JPS5948135B2 - Mixed gas separation device using thermal diffusion couple - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on patent application No. 80323 filed in July 1972 by the same applicant as the present case (title of invention: This method utilizes the "separation effect superimposition enlargement method").

The previously filed invention was intended to be applied to various physical and chemical operations by superimposing the transport phenomena of atoms, molecules, and ions due to thermal diffusion and increasing the transport effect. In particular, the present invention relates to applying this transport effect to gas molecules, and relates to a device for separating mixed gases using a thermal diffusion couple using a porous material as a diffusion medium.

Thermal diffusion occurs when there is a temperature gradient inside the gas mixture.
It is a phenomenon in which the molecules of a mixed gas move along the gradient, causing a relative concentration difference in the mixed gas.From around 1916 to 1917, S. Chapman and F.
Dooston confirmed its phenomenal existence and theoretically proved it.

This thermal diffusion is in the opposite direction to normal concentration diffusion,
The process progresses in such a way as to bring about the uneven distribution and concentration difference of the diffusing substances, and as a result, the concentration difference caused by this thermal diffusion causes concentration diffusion in the direction that cancels out the thermal diffusion, and a steady state is reached when a certain concentration difference appears. The apparent diffusion disappears.

As a definition of the term, in this specification, physical changes such as concentration differences and uneven distribution of diffusing substances brought about by thermal diffusion are referred to as thermal separation effects.

Originally, this thermal separation effect was very small, so in order to separate a mixed gas using thermal diffusion, it was necessary to superimpose the effect by some means, and the conventional method for this was the Crusian type. Separation towers are known.

However, this Crusius-type separation column connected separation units in multiple stages and used a high heat source to create a large temperature gradient.

Furthermore, although the device is simple, it involves gas convection and therefore has poor thermal efficiency.

Additionally, there were difficult problems in terms of device configuration, cost, etc.

Thermal separation effect exists for all gas mixtures, and although it has the advantage of being able to be used for isotope separation, etc., which cannot be treated with normal physical or chemical methods, it cannot be used on a laboratory scale. However, it has not been put into practical use.

As shown in Fig. 1, the Crusius type separation column has two cylinders arranged concentrically, with an inner side 101 serving as a high temperature section, and an outer side 102 serving as a high temperature section.
The cylindrical body 100 is used as a low-temperature part. For example, in the case of separating isotope 120 atoms of carbon element and 13C atom, specifically, using methane gas, which is a gas containing carbon element, As shown in FIG.
A temperature gradient is created by using cold water 104 as a low temperature section.

The principle of this Crusius-type separation column is as shown in FIG.
The temperature gradient with 02 causes thermal diffusion in the mixed gas of 12CH4 and 13CH4, and as a result, 13CH4 on the low temperature side 105, and 1 on the high temperature side 106.
2CH4 each has a high concentration.

Furthermore, convection occurs due to the temperature difference between the inner high temperature section 101 and the outer low temperature section 102.

For this reason, the gas on the low temperature side 105 flows downward and the gas on the high temperature side 105 flows downward.
06 gas moves upwards, and at the upper part 107 of the cylinder, 12
In the lower part 108, CH4 has a high concentration, and 13CH4 has a high concentration.

As shown in FIG. 4, a large number of such cylindrical bodies 100 are connected to perform concentration separation of 13C atoms.

However, since the generation of convection is an essential condition for this Crusius-type separation column, a huge amount of heat loss is unavoidable.

Furthermore, it is necessary to create a large temperature difference between the inside and outside of the cylinder, and a dedicated high heat source such as a heating wire must be used.

Furthermore, even if the effect was increased by re-manipulating the operation, it would be too time-consuming, so it was not generally used.

However, since this thermal separation effect also exists in any gas phase mixture system, commonly used physical and chemical methods such as liquefaction separation are effective, as in the case of the isotope mixture gas system mentioned above. It is effective even when there is no thermal separation effect, and therefore, if another method for appropriately superimposing this thermal separation effect is found, it will greatly contribute as a separation technology for gas phase mixed systems.

Furthermore, as a method applicable to isotope gas systems, gas diffusion has been conventionally used to separate mixed gases.

In this gas diffusion method, for example, 235U for nuclear power generation is enriched using uranium fluoride gas, UF6.The advantage of isotope separation using this gas diffusion method is that the mixed gas is permeated and diffused through a stationary diaphragm. The equipment and operation are extremely simple, and the stability and durability of the plant operation are extremely high.

On the other hand, the biggest drawback of the gas diffusion method is that the power consumption of the pump that provides the driving force for gas permeation through the diaphragm is large.Incidentally, the price of producing enriched uranium at a certain concentration, that is, about 50% of the separation cost, is the operating cost. It is said that there is.

The present invention was made in view of the above-mentioned problems, and provides a novel mixed gas separation device that applies thermal diffusion and connects a large number of thermal diffusion pairs using porous materials as diffusion media to mix the gases. This method separates gases, and while maintaining the simplicity of equipment and operation, which are the advantages of the gas diffusion method, it is possible to keep operating costs low.

In other words, the heat diffusion couple according to the present invention does not require any mechanical equipment to operate, so it has very high stability and durability, and does not require the intensive operating costs, which is the biggest drawback of the gas diffusion method. shall be.

In terms of energy consumption for driving the device, there is no heat loss due to convection compared to conventional Crusius separation columns, so it is much more thermally efficient, and if the number of connected heat diffusion pairs is increased, the energy consumption can be reduced by several tens of degrees. Mixed gases can be effectively separated even with temperature differences, and for this reason, low-quality energy such as factory waste heat, geothermal heat, seawater temperature differences, and solar heat can be used as energy sources without the need for a dedicated heat source. In many cases, operating costs can be kept low.

Hereinafter, the principle of the heat diffusion pair according to the present invention will be explained with reference to the drawings.

FIG. 5 is a schematic principle diagram of the heat diffusion pair substrate according to the present invention, where 1 is the heat diffusion pair substrate M, N is two different material systems, and N is a porous material 7. .

Thermal diffusion pair substrate 1 consists of two different material systems M.

N, and a porous material is used as a diffusion medium in one or both of them.

If porous materials are used for both M and N,
It is necessary to use porous materials with different properties.

Here, a porous substance is a substance that contains countless pores, and is also called a porous body, porous material, or porous substance, and specifically includes ceramics, glass, refractory cement, etc. Including ceramics, sintered metal materials, polymer materials,
Examples include fiber bundles.

Porous materials that are highly effective for use in the present invention are those whose pore diameter is close to or smaller than the mean free path of the gas molecules in the gas mixture to be separated, and which have communicating pores. It is necessary to.

In terms of pore size, uniformity of pore size distribution, durability, etc., even porous materials of lower quality than the diaphragm used in the gas diffusion method can be used effectively.

The purpose of using this porous material as a diffusion medium for one or both of M and H is, firstly, when the pore diameter of the porous material is close to or smaller than the mean free path of gas molecules, it becomes porous. It is well known that gas molecules passing through a substance form a molecular flow or a viscous flow, and the physical and chemical properties of the gas molecules there are significantly different from those in a gas phase system (bulk phase) under normal circumstances. This is because the phenomenon is used to create a difference in the diffusion environment of gas molecules passing through the two material systems M and N, thereby making it possible to construct a thermal diffusion pair.

The second purpose is to eliminate the need for permselective membranes, which are often required for the separation of ordinary mixed gas phase systems, and for gases that do not have an effective permselective membrane. This is to enable separation of mixed gases.

The third purpose is to prevent the diffusion rate of gas molecules in M and N from being significantly impaired.

In the thermal diffusion pair substrate 1 shown in Fig. 5, a porous material 7 is used only for N, and M is left in a normal gas phase system (bulk phase), and two materials with different M and N are used. The case where it is assumed to be a system is shown.

It is.

When both M and N are filled with a gas mixture, initially,
The composition of the gas mixture is constant throughout M and H.

Two different material systems M and N are in contact at one end 6, and gas molecules can be exchanged at this one end 6.

M and N are designed to have a temperature gradient due to the high temperature section 8 and the low temperature sections 9 and 9'.

Here, a temperature gradient may be provided by making the high temperature section 8 a low temperature section and the low temperature sections 9, 9 a high temperature section.

The porous substance 7 used for N has the following conditions in addition to the above-mentioned conditions regarding the pore size.

It is preferable to use a material that has low thermal conductivity that makes it easy to maintain a temperature gradient, and also has corrosion resistance and non-reactivity with mixed gases.

Note that low thermal conductivity is generally recognized as a common property of many porous materials.

In the heat diffusion pair substrate 1 configured as described above, since a temperature gradient exists in both of the two different material systems M and N, a thermal separation effect occurs in both.

Now, for the sake of simplicity, we will consider a two-component system, and if we assume that the diffusive substance D1 in the gas mixture has a smaller molecular weight than the other gas mixtures, then in general, the thermal diffusion versus the gas phase system (bulk phase) of the substrate 1.
In M, due to the thermal separation effect due to the temperature gradient between the high temperature section 8 and the low temperature section 9, the concentration (mole fraction) of the diffused substance D1 becomes high on the high temperature side 2 of M, while on the other hand, the concentration (mole fraction) of the diffused substance D1 increases on the low temperature side 3 of M. The concentration of D□ becomes low.

(The mole fraction of M on the high temperature side 2 is Co, and the mole fraction of M on the low temperature side 3 is 01.

). In addition, in N using the porous material 7 of the thermal diffusion substrate 1 as a diffusion medium, due to the thermal separation effect due to the temperature gradient between the high temperature part 8 and the low temperature part 9', in many cases as in the case of the bulk phase. , on the high temperature side 4 of N, the diffused substance D
The concentration of 1 increases, and on the low temperature side 5 of -10,000 N, the diffused substance D
The concentration of 1 becomes lower.

(The concentration of the N diffused substance D1 on the high temperature side 4 is expressed as the molar fraction C8' of the mixed gas bulk phase that is in equilibrium with it, and the concentration of N on the low temperature side 5 is similarly assumed to be 02.

) The thermal separation effect is unique to the diffusing substance D1, the material system in which it is placed, and the temperature difference.

Even if the temperature difference in M and N is the same when the low temperature parts 9 and 9' of the substrate 1 are at the same temperature, N is used as a diffusion medium and the pore diameter is close to the mean free path of the diffusive substance D1. The porous material 7 in which the pores are connected is used, and it is considered to be a material system that is significantly different from M, which is a normal gas phase system (bulk phase), so the thermal separation effect in M is There will be a difference between the values of concentrations C8 and C1 on the high and low temperature sides due to the thermal separation effect of N and the values of C6' and C2 on the high and low temperature sides due to the thermal separation effect of N.

By the way, one end 6 of two different material systems M and N is brought into contact and it is possible to exchange the diffused substances.

The concentrations C6 and C8' of the diffused substance D1 on the high temperature side of N are equal in value.

Therefore, even if M and N are initially filled with a mixed gas having the same component ratio, the final Generally speaking, there will be a difference in the concentration of the diffusive substance D1 between the low temperature side 3 of M and the low temperature side 5 of N, so that C
The values of 1 and 02 will be different.

Whether the concentration CI, C2 of this diffusing substance is C, > C2 or Ct < C2 depends on the mixed gas used, the diffusing substance D1 to be concentrated, and the type of porous material 7 used for N as a diffusion medium. , and the direction of the temperature gradient given to the heat diffusion versus substrate 1 (8 is the high temperature part and 9 and 9' are the low temperature part, or 8 is the low temperature part and 9 and 9' are the high temperature part).

) is determined by

Here, it is assumed that C1>C2. At this time, the low temperature side 3 of M
In this case, the diffusion substance D4 can be concentrated relative to the N low temperature side 5.

Furthermore, as described above, if 8 is a low temperature part and 9 and 9' are high temperature parts and the direction of the temperature gradient is reversed, the diffusion substance D1 is This means that concentration can be performed.

In the above description, one heat diffusion pair substrate 1 has been described.

With one such heat diffusion pair, the difference between C1 and 02 is very small.

Therefore, in order to actually separate a mixed gas, it is necessary to connect a large number of heat diffusion pair substrates 1 as described above to superimpose the heat separation effect.

There is an advantage in using a heat diffusion pair where such superposition is possible.

FIG. 6 shows a state in which two heat diffusion pair substrates 11.21 are connected in series to form a heat diffusion pair array.

When connecting the heat diffusion pair substrates, in order to match their polarities, N1 using the porous material 17 of one heat diffusion pair substrate 11 and a normal gas phase system (bulk) of the other heat diffusion pair substrate 21 are used. phase) N2 is connected to the contact portion 16' so that the diffusion substance D1 can be exchanged.

Even when connecting hundreds or thousands of thermal diffusion pairs, the polarity can be matched by bringing N using a porous material of the adjacent thermal diffusion pairs into contact with a normal gas phase system (bulk phase) M. After that, connect and heat spread.

It is necessary to construct a distributed array.

In the figure, 18.28 is the high temperature part, 19.29.29' is the low temperature part, Ml, Nl.

N2. A temperature gradient is applied to the N2.

Here, regarding the diffusive substance D1 in the two thermal diffusion pair substrates 11.21, the concentrations (molar fractions) of Ml and N2 on the high temperature side 12.22 are C1o, C2o, and Mt, N2
Let the concentrations at the low temperature side 13.23 be C1l, C2□,
Furthermore, N1. The mole fraction C1o', C of the bulk phase of the mixed gas that equilibrates the concentration of N2 on the hot side 14, 24 with it.
2o', and N1. N2 low temperature side 15.2
Similarly, the concentrations at 5 are assumed to be C1□ and C22.

Also when connecting these two heat diffusion pair bases 11.21,
Assume that Ct > C2 as described with reference to FIG.

Then, due to the superimposed effect of the two thermal diffusion pairs on the substrate 11.21, the concentration (mole fraction) of the diffusive substance D1 becomes C11>C2□
In comparison with the case of one heat diffusion base, C1□
The following relationship holds true: > C1 > C2 > C2□.

The superposition of thermal separation effects when these two thermal diffusion pair bases 11 and 21 are connected will be explained in more detail as time passes as the diffusion phenomenon progresses, as follows.

First, the two heat diffusion pair substrates 11.21 are connected at the contact portion 16'.

In the initial state filled with a gas mixture, Mt, Nl,
N2. The concentration of the diffused substance D1 everywhere in N2, that is, C
o, C1ot C10't C12, C21, C20
9C2o'tC22 is constant.

Next, a temperature gradient is applied to the heat diffusion pair connecting these two heat diffusion bases 11.21.

That is, 18.28 is a high temperature section, and 19.29.29' is a low temperature section.

Then, each material system M 1°Nl, N2. N
2, the thermal separation effect due to this temperature gradient causes the diffusion substance D1 to
For the concentration of the diffusing substance D1, for each thermal diffusion versus substrate it, 21, C1□>C, in the same way as described with respect to FIG.

, C2□>C2□. However, since the two heat diffusion pair substrates 11 and 21 are connected at the contact portion 16' so that the diffusion substance D1 can be exchanged, the low temperature portion 15 of N1
As a result, the concentrations C1□ and 02□ of the low temperature part 23 of N2 become 01□-02□.

In the two heat diffusion pair substrates 11 and 21 shown in FIG. 6, Co > C12°C as explained in FIG. 5.
2 > C2 As a result, if there is no exchange of gas molecules at the contact portion 16', 01□>C2□.

Since the diffusive substance D1 can be exchanged in the contact part 16', and since the low temperature side 15 of N1 and the low temperature side 23 of N2 are the same low temperature part 29 and there is no temperature gradient, no thermal diffusion occurs.
If C1□<C2□, the diffused substance D1 moves from the low temperature side 23 of N2 to the low temperature part 15 of N1 due to concentration diffusion across the interface, and as a result, it is maintained at 02□-01□.

Then, in one heat diffusion pair substrate 11, the N4 low temperature side 1
Since the concentration C1□ of 5 becomes high as a result of the diffusion of N2 from the low temperature side 23, the diffused substance D1 is transported to the high temperature part 14 of N1 in order to balance the thermal separation effect in N1, and the concentration of CIO' becomes high.

Here, since the diffusion substance D1 can be exchanged at the contact portion 16 between Ml and N1 of the heat diffusion pair substrate 11, the diffusion substance D1. moves and C
IQ' = cto, maintained.

Then, the concentration CIO of Mo on the high temperature side 12 becomes high as a result of the diffusion of N1 from the high temperature side 14, so the concentration of the diffused substance D1 in Ml increases, and the concentration C1 of the diffused substance D0 in the low temperature side 13 of Ml increases. □ will also be higher.

In addition, in the other thermal diffusion pair base 21, the concentration C21 of the diffused substance D1° in the low temperature part 23 of M2 becomes low as a result of the diffusion of N1 to the low temperature side 15, so that the concentration of N2 The diffused substance D is further transported from the low temperature side 25 to the low temperature side 23 of M2.

Then, it will also be transported to the low temperature section 13 of M□.

Due to the superimposed effect due to the connection of the two heat diffusion pairs with the substrate 11.21 as described above, C1□〉C1〉C for the diffusing substance D1.
The relationship 2>C22 holds true.

child. The weight of the thermal separation effect due to the connection of the heat diffusion pair to the substrate as shown in FIG.

In this way, when a large number of heat diffusion pair substrates are connected to overlap the thermal separation effect, as shown in FIG. Phase system (
Bulk phase) M must be brought into contact with the bulk phase, and high-temperature parts and low-temperature parts must be alternated to provide a temperature gradient.

FIG. 7 is a schematic diagram showing a state in which the heat diffusion pair substrate 1 is connected, and N, N, N, . . . are systems using a porous substance 7 as a diffusion medium. Yes, also
M.

M, M, ...... are normal gas phase systems (Bul
k phase).

8, 8. 8. ... is a high temperature section, and 9. 9
．． 9. ... is a low temperature section.

Thus heat spreads versus the poles of the substrate. By matching the characteristics and connecting them in series, the superimposition of the thermal separation effect explained in connection of the two heat diffusion units and the substrate using Figure 6 will be expanded as the number of connections of the thermal diffusion unit and the substrate is increased. It turns out.

Also, as mentioned above, 8, 8, 8. ...... is the low temperature part, 9°9.9. . . . may be used as a high temperature portion to provide a temperature gradient.

The concepts of high temperature and low temperature used here mean relative temperatures, and it is not necessary that the high temperature and low temperature areas for each heat diffusion pair and substrate are the same, and the temperature difference between high and low temperatures does not need to be the same. By increasing the number of connections between the heat diffusion pair and the substrate, it can be used from a temperature difference of several hundred degrees or more to a temperature difference of several degrees.

Next, if we use the concentration (molar fraction) C1 and C2 of the diffusive substance D1 explained in FIG. When two heat diffusion pair substrates as shown in Fig. 6 are connected in series, C1l/Cl2-C2□/C22
-, C1□/C2°- becomes 2.

In general, when n heat diffusion pair substrates are connected in series as shown in FIG. 7, the degree of separation is represented by 0.

In FIG. 8, two diffusion media M and N constituting the heat diffusion pair are shown in order to extract the heat separation effect by the heat diffusion pair to the outside.
The state in which the affected systems R and S are in contact with each other is shown.

The affected systems R and S that should exert the action of this thermal diffusion couple are a normal gas phase system (B
(ulk phase), a system using a porous material may also be used, and both affected systems R9S may be replaced with a normal gas phase system (bulk phase).
It may be connected to M and N as is, and furthermore,
When the diffusing substance D1 has an effective permselective membrane,
It may be provided at the ends of M and H and then connected to the affected systems R and S.

These affected systems R and S depend on the properties of the diffused substance D1, the types and conditions of the high and low heat sources used, the physical properties of the porous material used, the overall configuration of the mixed gas separation device, etc. The most suitable material system in which it is possible to exchange is the affected system R, S
Just connect it to M and N as follows.

The affected systems R and S are used not only to extract the heat separation effect superimposed by the heat diffusion pair to the outside, but also to extract the mixed gas by the heat diffusion pair when a large number of series connections of heat diffusion pairs are required. It is also used to provide pressure adjustment equipment for each fixed number of bases to adjust pressure changes that occur due to superimposed changes in composition ratio.

In the present invention, the term gas molecules means that the molecules or atoms diffusing in the thermal diffusion pair are in a gas state in the system R, S that should exert the action of the thermal diffusion pair. In a diffusion medium, especially a porous material, it does not matter whether the diffusion molecules are adsorbed on the pore walls or form a condensed phase in the pores.

Next, a detailed explanation of the heat diffusion pair according to the present invention will be given.

As explained in the principle, the present invention can be used to separate isotopes and various gas mixtures, but the following will explain the enrichment of 235U for use as fuel for nuclear power generation as an example.

・235U, which is used as nuclear fuel for nuclear power generation, accounts for approximately 0.715% of naturally occurring uranium, with most of the rest being 238U.

In the specific application of the present invention to gas bodies,
As with the conventional gas diffusion method, uranium-235 (235U) will be enriched using uranium hexafluoride (UF6), a compound of uranium and fluorine, as a raw material. 235UF6 and 238UF
6, the thermal separation effect is superimposed by a thermal diffusion array in which a large number of thermal diffusion pairs according to the present invention are connected,
Effectively concentrates 235UF6.

First, before explaining a specific example of concentrating 235UF6, we will explain the outer frame, shape, and porous material that can be used as a heat diffusion pair for UFe, which is a highly corrosive gas, and the heat diffusion We will discuss the degree of pairwise separation.

Although UF6 is a highly corrosive gas, diaphragms conventionally developed for gas diffusion methods can be used as they are as the porous material used in the heat diffusion pair substrate of the present invention.

The mean free path of UFe gas molecules is 75℃, 450 mmp
~500 people under conditions of H, gas pressure when processing,
It is sufficient to use a porous material having a pore size of several hundred, depending on the temperature.

Specifically, diaphragms made of Teflon, alumina, nickel, etc. have been developed in the past (Reference: Ryohei Nakane, Chemical Engineering, Vol. 34, No. 4, P355-P358, (197
0)).

In addition, the porous material used in the heat diffusion pair substrate of the present invention may be a material that has relaxed conditions such as pressure resistance and uniformity of pore size distribution, as compared to the diaphragm of the gas diffusion method.

The material that constitutes the outer frame and shape of the device is Al5M.
It is sufficient to use a material that forms a thin fluorine compound film on the surface and inhibits internal corrosion, such as aluminum, Cu, Fe, or Ni.

Incidentally, in an example in which UF6 was separated using a Crusius-type separation column, it has been reported that Cu was used as the material for the low-temperature side cylinder and Ni was used as the material for the high-temperature side cylinder.

Under 1 atm, UF6 solidifies at 59°C, and
Since it does not decompose and is stable at 440° C., when processing near normal pressure, it is necessary to set the temperature on the low temperature side and high temperature side of the heat diffusion pair within this range.

In the case of a two-component gas system, the degree of separation due to thermal diffusion is usually determined by the thermal diffusi factor a (thermal diffusi
onfactor).

Now, considering the case of one-dimensional diffusion, in a steady state where the thermal diffusion caused by the temperature gradient and the concentration diffusion caused by the resulting bundled concentration gradient are balanced, the following relationship is established. The formula holds true.

Here, xa and xb are the mole fractions of component a and component A, respectively, ΔI is the change in mole fraction of component A, T is the absolute temperature, and ΔT is the temperature difference.

Regarding the 238UF5-235UF6 system, α = ~0.01 from the results of a separation experiment using a Crusius type separation column.
The value has been derived (Karl, F, Ale
xander.

Fortschritte der Physik,
8. ppl-41, (1960)).

Now, in equation (1), if the component is 235UF6, then x is 0.72X10, so xa2~
1. If the temperature difference between the low-temperature side and the high-temperature side of the heat diffusion pair is 50 degrees, and separation is performed by the heat diffusion pair near 370, that is, the concentration of 235UF6 is 1 across the 50 degree temperature difference. This indicates that it will be .0014 times, or 1/1.0014.

In the case of a heat diffusion pair, the difference in the effects of two types of diffusion media can be extracted to the outside.

The value of α mentioned above is for the bulk phase surface of the mixed gas, and if the value in a porous material is α, then if the signs of both are the same, it is the tooth and false difference, and if the signs of the two are different, it is the difference between tooth and false. The sum of αM and α appears as the action of one heat diffusion substrate.

Whether the signs of α and α are the same or different depends on the gas mixture and the porous material used.

Although the value of α′ due to this single thermal diffusion versus substrate varies depending on the porous material used, etc., as mentioned above,
The order of the numerical values is almost the same, and if the concentration ratio of 235UF6 by one heat diffusion pair substrate is 1.001, then 2
．． When enriching 3.5 times to obtain about 5% nuclear fuel, (1,001)1253 = ~3.5,
It is sufficient to connect more than 1,000 heat diffusion pair substrates in series.

In addition to the flow due to relative thermal diffusion between the mixed gas components shown by equation (1), the action of the thermal diffusion pair is caused by the flow from one of the affected systems R and S at both ends of the thermal diffusion pair to the other. There is a flow of the entire gas toward (phenomenologically explained as the Knudsen effect), which defines the throughput of the device.

The rate of flow is thought to be determined by diffusion in porous materials with high diffusion resistance, and the driving force for thermal diffusion generated in porous materials due to this temperature gradient is equal to that and the concentration diffusion when a steady state is reached. If the thermal diffusion factor between the porous material and the gas molecules is α = 0.4 and the other conditions are the same as above, then the total concentration and concentration of the mixed gas with the porous material sandwiched are ΔC/C as the ratio ΔC/C
=~0.05.

obtain.

Assuming that the diffusion constant of the porous material of UFs is D = -0.05 (cm'/5ec), the porosity is 50%, the pressure is near normal pressure, the thickness of the porous material is 5 mm, and the cross-sectional area is 10 m'. , as the flow rate of UF6 ~1. lX1
0" mol/sec 7-15 ml/mln (standard state) is obtained.

That is, 15 ml of mixed gas can be processed per minute.

Next, specific examples of the heat diffusion pair according to the present invention will be explained using the drawings.

FIG. 9 shows the above-described heat diffusion pair configured in a flat type.

3 shows a side cross-sectional view of a flat heat diffusion pair 31.

The flat heat diffusion pair 31 has an upper plate 3 provided with an upper blocking wall 33.
1a, a lower plate 31b provided with a lower blocking wall 33', and side plates 32,32.

These upper and lower plates 31a and 31b and upper and lower blocking walls 33
．． 33' and the side plates 32.32 are made of copper, nickel, etc. that are corrosion resistant to UF6.

These upper blocking walls 33 and lower blocking walls 33' serve as diffusion media for N and UF using porous materials such as Teflon and sintered alumina with pore diameters of several hundreds.
Two material systems of M are connected in series using the 6-238UF6 mixed bulk gas phase system as is.

Then, N
The area of the contact surface 34, 34' between the gas phase system M and the gas phase system M is made large.

I did it like this. The reason for this is that the movement of diffused substances has greater resistance in porous materials than in gas phase systems, so by increasing the cross section of N diffusion using porous materials, it is possible to This is to increase the rate of diffusion.

This flat heat diffusing pair 31 is on its top. The plate 31a is used as a high temperature part and the lower plate 31b is used as a low temperature part to provide a temperature gradient.

Various heat sources can be used as this heat source, but UF
In the case of normal pressure treatment, from the physical properties 6, it is required that the temperature of the low-temperature part be 59°C or higher and the temperature of the high-temperature part be 440°C or lower.

In this embodiment, the high temperature part of the upper plate 31a is set to 120°C, and the low temperature part of the lower plate 31b is set to 70°C, providing a temperature difference of 50 degrees.

FIG. 10 shows a cross-sectional view of a tubular heat diffusion pair 61 in which the heat diffusion pairs are arranged in a tubular manner.

This tubular heat-diffusing couple 61 consists of an inner tube 62 with a concentric inner blocking wall 63 and an outer tube 65 with an outer blocking wall 63', thereby making it similar to the flat heat-diffusing couple 31.
The gas phase system M in the form of a gas phase and the N using a porous material are made to alternate.

Then, hot water or hot air is passed inside the inner tube 62 to make it a high-temperature part, and the outside of the outer tube 65 is made into a low-temperature part by cooling it with air, water, or keeping it moist and leaving it in the atmosphere. 61 to provide a temperature gradient.

Further, depending on the situation, the outer tube 65 may be heated and cold water may be passed through the inner tube 62, or the inner tube 62 may be made into a high temperature section using a heating wire or the like.

The system N using a porous substance and the gas phase system M are at the contact surface 34.3
4' (64, 64') only diffused material 235UF6.
""The blocking wall 33° 33 so that the UF6 can be replaced.
' (63, 63') are provided, but the pores on the side surfaces of the porous material may be closed without providing a special blocking wall 33.33' (63, 63').

Figure 11 shows six rows of flat heat diffusion pairs 31 shown in Figure 9 stacked up in the thickness direction as one unit element, connected in parallel with the connected systems R and S in common. 3 is a plan cross-sectional view showing a flat heat diffusion pair plate 35. FIG.

The affected systems R and S are provided with suction and exhaust ports 36 and 37 for connecting them to S and R of the heat diffusion pair substrate 35 of the next stage and for taking out the gas to be separated.

FIG. 9 shows six heat diffusion pairs connected in series, and FIG. 11 shows six rows of flat heat diffusion pairs 31 connected in series.
, S are shown in common and connected in parallel, but the number of these can be increased or decreased as appropriate.

FIG. 12 shows the simplest batch type mixed gas separation apparatus in which a large number of flat heat diffusion plates 35 as described above are connected.

One mixed gas separation tank 41 has a mixed gas supply port 4.
2. A separation gas recovery port 43 and a heat diffusion pair connection port 44 are provided, and a mixed gas supply valve 52, a separation gas recovery valve 53, and a heat diffusion pair connection valve 54 are attached to each of them.

The other mixed gas separation tank 45 has a heat diffusion pair connection port 4.
6. A mixed gas discharge port 47 is provided, and a heat diffusion pair connection valve 56, a mixed gas discharge valve 57, and a pump 58 are attached to each of the mixed gas discharge ports 47.

Between the two heat diffusion couple connection valves 54.56 attached to both mixed gas separation tanks 41.45, the flat heat diffusion couple plates 35 are connected to the adjacent flat heat diffusion couple plates 35. Suction and exhaust ports 36 and 37 provided in the operated systems R and S are connected alternately.

Then, the upper plate 35a of the flat heat diffusion pair plate 35 is attached to the high temperature section 4.
8 (120°C), the lower plate 35b is placed in the low temperature section 49 (70°C
) as a flat heat diffusion pair plate 35 for all systems M, H
It is designed to provide a temperature gradient of 50 degrees.

By this, the flat heat diffusion pair plates 35 are connected in series,
Thermal separation effects can be superimposed.

In addition, the mixed gas separation tank 41°45, valve 52.53
．． 54.56.57 Other connecting pipes, etc. are of course made of materials such as Cu and Ni, which have corrosion resistance to UFe.

Next, the separation process of the apparatus shown in FIG. 12 will be explained.

First, close the gas recovery valve 53 to be separated, and close the mixed gas discharge valve 57.
, a mixed gas supply valve 52, two heat diffusion pair connection valves 54, 5
6 and 235UF6-23 from the mixed gas supply port 42.
Supply 8UF6 mixed gas.

At this time, a pump 58 is used to shorten the time for filling the other mixed gas recovery port 47 with the mixed gas.

In this way, when the inside of the device is filled with the mixed gas, the mixed gas supply valve 52 and the other mixed gas discharge valve 57 are closed,
Flat heat diffusion pair plate 35.35.35. Apply a temperature gradient to ... and wait for it to reach a steady state.

Then, as described in detail in the principles of the present invention, 235UF6 is concentrated in one mixed gas separation tank 41 and diluted in the other mixed gas separation tank 45.

When a steady state is reached or the degree of enrichment reaches a certain level, the two heat diffusion pair valves 54 and 56 are closed, the separated gas recovery valve 53 is opened, and the separated gas is discharged from the separated gas recovery port 43. to recover.

Then, the separated gas recovery valve 53 is closed, and the mixed gas discharge valve 5
7, mixed gas supply valve 52, two heat diffusion pair connection valves 54.5
6 and open the mixed gas supply port 42 to 235UF6-23.
Supply 8UF6 mixed gas and repeat the same process.

The recovered gas enriched with UF6 is further concentrated as a raw material gas in the next similar device, which is similar to the isotope separation using the Crusius separation column shown in FIG.

As mentioned above, in order to enrich uranium-235 by 2.5%, it is necessary to connect approximately 1,200 thermal diffusion pair substrates in series. Approximately 200 pairs of substrates 35 are connected in series.

In this case, it is of course possible to use a cascade connection similar to the isotope separation using the Crusius type separation column shown in FIG. 4, and to connect many devices in parallel at the stage where the concentration ratio is low.

Regarding the processing capacity, as mentioned above, when the temperature gradient is 50 degrees, the thickness Q of the porous material is 5 mm, and the cross-sectional area is 10 cm2, and approximately 1200 heat diffusion pairs are connected in series, the processing capacity is 2.5%. Approximately 15% of UFs concentrated to
m1. / face n can be obtained.

Also, regarding heat diffusion versus energy consumption, when calculating heat loss through porous materials, the thermal conductivity of the porous material is 0.02Kcal 7m, hr, deg.

As, the thickness Q of the porous material is 5 mm, and the cross-sectional area IQ cm
', assuming a temperature gradient of 50 degrees, ~33 cal/min for one heat diffusion pair, ~40K for 1200 pairs
cal/min.

In other words, UF6 enriched to about 2.5%, which can be used as nuclear fuel, is pumped at about 15 m1/min under standard conditions.
Approximately 40 Kcal/min of heat is required to obtain this.

The results from the aforementioned Crusius-type separation column show that ~50 g/day of gas (UF6) for 1.3 times concentration.
It has been reported that a heat consumption of 27 Kcal/sec was obtained.

This is 0.9% at ~2.2ml/min under standard conditions.
obtained UF6 concentrated to a degree of
2. of the present invention corresponds to consuming the amount of heat of Kcal.
5%, converted to 15m1/ruin, ~30000
It becomes Kcal/1rjn.

That is, under the same enrichment conditions, the uranium enrichment according to the present invention requires far less energy consumption than that of a Crusius separation column.

An example of separation of a gas mixture other than UF6 is to obtain oxygen-enriched air by enriching the oxygen in the air using the heat diffusion pair according to the present invention in order to increase combustion efficiency, etc. be able to.

Here, we will roughly estimate the thermal diffusion versus N202 system (air).

Since the N2-0□ system (air) is α-0.02 near room temperature, approximately 20% of the oxygen contained in the air is doubled, about 4
In the case of setting it to 0%, the temperature difference between the high temperature side and the low temperature side is 25 degrees, and if the separation is performed by thermal diffusion in the vicinity of room temperature T = 300, in equation (1), component a is N2, component 02 to obtain Δxb/xb =0.0013.

Thermal diffusion versus substrate-group enrichment rate (oxygen enrichment rate) = 1. o
o13, in order to obtain double enrichment, (1,00
13) Since 534=~2, it is sufficient to connect more than 500 heat diffusion pair substrates in series.

Assuming the same assumption as in the case of the UF6 system, the flow rate is approximately 7.5 ml/njn of air enriched with twice as much oxygen.
(standard state).

The separation devices in this case include the flat heat diffusion pair 31 shown in FIG. 9, the tubular heat diffusion pair 61 and 1 shown in FIG.
The flat heat diffusion pair plate 35 shown in FIG. 1 can be used in the same way as in the case of the UF6 system.

Since air is not corrosive like UF6, the material used for the outer shape and the porous material used as the diffusion medium are UF.

Various types can be used in addition to those used in the case of .

Specifically, the mean free path of gas is 02°N near normal pressure.
Both of them are 7008 ~ SOO, and in addition to the diaphragm of the gas diffusion method in the case of UFe, there are silica gel, Vycor glass (manufactured by Corning), etc. (Porous materials, edited by Ren Kondo, Shihodo, Showa (Published September 5, 1948); (Ryohei Nakane, Chemical Engineering, Vol. 34, No. 4, (1970)).

Regarding the heat source, since both N2.02 and N2.02 exceed the critical point near normal temperature, there are no restrictions like in the case of UF6. For example, use 20°C room temperature water in the low temperature section,
If the cooling is released into the atmosphere and the high-temperature parts are recycled using low-quality energy such as waste hot water from factories such as steel mills or solar heat, operating costs can be made free or extremely low.

As described above, the mixed gas separation device using the heat diffusion couple of the present invention has very high stability and durability since no mechanical equipment is required for the action of the heat diffusion couple, and the device and operation are simple. It can also be applied to special separations such as isotope separation that takes advantage of the characteristics of thermal diffusion couples.

In addition, by increasing the number of connected heat diffusion pairs, it is possible to effectively separate mixed gases even with a temperature difference of several tens of degrees. It enables the use of energy and keeps operating costs low.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams showing a conventional Crusius type separation column. Figure 1 is a conceptual diagram of the Crusius type separation column, Figure 2 is a cross-sectional view of the Crusius type separation column, and Figure 3 is a cross-sectional view of the Crusius type separation column. is also a schematic diagram explaining the action of the Crusius type separation column, No. 4
The figure is an overall view of an isotope separation device using a Crusius type separation column, Figures 5 to 12 are diagrams showing the present invention, and Figure 5 is a schematic principle diagram of the thermal diffusion pair substrate according to the present invention. Figure 6 is a schematic principle diagram illustrating the superposition of the effects of two heat diffusion pairs connected in series according to the present invention;
FIG. 7 is a diagram showing a part of a heat diffusion pair in which a large number of heat diffusion pairs according to the present invention are connected, and FIG. 8 is a diagram showing a part of a heat diffusion pair according to the present invention connected to affected systems R and S. 9 is a side cross-sectional view of a flat heat diffusion pair according to the present invention, FIG. 10 is a cross-sectional view of a tubular heat diffusion pair according to the present invention, and FIG. 11 is a cross-sectional view of a tubular heat diffusion pair according to the present invention. FIG. 12 is a conceptual diagram showing an embodiment of the present invention. 1, 11.21... Heat diffusion versus substrate, M, M,
, M2... Normal gas phase system (Bulk phase), N
, N1. N2...System using porous material as a diffusion medium, 7.17°27...Porous material,
8.18.28.48...High temperature section, 9, 9',
19.29.29', 49...low temperature section, R
, S... Acted system, 31... Flat heat diffusion pair, 35... Flat heat diffusion pair, how many plates, 61...
...Tubular heat diffusion vs. 100...Crusius type separation column.

Claims (1)

[Scope of Claims] 1 Two material systems M and N are formed in which diffused gas molecules are in contact with each other in an exchangeable manner, and at least one of these material systems M,=N has a mean free path of the diffused gas molecules. Using a porous material with pores connected to each other with pore diameters of nearby or smaller size, two pores are used. 1. A device for separating a mixed gas using a heat diffusion pair, characterized in that a heat diffusion pair base is constructed by having one end where the material systems M and N come in contact with each other at a high temperature and the other end at a low temperature. 2 Construct two material systems M and N in which diffused gas molecules are in contact with each other in an exchangeable manner, and at least one of these material systems M and N has a pore diameter near or smaller than the mean free path of the diffused gas molecules. Using a porous material with pores that are connected by Mixed gas separation device.