Separation section location

Reactor effluents are almost never products that meet purity specifications. Besides the products, effluents may contain reactants, inerts, products of undesired side reactions, and feed impurities. Thus, almost every chemical process that involves a chemical reaction section also involves one or more separation sections in addition to one or more recycle streams. A major challenge of process design is to devise an optimal scheme for uniting the reaction and separation functions of a process. This chapter presents many of the considerations involved in that optimization. Although Figure 7.1 shows only one reactor section, multiple reactor sections are sometimes required, with separation sections located between each pair of reactor sections... 

This edition of the Fuel Cell Handbook is more comprehensive than previous versions in that it includes several changes. First, calculation examples for fuel cells are included for the wide variety of possible applications. This includes transportation and auxiliary power applications for the first time. In addition, the handbook includes a separate section on alkaline fuel cells. The intermediate temperature solid-state fuel cell section is being developed. In this edition, hybrids are also included as a separate section for the first time. Hybrids are some of the most efficient power plants ever conceived and are actually being demonstrated. Finally, an updated list of fuel cell URLs is included in the Appendix and an updated index assists the reader in locating specific information quickly. 

Appendix IIA is presented in two places (1) here, in its proper location in the sequence of appendices, and (2) as a separate section in a pocket inside the back cover. 

The lining was 0.75-1.5 in. thick and was built up from layers about 0.25-in. thick. Control joints were used to separate sections of different test design. They were also placed at locations of changing contour, such as along the base of the berm. The largest section was a quadrilateral of about 680 ft (2). 

In addition to recycle streams returned back to upstream units, thermal integration is also frequently done. Energy integration can link units together in locations anywhere in the flowsheet where the temperature levels permit heat transfer to occur. The reaction and separation sections are thus often intimately connected. If conditions are altered in the reaction section, the resulting changes in flowrates, compositions, and temperatures affect the separation section and vice versa. 

Figure 2.17 illustrates that we must lie somewhere on the hyperbolic line in the zA - zB plane. At any position on one of the constant reactor volume lines, the production rate is constant. The concentrations fed to the separation section vary with our choice of location on this curve. For large zA and small zs, the recycle of A (D2) is large. For large zB and small zA, the recycle of B (B ) is large. 

Comparison of these results with the operating point obtained by the first short cut method for nonlinear isotherms shows that, especially for the separation sections II and III, a point (mn, mln) has been found that is located within the area of complete separation (Fig. 7.19). 

The vapors rising from the extractive distillation section consisting of non-aromatic components still contain small quantities of solvent. These solvent traces are separated in the raffinate section located above the extractive distillation section. The purified non-aromatics are withdrawn as overhead product. 

For suppressed conductivity detection, the end of the separation column is connected to a tubular ion exchange membrane suppressor surrounded by a reservoir of regenerant solution [512,513]. The electrodes for conductivity detection are located in a separate capillary downstream of the suppressor. The high voltage electrode for the separation is located in the regenerant reservoir. In this way, the detector is decoupled from the electric field for the separation, and the electroosmotic flow generated in the separation column is used to drive the electrolyte solution through the suppressor and detector. The function of the suppressor (see section 5.7.4.1) is to neutralize electrolyte solution ions. 

Fitzgerald and Knudsen [286] have described the mechanics of crimp development in bicomponent yams. The extent of crimp development will depend on (1) the shrinkage differential between the components, (2) the distribution of components in the fiber, and (3) the translational restraints that may inhibit crimp development. Obviously, the maximum crimp would be developed when the fibers were comprised of equal parts of each component and these components were separated and located on opposite sides of the fiber. On the other hand, if the cross section revealed a distribution in which one polymer was separated into two regions, each on one side of the center slice, then any differential shrinkage forces would be neutralized and no crimp would be developed. In practice, many different distributions of the two components may be observed depending upon the technique used to mix the two polymer dope streams and deliver them to the spinneret hole [287-290]. 

The way in which the three sections can be laid out is illustrated in Figure 6.24. The location of the boxes on the page is not critical. For example, some companies prefer to place the authorization block at the top of the page (or else they group the authorization blocks in a separate section). 

Chapter 8 extends the coverage in Chapters 6 and 7 to provide a treatment of reactor-separator-recycle networks, with emphasis on the best location of the separation section and the optimal reactor conversion. 

Be able to determine the best location for the separation section, either before or after the reactor. 

LOCATING THE SEPARATION SECTION WITH RESPECT TO THE REACTOR SECTION... 

In many, perhaps most, chemical processes, a separation section is located after the reaction section, as shown in Figure 7.1. In this separation section, products are purified and unconverted reactants are recovered for recycle back to the reactor. In this manner, a process involving reactions with unfavorable chemical equilibrium constants, Kc, at reactor conditions can achieve high overall process conversions to desired products. Important industrial examples are the hydrogenation of nitrogen to ammonia. 

Understand the considerations in determining the best locations, with respect to the reactor section, of the separation sections. 

Testing of materials is carried out on small specimens under laboratory conditions. Their results are characteristic only of the tested polymeric material without any reference to the location and mode of its application. In the interpretation of material tests, the stage of burning of the specimen to which the results are referred should always be indicated. Flammability tests of high-temperature plastics are discussed separately. A separate section is devoted to the explosion hazard of plastics powders. 

The heat supplied to the steam generators produces steam from the water that flows over the outside of the tubes. Moisture is removed from the steam by the steam separating equipment located in the drum (upper section) of the steam generator. The steam then flows via four separate steam mains, through the wall of the reactor building, to the turbine where they connect to the turbine steam chest via a main steam line isolation valve. 

Figure 2.14a shows a flowsheet of the column of extractive distillation and, in Fig. 2.14b, an example of acetone(l)-water(entrainer)(2)-methanol(3) mixture with section trajectories is shown. This mixture, which is impossible to separate sharply into acetone (xd) and methanol-water mixture (xb) in the single-feed column, may be separated into these products in the column with an extractive section located between two feed inlets. 

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