Concentration, cycles

PoUowing further development (38), a two-cycle process has been adopted by industry. In the first concentration cycle, the clarified feed acid containing 100—200 mg/L U Og [1334-59-8] is oxidized, for example, with hydrogen peroxide or sodium chlorate [7775-09-9] to ensure that uranium is in its 6+ valence state is not extracted. Uranium is extracted with a solvent composed of 0.5 Af D2EHPA and 0.125 Af TOPO dissolved in an aUphatic hydrocarbon diluent. 

Scale control can be achieved through operation of the cooling system at subsaturated conditions or through the use of chemical additives. The most direct method of inhibiting formation of scale deposits is operation at subsaturation conditions, where scale-forming salts are soluble. For some salts, it is sufficient to operate at low cycles of concentration and/or control pH. However, in most cases, high blowdown rates and low pH are required so that solubihties are not exceeded at the heat transfer surface. In addition, it is necessary to maintain precise control of pH and concentration cycles. Minor variations in water chemistry or heat load can result in scaling (Fig. 12). 

Blowdown discards a portion of the concentrated circulating water due to the evaporation process in order to lower the system solids concentration. The amount of blowdown can be calculated according to the number of cycles of concentration required to limit scale formation. Cycles of concentration are the ratio of dissolved sohds in the recirculating water to dissolved solids in the makeup water. Since chlorides remain soluble on concentration, cycles of concentration are best expressed as the ratio of the chloride content of the circulating and makeup waters. Thus, the blowdown quantities required are determined from... 

Concentration Cycles Comparison of dissolved solids in makeup water with solids concentration in the circulating water. 

Such results generally hold for the differential equations of van der Pol, Li6nard, and some others of the same type. In view of the constant rotation [Pg.340]

AVT Barg BD BDHR BF BOF BOOM BOP BS W BSI BTA Btu/lb BW BWR BX CA CANDUR CDI CFH CFR CHA CHF CHZ Cl CIP CMC CMC CMC COC All-Volatile treatment bar (pressure), gravity blowdown blowdown and heat recovery system blast furnace basic oxygen furnace boiler build, own, operate, maintain balance of plant basic sediment and water British Standards Institution benzotriazole British thermal unit(s) per pound boiler water boiling water reactor base-exchange water softener cellulose acetate Canadian deuterium reactor continuous deionization critical heat flux Code of Federal Regulations cyclohexylamine critical heat-flux carbohydrazide cast iron boiler clean-in-place carboxymethylcellulose (sodium) carboxy-methylcellulose critical miscelle concentration cycle of concentration... 

Walter, S., Liauw, M., Fast concentration cycling in microchannel reactors, in Proceedings of the 4th International Conference on Microreaction Technology,... 

For a short description of the aims of experimental concentration cycling with respect to citraconic acid formation, see [13]. It is also demonstrated there that the response to rectangular concentration pulses for a given reactor configuration of a multi-channel-stack micro reactor can be improved by increasing the number of platelets and channels (while reducing their diameter). Such behavior was shovm for an incompressible fluid, i.e. is not solely related to the above-mentioned reaction. 

Reaction Rate Resonance in the Concentration Cycling of the Catalytic Oxidation of Carbon Monoxide... 

The effect of forced concentration cycling was investigated on the oxidation of CO over industrial V2O5 catalyst. The resulting rate, when time-averaged, exhibited frequency-dependent harmonic behavior, with multiple extrema. Some preliminary interpretation is provided by analogy to an electrical network containing resistance and inductance. 

Some experimental studies (1-7) have demonstrated the possibility of improving the performance of a catalytic reactor through cyclic operation. Eenken et al. (4) reported an improvement of 70% in conversion of ethylene to ethane under periodic operation. In a later article (2), they concluded that periodic operations can be used to eliminate an excessively high local temperature inside the catalytic reactor for a highly exothermic reaction. In our laboratory, Unni et al. (5) showed that under certain conditions of frequency and amplitude associated with the forced concentration cycling of reactants, the rate of oxidation of SC>2 over catalyst can be increased by as much as 30%. Re-... 

Figure 1. Waveforms of concentration cycles used for forced periodic operation.

Abdul Kareem, H. K Silveston, P. L. and Hudgins, P. R., 1980, Forced cycling of the catalytic oxidation of CO over a V205 catalyst. I—Concentration cycling. Chem. Engng Sci. 35, 2077-2084 II—Temperature cycling. Chem. Engng Sci. 35, 2085-2088. 

Zhou, X., Barshad, Y. Gulari, E. 1986 CO oxidation on Pd/Al203. Transient response and rate enhancement through forced concentration cycling. Chem. Engng Sci. 41(5), 1277-1284. 

The substantial change in the temperature profile that accompanies forced concentration cycling is shown in Figure 5. The dark circles represent the steady state temperature profile in the fixed bed. The open circles represent mean behavior for a cycle-period of 20 minutes. The hatched region indicates the temperature fluctuation. It can be seen that the maximum temperature is increased by about 1°C as a result of periodic operation and is shifted downstream slightly. This is... 

The reaction rate can be increased by concentration cycling in systems with substantial inhibition of adsorbed reaction product, as for example the addition of ethylene to acetic acid (Table 1, example 2). A positive effect is achieved at high frequency oscillation of acetic acid concentration. Cycle average concentration of intermediate product A (see Table 1) is lower than in the steady state. This facilitates ethylene adsorption and a favorable distribution between the two adsorbed species. 

X. Zhou and E. Gulari. CO oxidation on Pt/Al203 and Pd/Al203 transient response and concentration cycling studies. Chem. Eng. Sci. 47 883 (1986). 

G. Vaporciyan, A. Annapragada. and E. Gulari. Rate enhancements and quasi-periodic dynamics during forced concentration cycling of CO and O2 over supported Pt-Sn02. Chem. Eng. Sci. 43 2951 (1988). 

Primers Specifications Primerconcentration MgCl2 concentration Cycling conditions Preheat step, cycle number and final steo PCR machine... 

The number of cycles that separates each decade difference in initial template concentration Cycles/log [DNA]) is I/log (efficiency). The calibration curve slope is the negative of this value -1/log (efficiency)), assuming the log [initial template] is plotted on the x-axis as the independent variable, and cycle number is plotted on the y-axis as the dependent variable. 

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