US3418788A

US3418788A - Process for disposing solid radioactive wastes

Info

Publication number: US3418788A
Application number: US583152A
Authority: US
Inventors: Sugimoto Senichi
Original assignee: NIHON GENSHIRYOKU KENKYUJO
Current assignee: NIHON GENSHIRYOKU KENKYUJO
Priority date: 1962-12-28
Filing date: 1966-09-29
Publication date: 1968-12-31
Anticipated expiration: 1985-12-31
Also published as: GB1035330A; DE1457100A1

Description

PROCESS FOR DISROSING SOLID RADIOACTIVE WASTES I of 6 Sheet Original Filed Dec. 24, 1963 INVENTOR; J [/6 M o ia BY 5 /L Sky/um ATTORNEY.

ec- 19.68 SENICHI SUGIMOTO 3, ,7

' PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24. 1963 Sheet 2 of 6 INVENTOR: .Sf/V/(H/ Sue/Ma 70 BY M. ATTORNEY.

D 1968 ssmcm suemcro 3,418,788

PROCESS FOR DISPQSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24. 1963 Sheet ,1 of 6 INVENTOR: SIM/0W SIG/I70 7' c- 1968 szwcm SUGIMOTO 3,413,788

PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24. 1963 Sheet 5' ore INVENTOR JA//(/// 506 /M0 in:

BY 8M S ATTORNEY.

3 1968 SENICHI SUGIMOTO 3, 18, 88

PROCESS FOR msposme soup RADIOACTIVE WASTES Original Filed Dec 24, 1963 Sheet INVENTOR. f/V/CH/ JUG- lMa 70 BY 5. M gait ATTORNEY United States Patent 3,418,788 PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES Senichi Sugimoto, Tokai-mura, Naka-gun, Ibaragi-ken, Japan, assignor to Nihon Genshiryoku Kenkyujo, Tokyo, Japan, a corporation of Japan Continuation of application Ser. No. 333,063, Dec. 24, 1963. This application Sept. 29, 1966, Ser. No. 583,152 Claims priority, application Japan, Dec. 28, 1962, 37/59,151 3 Claims. (Cl. 558) ABSTRACT OF THE DISCLOSURE A method for disposing of solid radioactive wastes which comprises incineration to effect a reduction in volume, mixing the ash with water to prevent its dispersion into the atmosphere, and filtering the flue gas to remove solid particles therefrom. The filtering involves cyclone separation for the coarser particles, electrical precipitation for finer particles, cloth filtering for the still finer particles, and high performance filtering for the finest particles.

This application is a continuation of my earlier application, Ser. No. 333,063, filed Dec. 24, 1963 and now abandoned.

This invention relates to a process for compacting solid radioactive waste material prior to its ultimate disposal, or more particularly to a process for the compacting by incineration of low level radioactive wastes contained in combustible solid materials.

The radioactive solid wastes, like the radioactive liquid wastes, are waste products inherently produced in connection with nuclear power industries or laboratories working with radioactive materials.

The kind, size, radioactive level or volume of radioactive wastes will vary in characteristics generally in accordance with their sources of radioactivity. As for instance, the nuclear reactor principally produces high level resin or filtered material, but the laboratories handling radio isotopes mostly discharge low level combustible or incombustible wastes and these low level wastes form a quantitatively greater proportion of the waste materials. Therefore, it is desirable to provide an effective treatment to reduce the volume of the radioactive waste products to facilitate their ultimate disposal.

There are two usual processes for the volume reduction or compacting treatment. One is the boiling process and the other is the incineration or burning process and the incineration method comprises the wet system and the dry system.

Generally speaking, the boiling process has the advantages of simplicity and low cost both for installation and operation as compared with the incineration process, but it has a great disadvantage of being low in its volume reduction as compared with the dry incineration process. That is to say, the burning process provides a residual waste volume of /20 to of the original volume, While the boiling process results in a final residual volume of only A1. to /6.

The present invention relates to an improved process of dry incineration which has been proven to be highly efficient and economical. There is employed an electrical precipitator in place of a venturi scrubber which is used in a wet incinerating system. There is further applied a multi-stage cloth filter for removal of the radioactive materials in the flue gas. The precipitator is an electrostatic device in which aluminium foils are used as collecting 3,418,788 Patented Dec. 31, 1968 electrodes being rolled up, after use, into a removable roll together with the collected dust. There is also provided a multi-stage changeable cloth filter comprising a number of stacked filtering frames and the filter cloth, such as cotton flannel is removable together with the dust collected on the surface thereof by rolling up the cloth from one end. Each of these filters can be employed individually as a pre-filter for a high performance filter of the type manufactured by the Cambridge Filter Corporation, Syracuse, N.Y. When the cloth filter is connected the electrical precipitator, the removal of dust from flue gas becomes more effective and sometimes will permit the Cambridge filter to be omitted.

The invention will now be more fully described with reference to the accompanying drawings illustrating a preferred embodiment thereof.

FIG. 1 is a schematic or flow diagram of a complete incinerating system in accordance with the invention.

FIGS. 2-4 illustrate the electrical precipitator.

FIG. 2 is a side elevational view partly shown in section along the line IIII of FIG. 3.

FIG. 3 is a sectional view in elevation taken along the line III-III of FIG. 2.

FIG. 4 is a perspective view of the electrode system of FIGS. 2 and 3.

FIG. 5 is a plan sectional view with the top cover portion omitted.

FIG. 6 is a sectional view in elevation taken along the lines VI-VI of FIG. 5, looking in the direction of the arrows.

FIG. '7 is a sectional side elevational view with side wall omitted at the inlet side.

FIG. 8 is a perspective view of the inner structure.

FIG. 9 is an enlarged cross sectional view showing four of the stacked filtering frames.

As shown in FIG. 1, contaminated combustible wastes consisting of such as papers, cloths, filters and miscellaneous materials are thrown into the incinerating furnace 2 from the inlet 1 and burnt in the furnace by a gas burner 3. The gas burner 3 incinerates at a temperature of about 800 C. The resulting ash is mixed with water supplied by a pipe 5 to a receiving container 22 so as to avoid its dispersion and it is collected in an ash collecting tank 6 through an exhaust pipe 22a, while the surplus water remaining in the ash collecting tank is delivered to the waste water storage tank 8. The flue gas from the furnace 2 passes through a duct 9 to a cyclone 13. Prior to entering the cyclone 13, the flue gas is sprayed and mixed with a dilute solution of NaOH flowing through the pipe 12 and a nozzle 10 from the tank 11. The NaOH solution is eflicient in neutralizing the acidity of the waste gas and it also lowers the temperature of the waste gas by evaporation heat. The solids in the flue gas in the form of small particles are discharged from the bottom of the cyclone 13 into the drain tank 14 through the exhaust pipe 13b together with small quantities of liquid, and then transferred to the waste liquid tank 8 through a pipe 14a. Thus the flue gas which leaves the cyclone '13 passes into a cooler 15 through a duct 13a. A portion of the flue gas becomes liquefied in the cooler and the liquefied material is sent to the drain tank 14, through a pipe 15b. The remaining flue gas is delivered to a reheater 16 through a pipe 15a, where it is raised in temperature slightly and sent into the electrical precipitator 17.

This electrical precipitator 17 is constructed as shown in FIGS. 2, 3 and 4 and its operation is described in described in detail below.

The afore-mentioned flue gas enters the inlet 17a in the upper portion of the precipitator and leaves through the outlet 17b in the lower portion. The discharge electrodes are formed by a series of vertical wires 31 which are horizontally spaced at proper intervals. The upper ends of the wires 31 are suspended from a horizontal rod 34 in the precipitator chamber, to which wires there is applied a voltage of to kv. for operation. Therefore, the support frames 34 are fixed to the

cover flanges

36, 36a in the high tension chamber by

insulators

35, 35a which provide high voltage insulation. Each wire 31 of the discharge electrode is formed by a plurality of thin wires in order to enhance corona discharge therefrom. The lower end of each wire 31 carries and inverted U- shaped tensioning weight 37, the legs of which straddle a horizontal rod 38 to prevent swinging. The rod 38 is supported by insulators 39.

In the precipitator chamber 32, there are, as shown in FIGS. 3 and 4, two horizontally spaced vertical collecting electrodes 41, 41a formed of aluminum or other metallic foil. The collecting electrodes 41, 41a are parallel to the plane of the wires 31 and are spaced equidistantly therefrom. The collecting electrodes 41, 41a are intially rolled up on the

rods

42, 42a located in the upper portion of the precipitator. When the dust deposits sufficiently on the collecting electrodes 41, 41a, these electrodes are progressively rolled up on the

rods

44, 44a located in the lower portion of the precipitator. The electrodes 41, 41a pass over guide bars 33, 33a and are rolled up on the rods 44, 4411 with the dust collecting surface turned inward. The broken lines shown transmission chain interconnecting the guide bars 33, 33a so that they rotate in unison. The dust in the flue gas flowing continuously into this dust collecting chamber 32 is charged by corona discharge emitted from the discharge electrode wires 31 and deposits on the surface of the collecting electrodes of metallic leaves electrostatically. This electrical precipitator can separate dust having a particle size as small as 1,, so that it is capable of removing minimal quantities of radioactive dust. By using aluminum foil of 0.05 mm. thickness for the collecting electrodes 41, 41a, the electrodes may readily be rolled up without breaking. After the dust coated aluminum foils 41, 41a have been progressively taken up on the

bars

44 and 44a to a sufficient extent to provide a predetermined desired minimum outside diameter for the rolled foil, the couplings 47 are disconnected and the bars together with their rolled foils are placed in a suitable cartridge for wastes and stored in a safe place.

The flue gas flowing out the electrical precipitator through the outlet 17b is conducted to the multi-stage cloth filter 18. This filter is provided with a plurality of

inlet pipes

51, 52, 53, 54, 55, through which the flue gas flows and enters stacked filter frames 60, 60a of square shape. The filter frames 60, 60a are formed by rectangular pipes, as shown in FIG. 6, and, when free are supported horizontally in slightly spaced vertical relationship by strong tension springs 57, 57 connected to opposite sides of each of the filter frames. Inside the filter frames 60, 60a, there are provided a series of small holes 61 arranged in horizontal rows, through which the gas enters the central gas chamber 62 defined by the rectangular pipes forming each filter frame 60. From each chamber 62, the gas passes through a filter cloth 63 closely fitted to both upper and lower faces of the filter frame 60 and enters the outlet chambers 64 defined by the frames 60a each disposed above one of the filtering frames 60. The inlet gas chambers 62 and the outlet gas chambers 64 are of the same size and construction. Each of the inlet pipes 51 to 55 communicates with one of the gas chambers 62 and each of the outlet pipes 71 to 75 communicates with an outlet chamber 64. Therefore, the gas delivered from the electrical precipitator 17 flows from the inlet chambers 62 to the outlet chambers 64 passing through the filter cloth 63. The stacked filtering frames 60, 60a are pressed downwardly against a bottom supporting plate 59 by a lever 65 controlled by a hand wheel 66 by a top pressure plate 58. This pressure assures gastightness for the inlet and Outlet chambers.

In order to change the filter cloth, the hand wheel 66 is turned reversely, so that the top pressure plate 58 is released and the filtering frames 60, 60a become supported by suspension springs 57 and the contact between the filter cloth 63 and filtering frames 60, 60a is broken. This permits the filter cloth to pass freely between the

frames

60, 60a so that the used cloth may be rolled up. In this case any material may be chosen for the filter cloth, but preferably it is desirable to use rolls of flannel cloth of standard size usually sold on the market (0.68 m. x 45 m.). This is mounted on the supply roll shaft 76 and passes upwardly in a serpentine configuration around vertically spaced

guide rods

77, 78 provided at the right and left sides, respectively, of the stacked frames as shown in FIG. 7. It is led from beneath the pressure plate 58 to receiving shaft 79 turned by a hand wheel 80. The used filter cloth 63 is rolled up and, together with its rod 79 stored for ultimate disposal.

The gas, after passing through the multi-stage filter 18 is discharge by a blower 20 into the exhaust air pipe 21, as shown in FIG. 1, after passing through a further filter 19 which is a conventional Cambridge Filter.

During this process, the electrical precipitator 17 and the cloth filter 18 work as prefilters for the Cambridge filter 19. By this prefiltering, the useful life of the Cambridge filter 19 becomes longer and its operation is more economical than if the wet system is used.

According to the past operation, it is known that the dust content of the filter 19 is decreased to a greater extent when the cloth filter 18 is connected in series behind the electrical precipitator 17 than when the cloth filter 18 is used separately without the precipitator 17.

It seems to be that the small dust particles in the flue gas become aggregated by the corona discharge, forming larger composite particles which are readily filtered by By the afore-mentioned device, the radioactive waste dust is effectively completely removed from the incinerator flue gas containing radioactive materials. The final dust removal operation using the high performance filter 20 is effective to bring the total removal to 99.9%.

While I have shown and described what I believe to be the best embodiment of my invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. The method for concentrating and accumulating solid radioactive waste material for ultimate disposal which comprises the steps of:

(l) incinerating combustible waste material containing said radioactive waste material in a furnace to produce a coarse ash which falls to the bottom of said furnace and a flue gas containing fly ash;

(2) adding water to said coarse ash;

(3) passing said gas from said furnace to the inlet of a cyclone separator while spraying a dilute solution of sodium hydroxide into said cyclone inlet;

(4) passing said gas through said cyclone;

(5) separating water and fly ash from the gas as its passes through the cyclone;

(6) collecting the separated water and fly ash;

(7) passing the gas from the cyclone to a cooler;

(8) cooling the gas in the cooler to condense at least some of the condensible components of the gas;

(9) collecting the condensed components;

(10) passing the gas from the outlet of the cooler to the inlet of an electrostatic precipitator;

(ll) reheating the gas during the course of its passage from the cooler to the precipitator;

(l2) collecting particles of fly ash on metallic foils within the precipitator;

(13) progressively rolling up the metal foils during the course of said particle collection;

(14) removing the rolled foils for ultimate disposal;

(15) collecting other fly ash particles from the bottom of said precipitator;

(16) passing gas from said precipitator to filter means including a porous filter cloth;

(17) accumulating fly ash particles on said cloth;

(18) progressively winding up said cloth during said accumulating step;

(19) removing the wound up cloth for ultimate disposal;

(20) passing said gas after passage through said cloth from said filter means to high performance filter means; and

(21) discharging said gas after passage through said high performance filter means into the atmosphere.

2. The method according to claim 1, comprising the further step of:

(22) passing the watered coarse ash from the furnace, the water and fly ash from the cyclone, the condensed components from the cooler and the fly ash particles from the precipitator to common storage means.

3. The method according to claim 2, comprising the further steps of:

(23) providing means for selectively by-passing the gas around the precipitator;

(24) providing means for selectively by-passing the gas around the filter means having a filter cloth; and

(25) providing means for selectively by-passing the gas around the high performance filter means.

References Cited UNITED STATES PATENTS 643,022 2/ 1900 Wilson 210-255 964,725 7/ 1910 Whiting 210-227 2,186,501 1/1940 Seligman et al. 210-230 X 2,303,262 11/ 1942 Dumire 2103 87 X 2,522,568 9/1950 Dahlman 2103 87 X 2,535,697 12/1950 Roos 149 X 2,714,849 8/ 1955 Carver 210231 X 2,752,003 6/ 1956 Hersey et al. 55354 X 2,840,454 6/ 1958 Tomlinson, et. al. 2,851,124 9/1958 Howell 557 2,932,399 4/ 1960 Emele 210225 2,958,392 11/ 1960 Dietrich 55-126 2,983,234 5/1961 Reilly -165 3,028,714 4/1962 Mayer 55--116 X 3,261,149 7/1966 Althuser 55354 FOREIGN PATENTS 534,950 3/ 1941 Great Britain.

551,815 3/ 1943 Great Britain.

692,565 6/ 1953 Great Britain.

842,669 7/1960 Great Britain.

63,554 6/ 1941 Norway.

HARRY B. THORNTON, Primary Examiner.

D. TALBERT, Assistant Examiner.

U. S. Cl. X.R.