Isothermal Design Method

Applicability of Physical Design Methods Physical design methods such as the classical isothermal design method or the classical adiabatic design method may be applicable for systems in which chemical reac tions are either extremely fast or extremely slow or when chemical equihbrium is achieved between the gas and liqmd phases. 

For preliminary screening and feasibility studies or for rough estimates, one may wish to employ a version of the isothermal design method which assumes that the liquid temperatures in the tower are everywhere equal to the inlet-liquid temperature. In their analysis of packed-tower designs, von Stockar and Wilke [Ind. Eng. Chem. Fun-dam., 16, 89 (1977)] showed that the isothermal method tended to underestimate the required height of packing by a factor of as much as... 

Finally, note that the adiabatic and isothermal pipe methods produce results that are reasonably close. For most real situations the heat transfer characteristics cannot be easily determined. Thus the adiabatic pipe method is the method of choice it will always produce the larger number for a conservative safety design. 

This chapter deals with the design of reactors which do not conform to these ideal models its attention is restricted to constant volume, single phase, isothermal reactors which are operated in the steady state. It is not intended to be a state of the art review of non-ideal reactor design methods, but rather an introduction to basic ideas and techniques frequently, the reader will be referred to more extended or specific coverage of the material being considered. 

For compressible fluid flow in plant piping, one can use Mak s Isothermal flow chart (Figure 1). Mak s chart was provided originally for relief valve manifold design and adopted by API. The relief valve manifold design method, and its derivation, is discussed in Section 20, Safety. Mak s methods can be applied to other common plant compressible flow situations. 

While DFT allows us to calculate values for q(p, e), it of course provides no analytic form for the function, and in general the form of f(e) is also unknown. However, by using carefully designed numerical methods, model isotherms calculated by MNLDFT can be used in carrying out the inversion of the discrete form of the integral equation of adsorption. In this way one can determine the effective adsorptive potential distribution of the adsorbent from the experimental adsorption isotherm. The method used can be expressed by... 

Nonisothermal stirred tanks are governed by an enthalpy balance that contains the heat of reaction as a significant term. If the heat of reaction is unimportant so that a desired Tout can be imposed on the system regardless of the extent of reaction, then the reactor dynamics can be analyzed by the methods of the previous section. This section focuses on situations where Equation 14.3 must be considered as part of the design. Even for these situations, it is usually possible to control a steady-state CSTR at a desired temperature. If temperature control can be achieved rapidly, then isothermal design techniques again become applicable. Rapid means on a time scale that is fast compared to reaction times and composition changes. 

In the simplest type of adsorption processes in which an adsorption column is used to remove a trace impurity from a process stream, the main requirement for rational design is an estimate of the dynamic or breakthrough capacity of the bed. In such systems the adsorbable impurity is invariably strongly adsorbed with a favorable isotherm and the concentration profile therefore rapidly approaches constant-pattern form. The constant-pattern assumption provides the basis of a very simple design method which permits reliable scale-up from small-scale laboratory experiments. 

The LUB design method requires that constant pattern behaviour occurs. It provides the basis for a very simple design method which allows the design and scale-up from small-scale laboratory experiments particularly for dilute single-component systems in which there is a favourable isotherm. A dilute system implies that the process will be isothermal. Care must be taken if the process is not isothermal because it is possible for the temperature effects to cause a favourable isotherm to take on effectively an unfavourable shape. 

In practice the traditional standard test method (see Appendix on p49) provides a fairly rapid method for determination of Cp and many manufacturers provide software specifically designed to comply with this. Three runs are required, each consisting of an isothermal period, temperature ramp and final isotherm. This method is applied identically to the succeeding runs ... 

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