Temperature profile in tubular

R. Jackson and I. Coward, Optimum Temperature Profiles in Tubular Reactors, Chem. Eng. Sci., 20, 911 (1965). 

R. Jackson and 1. Coward, Optimum Temperature Profiles in Tubular... 

As a consequence it is necessary to study heat regime in reaction zone and to reveal the ways of effective regulating of temperature profile in tubular turbulent apparatus under realization of fast chemical processes at the expense of external heat removal in technically admissible conditions. 

V. Heat Transferi Energy Transport and Temperature Profiles in Tubular Packed Bed Reactors... 

Plug Flow Reactor (PFR) A plug flow reactor is a tubular reactor where the feed is continuously introduced at one end and the products continuously removed from the other end. The concentration/temperature profile in the reactor varies with position. 

The ability to manipulate reactor temperature profile in the polymerization tubular reactor is very important since it directly relates to conversion and resin product properties. This is often done by using different initiators at various concentrations and at different reactor jacket temperature. The reactor temperature response in terms of the difference between the jacket temperature and the peak temperature (0=Tp-Tj) is plotted in Figure 2 as a function of the jacket temperature for various inlet initiator concentrations. The temperature response not only depends on the jacket temperature but also, for certain combinations of the variables, it is very sensitive to the jacket temperature. 

Figure 17.23. Representative temperature profiles in reaction systems (see also Figs. 17.20, 17.21(d), 17.22(d), 17.30(c), 17.34, and 17.35). (a) A jacketed tubular reactor, (b) Burner and reactor for high temperature pyrolysis of hydrocarbons (Ullmann, 1973, Vol. 3, p. 355) (c) A catalytic reactor system in which the feed is preheated to starting temperature and product is properly adjusted exo- and endothermic profiles, (d) Reactor with built-in heat exchange between feed and product and with external temperature adjustment exo- and endothermic profiles.

Experimental data on multiple steady-state profiles in tubular packed bed reactors have been reported in the literature by Wicke et al. 51 -53) and Hlavacek and Votruba (54, 55) (Table VI). The measurements have been performed in adiabatic tubular reactors. In the following text the effects of initial temperature, inlet concentration, velocity, length of the bed, and reaction rate expression on the multiple steady state profiles will be studied. 

This equation allows calculating the temperature profile in a polytropic tubular reactor. 

A tubular reactor is to be designed in such a way that it can be stopped safely. The reaction mass is thermally instable and a decomposition reaction with a high energetic potential may be triggered if heat accumulation conditions occur. The time to maximum rate under adiabatic conditions of the decomposition is 24 hours at 200 °C. The activation energy of the decomposition is 100 kj mol-1. The operating temperature of the reactor is 120 °C. Determine the maximum diameter of the reactor tubes, resulting in a stable temperature profile, in case the reactor is suddenly stopped at 120 °C. 

The flow patterns, composition profiles, and temperature profiles in a real tubular reactor can often be quite complex. Temperature and composition gradients can exist in both the axial and radial dimensions. Flow can be laminar or turbulent. Axial diffusion and conduction can occur. All of these potential complexities are eliminated when the plug flow assumption is made. A plug flow tubular reactor (PFR) assumes that the process fluid moves with a uniform velocity profile over the entire cross-sectional area of the reactor and no radial gradients exist. This assumption is fairly reasonable for adiabatic reactors. But for nonadiabatic reactors, radial temperature gradients are inherent features. If tube diameters are kept small, the plug flow assumption in more correct. Nevertheless the PFR can be used for many systems, and this idealized tubular reactor will be assumed in the examples considered in this book. We also assume that there is no axial conduction or diffusion. 

Figure 5.20 shows the temperature profiles in the cooled tubular reactor for the optimum designs with the two catalysts. The optimum recycle flowrate is larger with the expensive catalyst, as expected, which yields an optimum inlet temperature that is higher. 

FIG. 19-13 Noncatalytic gas-phase reactions, (a) Steam cracking of light hydrocarbons in a tubular fired heater, (b) Pebble heater for the fixation of nitrogen from air. (c) Flame reactor for the production of acetylene from hydrocarbon gases or naphthas. [Patton, Grubb, and Stephenson, Pet. Ref. 37(11) 180 (1958).] d Flame reactor for acetylene from light hydrocarbons (BASF), (e) Temperature profiles in a flame reactor for acetylene (Ullmann Encyclopadie der Technischen Chemie, vol. 3, Verlag Chemie, 1973, p. 335). 

A theoretical and experimental study of multiplicity and transient axial profiles in adiabatic and non-adiabatic fixed bed tubular reactors has been performed. A classification of possible adiabatic operation is presented and is extended to the nonadiabatic case. The catalytic oxidation of CO occurring on a Pt/alumina catalyst has been used as a model reaction. Unlike the adiabatic operation the speed of the propagating temperature wave in a nonadiabatic bed depends on its axial position. For certain inlet CO concentration multiplicity of temperature fronts have been observed. For a downstream moving wave large fluctuation of the wave velocity, hot spot temperature and exit conversion have been measured. For certain operating conditions erratic behavior of temperature profiles in the reactor has been observed. 

Figure 1 illustrates typical performance of a validated one-dimensional model in the prediction of temperature profiles in a plant-scale tubular hydrogenation reactor. Note that the major problem area is in the relatively low-temperature region near the inlet. The peak temperature is properly located in the tube, but is slightly lower than the actual temperature. With reactions and reactors of this type, the major reaction is over slightly after the peak temperature has been reached, and the remainder of the reactor is described primarily by a cooling curve. The outlet composition of the reactor will be essentially at equilibrium with respect to the principal reaction. 

Temperature profiles in a tubular reactor operating nonisothermically and conducting an exothermic reaction. T is the temperature of the coolant fluid. 

The comparison between the homogeneous tubular reactor and the packed-bed case depends on the velocity level and dpjd. It is possible for the temperature profile in the packed bed to be more uniform than the profile shown for case b). 

Figure 20.8 Temperature profiles in a tubular catalytic reactor.

In practice, pure-component molar enthalpies are employed to approximate A/7rx. This approximation is exact for ideal solutions only, when partial molar properties reduce to pure-component molar properties. In general, one accounts for more than the making and breaking of chemical bonds in (3-35). Nonidealities such as heats of solution and ionic interactions are also accounted for when partial molar enthalpies are employed. Now, the first law of thermodynamics for open systems, which contains the total differential of specific enthalpy, is written in a form that allows one to calculate temperature profiles in a tubular reactor ... 

Hence, conversion and temperature profiles in a plug-flow tubular reactor with constant outer wall temperature are simulated by solving two coupled first-order ODEs that represent mass and thermal energy balances at high Peclet numbers. They are summarized here for completeness in terms of a generic rate law 3R when only one chemical reaction occurs ... 

Figure 5.15 Radial temperature profile in a packed-bed tubular reactor.

Fig. 2.2-10 Temperature profile in a tubular reactor (for bounda conditions, see text). The adiabatic...

Reactor testing setup The catalyst was tested in a down-flow 3/8" OD stainless steel tubular fixed bed reactor. The charge consisted of 6.8 g of the C03O4 catalyst diluted with 18 g of quartz powder. Reduction of C03O4 should then result in a 5 g yield of cobalt black. To even out the temperature profile, in... 

Optimization can be done by proper reactor choice followed by a suitable temperature progression in the case of a batch or semibatch reactor, or by temperature profiling in the case of a tubular reactor. An even more effective way is to optimize reactant concentrations, pressure, and/or temperature by applying certain simple rules of kinetics and manipulation of the chemistry (wherever possible). Hence the combined efforts of chemist and chemical engineer are needed to optimize selectivity in a given complex reaction. 

Fig. 3.6. Temperature profiles in methanol reactors. Left) WatCT cooled tubular reactor right) quench reactor (saw tooth profile)...

To determine the axial temperature profile in the tubular reactor. Equations 5.34 and 5.36 must be solved simultaneously by numerical integration. The design of microchannel reactors is discussed in detail in Example 5.3 and 5.4... 

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