JPH0456647B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for producing oxygen-rich gas. More specifically, the present invention uses an adsorbent that selectively adsorbs nitrogen, and adsorbs and removes nitrogen from a mixed gas containing oxygen and nitrogen, such as air, by pressure fluctuation adsorption under atmospheric pressure. This invention relates to a method for producing gas. Prior art It is known that oxygen-enriched gas can be produced by separating an oxygen/nitrogen mixed gas such as air by pressure fluctuation adsorption using the selective adsorption of nitrogen by adsorbents such as synthetic zeolite and natural zeolite. (For example, Japanese Patent Publication Nos. 51-40549 and 51-40550, and Japanese Patent Publications No. 52-122273 and 58-84020). In producing oxygen-enriched gas using this method, an oxygen/nitrogen mixed gas is introduced into each of multiple adsorption towers containing beds of adsorbent to remove nitrogen by adsorption, and remove oxygen, which is difficult to adsorb. The concentrated and enriched gas is extracted from the adsorption tower and used as product gas. Then, the steps of depressurization, purging, exhaust, etc. for regenerating the adsorbent in the adsorption tower and the adsorption/separation step are sequentially switched in each adsorption tower. Each technology is characterized by pressure fluctuation range, cycle and gas flow characteristics. For example, in Japanese Patent Publications No. 51-40549 and No. 51-40550, it was carried out in the pressure operation range on the pressure side above atmospheric pressure;
In 84020, the pressure operation range is from vacuum pressure to the pressurized side, and in JP-A-52-122273, all operations are carried out under atmospheric pressure. It is known that such a pressure fluctuation width can be set arbitrarily, and its characteristics are exhibited depending on the pressure fluctuation width, cycle, and gas flow. However, in the conventionally known method for producing oxygen-rich gas using pressure fluctuation adsorption, the efficiency of oxygen separation and recovery is insufficient, and the amount of energy consumed per amount of product gas produced is high. There are still problems, and there is still room for improvement. OBJECTS OF THE INVENTION The main object of the present invention is to provide a method for producing oxygen-rich gas by pressure fluctuation adsorption, which has high oxygen separation and recovery efficiency and low energy consumption per product gas production. Structure of the Invention According to the present invention, three adsorption towers filled with beds of adsorbent that selectively adsorb nitrogen are used, and a mixed gas containing oxygen and nitrogen is passed through the adsorption towers to remove nitrogen. A method is provided for producing oxygen-rich gas by adsorption and removal. In this method according to the present invention, in the first adsorption tower, (1) the mixed gas is introduced from the end of the raw material, and at the same time the mixed gas is introduced into the second adsorption tower.
(2) introducing the mixed gas from the raw material end to selectively adsorb nitrogen; , At the same time, the pressure in the column is increased while oxygen-rich gas is sucked out from the product end by the product suction pump, (3) The introduction of the mixed gas is stopped, and the oxygen-rich gas is sucked out from the product end by the product suction pump. a step of supplying a part of this oxygen-rich gas to the product end of the third adsorption tower while drawing it out to equalize the pressure with the third adsorption tower; (4) oxygen-rich gas from the product end; a step of deriving the gas and supplying the oxygen-rich gas to the product end of the second adsorption tower for purging the second adsorption tower; (5) evacuation from the raw material end; A step of purging the inside of the tower by introducing oxygen-rich gas from the third adsorption tower from the end of the product while evacuating the end of the raw material. All of the above steps are carried out under atmospheric pressure, and during this period It is characterized in that the process cycle is carried out in different phases in each of the second and third adsorption towers. DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes pressure fluctuation adsorption to separate nitrogen from a mixed gas mainly containing oxygen and nitrogen, such as air, to obtain an oxygen-rich gas. That is, a mixed gas is supplied to an adsorption tower under vacuum pressure filled with an adsorbent such as synthetic zeolite or natural zeolite, and the adsorbent adsorbs nitrogen, condenses oxygen, and returns it to atmospheric pressure as a product gas. The product is discharged using a suction pump from near vacuum pressure. next,
The nitrogen adsorbed by the adsorbent is desorbed by vacuuming the adsorption tower filled with the adsorbent adsorbing nitrogen from the raw material end side. In the present invention, three adsorption towers filled with adsorbents are used, and while a mixed gas is supplied from the raw material end of one tower, the mixed gas has already been pressurized to a predetermined pressure and enriched with oxygen. A pressure equalization process is carried out in which the product ends of each column are connected to another column which is releasing the product gas, and the pressure between the two columns is equalized. In addition, while nitrogen is being desorbed by vacuum suction from the raw material end, a purge process is carried out in which oxygen-rich gas from another tower is introduced from the product end of the tower to clean the inside of the tower. . The oxygen-rich gas of the product is then continuously sucked and discharged by the product suction pump without interruption during the process cycle. Therefore, by supplying oxygen-rich gas from the product end of the adsorption tower, pressure equalization has the effect of keeping the nitrogen adsorption front in the tower short and increasing the oxygen concentration in the resulting gas. Purging is performed by supplying oxygen-rich gas from the end of the product during vacuum desorption of nitrogen and passing it through the column, thereby lowering the nitrogen partial pressure in the column and increasing the desorption effect.
This has the effect of shortening the time for vacuum attachment and desorption and reducing power costs. Further, since all cycles are performed under atmospheric pressure, a supply pressure pump for supplying the raw material mixed gas is not required, and the product oxygen is sucked out by the product suction pump. Therefore, it is only necessary to suck in a volume of product oxygen that is about 1/10 of the raw material mixed gas, resulting in a significant power saving. For example, in JP-A-52-122273, like the present invention, all cycles are carried out under atmospheric pressure, but the product is first taken out from the first adsorption tower, and the next step is to supply it to the other towers. Using it as a part of the raw material gas improves the recovery rate of the product, but the present invention improves the problem that the flow becomes complicated and the gas flow inside the column becomes long. In addition, changes in the flow rate to the adsorption tower disturb the adsorption front and are disadvantageous for obtaining a high concentration of product gas.Especially at the maximum flow rate, the pressure loss in the adsorption tower becomes maximum and the power of the product suction pump increases. There is. In addition, if the feed gas flows into the adsorption tower at the maximum flow rate, there is a risk that the adsorbent will become fluidized, causing destruction or powdering of the adsorbent. The present invention also overcomes the above-mentioned drawbacks.
In other words, by equalizing the pressure of the oxygen-rich gas from the product end at the same time as the mixed gas from the raw material end, it is possible to prevent the mixed gas from being introduced at the maximum flow rate, keep the adsorption front in the column short, and reduce the product gas concentration. This has the effect of increasing the According to the method of the present invention having such a configuration, it becomes possible to produce an oxygen-rich gas with a high oxygen concentration, particularly an oxygen concentration of 90 to 93% or more, with extremely high efficiency. And the vacuum pump is also activated throughout the cycle. Hereinafter, the method of the present invention will be specifically explained with reference to FIG. 1, but it should be understood that the operations shown below are merely examples and are not limited to these operations. In operation, oxygen-rich gas is continuously released while repeating the six steps described below in sequence. Further, the operation time of each step can be arbitrarily controlled by a timer. Step 1 Valve 1A is opened and air 20 is supplied from the lower part of column A, ie, the raw material end. At the same time, valves 2A and 2C are opened, and while the pressure has already been increased to a predetermined pressure with air in the previous step (step 6), valve 12C is opened and the product suction pump 21 is discharging oxygen-rich gas from the C column. By introducing the oxygen-rich gas from the upper part of the C column, that is, the product end, into the product end of the A column, the pressure between the A column and the C column is equalized. pressure). At this time, the outflow rate of oxygen-rich gas from the C tower is controlled by valves 6A and 6C. On the other hand, the valve 4B is opened to reduce the pressure, and the B tower is evacuated by the vacuum pump 19. Step 2 At the same time as valves 2A and 12C are closed, valve 12A
is opened, and the product gas is transferred from the A tower to the product suction pump 2.
1 is suctioned and released. Tower A receives air supply through valve 1A while releasing product gas, and the pressure inside the tower is gradually increased. on the other hand,
The valve 3B is opened, and oxygen-rich gas is supplied from the product end of the C tower to the product end of the B tower, and is discharged to the outside of the system by the vacuum pump 19 while washing the inside of the B tower in the countercurrent direction. purge. The C tower further reduces the pressure while supplying oxygen-rich gas to the B tower. The rate of supply of oxygen-rich gas from the C column is controlled by valve 17. Step 3 Valves 1A, 2C, and 4B are closed, and valve 1B is newly opened.
is opened and air is supplied from the feed end of the B column. At the same time, valves 2A and 2B are opened, oxygen-rich gas is supplied from the product end of column A to the product end of column B, and the pressure between column A and column B is equalized (pressure equalization). At this time, the outflow rate of the oxygen-rich gas from the A tower is controlled by valves 6A and 6B. On the other hand, the valve 3B is closed, the valve 4C is opened to reduce the pressure, and the C tower is evacuated by the vacuum pump 19. Step 4 At the same time as valves 2B and 12A are closed, valve 12B
is opened, and the product gas is transferred from the B tower to the product suction pump 2.
1 is suctioned and released. While releasing product gas, tower B receives air supply through valve 1B, and the pressure inside the tower is gradually increased. on the other hand,
The valve 3C is opened, and oxygen-rich gas is supplied from the product end of the A column to the product end of the C column, and is discharged to the outside of the system by the vacuum pump 19 while washing the inside of the C column in the countercurrent direction. purge. Tower A further reduces the pressure while supplying oxygen-rich gas to tower C. The rate of supply of oxygen-rich gas from the A column is controlled by valve 17. Step 5 Valve 1B, 2A, 4C is closed, and valve 1C is newly opened.
is opened and air is supplied from the feed end of the C column. At the same time, valves 2B and 2C are opened, and oxygen-rich gas is supplied from the product end of the B column to the product end of the C column, thereby equalizing the pressure between the B and C columns. (equal pressure). At this time, the outflow rate of the oxygen-rich gas from the B tower is controlled by valves 6B and 6C. On the other hand, valve 3C is closed, valve 4A is opened to reduce the pressure, and tower A is evacuated by vacuum pump 19. Step 6 At the same time as valves 2C and 12B are closed, valve 12C
is opened, and the product gas is sucked and discharged from the C tower by the product suction pump 21. While the C tower sucks and discharges the product gas, air is supplied through the valve 1C, and the pressure inside the tower is gradually increased.
On the other hand, the valve 3A is opened, and oxygen-rich gas is supplied from the product end of the B column to the product end of the A column, and while washing the inside of the A column in the countercurrent direction, it is pumped out of the system by the vacuum pump 19. Purge. The B tower further reduces the pressure while supplying oxygen-rich gas to the A tower. The rate of supply of oxygen-rich gas from the B column is controlled by valve 17. In FIG. 1, 22 indicates the outflow of oxygen-rich gas as a product, and 23 indicates the outflow of separated and removed nitrogen. As can be understood from the above explanation, the above 6
The process is repeated with steps 1 and 2 as one unit and the phase of the relationship between the columns is changed one by one. FIGS. 2 and 3 are schematic diagrams illustrating these two basic steps (steps 1 and 2). As explained above, in the method of the present invention, all cycles are performed under atmospheric pressure, so it can be carried out using the power of an oxygen suction pump with a capacity of approximately 1/10 of the raw material mixed gas, significantly reducing power costs. became possible. In addition, the pressure inside each tower is
The pressure is constantly changing and never stays at a constant pressure for even a moment. This utilizes the properties of adsorption and desorption rates of nitrogen and oxygen with respect to pressure changes. In other words, when the pressure increases, the adsorption rate of nitrogen is faster than that of oxygen, and when the pressure decreases, the desorption rate of oxygen is faster than that of nitrogen, so that it can be efficiently recovered as product oxygen.Also, it is possible to exchange oxygen between each column. This is to improve the oxygen yield by minimizing the amount of oxygen discharged outside the system, and even if the maximum adsorption pressure is atmospheric pressure and the ultimate vacuum pressure is in a high range, The purpose is to lower the average vacuum pressure as much as possible to reduce power costs. Furthermore, although purging is an essential operation to stably obtain product gas with a high oxygen concentration, it is not necessary to know the absolute amount to control the maximum purge amount; instead, it is necessary to supply oxygen for purging. It can be considered as the amount of pressure drop in the tower (represented by purge Δp). Purge Δp is typically 50-200
Within the mmHg range, determine the purge amount that provides the highest oxygen concentration and recovery rate for each highest grade pressure, ultimate vacuum pressure, and cycle time. The factors that evaluate the efficiency of the oxygen-rich gas production process by pressure fluctuation adsorption are oxygen concentration and recovery rate, but other factors are the amount of adsorbent, such as molecular sieve, per unit time and oxygen production. The ratio to quantity can be mentioned. In the following examples, this factor is used as the bed size factor (BS
F.), and its unit is (Kg・MS)/(t・
O ₂ /d) [(Kg・Molecular sieve)/(ton・100% O ₂ /day)]. This BSF is
This is a factor related to the quality of the process and the molecular sieve, but it is useful as a factor for process evaluation when molecular sieves of the same quality are used. As is clear from the above unit, it can be said that a process with a small BSF is preferable. Examples Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 A three-column type adsorbent in which each column has an inner diameter of 81 cm and a height of 2.5 m has a volume of 1.6 mm diameter pellets of molecular sieve 5A as an adsorbent at a rate of 9.2 mm per column.
Kg was used. As an operating condition, the maximum adsorption pressure is −50
mmHg, ultimate vacuum pressure -600mmHg, purge Δp0.1Kg/
cm ² , and the cycle time was changed for each experiment number, and continuous operation was performed according to the above-mentioned process, and the results shown in Table 1 were obtained. 【table】

[Brief explanation of the drawing]

FIG. 1 is a system diagram for explaining the method of the present invention, and FIGS. 2 and 3 are schematic diagrams showing the order of process operations of the method of the present invention, respectively. A, B, C... adsorption tower; 1A~2C, 2A~2
C, 3A to 3C, 4A to 4C... Valve; 19... Vacuum pump; 21... Product suction pump.

Claims (1)

[Claims] 1. Using three adsorption towers filled with beds of adsorbent that selectively adsorbs nitrogen, and flowing a mixed gas containing oxygen and nitrogen through the adsorption towers to adsorb and remove nitrogen. This is a method for producing oxygen-rich gas by sequentially (1) introducing a mixed gas from the end of the raw material in the first adsorption tower, and simultaneously introducing the mixed gas into the second adsorption tower.
(2) introducing the mixed gas from the raw material end to selectively adsorb nitrogen; (3) The process of increasing the pressure inside the column while simultaneously suctioning and deriving oxygen-rich gas from the end of the product; (3) Stopping the introduction of the mixed gas, and increasing the supplying a portion of the oxygen-rich gas to the product end of the third adsorption column;
a step of equalizing the pressure with the third adsorption tower; (4) deriving oxygen-rich gas from the end of the product and supplying the product of the second adsorption tower with this oxygen-rich gas for purging the second adsorption tower; (5) a step of evacuation from the end of the raw material, and (6) a step of evacuation from the end of the raw material, while introducing oxygen-rich gas from the third adsorption tower from the end of the product to the tower. All of the above steps are carried out under atmospheric pressure, and the process cycle is carried out in different phases in each of the second and third adsorption towers.