Reactors tower

Wet Oxidation Reactor Design. Several types of reactor designs have been employed for wet oxidation processes. Zimpro, the largest manufacturer of wet oxidation systems, typically uses a tower reactor system. The reactor is a bubble tower where air is introduced at the bottom to achieve plug flow with controlled back-mixing. Residence time is typically under one hour. A horizontal, stirred tank reactor system, known as the Wetox process, was initially developed by Barber-Cohnan, and is also offered by Zimpro. 

Figure 18, Dow Chemical Co, patented eggbeater " agitated tower reactor (27)...

There are many other reactors of various types not included among those discussed above. These include tower reactors (Chapter 24), which may be modeled as PF or modified PF reactors. We describe one further example in this section. 

As its name implies, a tower reactor typically has a height-to-diameter (h/D) ratio considerably greater than 1. Types of tower or column reactors (the words tower and column may be used interchangeably) go by descriptive names, each of which indicates a particular feature, such as the means of creating gas-liquid contact or the way in which one phase is introduced or distributed. The flow pattern for one phase or for both phases may be close to ideal (PF or BMF), or may be highly nonideal. 

In the quantitative development in Section 24.4 below, we assume the flow to be ideal, but more elaborate models are available for nonideal flow (Chapter 19 see also Kastanek et al., 1993, Chapter 5). Examples of types of tower reactors are illustrated schematically in Figure 24.1, and are discussed more fully below. An important consideration for the efficiency of gas-liquid contact is whether one phase (gas or liquid) is dispersed in the other as a continuous phase, or whether both phases are continuous. This is related to, and may be determined by, features of the overall reaction kinetics, such as rate-determining characteristics of mass transfer and intrinsic reaction. 

Values of the ratio V(IVR given in Table 24.1 emphasize that most of the volume in a tower reactor (apart from a bubble column, data for which would be similar to a sparger-equipped tank) is occupied by the gas phase, and conversely for a tank reactor. This means that a, a in a tower and a, - a t in a tank. For mass transfer-controlled situations, a, is the more important quantity, and is much greater in a tower. For reaction-controlled situations, in which neither ai nor a is important, a sparger-equipped tank reactor, the cheapest arrangement, is sufficient. 

Figure 243 Plow diagram and notation for packed-tower reactor for reaction A(g)+hB(f) - ...

The BASF continuous mass polymerization process employed a tower reactor with an upstream continuous stirred tank reactor (16) (Figure 1). 

The continuous mass process is divided into 4 steps rubber solution in styrene monomer, polymerization, devolatilization and compounding. In 1970 N. Platzer (40) drew up a survey of the state of the art. Polymerization is divided into prepolymerization and main polymerization for both steps reactor designs other than the tower reactors shown in Figure 2 have been proposed. Main polymerization is taken to a conversion of 75 to 85% residual monomer and any solvent are separated under vacuum. The copolymer then passes to granulating equipment, frequently through one or more intermediate extruders in which colorant and other auxiliaries are added. 

Figure 12-9 Bubble column and spray tower reactors. Large drop or bubble areas increase reactant mass transfer,...

Figure 12-10 Sketches of reactant concentration Ca around a spherical bubble or drop that reacts after migrating from ftie gas phase into the liquid phase in bubble column and spray tower reactors.

If we simply turn the drawing of the bubble column upside down, we have a spray tower reactor. Now we have dense liquid drops or solid particles in a less dense gas so we spray the liquid from the top and force the gas to rise. The same equations hold, but now the mass transfer resistance is usually within the hquid drop. 

A continuous bulk polymerization process with three reaction zones in series has been developed. The degree of polymerization increases from the first reactor to the third reactor. Examples of suitable reactors include continuous stirred tank reactors, stirred tower reactors, axially segregated horizontal reactors, and pipe reactors with static mixers. The continuous stirred tank reactor type is advantageous, because it allows for precise independent control of the residence time in a given reactor by adjusting the level in a given reactor. Thus, the residence time of the polymer mixtures can be independently adjusted and optimized in each of the reactors in series (8). 

Tower Reactor The tower reactor is convenient when working with flocculating yeast cells. The reactor consists of a cylinder provided with bottom and upper zones for feeding substrate and cells and sofid/liquid separation. The overall aspect ratio is of 10 1, with 6 1 for the reaction zone. A tower reactor does not use mechanical mixing, and is simpler to build. Cell concentrations up to 100 g/1 can be achieved with productivities 30-80 times higher than in batch reactors. The residence time is below 0.4 h and the yield up to 95% of the theoretical one. A design procedure is available [18]. 

Q., Giudid, R., Continuous ethanol fermentation in a tower reactor,... 

STY is high for a fermentative procedure and ranges from 140 g L-1 d 1 for a continuous tank reactor to 1.2 kg IT1 d 1 in a continuous tower reactor with cell recycle. Depending on the ethanol tolerance of the production species, ethanol is produced to a concentration of 12-20%. The ethanol is traditionally recovered from the fermentation broth via an energy-intensive distillation step, but it is sought to replace the latter by pervaporation or reversed osmosis [25]. 

Application New process to produce polyesters from the polyalkylene terephthalate family from terephthalic acid (PTA) or dimethyl terephthal-ate (DMT) and diols using the UIF proprietary two-reactor (2R) process consisting of tower reactor ESPREE and DISCAGE finisher or, alternatively a solid-state finishing. 

Description A slurry composed of a dicarboxylic acid and a diol is prepared at a low mole ratio. The slurry is fed to the tower reactor s bottom where the main esterification occurs under pressure or under vacuum at temperatures ranging between 170°C to 270°C. This reaction may be catalyzed or autocatalyzed. 

Figure 1.6 Schematic of BASF s improved tower process for the continuous polymerization of styrene. In this design (dated 1936) the styrene was first polymerized up to 30-35% conversion in a stirred kettle and then transferred to the tower reactor for polymerization up to 97% completion (courtesy of BASF, Ludwigshafen)...

This general phenomenon of buildup of solid polymer in static areas of the reactor is common to all continuous solution reactors. A major component of the design is to eliminate regions where this may occur. This is one of the drivers for incorporating agitators in the tower reactors which will be discussed in the next section and has also been a driver for removing heat transfer tubes from the reactor which add wall surface. 

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