Heuristics liquid separations

Desorption Displacement desorption Gas separation adsorption Liquid separation adsorption Pressure swing adsorption Thermal swing adsorption asbestos fibers, 3 304 for bioremediation, 3 782 capillary condensation, 1 585, 591 dessicants and, 3 375-377 detergency and, 3 428 129 in dispersions, 3 707 filler measurement via, 22 571 general separation heuristics for,... 

Table 3.11 General heuristics for separation sequencing of liquid mixtures.

These include absorption columns to remove a gaseous impurity as well as stripping columns to remove a VOC from a liquid (usually wastewater). Note that these involve a MSA (mass separation agent). For example, for stripping of VOC from wastewater, steam or air is used as the MSA. Hence, appropriate choice of MSA is an important consideration in the context of P2 for gas-liquid separations. Some important heuristics are as follows. 

Note that some of the heuristics offer some conflicts. For example, heuristic recommends removal of the H2S first heuristic 3 says separate the CO2 early heuristic says separate Ci from C2 early, or separate CO2 from C2 last. However, removing the corrosive component first makes the most sense. This will probably involve absorbing H2S preferentially in an absorbing liquid. Such H2S removal is used in every one of the four proposed options available to the design engineer. In each separation option, assume the H2S is removed first. 

Heuristic 9 Separate liquid mixtures using d tillation, stripping, enhanced... 

Azeotropic and extractive distillation Distillation processes Extractive distillation(s) argon, 13 460 for aroma isolation, 11 519 atmospheric, 13 646 batch versus continuous, 3 780 of coal-tar naphthalene, 17 78-79 corrosion, 3 779-780 of crude oil, 12 401-402 13 593 debottlenecking, 13 521 in fatty acid neutralization, 22 740 favorable vapor-liquid equilibria, 3 778 feed composition, 3 778 general separation heuristics for, 22 316-317... 

For sequencing the separation of liquid mixtures, there are general heuristics, as shown in Table 3.11. More specific rules for the separations of zeotropic mixtures by distillation will be discussed later in this chapter. 

In the early stages of conceptual design, simple design heuristics permit to exclude inadequate alternatives without detailed knowledge about the process. For instance, [530, 531] propose some rules for the design of separation systems for liquid and gas/vapour mixtures. 

The following heuristic should be obvious Do not separate two components and then remix them at a reactor inlet. We must also have in mind the significant difference between the cost of recycling a gas or a liquid. Compressors are very expensive and the cost of compression is very high, whereas the cost of pumping is much lower, except in special applications (viscous liquids, slurries, aggressive solutions, etc). 

The Hierarchical Approach developed in this chapter incorporates a knowledge-based procedure for the synthesis of separations. This consists of dividing the separation section in three subsystems gas vapour, liquid and solid separations. Each subsystem is further managed by selectors, which makes use of unit operations. Split sequencing is based mainly on heuristics, although may include algorithmic or optimisation techniques. This chapter describe in more detail the synthesis of distillation trains for zeotropic distillations, the non-ideal case being left for the Chapter 9. 

Be able to apply heuristics in selecting separation processes to separate liquids, vapors, vapor-liquid mixtures, and other operations involving the processing of solid particles, including the presence of liquid and/or vapor phases. 

Heuristic 4 Introduce purge streams to provide exits for species that enter the process as impurities in the feed or are formed in irreversible side reactions, when these species are in trace quantities andlor are difficult to separate from the other chemicals. Lighter species leave in vapor purge streams, and heavier species exit in liquid purge streams. 

Heuristic 28 Boil a pure liquid or close-boiUng liquid mixture in a separate heat... 

Heuristic 32 Quench a very hot process stream to at least l,15(fF brfore sending it to a heat exchanger for additional cooling and/or condensation. The quench fluid is best obtained from a downstream separator as in Figure 4.21 for the toluene hydrodealkylation process. Alternatively, if the process stream contains water vapor, liquid water may be an effective quench fluid. 

Case 4. Heuristic 11 can also be used to develop a system with one or more multieffect columns. If we use heuristic 7 to do the ethanol-isopropanol separation by itself, one option is to pressurize the liquid feed to column D in case 2 and operate column D at a higher pressure. This multieffect arrangement is shown below. There are many other options possible for using multieffect columns for this separation. 

Several heuristic rules directed to decrease energy and capital expenditures are used for selection The first rule is for the mixtures having the region of two liquid phases it is necessary to use the most interesting splits at heteroazeotropic and heteroextractive distillation described in the section 8.4.5. Such splits separate, in the cheapest way, the mixture into components. The second rule is to exclude sphts for which one of the products is binary azeotropic mixture, if other splits... 

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