Reactor homogeneous

Homogeneous Aqueous Reactors. As a part of the research on neutron multiphcation at Los Alamos in the 1940s, a small low power reactor was built using a solution of uranium salt. Uranyl nitrate [36478-76-9] U02(N0 2> dissolved in ordinary water, resulted in a homogeneous reactor, having uniformly distributed fuel. This water boiler reactor was spherical. The 235u... 

The homogeneous reactor experiment-2 (HRE-2) was tested as a power-breeder in the late 1950s. The core contained highly enriched uranyl sulfate in heavy water and the reflector contained a slurry of thorium oxide [1314-20-1J, Th02, in D2O. The reactor thus produced fissile uranium-233 by absorption of neutrons in thorium-232 [7440-29-1J, the essentially stable single isotope of thorium. Local deposits of uranium caused reactivity excursions and intense sources of heat that melted holes in the container (18), and the project was terrninated. 

The units of rv are moles converted/(volume-time), and rv is identical with the rates employed in homogeneous reactor design. Consequently, the design equations developed earlier for homogeneous reactors can be employed in these terms to obtain estimates of fixed bed reactor performance. Two-dimensional, pseudo homogeneous models can also be developed to allow for radial dispersion of mass and energy. 

Equations 12.7.48 and 12.7.39 provide the simplest one-dimensional mathematical model of tubular fixed bed reactor behavior. They neglect longitudinal dispersion of both matter and energy and, in essence, are completely equivalent to the plug flow model for homogeneous reactors that was examined in some detail in Chapters 8 to 10. Various simplifications in these equations will occur for different constraints on the energy transfer to or from the reactor. Normally, equations 12.7.48 and 12.7.39... 

At steady state, the PDF (and thus the RTD function) will be independent of time. Moreover, the internal-age distribution at a point x inside the reactor is just I(a x, t) = fr(a x, t). For a statistically homogeneous reactor (i.e., a CSTR), the PDF is independent of position, and hence the steady-state internal-age distribution 1(a) will be independent of time and position. 

FlameMaster v3.3 A C+ + Computer Program for OD Combustion and ID Laminar Flame Calculations. FlameMaster was developed by H. Pitsch. The code includes homogeneous reactor or plug flow reactors, steady counter-flow diffusion flames with potential flow or plug flow boundary conditions, freely propagating premixed flames, and the steady and unsteady flamelet equations. More information can be obtained from http //www.stanford.edu/group/pitsch/Downloads.htm. 

An assumption involving heat losses from the reactor is made in most treatments. The effect of heat transfer on the maximum reaction rates of a homogeneous reactor has been treated by DeZubay and Woodward (14). It was found that a lowering of the reactor surface temperature appreciably lowered the chemical reaction rates. Longwell and Weiss (43) found, for example, a loss equal to 5% of the maximum adiabatic heat liberated reduces the maximum heat release rate by more than 30%, while a 20% heat loss reduces the rate about 85%. One should not assume an adiabatic system without some definite knowledge of the magnitude of the heat losses. 

Stoichiometric Fuel Air Ratio Figure 6. Maximum heat release for a homogeneous reactor... 

The writer echoes the wishes of many workers in the combustion field in hoping that heterogeneous combustion systems will eventually lend themselves to treatments similar to those used with the homogeneous reactor. 

COMBUSTOR SIZE. The question of whether combustor volume is the limiting factor in altitude operation can be answered by comparing heat release rates measured in simple flames and homogeneous reactors with those obtained in engines. Simple flames and reactors give rates of the order of 7 X 108 B.t.u. per hour per cubic foot per atmosphere... 

In a substantial majority of the cases where packed tubular reactors are employed the flow conditions can be regarded as those of plug flow. However, dispersion (already discussed in Chapter 2 in relation to homogeneous reactors) may result in lower conversions than those obtained under truly plug flow conditions. 

The importance of dispersion and its influence on flow pattern and conversion in homogeneous reactors has already been studied in Chapter 2. The role of dispersion, both axial and radial, in packed bed reactors will now be considered. A general account of the nature of dispersion in packed beds, together with details of experimental results and their correlation, has already been given in Volume 2, Chapter 4. Those features which have a significant effect on the behaviour of packed bed reactors will now be summarised. The equation for the material balance in a reactor will then be obtained for the case where plug flow conditions are modified by the effects of axial dispersion. Following this, the effect of simultaneous axial and radial dispersion on the non-isothermal operation of a packed bed reactor will be discussed. 

Let Lp be the length of the simple ideal plug-flow homogeneous reactor with no dispersion for the same value of CA/CAm, and tp be the required residence time in the plug-flow reactor i.e. in equation A Dl = 0,... 

The building block of the superstructure representation is the generic reactor unit, which follows the shadow reactor concept (32). This generic unit is illustrated in Figure 4. Each generic unit consists of reactor compartments in each phase of the system, and each processes the reaction. The shadow reactor compartment assumes a state from the set of homogeneous reactors. The default units in the set include CSTRs and PFRs with side streams. The interface between a given pair of... 

Homogeneous reactors contain only one phase throughout the reactor. 

The choice of an adequate DO concentration. The desired DO concentration is a compromize between economy demands and hydraulic and biological demands. Moreover, in a non-homogeneous reactor a proper spatial distribution has to be determined. 

The spatial variation of concentrations in a non-homogeneous reactor will increase the control complexity. However, the concentration profiles provide extra information. The immediate problem of locating the DO probes suitably must be considered, which was remarked already in 1964 ( 16) "there is no one position in the tank which is representative of the whole tank all the time. This means that a one-point control system applied to a piston-flow plant is likely to be, at best, a compromise...". 

F. Examples Illustrating Use of Multi-mode Homogeneous Reactor Models 260... 

IV. Spatially Averaged Multi-mode (Multi-scale) Models for Homogeneous Reactors... 

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