Interbeds

Adl b tic Converters. The adiabatic converter system employs heat exchangers rather than quench gas for interbed cooling (Fig. 7b). Because the beds are adiabatic, the temperature profile stiU exhibits the same sawtooth approach to the maximum reaction rate, but catalyst productivity is somewhat improved because all of the gas passes through the entire catalyst volume. Costs for vessels and exchangers are generally higher than for quench converter systems. 

Fig. 3. Multiple fixed-bed configurations (a) adiabatic fixed-bed reactor, (b) tubular fixed beds, (c) staged adiabatic reactor witb interbed beating (cooling),...

Figure 22.6 Schematic diagram showing how plasticizer molecules interbed between polyvinyl chloride chains...

Hydrogenation of benzene to cyclohexane was effected in a fixed bed reactor at 210-230°C, but a fall in conversion was apparent. Increasing the bed temperature by 10°C and the hydrogen flow led to a large increase in reaction rate which the interbed cooling coils could not handle, and an exotherm to 280°C developed, with a hot spot of around 600° C which bulged the reactor wall. 

One of the main drivers for the development of new sulphuric acid catalysts over the last decades has been the desire to reduce S02 emissions from sulphuric acid plants without costly tail gas cleaning or an additional interbed... 

Table 1.3 Range of hydrologic properties of Lower Yakima basalt flows and interbeds (Freeze and Cherry 1979)...

ToRPAN, B. K. 1954. Chemical and Mineralogical Composition of Seams and Interbeds Seams of Kukersite. Tallinn Technical University, Tallinn, Series A, N 57, 22-31 (in Russian). 

Figure 17.13. Multibed catalytic reactors (a) adiabatic (b) interbed coldshot injection (c) shell and tube (d) built-in interbed heat exchanger (e) external interbed exchanger (f) autothermal shell, outside influent-effluent heat exchanger (g) multishell adiabatic reactor with interstage fired heaters (h) platinum-catalyst, fixed bed reformer for 5000 bpsd charge rate reactors 1 and 2 are 5.5 ft dia by 9.5 ft high and reactor 3 is 6.5 x 12.0 ft.

Sampling Fractionation Research Inc. (FRI) developed a sam-ling technique that eliminates the influence of "end effects and etects a maldistributed composition profile. This technique [Silvey and Keller, IChemE Symp. Ser. 32, p. 4 18 (1969)] samples the bed at frequent intervals, typically every 0.6 m or so. HETP is determined from a plot of these interbed samples rather than from the top and bottom compositions. 

It is imperative that the interbed samplers catch representative samples, which are an average through the bed cross section. Caution is required when the liquid is highly aerated and turbulent (e.g., above 1300 kPa psia or above 1 m/min). The author highly recommends the FRI sampling technique for all other conditions. 

The desulfurized feedstock is then mixed with superheated steam and passed over a nickel catalyst (730 to 845°C 1350 to 1550°F 400 psi) to produce a mixture of hydrogen, carbon monoxide, and carbon dioxide as well as excess steam. The effluent gases are cooled (to about 370°C 700°F) and passed through a shift converter which promotes reaction of the carbon monoxide with stream to yield carbon dioxide and more hydrogen. The shift converter may contain two beds of catalyst with interbed cooling the combination of the two catalyst beds promotes maximum conversion of the carbon monoxide. This is essential in the event that a high-purity product is required. 

Radionuclide transport in natural waters is strongly dependent on sorption, desorption, dissolution, and precipitation processes. The first two sections discuss laboratory investigations of these processes. Descriptions of sorption and desorption behavior of important radionuclides under a wide range of environmental conditions are presented in the first section. Among the sorbents studied are basalt interbed solids, granites, clays, sediments, hydrous oxides, and pure minerals. Effects of redox conditions, groundwater composition and pH on sorption reactions are described. 

Radionuclide Sorption and Desorption Reactions with Interbed Materials from the Columbia River Basalt Formation... 

The groundwater transport of radionuclides through waterbearing interbed layers in the Columbia River basalt formation will be controlled by reactions of the radionuclides with groundwater and interbed solids. These interactions must be understood to predict possible migration of radionuclides from a proposed radioactive waste repository in basalt. Precipitation and sorption on interbed solids are the principle reactions that retard radionuclide movement in the interbeds. The objective of the work described herein was to determine the sorption and desorption behavior of radionuclides important to safety assessment of a high-level radioactive waste repository in Columbia River basalt. The effects of groundwater composition, redox potential, radionuclide concentration, and temperature on these reactions were determined. 

This equation can be used to describe one-dimensional transport of radionuclides through porous media (e.g. radionuclide elution curves from laboratory columns packed with interbed solids) assuming instantaneous sorption and desorption. Van Genuchten and coworkers have demonstrated the importance of using both sorption and desorption isotherms in this equation when hysteresis is significant. Isotherm data for sorption and desorption reactions of radionuclides with interbed materials are presented in this paper which can be used to predict radionuclide transport. 

Three interbed materials from the Columbia River Basalt Group have been investigated in the radionuclide sorption experiments. Interbeds are porous sedimentary layers located between many of the basalt flows in the Columbia River Basalt Group and comprise a potential preferential pathway for groundwater and, therefore, radionuclide transport. 

Two interbed samples, a sandstone and a tuff, were taken from as outcrop of the Rattlesnake Ridge Interbed above the... 

Pomona basalt flow. A third interbed sample was taken from drilling cores of the Mabton Interbed, located between the Saddle Mountains and Wanapum Basalts. The Mabton Interbed is the first continuous, major interbed above the candidate repository horizons in the Grande Ronde Basalts. Mineralogical characteristics of the interbed materials are summarized in Table n. A more complete discussion of the characteristics of the interbed materials may be found in Reference (4). 

Procedures. Batch equilibrations of interbed solids (Mabton Interbed, Rattlesnake Ridge sandstone, or tuff), tracers, and groundwaters were used to measure radionuclide distributions between solid and liquid phases. Triplicate measurements were made for each combination of temperature, redox condition, tracer concentration, tracer type, groundwater composition, and interbed sample. Constant temperatures were maintained by placing the... 

Source/Characteristic Interbed sandstone Interbed sandstone/ claystone Interbed tuff... 

Source Rattlesnake Ridge Interbed Mabton Interbed Rattlesnake Ridge Interbed... 

Sorption and Desorption Isotherms. To model radionuclide transport in groundwater through geologic media, it is necessary to mathematically describe sorption and desorption in terms of isotherms. The Freundlich isotherm was found to accurately describe sorption and desorption of all radionuclides studied in the interbed-groundwater systems, except when precipitation of the radionuclide occurred. 

Sorption isotherms were also measured for sorption of selenium, technetium, tin, radium, uranium, neptunium, plutonium, and americium on the reference Mabton Interbed solids. The GR-1A groundwater composition was used in these experiments. Two temperatures (23°C 2°C and 60°C 1°C) were used, and both oxidizing and reducing conditions were used for each radionuclide. 

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