RU2594009C1 - Method of uranium hexafluoride evaporation from cylinder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing uranium hexafluoride (UHF) and can be used for extraction of uranium hexafluoride from cylinders of various capacity. Method of evaporation of uranium hexafluoride from a cylinder, including the cylinder heating with a two-section inducer, nitrogen supply into the cylinder in pulse mode. At the end of the process the cylinder is vacuumed via a collector of gaseous uranium hexafluoride to the pressure of 50kPa. Heated nitrogen is supplied into the cylinder via a suction pump tube at a pressure exceeding the gas pressure in the cylinder by 30-50 kPa, herewith the nitrogen supply is performed in pulse mode at the side wall temperature of 60-80 °C and the bottom temperature of 60-150 °C and the generated gas mixture pressure of 100-150 kPa, herewith the cylinder is additionally heated by switching on the bottom heater of 4-8 kW power when the inducer upper zone is of 60 °C and the lower one is of 65 °C.

EFFECT: invention ensures the increase of efficiency of gaseous uranium hexafluoride production in the cylinder, complete extraction of non-evaporated UHF residue from the cylinder, 3-4 times decrease of specific power consumption per unit of evaporated material, stabilization of nitrogen consumption, high quality of produced powders of uranium dioxide.

4 cl, 3 tbl, 2 ex

Description

The invention relates to the field of processing of uranium hexafluoride and can be used to extract uranium hexafluoride from cylinders of various capacities.

Closest to the proposed method is a method of evaporation of uranium hexafluoride with a pulsed nitrogen supply into the container and device (RF patent No. 2264987, IPC C01G 43/06).

The evaporation of uranium hexafluoride is carried out from a cylinder heated by a two-section inductor, and a pulsed nitrogen supply is produced inside the cylinder at a pressure exceeding the gas pressure in the cylinder by 15 ± 5 kPa. Nitrogen supply is carried out in a pulsed mode at a cylinder wall temperature of 60-150 ° C and a pressure of the resulting gas mixture of 50-150 kPa. When removing the unevaporated residue of uranium hexafluoride simultaneously with the supply of nitrogen, the cylinder is evacuated to a pressure of 50 kPa.

The device for the evaporation method consists of a cylinder heated by a side two-section inductor. The cylinder is equipped with supply and supply valves. During evaporation, compressed nitrogen is pulsed into the cylinder from the nitrogen supply line through a manual valve, a bellows valve, and a flow meter. Evaporating uranium hexafluoride is directed through a flow valve through a manifold to conversion into reactors.

However, despite a number of positive aspects of this method (increasing the rate of evaporation of uranium hexafluoride, reducing the amount of non-evaporated HFC residue, improving working conditions), it is not without some drawbacks, the main of which are as follows.

Previous works (“Studies of the laws of the process of evaporation of HFCs from solid and liquid phases and the ways of introducing this process.” Sergeev GS Cand. Thesis, architect No. 375 - 1970) showed that the main contribution to the process is mass transfer during evaporation of uranium hexafluoride from the solid phase introduces conductive heat transfer, i.e. direct contact of uranium hexafluoride with a heated wall. At the same time, the installation design of the UCI plant of the MSZ plant did not provide for the presence of bottom inductors for cylinders in the evaporation cells.

Measurements of the bottom temperature during normal evaporation showed that at a cylinder wall temperature in the 2nd (lower) zone equal to 150 ° C, the bottom temperature fluctuates in the range of 50-55 ° C and only in the final phase it reaches 90 ° C. And the main contribution during almost the entire duration of evaporation is made by convective heat transfer from the heated vertical cylinder wall through the gas gap between the cylinder wall and the mass of the evaporated HFC, which is characterized by very low rates.

The technical result of the proposed method for the evaporation of uranium hexafluoride consists in further intensification of the evaporation process, almost complete removal of the non-volatile HFC residue in the cylinder after it is emptied on the collector, a significant reduction in the specific energy consumption per unit of evaporated raw materials, in ensuring complete safety of the process at all its stages and improving the quality of the obtained uranium dioxide powders due to the uniform supply of HFC conversion reactors.

The technical result is achieved by the fact that in the method of evaporation of uranium hexafluoride, the cylinder is heated by a two-section inductor and the additional inclusion of a bottom heater with a power of 4-8 kW. Switch-on time - when the upper zone of the inductor reaches 60 ° C, and the lower - 65 ° C. Heated nitrogen is supplied to the cylinder through a suction tube at a pressure exceeding the gas pressure in the cylinder by 30-50 kPa, and nitrogen is supplied to the cylinder in a pulsed mode at a side wall temperature of 60-80 ° C and a bottom temperature of 60-150 ° C and pressure the resulting gas mixture of 100-150 kPa. The nitrogen flow rate per pulse is not more than 10 kg / h, the pulse time of the nitrogen supply does not exceed 2 minutes, and the interval between pulses is not more than 20 minutes. When the temperature of the upper zone reaches 60 ° C, and the lower 65 ° C, the regulation of these temperatures is set at 70 ° C for the upper zone and 80 ° C - for the lower one until the end of the cylinder emptying process. At the end of the process, the cylinder is evacuated through a collector of gaseous HFCs to a pressure of 50 kPa.

In this regard, a bottom heater with an electric power of 4 kW was fabricated and mounted in the lower part of the inductors in one of the cells of the MCI installation of the MSZ plant. In order to reduce thermal inertia, its body was made of thin sheet stainless steel, and the heating elements were made of KTMC cable. Two clamping chromel-alumel thermocouples were installed on the bottom of the container, the readings of which were recorded by the Ionogawa secondary instrument.

As tests have shown, the pulsed supply of heated nitrogen into the cylinder (prototype) due to a change in the hydrodynamic regime of the gas flow in the boundary layer from laminar to turbulent contributes to a significant intensification of the evaporation process from the entire surface of solid uranium hexafluoride. (“General Heat Engineering Course” edited by I.N.Sushkin, Moscow, “Metallurgy”, 1973), (Eckert E.R., Drake P.M. “Theory of Heat and Mass Transfer”, State Engergoizdat, 1961).

The lower limit for the duration of the pulsed nitrogen supply (2 min.) Is due to the achievement of the maximum evaporation rate (120-145 kg / h). According to the conditions of operation of the evaporation section of workshop No. 48, it is possible to reduce the nitrogen supply time and lower if maximum productivity is not required. As for the upper limit, an increase in the duration of more than 2 minutes will lead to an excess consumption of nitrogen.

Since the surface of solid uranium hexafluoride due to intensive evaporation is cooled and it takes some time (in our case, about 20 minutes), the surface is heated again after a pulse and becomes capable of achieving the performance of the next pulse.

The calculations of the Reynolds criterion, as a fundamental parameter characterizing both of the aforementioned modes, showed that an increase in nitrogen consumption up to 10 kg / h can significantly increase the evaporation rate without a significant increase in the specific nitrogen consumption per unit of evaporated feedstock.

Given the above, it is logical to assume that the regulation of heating of the upper and lower zones of the inductors should be changed in such a way as to only ensure the free exit of the gas mixture from the cylinder, i.e. when a gas gap is formed (the temperature of the upper zone is 60 ° C and the lower zone is 65 ° C), the temperature of the zones is switched to 70 ° C and 80 ° C until the end of the emptying process.

This mode will significantly save energy, reduce the corrosion of the walls of the cylinder, and the main process of evaporation of uranium hexafluoride is carried out through a combined method (conductive heat supply from the bottom heater and pulsed supply of heated nitrogen inside the cylinder).

Example 1

In addition to the main goal of the proposed method - the intensification of the evaporation process - close attention was paid to such an important factor as reducing power consumption per unit of evaporated raw materials (UEP - specific energy consumption).

For this purpose, in one of the UXI cells (inductor No. 7), during the tests, a continuous measurement of the readings of the SET-4 electric meter with a transformation ratio of 85 was carried out.

Comparative data on the change in the SEC depending on the evaporation conditions are given in table. one

Given in the table. 1, the data show that the use of conductive heat supply (the use of a bottom heater), as well as a change in the operation mode of the side inductors, allowed us to not only double the rate of HFC evaporation from the cylinder, but also reduce the specific energy consumption by 2.5 times.

With the combined method, the evaporation rate increases by 5 times, and the CES is reduced by four.

Example 2

To justify the regime of pulsed supply of heated nitrogen into the tank in order to further intensify the process of HFC evaporation, the Reynolds criterion was calculated as a fundamental factor characterizing the hydrodynamic regimes of gas mixture movement in a cylinder depending on the weight flow rate of nitrogen at a pulse.

The calculation results are shown in table 2.

The data obtained indicate that a pulsed nitrogen supply to the cylinder significantly changes the flow dynamics in the cylinder from the laminar mode (Re = 1070) to turbulent (2 and 3 evaporation modes: Re values 4295 and 6325, respectively), and taking into account the total volumes of the mixture of hexafluoride and nitrogen it increases to 7555 and 13040, respectively.

The design diameter of 0.9 m is the internal diameter of the cylinder 1 m ³ , with a maximum filling of the cylinder with condensed uranium hexafluoride, the internal diameter of the free space of the cylinder is D = 0.9-0.35 = 0.55 m with a thickness of the product layer on the wall of the cylinder 175 mm

It can be seen from the above data that with an increase in the nitrogen flow rate at a pulse of up to 10 kg / h, the process of HFC evaporation in the cylinder shifts significantly toward the turbulent mode in comparison with the laminar regime (Re no more than 2300), which allowed a significant increase in the rate of uranium hexafluoride .

Example 3

In the process of industrial testing of the proposed evaporation method, the combined effect of the proposed intensification methods was checked, namely, the simultaneous inclusion of a 4 kW bottom heater with a pulsed supply of heated nitrogen into the cylinder.

Simultaneous inclusion of the bottom heater with a pulsed supply of heated nitrogen into the cylinder was carried out for safety purposes when the temperature of the upper zone of the inductor reached 60 ° C and the lower 65 ° C; those. with guaranteed formation of an annular gap over the entire height of the container between the wall and the bulk of the solid hexafluoride. The results of the tests of the combined method of evaporation are given in table. 3.

The above data indicate the high potential of the proposed method of evaporation, both in terms of increasing the rate of evaporation, and saving energy for the whole process.

Claims (4)

1. The method of evaporation of uranium hexafluoride from a cylinder, including heating the cylinder with a two-section inductor, supplying nitrogen to the cylinder in a pulsed mode, and at the end of the process the cylinder is vacuumized through a collector of gaseous uranium hexafluoride to a pressure of 50 kPa, characterized in that heated is fed into the cylinder through a suction tube nitrogen at a pressure exceeding the gas pressure in the cylinder by 30-50 kPa, and the nitrogen supply is carried out in a pulsed mode at a side wall temperature of 60-80 ° C and a bottom temperature of 60-150 ° C and the pressure of the resulting gas mixture 1 00-150 kPa, and the heating of the cylinder is additionally carried out by turning on the bottom heater with a power of 4-8 kW, when reaching the upper zone of the inductor 60 ° C, and the lower 65 ° C. 2. The method according to p. 1, characterized in that the nitrogen flow at a pulse is not more than 10 kg / h. 3. The method according to p. 1 or 2, characterized in that the pulse time of the nitrogen supply does not exceed 2 minutes, and the interval between pulses is not more than 20 minutes 4. The method according to p. 1, characterized in that when the temperature of the upper zone reaches 60 ° C, and the lower 65 ° C and the bottom heater is turned on, these temperatures are transferred to 70 ° C for the upper zone and 80 ° C for the lower the end of the process of emptying the cylinder.