Evaporators capacity

Proper soap removal increases the pulp mill s evaporator capacity by 5%. Therefore, soap is often recovered as weU at other places in the pulp mill, such as the weak black Hquor storage tanks and the heavy black Hquor oxidation system (13,14). 

F (kW/°C) = evaporator capacity per unit inlet temperature difference... 

Control of an evaporator requires more than proper instrumentation. Operator logs snould reflect changes in basic characteristics, as by use of pseuao heat-transfer coefficients, which can detect obstructions to heat flow, hence to capacity. These are merely the ratio of any convenient measure of heat flow to the temperature drop across each effect. Dilution by wash and seal water should be monitored since it absorbs evaporative capacity. Detailed tests, routine measurements, and operating problems are covered more fuUy in Testing Procedure for Evaporators (loc. cit.) and by Standiford [Chem. Eng. Prog., 58(11), 80 (1962)]. 

Cyclone A B C D E F G Approximate weight, lb H Evaporation capacity, lb water/hf Price,1 FOB shops... 

Evaporative capacity (Ib/hr) Nominal area in plan (ftxft) Nominal height (ft) Price FOB shops (US )... 

Based upon 1200 F air-inlet temperature. With an inlet temperature of 700 F the evaporative capacity would he half that given in the table. Prices are based upon carbon steel construction with cyclone collector (January, 1995). Motors and secondary dust collectors excluded... 

In the above example, 1 lb of initial steam should evaporate approximately 1 lb of water in each of the effects A, B and C. In practice however, the evaporation per pound of initial steam, even for a fixed number of effects operated in series, varies widely with conditions, and is best predicted by means of a heat balance.This brings us to the term heat economy. The heat economy of such a system must not be confused with the evaporative capacity of one of the effects. If operated with steam at 220 "F in the heating space and 26 in. vacuum in its vapor space, effect A will evaporate as much water (nearly) as all three effects costing nearly three times its much but it will require approximately three times as much steam and cooling water. The capacity of one or more effects in series is directly proportional to the difference between the condensing temperature of the steam supplied, and the temperature of the boiling solution in the last effect, but also to the overall coefficient of heat transfer from steam to solution. If these factors remain constant, the capacity of one effect is the same as a combination of three effects. 

With shell boilers, economizers will generally only be fitted to boilers using natural gas as the main fuel and then only on larger units. It would be unlikely that a reasonable economic case could be made for boilers of less than 4000kg/hF and A100°C evaporative capacity. The economizer will incorporate a flue gas bypass with isolating dampers to cover for periods when oil is used and for maintenance. The dampers require electric interlocks to the selected fuel. 

Drum dryers for pastes and slurries operate with contact times of 3-12 sec, produce flakes 1-3 mm thick with evaporation rates of 15-30kg/m2hr. Diameters are 1.5-5.0ft the rotation rate is 2-10 rpm. The greatest evaporative capacity is of the order of 3000 Ib/hr in commercial units. 

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... 

The evaporative capacity of dryers is given below in lb water / hr ft2 of heat transfer surface (kg water/hr m2 of heat transfer surface) ... 

APV, whose Paraflow plate heat exchanger is illustrated in Volume 1, Chapter 9, supply climbing and falling-film plate evaporators with evaporative capacities up to 10 kg/s. Such units offer the advantages of short contact and residence times and low liquor hold-up, and hence are widely used for the concentration of heat-sensitive materials. 

Contivac dryers, for example, have heating surfaces of 4-60 m2 and volumes of 0.1-3 m3. They may be operated under vacuum or up to 400 kN/m2 with heating fluids at 330 K-670 K. The evaporative capacity is 0.03-0.55 kg/s and the agitator speed ranges from 0.1 Hz (6 rpm) for Theologically difficult materials, to 1 Hz (60 rpm) for easier applications. 

Continuously supplying water at a rate higher than the evaporating capacity of the heater so that less volatile impiirities could flow away. Distilling and preserving water imder nitrogen atmosphere to prevent adsorbing C02 and other impurities horn the air. 

See figs. 2 and X Evaporator feed is sometimes preheated to increase evaporator capacity. 

During the concentration of the press liquor to molasses, d-limonene is distilled and recovered. The recovery of c/-limonene is a function of evaporator capacity. Most citrus processors add the molasses back onto the wet peel. The difference between the press liquor and the molasses is the amount of distilled limonene. This is determined by Scott oil analysis. 

Energy Conservation in Caprolactam Recovery (by Using the Evaporative Capacity of Cooling Towers)... 

The difference in processing behavior between rotors provided with straight blades and those with pitched blades is shown in Figure 6 by an application referring to solvent recovery from a polymer solution of low initial viscosity. The evaporation capacity of a thin-film evaporator equipped with straight blades decreases considerably as soon as the concentrated polymer reaches a viscosity between 1000 and 2000 P. The greatly increased mean film thickness that characterizes this vis-... 

Figure 6. Comparison of evaporation capacity between thin-film machines equipped with straight-blade rotors and the high viscosity machine (angled blades), expressed as a function of the concentrated polymer (polypropylene-heptane-solution)...

The sizes of ovens and evaporating capacity will be related closely to the types of plastic and the paints being used, while the dimensions of painting chambers and arrangements of jigs must be planned in relation to sizes and configurations of pieces being painted. 

W ter evaporative capacities up to 2Cf,000 lb/hr or more Very high thermal efficiency achieved. Less control of granular product size and size distribution than with other dispersion methods. 

The water evaporative capacities of the range of standard industrial spray dryers offered by one manufacturer is given in Fig. 7.5 as a function of inlet drying air temperature. Units with capacities up to 40,000 Ib/h (18,100 kg/h) or more of water evaporation are available. Dryer size in Fig. 7.5 is related to the mass flow rate of drying air several drying chamber physical sizes are possible for each of these air rates, depending on inlet temperature,... 

Fig. 7.5. Water evaporative capacities of standard spray dryers fitted with ceiling air dispensers. (Courtesy Niro Atomizer, Inc.)...

Peripheral sirface area, ft2 (CUfV6S for dun and rotaiy dyers) Evaporative capacity, lb water/h (curves for spray dryers)... 

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