FR2642563A1 - METHOD AND DEVICE FOR TREATING LIQUID ORGANIC WASTE BY SULFURIC MINERALIZATION - Google Patents

Abstract

The invention relates to a method and a device for treating liquid organic waste by sulfuric mineralization. The liquid waste to be treated with 7 and nitric acid with 11 is introduced into the reactor 1 containing sulfuric acid 5 at flow rates such that carbonization with sulfuric acid of the liquid waste is carried out in the reactor. introduced, and oxidation of carbon and SO2 formed during carbonization while simultaneously regenerating sulfuric acid. The optical density of the liquid medium 5 is continuously measured in order to interrupt the supply of liquid waste when the C content of the liquid medium exceeds a set value. The liquid waste can be an organic solvent such as tributyl phosphate.

Description

Process and device for treating organic waste

  liquids by suifuric mineralization.

  The present invention relates to a method and a device for treating liquid organic waste It applies in particular to the treatment of liquid organic waste consisting of spent organic solvents, contaminated with radioactive or toxic products, originating, for example, from nuclear installations or research laboratories of the chemical industry, who need

  to be conditioned in a stable manner.

  Among the known methods of conditioning

  of waste, the coating in bitumen is unclear

  because liquid organic products lower the softening point of the bitumen; the coating in concrete is also discouraged because the dilution must be very important to avoid the phenomena of exudation; the incorporation in a polymerizable product is an interesting way but it is difficult to apply to the products

organic liquids.

  Thus, the processes most often

  Organic waste consists of converting it into a mineral material to condition it in the long term. This can be done by incineration

or dry pyrolysis of the waste.

  Incineration of organic liquid waste

  There are some problems with radioelements contaminated by radioelements because it is difficult to treat waste with an activity greater than 10-3Ci / m3 and an activity 6 or greater than -1Ci / m3. In addition, when the liquid waste is organophosphorus compounds, the combustion produces phosphoric acid vesicles that must be neutralized by addition of formate

  of calcium in The flame. Pyro-

  Calcium phosphate which increases the volume of ashes considerably and clogs the filtered ones. As well,

  to avoid these exceptional conditions of

  tion, the phosphorus content of the solvent must be

be limited to 0.1%.

  Dry pyrolysis processes are difficult

  to implement with liquid waste

  heavily contaminated because they lead to the manipulation of

very active ash.

  Another method of treating organic waste is sulfuric mineralization, which

  has been used so far only for the treatment of

  solid organic waste. This process

  to carbonize the waste with sulfuric acid and to oxidize the carbon formed by nitric acid

  and / or hydrogen peroxide. With an organic waste

  of the formula CmHn, this corresponds to the following reactions: CmHn + n / 2H2SO4i nH20 + n / 2SO2 + mC (1)

C + 2H 2 SO 4 * 2H 2 O + 2SO 2 + CO 2 (2)

3C + 4HNO3-2H20 + 4NO + 3CO2 (3)

3C + 2HNO3 H20 + 2NO + 3CO (4)

C + H2S04 - * .H20 + SO2 + C0 (5)

  The rate constants of reactions (2) to (5) at 255 ° C are as follows: K2 = 0.0016 min-1 K2 + K3 + K4 + K5 = 0.016 min-1 K3 = 0.011 min-1 K4 + K5 = 0.0029 min-1 Carbon oxidation is faster

  by nitric acid as sulfuric acid (K3 >> K2).

  There are two steps in this process: 1. Carbonization with H2SO4 2. Oxidation of carbon with CO and CO2 by

nitric acid.

  The gases formed in these reactions are SO 2, CO 2, NO and CO, but SO 2 can be converted to sulfuric acid by oxidation with the formed nitrogen oxides and nitric acid. So we can

  regenerate the sulfuric acid necessary for

  tion. Processes of this type are described by Lerch et al in Nuclear and Chemical Waste.

  Management, vol. 2, 1981, p. 265-277.

  The present invention specifically relates to a process for treating organic waste liquids by sulfuric mineralization which overcomes the disadvantages of known methods of incineration and dry pyrolysis, with the further advantage of being able to be implemented. artwork

continuously.

  According to the invention, the method. treatment of a liquid organic waste, consists of

  - to be introduced into a reactor maintained at a temperature

  at least 150 ° C and containing concentrated sulfuric acid, (a) the liquid organic waste to be treated and (b) nitric acid and / or hydrogen peroxide at debit such as in the reactor, the sulfuric acid carbonization of the introduced liquid waste and the oxidation of the carbon and SO 2 formed during the carbonization by simultaneously regenerating the sulfuric acid; - to continuously measure the optical density of the liquid medium present in the reactor, and - to regulate the flow rate of liquid organic waste and / or the flow rate of nitric acid and / or hydrogen peroxide

  introduced as a function of the measured optical density.

  According to the invention, this is done simul-

  momentarily in the same reactor the two stages of

  carbonization and oxidation of the mineralization process

  sulfuric acid, and the step of regeneration of sulfuric acid by oxidation of SO 2 by means of nitric acid and / or hydrogen peroxide introduced 1C into the reactor. In addition, the liquid waste and / or oxidant flow rates introduced are regulated.

  according to the measured optical density.

  Indeed, the optical density varies as a function of the elemental carbon concentration of the reaction medium. Also, when this optical density exceeds a set value corresponding to the elemental carbon concentration that can be tolerated in the reaction medium, or is reduced or stopped the waste feed rate

  2n organic liquid, or the flow of food is increased

  nitric acid and / or hydrogen peroxide to oxidize the excess carbon present in the reaction medium. As soon as the optical density returns to a value lower than the set value, the feed rate of liquid waste, or nitric acid and / or hydrogen peroxide is restored to its initial value. It is thus possible to carry out the process of the invention continuously without adding sulfuric acid. Preferably, according to the invention, the flow rates of organic liquid waste, nitric acid and / or hydrogen peroxide are fixed at given values.

  introduced into the reactor and the introduction of the

  liquid waste in the reactor, when the measured optical density is greater than one

setpoint.

  The sulfuric acid used for carbonization

  waste is usually sulfuric acid

  concentrated sulfuric acid, for example

16 to 18 M to 250 C.

  The nitric acid used for the oxidation of carbon and SO 2 is preferably also concentrated nitric acid, for example 12 to 14 M nitric acid.

  When using hydrogen peroxide, this is

  it is preferably 30% hydrogen peroxide (110 volumes). The process of the invention is particularly applicable to the treatment of organic liquid waste consisting of organic solvents such as those used in

  reprocessing of irradiated nuclear fuels.

  By way of example of such organic solvents

  examples include those comprising at least one compound selected from organophosphorus compounds such as tributyl phosphate, and amines such as

  trilaurytamine and their mixtures.

  When the liquid organic waste

  treat is an organic solvent which may contain

  an organic diluent, it is preferably

  this to a preliminary treatment of neutralization, (to eliminate the acids and the nitrate ions possibly present) and concentration by distillation to decrease the volume of liquid to be treated and to eliminate the diluent and the alcohols, light products which would tend to volatilize

  partly during mineralization.

  The neutralization treatment can be carried out at room temperature by contacting

  solvent with sodium carbonate solution.

  This solution makes it possible to eliminate any acids

  present and the nitrate ions that would produce

  undesirable reactions during distillation.

  It also makes it possible to solubilize cations such as those of uranium or plutonium.

  The concentration operation by distillation

  in most cases under reduced pressure. However, when the liquid waste contains very volatile products such as ethanol, propanol and propionic acid, the distillation is carried out at ambient pressure. This distillation makes it possible to reduce the volume of solvent to be mineralized, the distilled portion being decontaminated, and to eliminate the diluents as well as the chlorine derivatives that are usually very volatile in order to avoid the production of undesirable hydrochloric acid.

in the reaction chamber.

  This distillation can be carried out in a sealed enclosure using a device with a low residence time to avoid degradation.

  sclutants and limit the formation of tars.

  This device can be equipped with a rotating band

  to evacuate deposits left during evaporation.

  This avoids the multiplication of cleaning effluents. We can recover the organic residue

  concentrate obtained in a heated tank if necessary

  re in the case where it has a high viscosity,

  and / or to avoid precipitation.

  The condensates are evacuated in a

  separate watertight to avoid repollution

radioactive during its control.

  In the case where the solvent comes from an irradiated fuel reprocessing plant, all these operations are carried out in a glove box.

under a nitrogen atmosphere.

  To then perform the treatment according to the invention, introducing the organic residue into the reactor which is heated to an appropriate temperature, greater than 200 C, when the oxidant

used is nitric acid.

  Indeed, the organic nitrates can not be formed above 200 C. Also, it is preferably carried out in this case at a temperature

  from 220 ° C. to 270 ° C., for example to 250 ° C.

  With hydrogen peroxide, a temperature of between 150 and 200 ° C., for example 170 ° C., is sufficient. The invention also relates to a liquid organic waste processing device which comprises, as the devices of the prior art, a reactor, means for heating the reactor, means for introducing into the reactor the organic liquid waste to be treated and means for introducing into the reactor nitric acid and / or hydrogen peroxide, but which further comprises means for measuring the optical density of the liquid medium present in the reactor and means for regulating the flow of organic liquid waste and / or the flow of nitric acid and / or oxygenated water introduced

  according to the measured optical density.

  Preferably, the means for measuring the optical density comprise a first light guide and a second light guide arranged relative to each other so that a light beam guided in the first light guide can be guided in the second light guide after having traveled in the liquid medium of the reactor, means for introducing a light beam into this first light guide and means for measuring the intensity of the light beam

  coming out of the second light guide.

  Other features and advantages of the invention will become more apparent when reading

  the following description with reference to the attached drawing

  in which: - Figure 1 is a general diagram of the installation,

  FIG. 2 is a diagrammatic representation

  of a device according to the invention, and - Figure 3 shows an alternative embodiment of the density measuring means

ooti cue.

  In FIG. 1, it can be seen that the installation comprises a reactor (1) in which the organic solvent to be mineralized is introduced via the pipe (7) provided with the pump (9) and the tube (11) provided with

  of the pump (13) of the concentrated nitric acid.

  The reactor may be heated by the heating means (14). The gases resulting from the reaction are discharged via a pipe (19) connected to a first rectification column R associated with a condenser C into which air is introduced. At the outlet of the condenser, dilute HNO 3 and H 2 SO 4 are recovered which are stored and gas comprising nitrogen oxides and air which is catalytically recombined in the catalytic recombination column (20) forming nitric acid with water introduced at the top of this column (20). The gas freed of the nitrogen oxides then passes into the sodium trap 22 where the CO 2 and the last traces of impurities (HNO 3, HNO 2 and H 2 SO 4) are trapped

by soda.

  In FIG. 2, it can be seen that the device comprises a reactor (1), made for example of pyrex glass, which is closed at its upper part

  by a lid (3) made for example of polytetrafluoroethylene

massive fluoroethylene.

  The reactor (1) is partially filled with sulfuric acid (5) and the organic liquid waste to be treated is introduced through a pipe (7) not immersed in sulfuric acid (5). The liquid waste flow rate is regulated by a gear pump (9) which also makes it possible to introduce a small air flow to prevent any clogging of the pipe (7) by carbonization of the organic materials. The nitric acid or hydrogen peroxide used for the reaction is introduced through a tube (11) immersed in sulfuric acid (5) and its flow rate is regulated by a pump (13). The reactor is equipped

  further heating means (14), means for

  tation constituted by a turbine (15) made for example of polytetrafluoroethylene, a probe (17) for measuring the temperature of the liquid medium and means (21, 23) for measuring the optical density. The gases produced by the reaction can be evacuated outside the enclosure by a pipe (19) connected to the ventilation circuit of the confined enclosures of the nuclear installation after passing through a gas treatment assembly such as that

shown in Figure 1.

  In the embodiment shown in FIG. 2, the optical density is measured

  by a photoelectric sensor (21) located outside

  reactor in front of a light source (23) disposed in a transparent tube (25) to be isolated from the liquid medium. The light source can be an iodine lamp. Generally, the light source (23) is disposed approximately 1 cm from the wall of the reactor (1) which in this case is of course transparent. The photocell (21) indicates the optical density of the solution and is connected to a microprocessor (27) controlling the feed pump.

  tion (9) into liquid waste to be treated.

  The microprocessor (27) is programmed such that when the optical density exceeds a set value, corresponding for example to a carbon content of the reaction medium of 1 to 5 g / l, it actuates the pump (9) to temporarily interrupt or decrease the feed rate

in organic waste to be treated.

  In this embodiment, the flow rate of nitric acid or oxygenated water introduced by the dip tube (11) is regulated by the pump (13).

at a fixed value.

  Of course, it could also slave the pump (13) to the microprocessor (27) to increase the flow of nitric acid or hydrogen peroxide when

  the optical density exceeds the setpoint.

  FIG. 3 shows another embodiment of the density measuring means

  optical liquid medium present in the reactor.

  In this case, the dip tube (25) of FIG. 2 is replaced by the assembly (30) of FIG. 3. This assembly comprises a case (29).

  made, for example, of polytetrafluoroethylene comprising

  both orifices (31) allowing the reaction medium

  to go inside the case (29). Inside

  In this case, a first light guide (33) is arranged which is curved at its lower part (33a) and then extended at the openings 31 by a second light guide (35) which is situated above the guide light (33a) by providing a space between the two guides corresponding to

  an optical path T in the reaction medium.

  A light generator external to the reactor not shown in the drawing is arranged to introduce a light beam into the first light guide (33). This light beam then passes through the liquid medium on the path T, then is guided by the second light guide (35) which is associated with a photocell located outside the reactor, to determine the intensity of the outgoing light beam, and deduce therefrom the optical density of the liquid medium present on the optical path T. The photocell associated with the light guide (35) is connected to the microprocessor

  (27) which controls as before the introduction rate

  production of liquid waste to be treated.

  As before, the optical path T corresponds to about 1 cm of solution This second system is particularly suitable for working in a sealed enclosure, for example in a glove box because the light generator and the photocell detection can

  to be located both out of the glove box.

  The device of the invention can be provided with safety devices to prevent any accident in case of failure of the light source, the cell

  photoelectric or nitric acid feed-

  than. In all these cases, we interrupt the feeding

in organic liquid waste.

  In the event of a drop in temperature, it is likewise possible to interrupt the supply of organic liquid waste. The following examples are given for

  It illustrates the process of the invention.

  Example I: Treatment of tributy phosphate.

  In this example, a 1l reactor containing 0.51 of 18M sulfuric acid, heated to 250 ° C., is used and 14N nitric acid is introduced via line (11) at a rate of 197 2 ml / hr. operate the turbine (15) at a speed of 300rpm. Tributyl phosphate (TBP) is introduced at a flow rate of 100 ml / h via line 7 and the microprocessor (27) is adjusted so as to interrupt the supply of tributyl phosphate when the optical density exceeds a value corresponding to 1 g / l of carbon in the liquid medium. After 4 hours of operation, the average flow rate of TBP, and the consumption of HNO 3 and H 2 SO 4 with respect to C, as well as the consumption of OH- in the sodium trap with respect to C, are determined. The quantity of C is determined from the amount of TBP introduced. The results

  obtained are given in Table 1.

Comparative Example 1

  In this example, we follow the same mode

  only in Example 1, except that

  the visually the reaction and that one triggers and that one stops manually the feeding in

tributyl phosphate.

  The results obtained under these conditions

are given in Table 1.

  Comparing these results with those of Example 1, it can be seen that optical sensor servocontrol allows: - a gain in processing capacity, - a reduction in consumption of nitric acid and sulfuric acid, and - a reduction of consumption of washing reagent

alkaline gases.

  Examples 2 to 6: Treatment of tributyl phosphate.

  In these examples, we study the influence

  nitric acid flow rate on the treatment capacity.

reactor.

  Using a reactor of 11 maintained at 250 C, containing 0.5l of 18M sulfuric acid, and 14N nitric acid was introduced at a rate ranging from 208 to 300mL / h according to the examples. For the feeding of tributyl phosphate, we use

  a flow of 100ml / h and we interrupt this food

  as in Example I when the detector (21) detects an optical density greater than that

which corresponds to lg / l of carbon.

  The nitric acid flow rates, the average rates of tributyl phosphate and the nitric acid consumptions with respect to C, obtained in

  these conditions are given in Table 2.

  In view of Table 2, it can be seen that for a reactor of 1 l, the optimum value of the nitric acid flow rate is 250 ml / h because beyond this value

  The gain in processing capacity is zero.

Examples 7 to 10.

  In these examples, solvents are treated

  different organic substances by operating at a constant

  so much nitric acid and solvent flow rates

  interrupted by the optical sensor as in the

ple 1.

  The results and conditions of treatment

  are given in Table 3.

  In view of this table, it is found that the capacity is substantially lower when the solvent contains trilaurylamine. Indeed, the long carbon chains of trilaurylamine - are more resistant than those of tributyl phosphate. The results of Example 8 show that it is preferable to treat trilaurylamine

  mixed with tributyl phosphate.

TABLE 1

EXAMPLE EXAMPLE EXCLUSIVE

1 1

  Flow HNO3, mL.h-1 195 199 Average flow TBP mL.h-1 39 73 consumption in HNO3 HNO3

C (1) 1.75

Consumption in H2SO4 H2S04

C (1) 0.6 0.4

Consumption in OH-

(sodium trap) (2) OH-

C (1) 2 0.9

  (1) The quantity of C is calculated from the formula

TBP introduced.

  (2) The sodium trap globally halts HNO3, HNO2,

  H2SO4 in traces and all the CO2. Soda is replaced

  when a pH of about 8 is reached. Also CO2 is trapped in the form of HC03 and does not consume

than an OH- per CO 2.

? 642563

TABLE 2

  Example 2 3 4 5 6 Flow rate HN03 14N mL.h-1 208 216 250 272 300 Average flow rate TBP ml.h-1 76 74 80 80 81 Consumption HN03 Molar ratio HN03

C (1) 0.9 I 1.1 1.2 1.3

  (1) The amount of C is calculated from the formula

TBP introduced.

TABLE 3

  EXAMPLE No. 7 8 9 10 Nature of the solvent TBP-TLA 98% to be mineralized TBP TLA TLA Hyfrane 2% ratio

in volume

  me 1/1 Flow rate solvent mt.h-1 88 82 46 60 Flow rate carbon mol.h-1 3.9 4.1 2.6 3.4 Flow HN03 ml.h-1 272 291 238 251 Consumption HNO3

C (1) 1.04 1 1.4 1.2

H2S04 consumption

C (1) 0.13 0.11 0.12 0.17

OH- consumption

C (1) 1.03 1.2 1.4 1

  TBP = tributyl phosphate TLA = trilaurylamine

  (1) The quantity of C is calculated from the chemical formulas

of TBP and / or TLA introduced.

Claims (9)

  1. Process for the continuous treatment of a liquid organic waste, characterized in that it consists in introducing into a reactor maintained at a temperature of at least 1500 ° C. and containing sulfuric acid. treat, and b) nitric acid and / or hydrogen peroxide at flow rates such as is carried out in the reactor sulfuric acid carbonization of the liquid waste introduced, and oxidation of carbon and SO 2 formed during carbonization by simultaneously regenerating sulfuric acid, - continuously measuring the optical density of the liquid medium present in the reactor, and - adjusting the flow rate of liquid organic waste and / or nitric acid flow and / or oxygenated water introduced according to the measured optical density.   2. The process according to claim 1, wherein   characterized in that the flow rates of organic liquid waste, nitric acid and / or oxygenated water introduced into the reactor are fixed at given values and the introduction of the liquid waste into the reactor is interrupted when the measured optical density is measured.   is greater than a set value.   3. Process according to any one of   Claims 1 and 2, characterized in that   liquid organic waste is an organic solvent.   4. The process according to claim 3, wherein   characterized in that the organic solvent comprises at least one compound selected from tributyl and trilaurylamine.   5. Process according to any one of   Claims 3 and 4, characterized in that   organic solvent comprises an organic diluent.   6. Process according to any one of   Claims 3 to 5, characterized in that one   subjecting the organic solvent to a pre-treatment consisting of first neutralizing this organic solvent   to eliminate acids and possible nitrate ions   present, and to concentrate the neutralized organic solvent by distillation to remove the   very volatile before introducing it into the reactor.   7. Process according to any one of   Claims 1 to 6, characterized in that the reaction   is maintained at a temperature of 150 to 200 ° C, or at a temperature of 220 to 270 C according to the chosen oxidizer.   8. Device for treating liquid organic waste comprising a reactor (1), heating means (14) of the reactor, means (7, 9) for introducing into the reactor the organic liquid waste to be treated and means (11, 13) for introducing into the reactor nitric acid and / or hydrogen peroxide, characterized in that it further comprises means (21, 23) for measuring the optical density of the liquid medium present in the reactor and means (27, 9) for regulating the flow rate of organic liquid waste and / or the flow rate of nitric acid and / or oxygenated water introduced   according to the measured optical density.   9. Device according to claim 8, characterized in that the means for measuring the optical density comprise a first light guide and a second light guide arranged relative to each other so that a beam of light guided in the first light guide can be guided in the second light guide after having traveled in the liquid medium of the reactor, means for introducing a light beam into the first light guide and means for measuring the intensity of the light. Bright beam coming out of the second light guide.