Gas separating system and gas recovery system

Abstract: A rotary gas recovery system which comprises a fixed adsorption tower which is divided into a plurality of sections arranged in the circumferential direction around the center axis and filled with adsorbent, a first manifold for supplying and discharging gases on the side of the fixed adsorption tower, a second manifold for supplying and discharging gases on the side of pipe, and a rotatable valve plate which is interposed between the first manifold and the second manifold and sequentially connects the first manifold to the second manifold by a constant motion.

Description: This invention relates to a gas separating system and a gas recovery system. More particularly, it relates to a pressure swing type gas separating system (hereinafter sometimes called a PSA system) used for refining and recovering gases, as is known from EP-0 107 179 A2. A conventional PSA system comprises an absorber filled with adsorbent. Untreated gas is allowed to flow into the absorber, in which a particular component in the gas (for example, CO 2 , NH 3 , O 2 , flon, etc.) is adsorbed onto the adsorbent; as a result, treated gas which has passed through the absorber without being adsorbed onto the adsorbent can be obtained. By repeating the above cycle, a particular gas component in the untreated gas is recovered, or a particular gas component is refined. The above-described conventional PSA system has some disadvantages as described below because the adsorption and desorption processes are repeated and these processes are performed by an intermittent operation carried out by means of many valves. The disadvantages are as follows: (1) Large amounts of adsorbent are required because the time of one cycle is as long as several minutes. (2) A gas supplying means for untreated gas and an evacuating means (vacuum pump) are continuous rotating turbo machines, which do not match the intermittent operation, offering low efficiency. Specifically, the evacuating means operates wastefully in the adsorption process, whereas the gas supplying means does in the desorption process. (3) To increase the capacity of the PSA system, increased amounts of absorbent and many large-sized valves as well as the opening/closing control are required, resulting in higher cost. (4) The impact noise accompanying the opening/closing of valves and the noise caused by sudden change of gas pressure in the circuit are high. Also, a rotary gas recovery system shown in Fig.1 through 4 has so far been used. In Fig.1, 401 denotes an upper fixed seal plate, 402 denotes a lower fixed seal plate, 403 and 404 denote bearings installed to the seal plates, 405 denotes a rotating shaft which is mounted by the bearings for rotation, 406 denotes a key mounted on the rotating shaft, 407 denotes a rotary adsorbing/desorbing device which is fixedly secured to the rotating shaft 405 by the keys 406 and rotates between the upper fixed seal plate 401 and the lower fixed seal plate 402, 408 denotes a material gas supply port installed in the upper fixed seal plate 401, 409 denotes a particular gas discharge port installed in the upper fixed seal plate 401, 410 denotes a product gas discharge port installed in the lower fixed seal plate 402, 411 denotes a small hole for supplying purge gas which is installed in the lower fixed seal plate, 412 denotes a plurality of compartments extending axially through the rotary adsorbing/desorbing device, 413 denotes an adsorbent put into each compartment, 414 denotes a gas compressor for feeding the material gas under pressure through the material gas supply port 408, 415 denotes a vacuum pump which is connected to the particular gas discharge port and depressurizes and sucks the particular gas for discharge and recovery, 416 denotes a seal surface between the upper fixed seal plate 401 and the rotary adsorbing/desorbing device 407, and 417 denotes a seal surface between the lower fixed seal plate 402 and the rotary adsorbing/desorbing device 407. In the above-described system, the material gas is supplied by the gas compressor 414 to the compartments 412 of the rotary adsorbing/desorbing device through the material gas supply port 408. In the compartments 412, a particular gas is adsorbed onto the adsorbent 413 in the compartment 412, and the gas which has not been adsorbed, that is to say, the product gas is discharged through the product gas discharge port. By the rotation of the adsorbing/desorbing device 407, when the compartment which is filled with the adsorbent onto which a particular gas has been adsorbed comes into communication with the particular gas discharge port 409, the particular gas is removed from the adsorbent 413 by the evacuating action of the vacuum pump 415 and discharged for recovery. In this process, purge gas is fed through the small hole for supplying purge gas in the lower fixed seal plate 402. Thus, the product gas is produced and the particular gas is recovered continuously by the rotation of the adsorbing/desorbing device 407. In the above-described system, the adsorbing/desorbing device 407 rotates and the upper and lower seal plates 401, 402 are fixed. Therefore, the mating surfaces cannot be connected completely, and seal surfaces with a gap are provided, so that the material gas leaks from the seal surface 416. In recovering the particular gas, external gas also flows into the particular gas discharge port 409 through the seal surface 416. The leaked gas poses no problem of deteriorated system performance if it accounts for 1% or less of the supplied gas. However, when the system capacity is increased, the manufacturing accuracy of seal plates 401, 402 decreases, and hence the gaps of seal surfaces 416, 417 increase. As a result, the increase in leaked gas deteriorates the system performance. Since the amount of leaked gas is proportional to the third power of gap, the effect of gap is very large. In addition, the wear of seal surface increases the gap, so that the system performance deteriorates with time. To overcome this problem, it is necessary to carry out maintenance frequently, which increases the running cost of the system. An object of the invention is to provide a gas separating system and a gas recovery system (including a PSA system) which eliminate the above disadvantages. A pressure swing type gas separating system in accordance with this invention suitable to solve this problem is defined in the appendent claim. The use of rotatable valve plate reduces the consumption of adsorbent, improves the efficiency of gas separating system, thereby the cost being reduced, and decreases the noise. Thus, the disadvantages of the conventional gas recovery system can be eliminated. The adsorption and desorption processes are performed sequentially and continuously in the adsorbing portions by the rotation of the valve plate of the selector valve. Therefore, the following effects can be achieved: (1) Since the valve plate performs a rotating motion with a small radius of rotation, the sliding speed of valve plate in relation to the first and second manifolds can be decreased, thereby the required driving power being reduced. (2) The openings in the first and second manifolds and the valve plate are not necessarily arranged radially, which provides larger degree of freedom in arrangement, thereby the system being made compact. (3) The cycle time can be shortened, and the amount of adsorbent with which the adsorbing portions are filled can be decreased. (4) The power loss is lot and the gas separation efficiency can be increased because the gas supplying means and the evacuating means have no wasteful waiting time. (5) A system of high capacity and lots cost can be easily provided because a rotating valve plate is used in place of the conventional on-off valve. (6) There is no need for using large seal members because the seal can be installed independently for each adsorbing portion or for each opening of the first manifold on the side of adsorbing portion. The invention will be described in detail with reference to the accompanying drawings. In the drawings, Fig. 1 is a vertical sectional view of a conventional rotary gas recovery system, Fig. 2 is a sectional view taken along the plane of line L-L of Fig. 1, Fig. 3 is a sectional view taken along the plane of line M-M of Fig. 1, Fig. 4 is a sectional view taken along the plane of line N-N of Fig. 1, Fig. 5 is a vertical sectional view illustrating an embodiment of the invention, Fig. 6 is a sectional view of the main part of the embodiment of Fig. 5, Fig. 7 is an arrangement of openings in the second manifold and valve plate of the embodiment in Fig. 5, and Fig. 8 is a view illustrating the relationship of openings in the second manifold and valve plate of Fig. 5. An embodiment of this invention will be described with reference to Fig.5 through 8. Reference numeral 12 denotes a cylindrical adsorption tower having four vertically divided adsorbing portions 12' which are filled with adsorbent 11. Under the adsorption tower, a disc-shaped first manifold 14 is disposed. The first manifold 14 has circular openings 14a which open at the lower part of the adsorbing portions 12' and circular openings 14b on the outer side of the opening 14a, the opening 14b being connected to a pipe 13 communicating with the upper part of the adsorbing portion 12'. Four sets of openings 14a, 14b corresponding to the adsorbing portions 12' are arranged in the radial direction of the adsorption tower 12. Reference numeral 15 denotes a disc-shaped second manifold disposed in parallel under the first manifold 14. The second manifold 15 has circular openings 15a, 15b, 15c, 15d arranged from the inside to the outside in that order in the radial direction of the adsorption tower 12 as shown in Fig.8. These openings correspond to the openings 14a, 14b of the first manifold which correspond to the adsorbing portion 12'. The openings 15a, 15b are under the opening 14a of the first manifold, and the openings 15c, 15d are under the opening 14b of the first manifold. Reference numeral 16 denotes a valve plate interposed slidably between the first and second manifolds 14, 15. The valve plate 16 is rotated by eccentric discs 17a, 17b which rotates in the same direction with the same eccentricity r around shafts 17'a, 17'b perpendicular to the valve plate 16 at both ends opposing to the center of the adsorption tower 12. The valve plate also has circular openings 16a, 16b in the radial direction of the adsorption tower 12. The openings 16a, 16b move so as to be tangent internally to the openings 14a, 14b of the first manifold 14 during the rotation of valve plate and have the same diameter as that of the openings 15a-15d of the second manifold 15. As the valve plate 16 rotates, the openings 16a and 16b are open sequentially to the corresponding openings 15a, 15b, and 15c, 15d of the second manifold 15 as shown in Figs.7 and 8. The opening 15a of the second manifold 15 is connected to a vacuum source, the opening 15b to an untreated gas source, the opening 15c to a refining gas source, and the opening 15d to a treated gas source. In Fig.7, α , β , γ , δ indicate the sections corresponding to the adsorbing portions 12'. In the adsorbing portion 12', the angle formed by the vector directed from the openings 16a, 16b of the valve plate 16 to the virtual center of motion and the vector directed from the opening 15a to 15b and from 15c to 15d differs by π /2 radian respectively. In this embodiment, where the adsorbing portion is divided into four, it is the best to change the angle by π /2, but generally when the adsorbing portion is divided into n, it is the best to change the angle by 2π /n. Fig.8 shows the relationship between the opening 16a of the valve plate 16 and the openings 15a, 15b for a particular adsorbing portion 12'. Fig.8 indicates the relationship for 1/8 cycle by (A) through (I). In the figure, the condition in which the opening 16a is superposed on the opening 15a or 15b is indicated by hatching, and the direction of movement of opening 16a is indicated by the arrow a. The relationship between the opening 16b of the valve plate 16 and the openings 15c, 15d of the second manifold 15 is similar to (A)-(I) in Fig.8, though not shown in the drawings. As shown in Fig.8, the opening 6a performs circular motions of radius r around the virtual center O as indicated by the arrow a as the valve plate 16 rotates. In the condition of (B)-(D) in Fig.8 where the opening 16a communicates with the opening 15b (at this time, the opening 16b also communicates with the opening 15d), the adsorption process is performed: The untreated gas is introduced into the adsorbing portion 12' through the openings 5b, 6a, and 4a. In the adsorbing portion 12', a particular component in the untreated gas is adsorbed onto the adsorbent 11, and the treated gas is discharged through the pipe 13 and the openings 4b, 6b, and 5d. In the condition of (F)-(H) in Fig.8 where the opening 16a communicates with the opening 15a (at this time, the opening 16b also communicates with the opening 15c), The desorption process is performed: the refining gas is introduced into the adsorbing portion 12' through the openings 15c, 16b, and 14b and the pipe 13, while the adsorbing portion 12' is connected to a vacuum source through the openings 14a, 16a, and 15a, so that the particular component adsorbed onto the adsorbent 11 is discharged from the adsorbing portion 12'. (A), (E) and (I) are neutral processes between the above-described adsorption and desorption processes. The above processes are performed repeatedly, one cycle for one rotating motion of the valve plate 16. In adsorbing portions 12', the above-described adsorption, desorption, and neutral processes are performed with the phase being shifted by 1/4 as shown in Fig.7, so that adsorption by the adsorbent 11 and desorption are performed simultaneously in some adsorbing portions 12'. The motion of the valve plate 16 for performing the above processes is a rotating motion by the rotation of eccentric discs 17a, 17b with an eccentricity r. The eccentricity r, which is the rotation radius of rotating motion, may be sufficiently small; therefore, the sliding speed of the valve plate 16 can be reduced in this embodiment as compared with the PSA system with a rotary valve rotating about one axis, thereby the required driving power being reduced.

Claims: A pressure swing type gas separating system having adsorbing portions (12') connected to a gas supply source and a vacuum source via a selector valve, in which the selector valve comprises a first manifold (14) having openings connected to the adsorbing portion, a second manifold (15) having openings connected to a gas supply source and openings connected to a vacuum source, and a valve plate (16) which is interposed between the first manifold (14) and the second manifold (15) and has openings (16a, 16b) connected to the openings (14a, 14b) in the first manifold (14), wherein the valve plate (16) is disposed with a space between the first and second manifolds and rotated to segmentially establish connections with the gas supply and the vacuum source characterized in that the valve plate is rotatable in the same direction with an equal radius of rotation around two parallel axes of shafts (17'a, 17'b) perpendicular to the valve plate (16) so that its openings are sequentially connected to the openings communicating with the gas supply source and the openings communicating with the vacuum source in the second manifold (15).

Inventors: ISHIZAKI YASUYOSHI, IZUMI JUN, KAGIMOTO YOSHIMI, NAWATA HIDEO, OHSHIMA KAZUAKI, SAKI KUNIO, TAKAHASHI SADAMU, ISHIZAKI, YASUYOSHI, IZUMI, JUN, KAGIMOTO, YOSHIMI, NAWATA, HIDEO, OHSHIMA, KAZUAKI, SAKI, KUNIO, TAKAHASHI, SADAMU, ISHIZAKI, YASUYOSHI C/O MITSUBISHI JUKOGYO K.K., Izumi, Jun, c/o Nagasaki Technical Institut, Kagimoto, Yoshimi, c/o Technical Institute, NAWATA, HIDEO C/O MITSUBISHI JUKOGYO K.K., Ohshima, Kazuaki, Nagasaki Shipyard &amp; Engine Works, Saki, Kunio, c/o Technical Institute, Takahashi, Sadamu, c/o Nagasaki Technical Institut
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: B01D53
IPC codes: B01D53