Industrial separation flowsheets

When the composition of an azeotrope is sensitive to moderate changes in pressure, then pressure-swing distillation may be used to separate almost pure components. The flowsheet displayed in the Fig. 7.28 consists of two columns operated at different pressures. The first column separates pure A in top or in bottom, if this is a minimum or maximum boiler, respectively. The second feed is placed on the other side of the azeotrope, which makes possible the separation of pure B. The other product is recycled to the first column. Some industrial separations may be cited as hydrochloric, hydrofluoric and formic from water solutions. 

In industry, it is necessary to deal with very complicated mixtures for which structural matrices can serve as an instrument of separation flowsheets synthesis. In Wahnschafft (1997), the example of plant for separation of coal tar in South Africa (20 components, more than 200 azeotropes) consisting of 40 columns is given. 

The extractants used in the solvent extraction processing include organo-phosphorus compounds, amines and carboxylic acids. The Rhone-Poulenc solvent extraction separation flowsheet has become the standard for all industrial producers. 

Kraft pulping is a common process in the paper industry. Figure 8.4 shows a simplifled flowsheet of the process. In this process, wood chips are reacted (cooked) with white liquor in a digester. White liquor (which contains primarily NaOH, NaiS, Na2C03 and water) is employed to dissolve lignin from the wood chips. The cooked pulp and liquor are passed to a blow tank where the pulp is separated from the spent liquor weak black liquor which is fed to a recovery system for... 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

Commercial-scale application of solvents coming under the category of neutral reagents is largely found as applied to the nuclear industry materials, as in example, for the separation and refining of uranium, plutonium, thorium, zirconium, and niobium. A process flowsheet for extracting niobium and tantalum from various resources is shown in Figure 5.23. It will... 

Innovation is the key issue in today s chemical process industries. The main directions are sustainability and process intensification. Sustainability means in the first place the efficient use of raw materials and energy close to the theoretical yields. By process intensification the size of process plants is considerably reduced. The integration of several tasks in the same unit, as in reactive separations, can considerably simplify the flowsheet and decrease both capital and operation costs. 

The traditional textbook flowsheet for the dehydration of ethanol involves three distillation columns. However, some industrial implementations for exactly the same separation use only two columns with a corresponding savings in capital cost (Doherty and Knapp, 1993). How can these two alternative designs be systematically understood ... 

Some real unit operations can find direct correspondence with the blocks used in flowsheeting, as flashes, distillation columns, heat exchangers, etc. However, the equivalence could be difficult for many others. This is typical the case of the industrial chemical reactors and a number of separators. In some cases, a simple model may be satisfactory for a quite complex unit from mechanical point of view. Consequently, the modelling of real units can follow one of the following possibilities ... 

As the main responsible for the changes in the material balance, the chemical reactor must be modelled accurately from this point of view. Basic flowsheeting reactors are the plug flow reactor (PFR) and continuous stirred tank reactor (CSTR), as shown in Fig. 3.17. The ideal models are not sufficient to describe the complexity of industrial reactors. A practical alternative is the combination of ideal flow models with stoichiometric reactors, or with some user programming. In this way the flow reactors can take into account the influence of recycles on conversion, while the stoichiometric types can serve to describe realistically selectivity effects, namely the formation of impurities, important for separations. Some standard models are described below. 

The Ruhrchemie works in Oberhausen produces over 300000 t/a of butyraldehyde using a two-phase water/organic phase system. The process gives improved product selectivity n/i ratio > 95/5), and the separation of the catalyst and its recycling are straightforward. Figure 3-1 shows a flowsheet of the process. Such two-phase processes in which the reaction occurs at the phase boundary are expected to be of major fiitnre importance in industrial chemistry [16]. 

Separation processes are of central importance in the chemical industry. Appropriate choice and efficient design of separation equipment is essential because it represents a large proportion of the capital and operating costs of a plant. The vinyl acetate flowsheet in Figure 7.2 is almost entirely concerned with separation of the reaction products—this is typical of very many processes. Whenever there is incomplete conversion in a reactor a separation followed by recycle may be necessary. Toxic substances in waste streams must often be removed in order to meet legal requirements. The availability of suitable separation processes is, therefore, crucial when considering the feasibility of any new chemical process. 

Continuous Countercurrent Multistage Fractional Extraction. The industrial process utilizing the double-solvent principles is continuous and is carried out according to the flowsheet of Fig. 7.18 (2, 15). The feed, consisting principally of a mixture of B and C to be separated, is introduced into the central portion of a cascade of stages, 1 to 1. To facilitate... 

Most of the process industries in which particulate slurries are handled use some form of solid-liquid separation within their flowsheets. It is used in many processes with the aim of ... 

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