FR2577441A1 - Improved device for desorption of active carbon - Google Patents

Abstract

Improved device for the treatment of active carbon, comprising a desorption apparatus 4, a condenser 6, a settler, a device for recirculating the water originating from the said settler, involving the introduction of the said water into the said condenser and the drawing off of the steam produced in the said condenser by means of a thermocompresser 2 with introduction of the said steam into the desorption apparatus 4, the said device being characterised in that it comprises a second thermocompressor 11 fed with steam from the boiler 1 supplying the said steam and which is connected to a condenser 6 and which discharges into the suction of the said thermocompressor 2, it being possible for the said second thermocompressor to be shortcircuited 15-17-14 during a stage of the desorption operation.

Description

Improved device for desorption of activated carbon.

  The present invention relates to a perfected device

  mentioned desorption of activated carbon.

  In the solvent recovery processes using activated carbon, the latter is regenerated by treatment with water vapor. The total quantity of steam required to desorb the activated carbon is around 3 to 8 kg of steam per kilogram

of solvent recovered.

  The water vapor leaving the apparatus where the desorption of the activated carbon has taken place is condensed and admitted into a decanter where a demixing takes place between the water and the solvent when these two constituents are not miscible. When the recovered solvent is miscible with water, the decanter is replaced by an appropriate separation system such as distillation, liquid-liquid extraction ... The solvent is recovered and the water can be recycled either, generally after treatment in the o boiler

  steam is produced, that is, at least in part, in the condenser.

  It has already been pointed out the advantage of using thermo

  compressors (ejectors) in installations of this type. These thermocompressors receive steam at a pressure of 8 to 16 bars from the boiler; this vapor expands in the thermocompressor and causes water vapor (pure or impure) which comes from the liquid located in the condenser where it has

  served as indirect exchange liquid.

  If we study the cycle of desorption of activated carbon by water vapor, we note that in a first phase the steam is used to heat the mass of activated carbon and during this phase no product leaves the device. Then in a second phase, we see that a mixture of desorption comes out

  vapor rich in desorbed solvent which very often has a temperature

  Condensation too low for the resulting vapor pressure to be taken up by the thermocompressor. Finally, in a third phase, the mixture leaving the desorption apparatus becomes increasingly rich in water and therefore condenses at a temperature high enough that the resulting vapor pressure is sufficient to initiate the entrainment of this vapor by the thermocompressor. During the second phase of desorption, it is

  possible to prime the thermocompressor by additional heating

  momentary silence of vapor. But this simple solution does not seem

economically interesting.

  It has been found, and this is the object of the present invention, that one could very early in this second desorption phase, prime the thermocompressor (ejector) using a second thermocompressor which is supplied with steam under 8 to 16 bars from the boiler and connected to a condenser, which delivers

  on the suction of the first thermocompressor, said second thermo-

  compressor can be short-cfiuitg at the end of said second

desorption phase.

  Preferably, according to the invention, this second thermo-

  compressor has its suction connected to a second condenser mounted

  in series with a first condenser which is itself connected to the vacuum

  ration of the first thermocompressor.

  This second condenser operating at a temperature lower than the first, thus condenses water vapor which has

  enriched in solvent in the first condenser.

  The invention will be better understood by referring to the nonlimiting examples attached which illustrate two modes of implementation.

of the invention.

  Figure 1 shows a diagram of an installation

  classic activated carbon desorption.

  FIG. 2 represents a diagram of an installation for desorption of activated carbon similar to the installation of the

  Figure 1 but provided with the device according to the present invention.

  FIG. 3 represents the diagram of an improved installation in which recirculation of water is used

impure at the level of the condensers.

  In diagram 1 we have shown: - in 1 the steam-producing boiler, this conventional boiler advantageously produces steam at about 8 to 16 bar pressure; - in 2 an ejector in which, by causing an expansion of 8 to about 1 to 1.5 bar of the steam coming from the boiler, low pressure steam is drawn coming through the piping 3 of the indirect heat exchanger ; - in 4 the adsorber; in this adsorber the solvent adsorbed on the activated carbon is desorbed by water vapor coming from the ejector 2. The distillates (mixture of water vapor

  and solvent vapor) come out of this adsorber through the

tion 5.

  The vapors leaving the adsorber through the pipe

  tion 5 are allowed in an indirect heat exchanger 6 which can advantageously be of the liquid film type with good exchange coefficient. In this exchanger, the vapors from 5 are used to vaporize the impure water admitted elsewhere in said exchanger. To ensure this vaporization, one must operate under a partial vacuum so that the pressure of the vapor leaving the indirect heat exchanger 6 is between 0.1 and 1 bar and preferably between 0.5 and 0.8 bar; this partial vacuum is good

  obviously provided by ejector 2.

  The distillates coming from 5 and not used in the exchanger 6 finish condensing in an indirect cooling condenser 7 and the cooled liquid obtained is admitted into the decanter 8 o, by simple decantation, a layer of solvent is formed which the evacuated and a layer of impure water, that is to say water which, because it still contains a certain proportion of solvent, is unsuitable for direct use in the

boiler 1.

  The impure water from the decanter is stored in

a storage bin 9.

  The impure water coming from the storage tank 9 is returned

  seen, at least in part, to the indirect heat exchanger through line 10; but said water can also be returned

  to boiler 1 after treatment if necessary.

  In diagram 2, only devices 1 (boiler), 2 (thermocompressor, i.e. ejector), 4 (activated carbon desorber), 6 (indirect heat exchanger) have been included and added to it the device according to the invention, namely - a second thermocompressor (injector) 11 which is supplied through the valve 14 by steam coming from the boiler 1 and which sucks through the valve 15 the steam located in the exchanger 6; this second injector is connected via the valve 17 with the suction of the first injector

  tor 2. When the second thermocompressor 11 is in operation

  the supplies to the first thermocompressor coming from the boiler and the exchanger are cut off thanks to the valves 13

and 16.

  In diagram 3, an improved device is shown comprising: a steam boiler 1, - an ejector 2 supplied from the boiler and sucking the steam coming from the indirect exchanger 6, - the desorber 4 with activated carbon, - the indirect exchanger 6, - another indirect exchanger 7, - a settling tank (settling tank) 8, - a storage tank 9 which receives the impure water coming from the settling tank 8 and which, via the piping 14 , sends this impure water to the top of the indirect exchanger 6, - at 15 a return of purified water coming from the exchanger 6, this purified water is returned by the pipe 16

to the boiler 1.

  According to the invention, the vapor coming from the desorber 4 and passing through the exchanger 6 then enters a second indirect exchanger 17; this second exchanger is connected to the suction of a second ejector 18 which itself is supplied through the valve 19 by steam coming from the boiler, the outlet of this second ejector being connected to the suction of the

  first ejector 2 via valve 20.

Claims (1)

CLAIM   Improved active carbon treatment device comprising a desorption apparatus (4), a condenser (6), a decanter (8), a device for recirculating the water coming from said decanter, involving the introduction of said water into said condenser and the suction of the steam produced in said condenser by means of a thermocompressor (2) with introduction of said steam into the desorption apparatus (4), said device being characterized in that it comprises a second thermocompressor (11 -18) supplied with steam from the boiler (1) supplying said steam   and which is connected to a condenser (6-17) and which flows on the vacuum cleaner   ration of said thermocompressor (2), said second thermocompressor being able to be short-circuited during a phase of the desorption operation.