DE3117357A1 - PASSIVE SELF-CLEANING AEROSOL SCRUBBER DEVICE - Google Patents

Description

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United States Department of Energy, Washington, D.C, V.St.A.

Passive self-cleaning aerosol scrubber

The invention relates generally to aerosol scrubbers and particularly to aerosol scrubbers which have a porous bed in combination with a Use scrubber fluid.

The present invention arose in connection with the design of an air cleaning system for use in Enclosure buildings and facilities for nuclear reactors. The purpose of the special air purification system was to limit the release of aerosol particles and absorbable gases including radioactive materials, namely from the containment facilities during postulated major accidents. A system was designed which in the passive state requires no energy and no active energy either, with the exception of pressurization the one to be cleaned, i.e. the scrubber device to be exposed, gas flow. In its passive state, the system is instantly available for use.

The system described combines both desirable features a scrubber device of the tub type as well as a sand or gravel filter in a scrubber device of the hybrid type.

A tub-type scrubber consists of a gas inlet duct extending downward into a container or Tub protrudes from liquid. Gas flows from the inlet port into the liquid pan / bubbles and flows then up through the liquid supply in the tub. Aerosols are carried out from the gas in the bubbles removed various forces, which in general strongly depend on the bubble diameter. Although at the exit of the gas duct Devices to reduce the size of the bubbles can be added, so these systems typically produce iodo relatively large gas bubbles and are subject to clogging by aerosol deposition. The aerosol removal is accordingly low. The tub-type scrubbers, however, have the desirable feature namely that they are able to collect a large amount of Process material when it is removed from the gas stream.

Sand or gravel filters are constructed using layers of graded granular material, the largest being the largest Granular sizes are usually arranged at the bottom of the filter bed, while subsequent layers are smaller granular materials starting from the bottom layer are arranged at the top. The aerosol-containing gas runs from the bottom to the top of the bed. Aerosol gets through Inertia, diffusion, interception and gravity forces removed. Because of the layers of fine granules on the upper ones In parts of such a bed, the sand or gravel filters show high aerosol removal efficiency. Because, however, a such a bed has a limited volume of voids, The filter can only process a small amount of collected material per unit volume of the filter and must then replaced, rinsed or otherwise cleaned.

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The hybrid scrubber device described consists of a porous bed, which is at least partially within is submerged in a tub (a quantity of liquid). The porous bed can be granular material such as for example sand or gravel. The liquid can be water. A pressurized stream of air or another gas loaded with Aersol is directed to the bottom of the bed. He spreads himself over the bed away and flows up through the irregular (irregular) channels formed in the spaces between the beds. Aerosol is made from the gas by interception, diffusion and inertial forces as well as particle growth and deposition removed. The porous bed itself is continuously cleaned by the liquid trapped with the gas. The cleaned Gas emerges from the top of the porous bed.

A passive self-cleaning aerosol scrubber for removing particulate matter from a stream of pressurized gas uses a liquid-tight enclosure containing a quantity of liquid which partially fills the interior. A container is arranged within the envelope or enclosure. The container has gas impermeable side walls extending from a lower end which is immersed in the liquid is; these side walls extend to an upper end. The top of the container and the porous bed inside it can be arranged below, on the same level with or above the liquid surface. A porous one Bed is surrounded by the gas-impermeable side walls of the container. The porous bed extends vertically above from a submerged floor level, namely mxt spaced above the lower end of the side walls of the container. A gas supply line extends into the enclosure and has a discharge port on a submerged one Place below the porous bed to remove pressurized gas and particulate matter to the bottom

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of the porous bed. The top of the porous bed is open to allow flow from within Gas trapped liquid is returned from inside the container becomes the amount of liquid remaining within the enclosure. That subject to the scrubber action Gas can escape through the top of the porous bed.

A first object of the invention is to improve the rubber mass collecting ability a tub scrubber (liquid volume scrubber) combine with the removal efficiency of a wetted porous filter. The result is a highly efficient filter system with a high particle mass collection capacity. Another object of the invention is to provide a high capacity aerosol scrubber that remains in a passive state for months or years and, if necessary, instantaneously is usable. Another object of the invention is to provide a scrubbing device which is shown in FIG in its passive state has no energy requirements whatsoever. When completely enclosed, the device does no maintenance required until after it has been used. Another object of the invention is to provide a scrubber device which, in use has low energy requirements. The scrubber device according to the invention is solely by the gas pressure of the to cleaning power is activated and does not require any external pumps or controls. More benefits, goals, and details the invention emerges in particular from the description of exemplary embodiments with reference to the drawing; in the Drawing is shown a preferred embodiment; in the drawing shows:

1 shows a schematic cross section through the scrubber device;

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2 shows a modified scrubber device.

The scrubber device according to the invention basically exists from a porous bed, which is at least partially submerged in a tub with liquid (amount of liquid) is. An incoming gas stream is directed to the port of the bed. Upward gas flow is caused by gas is withdrawn from the outlet channel at the top of the device. Aerosol-laden gas runs down into the inlet duct and up through the irregular or irregular porous channels in the bed. Fluid is through the Bed cleaned due to the difference in density of the liquid outside the bed and the effective density the gas-liquid mixture within the bed. This cleaning action continuously washes the porous bed off the accumulated aerosol.

As shown in the drawing, has a practical embodiment a liquid-tight enclosure or envelope 10, with a bottom wall 11 and thus connected upright side walls 12, thereby forming an inner liquid tank. The tank is preferably completely enclosed and is completed by a top wall 13, but can be open at the top, as follows will be described.

The amount of liquid 14 is contained within the enclosure 10. The liquid can be water or any other desired liquid that is physically stable and compatible with the design and use of the filter. The liquid partially fills the inner liquid tank formed by the enclosure 10, up to a liquid surface height, denoted by reference numeral 15.

An open ended container 16 is positioned within enclosure 10. He has gas-impermeable upright Side walls 17, which vjn a lower end 18 to a

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extend upper end '20 towards. The bottom of the container 16 is immersed in the liquid 14. The upper end is either adjacent to, above or below the at

15 liquid level shown.

A porous bed 21 of gravel or other filter material is secured by the gas impermeable side walls 17 of the container

16 surrounded. The bed 21 extends vertically upward within the container 16 from a floor location, which with Distance above the lower end 18 of the gas-impermeable upright side walls 17 of the container 16 is arranged. This location is defined by a transverse porous or perforated plate 22 that extends over the side walls extends towards. In the preferred exemplary embodiment shown, approximately half of the vertical height is the porous Bed 21 is arranged below the height of the liquid surface at 15 and is therefore submerged in the liquid 14.

An inlet cap 23 is provided to allow a flow from under Pressurized gas and particulate! Material or aerosol to a submerged point vertically below the to conduct porous bed 21. This is in the form of a vertical tube made of a gas impermeable material, 4 which extends through the center of the porous bed 21. The inlet channel 23 ends at an open one Bottom end 24 positioned at a level between the bottom of the porous bed 21 and the lower end 18 of the gas impermeable Container side walls 17.

The upper end of the porous bed 21 is closed with a transverse porous or perforated plate 25 shown. Although such a plate is useful, it is not always necessary to enclose the bed 21 to keep. The upper end of the bed 21 is transversely open to liquid flow to thereby allow that liquid trapped with the gas stream by gravity over the sides of the container 16 to the liquid

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is returned within the inner liquid tank provided by the enclosure 10.

Various materials can be used within the porous bed 21. The porous material should be in the Liquid not be soluble. It could be natural or artificial sand or gravel, fibrous materials come into question or other packing materials, which are usually used for both dry and wet filters be used.

An outlet channel 26 is open through the enclosure 10, at a level above the liquid surface at 15. The channel 26 emits the gas stream after it has passed through the porous bed 21.

The presence of the gas within the container 16 surrounding the porous bed 21 reduces the apparent Density of the liquid 14 within the bed boundaries. As the gas flow through bed 21 increases, it flows as a result Liquid from within the enclosure 10 into the bottom of the bed, moves upward, and subsequently flows over the top. The aerosol collected within the porous bed 21 thereby becomes continuous therefrom washed out. This passive self-cleaning action of the porous bed 21 is one of the new features of this device.

The device shown effectively removes aerosols from the gas stream. The efficiency of aerosol removal can be adjusted by changing the depth of the porous bed 21 and the thickness of the packing materials of the bed 21 and the speed of the inlet pipe 23 and bed 21 directed gas stream modified. The only limit on the amount of material collected, which can be accommodated in the device is the volume of the amount of liquid (liquid tub) 14 and the

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Solubility of the removed aerosol materials within the liquid. Another limit is the volume of non-dissolvable particles housed within the enclosure 10 can be.

The scrubber is a three-phase liquid scrubber. The solid phase is firmly in place and has the porous material within the bed 21 on. The gas and liquid phases flow countercurrently through bed 21. Because of the complexity of one Such systems have been tried to develop both the concept and the scrubber performance to eat.

A scrubber prototype was constructed essentially as shown in FIG. The bed was 0.30 m in diameter, 0.61 m deep and packed with basalt rock, sieved to sizes between +0.95 cm and -1.27 cm. The cross-sectional area available for gas flow was 0.069 m ² . The vacancy rate was 0.45 + 0.50.

The granular basalt rock used in these experiments, is characterized by the fact that it has no smooth sides. It was sifted into the three segments by hand. It was held between horizontal plates 22 and 25 which run across the container side walls 17. The examined Plates 22 and 25 were made of solid flat sheet materials with openings formed therein, which had a staggered pattern and had a central opening, to receive the inlet pipe 23. A second type of support plate that can be used in this device could be made of a suitable screen material.

It should be noted that the lower end 18 of the container side walls 17 is equipped with openings 27. They are at a distance above the bottom wall 11 of the enclosure U arranged to recapture insoluble solids

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to prevent within the liquid ^"1 · and gas stream which moves in the porous bed 21st The openings 27 permit the flow of the fluid 14 below the porous bed 21. The area between the apertures 27 and the bottom of the bed 21 forms a surrounding Jacket within which the incoming gas collects briefly / before it moves up through the porous bed 21.

As can be seen from Fig. 1, the horizontal cross-sectional area of the container 16 is much smaller than the inner one horizontal cross-sectional area within the enclosure 10. The cross-sectional area of the container 16 is a function of the • Volume of gas that is directed upwards through the BetL 21 got to. The cross-sectional area and depth of the liquid 14 within of the enclosure 10 is a function of the storage capacity required to handle the removed from the gas stream Aerosol is required.

The upright side walls 12 of the enclosure 10 are transversely to the outside at a distance Arranged over the side walls 17 of the container 16. This allows the liquid to flow into the container 16 from all sides through the openings 27 and also allows the emerging from the container 16 Liquid can overflow around its entire circumference.

The special embodiment of the scrubber device employs cylindrical side walls around the container 16, vertically arranged and centered about a vertical one inner axis running along the center of the inlet channel 23 shown. The channel 23 was considered a straight line vertical tube constructed which was coaxially centered within bed 21 along the vertical axis of the container.

A number of experiments were carried out using different

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The sodium compound aerosols are designed to improve acrosol removal efficiency to be measured using water as the washing liquid inside the enclosure Table I gives the test parameters for a gas velocity based on a bed cross-sectional area of

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0.069 m. The flow rate of the gas stream was varied during each test and aerosol samples were taken from both inlet channel 23 and outlet channel 26 periodically. A conventional dry filter was placed downstream of the scrubber in outlet channel 26 and was leached and analyzed for sodium after each test.

The results of the tests are summarized in Table II. The overall efficiency was calculated using the total mass of the sodium collected in the scrubber solution and on the fiber filter. The average efficiency was calculated using the arithmetic mean of the individual efficiencies, determined from instantaneous gas concentration measurements. These data indicate that changing the granular sizes within bed 21 had no effect exercised the ability to collect. Reducing bed height by a factor of 2 increased aerosol penetration by one Factor 7.

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Table -I Test conditions

Ver Aerosol Aerosol Attempt search source art duration (h) 1 Spray fire Na ₂ CO ₃ 9.7 2 Mass fire Na ₂ O ₂ 4.3 3 Mass fire Na ₂ O ₂ 2.7 4th Mass fire Na ₂ O ₂ 4.0 5 Spray fire NaOH 24

Superficial gas velocity (m / min-

2 - 30 1, 2 - 22 2 - 27 0, 8th - 20th 1 7th - 27

Table II

Test results

Ver
search total
effect
Degree By-
sectional
efficiency Collected
Na mass
(Gram) Examined
parameter 1 99.8 99.18 748 Aerosol type 2 99.8 99.97 590 Aerosol type 3 98.6 98.78 401 Diminished bed
height (0.305 m) 4th 99.8 99.97 566 Reduced
Pack size
(0.64 - 0.95 cm) 5 99.996 99.998 4,517 Added
Fiber element

In the last experiment given in Tables I and II, a polypropylene fiber element was added to the scrubber to remove the Eliminate fog entrainment and improve small particle capture. The fiber unit had an outside diameter of 0.61 m, an inner diameter of 0.46 m and one

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Length of 0.61 m. The unit was placed directly above the porous bed 21. The gas exiting bed 21 flowed upward into the central zone of the fiber unit and then horizontally through the fiber materials. In the one leaving the porous bed 21 Water droplets trapped in gas continuously washed the collected aerosol from the fiber unit. The special one in the The test mentioned in Tables I and II was performed using a NaOH aerosol running. The pressure drop across the fiber unit remained constant throughout the test, indicating that the Fibers in the fiber unit have been sufficiently washed by the captured water. This demonstrated the increased removal efficiency achieved by combining the hybrid scrubber with an available fiber filter is attainable. A schematic representation of this modified scrubber unit is shown in FIG. The fiber unit is indicated at 28. All other elements of the device are as previously described and are replaced by those previously illustrated reference numerals.

Hydraulic studies were carried out without aerosols for different bed configurations to determine the pressure drop, the water circulation rate and measure the water level effects. The pressure drop across the porous bed 21 has been found to be independent of the gas flow rate for velocities between the gas surface velocities of 0.002 to 0.507 m / exposed. The pressure drop through the device depends primarily on the static liquid level at the submerged one open bottom end 24 of the inlet channel 23 from. The internal water circulation rate has been found to be a function the gas flow rate, bed depth, granular size, and inlet channel submersion size. When checking the water flow rate depending on the gas flow rate for various Bed parameters using granular rock bed has been found to decrease with water

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Speed was pumped when the water level dropped, '

namely until the level is about half the bed depth!

had sunk. The test parameter that has the greatest \

Influence on the water flow rate was the immersion depth of the inlet port 23.

The present apparatus is capable of handling gas flow at pressures from 10 to 50 psi (pounds per square inch), which are typical containment pressures for vessels used in nuclear reactor installations. Gas flows derived from such containment vessels can be throttled as necessary in order to meet the flow rate limits of a special scrubber device; fulfillment. There is no additional pumping of the gas flow. ], thereby eliminating any power requirements for activating the scrubber. The tests carried out on the test model showed that a passive self-cleaning aerosol scrubber based on a surface gas velocity of 0.507 m / s and a bed depth of _: 0.608 m can be built up. The aerosol removal efficiency can be predicted exceeding than 9 9%, respectively, for aerosols in a nuclear reactor _{installation:} can be expected. The aerosol removal efficiency would · 99.9% for all eligible Teilchenverteilun-

gen when a passive fiber filter, as shown in Fig. 2 \ , is used. ^:

In this device, an "airlift" is used to remove washing liquid circulate through the packing within the porous bed 21. The pack is in use while the Keeping scrubbers clean without the use of external liquid pumps, which in turn requires an energy source would do. This is an extremely important benefit in conditions where electrical power is present not available.

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The removal efficiency of the scrubber can thus be provided become / that it has a required value for some special application. A high small particle removal efficiency can be realized. this is a distinct advantage over submerged pipes, where large bubbles result in low removal efficiencies for lead to finer particles.

Since the porous bed 21 is continuously wetted, it becomes more trapped Dust either dissolved or from the BcttiiiaLeri al washed out. Therefore, large masses of airborne particles can be trapped without the porous Bed 21 becomes clogged.

Compared to a simple submerged pipe, this device has a much lower pressure drop in a facility designed for the same removal efficiency. This results from the breaking up of the gas flow into small particles as the stream enters the porous bed 21.

All flow paths through the porous bed 21, the one are small in size, are washed by the liquid and therefore do not clog. The inlet duct that is not washed can be as large as appropriate to ensure that clogging is prevented. this is a great improvement over other bubble breaker devices, such as the use of submerged, small diameter tubes.

The device according to the invention can be manufactured from simple, readily available components, the can be easily fabricated. The device according to the invention can be manufactured at a relatively low cost.

The device according to the invention also has a high Reliability and can maintain its performance after years of inactivity or submit "stand-by status". Only the river

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The level of fluidity would have to be maintained periodically. No complicated parts or controls are required, to ensure the functionality of the scrubber. In addition, no auxiliary power source is required. The device according to the invention therefore has hardly any chance of failure and has a very high reliability,

In summary, the invention thus provides a liquid-tight one Enclosure that is partially filled with water. A container supports a porous bed of sand and gravel and is partially submerged in the liquid. The lower end of the porous bed is at a distance upwards opposite arranged in the bottom of the enclosure. A gas supply channel feeds gas at a point vertically below the porous Bed,. To allow a gas stream to pass up through the porous bed and draw water with it to continuously clean the gravel.

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Claims (10)

3 11 Ί 3 b 7 claims 1. Gas scrubber device for removing particulate matter Material composed of a stream of pressurized gas and having a liquid-tight enclosure and a quantity of liquid within the enclosure, which partially extends the interior of the enclosure to a liquid surface level fills up, characterized in that an open ended container is disposed within the enclosure and has gas impermeable upright side walls, extending upward from a lower end submerged in the liquid, that a porous bed is disposed adjacent to the gas impermeable side walls of the upright container and extends vertically upwardly adjacent the container from a bottom end, open in the liquid submerged and spaced above the lower end of the gas impermeable upright side walls of the container towards an upper end. that inlet channel means extend into the enclosure and have an outlet opening at a submerged one Place in the liquid positioned underneath the porous bed to create a stream of pressurized Directing gas and particulate matter to the bottom of the porous bed, and that the upper end of the porous bed is open to liquid flow caused by the differential apparent Density between the liquid inside and without the porous bed, thereby allowing the inside Liquid trapped in the gas stream is returned by gravity to the liquid contained within the enclosure remains, thereby allowing the porous bed to self-clean, and that finally outlet channel means are provided, which open through the enclosure, and at a level above the liquid surface within the enclosure, so as to allow the exit of a Allowed gas flow after its passage through the porous bed COPY I I / ¥ 7 - 2. Gas scrubber device according to claim 1, characterized in that the horizontal cross-sectional area of the container is smaller than the inner horizontal cross-sectional area within the enclosure. 3. Device according to claim 1 and / or 2, characterized in that that the inside of the enclosure is limited by upright solid walls, spaced transversely outward from the side walls of the container. 4. Device according to one or more of the preceding Claims, in particular according to Claim 1, characterized in that the gas delivery line means have a vertical pipe, which extends through the porous bed and open liodenendc terminates at a level between that of the bottom of the porous bed and that of the lower end of the container side walls . 5. Device according to one or more of the preceding Claims, particularly according to Claim 1, characterized in that the porous bed is a packed bed of granular material which is not soluble in the liquid. 6. Gas scrubber apparatus for removing particulate matter from a stream of pressurized gas, characterized by a liquid-tight enclosure having a bottom wall and associated upright side walls, whereby an inner liquid tank is formed, a quantity of liquid within the enclosure for filling the inner liquid tank to a liquid surface level, an upright open ended container positioned within the enclosure and with upright gas impermeable Sidewalls extending from a lower end submerged in the liquid to an upper end, and wherein the soite walls of the container at a distance inwardly opposite 3 Π 7357 - VS - placed on the upright sidewalls of the enclosure are, a porous bed, surrounded by the gas-impermeable side walls of the upright container and extending vertically extending at the top within the container from a position spaced above the lower end of the gas impermeable upright side walls of the container, being at least half the vertical height of the porous bed in the Liquid is submerged, Inlet channel means to flow a stream of pressurized gas and particulate! Material to a submerged Place vertically below the porous bed, the inlet channel means an upright tube of gas impermeable Have material extending through the porous bed and terminating in an open bottom end, namely positioned at a level between that of the bottom of the porous bed and that of the lower end of the gas-impermeable Container side walls, the upper end of the porous bed being open to liquid flow caused by the differential apparent Density between the liquid inside and without the upright container, thereby allowing a Part of the liquid trapped within the gas stream by gravity from within the container to the liquid which remains inside the inner liquid tank to thereby self-clean the to allow porous beds and finally outlet channel means extending through the enclosure open at a height above the liquid surface level inside the same to give off the gas stream after it has passed through the porous bed. 7. Apparatus according to claim 6, characterized in that the gas-impermeable side walls of the container are vertical and run centered around a vertical container axis. 8. Device according to one or more of the preceding Claims, in particular according to Claim 6, characterized in that the gas-impermeable side walls of the container are vertical and centered about a vertical axis, the upright tube centering the gas delivery conduit means coaxially is within the porous bed along the vertical container axis. 9. Device according to one or more of the preceding claims, in particular according to claim 6, characterized in that that fiber filter means are located above adjacent the upper end of the porous bed, around the gas and the entrained Take up liquid when this Cas leaves the porous bed, namely before the discharge of the gas to the outlet channel. : middle. 10. Gas scrubber apparatus for removing particulate matter from a stream of pressurized gas, characterized by: a liquid-tight enclosure, an amount of liquid within the enclosure, partially filling the inside of the enclosure to a liquid surface level , an open ended container positioned within the enclosure and with gas-impermeable upright side walls that dipped upward from a lower end into the Extend fluid from, a porous bed adjacent the gas impermeable side walls of the upright container and extending vertically upwardly adjacent the container from a bottom end from, which is openly submerged in the liquid, and at a distance above the lower end of the gas-impermeable upright side walls of the container to an upper end, Inlet channel means extending into the enclosure and having an outlet opening on a submerged one Place in the liquid placed below the porous bed to prevent the flow of pressurized gas ι "ο ι ι / ο υ / and particulate matter to the bottom of the porous bed to direct the upper end of the porous bed being open to the flow of liquid caused by the difference in apparent Density between the liquid inside and without the porous bed, thereby permitting the with the Stream of gas entrained liquid is returned by gravity to the liquid contained within the Enclosure remains, and to allow the porous bed to self-clean, and furthermore Outlet channel means opens through the enclosure at a level above the liquid surface level within of the container to vent the flow of the gas after it has passed through the porous bed.