JP2011255307A - Method for separating and recovering target gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method suitable for suppressing an increase in power unit requirement when acquisition amount of target gas is decreased in the separation and recovery of the target gas from mixed gas including the target gas and unnecessary gas by a PSA (Pressure Swing Adsorption) method.SOLUTION: There is provide the method for separating and recovering product oxygen gas from the mixed gas including oxygen (target gas) and nitrogen (unnecessary gas) by the PSA method which is performed by using two adsorption columns 1A, 1B filled with an adsorbent. The method includes: an adsorption process of adsorbing nitrogen in the mixed gas onto the adsorbent by introducing the mixed gas into the adsorption columns by a blower 2, and guiding out the product oxygen gas from the adsorption columns and sending the product oxygen gas to a storage tank 4 for storing the product oxygen gas; a desorption process of desorbing nitrogen from the adsorbent by decompressing the adsorption columns with a vacuum pump 3 and guiding out the gas from the adsorption columns; and an interruption process of intercepting entrance/exit of the gas to/from each of the adsorption columns. A cycle comprising the adsorption process, the desorption process and the interruption process is repeatedly carried out in each of the adsorption columns and the product oxygen gas is continuously acquired from the storage tank 4 by the cycle.

Description

  The present invention relates to a method for separating and recovering a target gas from a mixed gas containing a target gas and an unnecessary gas by a pressure fluctuation adsorption method.

  A pressure fluctuation adsorption method (PSA method) is known as a method for separating and recovering oxygen as a target gas from a mixed gas containing oxygen (target gas) such as air and nitrogen (unnecessary gas). The oxygen-enriched oxygen gas obtained by the PSA method is used in fields that consume a large amount of oxygen, such as electric furnace steelmaking, garbage incineration, papermaking, and oxygen aeration in water treatment facilities. In the separation and recovery of oxygen gas by the PSA method, a cycle including an adsorption step and a desorption step is repeatedly performed in each adsorption tower using, for example, a PSA gas separation apparatus having two adsorption towers filled with an adsorbent. . In the adsorption step, for example, a mixed gas is sucked in by a blower, the mixed gas is introduced into an adsorption tower, nitrogen in the mixed gas is adsorbed by the adsorbent, and oxygen gas is led out from the adsorption tower. In the desorption process, for example, the adsorption tower is decompressed by a vacuum pump to desorb nitrogen from the adsorbent, and the gas is led out from the adsorption tower. Techniques for obtaining oxygen gas by the PSA method are described in Patent Documents 1 and 2, for example.

  The amount of oxygen gas generated by the PSA method (acquired amount per unit time) is set to correspond to the maximum consumption amount of the oxygen gas, for example. In the gas separation operation by the PSA method, the load of the gas separation operation is 100% from the viewpoint of efficiency (suppression of power consumption) in accordance with the maximum consumption of oxygen gas, and the adsorption pressure and desorption pressure. The operation conditions are set so that the operation time of each process is optimized. On the other hand, the oxygen consumption required in facilities using oxygen gas is not always constant. For this reason, when the oxygen consumption is reduced, for example, the amount of oxygen gas acquired from the outlet of the PSA gas separation device is adjusted and reduced to cope with the fluctuation of the oxygen consumption.

  However, if the amount of oxygen gas acquired is reduced as described above, the oxygen generation amount is reduced while the power consumption of a rotary machine such as a blower or a vacuum pump remains unchanged. Such power consumption (per unit of power) increases in inverse proportion to the acquisition amount. Also, if the amount of oxygen gas acquired is reduced, the adsorption pressure (the maximum pressure in the tower in the adsorption process) will increase, and as a result, the power consumption of the rotary machine, which is a blower, will increase, and the power consumption will also increase was there.

  In addition, when the adsorption pressure increases due to a decrease in the amount of oxygen gas acquired as described above, the operating conditions by the PSA method may deviate from the appropriate range set. As a result, there is a risk of increasing the power consumption (unit power consumption) related to the gas separation operation per unit oxygen generation amount.

JP-A-8-239204 JP 11-292506 A

  The present invention has been conceived under such circumstances, and when the target gas is separated and recovered from the mixed gas containing the target gas and the unnecessary gas by the PSA method, the acquisition amount of the target gas is reduced. However, it is an object of the present invention to provide a method suitable for suppressing an increase in power consumption (unit power consumption) related to a gas separation operation per unit target gas generation amount.

  The method for separating and recovering a target gas provided by the present invention is a pressure fluctuation performed using two adsorption towers filled with an adsorbent that selectively adsorbs the unnecessary gas from a mixed gas containing the target gas and the unnecessary gas. A method of separating and recovering the product gas enriched in the target gas by an adsorption method, wherein a mixed gas is introduced into the adsorption tower by a blower, and the unnecessary gas in the mixed gas is adsorbed to the adsorbent. An adsorption step of deriving the product gas from the adsorption tower and sending it to a storage tank for storing the product gas; and depressurizing the adsorption tower by a vacuum pump to desorb the unnecessary gas from the adsorbent; A cycle including a desorption process for deriving gas from the adsorption tower and an interruption process for blocking gas from entering and exiting each of the adsorption towers is repeated in each of the adsorption towers. Serial continuously obtains the product gas from the storage tank.

  Preferably, the target gas is oxygen and the unnecessary gas is nitrogen.

  Preferably, in the interruption step, a first operation for circulating the mixed gas that has passed through the blower so as to flow into the blower while continuing the operation of the blower, and the mixed gas that has passed through the blower is released into the atmosphere. Any one of the second operation to perform and the third operation to stop the operation of the blower is performed.

  Preferably, in the interruption step, air is sucked by the vacuum pump while the operation of the vacuum pump is continued.

  Preferably, the interruption step is performed immediately before switching from the adsorption tower to be subjected to a pressure reduction operation by the vacuum pump.

  Preferably, the calculation of the duration Ta of the interruption process in the cycle is Tb when the load of the gas separation operation is 100% without the interruption process, and the load of the gas separation operation is 100%. When the acquisition ratio of the target gas with respect to the acquired amount of the target gas is A%, the calculation formula Ta = (100 / A) × Tb−Tb.

  In the method for separating and recovering oxygen according to the present invention, an interruption step is inserted in a cycle in which the load of the gas separation operation by the PSA method is 100%, and in the interruption step, the gas flow into and out of each adsorption tower is blocked. Yes. In the interruption process, the pressure in each column of the adsorption tower is maintained almost constant, and the gas separation operation by the PSA method is interrupted. Therefore, even if the load factor of the gas separation operation by the PSA method is reduced by inserting the interruption process, the PSA gas separation device is operated under the optimized operation condition when the load of the gas separation operation is 100%. be able to. As a result, it is possible to suppress an increase in power consumption (unit power consumption) related to the gas separation operation per unit target gas generation amount.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a schematic block diagram of the PSA gas separation apparatus for implement | achieving the separation-and-recovery method of the target gas which concerns on the 1st Embodiment of this invention. It is a time chart which shows the process of 1 cycle performed in each adsorption tower in the separation-and-recovery method of the target gas which concerns on the 1st Embodiment of this invention. It is a gas flow chart corresponding to each process of the separation recovery method of the object gas concerning a 1st embodiment of the present invention. It is a schematic block diagram of the PSA gas separation apparatus for implement | achieving the separation-and-recovery method of the target gas which concerns on the 2nd Embodiment of this invention. It is a time chart which shows the process of 1 cycle performed in each adsorption tower in the separation-and-recovery method of the target gas which concerns on the 2nd Embodiment of this invention. It is a gas flow diagram corresponding to each process of the separation recovery method of the object gas concerning a 2nd embodiment of the present invention.

  Hereinafter, as a preferred embodiment of the present invention, a method for separating and recovering oxygen from a mixed gas containing oxygen as a target gas and nitrogen as an unnecessary gas will be specifically described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a PSA gas separation apparatus X1 that can be used to execute the method for separating and recovering oxygen according to the first embodiment of the present invention.

  The PSA gas separation device X1 includes adsorption towers 1A and 1B, a roots blower 2, a vacuum pump 3, a storage tank 4, and a line connecting them, and utilizes a pressure fluctuation adsorption method (PSA method). Oxygen can be concentrated and separated from a mixed gas containing oxygen and nitrogen.

  Each of the adsorption towers 1A and 1B has gas passages 1a and 1b at both ends, and is filled with a filler for selectively adsorbing nitrogen contained in the mixed gas between the gas passages 1a and 1b. Yes. Examples of the adsorbent include CaA-type zeolite, CaX-type zeolite, and LiX-type zeolite, and these may be used alone or in combination.

  The gas passage ports 1a of the adsorption towers 1A and 1B are connected to a common line 5 via branch lines 5a and 5b. The branch lines 5a and 5b are provided with switching valves 6a and 6b that can be switched between an open state and a closed state.

  The roots blower 2 is for sending the mixed gas to the adsorption towers 1 </ b> A and 1 </ b> B, and is provided in the line 5. With the roots blower 2, the maximum pressure in the tower in the adsorption step to be described later is, for example, about 40 to 50 kPaG.

  A bypass line 7 is connected to the line 5. The bypass line 7 is for sucking the mixed gas sent from the roots blower 2 again into the roots blower 2 and circulating it. Connected to the upstream side of the inlet. A switching valve 8 is provided in the bypass line 7.

  The line 5 is also provided with a cooler 9. The cooler 9 is provided between the outlet of the roots blower 2 and the one end of the bypass line 7, and cools the mixed gas before being supplied to the adsorption towers 1 </ b> A and 1 </ b> B, or the line 5 and the bypass line 7. For cooling the mixed gas circulating between the two.

  The gas passage ports 1a of the adsorption towers 1A and 1B are connected to a common line 10 via branch lines 10a and 10b. Switching valves 11a and 11b are provided in the branch lines 10a and 10b.

  The vacuum pump 3 is for depressurizing the adsorption towers 1 </ b> A and 1 </ b> B to lead out the gas in the tower through the gas passage port 1 a, and is provided in the line 10. As the vacuum pump 3, for example, a roots blower is used, and the minimum pressure in the tower in the desorption process is about -70 to -60 kPaG.

  An atmospheric suction line 12 having an open end is connected to the line 10. The atmospheric suction line 12 is connected between the adsorption towers 1A and 1B and the vacuum pump 3, and is used for causing the vacuum pump 3 to suck the atmospheric air in a predetermined process. A switching valve 13 is provided in the atmospheric suction line 12.

  The gas passage ports 1b of the adsorption towers 1A and 1B are connected to a common line 14 via branch lines 14a and 14b. In the branch lines 14a and 14b, switching valves 15a and 15b are provided.

  The gas passage ports 1b and 1b of the adsorption towers 1A and 1B are also communicated via a line 16 connected between the branch lines 14a and 14b. The line 16 is provided with a switching valve 17.

  The storage tank 4 is an empty container for temporarily storing gas (product oxygen gas described later) derived from the adsorption towers 1 </ b> A and 1 </ b> B, and is provided in the line 14. A flow rate adjustment valve (not shown) is provided at the outlet of the storage tank 4. The product oxygen gas in the storage tank 4 is continuously taken out from the storage tank 4 and is always consumed for a predetermined use.

  In the PSA gas separation device X1 configured as described above, the gas flow direction and pressure in the adsorption towers 1A and 1B are adjusted by selecting the open / close state of each switching valve. In each of the adsorption towers 1A and 1B, a cycle including, for example, an adsorption process, a desorption process, a pressure equalization process, and an interruption process is repeated according to the switching state of the switching valve.

  In the adsorption step, a mixed gas is introduced into any of the adsorption towers 1A and 1B in a predetermined high pressure state, and nitrogen in the mixed gas is adsorbed by the adsorbent, and oxygen is enriched from the adsorption tower. This is a process for deriving the product oxygen gas (product gas). For example, the desorption process is a process for depressurizing any of the adsorption towers 1A and 1B that have completed the adsorption process to desorb nitrogen from the adsorbent, and leading the gas in the tower out of the tower as an off-gas. In the pressure equalizing step, for example, either one of the adsorption towers 1A, 1B that has finished the adsorption step and the other adsorption tower 1A, 1B that has finished the desorption step are communicated, and both of them are caused by the pressure difference in both adsorption columns 1A, 1B. In this step, a gas flow is generated between the adsorption towers 1A and 1B.

  The interruption process is a process in which the load of the gas separation operation by the PSA method is inserted into a 100% cycle when the consumption of the product oxygen gas decreases. In the interruption process, the entrance and exit of gas to each of the adsorption towers 1A and 1B is blocked.

  Next, a method for separating and recovering oxygen according to the first embodiment of the present invention will be described with reference to FIGS. In the gas separation by the PSA method according to the present embodiment, in each of the adsorption towers 1A and 1B, for example, each process (step) is performed in the operation time shown in FIG. 2, and steps 1 to 10 are defined as one cycle. Is repeated. FIG. 3 schematically shows the gas flow of the PSA gas separation device X1 in each step.

  In Step 1, only the switching valves 6a, 11b, and 15a are opened, the adsorption process is performed for the adsorption tower 1A, and the desorption process is performed for the adsorption tower 1B, as shown in FIG. It is in a gas flow state.

  Specifically, air as a mixed gas is introduced into the adsorption tower 1A from the gas passage port 1a through the line 5 and the branch line 5a by the roots blower 2. In the adsorption tower 1A, nitrogen is selectively adsorbed by the adsorbent, and the product oxygen gas is led out from the gas passage port 1b. The product oxygen gas is sent to the storage tank 4 via the branch line 14 a and the line 14. The product oxygen gas in the storage tank 4 is taken out and used after the flow rate is adjusted. In all steps 1 to 10 including step 1, product oxygen gas is continuously acquired from the storage tank 4 at a constant flow rate.

  The adsorption tower 1B has already been subjected to a desorption process (see step 10 shown in FIG. 3 (j)). Subsequently, the inside of the tower is depressurized by the vacuum pump 3 and nitrogen is desorbed from the adsorbent. Is led out of the tower as off-gas through the gas passage port 1a. The off-gas is discharged out of the system via the branch line 10b and the line 10. Step 1 is continued for 24 seconds, for example.

  In step 2, only the switching valves 8, 11b, and 17 are opened, the depressurization process is performed in the adsorption tower 1A, and the desorption and cleaning process is performed in the adsorption tower 1B. The gas shown in FIG. It is in a flow state.

  Since the adsorption tower 1A has performed the adsorption process first, while the adsorption tower 1B has performed the desorption process first, the inside of the adsorption tower 1A has a higher pressure than the inside of the adsorption tower 1B. Therefore, a gas containing a large amount of product oxygen gas (residual product oxygen gas) is introduced from the adsorption tower 1 </ b> A to the adsorption tower 1 </ b> B via the line 16. On the other hand, the gas in the tower is continuously led out from the gas passage port 1a of the adsorption tower 1B by the vacuum pump 3 and discharged out of the system through the branch line 10b and the line 10. The remaining product oxygen gas introduced from the adsorption tower 1A to the adsorption tower 1B effectively cleans the adsorbent in the adsorption tower 1B.

  In Step 2, the operation of the roots blower 2 is continued, and the switching valves 6a and 6b provided in the branch lines 5a and 5b leading from the roots blower 2 to the adsorption towers 1A and 1B are closed. Supply of the mixed gas to the towers 1A and 1B is shut off. On the other hand, the switching valve 8 provided in the bypass line 7 is open. For this reason, the mixed gas delivered from the roots blower 2 is again sucked into the roots blower 2 via the bypass line 7 and circulates between the line 5 and the bypass line 7. Therefore, the discharge pressure of the mixed gas from the Roots blower 2 does not increase from the vicinity of the atmospheric pressure, and the discharge side and the suction side are almost the same pressure. The above step 2 is continued for 8 seconds, for example.

  In step 3, only the switching valves 8 and 13 are opened, the interruption process is performed for the adsorption towers 1A and 1B, and the gas flow state shown in FIG.

  In step 3, the switching valves 6a, 6b, 11a, 11b, 15a, 15b, and 17 are closed, and the gas flow into and out of the adsorption towers 1A and 1B is blocked. Here, the inside of the adsorption tower 1A is at or above atmospheric pressure, while the inside of the adsorption tower 1B is at or below atmospheric pressure, and the inside of the adsorption tower 1A has a higher pressure than the inside of the adsorption tower 1B. The zeolite as the adsorbent packed in the adsorption towers 1A and 1B has a high adsorption rate, and almost reaches an adsorption equilibrium in a short time of about several seconds under a predetermined pressure. For this reason, the pressure in each of the adsorption towers 1A and 1B is maintained substantially constant. Thereby, in step 3, the gas separation operation by the PSA method is interrupted.

  In step 3, the operation of the roots blower 2 is continued, and the supply of the mixed gas to the adsorption towers 1A and 1B is shut off, while the switching valve 8 provided in the bypass line 7 is open. For this reason, the mixed gas delivered from the roots blower 2 is sucked into the roots blower 2 again via the bypass line 7 and circulates between the line 5 and the bypass line 7 in the same manner as in step 2. Therefore, the discharge pressure of the mixed gas from the Roots blower 2 does not increase from the vicinity of the atmospheric pressure, and the discharge side and the suction side are almost the same pressure.

  In Step 3, the operation of the vacuum pump 3 is also continued, and the switching valves 11a and 11b provided in the branch lines 10a and 10b leading from the vacuum pump 3 to the adsorption towers 1A and 1B are closed. The suction of the gas in the tower from the adsorption towers 1A and 1B is blocked. On the other hand, the switching valve 13 provided in the atmospheric intake line 12 is open. Thus, the vacuum pump 3 sucks air through the air suction line 12, and the suction pressure by the vacuum pump 3 is raised to about atmospheric pressure. Therefore, the discharge side and the suction side of the vacuum pump 3 have substantially the same pressure. The above step 3 is continued for 17 seconds, for example.

  In Step 4, only the switching valves 6b, 11a, and 17 are opened, and the pressure equalization process is performed in the adsorption towers 1A and 1B. More specifically, the depressurization step is performed in the adsorption tower 1A, and the pressure increase step is performed in the adsorption tower 1B, and the gas flow state shown in FIG.

  Since the inside of the adsorption tower 1A was at a higher pressure than the inside of the adsorption tower 1B in the previous Step 3, in Step 4, following Step 2, the gas containing a large amount of product oxygen gas from the adsorption tower 1A (residual product) Oxygen gas) is introduced into the adsorption tower 1B via the line 16. In the adsorption tower 1B, the mixed gas is introduced from the gas passage port 1a through the line 5 and the branch line 5b by the roots blower 2.

  Here, since the inside of the adsorption tower 1B is still under atmospheric pressure, if the switching valve 8 is left open, not only the forced supply of the mixed gas by the roots blower 2 but also the natural supply through the bypass line 7 is performed. Is also done. A gas flow when the switching valve 8 is opened is shown by a broken line in FIG.

  On the other hand, in the adsorption tower 1A, nitrogen desorbed from the adsorbent due to the reduced pressure is led out from the gas passage port 1a by the vacuum pump 3 and discharged out of the system via the branch line 10a and the line 10. The above step 4 is continued for 4 seconds, for example.

  In step 5, only the switching valves 6b and 11a are opened, the desorption process is performed in the adsorption tower 1A, and the pressure increasing process is performed in the adsorption tower 1B. The gas flow state shown in FIG. Has been.

  In the adsorption tower 1A, vacuum desorption of nitrogen by the vacuum pump 3 is continued, and the gas in the tower is discharged out of the system via the branch line 10a and the line 10.

  In the adsorption tower 1B, the mixed gas is introduced from the gas passage port 1a through the line 5 and the branch line 5b by the roots blower 2. At this time, since the adsorption tower 1B is still under atmospheric pressure, when the switching valve 8 is left open, not only forced supply by the roots blower 2 but also natural supply through the bypass line 7 is performed. The above step 5 is continued for 4 seconds, for example, and as a result, the adsorption tower 1B is pressurized to, for example, atmospheric pressure (101 kPa). On the other hand, the desorption of the adsorption tower 1A is not completed in this step 5.

  In subsequent steps 6 to 10, as shown in FIGS. 3F to 3J, the operation performed on the adsorption tower 1A in steps 1 to 5 is performed on the adsorption tower 1B, and the operation performed on the adsorption tower 1B. It carries out for the adsorption tower 1A.

  And the product oxygen gas from which nitrogen was significantly removed from mixed gas is continuously acquired by repeatedly performing the cycle which consists of the above steps 1-10 in each adsorption tower 1A, 1B. In addition, the time (cycle time) of 1 cycle by step 1-10 is 114 seconds.

  In the separation and recovery of oxygen according to the present embodiment, an interruption process (Steps 3 and 8) is inserted in a cycle in which the load of the gas separation operation by the PSA method is 100%. In the interruption process, each adsorption tower 1A, Gas entry / exit to 1B is blocked. As described above, in the interruption process, the pressure in each of the adsorption towers 1A and 1B is maintained substantially constant, and the gas separation operation by the PSA method is interrupted. Therefore, even when the load factor of the gas separation operation by the PSA method is reduced by inserting the interruption process, the PSA gas separation device X1 is operated under the optimized operation conditions when the load of the gas separation operation is 100%. As a result, it is possible to suppress an increase in power consumption (unit power consumption) related to the gas separation operation per unit oxygen generation amount.

  In the interruption process, the mixed gas is circulated through the bypass line 7 for the roots blower 2 and the air is sucked through the air suction line 12 for the vacuum pump 3, so that the discharge side and the suction side respectively. Becomes almost the same pressure (about atmospheric pressure). Due to the characteristics of the capacity-type roots blower, the power consumption decreases as the pressure difference between the discharge side and the suction side decreases. Therefore, in the interruption process, the roots blower 2 and the vacuum pump 3 are in an unload operation (no load operation). This contributes to more effectively suppressing an increase in power consumption related to the gas separation operation per unit oxygen generation amount when reducing the load factor of the gas separation operation by the PSA method.

  As described above, in the interruption process, the internal pressures of the adsorption towers 1A and 1B are maintained substantially constant, and the gas separation operation by the PSA method is interrupted. For this reason, about the interruption process, even if it inserts at any timing with respect to the cycle when the load of gas separation operation is 100%, it is not necessary to change the operation conditions of each process other than an interruption process. Therefore, the interruption process can be incorporated in the middle of the adsorption process, for example.

  In this embodiment, as can be understood with reference to FIG. 3, steps 3 and 8 related to the interruption process are performed immediately before the adsorption tower to be subjected to the pressure reduction operation by the vacuum pump 3 is switched. When the interruption process is inserted at such timing, the number of operations of each switching valve can be substantially reduced, and control of the switching valve can be simplified and durability can be improved.

  When the load of the gas separation operation is 100% (hereinafter referred to as “100% load” as appropriate), the amount of product oxygen gas generated (oxygen acquisition amount per cycle) is constant under optimized operation conditions. It is. Here, even when the load factor of the gas separation operation by the PSA method is reduced by inserting the interruption process, the operation conditions other than the interruption process can be fixed to be the same as the optimized operation conditions. Then, the oxygen acquisition amount per cycle when the interruption process is inserted is the same as the oxygen acquisition amount per cycle of 100% load.

  When the ratio of the required oxygen acquisition amount (oxygen acquisition ratio) to A% (A <100) is set to A% (A <100) with respect to the oxygen acquisition amount of 100% load, the continuation time Ta (steps 3 and 8 above) The sum of the duration of step 3 and the duration of step 8) is calculated by Ta = (100 / A) × Tb−Tb, where Tb is the cycle time when the load of the gas separation operation is 100%. Can do.

  For example, assuming that the cycle time of 100% load is 80 seconds and the oxygen acquisition ratio is 70%, the duration Ta of the interruption process is (100/70) × 80−80 = 34 (seconds) from the above calculation formula. Become.

  The above calculation formula means that the cycle time including the interruption process is inversely proportional to the oxygen acquisition ratio. This is because the operating conditions of the gas separation operation can be fixed regardless of whether or not there is an interruption process, and since the oxygen acquisition amount per cycle is the same, depending on the extent to which the oxygen acquisition amount is reduced This is because the cycle time is extended and the total amount of product oxygen gas flowing into and out of the storage tank 4 is matched. Thus, in this embodiment, the duration Ta of the interruption process can be appropriately determined by a single factor of only the oxygen acquisition ratio.

  In addition, the product oxygen gas is intermittently derived from the adsorption towers 1A and 1B through one cycle including the interruption process, but the storage tank 4 functions as a buffer tank, so that the storage tank 4 responds to the oxygen acquisition ratio. The product oxygen gas can be obtained at a constant flow rate.

  FIG. 4 shows a schematic configuration of a PSA gas separation device X2 that can be used to execute the method for separating and recovering oxygen according to the second embodiment of the present invention. In the PSA gas separation device X2, the same or similar members and parts as those of the above-described PSA gas separation device X1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The PSA gas separation device X2 is different from the PSA gas separation device X1 described above in that a turbo blower 2 'is provided instead of the roots blower 2 and various changes are made accordingly.

  The turbo blower 2 ′ is for sending the mixed gas to the adsorption towers 1 </ b> A and 1 </ b> B, and is provided in the line 5. Due to the turbo blower 2 ', the maximum pressure in the tower in the adsorption step is set to about 30 kPaG or less, for example.

  In the PSA gas separation device X2, unlike the PSA gas separation device X1, the bypass line 7 is not provided. On the other hand, an atmospheric discharge line 18 having an open end is connected to the line 5. The atmospheric discharge line 18 is for releasing a part of the mixed gas sent from the turbo blower 2 'into the atmosphere, and is connected between the turbo blower 2' and the adsorption towers 1A and 1B. The atmospheric discharge line 18 is provided with a switching valve 19 whose opening degree can be adjusted.

  A method for separating and recovering oxygen according to the second embodiment of the present invention will be described with reference to FIGS. In the gas separation by the PSA method according to the present embodiment, in each of the adsorption towers 1A and 1B, for example, each process (step) is performed in the operation time shown in FIG. Is repeated. FIG. 6 schematically shows the gas flow of the PSA gas separation device X2 in each step.

  In Step 1, only the switching valves 6a, 11b, and 15a are opened, the adsorption process is performed for the adsorption tower 1A, and the desorption process is performed for the adsorption tower 1B, as shown in FIG. 6 (a). It is in a gas flow state.

  Air as a mixed gas is introduced into the adsorption tower 1A from the gas passage port 1a through the line 5 and the branch line 5a by the turbo blower 2 '. In the adsorption tower 1A, nitrogen is selectively adsorbed by the adsorbent, and the product oxygen gas is led out from the gas passage port 1b. The product oxygen gas is sent to the storage tank 4 via the branch line 14 a and the line 14. The product oxygen gas in the storage tank 4 is taken out and used after the flow rate is adjusted. In all steps 1 to 10 including step 1, product oxygen gas is continuously acquired from the storage tank 4 at a constant flow rate.

  The adsorption tower 1B has already undergone a desorption process (see step 10 shown in FIG. 6 (j)), and the inside of the tower is subsequently depressurized by the vacuum pump 3 so that nitrogen is desorbed from the adsorbent. Is led out of the tower as off-gas through the gas passage port 1a. The off-gas is discharged out of the system via the branch line 10b and the line 10. Step 1 is continued for 24 seconds, for example.

  In Step 2, only the switching valves 6a, 11b, 15a, and 17 are opened, the adsorption process is performed in the adsorption tower 1A, and the desorption cleaning process is performed in the adsorption tower 1B, as shown in FIG. It is set as the gas flow state shown.

  In the adsorption tower 1A, the adsorption process is performed subsequent to step 1, and the product oxygen gas led out from the gas passage port 1b is sent to the storage tank 4. In Step 2, part of the product oxygen gas is introduced into the adsorption tower 1B through the line 16. On the other hand, the gas in the tower is continuously led out from the gas passage port 1a of the adsorption tower 1B by the vacuum pump 3 and discharged out of the system through the branch line 10b and the line 10. The product oxygen gas introduced into the adsorption tower 1B from the adsorption tower 1A effectively cleans the adsorbent in the adsorption tower 1B. The above step 2 is continued for 8 seconds, for example.

  In Step 3, only the switching valves 13 and 19 are opened, the interruption process is performed for the adsorption towers 1A and 1B, and the gas flow state shown in FIG.

  In step 3, the switching valves 6a, 6b, 11a, 11b, 15a, 15b, and 17 are closed, and the gas flow into and out of the adsorption towers 1A and 1B is blocked. Here, the inside of the adsorption tower 1A is at or above atmospheric pressure, while the inside of the adsorption tower 1B is at or below atmospheric pressure, and the inside of the adsorption tower 1A has a higher pressure than the inside of the adsorption tower 1B. The zeolite as the adsorbent packed in the adsorption towers 1A and 1B has a high adsorption rate, and almost reaches an adsorption equilibrium in a short time of about several seconds under a predetermined pressure. For this reason, the pressure in each of the adsorption towers 1A and 1B is maintained substantially constant. Thereby, in step 3, the gas separation operation by the PSA method is interrupted.

  In Step 3, the operation of the turbo blower 2 'is continued, and the supply of the mixed gas to the adsorption towers 1A and 1B is shut off, while the switching valve 19 provided in the atmospheric discharge line 18 is open. Here, the switching valve 19 is adjusted so that the opening degree becomes relatively small without being fully opened. For this reason, a part (small amount) of the mixed gas delivered from the turbo blower 2 ′ is released into the atmosphere via the atmosphere release line 18. At this time, the discharge pressure in the turbo blower 2 'is the highest in terms of characteristics.

  In Step 3, the operation of the vacuum pump 3 is also continued, and the switching valves 11a and 11b provided in the branch lines 10a and 10b leading from the vacuum pump 3 to the adsorption towers 1A and 1B are closed. The suction of the gas in the tower from the adsorption towers 1A and 1B is blocked. On the other hand, the switching valve 13 provided in the atmospheric intake line 12 is open. Thus, the vacuum pump 3 sucks air through the air suction line 12, and the suction pressure by the vacuum pump 3 is raised to about atmospheric pressure. Therefore, the discharge side and the suction side of the vacuum pump 3 have substantially the same pressure. The above step 3 is continued for 17 seconds, for example.

  In Step 4, only the switching valves 11a, 17 and 19 are opened, and the pressure equalizing process is performed in the adsorption towers 1A and 1B. More specifically, the depressurization process is performed in the adsorption tower 1A, and the pressure increase process is performed in the adsorption tower 1B, and the gas flow state shown in FIG.

  In the previous step 3, the inside of the adsorption tower 1A was at a higher pressure than the inside of the adsorption tower 1B. Therefore, in step 4, a gas containing a large amount of product oxygen gas (residual product oxygen gas) is lined from the adsorption tower 1A. 16 is introduced into the adsorption tower 1B. Further, in the adsorption tower 1A, nitrogen desorbed from the adsorbent by depressurization is led out from the gas passage port 1a by the vacuum pump 3 and discharged out of the system through the branch line 10a and the line 10.

  In Step 4, the operation of the turbo blower 2 'is continued, and the switching valves 6a and 6b provided in the branch lines 5a and 5b leading from the turbo blower 2' to the adsorption towers 1A and 1B are closed. The supply of the mixed gas to the adsorption towers 1A and 1B is shut off. On the other hand, the switching valve 19 provided in the atmospheric discharge line 18 is open. Here, the switching valve 19 is adjusted so that the opening degree becomes relatively small without being fully opened as in step 3. For this reason, a part (small amount) of the mixed gas delivered from the turbo blower 2 ′ is released into the atmosphere via the atmosphere release line 18. At this time, like step 3, the discharge pressure in the turbo blower 2 'is the highest in terms of characteristics. The above step 4 is continued for 4 seconds, for example.

  In step 5, only the switching valves 6b and 11a are opened, the desorption process is performed in the adsorption tower 1A, and the pressurization process is performed in the adsorption tower 1B, and the gas flow state shown in FIG. Has been.

  In the adsorption tower 1A, the vacuum desorption of nitrogen by the vacuum pump 3 is continued, and the gas in the tower is discharged out of the system via the branch line 10b and the line 10. In the adsorption tower 1B, the mixed gas is introduced from the gas passage port 1a through the line 5 and the branch line 5b by the turbo blower 2 '. The above step 5 is continued for 4 seconds, for example, and as a result, the adsorption tower 1B is pressurized to, for example, atmospheric pressure (101 kPa). On the other hand, the desorption of the adsorption tower 1A is not completed in this step 5.

  In subsequent steps 6 to 10, as shown in FIGS. 6F to 6J, the operation performed on the adsorption tower 1A in steps 1 to 5 is performed on the adsorption tower 1B, and the operation performed on the adsorption tower 1B. It carries out for the adsorption tower 1A.

  And the product oxygen gas from which nitrogen was significantly removed from mixed gas is continuously acquired by repeatedly performing the cycle which consists of the above steps 1-10 in each adsorption tower 1A, 1B. In addition, the time (cycle time) of 1 cycle by step 1-10 is 114 seconds.

  In the separation and recovery of oxygen according to the present embodiment, an interruption process (Steps 3 and 8) is inserted in a cycle in which the load of the gas separation operation by the PSA method is 100%. In the interruption process, each adsorption tower 1A, Gas entry / exit to 1B is blocked. As described above, in the interruption process, the pressure in each of the adsorption towers 1A and 1B is maintained substantially constant, and the gas separation operation by the PSA method is interrupted. Accordingly, even when the load factor of the gas separation operation by the PSA method is reduced by inserting the interruption process, the PSA gas separation device X2 is operated under the optimized operation condition when the load of the gas separation operation is 100%. As a result, it is possible to suppress an increase in power consumption (unit power consumption) related to the gas separation operation per unit oxygen generation amount.

  In the interruption process (steps 3 and 8) and the pressure equalization process (steps 4 and 9), a small amount of the mixed gas sent from the turbo blower 2 'is released into the atmosphere via the atmosphere release line 18. In the turbo blower 2 ′, when the gas flow rate is reduced, the power consumption is reduced. On the other hand, when the deadline operation is performed, there is a risk of heat storage due to the generation of compression heat or damage due to mechanical vibration called a surging phenomenon. Occurs. In the present embodiment, in consideration of such characteristics of the turbo blower 2 ′, the opening amount of the switching valve 19 provided in the atmospheric discharge line 18 is adjusted to reduce the amount of gas released into the atmosphere. In the interruption step, the vacuum pump 3 sucks air through the air suction line 12 so that the discharge side and the suction side have substantially the same pressure (about atmospheric pressure). Therefore, the vacuum pump 3 is in an unload operation (no load operation). The operating conditions of the turbo blower 2 ′ and the vacuum pump 3 in such an interruption process are as follows: when the load factor of the gas separation operation by the PSA method is reduced, the power consumption (unit power consumption) related to the gas separation operation per unit oxygen generation amount ) Contributes to appropriately suppressing the increase.

  Other advantages obtained in the present embodiment are the same as those described above for the method for separating and recovering oxygen according to the first embodiment, and a description thereof will be omitted.

  In the first and second embodiments described above, the Roots blower 2 and the turbo blower 2 'are cited as blowers for sending the mixed gas in the gas separation operation. The Roots blower 2 is preferably used when operating at a relatively high pressure of about 40 to 50 kPaG, and the turbo blower 2 'is preferably used when operating at a relatively low pressure of about 30 kPaG or less. Is done. In consideration of the characteristics of the root blower 2 and the turbo blower 2 ′, in the first embodiment using the root blower 2, the supply of the mixed gas to the adsorption towers 1A and 1B is interrupted (steps 3 and 8). In the second embodiment using the turbo blower 2 ′, the mixed gas delivered from the roots blower 2 is circulated so as to be sucked into the roots blower 2 again (steps 2, 3, 7, and 8) including Then, supply of the mixed gas to the adsorption towers 1A and 1B is interrupted, and the mixed gas sent from the turbo blower 2 ′ in the steps (steps 3, 4, 8, and 9) including the interruption process (steps 3 and 8) is cut off. Part of it is released into the atmosphere.

  In the first and second embodiments, the operation of the roots blower 2 and the turbo blower 2 ′ is continued in the interruption process. Instead, the operation of the roots blower 2 and the turbo blower 2 ′ is stopped in the interruption process. May be. However, the root blower 2 and the turbo blower 2 'do not follow the operation of the rotating machine quickly by turning on and off the power supply. Therefore, if the operation of the root blower 2 or the turbo blower 2' is stopped during the interruption process, an appropriate operating condition at 100% load It is necessary to consider this point.

  As mentioned above, although embodiment of this invention was described, the range of this invention is not limited to above-described embodiment. For example, a cycle consisting of a plurality of steps that is repeatedly performed in each adsorption tower 1A, 1B by the PSA method is not limited to the above embodiment, and any cycle that includes an adsorption step, a desorption step, and an interruption step can be used as appropriate. It can be changed.

  Further, the target gas separation and recovery method according to the present invention is not limited to the application to oxygen PSA that concentrates and separates oxygen as in the above embodiment, but for gas separation by the PSA method using other gas components as the target gas. You may apply.

  Next, the usefulness of the present invention will be described with reference to examples and comparative examples.

[Example 1]
In this example, the PSA gas separation device X1 shown in FIG. 1 was used as a mixed gas under the following conditions by the method for separating and recovering oxygen comprising the steps described in the first embodiment. Oxygen was separated and recovered from the air.

As the adsorption towers 1A and 1B, cylindrical ones having a diameter of 2,900 mm and an adsorbent filling height of 1,500 mm are used. In each adsorption tower 1A and 1B, LiX zeolite (trade name: trade name: NSA-100, manufactured by Tosoh Corporation). The roots blower 2 has an adsorption pressure (maximum pressure) of 40 kPaG, the vacuum pump 3 has a desorption pressure (minimum pressure) of −67 kPaG, an operation time of 100% load and one cycle of 40 seconds × 2 = 80 seconds. For the operating condition where the oxygen acquisition amount is 792 Nm ³ / h in terms of 100% concentration, the interruption process is inserted for 17 × 2 = 34 seconds to make one cycle 114 seconds, and the oxygen acquisition ratio is 100% when loading. The gas flow rate from the storage tank 4 was reduced to 70%, and the gas separation operation was performed according to the steps shown in FIGS.

As a result, a product oxygen gas of 555 Nm ³ / h in terms of 100% concentration can be obtained from the storage tank 4, and the power consumption (unit power consumption) per 1 Nm ³ / h of oxygen in terms of 100% concentration is 0.398 kw / Nm ^3. It became.

[Comparative Example 1]
In this comparative example, as a result of performing the gas separation operation on the operation condition of 100% load without the interruption process with respect to the above Example 1, when the oxygen acquisition amount is 792 Nm ³ / h in terms of 100% concentration, % power consumption per oxygen 1Nm ³ / h of concentration conversion became 0.35kw / Nm ^3.

Next, the gas flow rate from the storage tank 4 was reduced so that the oxygen acquisition ratio would be 70% at the time of 100% load (555 Nm ³ / h in terms of 100% concentration). As a result, the power consumption (power consumption unit) per 1 Nm ³ / h of oxygen in terms of 100% concentration was 0.50 kw / Nm ³ .

[Example 2]
In this example, the PSA gas separation device X2 shown in FIG. 4 was used as a mixed gas under the conditions shown below by the method for separating and recovering oxygen comprising the steps described in the second embodiment. Oxygen was separated and recovered from the air.

As the adsorption towers 1A and 1B, cylindrical ones having a diameter of 2,900 mm and an adsorbent filling height of 1,500 mm are used. In each adsorption tower 1A and 1B, LiX zeolite (trade name: trade name: NSA-100, manufactured by Tosoh Corporation). The turbo blower 2 ′ has an adsorption pressure (maximum pressure) of 20 kPaG and the vacuum pump 3 has a desorption pressure (minimum pressure) of −69 kPaG. The operation time is 100% load and the operation time is 40 seconds × 2 = 80 seconds. For the operating condition where the oxygen acquisition amount is 652 Nm ³ / h in terms of 100% concentration, the interruption process is inserted for 17 × 2 = 34 seconds and one cycle is 114 seconds, and the oxygen acquisition ratio is 100% when loading. The gas flow rate from the storage tank 4 was reduced so as to be 70%, and the gas separation operation was performed according to the steps shown in FIGS.

As a result, a product oxygen gas of 456 Nm ³ / h in terms of 100% concentration can be obtained from the storage tank 4, and the power consumption (power intensity) per 1 Nm ³ / h of oxygen in terms of 100% concentration is 0.371 kw / Nm ^3. It became.

[Comparative Example 2]
In this comparative example, as a result of performing the gas separation operation on the operation condition of 100% load with no interruption process with respect to the above Example 2, when the oxygen acquisition amount is 652 Nm ³ / h in terms of 100% concentration, % power consumption per oxygen 1Nm ³ / h of concentration conversion became 0.35kw / Nm ^3.

Next, the gas flow rate from the storage tank 4 was reduced so that the oxygen acquisition ratio would be 70% at the time of 100% load (456 Nm ³ / h in terms of 100% concentration). As a result, the power consumption (power consumption unit) per 1 Nm ³ / h of oxygen in terms of 100% concentration was 0.50 kw / Nm ³ .

  As can be understood by comparing Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2 above, an example in which an interruption process is inserted when the oxygen acquisition ratio is reduced to 70% at 100% load. In 1 and 2, it was possible to significantly suppress the increase in power consumption rate.

X1, X2 PSA gas separation device 1A, 1B Adsorption tower 1a, 1b Gas passage 2 Roots blower (blower)
2 'Turbo Blower (Blower)
3 Vacuum pump 4 Storage tank 5, 10, 14, 16 Lines 5a, 5b, 10a, 10b, 14a, 14b Branch lines 6a, 6b, 8, 11a, 11b, 13, 15a, 15b, 19 Switching valve 7 Bypass line 9 Cooler 12 Air intake line 18 Air discharge line

Claims (6)

Product gas enriched with the target gas by a pressure fluctuation adsorption method using two adsorption towers filled with an adsorbent that selectively adsorbs the unnecessary gas from a mixed gas containing the target gas and unnecessary gas A method for separating and recovering
A mixed gas is introduced into the adsorption tower by a blower, the unnecessary gas in the mixed gas is adsorbed on the adsorbent, and the product gas is led out from the adsorption tower to a storage tank for storing the product gas. Adsorption process to send out, desorption process to desorb the unnecessary gas from the adsorbent by depressurizing the adsorption tower with a vacuum pump, and desorption process to lead out the gas from the adsorption tower, and interruption to shut off the gas in and out of each adsorption tower A method of separating and recovering a target gas, wherein a cycle including a step is repeated in each of the adsorption towers, and the product gas is continuously obtained from the storage tank through the cycle.   The method for separating and recovering a target gas according to claim 1, wherein the target gas is oxygen and the unnecessary gas is nitrogen.   In the interruption step, a first operation for circulating the mixed gas that has passed through the blower so as to flow into the blower while continuing the operation of the blower, and a second operation for releasing the mixed gas that has passed through the blower into the atmosphere. The method for separating and recovering a target gas according to claim 1, wherein any one of the operation and the third operation for stopping the operation of the blower is performed.   The method for separating and recovering a target gas according to any one of claims 1 to 3, wherein, in the interruption step, the air is sucked by the vacuum pump while the operation of the vacuum pump is continued.   The method for separating and recovering a target gas according to any one of claims 1 to 4, wherein the interruption step is performed immediately before switching from the adsorption tower to be subjected to a pressure reduction operation by the vacuum pump.   The calculation of the duration Ta of the interruption process in the cycle is Tb as the cycle time when the load of the gas separation operation is 100%, and the load time of the gas separation operation is 100%. 6. The target gas according to claim 1, wherein the target gas is obtained by the calculation formula Ta = (100 / A) × Tb−Tb, where A% is the acquisition ratio of the target gas with respect to the target gas acquisition amount. Separation and recovery method.

Images