Certain chemical processes requires the operation of the high temperature chemical reactors to exploit more favorable chemical thermodynamics and kinetics. The conversion of UF.sub.6 to UO.sub.2, for example, requires the chemical reactor operation to around 800 to 900.degree. C. The feed gases must be well mixed to ensure a homogeneous chemical system and uniform product distribution.
Representative of these prior art techniques, and in addition to those cited in copending Ser. No. 08/635,190, above, is a first patent, U.S. Pat. No. 3,796,672 entitled "Process for Producing Uranium Dioxide Rich Compositions from Uranium Hexafluoride." This patent discloses the conversion of uranium hexafluoride to uranium dioxide in the presence of an active flame in a reaction zone by separately introducing a gaseous reactant comprising a reducing gas and a gaseous reactant of a mixture of uranium hexafluoride and an oxygen-containing carrier gas. A shielding gas is critical to the successful thermal conversion process; it insures that the reactants are temporarily separated and prevented from substantial mixing and reacting until sufficient cross diffusion occurs.
Other patents include U.S. Pat. No. 4,005,042 entitled "Process for Producing Uranium Rich Compositions from Uranium Hexafluoride Using Fluid Injection in the Post Oxidation Step" and U.S. Pat. No. 4,031,029 entitled "Process for Producing Uranium Rich Compositions from Uranium Hexafluoride Using Fluid Injection in the Post Oxidation Step." These patents cover certain improvements in the uranium hexafluoride thermal conversion process; namely, the step of introducing an atomized fluid having a high latent heat of evaporation into either the reaction zone or into the gaseous reactant's stream which is converted to a gas and cools the materials in the reactor. None of the gaseous feed systems disclosed in these patents preheats the gaseous reactant streams prior to mixing of these streams in the flame reactor; nor do they provide for an efficient way to mix the multiple reactant gaseous streams.
The high temperature conversion of UF.sub.6 is complicated by the extreme reactivity of UF.sub.6 at the prerequisite temperatures of the UF.sub.6 reactor. In this case, it is desirable to operate the reactor at the highest temperature allowable by the particular materials of construction without any temperature in the system exceeding the maximum service temperature of the materials of construction. High temperature and corrosive feeds together pose severe process conditions that greatly restrict the materials of construction to special ceramics and certain metal alloys that are difficult to fabricate into a conventional feed apparatus. For example, suitable materials of construction for fabrication of a high temperature UF.sub.6 apparatus are generally limited to certain ceramic materials such as high density alumina (Al.sub.2 O.sub.3), calcium fluoride (CaF.sub.2), yttria stabilized zirconia (ZrO.sub.2), lanthanum hexaboride (LaB.sub.6), and spinel (MgO.multidot.Al.sub.2 O.sub.3). The essential requirement for the selection of a UF.sub.6 material is the formation of a stable protective fluoride film. Alumina, for example, forms AlF.sub.3 in the presence of UF.sub.6. AlF.sub.3 is stable at service temperatures up to 1000.degree. C. and is, therefore, suitable for the high temperature UF.sub.6 application below the maximum service temperature. Feed materials suitable for high temperature steam and hydrogen include the ceramics listed above in addition to certain nickel-based metal alloys. A complication with the use of ceramic materials is the lack of practical manufacturing techniques for the fabrication of the specialized shapes and forms other than tubes and flat plates. Another complication is the mechanical sealing of the mating surfaces of the parts of the feed system for environmental confinement of the process gases.
One objective of this invention is to provide a superior high temperature feed apparatus with preheater and integral mixer with only tubular and flat plate elements without critical joints or seals exposed to the feeds at high temperatures.
Another objective is to assure introduction and mixing of the feeds at well defined locations within the chemical reactor, under specific conditions, and with sufficient energy to ensure near optimum homogeneous conditions for efficient reaction to final product(s).
Another objective is to provide a controlled temperature of preheat while limiting the maximum temperatures so that the apparatus materials properties (corrosion, strength, vapor pressure, etc.) are within allowable service values for dependable use.
Still a further object is to provide an improved process for the high temperature conversion of UF.sub.6 to uranium oxides.
Other and further objects of the present invention will become apparent to a person skilled in the art from a reading of following preferred embodiments and appended claims and by reference to the accompanying drawings described hereinafter.