IL24823A - Methods and apparatus for the production of uranium tetrafluoride - Google Patents

Description

AND A FOR OF A 24823 3 The invention relates to a method and apparatus the manufacture of uranium tetrafluoride by reaction of gaseous hydrogen fluoride HP with uranium oxide British Patent 970994 describes a continuous for obtaining uranium fluoride which includes feeding uranium dioxide granules through a vertical conduit leading directly into a ating feeding excess hydrogen fluoride into the furnace in to the uranium dioxide granules and absorbing in the said conduit the residual gas leaving the ating furnace by uranium dioxide granules contained in the said A preferred form of the method includes feeding uranium trioxlde or a mixture of uranium trioxide and uranium dioxide through a reducing furnace to obtain the uranium dioxide granules for passing directly through the said conduit into the hydro fluorinating the absorption of the residual gas being so regulated and controlled as not to interfere with the reducing operation in the reducing It is expedient la practice to arrange for a portion of the conduit between the two furnaces to be of wider at the bottom than the so as to allow for the swelling of the granules intended to pass Advantageously 10 to 30 excess gaseous hydrogen fluoride is The present invention has the object to improve the yield of uranium tetrafluoride obtainable by the above mentioned According to the present invention there is provided a method and apparatus for the manufacture of uranium fluoride by the reaction of gaseous hydrogen fluoride with uranium oxide the apparatus comprising a furnace and a coolin zone throu h which the h dro en fluoride and the uranium disposed downstream of the furnace in the direction of flow of hydrogon fluoride gas and having a temperature which is sufficiently lower than the reac ion temperature of the furnace to ensure the absorption of residual hydrogen the apparatus further comprising means controlling the of feed of hydrogen fluoride to furnace or the rate of flow of the uranium oxide in accordance with the temperature of the uranium oxide entering this to cause the apparatus continuously to produce an optimum yield of uranium For a better understanding of the present reference will now be made by way of example to the accompanying drawings in whic Figure 1 is a diagramma vertical section view of an apparatus according to the present invention for the manufacture of uranium tetra Figure 2 is a diagram showing the temperature distribution throughout the the apparatus being shown in relation to a graph in which the ordinate represents height and the temperature in degrees and Figure is a diagram drawn to an enlarged illustrating details of As in Figure apparatus comprises reduction furnace A into which is fed at 2 granular uranium oside to transformed under the action of a reducing gas for introduced into the apparatus at 1 and emerging therefrom at into uranium oside An electric coil is provided to ensure a reduction temper of Beneath the reactor A is a hydrofluorination unit comprising essentially a vortical furnace and a horizontal furnace G in series these furnaces being heated by furnace C is provided with an endless screw for conveying U towards a receiver Gaseous hydrogen fluoride is fed both at to the bottom of the furnace C and at 4 to the bottom of the furnace for example at the rate of of the total feed at 3 and thereof at such as 20 and 21 are provided to adjust the amount of HF gas fed to the Between the vertical furnace B and the reduction furnace is an extension of conical shape and being tapered towards its upper the function of this extension British ir Specification 970994 mentioned to ensure in combination with cooling means absorption of the residual gaseous hydrogen fluoride and thus permitting the use of the exact stoichiometric In uranium oxide in the form of delivered the bottom of the reduction furnace in the h defluorination unit according to the balanced state of equilibrium depends essentially upon the From the curve of the coneentration of in the gaseous phase plotted as a function of the it is apparent that this which reaches at drops to at The reaction speed also depends however on the temperature and it is impossible to work at the speed of reaction being too low at this It is therefore in order to ensure the best possible utilization of HF in amounts close to the stoichiometric amounts to make a compromise between the speed of reaction and the that is to say as stated in the to provide in the main reaction zone of the treatment in particular in the extraction C and in the vertical high temperatures for example of but to provide between the top of the and of the reduction in the extension 9 above the cooling means such that temperature is reduced to a relatively value of for from the upper end of to the lower end of the furnace as illustrated in the cooling means consist of several cooling elements corresponding to different temperature the residence times of the reactants in these zones being fixed in accordance with the desired speed of is provided for example as in above the vertical furnace B with its heating coil firstly a zone 8 about initially an electric heating coil may be the coil being subsequently removed or withdrawn in such manner that said zone which may be provided with cooling blades for the circulation of cooling air has a cooling reducing temperature to values of zone 9 which the temperature is reduced from to and may fall as low as by means of cooling such as and disposed at different The first cooling device may be fed for example with steam at a pressure of the second cooling device being fed with steam at a pressure of 2 r Figure 2 shows the temperature diagram of apparatus of It will be that the apparatus is intended to produce about 50 of per The cross in square decimeters of the extraction furnace is degree a of filling of the g in furnace elements 8 and 9 from at the bottom of the B to about or 2 at the upper end of the element e combined height and of the sones 8 and 9 preferably ranges from to times the height of the furnace She residence time of the reactants in the element to 8 is about residence time hours in the element 8 and then to values ranging from hours to 1 hour in the element In the time during which the reactants remain at the which is reached at is being hours at the lowest temperature which is reached at dimensions being taken of the conical shape of the correspond to these residence times are as the respective heights of the portions of the apparatus designated and in 1 are of the same order of that is to say and the length the extraction furnace 0 being a lit le With the apparatus described above it possible to use the of the gaseous fluoride fed to the so that the gaseous stream passes to the reduction furnace A contains only water vapour and the reducing gas into the apparatus at She presence of this water vapour assists in cooling located between the reduction and the hydrofluorination unit for recovering an excess of hydrogen fluoride acid as in the case of known apparatus need therefore be the gaseous stream from the hydrofluorination unit consists of water which be put to It may happen that the temperature at the top of the element 9 and the total flow rate of fed to the apparatu do not quite correspond to each othe in particular as a result of variations in the nature and the grain sizes of uranium We therefore means responsive to the temperature the solid material entering the hydrofluorination unit for acting either upon the flow rate of gaseous hydrogen fluoride fed at to the bottom of the vertical hydrofluorination reactor B or upon the rate of circulation of the solid material and in particular upon the speed of revolution of the extractor screw of the horizontal furnace Where the flow rate of the gaseous hydrogen fluoride be entering the furnace B at is upon that ie to say of the total flow rate is to be acted upon the remainder of the total to the furnace at is we provide a pyrometer 23 arranged to measure the temperature in the mass of uranium oxide entering the element 9 of the hydrofluorination the output voltage of the pyrometer being caused to act upon a control apparatus 24 capable of controlling the valve 21 which controls the HP inflow to the reactor B at 4 in such manner any rise in this temperature above a predetermined value produces a reduction in flow rate to the furnace at a reduction of this temperature below predetermined This control is preferably effected automatically through apparatus for example as shown in Valves 20 and 21 are pneumatically operated by means of diaphragms 25 and The valve 20 is adjusted to produce a predetermined and constant value of the rats therethrough a rule of the total flow the valve 20 being connected to a feed conduit 27 through a flowmeter 20 of known type which transmits pulses to an electric receiver The receiver 29 is both an indicator and a which records to pulses emitted by the that is to say the values of the upon a circular for example within a range from 700 to litres hour and also transmits a corresponding pneumatic signal to the control diaphragm The receiver 29 thus acts as a regulating device finally to adjust valve 20 to a corresponding to a predetermined value of the flow that is to say to a predetermined position of indicating means with respect to said The 21 is adjusted in an analogous through adjustment but in a receiver is arranged to be controlled by means responsive to variations in the temperature value detected by the pyrometer Said adjustment means on the one a converter 30 capable of transforming electric signals emitted by the pyrometer 23 into proportional pneumatic signals and on the other an auxiliary receiver incorporated in receiver and operated by said pneumatic for adjusting the indicating means of receiver 2 and therefore the HP flora determined by the value in response to variations in the tem e e u ed b romete insufficientOCRQuality

Claims (16)

1. A method for the manufacture of uranium tetra fluoride by reaction of gaseous hydrogen fluoride with uranium oxide UO^ wherein the gaseous hydrogen fluoride and the uranium oxide are arranged to flow in counter current through an apparatus comprising a furnace and a cooling zone, the temperature in the cooling zone is maintained sufficiently lower than the reaction temperature in the furnace to ensure absorption of any unreacted hydrogen fluoride and the rate of flow of the hydrogen fluoride or of the uranium oxide entering the furnace is so controlled as to ensure an optimum yield of uranium tetrafluorid©.

2. A method according to Claim 1 , wherein the gaseous hydrogen fluoride is fedj on the one hand, at a point corresponding to the end of the hydrofluorination treatment, in counter-current with the material which flows out; and on the other hand, at a point corresponding to an intermediate phase of the treatment, and the flow rat© of this supplementary adduction is controlled.

3. · A method according to Claim 1 therein the cooling means disposed on the side of inflow of the uranium oxide are arranged to produce a gradual drop of temperatur© toward the inlet, first to 400°C, then to 300°0 and then to 200°C.

4. A method according to Claim 3» wherein the cooling is effected in several portions, on© acting by means of air, another by means of water vapour at a predetermined temperature, and a third one by means of water vapour at a lower temperature.

5. An apparatus for carrying out the method according to any of Claims 1 to 4 comprising a furnace and a cooling zone through which gaseous hydrogen fluoride and uranium oxide are arranged to flow in counter current, the cooling zone being 24823/2 sufficiently lower than the reaction temperature of the furnace to ensure the absorption of residual gaseous hydrogen luoride , tha apparatus further comprising means for controlling the rate of feed of gaseous hydrogen fluoride to the furnace or the rate of flow of the uranium oxide in accordance with the temperature of the uranium oxide entering said zone, to cause the apparatus continuously to produce an optimum yield of uranium tetrafluoride.

6. Apparatus according to Claim 5, in which the furnace comprises a main vertical treatment furnace associated with an extraction furnace, for example a horizontal furnace, the gaseous hydrogen fluoride being introduced on the one hand into the extraction furnace and on the other hand into the base of the vertical furnace, the rate of feed of the gas into the extraction furnace being fixed at a constant value and the rate of feed of the gas into the vertical furnace being determined by the said controlling means.

7. Apparatus according to Claim 6, in which about two thirds of the gas fed into the apparatus is fed into the extraction furnace, the remainder being fed into the vertical furnace under the control of the controlling means.

8. Apparatus according to Claim 6 or 7 n which there is disposed above the vertical furnace a zone in which the treatment temperature is lower than that of th© vertical furnace, this zone having disposed above it a cooling sleeve which constitutes th© cooling zone, th© controlling means being actuated by signals originated by a pyrometer in th© end of the sleeve through which the uranium oxide is introduced.

9. Apparatus according to Claim 8, in which the pyrometer acts upon an electric receiver emitting signals which are converted 24823/2 · into proportional pneumatic signals which act upon a diaphragm controlling a valve to determine the feed rate of gaseous hydrogen fluoride to the vertical furnace.

10. Apparatus according to Claim 6, in which the vertical furnace has a temperature ranging from 500° to 600°C, and is succeeded by an intermediate zone at a temperature of between 400°C and 5OO°0, cooling being arranged to be effected in the cooling zon » which is disposed above the intermediate zon©9 preferably in two steps, e.g. do¾n to 200°C.

11. Apparatus according to Claim 10» in which the vertical furnace is substantially cylindrical and the cooling zone is frustoconical, the upper cross section of the cooling zone being preferably 2/5 of the cross-section of the bottom of the cooling zone.

12. Apparatus according to Claim 10 and 11, in which the combined height of th© intermediate and cooling zones rang© from 1.5 to 2 times the height of th© vertical furnace.

13. · Apparatus according to Claims 10, 11 or 12 in which the duration of treatment is in the proportions of twenty-four in the vertical furnace, twenty in the intermediate zone and ten in the cooling gone, respectively,

14. Apparatus according to any one of Claims 10 to 3? in xflhich the vertical furnace, the intermediate zone and the cooling zone are constituted by a tube which is cylindrical at the bottom and which decreases in cross-section towards the top, the height of the vertical furnace, the intermediate zone and th© cooling zone being substantially of the same order of magnitude, and 1.40 m. for example 1.70 m. „ 1.40 . respectively.

15. Apparatus according to any one of Claims 10 to 14, in which the intermediate zone is cooled by means of air and th© 24823/2 cooling sons by means of steam circulating through two 2 successive jackets, one at a pressure of δ Kg/cm 9 the other at a pressure of 2 Kg/cm .

16. Apparatus according to any of Claims 10 to 15 in which tho gaseous hydrogen fluoride is distributed in the proportion of about 2/3 at the outlet of the extraction furnac© and about 1/3 at th® bottom of the vertical furnace, by.means of valves upon one of which acts a control system actuated by a pyrometer immersed in the reactant material in the cooling zone. 17* Apparatus for the manufacture of uranium tetrafluorid© substantially as hereinbefor® described tilth reference to and as shorn in th© accompanying drawings.