Plug flow reactor heat transfer

The first distinction to be drawn, as far as heat transfer is concerned, is between the plug-flow and continuous well-mixed reactor. In the plug-flow reactor shown in Fig. 13.1, the heat transfer can take place over a range of temperatures. The shape of the profile depends on... 

Figure 13.1 The heat transfer characteristics of plug-flow reactors.

Figure 1. Typical reactor temperature profile for continuous addition polymerization a plug-flow tubular reactor. Kinetic parameters for the initiator 1 = 10 ppm Ea = 32.921 kcal/mol In = 26.492 In sec f = 0.5. Reactor parameter [(4hT r)/ (DpCp)] = 5148.2. [(Cp) = heat capacity of the reaction mixture (p) = density of the reaction mixture (h) = overall heat-transfer coefficient (Tf) = reactor jacket temperature (r) = reactor residence time (D) = reactor diameter].

Consecutive reactions, isothermal reactor cmi < cw2, otai = asi = 0. The course of reaction is shown in Fig. 5.4-71. Regardless the mode of operation, the final product after infinite time is always the undesired product S. Maximum yields of the desired product exist for non-complete conversion. A batch reactor or a plug-flow reactor performs better than a CSTR Ysbr.wux = 0.63, Ycstriiuix = 0.445 for kt/ki = 4). If continuous operation and intense mixing are needed (e.g. because a large inteifacial surface area or a high rate of heat transfer are required) a cascade of CSTRs is recommended. 

Consider the reaction used as the basis for Illustrations 10.1 to 10.3. Determine the volume required to produce 2 million lb of B annually in a plug flow reactor operating under the conditions described below. The reactor is to be operated 7000 hr annually with 97% conversion of the A fed to the reactor. The feed enters at 163 C. The internal pipe diameter is 4 in. and the piping is arranged so that the effective reactor volume can be immersed in a heat sink maintained at a constant temperature of 160 °C. The overall heat transfer coefficient based on the... 

In the mode of uniform surface renewal, all elements of emulsion contact the surface for the same length of time such a situation is representative of emulsion flowing smoothly past a small heat transfer surface. Here, the age distribution function is represented by that of a plug flow reactor, as given by... 

With Heat Transfer. The tubular reactor is constructed in a similar way as a tube-in-shell heat exchanger or a fired furnace. Process fluid flows inside the tubes and is cooled or heated by the heat transfer medium within the shell. Radial temperature gradients are inherent in tubular reactors with heat transfer, so the plug flow assumption... 

The main physicochemical processes in thin-film deposition are chemical reactions in the gas phase and on the film surface and heat-mass transfer processes in the reactor chamber. Laboratory deposition reactors have usually a simple geometry to reduce heat-mass transfer limitations and, hence, to simplify the study of film deposition kinetics and optimize process parameters. In this case, one can use simplified gas-dynamics reactor such as well stirred reactor (WSR), calorimetric bomb reactor (CBR, batch reactor), and plug flow reactor (PFR) models to simulate deposition kinetics and compare theoretical data with experimental results. 

Figure 6-8. Tubular (plug) flow reactor with heat transfer system.

For a steady-state plug flow reactor, the increase of enthalpy over an infinitesimal reactor element results from the enthalpy production by reaction and the transfer of heat from the surroundings, leading to ... 

The advantages of the ring-shaped particles are also found for other type of reactions. To demonstrate this, consider an adiabatic plug flow reactor assuming that the external mass and heat transfer limitations are negligible. Equations for fluid-phase concentration and temperature (which are equal to the concentration and temperature at the surface of the pellet) are... 

The flow of heat across the heat-transfer surface is linear with both temperatures, leaving the primary loop with a constant gain. Using the coolant exit temperature as the secondary controlled variable as shown in Fig. 8-55 places the jacket ( mamics in the secondary loop, thereby reducing the period of the primary loop. This is dynamically advanti reous for a stirred-tank reactor because of the slow response of its large heat capacity. However, a plug flow reactor cooled by an external heat exchanger lacks this heat capacity and requires the faster response of the coolant inlet temperature loop. 

Table 3.14 Dimensionless mathematical model forthe heat and mass transfer in a plug flow reactor for a fast exothermic reaction.

The first step is to calculate limits for the reaction volume. One CSTR will give the maximum volume and a plug-flow reactor will give the minimum volume. The total reaction voliune for multiple CSTRs will lie somewhere between these two limits. After calculating the reaction volume, calculate the required heat transfer and the heat-transfer area. Then, either select a jacket, a coil, jacket plus a coil, or an external heat exchanger. 

Most of the simulators allow heat input or removal from a plug-flow reactor. Heat transfer can be with a constant wall temperature (as encountered in a fired tube, steam-jacketed pipe, or immersed coil) or with counter-current flow of a utility stream (as in a heat exchanger tube or jacketed pipe with cooling water). 

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