FR2489305A1 - PROCESS FOR CONCENTRATING AQUEOUS SOLUTIONS OF GLYCOLS - Google Patents

Abstract

PROCESS FOR THE CONCENTRATION OF AQUEOUS SOLUTIONS OF GLYCOLS. THE PROCESS RELATES TO THE CONCENTRATION OF AQUEOUS GLYCOLS SOLUTIONS BY EVAPORATION IN THE FORM OF THIN FILMS IN A SERIES OF MULTI-EFFECTING VERTICAL FILM EVAPORATORS.

Description

Process for the concentration of aqueous solutions

glycols.

  The present invention relates to a new process for the concentration of aqueous solutions of glycols, in which the multi-effect distillation process is used with the aid of vertical film exchangers arranged in the

  successive stages of one or more vertical columns.

  Currently, the concentration of the aqueous solutions of glycols is carried out by means of a series of reboilers and successive evaporators as shown in the diagram of the process

of Figure 1.

  In this scheme, the aqueous solution of low concentration glycols passes through the pipe 1 and the exchanger 2 (where it is heated at the expense of the steam 3) to the first evaporator V1. From the bottom of the evaporator V1, through 4, a more concentrated solution comes out which, at

  5 and the exchanger 6 is sent to the second evapo-

  Vator, through which 7, the exchanger 8 and the pipe 9, is sent to the third evaporator V; of these through 10, the heat exchanger 11 and the pipe 12, the solution

  even more concentrated is sent to the last evapo-

  V4, kept under vacuum (about 200 millibars) at

means of the ejector 16.

  In the evaporator V 4 the solution concentrates

  through 13 and the pump 14, it is sent

to the tank 15.

  From the top of the first three evaporators, the water vapor is mixed with small amounts of glycol, which is condensed in the exchangers 6, 8 and 11 and is collected.

in the containers 17 and 18.

  The vapors coming out of the head of the fourth evapo-

  V4 are condensed in the refrigerant 19 and at the same time as the other condensates loaded with glycols,

  they are recycled to the installation of glycols.

  In order to avoid excessive losses of glycols in the vapors, the wash water is sent through 20 in the

evaporator head V3 and V4.

  The present inventors have now discovered that this method of concentrating glycols can be carried out in a simpler way and with a considerable saving of water vapor in a single column divided into a number of stages, using the principle of multi-effect distillation and using heat exchangers

with vertical film.

  It is an object of the present invention to provide a novel process for the concentration of aqueous solutions of glycosilicone in that for said concentration a single vertical column is used divided into a number of cylindrical sections each of which comprises (a) one or more film evaporators with vertical tube bundles without any outer wraps; (b) one or more small trays, each of which is connected with its bottom to the upper tube bundles of one of the film evaporators which are in the same section, said small trays being connected in the last

  part without tube film evaporator which leads to the

  see the concentrated solution of glycols, while with its upper part, the plate is connected to the lower tube plate of one of the film evaporators which are found in the upper section, said small plates being connected in the first section directly to the tubes of feeding the solution of glycols to concentrate; (c) a closure and flow control system located on the bottom of each small tray, for controlling the passage of the glycol solution from the small tray to the film exchanger located below;

  (d) openings at the top of the side

  each small plateau, except for the small plateaux of the first section; (e) one or more siphon tubes connecting two successive sections and intended to transfer the condensate collected in each section to the next section, the first section also being provided with tubes for feeding the solution to be concentrated to the small trays (b) and for introducing the saturated water vapor provided for heating said solution, the last section being provided with tubes for discharging the condensates, for extraxion of concentrated solutions of glycols and for joining with the vacuum system. Referring to Figure 2 which represents said vertical column, the new process for concentration

  aqueous solutions of glycols will now be described.

  It is assumed that the total number of floors, simply for illustrative purposes, is 9 and that there is only one small plateau

  and a single film evaporator provided in each stage.

  In the drawing of column 1, are indicated by the, 2a and 3ales first three sections or stages by 7a, 8a, 9a1the last three sections, while the three sections

  intermediaries are not indicated for lack of space.

  The solution to concentrate that is already hot from the plant

  ethylene oxide, because the reaction ethylene oxide + H20 = exothermic glycols is sent to the small plate

  4 of the first floor through the pipe 2.

  From the small tray 4, said solution passes through the closure systems and the flow control system 6 into the film evaporators 8 where it is further heated by live steam from 5; then it goes into the small trays and into the evaporators 8 placed below, thus becoming. more and more concentrated <to the last floor 9a where it reaches maximum concentration, and from there, it

  is sent through line 10 into the tank.

  The vapors that emerge in the small trays placed after the first stage, exit outside through the holes of the openings 7 and are condensed outside the tubes 8 of the film evaporators while heating at the same time the solution flowing . inside the tubes in question. The condensates which are collected at the bottom of each stage pass from one stage to the next by the tubes or the siphon pipes 9 up to the last stage from where they are discharged by the pipe 11. The vapors leaving the small plateau of the last stage 9a are condensed by the refrigerant

jacketed 14.

  The tubes and the valves 12 serve to transfer any inert gases that may be present from one stage to the other by descending to the last one which is connected by the pipe 13.

to the vacuum system.

  In order to show the advantages achieved by the new process for the concentration of aqueous glycol solutions, in the conventional method, a concentration test of a glycol solution is carried out, for example, by feeding two installations, a classic and a new one, consisting of a single column with the same amount per hour of an aqueous solution of glycols, at the same temperature and under the

same pressure.

  The results are summarized in the table below:

  CLASSICAL INSTALLATION POWER SUPPLY INSTALLATION OF THE INVENTION

  41370 Kg / h (Glycol solution 41370 Kg / h

at 12.7%)

   C Temperature 150 C 13 bar Pressure 13 bar 5952 Kg / h Solution quantity 5900 Kg / h concentrated obtained 84.85% by weight Concentration 88% by weight 84 C Output temperature 73 C 0.2 bar Pressure at the outlet 0 , 1 bar 9150 Kg / h at 17 bar Steam Consumption 1690 Kg / h at 3.7 bar In the above mentioned example, the concentration of the solution which enters is 12.7% by weight and that of the solution that comes out is 88% by weight. If the concentrations

  at the entrance or exit vary, the pressures and tempera-

  eratures at the entrance and exit of the column will also vary. Normally, for a concentration range of 0% to 100% of glycols, the concentration is carried out in the range of pressures between 20 bar and 0.03 bar and in

  the temperature range is between 2000 C and 30 C.

  In summary, the adoption of the new process according to the present invention provides the following advantages (a) a considerable saving of water vapor for heating; the consumption of steam to concentrate 41370 Kg / h of solution with the known process is 9150 Kg / h while the consumption to treat the same amount of solution by the new process is about 1690 Kg / h; the steam saving is therefore

9150 - 1690. 100 = 81.5%;

  (b) lower costs of producing saturated steam for heating since with the new process * a vapor pressure of 3.7 bar is sufficient whereas with the known method, the steam must be under a pressure of 17 bar; saturated steam pressure for heating is between 2 and 4 bar depending on the initial concentration and the final concentration of the solution; (c) greater simplicity and reliability of the system as a whole; in fact, in the new method, a single column replaces the set of several columns of the known system; (d) the lower cost of operation makes it possible to amortize the first cost for the new type of installation after about two years; in fact, the cost of a new installation. treating type 41370 Kg / h of solution was estimated to be around 1050 million. Assuming that the number of hours of operation is 8000 per year, that the price of saturated steam at 3.7 bar is 7 lire / kg and that the price of saturated steam at 17 bar is 10 lire / Kg, the annual savings will be (10 x 9150 - 7 x 1690) x 8000 = 637.4 million / year, which will amortize the invested capital of 1050 million

before two years.

Claims (4)

  A process for the concentration of aqueous solutions of glycols, characterized in that said solutions are evaporated in the form of liquid film in a large number of vertical film evaporators using the   principle of multi-effect distillation.   2. Method according to claim 1, characterized in that the concentration of aqueous solutions of glycols is carried out in a single vertical column divided into a number of cylindrical sections each of which comprises: (a) one or more film evaporators with vertical bundles of tubes without outer casing; (b) one or more small trays each of which is connected with the bottom to the upper tube plate of one of the film evaporators which are in the same section, in the last section without a film evaporator, said small trays being connected to the tube leading to the reservoir of the concentrated solution of glycols, whereas with   the upper part, it is connected to the tube-   the bottom of one of the film evaporators that are themselves   same in the upper section, in the first section, laesdts small trays being connected directly to the supply lines of the glycol solution to concentrate; (c) a system for maintaining and adjusting the flow rate placed at the bottom of each small plate, for the purpose of adjusting the passage of the glycol solution from the small plate to the film exchanger below; (d) openings provided at the top of the lateral part of each small plate and not in the small trays of the first section; (e) one or more siphon tubes connecting two successive sections and intended to transfer the condensate collected in each section to the next section; the first section is also provided with conduits for feeding the solution to be concentrated to small trays   (b) and for the introduction of saturated steam for heating   of said solution1 and the last section being provided with conduits for discharging the condensed water, for extracting the concentrated solution of glycols and for junction with the vacuum system.   3. Method according to claim 2, characterized in that the pressure of the saturated steam used for the subsequent initial heating of the glycol solution is between 2 and 4 bars.   4. Method according to claim 2, characterized in that the concentration of the aqueous solution of glycols is carried out in the pressure range between 20bar and 0.03 bar and in the temperature range between   and 300C, throughout the concentration range of glycols.