JP2848656B2 - Method and apparatus for liquid organic waste treatment by sulfuric mineralization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for treating liquid organic waste.

The invention has particular application in the treatment of liquid organic waste, which must be kept in a stable state, for example constituted by organic solvent liquid waste contaminated with radioactive or toxic substances coming from nuclear facilities or chemical industry laboratories. You.

Coating with bitumen in known waste preparation methods is undesirable because liquid organic products reduce the softening point of bitumen. Concrete coatings are also undesirable because diluting the waste is extremely difficult to prevent leaching. Incorporation into polymerizable products is also conceivable, but is difficult to apply to liquid organic products.

Therefore, the most reliable treatment method for treating organic waste consists of converting the organic waste to an inorganic substance in order to maintain its state for a long time. This can be done by incineration of the waste or by dry pyrolysis.
It ashing an organic liquid wastes contaminated with radioelements, the waste having a high β or γ activity than 10 higher than ^-3 Ci / m ^{3 α} activity and 10 ^-1 Ci / m ³ this It is difficult to process in this way, so that a problem necessarily arises. Furthermore,
If the liquid waste is composed of organophosphorus compounds, burning will produce phosphoric acid droplets that need to be neutralized by adding calcium formate to the flame. This produces calcium pyrophosphate, which significantly increases the ash volume and clogs the filter. To avoid further exceptional operating conditions, the phosphorus content of the solvent must be limited to 0.1%.

Since dry pyrolysis processes deal with very active ash, it is difficult to perform on highly contaminated liquid waste.

Another method of treating organic waste is mineralization with sulfuric acid, which has not been used to treat solid organic waste so far. The method consists of carbonizing the waste with sulfuric acid and oxidizing the carbon formed with nitric acid and / or hydrogen peroxide. This reaction is an organic waste of the formula _{C m H n: C m H} n + n / 2H 2 SO 4 → nH 2 O + n / 2SO 2 + mC (1) C + 2H 2 SO 4 → 2H 2 O + 2SO 2 + CO 2 (2) 3C + 4HNO ₃ → 2H ₂ O + 4NO + 3CO ₂ (3) Corresponds to 3C + 2HNO ₃ → H ₂ O + 2NO + 3CO (4) C + H ₂ SO ₄ → H ₂ O + SO ₂ + CO (5) The rate constants of the reactions (2) to (5) at 255 ° C. are: K ₂ = 0.0016 min ⁻¹ K ₂ + K ₃ + K ₄ + K ₅ = 0.016 min ⁻¹ K ₃ = 0.011 min ⁻¹ K ₄ + K ₅ = 0.029 min It is ^-1 . Oxidation of carbon is performed faster with nitric acid than sulfuric acid (K ₃ 〉〉 K ₂ ). Thus, the method includes
One step: 1.H carbonization by ₂ SO _4, 2. there is oxidation to CO and CO ₂ carbons with nitric acid.

The gases formed in the above reaction are SO ₂ , CO ₂ , NO and
Although CO, SO ₂ can be converted to sulfuric acid oxidized by nitric oxide and nitric acid formed. Therefore, it is possible to regenerate sulfuric acid necessary for carbonization.

This type of method is described by Lerch et al. In Nuclear and Chemical Wa.
Ste Management, Vol. 2, 1981, pp. 265-277.

The present invention relates to a method for treating liquid organic waste by sulfuric mineralization, which has the advantage that the disadvantages of known dry pyrolysis and incineration processes can be overcome and that it can be carried out continuously.

The present invention comprises the steps of: a) maintaining a liquid organic waste to be treated, and b) nitric acid and / or hydrogen peroxide in a reactor maintained at a temperature of at least 150 ° C. and containing concentrated sulfuric acid; carbide with sulfuric acid of the introduced liquid waste was introduced at a flow rate such as the oxidation of carbon and sO ₂ which is formed during the carbonization to play simultaneously performed sulfate, liquid medium present in the reactor Continuously measuring the optical density of the liquid organic waste and adjusting the flow rate of the introduced liquid organic waste and / or nitric acid and / or hydrogen peroxide as a function of the measured optical density. An object processing method is provided.

That is, in the present invention, in the same reactor, sulfuric acid is regenerated by oxidizing SO ₂ by nitric acid and / or hydrogen peroxide introduced into the reactor in two stages of carbonization and oxidation in the sulfuric acid mineralization process. Are performed simultaneously. Furthermore, the flow rate of the introduced liquid waste and / or oxidant is adjusted as a function of the measured optical density.

The optical density varies as a function of the elemental carbon concentration of the reaction medium. Further, when the optical density exceeds a set level corresponding to an acceptable elemental carbon concentration in the reaction medium, the supply rate of the organic liquid waste is reduced or stopped, or the organic liquid waste is excessively added to the reaction medium. Increase the feed rate of nitric acid and / or hydrogen peroxide to oxidize any carbon present. As soon as the optical density again falls below the set level, the liquid waste or sulfuric acid and / or
Alternatively, the supply rate of hydrogen peroxide is returned to its starting value. Thus, the method of the present invention can be performed continuously without adding sulfuric acid.

In the present invention, the flow rate of the liquid organic waste, nitric acid and / or hydrogen peroxide to be introduced into the reactor is fixed at a predetermined value, and when the measured optical density exceeds a set value, the liquid waste is reduced. It is preferred to interrupt the introduction into the reactor and to automatically restart the feed, especially after a downtime according to the value selected for the liquid waste stream. When the flow rate is low, the stop time is several seconds, for example, 1 to 3 seconds, and when the flow rate is higher, the stop time is longer.

The sulfuric acid used to carbonize the waste is generally concentrated sulfuric acid, for example, 16-18M sulfuric acid at 250 ° C.

Nitric also agricultural nitrate used in the oxidation of carbon and SO _2, for example 12~14M nitrate are preferred.

If hydrogen peroxide is used, it is preferably 30% hydrogen peroxide (110 volumes).

The method of the present invention is particularly applicable to the treatment of liquid organic waste constituted by organic solvents as used in irradiated nuclear fuel reprocessing facilities.

Examples of such solvents are those having at least one compound selected from organophosphorus compounds such as tributyl phosphate and amines such as trilaurylamine, and mixtures thereof.

If the liquid organic solvent to be treated is probably an organic solvent containing an organic diluent, a pre-neutralization treatment (to remove any possible acid and nitrate ions) and a partial neutralization during mineralization In order to reduce the volume of the liquid to be treated by removing diluents and alcohols, which are light products that are easily vaporized, it is preferable to carry out concentration by distillation.

The neutralization treatment can be performed at ambient temperature by contacting the solvent with a sodium carbonate solution. This sodium carbonate solution can remove any acid and nitrate ions that may be present which would cause undesirable reactions upon distillation. In addition, cations such as uranium or plutonium can also dissolve.

The distillation concentration operation is almost always performed under reduced pressure.
However, if the liquid waste contains highly volatile products such as, for example, ethanol, propanol and propionic acid, it is preferred to carry out the distillation at ambient temperature. This distillation allows the distillate to be decontaminated and reduces the volume of solvent to be mineralized, and also generally requires high volatility to avoid the formation of undesirable hydrochloric acid in closed reaction systems. The indicated diluents and chlorine inducers can also be removed.

The distillation is preferably carried out in a closed vessel using equipment having a short residence time to prevent solvent degradation and limit tar formation. The apparatus may be provided with a rotating belt for discharging the deposits remaining during evaporation so that the cleaning wastes do not adhere. The concentrated organic residue obtained in the vessel can be recovered, if it has a high viscosity and / or reheated if necessary to prevent precipitation.

The concentrate is discharged into a separate enclosure to prevent any radioactive recontamination during the test.

If the solvent is from a irradiated fuel reprocessing facility, all these operations are performed in a glove box under a nitrogen atmosphere.

Then, in order to carry out the treatment of the present invention, the organic residue is introduced into a reactor heated to a suitable level at a temperature, for example, 200 ° C. or more if the oxidizing agent used is nitric acid.

Organic nitro derivatives cannot form above 200 ° C. In this case, it is preferable to operate at a temperature of 220 to 270C, for example, 250C.

In the case of hydrogen peroxide, the temperature is 150-200 ° C, for example, 170 ° C
Is appropriate.

The invention further provides a reactor, and means for heating the reactor,
Means for introducing the organic liquid waste to be treated into the reactor and means for introducing nitric acid and / or hydrogen peroxide into the reactor are included as in the conventional apparatus, but furthermore, they are present in the reactor. Means for measuring the optical density of the liquid medium to be converted and means for adjusting the flow rate of the introduced organic liquid waste and / or the flow rates of nitric acid and / or hydrogen peroxide as a function of the measured optical density. It also relates to an apparatus for the treatment of liquid intake waste.

Preferably, the means for measuring the optical density are complementary so that the light beam guided in the first optical waveguide is guided in a second optical waveguide after passing through a path in the liquid medium of the reactor. A first optical waveguide and a second optical waveguide arranged, and means for introducing a light beam into the first optical waveguide;
Means for measuring the intensity of the light beam emerging from the second optical waveguide.

The present invention will now be described in more detail with reference to non-limiting embodiments with reference to the accompanying drawings.

FIG. 1 shows a pipe 11 with an organic solvent to be mineralized introduced through a pipe 7 with a pump 9 and with a pump 13.
1 shows an installation comprising a reactor 1 through which concentrated nitric acid is introduced. The reactor 1 can be heated by the heating means 14. The gas generated by the reaction is discharged through the pipe 19. The pipe 19 is connected to a first rectification column R associated with a condenser C into which air is introduced. At the outlet of the condenser C, dilute HNO ₃ and H ₂ SO ₄ are recovered and stored. On the other hand, the recovered gas containing nitric oxide and air is catalytically recombined with water introduced from the top of the catalytic recombination column 20 in a catalytic recombination column 20 to form nitric acid. The gas from which the nitric oxide has been removed is transferred to a sodium trap 22, where the CO ₂ and the last trace impurities (HNO ₃ , HNO ₂ and H ₂ SO ₄ ) are captured by the soda.

FIG. 2 shows a device according to the invention comprising a reactor 1 made of, for example, Pyrex glass, which is sealed at the top by a cover 3, for example made of rigid polytetrafluoroethylene.

A part of the reactor 1 is filled with sulfuric acid 5 and the organic liquid waste to be treated is introduced through a pipe 7. Pipe 7 is not submerged in sulfuric acid 5. The flow rate of the liquid waste is adjusted by the gear pump 9. Gear pump 9
Also introduces a small air flow so that the pipe 7 is not clogged by carbonization of organic matter.

The sulfuric acid or hydrogen peroxide used for the reaction is introduced by a tube 11 immersed in sulfuric acid 5 and the flow rate is
Adjusted by. The reactor further comprises heating means 14, stirring means constituted by a turbine 15 made of, for example, polytetrafluoroethylene, a probe 17 for measuring the temperature of the liquid medium, and optical density measuring means 21, 23. ing. The gas generated by the reaction is exhausted from the enclosure by the pipe 19. After passing through the gas treatment assembly as shown in FIG. 1, the pipe 19 is connected to the ventilation circuit of a nuclear facility enclosure.

In the embodiment shown in FIG. 2, the optical density is determined by a photoelectric sensor 21 located at the end of the reactor opposite a light source 23 located in a transparent tube 25 for separation from liquid substances. Measured. The light source can be a quartz iodine lamp. The light source 23 is generally located about 1 cm from the wall of the reactor 1, which in this case is clearly transparent.

The photoelectric cell 21 is connected to a microprocessor 27 which indicates the optical density of the solution and controls the pump 9 which supplies the liquid waste to be treated.

The microprocessor 27 is adapted to temporarily stop or reduce the feed stream of the organic waste to be treated if the optical density exceeds a set level, for example corresponding to a carbon content of the reaction medium of 1 to 5 g /. It is programmed to activate the pump 9.

In this embodiment, the flow of nitric acid or hydrogen peroxide introduced by line 11 is regulated by pump 13 to a fixed value. Pump to increase nitric acid or hydrogen peroxide flow when optical density exceeds set level
Obviously, it is also possible for the 13 to follow the microprocessor 27.

FIG. 3 shows another embodiment of the means for measuring the optical density of the liquid medium present in the reactor. In this case, the down or immersion tube 25 of FIG. 2 has been replaced by the assembly 30 of FIG. The assembly 30 may be a holder or envelope made of, for example, polytetrafluoroethylene.
The envelope 29 has an orifice 31 through which the reaction medium can flow again. In the envelope 29, a first optical waveguide 33 whose lower portion 33a is curved is provided. Lower part 33a
Has reached the height of the orifice 31 and a second
The optical waveguide 35 is provided, and a space corresponding to the optical path T in the reaction medium is provided between the two waveguides. Although not shown, a light generator is provided outside the reactor so as to introduce a light beam into the first optical waveguide 33. The light beam then traverses the liquid medium along path T and is guided by the second optical waveguide 35.
The second optical waveguide 35 is combined with a photoelectric cell external to the reactor to measure the intensity of the emerging light beam and to derive from that value the optical density of the liquid medium present in the optical path T. They are combined. The photoelectric cell in combination with the optical waveguide 35 is connected to the microprocessor 27 which controls the amount of liquid waste to be treated as described above.
As mentioned above, the optical path T corresponds to about 1 cm of the solution.

This second device is particularly suited for operation in a closed body, since both the light guide and the photoelectric cell for detection can be installed outside a closed body, for example a glove box.

The device of the present invention may be provided with a safety device or an auxiliary device to avoid any accident in case of a failure of the light source, the photoelectric cell or the nitric acid supply. In all cases, the supply of organic liquid waste is stopped. Upon the temperature drop, the supply of the organic liquid waste can be stopped.

The following examples are given to illustrate the method of the present invention.

Example 1 Treatment of Tributyl Phosphate In this example, heated to 250 ° C. and
Using a single reactor containing, 14N nitric acid was introduced at a flow rate of 197 ± 2 ml / hour through a pipe 11, and the turbine 15 was operated at a speed of 300 rpm.
m. Tributyl phosphate (TBP) was introduced at a flow rate of 100 ml / hour through the pipe 7 and the microprocessor 2
7 was adjusted so that the supply of tributyl phosphate was stopped when the optical density exceeded a value corresponding to 1 g / carbon in the liquid medium. The feed of tributyl phosphate is automatically turned back on after a few seconds. After operation for 4 hours, the average TBP flow rate, and consumption levels of HNO ₃ and H ₂ SO ₄ to carbon, OH to carbon in the sodium trap ^- it was measured consumption levels. The amount of carbon was determined based on the amount of TBP introduced. Table 1 shows the obtained results.

Comparative Example 1 This example followed the same method as in Example 1, except that the reaction was visually inspected and the feed of tributyl phosphate was started and stopped manually. Table 1 shows the results obtained under these conditions.

Comparing these results under Example 1, it can be seen that the optical sensor control benefits the throughput, reduces the consumption of nitric and sulfuric acids, and reduces the consumption of reagents in the case of alkaline gas cleaning.

Examples 2-6: Tributyl phosphate treatment In these examples, the effect of nitric acid flow rate on reactor throughput was investigated. Maintained at 250 ° C and 18M sulfuric acid 0.
One reactor containing 5 was used. 14N nitric acid was introduced at varying flow rates of 208-300 ml / hr as a function of the example. Tributyl phosphate was supplied at a flow rate of 100 ml / hour, and the supply of tributyl phosphate was stopped when the detector 21 detected an optical density higher than 1 g / carbon as in Example 1.

Table 2 shows the flow rate of nitric acid, the average flow rate of tributyl phosphate, and the consumption of nitric acid for carbon obtained under these conditions.
From Table 2, it can be seen that the optimum value of the nitric acid flow rate is 250 ml / h in the 1 l reactor, since there is no increase in the treatment capacity at 250 ml / h or more.

Examples 7 to 10 In these examples, the flow rate of nitric acid was kept constant, and
In the same manner as in the above, the operation of stopping the flow of the solvent by the optical sensor was carried out to treat various organic solvents. Table 3 shows the results and the processing conditions.

From the table, it can be seen that when the solvent contains trilaurylamine, the performance is greatly reduced. That is, the long carbon chain of trilaurylamine is more resistant than that of tributyl phosphate. The results of Example 8 show that it is preferable to treat trilaurylamine mixed with tributyl phosphate.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the equipment, FIG. 2 is a schematic diagram of the apparatus of the present invention, and FIG. 3 is a diagram of a modified structure of the optical density measuring means. 1… Reactor, 5… Sulfuric acid, 7,19… Pipe, 9,13 ……
Pump, 11 pipe, 14 heating means, 20 contact recombination tower, 22 sodium trap, 23 light source, 29 envelope, 31 orifice, 33 first optical waveguide , 35... Second optical waveguide, C... Condenser, R.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Bernard Guillaume France, 91350 Grigny, Cool Pitagor 5 (58) Fields investigated (Int. Cl. ⁶ , DB name) G21F 9/06

Claims (9)

(57) [Claims] 1. In a reactor maintained at a temperature of 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 in the reactor. in, introduced at a rate such that reproduction carbide with sulfuric acid of the introduced liquid waste, when the oxidation of carbon and sO ₂ which is formed during the carbonization is performed sulfuric acid simultaneously present in the reactor Continuously measuring the optical density of the liquid medium to be introduced, and adjusting the flow rate of the introduced liquid organic waste and / or nitric acid and / or hydrogen peroxide as a function of the measured optical density. To continuously treat liquid organic waste. 2. The method according to claim 1, wherein the flow rates of the liquid organic waste, nitric acid and / or hydrogen peroxide introduced into the reactor are fixed at predetermined values, and the introduction of the liquid waste into the reactor is measured. 2. The method according to claim 1, wherein the stop is performed when the determined optical density is above a set level. 3. The method according to claim 1, wherein the liquid organic waste is an organic solvent. 4. The method according to claim 3, wherein said organic solvent contains at least one compound selected from tributyl phosphate and trilaurylamine. 5. The method according to claim 3, wherein the organic solvent contains an organic diluent. 6. Prior to introducing the organic solvent into the reactor, the organic solvent is first neutralized to remove any possible acid and nitrate ions, and then the neutralized organic solvent is converted to a highly volatile organic solvent. Process according to any of claims 3 to 5, characterized in that it is subjected to a pretreatment consisting of concentrating by distillation in order to remove substances with a high concentration. 7. The method according to claim 1, wherein the reactor is maintained at a temperature of 150 to 200 ° C. or 220 to 270 ° C. as a function of the oxidizing agent selected. Method. 8. A reactor, reactor heating means, means for introducing organic liquid waste to be treated into said reactor, and means for introducing nitric acid and / or hydrogen peroxide into said reactor. An apparatus for treating organic liquid waste, including means for measuring the optical density of a liquid medium present in the reactor, and as a function of the measured optical density.
Means for adjusting the flow rate of the liquid organic waste introduced and / or the flow rate of nitric acid and / or hydrogen peroxide. 9. The optical density measuring means is arranged so that a light beam guided in the first optical waveguide can be guided in the second optical waveguide after passing through a path in the liquid medium of the reactor. A first optical waveguide and a second optical waveguide positioned at a position, means for introducing a light beam into the first optical waveguide, and means for measuring the concentration of the light beam exiting the second optical waveguide. 9. The device according to claim 8, comprising: