JPH0146171B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention proposes that the interaction between the filter material and the particles (interaction between the filter material and the particles is defined as adsorption of the particles, The action of retaining these fine particles by penetrating into the filter material, diffusion of the particles within the material, and adhesion retention of the particles by attaching them to the material and keeping them from moving into the gas flow. purifies the flowing gas for substances present as atomic or molecular particles, extending over a length l in the direction of said gas flow and having a hydrodynamic diameter d _eff with respect to said gas flow. The present invention relates to a method for manufacturing a filter. In known filters of the above-mentioned type, the filter material consisting of bulk material, such as granular material, is accommodated in a jacket of the filter through which the gas flows. In designing the filter, for example, the determination of the length l of the filter material to be flowed through is based on known experimental values for the given filter material.
Therefore, in order to obtain a filter suitable for a given operating condition, very expensive and lengthy experiments are required under the given operating conditions for various filter variants. An object of the present invention is to be able to create a filter by taking into account the material properties of the filter material that are standard for the interaction of fine particles that should be maintained for the filter material, as well as its dimensions, and to solve the problems imposed on this filter. The object of the present invention is to provide a method for producing a filter of the above-mentioned type, which is optimally calculated and which in this case does not require carrying out a series of expensive tests in order to adapt the filter to the set requirements. The problem underlying the invention is solved in the method according to the invention in the above-described manner as follows. That is, for a predetermined gas containing particulate matter, a predetermined flow rate of the gas, and a particulate matter retained in the filter material, for a predetermined operating time t of the filter, the particulate flow rate j when entering this filter. The target permeability coefficient is δ(l,t) = j(l,t)/j(o,t), which is equal to the quotient of particulate flow rate j(l,t) when leaving this filter divided by (o,t). equal to the value e ^-De , δ(l,t)=e ^-De , and η ^* √<1, and for De the following relation I This is solved by selecting the filter material so that d eff is satisfied, and setting the length l and hydrodynamic diameter d _eff of the filter material. In the above formula, De: Von der Detken number (newly introduced name) d _eff = 4V ₀ /F: Hydrodynamic diameter in cm l: Length of the filter material in cm V ₀ : cm ³ The volume of the hollow chamber remaining after the filter material is placed inside the jacket within the length l range F: The surface area of the filter material wetted by the gas in cm ² St'=h/V: Second Stanton number h: Mass transfer rate in cm/sec V: Gas flow rate in cm/sec

[Formula] and α: Deposition probability of fine particles on the surface of the filter material (if no activation method is used, partial pressure P
(at 10 ^-10 atmospheres, α is approximately equal to 1) A: Mass number of fine particles T: Surface temperature of filter material shown as 〓 ^* =〓 {h + (1 - β) α ^* / α ^* + h} sec ^-1 It is

Desorption constant expressed by [Formula] ω ₀ = ~1.308×10 ¹¹ Thebeian frequency expressed in T sec ^-1 Q: Desorption energy expressed in Cal/Mol R: Universal gas constant expressed in Cal/(°) Mol λ: sec ^-1 is the decay constant of the radioactive substance I ₁ (x): Modified Betzell function ζ=4l/d _eff・St'hα ^* 〓β/(α ^* +h) ² sec ^-1 1-β: Permeation coefficient: Probability of irreversibly binding particulates t: Filter operating time

[Formula]: Unit scale step function

[Formula] and D: Diffusion coefficient of filter material for fine particles in cm ² /sec η = (1-β) α ^*・N _G /φ∞ cm/sec, N _G : Gas in Atome/cm ³ Density of fine particles φ∞: Means the maximum number of fine particles expressed in Atome/cm ³ that the expected filter material can absorb in a unit volume. As mentioned above, the method according to the invention is used under the following conditions: (1) gases containing particulate matter to be retained; (2) Used for particulate matter to be retained. (3) Used with desired volume throughput. Therefore, the velocity and mass transfer rate are given in advance. That is, the second Stanton number St' is known. (4) The operating time of the filter is given in advance.
That is, t is known. (5) The constant effective value of the filter is as desired. That is, the permeability coefficient δ(l,t) (the quotient of the particle rate leaving the filter material divided by the particle rate entering the filter material) is known. This is done under the condition that. The mass transfer coefficient h follows the heat-mass-transport analogy, i.e. the known data on heat transfer within the material and the heat transport within the material are analogous to the calculation of the mass transfer coefficient and the tables known in this regard are Calculated based on When it is necessary to make a filter to be used to purify gas containing radioactive particles, the following relationship holds: √>n If the condition η ^* √<1 is satisfied for all values of t, and The relational expression always holds true. The method according to the invention makes it possible to produce filters that can be adapted to suitably set conditions and thus also to the particularities of a certain device. In general, the above-mentioned values are then set in such a way that the Von der Detken number is as large as possible or at least that which is necessary to obtain the desired value for a constant transmission coefficient. A filter that satisfies the condition δ(l,t)=e ^-De has the desired filter effect and the desired transmission coefficient δ(l,t)
A filter that does not satisfy this condition will retain some substance, but it will be so small that it will not be able to achieve the intended purpose. That is, the quality of the filter is poor. On the basis of the above-mentioned mathematical relations, it is also advantageous to carry out testing of filters for large installations on a small model scale in order to save costs. The two filters have the same transmission coefficient δ, i.e. the same Von der Detken number De.
are equivalent with respect to the deposition or filtering action. A simple filter modification, for example, starting from a straight piece of pipe material through which the gas to be purified can flow, also makes it possible to obtain the necessary parameter values for the manufacture of a filter for use in large installations. At this time, this simple filter is placed under the influence of various operating conditions, and the above parameter values are obtained by the relational expressions. In the process according to the invention, the diffusion of these particles into the filter material is also taken into account. Therefore 400℃
Advantageously, filters can be made that can operate at temperatures ranging from about 1000°C to about 1000°C. On the other hand, in the prior art, when making a filter, only the desorption and adsorption of fine particles on the surface of the filter material or the chemical reaction of the fine particles with the surface of the filter material are taken into account. Efforts were therefore made to use as large a surface as possible.
As a result, many known filters lack the necessary efficiency in the temperature range above 400°C. This is because the temperature of the filter must be maintained at a low temperature by the cooling effect. In order to increase the activity of these known filters, a larger number of filters are connected one after the other, resulting in bulky purification devices. A preferred variant of the production method according to the invention provides that during the desired operating time t for the material selected as the filter material used for the microparticles, adsorption-desorption of the microparticles on the surface of the filter material is possible. - As filter material for filters at temperatures below about 400 °C where equilibrium has not been reached (ignoring both decay and desorption of matter), use the equations (a) 2√≪1 and (λ+〓 ^* )xt≪1. Alternatively, use a material that satisfies the formula (b) λ≫〓 ^* for radioactive substances (assuming that decay is more dominant than desorption of the substance). Under these assumptions, when using a filter that purifies gas at low temperatures, for example, the Von der Detken number can be simplified to the following relational expression to obtain a desired value. De=4l/d _eff・St′・α ^* /α ^* +h … If condition (b) is satisfied, then condition (a)
holds true for all values of t, and a filter created according to the relational expression can be operated indefinitely in terms of time. According to the relational expression, a material with a sufficient deposition probability for the fine particles to be retained is used, and the dimensions of the filter are determined so that the desired transmission coefficient δ is either as small as possible or equal to a predetermined value. It is set so that Another preferred variant of the method according to the invention provides that for the material selected as the filter material used for the microparticles, during a predetermined operating time t, the deposition of the microparticles on the surface of the filter material is adsorption-desorption.
For filters in the temperature range above about 600°C where equilibrium is reached, the filter material should have the highest possible permeability coefficient (1-β) and the following formula: 2√≫1 and (λ+〓 ^* ) t>2√ If we use a material such that ^〓
can be simplified to the following relational expression to obtain the desired value. De=4l/d _eff・St′(1−β)・α ^* /h+(1−
β・α ^* … In the case of this variant of the filter according to the invention,
Diffusion of particulates into the filter material is fully exploited. Even in this case, the dimensions of the filter must be set so that De is as large as possible or the transmission coefficient δ is a predetermined value. Depending on the choice of filter material and filter dimensions, such filters have a high degree of activity even at high temperatures of up to 1000° C., respectively. A further highly preferred variant of the method according to the invention is as follows. That is, in order to obtain as long an operating time t as possible with a low transmission coefficient δ, the thickness ε of this filter material is determined according to the relational expression for radioactive substances. and for non-radioactive substances, the relational expression ε≫√ (where D means the diffusion coefficient for fine particles in the filter material) holds true. Particularly in the case of the above-mentioned modification method, which is different from conventional manufacturing methods, not only the adsorption/desorption behavior of fine particles on the surface of the filter material but also the diffusion of fine particles into the filter material are affected. Used in filter manufacturing.
Whereas in the case of known filters the service life of the filter depends exponentially on the reciprocal of the temperature, in the present invention the selection of a filter material with a sufficient thickness ε ensures that the filter material remains stable even at particularly high temperatures. Since the diffusion effect of fine particles inward is fully utilized, a filter having a long operating life (time) t can be manufactured. In the first embodiment described below, attached drawings Nos. 1 and 2
The manufacture of a filter made of a given material and possible variations of the design data for various operating conditions will be explained with reference to the diagram shown in the figure. In the second and third examples, the results of experimental research using a large number of filters and the values obtained according to the relational expression regarding the transmission coefficient δ are displayed in comparison. Further, in the fourth to sixth embodiments, design data for various operating conditions necessary for manufacturing this filter are shown. First Example In order to obtain design data for manufacturing a filter consisting of a large number of pipes arranged parallel to each other, the Huon der Detzken number De is calculated from the relational expression, and from De the transmission coefficient δ is calculated for a single pipe. It is calculated back according to the mass flow m of gas flowing through the pipe. One pipe used for this calculation has length l=
At 800cm, the diameter d=1cm. The throughput range considered is from 10 ^-2 to 12 g/sec. The gas temperature and the wall temperature of one pipe are set at 950°C and the gas pressure P = 40 bar. Cesium-137 atoms are considered to be particulates that should be purified from helium. In that case, the permeability coefficient 1-β=0.7‰ and 1
We assume two different wall materials with −β=100%. For Cs−137, a value of 0.7‰ is characteristic of a material with a face-centered cubic lattice, whereas a permeability coefficient of 100% means that the material used is a perfect “diffuser.” It means that. For the schematic diagram of the characteristic curve of this filter, the mass throughput is varied according to the parameter K, which is determined by the following relation. m〓=K×m〓 _0Here , m〓 ₀ is a provisional standard mass throughput. Since a linear relationship is established between the Reynolds number Re and the mass throughput m〓, the following relational expression Re=K×Re ₀ (In the formula, Re ₀ is the provisional standard mass throughput _m〓 ) holds true. As can be seen from the graphs in Figures 1 and 2 of the attached drawings, the filter characteristic curve for the parameter K has a jump or discontinuity for a constant value of K = 0.077 (the difference between turbulent flow and laminar flow is ). That is, the above values for K correspond approximately to the values for the Reynolds number of Re=2300. The above-mentioned discontinuity is constituted by the fact that the shearwood number and thus the mass transfer rate h or the Staunton number St' have a discontinuity similar to the transition from turbulent to laminar flow. The height of the above leap is
It depends on its geometry, ie the ratio l/d, and on the materials used. Furthermore, it is possible to read from the graph the flow range in which the transmission coefficient δ reaches its minimum value, the Von der Detken number increases accordingly, and therefore the filter efficiency reaches its maximum value. Generally, as can be seen from this graph, the above minimum or maximum value is found in the region of completely laminar flow or in the transition region of the Reynolds number slightly above 2,300 and approximately between 2,500 and 5,000. When constructing a filter, for example, if the filter is a pipe bundle, the gas flows through the pipes on the outside and on the inside, making it possible to apply both areas simultaneously. In the examples described above, the absolute values shown in the graphs are valid only for the case in question, but the filter characteristic curves shown therein also apply to other operating conditions and to other operating conditions with this filter material. This makes it possible to qualitatively describe other geometric arrangements. The desired absolute value of the efficiency of this filter can easily be achieved by providing a suitable number of parallel pipes. 2nd Example In order to test the efficiency of a filter made of a simple straight pipe material, the fission products Cs−
A helium gas stream containing 137, Cs-134 and Ag-110m was guided in two independent tests through a piece of pipe material each consisting of 99.5% titanium and exited the filter. A complete filter was connected to the back of the single pipe to check the amount of fission products coming out. The content of helium fission products in both tests was different.
The above single pipe material has a length of 2730mm and an outer diameter of 24.5mm.
mm and wall thickness were 1.65 mm. The temperature of the helium entering this filter is 825°C in the first example, and 825°C in the second example.
In the example, the temperature was 750°C, and the temperature coming out of this filter was 210°C in each case. The temperature of the wall of this pipe material was stable during operation and could therefore be measured successfully. The helium flow during operation of this filter is 15N
It was adjusted to achieve a throughput of m ³ /hr. The operating time was 785 hours for the first test, and the operating time for the second test was 785 hours.
In the case of the test, it was 1029 hours. To calculate the transmission coefficient δ of this film and therefore the efficiency of this filter, the following values were substituted into the relation: For Cs-137: 1-β = 0.2‰; Q = 38 Kcal/Mol Cs-134 For Ag-110m: 1-β = 0.04‰; Q = 50 Kcal/Mol and ω ₀ = 1.308×10 ¹¹ T sec ^-1 . In order to obtain the temperature gradient of the pipe material, the filter was divided into a number of parts for calculation according to the equations. With the calculated permeability coefficient δ, an integrated activity value in μCi was obtained for the fission products arriving through this filter during the operating time described above and was compared with the value measured with a complete filter. The calculated values and experimental values are compared with each other below. 1st test Calculated value Experimental value Cs−137 1.00 1.20 Cs−134 0.79 0.84 Ag−110m 11.4 11.7 2nd test Calculated value Experimental value Cs−137 0.52 0.59 Cs−134 1.6 1.7 Ag−110m 5.1 5.6 3rd example 2nd Corresponding to the tests described in the examples, a filter consisting of a pipe made of stainless steel was tested. The temperature of the gas entering this filter is 625°C in both cases, and the temperature of the gas exiting from this filter is 210°C, and the operating time of this filter is:
They were 818 hours and 790 hours. To calculate the transmission coefficient δ, the following values were substituted into the relational expression; 1-β = 0.7‰ for Cs-137; Q = 45Kcal/Mol 1-β = 0.33‰ for Cs-134; Q = 45Kcal/ 1-β = 0.2‰ for Mol Ag-110m; Q = 28 Kcal/Mol and ω ₀ = 1.308×10 ¹¹ T sec ^-1 . The following results were obtained; 1st test Calculated value Experimental value Cs−137 2.1 2.2 Cs−134 1.07 0.96 Ag−110m 6.2 6.5 2nd test Calculated value Experimental value Cs−137 1.92 2.1 Cs−133 1.03 1.1 Ag−110m 3.26 3.51 Fourth Example The design data for the filter shown in Figures 3 and 4 and consisting of a number of parallel pipes was obtained for the given operating conditions; as can be seen from Figure 3. This filter consists of a number of pipes 1 arranged in parallel and at the same distance from each other, said pipes being arranged inside a jacket 2 surrounding the hollow space of the filter. The outside diameter of the individual pipes of this pipe bundle is da, the inside diameter of the pipes of this pipe bundle is di, the length of this pipe is l, and the inside diameter of the jacket is Di. As can also be seen from FIGS. 3 and 4, the pipes of this filter allow the gas to be purified to flow through it on the inside and around it on the outside. The gases to be purified are fission products Cs-137 and Ag.
-110m of helium. The predetermined operating conditions are as follows: Mass throughput of helium: m = 111.25Kg/sec Temperature of helium when entering the filter: T =
950℃ Helium pressure: P = 40 bar Specified operating time: t = 30 years The material used for the above pipe is a heat-resistant steel with a body-centered cubic structure or a face-centered cubic structure such as Incoloy 802 and Inconel 625. It was used. For the above mentioned materials the values are 1-β=0.7‰ for Cs-137 and 1-β=0.7‰ for Ag-110m.
It was 0.2‰. T = 950°C and P = 40 bar were applied for the binary diffusion coefficients quoted to calculate the mass transfer rate h. D _Cs −He=0.146cm ² /sec D _Ag −He=0.272cm ² /sec Von der Detken number De for h and St′
The values required to calculate
Trausfer) Volume 14, pages 1235-1259.
In the above case, the following conditions 2√≫1 and (λ+〓
^* ) t > 2√ and 〓 ^* ≫ λ,
The design data for this filter was calculated according to the relational expression. The volume of this filter should not exceed ^40m3 ,
The pressure drop is not higher than 0.1 bar and the permeability coefficient δ for silver is between 6×10 ^-4 and 8.8×10 ^-3 and the permeability coefficient δ for cesium is 12×10 ^-5
The design data shown in the table ^below was calculated for this filter on the assumption that In that case di and da and Di
The values for and l are shown in cm, where N is the number of parallel pipes of this filter. In addition to these design data, the pressure drop values within this filter in bars are shown as well as the values for the respective permeability coefficients. The values for △P are from VDI-Heat Table and Bergamon Publishing Int.J.Heat.Mass Trausfer.
Calculated according to Vol. 14, pp. 1235-1259.

[Table] Fifth Example Same operating conditions as the fourth example, but
However, we obtained design data for a filter consisting of a number of pipes installed in parallel to each other for a gas inlet temperature of 300℃. 15MoO ₃ ferrite steel was used as the pipe material for the above filter. For the above materials, the permeation coefficient, desorption energy Q and binary diffusion coefficient have the following values: That is, 1-β=1.2‰ for Cs-137; D _Cs −He=0.039cm ² /sec Q=65Kcal/Mol and ω ₀ =1.308×10 ¹¹ T sec ^-1 1-β=0.3‰ for Ag-110m D _Ag −He=0.072cm ² /sec Q=52Kcal/Mol and ω ₀ =1.308×10 ¹¹ T sec ^-1 In the above case, the following relational expressions 2√≪1 and (λ+〓 ^* )t≪1 are satisfied. Then, design data regarding this filter was calculated according to the relational expression. The volume of this filter should not exceed 17.2 m ³ , the pressure drop ΔP should not be higher than 0.11 bar, and the permeability coefficient δ for cesium should be 1.06 × 10 ^-4
The following design data was obtained based on the assumption that the transmission coefficient δ for silver is 5.61×10 ^-6 : N=10 ⁵ pieces Di=230cm di=0.3cm l=350cm da=0.55 cm Pressure drop △P = 0.105 bar. Sixth Example With respect to the operating conditions shown for the fifth example, design data were obtained for a filter consisting of a number of bars placed in a jacket, parallel to each other and at the same distance, similar to the pipe described above. The same materials as shown for Example 5 were then used, but with the following values; for Cs-137 the transmission coefficient δ = 1.62 x 10 ^-3 and for Ag-110m Regarding the permeability coefficient δ = 4.4 × 10 ^-5 and assuming that the volume of this filter is 10.5 m ³ and the pressure drop is △P 0.125 bar, the following results are obtained: N = 1.2 × 10 ⁵ pieces l=250cm da=0.5cm Di=230cm The pressure drop was ΔP=0.124 bar. When the material is the same as in the fifth embodiment and the values of N, da, and Di are the same, the transmission coefficient δ for Cs-137 is 5.84×10 ^-3 and the transmission coefficient δ for Ag-110m is 3, 272× 10 ^-4 , length l = 200 cm and ΔP = 0.11 bar.

[Brief explanation of drawings]

Figure 1 graphs the Von der Detken number De as a function of mass throughput or Reynolds number; Figure 2 graphs the permeability coefficient δ as a function of mass throughput or Reynolds number; The figures show a cross section through a filter consisting of a bundle of a number of parallel pipes, and FIG. 4 shows a longitudinal section through the filter according to FIG. 1: pipe, 2: jacket, da: outside diameter of pipe, di: inside diameter of pipe, l: length of pipe,
Di: Inner diameter of jacket.

Claims (1)

[Scope of Claims] 1. In a hollow chamber provided for the gas to flow through and surrounded by a gas-tight jacket, a filter material which acts to retain the fine particles by interaction with the fine particles is used to control the flow of the gas. A method for manufacturing a filter for purifying a flowing gas for substances present as atomic or molecular particles extending over a length l in the direction and having a hydrodynamic diameter d _eff with respect to the flow of this gas, comprising: For a given gas containing a substance, a given flow rate of that gas, and particulate matter retained in the filter material, for a given operating time t of the filter, the particulate flow rate j(o, t ) is the permeability coefficient equal to the quotient of particulate flow rate j (l, t) when exiting from this filter divided by δ (l, t) = j (l, t) / j (o, t), and the value e is set as the target value. ^-De , δ(l,t)=e ^-De , and η ^* √<1, and for De the following relational expression (In the above formula, De: Von der Detken number (newly introduced name) d _eff = 4V ₀ /F: Hydrodynamic diameter in cm l: Length of the filter material in cm V ₀ ; cm Volume of the hollow chamber remaining after placing the filter material inside the jacket within the length l range shown by ³ F: Surface area of the filter material wetted by the gas shown in cm ² St'=h/V: Second Stanton number h : Mass transfer rate expressed in cm/sec V: Gas flow rate expressed in cm/sec [Formula] α: Deposition probability of fine particles on the surface of filter material (if no activation method is performed, partial pressure P
(at 10 ^-10 atmospheres, α is approximately equal to 1) A: Mass number of fine particles T: Surface temperature of filter material shown as 〓 ^* =〓 {h + (1 - β) α ^* / α ^* + h} sec ^-1 The desorption constant ω ₀ = ~1.308×10 ¹¹ T sec ^-1 Q: Desorption energy expressed in Cal/Mol R: Universal gas constant λ expressed in Cal/(°)Mol : Decay constant of radioactive substance expressed in sec ^-1 I ₁ (x): Modified Bessel function ζ=4l/d _eff・St'hα ^* 〓β/(α ^* +h) ² sec ^-1 1-β: Penetration Coefficient: Probability of irreversibly binding fine particles t: Filter operating time [Formula] Unit step function [Formula] D: Diffusion coefficient of filter material for fine particles expressed in cm ² /sec η = (1 - β) α ^*・N _G /φ∞cm/sec where N _G : Density of gas particles expressed in Atome/cm ³ φ∞: Maximum number of particles expressed in Atome/cm ³ that the expected filter material can absorb in a unit volume It means. ) A method for manufacturing a filter, characterized in that a filter material is selected so that the following is satisfied, and a length l and a hydrodynamic diameter d _eff of the filter material are set. 2. Adsorption for the material selected as filter material for the particulates during a given operating time t, regarding the adsorption of the particulates on the surface of this filter material.
For filters that do not reach desorption equilibrium, the filter material should be a material in which the relations 2√≪1 and (λ+〓 ^* )t≪1 hold, or for radioactive substances, the relation λ≫〓 ^* holds true. A method according to claim 1, characterized in that: 3. During a predetermined operating time t, the filter material is adjusted as much as possible for the filter to reach an adsorption-desorption equilibrium for the adsorption of the particles on the surface of this filter material with respect to the material selected as the filter material for the particles. Claim 1, characterized in that the material has a large permeability coefficient and the relational expressions 2√≫1 and (λ+〓 ^* ) t>2√ and 〓 ^* ≫1 hold true. The method described in. 4 In order to obtain as long an operating time t as possible with a constant low transmission coefficient, the relational expression for radioactive substances regarding the thickness ε of the filter material is 3. The method according to claim 1, wherein the relational expression ε≫√ holds true for non-radioactive substances.