Batch-type fluidized bed

In this paper experimental results are presented on crude oil pyrolysis which was carried out by use of a bench scale batch type fluidized bed reactor heated by an electric furnace. Good yields of olefins and aromatics were obtained from several crude oils. Monographs are also presented which provide the means for estimating the products yield based on the characterization factor of the feed stock and the intensity function representing the severity of pyrolysis. 

Paddy dryers can be easily classified by the movement of the grains in the dryer into two types, that is, a dryer for stationary paddy and a dryer for moving paddy. Deep-bed dryer and in-store dryer are the common industrial dryers of the first type. Fluidized-bed dryer, LSU dryer, cross-flow dryer, concurrent-flow dryer, countercurrent-flow dryer, and recirculating batch dryer are of the latter type. Dryers commonly used in Sontheast Asia are deep-bed dryer, in-store dryer, LSU dryer, flnidized-bed dryer, and some variations of cross-flow dryer. The recirculating batch dryer is also popular in Japan, Korea, and China. 

Catalytic reactors are continuous reactors more often than not. The main subdivision types include fluidized or fixed bed. Fixed bed types may be either tubular, bed, or multitray types. Fluidized bed types further break down into stationary or moving (recirculating) bed types and tubular (transfer tube) types. The catalyst is generally in powdered suspension and may be removed either in batches or continuously withdrawn and regenerated. In transfer tube types, the catalyst stays in suspension with the fluid flow through the tubes. 

Carbon should be prewetted prior to being placed in the test columns. Backwashing the carbon at low rates (2.5 m/hr) does not remove the air. Rates that would expand the bed 50 percent or 15-30 m/hr, are required. The liquid used for prewetting can either be water, if it is compatible with the liquid to be treated, or a batch of the liquid to be treated which has been purified previously. There are three types of carbon systems (1) fixed beds, (2) pulse beds, and (3) fluidized beds, and these can be used singly, in parallel, or in combination. The majority of systems are either fixed or pulse beds. The two basic types of adsorbers which can be designed to operate under pressure or at atmospheric pressure are the moving or pulse bed and the fixed bed. Either can be operated as packed or expanded beds. 

Our treatment of Chemical Reaction Engineering begins in Chapters 1 and 2 and continues in Chapters 11-24. After an introduction (Chapter 11) surveying the field, the next five Chapters (12-16) are devoted to performance and design characteristics of four ideal reactor models (batch, CSTR, plug-flow, and laminar-flow), and to the characteristics of various types of ideal flow involved in continuous-flow reactors. Chapter 17 deals with comparisons and combinations of ideal reactors. Chapter 18 deals with ideal reactors for complex (multireaction) systems. Chapters 19 and 20 treat nonideal flow and reactor considerations taking this into account. Chapters 21-24 provide an introduction to reactors for multiphase systems, including fixed-bed catalytic reactors, fluidized-bed reactors, and reactors for gas-solid and gas-liquid reactions. 

The classic analysis of reactors involves two idealized flow patterns— plug flow and mixed flow. Though real reactors never fully follow these flow patterns, in many cases, a number of designs approximate these ideals with negligible error. However, deviation from ideality can be considerable. Typically, in a reaction vessel, we can have several immediate cases closer to plug or mixed flow. Of course, nonideal flow concerns all types of reactors used in heterogeneous processes, i.e. fixed beds, fluidized beds, continuous-flow tank reactors, and batch reactors. However, we will focus on fixed beds and batch reactors, which are the common cases. 

In order to combine the advantages of batch-type and continuous production, a prototype for a quasi-continuous production line was developed [15-18]. The principle of this quasi-continuous production line is based on a semicontinuous production of minibatches in a specially designed high-shear mixer/granulator connected to a continuous multicell-fluidized-(Glatt Multicell ) bed dryer (see Fig. 7). 

Figure 9.4. Types of dryers cited in Tables 9.1 and 9.2. (a) Tray or compartment, (b) Vacuum tray, (c) Vertical agitated batch vacuum drier, (d) Continuous agitated tray vertical turbo, (e) Continuous through circulation, (f) Direct rotary, (g) Indirect rotary, (h) Agitated batch rotary (atmos or vacuum), (i) Horizontal agitated batch vacuum drier, (j) Tumble batch dryer, (k) Splash dryer. (I) Single drum, (m) Spray, (n) Fluidized bed dryer, (o) Pneumatic conveying (mostly after Nonhebel and Moss, 1971).

Knowledge of these types of reactors is important because some industrial reactors approach the idealized types or may be simulated by a number of ideal reactors. In this chapter, we will review the above reactors and their applications in the chemical process industries. Additionally, multiphase reactors such as the fixed and fluidized beds are reviewed. In Chapter 5, the numerical method of analysis will be used to model the concentration-time profiles of various reactions in a batch reactor, and provide sizing of the batch, semi-batch, continuous flow stirred tank, and plug flow reactors for both isothermal and adiabatic conditions. 

Imafuku et al.46 measured the gas holdup in a batch (i.e., no liquid flow) three-phase fluidized-bed column. They found that the presence of solids caused significant coalescence of bubbles. They correlated the gas holdup with the slip velocity between the gas and liquid. They found that the gas holdup does not depend upon the type of gas distributor or the shape of the bottom of the column when solid particles are completely suspended. Kato et al.53 found that the gas holdup in an air-water-glass sphere system was somewhat less than that of the air-water system and that the larger solid particles showed a somewhat smaller... 

Different types of reactors are utilized for a wide variety of pyrolysis applications, including processing of waste plastics. The worldwide waste plastic pyrolysis systems utilize the fixed-bed designs of vertical shaft reactors and dual fluidized-bed, rotary kiln and multiple hearth reactor systems. The type of reactor used is chiefly based on material to be pyrolyzed and expected products from the pyrolysis. Stainless steel shaking type batch autoclave and stainless steel micro tubular reactors have also been used extensively [14]. Fluidized-bed reactors have been extensively used in producing raw petrochemicals from the pyrolysis of waste plastics [22, 24]. 

In a later section, the characteristics and performances of the most widely used equipment will be described in some detail. Many types are shown in Figure 9.4. Here some comparisons are made. Evaporation rates and thermal efficiencies are compared in Table 9.2, while similar and other data appear in Table 9.3. The wide spreads of these numbers reflect the diversity of individual designs of the same general kind of equipment, differences in moisture contents, and differences in drying properties of various materials. Fluidized bed dryers, for example, are operated as batch or... 

The aim of the preceding discussion on commercial reactors is to give a more detailed picture of each of the major types of industrial reactors batch, semibatch, CSTR, tubular, fixed-bed (packed-bed), and fluidized-bed. Many variations and modifications of these commercial reactors are in current use for further elaboration, refer to the detailed discussion of industrial reactors given by Walas. ... 

Four types of ion-exchange reactions are given in Table 1. The degree of target ion uptake is dependent on the chemical and physical properties of the resins and the solution chemistry. The calculations in relation to ion-exchange processes include determination of equilibrium state conditions and kinetics in batch reactors as well as transportation in fixed-bed and fluidized-bed reactors. 

These models use experimental data from drying kinetics tests in a laboratory, pilot-plant or full-scale dryer, and are thus more accurate and reliable than methods based only on estimated drying kinetics. They treat the dryer as a complete unit, with drying rates and air velocities averaged over the dryer volume, except that, if desired, the dryer can be subdivided into a small number of sections. These methods are used for layer dryers (tray, oven, horizontal-flow band, and vertical-flow plate types) and for a simple estimate of fluidized-bed dryer performance. For batch dryers, they can be used for scale-up by refining the scoping design calculation. 

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