Evaporation load

Extract is stored in insulated tanks prior to drying. Because high soluble soHds concentration is deskable to reduce aroma loss and evaporative load in the driers, most processors concentrate the 15—30% extract to 35—55% prior to drying (33). This may be accompHshed by vacuum evaporation or freeze concentration. Clarification of the extract, normally by centrifiigation, may be used to assure the absence of insoluble fine particles. 

Figure 1 shows the relationship between dry and wet bases. When the wet basis is used to state moisture content, a 2—3% change at moisture contents above 50% may represent a 10—30% change ia evaporative load per unit weight of dry material. 

Because each effect of an evaporator produces almost as much vapor as the amount it condenses, the total evaporation accompHshed per unit of prime steam, or steam economy, iacreases ia almost direct proportioa to the number of effects used. The total heat load is also spHt up betweea the effects so that each effect has a much lower heat duty than a single effect for the same total evaporation load. However, the total available AT is also spHt up similarly so that each effect of a multiple effect requites about as much heating surface as a single effect operating over the same total temperature difference. Thus ia selecting the number of effects to use ia any iastallatioa, steam cost savings and capital cost of effects have to be balanced. Even before... 

FIG. 8 54 Controlling evaporators requires matching steam flow and evaporative load, here using feedforward control. 

While the rotary dryer shown is commonly used for grains and minerals, this system has been successfully applied to fluid-bed diying of plastic pellets, air-hft diying of wood fibers, and spray drying of milk solids. The air may be steam-heated as shown or heated By direct combustion of fuel, provided that a representative measurement of inlet air temperature can be made. If it cannot, then evaporative load can be inferred from a measurement of fuel flow, replacing AT in the set point calculation. 

Performance Data for Direct-Heat Tray Dryers A standard two-truck diyer is illustrated in Fig. 12-48. Adjustable baffles or a perforated distribution plate is normally employed to develop 0.3 to 1.3 cm of water-pressure drop at the wall through which air enters the truck enclosure. This will enhance the uniformity of air distribution, from top to bottom, among the trays. In three (or more) truck ovens, air-reheat coils may be placed between trucks if the evaporative load is high. Means for reversing air-flow direction may also be provided in multiple-truck units. 

Evaporation load from wet surfaces or floors can be evaluated using the following equation ... 

Evaporator load + compressor power = condenser load... 

Condenser rating is correctly stated as the rate of heat rejection. Some manufacturers give ratings in terms of the evaporator load, together with a de-rating factor, which depends on the evaporating and condensing temperatures. 

These expl mixtures were developed at Pica-tinny Arsenal just prior to WWII. For their, prepn wet EDNA was added slowly to molten TNT heated to ca 105°C in a steam jacketed melting kettle equipped with a stirrer. Heating and stirring were continued until, all moisture was evaporated. Loading in ammunition was done by pouring the mixture cooled to 85°... 

Figure 8.24. Simpler circuits of compression refrigeration (see also Example 8.17). (a) Basic circuit consisting of a compressor, condenser, expansion valve and evaporator (load), (b) Conditions of the basic circuit as they appear on a pressure-enthalpy diagram the primed points are on the vapor-liquid boundary curve, (c) Circuit with circulation of refrigerated brine to process loads, (d) Circuit with two-stage compression and intercooling.

Sedimentation, Filtration, Decantation, Evaporation, Loading, Sieving and Distillation. 

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