Liquid-Separation System

Removing light and heavy-end impurities is compulsory before other separations. 

Series of flashes, by reducing the pressure or/and by increasing the temperature. 

Distillation with vapor product. When a partial condenser is used, the flash drum plays the role of a vapor/liquid separator. In the setup known as a stabilizer there is only vapor distillate, while the liquid is returned as reflux. The column has a pasteurization section when a gaseous stream leaves at the top, while the 

Reboiled stripping. In this case, the vapor needed for stripping is produced internally. This method may replace conveniently steam distillation. Note that the initial mixture should be fed at sufficiently low temperature on the top stage. 

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Assume initially that a phase split can separate the reactor effluent into a vapor stream containing only hydrogen and methane and a liquid stream containing only benzene, toluene, and diphenyl and that the liquid separation system can produce essentially pure products. 

Crystallization Process Systems brings together essential aspects of the concepts, information and techniques for the design, operation and scale up of particulate crystallization processes as integrated crystal formation and solid-liquid separation systems. The focus of the book, however, is on crystallization only dealing with related unit operations as far as is necessary. It is therefore... 

Although the methods developed here can be used to predict liquid-liquid equilibrium, the predictions will only be as good as the coefficients used in the activity coefficient model. Such predictions can be critical when designing liquid-liquid separation systems. When predicting liquid-liquid equilibrium, it is always better to use coefficients correlated from liquid-liquid equilibrium data, rather than coefficients based on the correlation of vapor-liquid equilibrium data. Equally well, when predicting vapor-liquid equilibrium, it is always better to use coefficients correlated to vapor-liquid equilibrium data, rather than coefficients based on the correlation of liquid-liquid equilibrium data. Also, when calculating liquid-liquid equilibrium with multicomponent systems, it is better to use multicomponent experimental data, rather than binary data. 

A direct liquefaction technique, the SRC process involves mixing dried and finely pulverized coal with a hydrogen donor solvent, such as tetralin, to form a coal-solvent slurry. The slurry is pumped together with hydrogen into a pressurized, vertical flow reactor. The reactor temperature is about 825°F (440°C) and pressures range from 1,450 to 2,000 psi. A residence time in the reactor of about 30 minutes is required for the carbonaceous material to dissolve into solution. From the reactor, the product passes through a vapor/liquid separation system. The slurry solids remaining in the reactor are then removed and filtered. Various filtration techniques have been developed to remove solids from recoverable oil. 

As a strategy, the synthesis procedure should start with vapor recovery and gas separations, from which some components are sent to liquid separations. For the same reason, the solid-separation system should be placed in the second place. Note that the subsystems of gas and solid separations are largely uncoupled. As a result, the liquid-separation system should is handled the last. 

Figure 5.15 Flowsheet for the liquid-separation system by direct sequence.

Wahnschafft, O. M., LeRudulier, J. P., Blania, P., and Westerberg, A. W. SPLIT II. Automated Synthesis of Hybrid Liquid Separation Systems, Comput. Chem. Eng. 16, S305-S312 (1992). 

Solid-liquid separation systems generally consist of four stages, which are 1) pretreatment to increase particle size 2) solid concentration in thickeners 3) solid separation in filters and centrifuges and 4) posttreatment to remove solubles and reduce liquid content. Fig. 6 shows the relationship among these stages. 

Solid-liquid separation systems generally consist of four stages including pretreatment, solid concentration in thickeners, solid separation in filters or centrifuges, and post-treatment by expression and washing operations. There are different types of SLS equipment served for different functions in relation to the four stages. Product specification, characteristics of solid-liquid suspension, solid settling velocity, rate of cake... 

Tiller, F.M. Li, W. Dangers of lab-plant scaleup for solid/liquid separation systems. Chem. Eng. Commun. 2002, 189, 1655-1677. 

The simulation of the liquid separation system is more complicated. The simplest approach is to lump all the items in a black-box unit named Separation, simulated by a Separator module. This is specified in term of desired recoveries of components. In this way, we can concentrate the attention on the influence of the recycle on the reaction system rather than on the simulation of separators. 

Fig. 7.12 displays the stmcture of the separation problem of type 1 with a single liquid separation system. 

A heterogeneous gas/liquid reactor illustrates a two-phase effluent (Fig. 7.13). The two phases are already present inside the reaction space. Vapour phase may undergo a new phase-split after condensation. The secondary vapour enters the vapour separation system. Gaseous reactants are recycled to the reactor, but purge may be necessary to eliminate gaseous products or avoid the accumulation of inert. The liquid streams from phase split and vapour recovery are sent to the liquid separation system, from which the liquid reactant is recycled. 

Firstly, the mixture must be condensed and split in gas and liquid phases in a flash vessel (Fig. 7.14). The condensable components are sent to the liquid separation system, while the non-condensable components are treated in the gas separation system. Another solution is applying a quench to the reactor outlet with recycled solvent. 

The phase-split block can be a single flash, a series of flashes, or a combination of flash and absorption/stripping columns. Flash temperature and pressure are design variable that may be optimised to fulfil a separation objective, as sharp gas/liquid split or recovery of some components. For water-driven condensers the recommended condensation temperature is of about 35 °C. Vapour components can be condensed and sent to the liquid separation system. The supercritical components carried in the liquid phase can be recovered in a stabiliser column (see later in this section). Further, these can be sent to the gas separation system, used as fuel, or purged. 

After solving the first separation step the solution of the whole problem is greatly simplified. Hydrogen-rich gas is recycled, but alternatively it can be sent to the gas separation system for methane recovery. The synthesis of the liquid separation system can be also examined separately. 

The synthesis of the liquid separation system is better founded by systematic methods as for vapour-phase or solid-phase separations. Computer simulation can be used to support the procedure, namely when distillation is the preferred method. 

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