of lumber but it can be made of rebar or, preferably, from PVC pipes and joints so that it can be assembled and disassembled with ease. The frame is enclosed with plastic drop cloths or any semiclear plastic sheeting. The front face of the hood is halfway covered with plastic while the bottom half is exposed to allow one to move objects in or out and to manipulate things. On top of the chamber is attached some clothes dryer duct or some such crap which is led to a leaf blower or blower motor. The exhaust from the blower is led away to the outside. 

Dry bead process Dry-cell batteries Dry chemistry Dry-cleaning Dry cleaning fastness Dry-cleaning fluid Dry-cleaning solvent Dryers... 

Cmmbles are formed by grinding pellets to the desired sizes. Specialty feeds such as flakes can be made by mnning newly manufactured pellets through a press or through use of a double dmm dryer. The latter type of flakes begin as a slurry of feed ingredients and water. When the slurry is pressed between the hot rollers of the double dmm dryer, wafer thin sheets of dry feed are produced that are then broken into small pieces. The different colors observed in some tropical fish foods represent a mixture of flakes, each of which contains one or more different additives that impart color. 

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