GB2167679A - Multichamber type fluid bed reaction apparatus - Google Patents

Abstract

A fluid bed reaction apparatus comprising a plurality of chambers formed by dividing the particle bed and the gas compartment thereof with partition walls. The partitions may overlap to provide a tortuous path through the bed (Figure 3c). Each divided chamber may be supplied with a reaction gas and/or an inert gas of which the composition, flow and temperature can be independently selected, the partition walls being so arranged that particles from the particle bed can transfer between adjoining chambers. The apparatus can be used for the conversion of uranium to UF6. The apparatus is less bulky and simpler to use than conventional multitower type apparatus. <IMAGE>

Description

SPECIFICATION Multichamber type fluid bed reaction apparatus The present invention relates to a multichamber type fluid bed reaction apparatus. In particular it relates to such an apparatus wherein the fluid bed part and the gas compartment part are divided into a plurality of chambers, each separate chamber being supplied with a reaction gas of which the composition, flow and temperature can be selected. A fluid bed, a moving bed or a fixed bed can thus be formed in each chamber according to the reaction required in each chamber, and the particles can be transferred between the chambers.

A gas-solid system fluid bed reaction apparatus forms a fluid bed by fluidizing solid particles with a fluidizings gas. The gas-solid reaction is carried out by bringing the fluidizing particles into contact with the reaction gas. Such apparatus is widely used in the industrial field. However, if it is desired to carry out several different reactions continuously using such apparatus, the apparatus must be multiplied.

For multiplying the apparatus, there are two systems; firstly, a multitower system which comprises a linked plurality of separate appartus and secondly a multichamber system wherein the inner part of a single apparatus is multiplied. The latter may be used to improve reaction efficiency by multiplying the same reaction, or can be used for drying and cooling particles (Anonymous; Chem.

Eng., 63, 116[1956]). However, such a system does not have the ability to control the reaction of the solid-phase particles, nor the transfer thereof, and thus it is not suitable for carrying out a multi-step reaction. On the other hand, the multitower system is more generally used for carrying out multi-step reactions (C.D. Harrington et al; Uranium Production Technology, D. Van Nostrand Company, INC P550-501 [19511). However, such a multitower system does have disadvantages; as the number of separate fluid bed reaction apparatus is multiplied, the need to transfer particles between the towers increases, and so many pipes, pumps and transfer systems are required.Therefore, the design and the operation of the apparatus, and the reaction scheme itself, becomes quite complex, all of these factors leading to a disadvantageous cost factor.

It was noted by the present applicants that in the above mentioned multichamber system, efficiency of the reactions is good even when reactions are identical. They have investigated the provision of a multichamber type fluid bed reaction apparatus which enables different reactions to be carried out and brings about an improvement in the efficiency of the apparatus and simplification of the operation system, thus overcoming the above mentioned defects of the conventional multichamber and multitower system.

According to one aspect of the present invention, there is provided a fluid bed reaction apparatus comprising a plurality of chambers formed by dividing the particle bed part and the gas compartment part thereof with partition walls, each divided chamber being supplied with a reaction gas and/or an inert gas of which the compositions, flow and temperature can be independently selected, the partition walls being so arranged that particles from the particle-bed can transfer between adjoining chambers.

According to a further aspect of the present invention there is provided a fluid bed reaction apparatus including a multiplicity of chambers as defined by a system of internal baffles in which at least one baffle extends upwardly from the bottom of the bed and at least one baffle extends downwardly, these baffles overlapping to provide a tortuous path through the bed.

The apparatus according to the present invention enables a multi-stage reaction to be carried out.

The effective multichamber system enables, e.g.

the amount of reaction gas, or the gas temperature in each chamber to be selected arbitrarily. Formation of a fluid bed, a moving bed or a fixed bed in each chamber and regulation of particle reaction and particle transfer becomes possible by suitably selecting the height of the partition wall and by regulation of the flow of the gas. Particles formed can be recovered effectively by provision of a gasparticle separator in each chamber. The multichamber system also enables the provision of a 'gas-seal' within a selected chamber to avoid cross-reactions and to regulate the process. The invention will now be described more fully and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of a preferred example of a multichamber type fluid bed reaction appartus according to the present invention suitable for the conversion of uranium oxide to UF6.

Figure 2 is a schematic elevation of a conventional multitower type apparatus corresponding to the appartus shown in Figure 1.

Figure 3ta) is a schematic elevation of a fluid bed reaction apparatus wherein the partition walls are fitted in contact with the basal surface of the fluid bed.

Figure 3(b) is a schematic elevation of a fluid bed reaction apparatus wherein the partition walls are fitted over a gap above the basal surface level of the fluid bed.

Figure 3(c) is a schematic elevation of the fluid bed reaction apparatus of the present invention which combines the partition wall of Figure 3(a) and the partition wall of Figure 3(b).

Figure 4 is a schematic elevation of a further embodiment of the present invention wherein a plurality of fluid bed reaction apparatus are connected by connecting pipes owing to difficulty of uniting the reaction apparatus.

Figure 5(a), rub), (c), (d) are all schematic plan views of differing arrangements of the apparatus showing a high degree of freedom in the arrangement of the apparatus of the present invention.

Figure 6 is a schematic plan view of a slab shape type fluid bed reaction apparatus which can be extended in both horizontal and vertical directions.

Figure 7 is a schematic plan view showing a recycling type fluid bed reaction apparatus for the recycling of particles.

As an example of the present invention, the mul tichamber type apparatus will be compared with the conventional multitower system used in the process for the conversion of uranuim oxide into UF,. Further exemplification is made to a slab shape type multichamber apparatus.

In Figure 1, chambers 1-14 constitute a multichamber type fluid bed (in some cases, a part thereof may become a moving bed or a fixed bed), parts 1a-14a are gas compartments for supplying fluidizing gas corresponding to the chambers 1-14, and 1b-14b are nozzles for supplying the fluidizing gas to chambers 1-14. Of chambers 1-14, chambers 1-2 have the function of reducing U2OS or U03 to UO2 and chambers 3-6 have the function of cooling and storing the particles, gas-sealing, and regulating transfer of the particles respectively. Chambers 7-8 have the function of converting UO2 to UF4, and chambers 9-12 have the function of cooling and storing the particles, gas-sealing and regulating transfer of the particles respectively. Chambers 1314 have the function of converting UF4 to UF6.The raw material U308 or U03 is supplied through a raw material supplying pipe 15 to chamber 1 wherein U308 or U03 is reduced to UO2 with hydrogen gas contained in the fluidizing gas supplied through nozzle 16 and gas compartment 1a. In chamber 1, as UO2 particles forming the fluid bed increases the height of the bed due to the supplied amount of uranium compound as the raw material, they transfer from chamber 1 to chamber 2 through the lower gap of the partition wall under the pressure of the bed.

In chamber 2, unreacted U308 or U03 which has entered from chamber 1 is almost completly converted to UO2 by reaction of the hydrogen gas in the fluidizing gas supplied through gas compartment 3a. Fluidizing gas from nozzle 3b forces out hydrogen gas remaining among UO2 particles and at the same time prevents the hydrogen gas from entering the following chamber by means of a gasseal. Chamber 4 and chamber 5 have the function of cooling and storing the particles, nitrogen gas being supplied through nozzles 4b and 5b and gas compartments 4a and 5a. In chamber 4, as fluid bed is formed, and in chamber 5, a fluid bed or moving bed is formed. Chamber 5 and chamber 6 also have the function of regulating particle transfer. Regulation of the amount of particles transferred is achieved by the amount of gas supplied to chamber 5 and chamber 6.

By regulating the amount of nitrogen gas supplied to chamber 6, the height of the fluid bed in chamber 6 changes and thus the amount of the particles which overflow to chamber 7A changes.

The amount of particles transferring from chamber 5 to chamber 6 is decided by the relation between the height of the bed in chamber 5, the amount of nitrogen gas supplied to chamber 5 and the amount of nitrogen gas supplied to chamber 6.

Further, when the amount of nitrogen gas supplied to chamber 6 is decreased at a limiting flow rate (velocity for incipient fluidizion), the fluidization is stopped to form a fixed bed in chamber 6 and the transfer of particles to chamber 7A is stopped.

Consequently, chamber 5 and chamber 6 serve the function of storing particles, and chamber 6 additionally has a function of gas-sealing. As HF gas is used in chamber 7, nitrogen gas supplied to chamber 6 prevents the HF gas from entering the neighbouring chambers. In chambers 7A, 7B, 7C and chamber 8, UO2 is converted to UF4 with HF gas.

HF gas is supplied as a component of the fluidizing gas through 7Ab, 7Aa and 8b, 8a. Completion of the rection of UO2 to UF4 is rather slow and careful supervision of the operating conditions is required.

It is known that according to the reaction of the initial stages and that of the later stages a change in the reaction conditions is necessary to preceed efficiently the progress of the reaction. Therefore for the later part of the reaction the fluid bed part is made multistage in order to be able to change the operating condition of each stage in turn, thus the chamber is divided into 7A, 7B, 7C and 8 in order that the temperature of each chamber and composition of the supplied HF gas can be varied. Chamber 9 to chamber 12 have a function similar to that of chamber 3 to chamber 6, and in chamber 9 HF gas remaining amongst the particles is driven out and is prevented from entering into in an after chamber 1 by gas-sealing. Chamber 10 and chamber 11 have a function of cooling and storing of the partices and at the same time that of regulating particle transfer.Chamber 12 has function of gas sealing, keeping out HF gas used in chamber 13 or chamber 14 and also a function of regulating particle transfer in cooperation with chamber 11. In chamber 11, a fluid bed, moving bed or fixed bed is formed, and in chamber 12, a fluid bed or fixed bed is formed.

Chamber 13 and chamber 14 have a function or converting UF4 to UF6 with F2 gas supplied as a fluidizing gas through 13b, 13a and 14b, 14a. In the UF6 conversion process, increasing the utilization efficiency of expensive F2 gas to as high as possible is important, as it is directly linked to any lowing of the manufacturing cost. For this purpose, it is required to control the quantitative relation between UF4 and F2 gas supplied to the reaction chamber; consequently the function of quantitatively regulating particle transfer has an important significance.

In chamber 13 and chamber 14, alumina of Caf2 particles are used as a fludizing media. UF4 particles supplied to chamber 13 react with F2 gas in fluidizing with the fluidizing media to form UF6, and unreacted UF4 particle enters chamber 14. In chamber 14, the unreacted UF4 particles again react with F2 gas to form UF6, but any unreacted UF4 partly remain here to be returned to chamber 13. Thus, between chamber 13 and chamber 14 UF4 particles circulate with the fluidizing media, and by changing the quantity of F2 gas supplied through 13b and 13a and F2 gas through 14b, 14a, the degree of utilization of F2 gas can be higher than that in the case of a single fluid bed. 16-22 are gas-particle separation parts wherein the particles accompanied by gas from the fluid bed are separated from the gas. The separation part is divided by kinds of particle and gas, and each divided separation part is fitted with gas-particle separating fil ter. Gas-particle separation parts 16 and 17 share a common waste gas line, but in chamber 1 and 2 they are separated to avoid any mixing of particles from chambers 1 and 2. Gas-particle separation part 18 is independant because the greater part of the gas used therein is nitrogen gas.

In gas-particle separation parts 19A, 19B and 20, the main consituents of gas are HF and steam, but owing to a difference of the reaction conditions, especially a difference of the concentration of HF gas in each chamber, the gas-particle separation part is divided into three parts in each of which after-treatment is possible. Gas particle separation part 21 is similar to separation part 18. The gas introduced to gas-particle separtion part 22 is a mixture of UF6 gas, excess F2 gas and nitrogen gas.

The mixed gas is separated in gas-separation part 22 and sent to a cold trap for recovering UF6 and a through clean up reactor line for increasing the degree of utilization of the remaining F2 gas.

The apparatus of the present invention can be further explained by comparing its consitution elements with those of the conventional apparatus of Figure 2.

In Figure 2 a fluid bed reaction apparatus 30 reduces U306 or UO3UO2, whilst each of 38 and 41 is a fluid bed reaction apparatus which will carry out the reaction of UO2 to UF4 and 48 is a fluid bed reaction apparatus which converts UF4 to UF6. Each of 33-36 has a function of cooling and storing particles, gas-sealing and transferring particles by gas stream. 37 is an apparatus for supplying a fixed amount of particles. Each of 39 and 40 has a function of gas-sealing and supplying a fixed amount of particles, and 43-46 have a function of cooling and storing particles, gas-sealing and transferring particles by gas stream. 47 is an apparatus for supplying a fixed amount of UF4. 30b, 38b, 41a are solid-gas separation filters for the fluid bed reaction apparatus.

The correspondence of these constitution elements of the conventional apparatus of those of the apparatus of the present invention is as follows; Fluid bed reaction apparatus 30 of Figure 2 corresponds to chambers 1 and 2 of Figure 1, and 3337 have the same functions as those of chambers 3 and 6. Fluid bed reaction apparatus 38 and 41 correspond to chambers 7 and 8, and 43-47 have the same function as that of chamber 9 to chamber 12.

Fluid bed reaction apparatus 48 corresponds to chamber 13 and chamber 14. As for the solid-gas separation filters, 30b corresponds to 16 and 17, 35b to 18, 38b to 19, 41a to 20, 45b to 21 and 48b to 22 respectively. The conventional fluid bed reaction apparatus are all of cylinder type. In Figure. 2, U2Os or U03 supplied by supplying pipe 31 is reacted with H2 gas supplied through inlet 32 in the apparatus 30 to give UO2. After UO2 formed is received by receiving hopper 33, it is transferred through supplying hopper 34 then transferred by a nitrogen gas stream supplied by 34a through a solid-gas separating hopper and reaches supplying hopper 36 for fluid bed reaction apparatus 38. A fixed amount of UO2 supplied by 37 reacts in the apparatus 38 with HF contained in waste gas 41 to from UF4.Successively, the particles are received by receiving hopper 39 and sent by quantitatively supplying device 40 to fluid bed reaction apparatus 41 where unreacted particles react with HF to form UF4. 43-47 have a function similar to that of 33-37 and carrying out the supply of particles to fluid bed reaction apparatus 48. In 48, UF4 reacts with F2 gas supplied by 49 to form UF6, and then UF6 is sent to system 48a containing the cold trap for recovering UF6 and for increasing the degree of utilization of any remaining F2 gas.

As described above,in the conventional apparatus, as each tower is independent, the transfer of particles therebetween is effected by gravity, so the height becomes greater as the arrangement becomes larger, as does the area occupied. Further, the height and area of the building to house the apparatus becomes higher and larger, and so the ventilation capacity peculiar to a nuclear facility increases. For lowering the height, there is a method which transfers particles to a high position by gas stream as the apparatus of the present invention shows in Figure 1, but such a system makes the apparatus even more complex, the occupied area becomes larger and further, the arrangement and operation becomes even more complicated. The system suffers other disadvantages, namely, that increasing the number of towers, e.g. for improvement of reaction efficiency is difficult.

The apparatus of the present invention, however, enables particles to be transferred hozizontally, thus considerably reducing the height of the apparatus and obviating complex transfer arrangements. Stage multiplying effective for improving the efficiency of the fluid bed reaction apparatus can be easily achieved by increasing the number of chanbers. Further, as the reaction condition in each chamber is independently selected, reaction efficiency can easily be improved by "fine adjustment" of the operating conditions. In the apparatus of the present invention, the multiplication in the region for converting UO2 to UO4 is a good exam ple of this.

Although the apparatus of the present invention is mainly composed of a fluid bed reaction process, a moving bed or a fixed bed in any chamber can be easily realized by changing the amount of gas supplied; consequently, for example, there is the advantage tht the apparatus is also applicable instantly to a process wherein the improvement of reaction efficiency is effected by combining a fluid bed reaction process with a moving bed reaction process.

There are two methods for fitting the partition wall into each chamber, that is, a method in which the partition wall is fitted in contact with the basal surface of the fluid bed and a method in which the partition wall is fitted over a gap above the basal surface level of the fluid bed.

In the conventional multichamber type fluid bed reaction apparatus shown in Figure 3a and Figure 3b, only one of these two kinds of partition walls is fitted. In the system of Figure 3a in which the parti tion wall is fitted in contact with the basal surface of the fluid bed, when coarse particles are mixed in the particles, there arises the problem that the coarse particles remain in the lower part of the fluid bed and do not overflow the partition wall. In the system of Figure 3b in which the partition wall is fitted over a gap opened over the basal surface of the fluid bed, the problem of Figure 3a does not arise, but the probability of short-circuit of particles between the chambers becomes high enough to as to be undesirable for reaction.However, by combining both systems, as Figure 3c shows, these problems can be avoided and at the same time efficiency of the reaction can be increased as the flow of particles approaches a piston-like flow. Further, by combining both systems, there can be realised a combination of a fluid bed and a moving bed which is impossible in conventional systems.

In the present example, there is shown a slab shape type fluid bed reaction apparatus as an united body. However, in the case wherein there is a plurality of kinds of materials used and forming these materials into an united body is difficult or not rational or in the case wherein owing to extremely different temperatures between the cham bers, uneven thermal expansion occurs and it is hard to control operating conditions, an united body is difficult. By connecting a plurality of reaction apparatus with pipes, these problems can be avoided without changing the basic concept of the present invention.

Figure 4 shows an example of such a case. In Figure 4, 50-52 are divided reaction apparatus, and 53 and 54 are connecting pipes which connect these apparatus. The pipes also serve the function of accommodating thermal expansion as required.

Moreover, the apparatus has the further advantage that the degree of freedom of arrangement of the apparatus is extremely large.

Figure 5(a), (b), (c), (d) show possible arrange ments of slab shape fluid bed reaction apparatus of the present invention. Further, as shown in Fig ure 6, a system can be built which extends a slab shape type fluid bed vertically and horizontally, giving increased capacity. In the arrangement shown in Figure 7, the apparatus of the present invention can be utilized as a single-stage type fluid bed reaction apparatus.

Claims (13)

1. A fluid bed reaction apparatus comprising a plurality of chambers formed by dividing the parti cle bed part and the gas compartment part thereof with partition walls, each divided chamber being supplied with a reaction gas and/or an inert gas of which the composition, flow and temperature can be independently selected, the partition walls being so arranged that particles from the particle bed can transfer between adjoining chambers.

2. A fluid bed reaction apparatus as claimed in claim 1 wherein one or more of the divided cham bers is provided with a gas-particle separator.

3. A fluid bed reaction apparatus as claimed in claim 1 or claim 2 wherein a gas seal of reaction gas occurs across adjoining chambers.

4. A fluid bed reaction apparatus as claimed in any one of claims 1 to 3 wherein some of the partition walls extend upwardly from the base of the particle bed.

5. A fluid bed reaction apparatus as claimed in any one of claims 1 to 3 wherein some partition walls extend downwardly towards but do not reach the base of the particle bed.

6. A fluid bed reaction apparatus including a multiplicity of chambers as defined by a system of internal baffles in which at least one baffle extends upwardly from the bottom of the bed and at least one baffle extends downwardly, these baffles overlapping to provide a tortuous path through the bed.

7. A fluid bed reaction apparatus as claimed in any one of claims 1 to 6 wherein the particle bed is in the form of a moving bed in at least one of the divided chambers.

8. A fluid bed reaction apparatus as claimed in any one of claims 1 to 7 arranged as a slab shape.

9. An apparatus comprising a series of separate apparatus as claimed in any one of claims 1 to 8 joined by pipes.

10. Afluid bed reaction apparatus as claimed in any one of claims 1 to 9 adapted for the conversion of uranium oxide to UF6.

11. A process for the production of UF6 which comprises the use of a fluid bed reaction apparatus as claimed in claim 10.

12. A fluid bed reaction apparatus as claimed in claim 1 and substantially as hereinbefore described.

13. The use of a fluid bed reaction apparatus as claimed in claim 1 for carrying out a muitistage chemical reaction.