FR2995715A3 - METHOD AND APPARATUS FOR THE WET-OXIDATION TREATMENT OF RADIOACTIVE LIQUID WASTE CONTAINING MISCELLANEOUS LOADS - Google Patents

Abstract

The present invention relates to a process and a device for the treatment by wet oxidation of waste containing oxidizable charges of various materials, in particular mineral materials, organic materials and possibly bio-mineral materials, in particular organic resins, these oxidizable charges being radioactive. This device (10) comprises a reactor (11) consisting of a treatment column, a first heat exchanger (12) disposed upstream of the reactor (11) and a second heat exchanger (13) disposed downstream of this reactor . The solution to be treated containing mineral charges to which an oxidizing gas has been added is injected for treatment in the reactor (11) after its preheating in the first heat exchanger (12). On leaving the reactor (11), the hot treated mixture is divided into two hot flux fragments. The first flow fragment, whose flow rate is kept constant by a column of diaphragms (30), is used to regulate the temperature of the first heat exchanger (12).

Description

FIELD OF THE INVENTION Technical Field The present invention relates to a process for the wet-oxidation treatment of waste containing charges of various materials, in particular mineral materials, waste materials and the like. organic materials and possibly bio-mineral materials, in particular organic resins, these charges being radioactive. The invention also relates to a device for carrying out this method of treatment by wet oxidation of waste containing charges of various materials, in particular mineral materials, organic materials and possibly bio-mineral materials, in particular organic resins, these charges being radioactive, this device comprising means arranged for mixing an oxidizing gas with a solution to be treated with oxidizable substances, at least one first heat exchanger for preheating the mixture of solution to be treated and oxidizing gas, at least one reactor for oxidizing said oxidizable substances contained in said solution, at least a second heat exchanger for cooling the treated mixture, and means disposed at the outlet of said second heat exchanger and arranged to separate the treatment gases of the mineral residues from the treated mixture cooled before their respective evacuation.

PRIOR ART The principle of this process has found an industrial application for the continuous treatment of liquid waste containing mineral charges, this treatment being carried out by wet oxidation. It is described in the international publication WO 2010/108290 A1.

However, this method has never been used to treat waste having various concentrations of radioactive elements, the upper limit of the radioactivity being the one related to the radiological constraints of protection of people in contact with the elements.

The problem to be solved with regard to the long-term storage of radioactive residues according to the standards of each country or the recommendations of the IAEA, is that of the elimination or at least the maintenance of the concentration of wastes in organic matters, below an acceptable value defined by said standards. Indeed, it is essential to minimize the organic matter content of radioactive waste, with a view to putting it in "long-term" storage. In addition, because of the extremely high cost of storage solutions, this cost being substantially proportional to the volume of stored material, to reduce this cost and save money, an obvious solution is to reduce the volume. DISCLOSURE OF THE INVENTION The present invention provides a solution to the problems mentioned above by providing a method and a device for treating, by wet oxidation, radioactive waste containing in particular organic matter. In this way, it is possible to substantially reduce the volume of materials to be stored in the context of operations called "long-term storage" and therefore reduce the cost of storage. For this purpose, the process according to the invention, as defined in the preamble, is characterized in that a waste solution containing said oxidizable charges is prepared, an oxidizing gas is mixed with said solution, the solution mixture is preheated. waste to be treated and oxidizing gas in a first heat exchanger, said waste solution mixture to be treated and said oxidizing gas heated in a reactor at temperatures sufficient to oxidize said oxidizable charges, said mixture is cooled after treatment in a second exchanger heat and the treatment gases are separated from the residues of said cold treated mixture at the outlet of said second heat exchanger prior to their respective evacuation, and in that the flow of said hot treated mixture is divided at the outlet of said reactor into a first flow fragment and a second flow fragment, in that it is cooled and the second hot flow fragment dud is removed. said treated mixture, in that said first hot flow fragment of said treated mixture is used to regulate the preheating temperature of said first heat exchanger, and in that said first flow fragment is discharged after its use in the first heat exchanger. Advantageously, a double control loop of the temperature of the first temperature exchanger is defined by regulating the flow rate of said waste solution mixture to be treated and the cold oxidizing gas at the inlet of said first heat exchanger as a function of the temperature. of the solution to be treated hot at its outlet from this exchanger and as a function of the temperature of the reactor, said reactor temperature determining the temperature of the first hot flow fragment of said waste solution mixture to be treated and oxidizing gas before its use in said first heat exchanger. In said first heat exchanger, the flow rate of the first flow fragment of said waste solution mixture to be treated and the hot treated oxidizing gas are kept constant regardless of the flow rate of the solution to be treated. Preferably, the flow rate of the first mixture flow fraction is maintained by means of at least one diaphragm disposed after the outlet of said first cooled flow of the first heat exchanger. In the preferred embodiment of the process of the invention, the mixture is preheated to a temperature of substantially 130 to 200 ° C. This temperature depends on the chemical characteristics of the liquid to be treated. It must be determined experimentally and must be regulated to a value that remains as constant as possible, at most + 1-10 ° C.

The oxidation treatment of the mixture is then carried out in the reactor at temperatures substantially between 260 and 350 ° C. and at a pressure that is substantially between 70 and 200 bars.

The device for the treatment of liquid waste according to the invention as defined in the preamble is characterized in that it further comprises means arranged to effect a division of the flow of the hot treated mixture at the outlet of said reactor into a first fragment of flow and a second flow fragment, and means arranged to maintain a constant flow rate of said first hot treated mixture stream fragment in order to use it to control the preheat temperature of said first heat exchanger. According to a preferred embodiment, said means arranged to maintain a constant flow rate of the first stream of hot treated mixture comprise at least one diaphragm disposed after the outlet of said first cooled stream of the first heat exchanger. In the preferred embodiment of the device, said means arranged to keep the flow rate of the first hot treated mixture stream 25 constant comprise several diaphragms arranged in a column and separated in pairs by spacers. Preferably, said diaphragms each consist of a cylindrical piece having a bottom provided with a calibrated opening and said spacers each consist of a cylindrical piece having substantially the same dimensions as the diaphragms.

Advantageously, said first heat exchanger comprises an internal circuit and a peripheral circuit, said inner circuit of this first heat exchanger being traversed by the mixture of solution to be treated and oxidizing gas, and the peripheral circuit being traversed by said first fragment of flow of hot treated mixture divided at the outlet of said reactor. Said second heat exchanger also comprises an internal circuit and a peripheral circuit, said internal circuit of this second heat exchanger being traversed by said second hot treated mixture flow stream divided at the outlet of said reactor, and the peripheral circuit being traversed by a coolant. In the preferred embodiment, the means disposed at the outlet of said second heat exchanger and arranged to separate the treatment gases of the mineral residues from the cooled treated mixture comprise a degasser. BRIEF DESCRIPTION OF THE DRAWINGS The present invention and its advantages will appear better in the following description of an embodiment given by way of non-limiting example, with reference to the appended drawings in which: FIG. 1 represents a general schematic view of the device according to the invention, and FIGS. 2A, 2B, 2C, 2D and 2E are vertical and cross sectional views showing an embodiment of the diaphragm that controls the flow rate of said first flow fragment. BEST MODE OF CARRYING OUT THE INVENTION With reference to FIG. 1, the device 10 for the wet oxidation treatment of radioactive waste mainly comprises at least one reactor 11 consisting of a treatment column, at least a first reactor. 6 heat exchanger 12 disposed upstream of the treatment column and at least a second heat exchanger 13 disposed downstream of the treatment column. The treatment column advantageously consists of a vertical cylindrical chamber 11a in which a mixture is injected in the form of a waste solution containing said oxidizable charges and said oxidizing gas, said waste solution containing said radioactive oxidizable charges at treat. This enclosure is surrounded by a peripheral mantle 11b intended to maintain the enclosure and its contents at the treatment temperatures provided for carrying out the oxidation reactions, according to the wet oxidation process. For this purpose, the mantle may for example be in the form of a hollow envelope in which circulates a coolant injected at the base along the arrow A and collected at the top along the arrow B. Said first heat exchanger 12, said preheating exchanger, has a function of preheating the solution to be treated and maintaining the temperature between constant extreme values in order to avoid deposits likely to clog up this exchanger. The device 10 further comprises a pump 14 which controls the entry of the solution to be treated, this pump being driven by a motor 14a driven by a control and regulating unit 14b, and means for injecting into a conduit 15 which conveying said solution, upstream of the inlet of the first heat exchanger 12, an oxidizing gas under pressure and at a controlled temperature, such as air or oxygen under pressure, in a conduit 16 connected to the conduit 15 Finally, the device 10 comprises a degasser 17, disposed downstream of the second heat exchanger 13 and which is arranged to evacuate the gases from the treatment process, by an upper outlet 18, to a gas treatment unit 30 (not shown). ) and to evacuate the mineral residues freed of all the organic substances that have been oxidized during the treatment, for example by a low outlet 19 through a conduit 20, to a biological unit of valor waste disposal (not shown). The heat exchangers 12 and 13 are shown as elements having an inverted U-profile with two vertical branches. The first heat exchanger 12 comprises an internal circuit 121 and a peripheral circuit 122. The second heat exchanger 13 also comprises an internal circuit 131 and a peripheral circuit 132. The internal circuit 121 of the first heat exchanger 12 is supplied by the ducts. 15 and 16 respectively conveying the solution to be treated and the oxidizing gas. This mixture passes through said first heat exchanger 12 and enters a pipe 21 to be injected at the base of the vertical cylindrical chamber 11a of the reactor 11 treatment column. The oxidation-treated mixture inside this column of treatment is captured in the upper part, by a vertical channel 22 mounted in the vertical cylindrical chamber 11a, to open into an outer conduit 23 to a point 24 of flow division. A first part of the hot treated mixture stream is used in the first exchanger 12 and, for this purpose, is injected through a conduit 25 into the peripheral circuit 121 of said first heat exchanger 12 before being discharged after use, via a conduit 26, in the direction of the biological waste recovery unit, via the conduit 20. A second portion of the stream divided at the point 24 of division of the flows is injected into the internal circuit 132 of said second heat exchanger 13, from which it leaves after cooling, through a conduit 27, in the degasser 17 mentioned above. Said second heat exchanger 13 furthermore comprises a coolant inlet 28 which is connected to the peripheral circuit 132, at the base of one of the vertical branches of this exchanger 13, and an outlet 29 of this cooling liquid arranged at the base of the other vertical leg of said heat exchanger 13. FIGS. 2A to 2E show longitudinal and cross-sectional views of a column 30 of diaphragms 31 for regulating the first treated mixture stream cooled at its outlet from the first heat exchanger 12, allowing to adjust the pressure drops to maintain a constant flow. The column is mounted inside a support 32 provided at its ends with two fixing flanges 33. The column 30 consists of a series of diaphragms 31 which are two by two separated by spacers 34. A spacer 34 is shown in plan in Figure 2B and in cross section in Figure 2C. These spacers are constituted by a cylindrical piece for defining a predetermined space between the diaphragms. The diaphragms 31, such as that shown in cross-section in FIG. 2D and in plan in FIG. 2E, also have a substantially cylindrical profile which has the same dimensions as that of the spacers 34. However, they comprise a closed bottom 31a provided with a calibrated aperture 31b which defines the flow rate of the through flow. This device makes it possible to regulate the flow, according to the number of diaphragms 31 mounted in the column 30 and according to the section of the calibrated openings 31b. In the operating mode, the device described above ensures a strict regulation of the temperature of the exchanger or preheating exchangers, according to the construction carried out, thanks to the principle of the division of the flows at the outlet of the reactor, which allows to avoid the formation of deposits. This formation of deposits which, in existing installations, requires disassembly and unclogging of the preheating exchanger takes place as soon as the temperatures go beyond the limits which are substantially between 130 and 200 ° C and in particular rise. above 200 ° C. The temperature regulation of the preheating exchanger 12 is done by regulating the flow rate of the cold effluent, by dividing the flows at the outlet of the reactor. In known installations, the regulation of the preheating temperature is effected by the hot effluent, which results in a poorly controlled result which has the serious consequence of the formation of deposits in the exchanger.

In practice, this temperature regulation is carried out in the following manner: the flow of the solution of the hot treated mixture is divided into two flux fragments at the outlet of the reactor; directing the first flow fragment to said first heat exchanger, said preheating exchanger, and the second flow fragment to said second heat exchanger, said cooling exchanger; the division of the flow is made in a particular manner and at a reaction pressure in the reactor so that the flow rate of the first flow fragment remains constant regardless of the flow rate of the solution to be treated. This division is obtained by at least one and preferably a series of diaphragms (see FIG. 2) which are installed after the outlet of the first cooled flow of the preheating exchanger. This system makes it possible to adjust the pressure drops in order to maintain the constant flow, with the consequence that any excess of liquid will be evacuated towards the cooling exchanger. The individual pressure drop of each diaphragm, when the device comprises a series of diaphragms, is low, of the order of 1 to 8 bars. The construction of these diaphragms is simple since they are cylinders comprising a turbulence chamber and having calibrated openings for the liquid outlet, the number and the dimensions of these cylinders being defined according to the operating pressure and the flow rates that we want to get.

This way of proceeding thus defines a double control loop of the temperature of the first temperature exchanger since the flow rate of cold solution to be treated at the inlet of said first heat exchanger is adjusted according to the temperature of the solution to be treated. hot at its outlet from this exchanger and depending on the temperature of the reactor, said reactor temperature determining the temperature of the first hot stream of treated mixture stream before its use in said first heat exchanger.

It is understood that various variants of achievements could be imagined. Although the device is shown schematically with a single first heat exchanger and a single second heat exchanger, for very large installations, several preheating exchangers, for example, could be installed. The shape of the elements could be varied according to the specific needs of a processing unit and the objectives sought for the treatment of a particular composition of waste. The variants devised do not go beyond the scope of the obvious modifications for those skilled in the art and are within the scope of the present invention.

Claims (15)

CLAIMS1 Process for the wet oxidation treatment of waste containing oxidizable charges of various materials, in particular mineral materials, organic materials and possibly bio-mineral materials, in particular organic resins, these oxidizable charges being radioactive, characterized in that that a waste solution containing said oxidizable charges is prepared, an oxidizing gas is mixed with said solution, the mixture of waste solution to be treated and oxidizing gas is preheated in a first heat exchanger, said solution mixture of waste is heated to treating and oxidizing gas in a reactor at temperatures sufficient to oxidize said oxidizable charges, cooling said mixture after treatment in a second heat exchanger and separating the treatment gases residues of said cold treated mixture at the outlet of said second heat exchanger before their respective evacuation, and the flow of said hot treated mixture at the outlet of said reactor is divided into a first flow fragment and a second flow fraction, in that the second flow fragment is cooled and discharged. hot said treated mixture, in that one uses said first hot flow fragment of said treated mixture to regulate the preheating temperature of said first heat exchanger, and in that said first flow fragment is removed after its use in the first heat exchanger. 2. Method according to claim 1, characterized in that one defines a double control loop of the temperature of the first temperature exchanger by adjusting the flow rate of said waste solution mixture to be treated and cold oxidizing gas at the inlet of said first heat exchanger according to the temperature of the hot treatment solution at its outlet from this exchanger and depending on the temperature of the reactor, said reactor temperature determining the temperature of the first hot flux fragment of said mixture waste solution to be treated and gas oxidant prior to use in said first heat exchanger. 3. Method according to claim 1, characterized in that, in said first heat exchanger, it maintains the flow rate of the first flow fragment of said waste solution mixture to be treated and hot treated oxidizing gas regardless of the flow rate of the solution to be treated. 4. Method according to claim 3, characterized in that the flow rate of the first mixture flow portion is kept constant by means of at least one diaphragm disposed after the output of said first cooled flow of the first heat exchanger. 5. Method according to claim 1, characterized in that one carries out the preheating of said mixture waste solution to be treated and oxidizing gas by bringing it to a temperature substantially between 130 and 200 ° C. 6. Method according to claim 1, characterized in that the oxidation treatment is carried out in the reactor at temperatures substantially between 260 and 350 ° C. 7. Process according to claim 1, characterized in that the oxidation treatment of said waste solution mixture to be treated and oxidizing gas is carried out under a pressure substantially between 70 and 200 bar. 8. Device (10) for the wet oxidation treatment of waste containing oxidizable charges of various materials, in particular mineral materials, organic materials and possibly bio-mineral materials, in particular organic resins, these fillers being radioactive, for carrying out the process according to claims 1 to 7, this device comprising means arranged for mixing an oxidizing gas with a solution to be treated with oxidizable substances, at least a first heat exchanger (12) for preheating the solution mixture of waste to be treated and oxidizing gas, at least one reactor (11) for oxidizing said oxidizable charges contained in said mixture solution to be treated and oxidizing gas, at least one second heat exchanger (13) for cooling the treated mixture, and means arranged at the outlet of said second heat exchanger (13) and arranged to separate the treatment gases from melan residues cooled treated ge before their respective evacuation, characterized in that the device further comprises means arranged to effect a division of the flow of said waste solution mixture to be treated and hot treated oxidizing gas at the outlet of said reactor (11) into a first fragment flow and a second flow fragment, and means arranged to maintain constant the flow rate of said first flow fragment of said waste solution mixture to be treated and hot treated oxidizing gas in order to use it to regulate the preheating temperature of said first exchanger heat (12). 9. Device according to claim 8, characterized in that said means arranged to maintain constant the flow of the first stream of hot treated mixture comprise at least one diaphragm (31) disposed after the output of said first cooled stream of the first heat exchanger (12). ). 10. Device according to claim 9, characterized in that said means arranged to maintain a constant flow of the first stream of said waste solution mixture to be treated and hot treated oxidizing gas comprise several diaphragms (31) arranged in a column (30) and separate two by two by spacers (34). 11. Device according to claim 10, characterized in that said diaphragms (31) each consist of a cylindrical piece having a bottom (31a) provided with a calibrated opening (31b). 2,995,715 14 12. Device according to claim 10, characterized in that said spacers (34) each consist of a cylindrical piece having substantially the same dimensions as the diaphragms (31). 5 13. Device according to claim 8, characterized in that said first heat exchanger (12) comprises an inner circuit (123) and a peripheral circuit (124), in that said inner circuit (123) of the first heat exchanger is traversed by the mixture of the solution to be treated and the oxidizing gas, and in that the peripheral circuit (124) is traversed by said first flow fragment of said waste solution mixture to be treated and the treated hot oxidizing gas divided at the outlet of said reactor ( 11). 14. Device according to claim 8, characterized in that said second heat exchanger (13) comprises an inner circuit (133) and a peripheral circuit (134), in that said inner circuit (133) of this second heat exchanger heat is traversed by said second flow fragment of said waste solution mixture to be treated and hot treated oxidizing gas divided at the outlet of said reactor (11), and in that the peripheral circuit (134) is traversed by a cooling liquid. 20 15. Device according to claim 8, characterized in that the means arranged at the outlet of said second heat exchanger (13) and arranged to separate the treatment gases of the mineral residues of said waste solution mixture to be treated and cooled treated oxidizing gas comprise a degasser (17).