APPARATUS AND PROCESS FOR THERMAL DENITRATION, USE OF SUCH AN APPARATUS AND PRODUCT OBTAINED BY MEANS OF SUCH A PROCESS

Abstract

An apparatus (1) for thermal denitration of a uranyl nitrate hydrate to uranium trioxide UO3. The apparatus (1) comprises a burner (114) and a reaction chamber (110) configured to carry out thermal denitration of uranyl nitrate hydrate and to form uranium trioxide UO3 in the form of particles. The apparatus also comprises a separating chamber (120) suitable for separating UO3 particles from the gases resulting from the thermal denitration carried out in the reaction chamber (110), and at least one filter (130) configured for purifying the gases. The separating chamber (120) is a decanting chamber into which the reaction chamber (110) directly opens out. The filter (130) is capable of performing the separation at a temperature greater than or equal to 350 C. The invention also relates to use of such an apparatus, to a thermal denitration process and to UO3 particles obtained by such a process.

Claims

1. A facility (1) for thermally denitrating a uranyl nitrate hydrate, having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6, into uranium trioxide UO.sub.3 including: a burner, a reaction chamber disposed at the outlet of the burner and including an inlet of uranyl nitrate hydrate, said reaction chamber and the burner being configured to make a thermal denitration of the uranyl nitrate hydrate and to form uranium trioxide UO.sub.3 having the form of particles, a separation chamber adapted to separate a part of the UO.sub.3 particles from gases from the thermal denitration made in the reaction chamber, and at least one filter configured to separate a another part of the UO.sub.3 particles from the gases and thus scrub the gases, wherein the separation chamber is a sedimentation chamber into which the reaction chamber directly opens, and wherein the filter is able to make the separation at a temperature higher than or equal to 350 C.

2. The facility according to claim 1, wherein the separation chamber includes at least one gas outlet towards the filter, and wherein the facility further comprises at least one gas deflecting means for deflecting the gases and the UO.sub.3 particles exiting the mouth of the reaction chamber into the separation chamber at a sedimentation location of the separation chamber the vertical dimension of which is lower than the vertical dimension of the gas outlet.

3. The facility according to claim 2, wherein the vertical dimension of the sedimentation location is lower than that of the gas outlet by a height h, the separation chamber having a height H, and wherein the ratio h to H is between 0.1 and 0.5.

4. The facility according to claim 2, wherein the gas deflecting means is provided by a partial housing of the reaction chamber in the separation chamber, the mouth of the reaction chamber in the separation chamber defining the sedimentation location.

5. The facility according to claim 2, wherein the gas deflecting means includes a deflecting wall separating the mouth from the reaction chamber of the gas outlet, the lower end of said deflecting wall defining the sedimentation location.

6. The facility according to claim 1, wherein the side walls of the separation chamber have only wall sections making an angle with the vertical which is lower than 60.

7. The facility according to claim 1, wherein the filter is of the sintered metal type filter.

8. The facility according to claim 7, including at least two parallel filters of the sintered metal type.

9. The facility according to claim 1, wherein the burner and the reaction chamber are configured to provide, at the outlet of the reaction chamber, a gas rate between 1 m/s and 2 m/s.

10. A use of a facility according to claim 1 for making a thermal denitrating of a uranyl nitrate hydrate having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6.

11. The use according to claim 10, wherein the uranyl nitrate hydrate is uranyl nitrate hexahydrate of the formula UO.sub.2(NO.sub.3).sub.2,6H.sub.2O.

12. A process for thermally denitrating a uranyl nitrate hydrate having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6, the process for thermally denitrating comprising: a step of thermally denitrating a uranyl nitrate in a reaction chamber by means of a burner, the reaction chamber being disposed at the outlet of said burner, whereby UO.sub.3 particles are obtained in a mixture with gases, a step of separating a part of the UO.sub.3 particles which are mixed with gases from the gases, the separating being made in a sedimentation chamber into which the reaction chamber directly opens, a filtration step for separating a another part of the UO.sub.3 particles which are mixed with gases from the gases and thus scrubbing the gases, the filtration step being made at a temperature higher than or equal to 350 C., and a step of recovering the UO.sub.3 particles thereby obtaining an thermally denitrating of the uranyl nitrate hydrate having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6.

13. The process according to claim 12, wherein the step of separating a part of the UO.sub.3 particles from the gases comprises the following sub-steps of: deflecting the UO.sub.3 particles and gases from the heat treatment step into a sedimentation location having a vertical dimension lower than a gas outlet of the filter used during the filtration step, sedimenting a part of the UO.sub.3 particles which is collected in the sedimentation chamber.

14. The process according to claim 12, wherein, during the separation step, the gases from the thermal denitration are introduced in the separation chamber with a gas rate between 1 m/s and 2 m/s.

15. UO.sub.3 particles directly obtained by a process according to claim 12, the UO.sub.3 particles having the following characteristics: a BET specific surface area higher than or equal to 17 m.sup.2/g, a water weight percentage lower than or equal to 0.4% wt, and a weight percentage of nitrate ions NO.sub.3.sup. lower than or equal to 0.8% wt.

16. The UO.sub.3 particles according to claim 15, wherein the BET specific surface area is between 17 m.sup.2/g and 21.5 m.sup.2/g.

Description

BRIEF DESCRIPTION OF THE FIGS.

[0100] The present invention will be better understood upon reading the description of exemplary embodiments, given by way of purely indicating and in no way limiting purposes, making reference to the following appended Figs.

[0101] FIG. 1 schematically illustrates the facility described for implementing the process for obtaining uranium trioxide UO.sub.3 by thermal denitration of uranyl nitrate taught by document [2].

[0102] FIG. 2 illustrates a facility for thermally denitrating a uranyl nitrate hydrate according to the invention along a cross-section view along the axis A-A of FIG. 3.

[0103] FIG. 3 illustrates a top view of a facility according to the invention in which a single filter is mounted among the four filters of the facility and in which the manhole is not closed.

[0104] FIGS. 4a and 4b schematically illustrate two alternatives of arrangement of the reaction chamber and the separation chamber for a facility according to the invention.

[0105] Identical, similar or equivalent parts of the different Figs. bear the same reference numerals so as to facilitate switching from one Fig. to the other.

[0106] The different parts represented in the Figs. are not necessarily drawn to a uniform scale, to make the Figs. more readable.

[0107] The different possibilities (alternatives and embodiments) should be understood as being not exclusive of each other and can be combined with each other.

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

[0108] FIG. 2 illustrates a facility 1 according to the invention for making a thermal denitration of a uranyl nitrate hydrate having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6, into uranium trioxide UO.sub.3.

[0109] Such a facility 1 includes: [0110] a burner 114, [0111] a reaction chamber 110 disposed at the outlet of the burner 114 and including an inlet of uranyl nitrate hydrate, said reaction chamber 110 and the burner being configured to make a thermal denitration of the uranyl nitrate hydrate and to form uranium trioxide UO.sub.3 having the form of particles, [0112] a separation chamber 120 adapted to separate a part of the UO.sub.3 particles from the gases from the thermal denitration made in the reaction chamber 110, the separation chamber 120 being a sedimentation chamber, and [0113] four filters 130, as illustrated in FIG. 3, configured to separate the other part of the UO.sub.3 particles from said gases and thus to scrub said gases, each of these filters 130 being connected to a gas outlet 131 of the separation chamber 120.

[0114] The burner 114 and the reaction chamber 110 are in accordance with the burner 4 and the reaction chamber 1 described in document [2], with the difference that the reaction chamber 110 directly opens into the separation chamber 120. Thus, for the present facility 1, there is no conduit 9 connecting the reaction chamber 110 to the separation chamber 120. Further, the reaction chamber 110 has no end extending into a cone reducing the outlet section.

[0115] Thus, as regards the operating principle and the structural characteristics of the reaction chamber 110 and the burner 114 as well as those of the outlet section of the reaction chamber 110, the description of document [2] is referred to.

[0116] The burner 114 comprises: [0117] a conduit 117 for feeding uranyl nitrate hydrate, said conduit 117 being connected to the inlet of the reaction chamber 110. [0118] a fuel gas supply 116, and [0119] an air supply 115.

[0120] The outlet of the burner 114 is connected to the reaction chamber 110. The latter includes an inlet cone through which the combustion gases and the uranyl nitrate hydrate 117 are introduced, a cylindrical shell and an outlet 113.

[0121] Unlike the reaction chamber 1 of document [2], the outlet 113 of the reaction chamber 110 extends the cylindrical shape with a straight section, that is a substantially constant section. The outlet 113 of the reaction chamber 110, or mouth, directly opens into the separation chamber 120.

[0122] The reaction chamber 110 is partly housed in the separation chamber 120. In this manner, the reaction chamber 110 opens into the separation chamber 120 at a vertical dimension lower than that of the gas outlet 131 of the filters 130.

[0123] The burner 114 and the reaction chamber 110 are configured to provide, at the outlet of the reaction chamber 110, a gas rate between 1 m/s and 2 m/s and advantageously between 1.4 m/s and 1.7 m/s.

[0124] The mouth 113 of the reaction chamber 110 defines a sedimentation location 121 in the separation chamber 120. Thus, when gases and UO.sub.3 particles exit from the reaction chamber 110 after the thermal denitration reaction, they are deflected by the mouth onto the sedimentation location 121. The vertical dimension of the sedimentation location 121 thus corresponds, as illustrated in FIG. 2, to the vertical dimension of the mouth 113 of the reaction chamber 110.

[0125] Such a partial housing of the reaction chamber 110 in the separation chamber 120 forms a deflecting means for deflecting the gases and UO.sub.3 particles into the sedimentation location 121.

[0126] The separation chamber 120 has, as shown in FIGS. 2 and 3, a circular horizontal section and a triangular vertical section. In this manner, the separation chamber 120 has generally a conical shape the apex of which is facing downwardly. The side walls 122 of the separation chamber 120 have an angle with respect to the vertical which is between 0 and 45. The side walls 122 of the separation chamber 120 thus have only wall sections making an angle with the vertical which is lower than 60, and more particularly than 45.

[0127] It will be noted that the side wall 122 at the mouth 113 has an angle with respect to the vertical which is close to 0. Thus, the depositions of particles which could occur onto the side walls 122 of the separation chamber 120 are cancelled.

[0128] The lower part of the separation chamber 120 includes, as shown in FIG. 2, a particle outlet 123 for recovering UO.sub.3 particles after they are separated from the gases. The upper part of the separation chamber 120 includes, as illustrated in FIG. 3, four gas outlets 131 each equipped with a filter 130 to discharge the gases after they are separated from the particles. The gas outlets 131 each define a vertical dimension of the gas outlet. In the present embodiment, the gas outlets 131 define a same vertical dimension of gas outlet which corresponds to the vertical dimension of the gas outlet. In the case where several filters 130 with gas outlets 131 having different vertical dimensions of gas outlet would be provided, the vertical dimension of the gas outlet corresponds of course to the smallest vertical dimension of the gas outlet.

[0129] The vertical dimension of the gas outlet 131 is higher than that of the mouth 113 of the reaction chamber 110 by a height h.

[0130] The upper part of the separation chamber 120 can also be provided, as illustrated in FIG. 2, with a man hole 140 to enable the separation chamber 120 to be inspected and maintained.

[0131] The separation chamber 120 has a height H. This height H of the separation chamber 120 is defined in connection with the height h which corresponds to the difference of vertical dimension between the sedimentation location 121 and that of the gas outlet 131 by a height h. Indeed, the ratio h to H, noted h/H, is between 0.1 and 0.5, advantageously between 0.2 and 0.3, and preferentially, between 0.23 and 0.27.

[0132] It will be noted that the ratio h/H is preferentially set to 0.25.

[0133] Thus, typically, the separation chamber 120 can have a maximum lateral dimension between 3 m and 8 m, advantageously between 4.5 m and 6.5 m. Thus likewise, the height H of the separation chamber 120 can be between 5 m and 12 m, advantageously between 6 m and 9 m.

[0134] The filters 130 are sintered metal type filters, as illustrated in FIGS. 2 and 3, a single filter 130 being represented in FIG. 3, three of the gas outlets 131 being represented without the filter 130. These filters enable the other part of the UO.sub.3 particles to be separated from the gases, which particles have not been separated upon separation by sedimentation. Like this, the gases are scrubbed.

[0135] During this separation at the filters 130, the UO.sub.3 particles which have been not separated from the gases by sedimentation are built up on the filters 130. Thus, in the facility 1, a continuous declogging means (not represented) is provided, for collecting these UO.sub.3 particles. During this collection, UO.sub.3 particles fall, under the gravity effect, into the separation chamber 120, to be recovered at the particle outlet 123 of the separation chamber 120.

[0136] Typically, each filter 130 can have a diameter between 0.7 m and 1.7 m, advantageously between 1.0 m and 1.4 m.

[0137] It is to be noted that if in this embodiment, the facility includes four filters 130, it is also contemplatable, without departing from the scope of the invention, that the facility includes a different number of filters. Thus, the facility can be alternatively equipped with only two filters 130, or even a single filter or even six filters, as long as these, or this, is (are) suitably dimensioned. Of course, the arrangement of the filters 130 as described in this embodiment is perfectly compatible with these alternatives as long as the filter distribution on the upper part of the separation chamber 120 is adapted to the number of filters present.

[0138] Alternatively to such an arrangement of the reaction chamber 110 partly housed in the separation chamber 120, FIGS. 4a and 4b schematically illustrate two other possible arrangements between the reaction chamber 110 and the separation chamber 120 for a facility 1 according to the invention.

[0139] A facility 1 according to the first alternative depicted in FIG. 4a is differentiated from the facility illustrated in FIG. 2 in that the reaction chamber 110 is not housed in the separation chamber 120 with however a mouth 113 of the reaction chamber 110 in the separation chamber 120 the vertical dimension of which remains lower than that of the gas outlet 131.

[0140] According to this first alternative of the invention, the separation chamber 120 has a portion of its upper part, that accommodating the mouth 113 of the reaction chamber 110, lowered with respect to the rest of the upper part which accommodates the filters 130. Such a lowering of a portion of the upper part of the separation chamber 120 forms a deflecting means for deflecting the gases and particles into the sedimentation location 121.

[0141] Indeed, in this first alternative, it is this lowering which enables positioning of the mouth 113 of the reaction chamber 110, and thus also the sedimentation location 121, in the separation chamber 120 with respect to the gas outlet 131.

[0142] A facility 1 according to a second alternative is depicted in FIG. 4b. Such a facility 1 is differentiated from the facility 1 illustrated in FIG. 3 in that the reaction chamber 110 opens into the separation chamber 120 substantially at the same vertical dimension as the gas outlet 131 and in that it is provided a deflecting wall 124 separating the mouth 113 from the reaction chamber 110 in the separation chamber 120 of the gas outlet 131. The lower end of the deflecting wall 124 defines the sedimentation location 121 and enables gas and particles at the outlet of the mouth 113 of the reaction chamber 110 to be deflected up to the sedimentation location 121.

[0143] Thus, according to this second alternative of the invention, the deflecting wall 124 forms a deflecting means for deflecting gases and particles into the sedimentation location 121.

[0144] A facility 1 according to the invention can be implemented to make a process for thermally denitrating a uranyl nitrate hydrate having the formula UO.sub.2(NO.sub.3).sub.2,xH.sub.2O with 2x6 in order to obtain UO.sub.3 particles.

[0145] Such a process comprises: [0146] a step of thermally denitrating a uranyl nitrate in a reaction chamber 110 by means of a burner 114, the reaction chamber 110 being disposed at the outlet of said burner 114, whereby UO.sub.3 particles are obtained in a mixture with gases, [0147] a step of separating these UO.sub.3 particles from the gases which is made in a sedimentation chamber 120 into which the reaction chamber 110 directly opens, [0148] a filtration step for separating the other part of the UO.sub.3 particles from said gases and thus scrubbing said gases, said step being made at a temperature higher than or equal to 350 C., and [0149] a step of recovering the UO.sub.3 particles.

[0150] The step of separating UO.sub.3 particles comprises the following sub-steps of: [0151] deflecting the particles and gases from the heat treatment step into a sedimentation location 121 having a vertical dimension lower than that of the filter 130 used during the filtration step, [0152] sedimenting a part of the UO.sub.3 particles which is collected in the sedimentation chamber 120.

[0153] Two syntheses of uranium trioxide UO.sub.3 particles have been made by thermally denitrating uranyl nitrate hexahydrate UO.sub.2(NO.sub.3).sub.2,6H.sub.2O.

[0154] The first synthesis, noted S1, has been made in a comparative facility, in accordance with the teaching of document [2] and illustrated in FIG. 1.

[0155] The second synthesis, noted S2, has been made in a facility in accordance with the invention and illustrated in FIGS. 2 and 3.

[0156] It is reminded that the burners 4 and 114 as well as the upper part of each of the reaction chambers 1 and 110, or reaction zone in which the thermal denitration reaction and the formation of UO.sub.3 particles occur, are identical.

[0157] The operating conditions for introducing the reaction gases and uranyl nitrate hexahydrate in the reaction chamber 1, or 110, via the burner 4, or 114, have also been identical for both syntheses S1 and S2: [0158] introduction flow rate for UO.sub.2(NO.sub.3).sub.2,6H.sub.2O in the piping 7 and the conduit 117: 70 kg/h, [0159] introduction flow rate for natural gas in the piping 6 and the supply 116: 5 kg/h, and [0160] introduction flow rate of air in the piping 5 and the supply 115: 150 kg/h.

[0161] The burner 4, 114 ensures natural gas combustion in the air overcharged by exciting a spark plug not represented in FIGS. 1 to 3. The combustion is fully made in the burner 4, 114, the uranyl nitrate hexahydrate injected is never in contact with the flame.

[0162] The gases resulting from the combustion, of a temperature of about 1 400 C., are accelerated in the burner 4, 114 to reach a rate of about 300 m/s in the upper conical part of the reaction chamber 1, 110, or reaction zone in which the contact of hot combustion gases and uranyl nitrate hexahydrate sprayed in fine droplets is made.

[0163] The UO.sub.3 particles obtained at the end of the first synthesis S1 have been collected, on the one hand by the conduit 10 and, on the other hand, by the conduit 13.

[0164] The UO.sub.3 particles obtained at the end of the second synthesis S2 have been collected by the single outlet 123 of the sedimentation chamber 120.

[0165] These different UO.sub.3 particles have been analysed so as to define their BET specific surface area as well as their water weight percentages, on the one hand, and nitrate ions NO.sub.3.sup., on the other hand.

[0166] Within the scope of the first synthesis S1, the same analyses have been conducted on the mixture formed by the UO.sub.3 particles collected by the conduits 10 and 13 (noted 10+13).

[0167] The intervals of values for the specific surface area and water and NO.sub.3.sup. weight percentages as obtained on several tests are reported in table 1 below. In this table 1, the collection yields of UO.sub.3 particles are also indicated.

TABLE-US-00001 TABLE 1 BET Water Col- specific weight NO.sub.3.sup. weight Syn- lection Yield surface percentage percentage thesis zone (%) area (m.sup.2/g) (% wt) (% wt) S1 10 30 from 20 to 25 from 0.4 to 0.6 from 1 to 4 13 70 from 2 to 10 from 1.5 to 7 from 2.7 to 17 10 + 13 100 from 12 to 15 from 1 to 1.2 from 1.2 to 5.3 S2 123 100 from 18 to 20 from 0.3 to 0.4 from 0.3 to 0.7

[0168] The UO.sub.3 particles as obtained by the implementation of the thermal denitration process in a facility in accordance with the invention (synthesis S2) thus have a BET specific surface area which is higher than that of the mixture of the UO.sub.3 particles collected by the conduits 10 and 13.

[0169] Furthermore, the UO.sub.3 particles obtained by the second synthesis S2 have very low contamination rates with water and nitrate ions, respectively lower than 0.4% wt and 0.7% wt. Such percentages further promote reactivity of UO.sub.3 particles for their subsequent transformation into UO.sub.2 and then UF.sub.4.

[0170] Further, it is to be noted that the facility of prior art implemented during the first synthesis S1 has required to cool the stream circulating through the conduit 11 by means of a complementary cooling device ensuring an air flow rate of 300 kg/h. The scrubbed gases have in turn been sucked at the outlet of the bag filter 12 by means of a fan ensuring a suction flow rate of 485 kg/h, hence it is necessary to use higher size pieces of equipment and a higher energy consumption than in the configuration of synthesis S2.

[0171] In the facility in accordance with the invention implemented during the second synthesis S2, the scrubbed gases have been sucked at the outlet of the filters 130 by means of fans ensuring a suction flow rate of 185 kg/h, that is lower than the previous one and in the absence of a complementary cooling device.

BIBLIOGRAPHY

[0172] [1] WO 84/02124 A1 [0173] [2] U.S. Pat. No. 5,628,048