Spherical Packed-Bed Reactors

Let s consider carrying out this reaction in a spherical reactor similar tc one shown in the margin and discussed in detail in the CD-ROM. In a sp. cal reactor, the cross section varies as we move through Che reactor ar greater than in a normal packed-bed reactor. Consequently, the superficial i velocity C = will be smaller. From Equation (4-22). we see th 

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Example 4-6 Calculating X in a Reactor with Pressure Drop Example 4 7 Gas-Phase Reaction in Microreactor—Molar Flow Rate Example 4-8 Membrane Reaeior Example CDR4.1 Spherical Reactor Example 4.3.1 Aerosol Reactor Example 4-9 Isothermal Semibatch Reactor Profe.ssional Reference Shelf R4.1. Spherical Packed-Bed Reactor. ... 

Rahimpour MR, Pourazadi E, Iranshahi D, Bahmanpour AM. Methanol synthesis in a novel axial-flow, spherical packed bed reactor in the presence of catalyst deactivation. Chemical Engineering Research and Design 2011 89 2457-2469. 

Iranshahi D, Pourazadi E, Paymooni K, Bahmanpour AM, Rahimpour MR, Shariati A. Modeling of an axial flow, spherical packed-bed reactor for naphtha reforming process in the presence of the catalyst deactivation. International Journal of Hydrogen Energy 2010 35 12784-12799. 

A certain spherical porous catalyst with a pellet diameter of 1/8 in. has a Thiele modulus of 0.5 for a first-order reaction and gives 90% conversion in a packed bed reactor. It is proposed to... 

Go to Professor Herz s Reactor Lab on the CD-ROM or on the web at mrw.reactorlah.net. Load Division 2. Lab 2 of The Reactor Lab concerning a packed-bed reactor (labeled PFR) in which a gas with the physical properties of air (lows over spherical catalyst pellets. Perfonn experiments here to get a feeling for how pressure drop varies with input parameters such as reactor diameter, pellet diameter, gas How rate, and temperature. In order to get sig-nific. int pressure drop, you may need to change some of the input values substantially from those shown when you enter the lab. If you gel a notice that you can t get the desired flow, then you need to increase the inlet pressure. In Chapters 10-12. you will learn how to analyze the conversion results in such a reactor. 

They used this model to predict the effective diffusivity in the partially impervious deposit (zone 4). They developed and solved the coupled mass balance equations for spherical pellets in a fixed bed reactor. To compare the model with experimental data, they measured the conversion of propane and propylene over partially poisoned pellets in a small isothermal packed bed reactor. For intrinsic kinetic rates of propane and propylene they employed the empirical rate equations proposed by Volts et al. and Hiam et al. The Hegedus model is briefly described below ... 

Now we can estimate the pressure drop in all devices with the presented relations Equations 6.5 and 6.7 for the foam Equations 6.9 and 6.10 for the microchannel reactor and Equation 6.4 for the packed bed with spherical particles. For the microchannel reactor we suppose that 60% of the cross section of the reactor is occupied by the channel walls and catalytic layer (see Figure 6.7). Therefore, the channel volume available for the fluid corresponds to the void volume in the packed bed i.e. =0.4 = e. For a given superficial fluid velocity u, the velocity in the void volume is given by = u/e. From Figure 6.10 it becomes evident that the pressure drop in packed bed reactors are several times higher than in foam reactors. The difference can be explained by the high porosity in the foam (efoam = .9) compared to the packed bed = 0.4). The lowest pressure and, therefore, the lowest energy dissipation is found for the multichannel microreactor. 

Fig.5 illustrates the PO selectivity (S) as a function of mass Peclet number. The selectivity was increased with increasing the total reaction gas flow rate (F) passing through the membrane pores, such as S= 18-41% according to F= 70-130 cmVmin at 483K, indicating an effective role of the convection flow in the membrane pores for the enhancement of S compared to intraparticle diffusion in spherical catalyst solid supports used for conventional packed bed reactors. This result experimentally proves the validity of our previous work based on the mathematical analysis [7]. 

A single-stage adiabatic reactor is illustrated in Fig 3.16 which shows the graded spherical packing used as a catalyst support at the bottom of the bed, and as a... 

Granules made by aging liquid drops spherical 1-20 mm Packed tubular reactors, moving beds... 

To be able to compare MSRs with randomly packed fixed-bed reactors, equivalent design criteria must be defined [69,70]. A fixed-bed reactor of cross-section Sbed and height Lbed filled with np spherical particles of diameter dp is compared with a multichannel MSR with a channel diameter dt and the same cross-section and the same height (Sbed = SstrUc/ kbed hstruc). 

Flow through the porous bed enhances the radial effective or apparent thermal conductivity of packed beds [10, 26]. Winterberg andTsotsas [26] developed models and heat transfer coefficients for packed spherical particle reactors that are invariant with the bed-to-particle diameter ratio. The radial effective thermal conductivity is defined as the summation of the thermal transport of the packed bed and the thermal dispersion caused by fluid flow, or ... 

As a model system a cylindrical reactor of the length L = 60 mm and inner diameter di = 7 mm packed with 400 uniform, nonporous spherical particles of the diameter dp = 1.8 mm was studied. The geometrical dimensions, as well as the average porosity, e = 0.47, of the packed bed were adjusted to those used in Section 5.2. Spatial discretization with the resolution of 30 lattice constant per sphere diameter was performed resulting in the computational domain of dimension 1300 X 117 X 117 points. The selected results given below intend to illustrate substantial differences and characteristics in the fluid dynamics in a FBR (Frs/Fss = 00) and PBMR. All the simulations presented were carried out on a Hewlett Packard Superdome parallel computer (64 processors, 120GB RAM). Typical simulation times for the complete model were about 24h on this architecture. 

Your task as a design engineer in a chemical company is to model a fixed bed reactor packed with the company proprietary catalyst of spherical shape. The catalyst is specific for the removal of a toxic gas at very low concentration in air, and the iifformation provided from the catalytic division is that the reaction is first order with respect to the toxic gas concentration. The reaction rate has units of moles of toxic gas removed per mass of catalyst per time. 

In this case. Equation 4.226 derived for packed bed catalytic reactor is applicable after suitable modification of certain terms appearing in that equation. The effectiveness factor q = 1 as the catalyst particle is very small in size and the resistance to internal pore diffusion is negligible. Taking the catalyst particles to be spherical in shape with radius R, Lq = R/3 and the equation for bed height Z reduces to... 

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