Industrial packed-bed reactor

Reactor Model. The design of an industrial packed-bed reactor requires a reactor model as well as the chemical and the heat and mass transfer parameters of the catalyst bed - gas stream system. Since these parameters are model-specific, it seemed advisable to employ a continuum model for the reactor calculation. This is the only model to date for which the literature contains consistent data for calculating heat and mass transfer parameters (5,6,7). This model in its... 

The quasistationary model without dispersion can satisfactorily describe the majority of deactivation processes taking place in industrial packed bed reactors and can be used safely for calculations. 

This reactor is similar to the industrial packed bed reactor in which part of the product stream is recycled to the reactor inlet [41]. As shown in Figure 5.4, a recycle reactor con-... 

Rea RTD data from an industrial packed bed reactor operating under poor operation. [3rd Ed. P13-5]... 

Further simulations showed that a high (>95%) HCHO yield can be achieved even in the case of reactor tubes with a diameter incremented from one, the current industrial standard, to three inches, which would afford important savings in reactor investment costs. However, the volume fraction of the conductive monolith support needs to be incremented by a factor of four to compensate for the greater heat-transfer resistances. For all the simulated conditions the estimated pressure drop was less than 1% of the inlet pressure, versus over 10% in the industrial packed-bed reactor. 

Some modes of heat transfer to stirred tank reacdors are shown in Fig. 23-1 and to packed bed reactors in Fig. 23-2. Temperature and composition profiles of some processes are shown in Fig. 23-3. Operating data, catalysts, and reaction times are stated for a number of industrial reaction processes in Table 23-1. 

Figure 4-8 shows a continuous reactor used for bubbling gaseous reactants through a liquid catalyst. This reactor allows for close temperature control. The fixed-bed (packed-bed) reactor is a tubular reactor that is packed with solid catalyst particles. The catalyst of the reactor may be placed in one or more fixed beds (i.e., layers across the reactor) or may be distributed in a series of parallel long tubes. The latter type of fixed-bed reactor is widely used in industry (e.g., ammonia synthesis) and offers several advantages over other forms of fixed beds. 

There are two basic types of packed-bed reactors those in which the solid is a reactant and those in which the solid is a catalyst. Many e.xaniples of the first type can be found in the extractive metallurgical industries. In the chemical process industries, the designer normally meets the second type, catalytic reactors. Industrial packed-bed catalylic reactors range in size from units with small tubes (a few centimeters in diameter) to large-diameter packed beds. Packed-bed reactors are used for gas and gas-liquid reactions. Heat transfer rates in large-diameter packed beds are poor and where high heat transfer rates are required, Jluidized beds should be considered. ... 

The models of Chapter 9 contain at least one empirical parameter. This parameter is used to account for complex flow fields that are not deterministic, time-invariant, and calculable. We are specifically concerned with packed-bed reactors, turbulent-flow reactors, and static mixers (also known as motionless mixers). We begin with packed-bed reactors because they are ubiquitous within the petrochemical industry and because their mathematical treatment closely parallels that of the laminar flow reactors in Chapter 8. 

Chapter 10 begins a more detailed treatment of heterogeneous reactors. This chapter continues the use of pseudohomogeneous models for steady-state, packed-bed reactors, but derives expressions for the reaction rate that reflect the underlying kinetics of surface-catalyzed reactions. The kinetic models are site-competition models that apply to a variety of catalytic systems, including the enzymatic reactions treated in Chapter 12. Here in Chapter 10, the example system is a solid-catalyzed gas reaction that is typical of the traditional chemical industry. A few important examples are listed here ... 

There are two basic types of packed-bed reactor those in which the solid is a reactant, and those in which the solid is a catalyst. Many examples of the first type can be found in the extractive metallurgical industries. 

Tubular reactors are normally used in the chemical industry for extremely large-scale processes. When filled with solid catalyst particles, such reactors are referred to as fixed or packed bed reactors. This section treats general design relationships for tubular reactors in... 

Fixed Bed Reactors. In its most basic form, a fixed bed reactor consists of a cylindrical tube filled with catalyst pellets. Reactants flow through the catalyst bed and are converted into products. Fixed bed reactors are often referred to as packed bed reactors. They may be regarded as the workhorse of the chemical industry with respect to the number of reactors employed and the economic value of the materials produced. Ammonia synthesis, sulfuric acid production (by oxidation of S02 to S03), and nitric acid production (by ammonia oxidation) are only a few of the extremely high tonnage processes that make extensive use of various forms of packed bed reactors. 

The design q>roblem can be approached at various levels of sophistication using different mathematical models of the packed bed. In cases of industrial interest, it is not possible to obtain closed form analytical solutions for any but the simplest of models under isothermal operating conditions. However, numerical procedures can be employed to predict effluent compositions on the basis of the various models. In the subsections that follow, we shall consider first the fundamental equations that must be obeyed by all packed bed reactors under various energy transfer constraints, and then discuss some of the simplest models of reactor behavior. These discussions are limited to pseudo steady-state operating conditions (i.e., the catalyst activity is presumed to be essentially constant for times that are long compared to the fluid residence time in the reactor). 

However, the most complex analysis is that in which heat transfer through the reactor walls is taken into account. This type of operation must be employed when it is necessary to supply or remove energy from the system so as to moderate the temperature excursions that would otherwise follow. It is frequently employed in industrial reactors and, to model such systems, one must often resort to two-dimensional models of the reactor that allow the concentration and temperature to vary in both the radial and axial directions. In the analysis of such systems, we make incremental calculations across the diameter of a given longitudinal segment of the packed bed reactor, and then proceed to repeat the process for successive longitudinal increments. 

Reactive Red 3.1 Activated sludge obtained from domestic and industrial effluent treatment plants Decolorization rates of up to 30 mg L 1 h 1 were observed in case of activated sludge under anaerobic conditions. In anaerobic packed bed reactor [15]... 

The most used industrial reactor is the catalytic packed bed reactor. This is typically a tank or tube fiUed with catalyst pellets with reactants entering at one end and products leaving... 

We have chosen to concentrate on a specific system throughout the chapter, the methanation reaction system. Thus, although our development is intended to be generally applicable to packed bed reactor modeling, all numerical results will be obtained for the methanation system. As a result, some approximations that we will find to apply in the methanation system may not in other reaction systems, and, where possible, we will point this out. The methanation system was chosen in part due to its industrial importance, to the existence of multiple reactions, and to its high exothermicity. 

To retain consistency throughout this presentation, we will consider a general nonadiabatic, packed bed reactor, as shown in Fig. 1, with a central axial thermal well and countercurrent flow of cooling fluid in an exterior jacket.1 We focus on the methanation reaction since methanation is a reaction of industrial importance and since methanation exhibits many common difficulties such as high exothermicity and undesirable side reactions. 

Fixed- or packed-bed reactors refer to two-phase systems in which the reacting fluid flows through a tube filled with stationary catalyst particles or pellets (Smith, 1981). As in the case of ion-exchange and adsorption processes, fixed bed is the most frequently used operation for catalysis (Froment and Bischoff, 1990 Schmidt, 2005). Some examples in the chemical industry are steam reforming, the synthesis of sulfuric acid, ammonia, and methanol, and petroleum refining processes such as catalytic reforming, isomerization, and hydrocracking (Froment and Bischoff, 1990). 

Under practical conditions, countercurrent operation in a packed bed reactor is not feasible, because flooding occurs (55,56). The reason is that in the small interstitial space, extended momentum transfer takes place between the liquid flowing down and the gas flowing upward. At velocities used in industry this would imply... 

The packed bed reactor is used to contact fluids with solids. It is one of the most widely used industrial reactors and may or may not be catalytic. The bed is usually a column with the actual dimensions influenced by temperature and pressure drop in addition to the reaction kinetics. Heat limitations may require a small diameter tube, in which case total through-put requirements are maintained by the use of multiple tubes. This reduces the effect of hot spots in the reactor. For catalytic packed beds, regeneration is a problem for continuous operation. If a catalyst with a short life is required, then shifting between two columns may be necessary to maintain continuous operation. 

The goal of this investigation was the development of a suitable reactor model for propylene oxidation in an industrial-size packed-bed reactor operated under industrially relevant conditions (4). 

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