Two-stage Systems

Strong Acid Cation-Strong Base Anion 

Loading. Hydrogen form column operation at typically 5-80 m m h linear flowrate. 

Regenerant. Dilute hydrochloric acid (1.4keqm ) or sulfuric acid (0.3-1.0 keqm ), the latter concentration being decided by the calcium content of the raw water thereby avoiding calcium sulfate precipitation. Regeneration levels are typically 1.3-2.0 keq m R injected over a period of about 30 minutes. 

Cation Column Effluent Quality As the water passes down the column stoichiometric ion exchange occurs to give a dilute mixture of acids as given by the following reactions  

The titratable acidity at the cation outlet is called the Free Mineral Acidity (EMA) and is related to the Equivalent Mineral Acidity EMA) by the relationship  

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The urea solution is evaporated in a two-stage system (99.8%) if the final product is prills, and a single-stage system (+95%) if granules are to be provided. 

FoUowiag Monsanto s success, several companies produced membrane systems to treat natural gas streams, particularly the separation of carbon dioxide from methane. The goal is to produce a stream containing less than 2% carbon dioxide to be sent to the national pipeline and a permeate enriched ia carbon dioxide to be flared or reinjected into the ground. CeUulose acetate is the most widely used membrane material for this separation, but because its carbon dioxide—methane selectivity is only 15—20, two-stage systems are often required to achieve a sufficient separation. The membrane process is generally best suited to relatively small streams, but the economics have slowly improved over the years and more than 100 natural gas treatment plants have been installed. 

FIG. 11-78 Typical two-stage system with two evaporating temperatures, flash-gas removal, and intercooling. 

Two-stage systems should be seriously considered when the evaporating temperature is below—20°C. Such designs will save on power and reduce compressor discharge temperatures, but will increase initial cost. 

Particle charging and collection can taltc place in different sections, as illustrated in Fig. 13.6. In this two-stage system, the collection of particles takes place in a region without gas ions, i,e the electric field is generated by the high-voltage electrode only. 

Determine the approximate horsepower and condenser duty for the two-stage system of Figure 11-47. Note A simpler system omits the suh-cooler and smaller evaporator (see diagram on Figure 11-37). 

Refrigerant evaporating temperature Consider the 25MM Btu/hr —40°F independently as a simple two-stage system. Thus, condensing at +120°F... 

In a two-stage system, the vapors from the compressor s first stage discharge are partially condensed and flashed in an interstage drum. The liquid hydrocarbon is pumped forward to the gas plant, either to the high pressure separator (HPS) or directly to the stripper. 

At the end of the chapter, we compare the use of membranes with the HC1 and bleach processes and with an enhanced liquefaction process in which a third stage is added to an operating two-stage system. 

Optimai per stage pressure ratio For a two-stage system, PRi=PR2. 

An SMB-type process has been disclosed to extract the 26DMN using liquid phase adsorption in a simulated moving bed two stage system [45, 46]. The source of the 26DMN is not specified but could be by one of the methods outlined by Lillwitz. Currently almost all separation of 26DMN is by crystallization. 

The above procedure can be extended directly to multistage operations however, here the argument for equal-size units is stronger still than for the two-stage system. 

Hicks, R.M., Chowaniec, J., and Wakefield, S.J. (1978). Experimental induction of bladder tumors by a two-stage system. in Mechanisms of Thmor Promotion and Cocarcinogenesis, Slaga, T.J., SrvAK, A. AND Boutwell, R.K., Eds., (Raven Press, New Tfork). 

Berry DL, Slaga TJ, DiGiovarmi J, et al. 1979. Studies with chlorinated dibenzo-(p)-dioxins, polybrominated biphenyls, and polychlorinated biphenyls in a two-stage system of mouse skin tumorigenesis Potent anticarcinogenic effects. Ann N Y Acad Sci 320 405-414. 

Dilution water calculations for a two stage system using recycle are slightly more complicated than for a single stage or two stage without recycle. These problems are better suited tn a computer, as hand calculations require several entries of dilution water variables in order to zero in on the proper balance. 

Figure 8.18 A two-stage system to produce a highly concentrated permeate stream. Selectivity, 20 pressure ratio, 20...

DiGiovanni J, Viaje A, Berry DL, et al. 1977. Tumor-initiating ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and Arochlor 1254 in the two-stage system of mouse skin carcinogenesis. Bull Environ Contam Toxicol 18 552-556. 

What can be done to achieve this necessary improvement Most plant cell products are secondary metabolites, which means that plant suspension culture systems involve a growth phase and a production phase. In any commercial system, one will probably want to separate physically these two phases. Unfortunately, one has to add a growth hormone such as 2-4-D for a successful growth phase, and these hormones must be completely removed before elicitors are added to the production phase to induce the secondary product. Optimizing this two-stage system is an engineering challenge. 

The reactor inlet temperature ranges from 50°C at start-of-run to about 65°C at end-of-run conditions. One important feature of the two-stage system is that the catalyst can be replaced in each reactor separately, without shutting down the ETBE unit. 

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