WET-PROCESS STACK GAS PURIFICATION METHOD AND APPARATUS

Abstract: Wet-process stack gas cleaning method and appts. use a 1st cleaning section provided with a level maintenance system for keeping the level of a 1st cleaning soln. constant; a stack gas introduction pipe which extends below the surface of the 1st cleaning soln. and is fitted with a gas dispersion system; and a cleaning tower in which stack gas cleaned in the 1st cleaning section is brought into counter-current contact with a 2nd cleaning soln.; 1st cleaning soln. exhausted by the level maintenance system is recirculated to the stack gas introduction pipe and the 2nd cleaning soln. is circulated into the cleaning tower again following contact with gas.

Description: The present invention relates to a method of and apparatus for purification of stack gas, and more specifically, a purification method and apparatus which are particularly useful in cases where an extremely high effect of decontamination should be attained as in for example decontamination of stack gas from a radioactive waste incinerator. Conventionally known methods of the treatment and disposal of stack gas from radioactive waste incinerators are dry-processes utilizing a ceramic filter for example and wet-processes utilizing a venturi scrubber for example. In order to attain a high decontamination factor according to such known methods, usually it is arranged to repeatedly effect a decontamination treatment. As a result of this, it is required to provide a large scale installation and accordingly a large scale building, whereby the installation cost has been expensive in the prior art. With the dry-processes, moreover, although they are effective in capturing solids, they are almost ineffective in removing gaseous harmful substances and volatile matters, for example iodine. An object of the present invention is to provide a method and apparatus by means of which radioactive solids, gaseous harmful substances and volatiles can be removed at the same time and nevertheless a considerable reduction in the size of the installation can be realized while, in the light of the decontamination factor, an effect can be produced which is comparable to that of a 3- or more-stage wash-treatment method in the prior art. In FR-A-2,247,272, there is disclosed a wet-process stack gas purification method by which dust and other contaminants contained in stack gas are removed by contacting the stack gas with a scrubbing liquid, the said method comprising the steps of scrubbing the stack gas by bubbling the gas out of a stack-gas introduction pipe into a first scrubbing liquid; further purifying the so scrubbed gas by subjecting it to a second scrubbing liquid in a scrubbing liquid in a scrubbing tower; recycling used first scrubbing liquid into the stack-gas introduction pipe to cool stack gas being sent thereinto; and recycling used second scrubbing liquid into the scrubbing tower. According to the present invention, there is provided a wet-process stack gas purification method by which dust and other contaminants contained in stack gas are removed by contacting the stack gas with a scrubbing liquid, the said method comprising the steps of scrubbing the stack gas by bubbling the gas out of a stack-gas introduction pipe into a first scrubbing liquid in a first container means and further purifying the so scrubbed gas by subjecting it to a second scrubbing liquid in a scrubbing tower and, optionally, to a third scrubbing liquid; characterised in that there are provided container means for the second/third scrubbing liquid which are separate from the container means for the first scrubbing liquid, and in that the first scrubbing liquid is maintained at a constant liquid level by a liquid level maintaining means, the gas which has been scrubbed by the first scrubbing liquid being subjected to counter-current contact with the second scrubbing liquid, and a portion of the used second or third scrubbing liquid being collected together with the used first scrubbing liquid and recycled to the stack gas introduction pipe for contact with the stack gas, the remainder of the used second scrubbing liquid being recycled into the scrubbing tower. There may be both the said second scrubbing liquid and a third scrubbing liquid, a portion of the third scrubbing liquid being cycled to the stack-gas introduction pipe, the second scrubbing liquid which has been subjected to the said counter-current contact being recycled to the top of the scrubbing tower without being mixed with the third scrubbing liquid. Preferably, the said second scrubbing liquid is maintained at a constant fixed level by means of a further liquid level maintaining means. In one embodiment, the method comprises purifying the stack gas scrubbed by the first scrubbing liquid by bubbling it into a third scrubbing liquid the level of which is maintained constant by second liquid level maintaining means which are disposed in the scrubbing tower, the scrubbing tower having an open lower end disposed below the level of the third scrubbing liquid, and subjecting the stack gas purified by the third scrubbing liquid to counter-current contact with the second scrubbing liquid. The invention also comprises a wet-process stack gas purification apparatus of the type in which dust and other contaminants contained in stack gas are removed by contacting the stack gas with a scrubbing liquid, the said apparatus comprising: a first scrubbing tank adapted to contain a first scrubbing liquid; a stack-gas introduction pipe extending into the first scrubbing liquid from a position above the level of the first scrubbing liquid and having an open leading end provided with means for dispersing the stack gas into the first scrubbing liquid; a second scrubbing tank for a second/third scrubbing liquid or liquids, the second scrubbing tank comprising a scrubbing tower including a gas-liquid contact part for further purifying the stack gas scrubbed with the first scrubbing liquid by subjecting it to a second scrubbing liquid; first scrubbing liquid recycling conduit means for guiding the used first scrubbing liquid into an upper portion of the stack-gas introduction pipe for spraying of the first scrubbing liquid; and a further conduit means for recycling the used second scrubbing liquid from the scrubbing tower for contact with the stack gas; characterised in that a conduit is provided for guiding a portion of the used second scrubbing liquid or of a third scrubbing liquid into the first scrubbing liquid recycling conduit means, the first scrubbing tank having liquid level maintaining means for maintaining constant the level of the first scrubbing liquid therein, the said liquid level maintaining means communicating with the first scrubbing liquid recycling conduit means, the gas which has been scrubbed by the first scrubbing liquid being subjected to counter-current contact with the second scrubbing liquid. The apparatus may, moreover, comprise a second scrubbing tank for containing a third scrubbing liquid therein; the scrubbing tower extending into the third scrubbing liquid from a position above the level of this liquid and having an open leading end provided with a gas dispersing means and a liquid level maintaining means for maintaining constant the level of the third scrubbing liquid received inside the second scrubbing tank; the gas-liquid contact part being provided in an upper portion of the scrubbing tower; the used first scrubbing liquid from the liquid level maintaining means of the first scrubbing tank and the used third scrubbing liquid from the liquid level maintaining means of the scrubbing tower being guided into an upper portion of the stack-gas introduction pipe for spraying of the liquid. There may be a conduit for recycling the used second scrubbing liquid from the bottom of the gas-liquid contact part to the top of the gas-liquid contact part. There may be a liquid reservoir tank for containing the used first scrubbing liquid from the liquid level maintaining means of the first scrubbing tank and the used third scrubbing liquid from the liquid level maintaining means of the scrubbing tower, the liquid reservoir tank being integral with the first scrubbing tank and the second scrubbing tank. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a schematic view, showing an embodiment of the wet-process stack gas purification apparatus according to the present invention; Figure 2 is a schematic view, showing another embodiment of the wet-process stack gas purification apparatus according to the invention; Figure 3 is a schematic view, showing still another embodiment of the wet-process stack gas purification apparatus according to the invention; and Figure 4 shows a flow chart of the wet-process stack gas purification method according to the present invention. Initially, the invention will be described in connection with the wet-process stack gas purification apparatus in conjunction with embodiments thereof illustrated in the accompanying drawings. As shown in Figure 1, a wet-process stack gas purification apparatus according to the invention comprises a first scrubbing tank 1, a stack-gas introduction pipe 2 extending in the first scrubbing tank 1 into a scrubbing liquid from a position above the level of this liquid and having an open leading end provided with a gas dispersing means 5, and a scrubbing tower 3 in which to further purify the stack gas scrubbed in the first scrubbing tank 1. The scrubbing liquid in the first scrubbing tank 1, namely a first scrubbing liquid, may be water. However, where sulfur oxides and so forth are contained in the stack gas to be treated, together with dust, it is desirable to use an aqueous caustic soda solution or a suspension solution or an aqueous solution of calcium hydroxide, magnesium hydroxide or a carbonate thereof so that the sulfur oxides and so forth can be fixed and removed. In the first scrubbing tank 1, stack gas to be treated is introduced into and bubbled in the first scrubbing liquid, and dust in the gas is removed through contact of bubbles with the first scrubbing liquid. The extent of the gas-liquid contact is variable depending on how far below the liquid level the open leading end of the stack-gas introduction pipe 2 is positioned. Accordingly, the first scrubbing tank 1 should necessarily be provided with means for maintaining the liquid level at the prescribed position. Such liquid-level maintaining means may be any of an arrangement which comprises a weir provided in the tank 1 and in which the liquid is permitted to flow out of the tank over the weir, an arrangement in which a change of the liquid level is detected by a float, a load cell or the like and the quantity of the liquid flowing into or out of the tank is controlled by signals issued responsive to the liquid level detection, and a mechanism as shown in Figure 1 in which a discharge pipe 4 is provided in a side wall portion of the tank 1 to let the liquid flow out of the tank. The structure of the opening of the stack-gas introduction pipe 2, which is provided with the gas dispersing means 5, may comprise rectangular slits as shown or it may otherwise be any of such structures which can permit gas to be blown into the liquid or, preferably, permit gas to be divided into portions and bubbled into the liquid such as triangular slits, a porous structure and so forth. In order to promote and more sufficiently effect the gas-liquid contact than merely by bubbling relied on blowing of stack gas out of the gas introduction pipe 2, it is possible to incorporate an agitator 6 below the gas dispersing means 5 of the gas introduction pipe 2. Moreover, where the stack gas to be treated contains sulfur oxides and so forth, it is also possible to provide an introduction pipe 7 for an oxygen-containing gas, in a bottom portion of the scrubbing tank 1 to promote oxidation of sulfites to sulfates. The stack gas scrubbed in the first scrubbing tank is guided into the scrubbing tower 3 and further purified therein. For the scrubbing tower 3, a packed tower or a plate column having a gas-liquid contact member 8 may be effectively utilized. The stack gas that ascends in the direction shown by an arrow A is further purified through counter-current contact with a second scrubbing solution which is sprayed from an upper portion of the scrubbing tower 3 and thereafter discharged through a discharge opening 12. The second scrubbing liquid which is passed down in the scrubbing tower 3 is collected in a second scrubbing tank 9, recycled into the tower 3 through a cooler 11 by a pump 10 and then sprayed again. Further, the composition stated above of the first scrubbing liquid is also applicable to the second scrubbing liquid. The portion of the second scrubbing liquid which is discharged through a discharge pipe 4' is passed through a conduit 34 to a liquid reservoir 17 where it is put together with the portion of the first scrubbing liquid which is discharged through the discharge pipe 4 and which has passed to the liquid reservoir 17 by way of a conduit 30. Liquid from the liquid reservoir 17 passes through a conduit 31 to a pump 18 by which it is recycled through a conduit 32 to the top of the stack-gas introduction pipe 2. Further, the first scrubbing tank 1 and the second scrubbing tank 9 are provided with scrubbing-liquid supply pipes 13 and 14 respectively. Figure 2 shows another embodiment of the apparatus according to the invention, in which stack gas is scrubbed and purified three times in repetition, and the apparatus of this embodiment differs from the apparatus of Figure 1 in respect of the following. First, the scrubbing tower 3, like the stack-gas introduction pipe 2, has at its lower end portion an opening 5' provided with a gas dispersing means. The scrubbing tower 3 extends below the level of the third scrubbing liquid in the second scrubbing tank 9 and also extends from above the liquid level. The stack gas scrubbed in the first scrubbing tank 1 is sent into the second scrubbing tank 9, and presses against the third scrubbing liquid as shown by arrows B, whereby the level of the third scrubbing liquid in the second scrubbing tank 9 lowers and, at the same time, the level of the third scrubbing liquid in the scrubbing tower 3 rises to cause the stack gas to bubble out through the opening 5' of the scrubbing tower 3 into the third scrubbing liquid in the scrubbing tower 3. The scrubbing tower 3 is provided with a discharge pipe 4' for maintaining constant the level of the third scrubbing liquid in the lower part of the scrubbing tower 3. The scrubbing tower 3 incorporates the same gas-liquid contact member 8 as in the embodiment shown in Figure 1. The second scrubbing liquid used for the gas-liquid contact in this gas-liquid contact member 8 is collected from the bottom of the latter in a scrubbing-liquid collecting part 15 and then recycled into the gas-liquid contact member 8 through a pump 10 and conduit 35, so as to be supplied to the top of the gas-liquid contact member 8. The portion of the third scrubbing liquid taken out through the discharge pipe 4' at the prescribed liquid level in the scrubbing tower 3 is put together with the portion of the first scrubbing liquid discharged from the discharge pipe 4 and having passed through a pump 18 is put for use for the gas-liquid contact in the stack-gas introduction pipe 2. The scrubbing liquid subjected to the gas-liquid contact is permitted to flow down in the first scrubbing tank 1 and receives replenishment of water, which was lost as a result of the wetting of the stack gas. Further, the second scrubbing liquid and the third scrubbing liquid may commonly be water or they may be a solution of the same composition as the first scrubbing liquid. According to the above described embodiment of Figure 2, the effect of purification can be enhanced without sacrifice to the structural simplicity of the embodiment of Figure 1. Figure 3 illustrates still another embodiment of the present invention, in which, while the stack gas can be scrubbed three times as in the embodiment of Figure 2, a scaled-down or size-reduced version of the apparatus is achieved by comparison with the embodiment of Figure 2. That is to say, in the embodiment of Figure 3, the liquid reservoir tank 17 is integrated with each of the first scrubbing tank 1 and the second scrubbing tank 9. The first scrubbing tank 1 is provided with a weir 16 so that the liquid level in this tank 1 can be maintained constant with the formation of the bubble layer in the tank 1 controlled and, at the same time, the gas-liquid separation can be promoted by the weir 16. The separated portion of the first scrubbing liquid is stored in the liquid reservoir tank 17 and then recycled into the stack-gas introduction pipe 2. Further, the weir 16 has the function of stabilizing the liquid level in the liquid reservoir tank 17. According to the above described embodiment of the invention, illustrated in Figure 3, it is possible to achieve a further reduction of the size of the apparatus by comparison with the embodiment shown in Figure 2 while a dust separating capacity comparable to or exceeding that of the apparatus of Figure 2 is retained. Now, with reference to Figure 3, a description will be given of the operation of the above described stack gas purification apparatus according to the invention. First, a stack gas G is charged through the gas introduction pipe 2. The portion of the first scrubbing liquid which was subjected to a gas-liquid separation by the weir 16 and merged in the liquid reservoir tank 17 with the third scrubbing liquid is sent by the pump 18 into the gas introduction pipe 2 and sprayed into the stack gas G introduced into the pipe 2 as described above, whereby the gas G is cooled to a saturation temperature. From the stack-gas introduction pipe 2, the stack gas is bubbled through the gas dispersing means 5 provided at the lower open end of the pipe 2 into the first scrubbing liquid, and as a result of the gas-liquid contact between minute bubbles of the stack gas and a continuous liquid phase of the first scrubbing liquid, particles such as dust, sulfur oxides and so forth in the stack gas are transferred into the scrubbing liquid and the stack gas is scrubbed. The so scrubbed stack gas is then bubbled through the gas dispersing means 5' at the lower open end of the scrubbing tower 3 into the third scrubbing liquid in the tower 3 and subjected to a second-time scrubbing through a gas-liquid contact, whereby entrained mist, remaining dust, sulfur oxides and so forth in the stack gas are removed. Then, the stack gas subjected to the second-time scrubbing as described above is subjected to a counter-current contact with the second scrubbing liquid preparatively cooled by an external cooler 11 and sprayed in the gas-liquid contact member 8 in the scrubbing tower. Accordingly, the gas is cooled and a thorough removal of entrained mist and remaining dust in the gas is effected, the gas which has been scrubbed for the third time being then discharged from the gas discharge opening 12. The second scrubbing solution is then recycled into the scrubbing tower. The dust captured in the first scrubbing tank 1 and in the second scrubbing tank 9 is sent by a pump 19 into a centrifugal separator 20, from which the isolated dust 21 is taken out. Example 1: Using a wet-process stack gas purification system as shown in Figure 4, a treatment was carried out of the offgas from an incinerator for radioactive wastes. The apparatus which was used is substantially the same as the apparatus shown in Figure 3 according to the third embodiment of the present invention. The offgas generated in an incinerator 22 was guided into the gas introduction pipe 2. A first scrubbing liquid from the first scrubbing tank 1 was circulated from the liquid reservoir tank 17 and sprayed into the gas introduction pipe 2 to cool the offgas whose temperature was about 1000°C to a saturation temperature of about 70°C. The so cooled offgas was bubbled through the gas dispersing means 5 provided at the lower open end of the gas introduction pipe 2 into the scrubbing liquid in the first scrubbing tank 1 and subjected to scrubbing. Then, the offgas produced by a gas-liquid separation by the weir 16 was guided into the second scrubbing tank 9 and bubbled through the gas dispersing means 5' at the lower open end of the scrubbing tower 3 into a third scrubbing liquid in the scrubbing tower 3 and subjected to a second scrubbing. The offgas subjected to the second scrubbing as described above was further purified by a second scrubbing liquid. The used second scrubbing liquid was captured in the scrubbing-liquid capturing part 15, circulated and sprayed into the top of the gas-liquid contact member 8. The offgas subjected to scrubbing three times and decontaminated as above was heated by a gas heater 23, passed through a final filter 24 and then released into the air through a suction fan 25 and an exhaust cylinder 26. Further, the numerals 27 in Figure 4 show piping for charging a neutralizer. The neutralizer was provided so that, since the scrubbing liquids in the first scrubbing tank 1 and in the second scrubbing tank 9 are acidified therein by sulfur oxides and so forth contained in the incinerator offgas, a pH control can be effected by way of supplying an alkali for example caustic soda, magnesium hydroxide or the like. Also, in order to control to a permissible value each of the amounts of soot and dust to be accumulated and the concentration of salts formed through neutralization of acids in the first scrubbing tank 1, the scrubbing liquid was intermittently discharged through the drainage pipes 27. Further, the amount of soot and dust in the second scrubbing liquid which was sprayed into the gas-liquid contact part 8, and the concentration of the neutralized salts therein, were maintained constant by the flood flow through the discharge of flood-flow pipe 4'. The scrubbing liquid discharged through the drainage pipes as above was sent into an incinerator where its contents were incinerated. Further, the numeral 28 denotes a water supply piping. The supply of water through this piping 28 can be done without if it is arranged that the amount of condensed water to be generated in the gas-liquid contact part 8 is adjusted by controlling the degree of cooling by the cooler 11. According to the above described Example, the offgas containing 5 g/Nm³ of soot and dust was introduced into the apparatus, and this amount of soot and dust was reduced to below a detection limit value subsequent to the three-time scrubbing. Example 2: Using the apparatus shown in Figure 1, the same treatment of gas as in the above described Example 1 was carried out, and it was possible to effect a purification of gas such that 5 g/Nm³ of soot and dust was reduced to 2 mg/Nm³. Capability of Exploitation in Industry In or with the wet-process stack gas purification method and apparatus described above, it is possible to effect scrubbing of a stack gas at least twice by a gas-liquid contact between the stack gas and a first scrubbing liquid at the lower open end of a stack-gas introduction pipe provided with a gas dispersing means and by gas-liquid contact between the gas and a second scrubbing liquid in a scrubbing tower. Accordingly, it is possible to effectively remove dust and so forth contained in stack gas. The present invention is particularly effectively useful in the treatment and disposal of stack gas from incinerators for radioactive wastes in which it is required to attain an extremely high decontamination effect. In addition, the apparatus of the present invention may merely comprise a combination together of a first scrubbing tank and a scrubbing tower, and consequently it is possible to achieve a reduction in size of the apparatus. Also, the carrying out of the present invention does not require any particularly complex operation. In one emboidment of the wet-process stack gas purification method and apparatus according to the present invention, a stack gas from a radioactive-waste incinerator may for example be treated to attain the following results: Soot and dust: a decontamination factor at the gas outlet of the gas introduction pipe 2 of 10³ to 10⁴, and a decontamination factor at the gas outlet of the scrubbing tower 3 of 10⁵. Iodine and the like: a decontamination factor at the gas outlet of the scrubbing tower 3 of a value of the order of 10³.

Claims: A wet-process stack gas purification method by which dust and other contaminants contained in stack gas are removed by contacting the stack gas (G) with a scrubbing liquid, the said method comprising the steps of scrubbing the stack gas (G) by bubbling the gas out of a stack-gas introduction pipe (2) into a first scrubbing liquid in a first container means (1) and further purifying the so scrubbed gas by subjecting it to a second scrubbing liquid in a scrubbing tower (3) and, optionally, to a third scrubbing liquid; characterised in that there are provided container means (9) for the second/third scrubbing liquid which are separate from the container means (1) for the first scrubbing liquid, and in that the first scrubbing liquid is maintained at a constant liquid level by a liquid level maintaining means (4), the gas which has been scrubbed by the first scrubbing liquid being subjected to counter-current contact with the second scrubbing liquid, and a portion of the used second or third scrubbing liquid being collected together with the used first scrubbing liquid and recycled to the stack gas introduction pipe (2) for contact with the stack gas (G), the remainder of the used second scrubbing liquid being recycled into the scrubbing tower (3). A method as claimed in claim 1 characterised in that there are both the said second scrubbing liquid and a third scrubbing liquid, a portion of the third scrubbing liquid being cycled to the stack-gas introduction pipe (2), the second scrubbing liquid which has been subjected to the said counter-current contact being recycled to the top of the scrubbing tower (3) without being mixed with the third scrubbing liquid. A method as claimed in claim 2 characterised in that the said third scrubbing liquid is maintained at a constant fixed level by means of a further liquid level maintaining means (4'). A method of as claimed in claim 1 characterised by purifying the stack gas scrubbed by the first scrubbing liquid by bubbling it into a third scrubbing liquid the level of which is maintained constant by second liquid level maintaining means (4') which are disposed in the scrubbing tower (3), the scrubbing tower (3) having an open lower end (5') disposed below the level of the third scrubbing liquid, and subjecting the stack gas purified by the third scrubbing liquid to counter-current contact with the second scrubbing liquid. A wet-process stack gas purification apparatus of the type in which dust and other contaminants contained in stack gas (G) are removed by contacting the stack gas with a scrubbing liquid, the said apparatus comprising: a first scrubbing tank (1) adapted to contain a first scrubbing liquid; a stack-gas introduction pipe (2) extending into the first scrubbing liquid from a position above the level of the first scrubbing liquid and having an open leading end provided with means (5) for dispersing the stack gas into the first scrubbing liquid; a second scrubbing tank for a second/third scrubbing liquid or liquids, the second scrubbing tank comprising a scrubbing tower (3) including a gas-liquid contact part (8) for further purifying the stack gas (G) scrubbed with the first scrubbing liquid by subjecting it to a second scrubbing liquid; first scrubbing liquid recycling conduit means (17,30-32) for guiding the used first scrubbing liquid into an upper portion of the stack-gas introduction pipe (2) for spraying of the first scrubbing liquid; and a further conduit means (33) for recycling the used second scrubbing liquid from the scrubbing tower (3) for contact with the stack gas; characterised in that a conduit (34) is provided for guiding a portion of the used second scrubbing liquid or of a third scrubbing liquid into the first scrubbing liquid recycling conduit means (17,30-32), the first scrubbing tank (1) having liquid level maintaining means (4) for maintaining constant the level of the first scrubbing liquid therein, the said liquid level maintaining means (4) communicating with the first scrubbing liquid recycling conduit means (17,30-32), the gas which has been scrubbed by the first scrubbing liquid being subjected to counter-current contact with the second scrubbing liquid. An apparatus as claimed in claim 5 characterised in that there is a second scrubbing tank (9) for containing a third scrubbing liquid therein; the scrubbing tower (3) extending into the third scrubbing liquid from a position above the level of this liquid and having an open leading end provided with a gas dispersing means (5') and a liquid level maintaining means (4') for maintaining constant the level of the third scrubbing liquid received inside the second scrubbing tank (9); the gas-liquid contact part (8) being provided in an upper portion of the scrubbing tower (3); the used first scrubbing liquid from the liquid level maintaining means (4) of the first scrubbing tank (1) and the used third scrubbing liquid from the liquid level maintaining means (4') of the scrubbing tower (3) being guided into an upper portion of the stack-gas introduction pipe (2) for spraying of the liquid. An apparatus as claimed in claim 6 comprising a conduit (35) for recycling the used second scrubbing liquid from the bottom of the gas-liquid contact part (8) to the top of the gas-liquid contact part (8). Apparatus as claimed in claim 6 or 7 characterised in that there is a liquid reservoir tank (17) for containing the used first scrubbing liquid from the liquid level maintaining means (16) of the first scrubbing tank (1) and the used third scrubbing liquid from the liquid level maintaining means (4') of the scrubbing tower (3), the liquid reservoir tank (17) being integral with the first scrubbing tank (1) and the second scrubbing tank (9).

Inventors: KIYOHARA, NOBUO, NISHINO, HARUO, WAKUI, HITOSHI, YAMAMOTO, OSAMU
Applicants: CHIYODA CHEMICAL ENGINEERING & CONSTRUCTION COMPANY LIMITED
Application year: 1987
Main classification: B01D53
IPC codes: B01D53, G21F9, B01D47