Distillation cocurrent

Stirred tanks are modeled assuming that both phases are well mixed. Tray columns are usually modeled as well mixed on each tray so that the overall column is modeled as a series of two-phase, stirred tanks. (Distillation trays with tray efficiencies greater than 100% have some progressive flow within a tray.) When reaction is confined to a single, well-mixed phase, the flow regime for the other phase makes little difference but when the reacting phase approximates piston flow, the flow regime in the other phase must be considered. The important cases are where both phases approximate piston flow, either countercurrent or cocurrent. 

Removal of reaction products can shift the equilibrium, forcing the reaction to go to completion. This can be effected by evaporation of products from the reaction mixture (reactive distillations), extraction (including supercritical extraction) of products from the reaction mixture (reactive extractions), or membrane processes. Counter- and cocurrent operation also falls within this category. If the reaction is equilibrium-limited or inhibited by reaction products countercurrent operation outperforms cocurrent operation. 

Many chemical and biological systems include multistage processes rather than only continuous contact ones. The most common multistage systems are absorption and distillation columns. Most of these systems involve more than one phase and they therefore fall under the category of heterogeneous multistage systems. Multistage systems can be cocurrent or countercurrent. 

In contrast to continuous packed bed columns, each stage, whether cocurrent or countercurrent, can be considered to be at equilibrium for many multi-phase mass-transfer processes such as distillation, absorption, extraction etc. Such stages are usually called ideal stages . 

Many chemical and biological processes are multistage. Multistage processes include absorption towers, distillation columns, and batteries of continuous stirred tank reactors (CSTRs). These processes may be either cocurrent or countercurrent. The steady state of a multistage process is usually described by a set of linear equations that can be treated via matrices. On the other hand, the unsteady-state dynamic behavior of a multistage process is usually described by a set of ordinary differential equations that gives rise to a matrix differential equation. 

Packed column Countercurrent, cocurrent Differential Liquid and/or gas Distillation, absorption, stripping, humidification, dehumidification, DCHT, washing... 

A variant on the froth contact is the reverse jet contactor (Example 22), which can be considered as an upside-down distillation tray operated above the flooding velocity in cocurrent flow of gas and liquid. It is limited to one stage. 

Reactive absorption can be realized in a variety of equipment types, e.g., in him absorbers, plate columns, packed units, or bubble columns. This process is characterized by independent how of both phases, which is different from distillation and permits both cocurrent (downflow and uphow) and countercurrent regimes. 

One of the most appealing methods for process intensification is the combination of more fimctions in a single unit. Reactive distillation— combining reaction and separation— is a prime example. However, reactive distillation can be applied only for processes in which the temperature window for reaction and separation coincides. In this respect, reactive stripping is more flexible. Another difference between the two is that reactive distillation is limited to countercurrent operation, whereas for reactive stripping both cocurrent and countercurrent operation are possible, because of the low degree of interaction between the two phases in this regime of separation (23). 

This study is on the development of high-purity isobutane production from isobutane-enriched stream by gaseous adsorption technology. Isobutane purification from Ci mixture, in which not only isobutane, but also n-butane and several kinds of Ct olefins in small or in trace are involved, is very difficult by a traditional distillation method because of their close relative volatilities between constituting components. The continuous layered 3-bed process in which was comprised of six steps as follows pressurization-1 by the cocurrent effluent gas from the other bed, pressurization-2 by isobutane (noduct, adsorption, cocurrent depressurization, countercurrent blowdown, and low pressure purge by isobutane product, was applied. From the experiment, isobutane product with over 99.9% purity and with the trace levels of olefin components could be obtained at ambient temperature. Silver impregnated cliq prefers to CMS for the removal of Ci olefins... 

Packed columns are used conventionally to obtain a low pressure drop or low liquid holdup when there is practically no heat to remove or supply or when the gas or the liquid is corrosive. They are not used when solids are present in the feed or are formed in the reaction. Although packed columns or reactors can be operated cocurrently, their operation is usually countercurrent. In particular, countercurrent use is preferred when a higher concentration driving force is needed, that is, for distillation or for most physical absorption. However, when irreversible reaction occurs between dissolved gases and the absorbent, the mean concentration driving force is the same for both modes of operation. In this case the capacity of cocurrent columns is not limited by flooding, and at any given flow rates... 

Louie, W.S. Mukherjee, U.K. Hamilton, G.L. Hydrocracking of Vacuum Gas Oils and Other Gas Oils in Cocurrent-Countercurrent Reaction Flow System with Post-Treatment Reactive Distillation U.S. Patent 6,514,403, Feb 4, 2003. 

The double pipe, cocurrent heat exchanger is used to cool a distillate product using cold water circulating through the jacket as illustrated in Fig. 2.3. The overall heat transfer coefficient is taken to be U and the mass flow of distillate and water is and Wq, respectively. Under turbulent flow conditions, the fluid temperatures are taken to be uniform across individual flow cross sections. Find the relationship to predict how steady-state temperature changes with axial position, and from this, deduce an expression to compute the average AT... 

In packed columns, it is conceptually incorrect to use the staged model even though it works if the correct height equivalent to a theoretical plate (HETP) is used. In this chapter we will develop a physically more realistic model for packed columns that is based on mass transfer between the phases. After developing the model for distillation, we will discuss mass transfer correlations that allow us to predict the required coefficients for common packings. Next, we will repeat the analysis for both dilute and concentrated absorbers and strippers and analyze cocurrent absorbers. A simple model for mass transfer on a stage will be developed for distillation, and the estimation of stage efficiency will be considered. After a mass transfer analysis of mixer-setder extractors. Section 16.8 and the appendix to Chapter 16 will develop the rate model for distillation. 

Fig. 2-83. Two stage cocurrent tube bundle distillation unit.

Differential extraction. This is a batch operation wherein a definite amount of solution to be extracted is contacted with differential portions of extracting solvent, the differential portions of extract being removed as fast as formed. The operation is exactly analogous to differential distillation and has been termed cocurrent infinite stageby Varteressian and Fenske (22). 

Differential extraction, as previously pointed out, is analogous in many respects to differential distillation. It is not used industrially and is of interest principally as a laboratory procedure and because it represents the limiting result of increasing the number of stages of a cocurrent extraction. Like its distillation counterpart, actual operations can probably only approach the more or less ideal situation described below. 

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