LU81110A1 - IMPROVEMENTS ON DISTILLATION FACILITIES - Google Patents

Description

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The present invention relates to improvements made to distillation installations and in particular to installations operating according to the principle of periodic distillation.

5 Distillation is one of the most important means of fractionation available to chemical engineering.

In a conventional continuous distillation column, the separation of the various volatile fractions is obtained by contact against the current of a liquid and a vapor.

The distillation column consists of a generally vertical ferrule equipped with devices allowing the intimate contact of the vapors which rise from

Then the boiler with the liquid condensed in a condenser and most of which returns to the column in the form of a reflux which descends by gravity into the column. During this reflux, the liquid passes through a succession of stages in which devices ensure the intimate contact of the vapors and the liquid. These | 20 contacting devices are of different types and are designated under the generic term ce plateaux. When the liquid reflux thus descends from one plateau to the next, it mixes with a liquid which is lower in volatile constituents. This reduces the efficiency: I 25 of the separation and we have therefore sought to ensure

Irer an improved circulation of reflux, in particular by avoiding such mixtures.

| Already in 1956, CANHOK (Oil and Gas J. 58, 68, 1956) indicated that by drawing the steam flow rate, we were pumping! * 30 obtain a favorable effect on the efficiency of the separation; * tion of a column. However, when transposed to an industrial scale, it was found that the theoretical results observed in the laboratory could not be confirmed, since the pulsation of the vapor flow rate did not - 2 τ.

did not satisfactorily cause reflux piston flow (see V.N. SCHRODT et al, Chem. Eng.

Sci. 22, 759, 1967).

In order to overcome the difficulties associated with the pulsa-tion of the steam flow, it has been proposed to use a so-called periodic distillation. This technique consists in acting directly on the flow of the liquid rather than acting indirectly on it by a pulsation of the vapor flow.

PO Based on theoretical considerations, laboratory-scale studies and practical tests have been carried out. These tests focused on the one hand on a total reflux and on the other hand on a distillation with production.

This is how we built the installations shown ^ p5 shown schematically in Figures 1 and 2.

In these two figures, B represents a boiler,

El to E5 the successive stages of distillation trays, RI to R4 of the tanks and C the condenser. On / off valves shown by VI to V5 and V'1 to V'5 are mounted as shown.

In the case of total reflux (FIG. 1) the vapor rises continuously in the stages El to E5 and a mass exchange takes place with the stationary liquida contained in the plates. The vapors condensed in the condenser C are collected successively and the fractions are stored sequentially in the corresponding tanks RI to R5. When all the tanks are filled to the volumetric capacity of a tray, the trays are emptied into the boiler and their content is replaced by the collected fractions. Then a new cycle begins again.

In the case of a distillation with production * (figure 2), it is possible to provide a supply on one or more trays (valve V'3), take the distillate 35 near the condenser (valve V6) at the start of the cycle and take off the residue (valve V7) to the boiler at the end of the cycle.

Ί s,; \ \ _ - 3 - 1 ... 1 thécnr indicates (G. BARON, PhDThesis., HAIFA Techni'iiu Israël, 1976.) that the working column of this hKiuiëre has a separating power double that of a coicr. don't continue.

5 dm done are the reflux no longer occurs under the effect of gravity from plateau to plateau, we can consider! to divide such a "column" horizontally. This however makes it necessary to resort to a completely new design of the plates.

20 ru effect, so far the trays used in them. According to the periodical laboratory distillation, they are either of simple construction and of revb it yield, or of high yield but of delicate construction 25 l; The present invention therefore aims to find a type -vat this trays suitable for pei odic distillation eu type described, that is to say in which one acts directly on the flow of liquid.

; _ goal thus achieved is obtained in an installation 20 of periodic dist · '.ation of the type described, characterized in that c- ·, - it comprises s at least one stage meeting the following criteria: constructive: or several pipes are arranged so as to collect 'c the steam coming from the boiler or from the stage 25 preceded "and to bring it under the plate itself; - v of these pipes carries a non-return valve, mounted in such a way that the difference between the pressure of the vapors. entrained in said pipe and the pressure prevailing in the stage, · garlic it blows is positive; 3q _ · _ volume my liquid occupying the bottom of each floor is, except without the case of the drain, subject to one or more ·. · throw this vapor coming from the above-mentioned pipes *, do. · the kinetic energy and the orientation are enough to cause ur.s circulation of the liquid favoring 35 11load · of material under the tray itself; ... * olatecu itself, the vapor dispersing orifices of which are of fox'mes and dimensions /

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known, is fixed to the walls of the floor or limited by | a short skirt, at a small distance from these walls, i the liquid from each stage being able to flow through j the orifices of the tray and / or between said skirt and the i, 5 walls towards a low point of the stage during of the operation | drain.

The bottom of the floor can be flat, good- | open, conical, pyramidal or other but has at least a low point to ensure efficient emptying.

10 The device can operate either in a foaming regime, or, at a high vapor flow rate, in a nebulizing regime, without the congestion due to an excessive pressure drop i * i being to be feared, since the very principle of | the periodic distillation eliminates the need for the gravity flow of the liquid from tray to tray.

Droplet entrainment can be avoided! at. using known devices such as baffles or trellis! metallic.

! r -; I With a view to obtaining an adequate circulation of the liquid 20 aimed at promoting the exchange of material under the plate; we can, according to an advantageous variant, conceive concevoir | the arrival of steam so as to create a flow '| vortex with vertical axis of the liquid under the plate.

Advantageously, baffles limit the oscillations of the foam, according to a technique known per se.

î: The invention will be described in more detail in reference; Refer to Figures 3 to 6 attached.

i These figures schematically represent preferred modes *: · I * of the invention.

! In Figure 3, there is shown a suitable stage; ç to be mounted in stages El to E5 of Figures 1 and; i 2.

In Figure 4, we show how nine stages of the type in Figure 3 can be grouped ί 35.

! j In Figures 5 and 6, there is shown respective i i • • s: i · - · 5 - vely a sectional view and a plan view of a preferred embodiment of an embodiment detail one floor.

In the installation shown in FIG. 3, the mark 1 represents the steam supply pipe, carrying the non-return valve 3, and terminated by the orifice 5. The actual tray 7 is here a perforated tray , bordered by a skirt 6 and surmounted by baffles 11. The outlet valve 9 is mounted at the apex of the pyramidal bottom 8 of the floor. The outlet 12 of this stage is protected by a baffle 4 .. The supply of liquid to the stage is done through the valve 10. The level of the liquid under the tray will take the profile shown here by 12.

Wall 2 can be the external wall of the landing column, or an internal wall separating two grouped stages as, for example, in FIG. 4.

In this figure, the nine stages of square section are grouped so as to constitute a distillation stage of 3 x 3 stages. There are shown the pa-20 kings 2, the plates 7 and the supply pipes 1 so as to highlight the general circuit followed by the steam in this case.

If the steam inlet under the tray is arranged as in Figures 5 and 6, the volume of liquid under the tray will be the seat of a vortex flow with a vertical axis, rather than a vortex flow to- as in Figure 3.

Although preferred embodiments of the invention have been described, it should be understood that many variants, in particular of constructions, are possible while remaining within the scope of the invention as defined by the claims that follow.

Claims (3)

4. Installation according to any one of the claims 1 to 3, characterized in that the entrainment of the droplets is avoided using metal baffles or lattices. ! '/ \ - 7 - 5. Installation according to any one of claims 1 to 4, characterized in that the steam inlet is designed so as to create a vortex flow. vertical axis of the liquid under the plate. 6, Installation according to any one of claims 1 to 5, characterized in that baffles limit the oscillations of the foam. s .......... / t ‘/ ✓ * s