Evaporators cascade

Because the number of evaporators represents an integer-valued variable, and because many engineers use tables and graphs as well as equations for evaporator calculations, some of the methods outlined in Chapters 9 and 10 can be applied for the optimization of multi-effect evaporator cascades. 

Examination of possible systems for boron isotope separation resulted in the selection of the multistage exchange-distillation of boron trifluoride—dimethyl ether complex, BF3 -0(CH3 )2, as a method for B production (21,22). Isotope fractionation in this process is achieved by the distillation of the complex at reduced pressure, ie, 20 kPa (150 torr), in a tapered cascade of multiplate columns. Although the process involves reflux by evaporation and condensation, the isotope separation is a result of exchange between the Hquid and gaseous phases. 

Disk or cascade evaporators are used in the pulp and paper industry to recover heat and entrained chemicals from boiler stack gases and to effect a final concentration of the black liquor before it is... 

Example. With the example cascaded system at an evaporator temperature of -100°F, the horsepower requirement is 6.2hp/ton refrigeration. A ton of refrigeration is equal to 12,000 BTU/hr. 

In mechanical refrigeration, a multicomponent refrigerant consisting of nitrogen, methane, ethane, and propane is used through a cascade cycle. When these liquids evaporate, the heat required is obtained from... 

An exothermic reaction with the stoichiometry A 2B takes place in organic solution. It is to be carried out in a cascade of two CSTR s in series. In order to equalize the heat load on each of the reactors it will be necessary to operate them at different temperatures. The reaction rates in each reactor will be the same, however. In order to minimize solvent losses by evaporation it will be necessary to operate the second reactor at 120 °C where the reaction rate constant is equal to 1.5 m3/kmole-ksec. If the effluent from the second reactor corresponds to 90% conversion and if the molal feed rate to the cascade is equal to 28 moles/ksec when the feed concentration is equal to 1.0 kmole/m3, how large must the reactors be If the activation energy for the reaction is 84 kJ/mole, at what temperature should the first reactor be operated ... 

Stewart, G. and BEVERIDGE, G. S. G. Computers and Chemical Engineering 1 (1977). 3. Steady-state cascade simulation in multiple effect evaporation. 

M or Plant water system Foam produced in ACE cascade evaporator during water-washing carried out into furnace through primary air system... 

Very major Plant water system Water being used to water-wash cascade evaporator and black liquor header around furnace entered furnace because (1) liquor guns were left in firing position when not firing liquor and (2) one liquor gun valve was inadvertently left open... 

Fig. 8.2 Principle of the MALDI process. Initially, analyte and matrix are co-crystal I ized. After evaporation of the solvent, a nanosecond laser pulse is directed onto the crystalline surface, and both matrix and analyte molecules are desorbed. A complex reaction cascade leads to the formation of charged analyte molecules that reach the mass spectrometer without significant fragmentation.

There are several variations of the basic vapor refrigeration cycle. A cascade cycle is used when the temperature difference between the evaporator and the condenser is quite large. The multistaged cycle is used to reduce the required compressor power input. 

The cooling load of the cascade vapor refrigeration cycle is the rate of heat added in the evaporator of the lowest temperature cycle. The power added to the cycle is the sum of the power added to the individual compressors ... 

Determine the mass rate flow of the top cycle, power required by compressors 1 and 2, total power required by the compressors, rate of heat added to the evaporator, cooling load, and COP of the cascade vapor refrigeration cycle. 

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