Parameters tubular reactor design

At the present state these correlations together with Eq. 23 for the prediction of the apparent heat conductivity amd Eq. 6, 7 for the particle-to-fluid heat transfer may be recommended for application in tubular reactor design. These correlations give fairly reliable parameters for either homogeneous or heterogeneous one or two dimensional models for the mathematical simulation of packed bed reactors. 

The importance of dilfusion in a tubular reactor is determined by a dimensionless parameter, SiAt/S = QIaLKuB ), which is the molecular diffusivity of component A scaled by the tube size and flow rate. If SiAtlB is small, then the elfects of dilfusion will be small, although the definition of small will depend on the specific reaction mechanism. Merrill and Hamrin studied the elfects of dilfusion on first-order reactions and concluded that molecular diffusion can be ignored in reactor design calculations if... 

This chapter contains a discussion of two intermediate level problems in chemical reactor design that indicate how the principles developed in previous chapters are applied in making preliminary design calculations for industrial scale units. The problems considered are the thermal cracking of propane in a tubular reactor and the production of phthalic anhydride in a fixed bed catalytic reactor. Space limitations preclude detailed case studies of these problems. In such studies one would systematically vary all relevant process parameters to arrive at an optimum reactor design. However, sufficient detail is provided within the illustrative problems to indicate the basic principles involved and to make it easy to extend the analysis to studies of other process variables. The conditions employed in these problems are not necessarily those used in current industrial practice, since the data are based on literature values that date back some years. 

The temperature of the feed to a CSTR has a fairly minor impact on the steady-state design. Unlike tubular reactors (to be discussed in Chapters 5 and 6), in which feed temperature is a critictal design parameter (lower inlet temperature requires a larger reactor), the temperature of the feed to a CSTR affects only the sensible-heat component of the total heat removal/addition rate. The heat of reaction is typically considerably larger than this sensible heat. 

It is useful to initially examine the tubular reactor as an isolated unit so that some insight can be gained about the effects of various design and operating parameters on its inherent behavior. The equations describing the steady-state operation of a tubular reactor are presented and illustrated for a specific numerical example. Both adiabatic and nonadiabatic tubular reactors are considered. 

Luyben, W.L., Effect of design and kinetic parameters on the control of cooled tubular reactor systems, Ind. Eng. Chem. Res., 40, 3623-3633 (2001)... 

In practice, it generally will be found that one-dimensional models are entirely adequate for optimization, provided that they are validated in some kind of pilot-scale tubular reactor. Validation comprises the adjustment of parameters in the reactor model equations so that observed and predicted temperature and concentration profiles match as closely as possible. Typical parameters are the relative catalyst activity factors Bj and, if necessary, the overall heat-transfer coefficient, U. A statistically-designed set of experiments in the pilot-plant is invaluable for model validation, and such a set was used in this project. 

Cichy, P.T. Russell, T.W.F. Two-phase reactor design tubular reactors—reactor model parameters. Ind. Eng. Chem. Res. 1969, 61, 15. 

Numerical methods such as the Runge-Kutta-Gill fourth-order correct integration algorithm are required to simulate the performance of a nonisothermal tubular reactor. In the following sections, the effects of key design parameters on temperature and conversion profiles illustrate important strategies to prevent thermal runaway. 

For a given length Lpfr of a tubular reactor packed with spherical catalytic pellets, one calculates the following values of five important dimensionless design parameters. The chemical kinetics are first-order and irreversible ... 

Separation of variables provides the analytical solution to this first-order ODE given by (30-60). When the external resistance to mass transfer is significant, the following result allows one to predict reactant conversion in the exit stream as a function of important design parameters based on isolated pellets as well as the entire packed catalytic tubular reactor ... 

Consider the following parameters in the design of this packed catalytic tubular reactor, which contains porous spherical pellets. The kinetic rate... 

One advantage of the second method is that the design need not be limited to the same type of reactor. Data taken in a stirred reactor and manipulated to get intrinsic kinetic parameters could be used to estimate the performance of a tubular reactor, a packed bed, or perhaps a new type of contactor for the same reaction. Fundamental kinetic parameters obtained from a small fixed-bed reactor might lead to consideration of a fluidized-bed reactor for the large unit. Of course, pilot-plant tests of the alternate reactor type would be advised. 

D model gave center temperatures 2-3°C higher than the 1-D model, and a runaway reaction occurred at a slightly lower feed temperature than with the 1-D model. However, the 1-D model could be modified to be conservative by decreasing to 3kg/R to compensate for the higher reaction rate in the center. In any case, it is unlikely that a tubular reactor would be designed to operate close to the stability limit because of uncertainties in the kinetic and heat transfer parameters. 

The necessity to implement new conditions for carrying out heat and mass exchange processes directly in the reaction zone of fast chemical reactions, resulted in unprecedented designs of tubular reactors with the hydrodynamic flow mode of a reaction mixture as a key parameter [33-35]. These devices are characterised by high specific productivity and make it possible to achieve a quasi-plug flow mode in a reaction zone, providing heat and mass exchange processes with duration comparable to that of a chemical reaction. 

To accomplish optimal operation of an existing LDPE tubular reactor or to design a new reactor system, it is necessary to know the sensitivity of system responses caused by deviations of system parameters from their nominal values. It is well known that pol3mie-rization reactors are very sensitive to changes in operating and kinetic parameters. Therefore, it is very important to know the underlying relationships between the system outputs and the model parameters. 

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