JPS60210507A - Method for controlling turn-down in pressure fluctuation adsorption process - Google Patents

Abstract

PURPOSE:To reduce effectively power necessary for a pressure fluctuation adsorption system by controlling the system for a period in which the velocity of outflow of oxygen enriched gas or other factor during outflow is reduced. CONSTITUTION:A compressed gaseous mixture of oxygen with nitrogen is successively fed to adsorption towers A, B, C, where nitrogen is selectively adsorbed to produce oxygen enriched gas. For example, the gaseous mixture is fed to the bottom of the tower A, and at the same time, the top of the tower A is made to communicate with the upper product outlet of the tower C from which oxygen enriched gas as a product is being released under internal pressure increased in the preceding step to equalize the pressures of the towers A, C. Nitrogen is desorbed in the tower B satd. with nitrogen. When oxygen enriched gas is released from the tower A, concd. oxygen enriched gas is fed from the top of the tower C to the top of the tower B to carry out the countercurrent cleaning of the inside of the tower B, and the gas is exhausted from the system with a vacuum pump 19. The internal pressure of the tower C is reduced. The tower A attains to a prescribed pressure by the release of oxygen enriched gas as a product. Oxygen enriched gas remaining in the upper part of the tower C is fed to the bottom of the tower B to equalize the pressures of the towers A, C. The operations are carried out in the towers A, B, C in different phases.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to the production of oxygen-rich gas by a pressure fluctuation adsorption method. The present invention relates to a method for controlling a system of pressure fluctuation adsorption during turndown.

It is known that oxygen-enriched gas can be produced by separating oxygen/nitrogen mixed gas such as air through pressure fluctuation adsorption using the selective adsorption of nitrogen by adsorbents such as synthetic zeolite and natural zeolite. (For example, Special Publick
No. 49, JP-A-53-96987 and JP-A-58-8
No. 4020).

In producing oxygen-rich gas by such a method, an oxygen/nitrogen mixed gas is introduced into each of a plurality of adsorption towers containing adsorbent beds to remove nitrogen by adsorption, and the pre-adsorptive oxygen is removed by adsorption. The concentrated and enriched gas is extracted from the adsorption tower and used as product gas.

Then, the processes of depressurization, purging, exhaust, etc. for regenerating the adsorbent in the adsorption tower and the adsorption/separation process 'ttlVA' are then switched within each adsorption tower.

A method of turndown control in such a pressure fluctuation adsorption system is disclosed in Japanese Patent Laid-Open No. 16375/1983. This method performs turndown control on a system of pressure fluctuation adsorption in a pressurization cycle on a specific atmospheric pressure leg. That is, in the first adsorption tower, the feed gas is subjected to pressure adsorption, and the product gas is taken out while the adsorption pressure is gradually increased. After the internal pressure of the tower reaches the maximum pressure, the introduction of feed gas is transferred to other adsorption towers, but the first
The product gas from the adsorption tower is taken out as a product by co-current depressurization and is simultaneously used for pressure equalization and parts in other adsorption towers. The internal pressure of the first adsorption column is then countercurrently reduced to atmospheric pressure, thereby eliminating desorption of the adsorbed material and further regenerating the adsorption bed by means of the countercurrent part. The adsorption tower consists of two adsorption towers and can continuously obtain product gas. In such a pressure fluctuation adsorption cycle, the amount of product gas generated per cycle and per adsorption bed is set, and when the required amount of product gas usage decreases, the amount of product gas generated increases. The cycle is not advanced to the next step until the set amount is reached; on the other hand, in an adsorption tower that is pressurized by the supply gas, the compressor is unloaded (no load) when the maximum adsorption pressure is reached.
In this case, the supply gas is stopped and the power is reduced. However, this turndown control is performed in a pressurized pressure fluctuation adsorption cycle, and an example of performing turndown control in a vacuum type pressure fluctuation adsorption cycle where the pressure fluctuation range extends from atmospheric pressure to the vacuum side. Conventionally, there is no such thing.

OBJECTS OF THE INVENTION The main object of the present invention is to perform turndown control in the production of oxygen-rich gas by pressure fluctuation adsorption, including increased pressure adsorption and vacuum desorption (regeneration), and to effectively reduce the power of this system. The goal is to provide a way to do so.

Components of the Invention The present invention provides a turndown control method in a pressure swing adsorption process, which uses three adsorption towers filled with beds of adsorbent that selectively adsorbs nitrogen; In producing oxygen-rich gas by passing the entire mixed gas mainly containing oxygen and nitrogen through the adsorption tower to adsorb and remove nitrogen, in each adsorption tower, the pressure inside the tower is increased by supplying a pressurized mixed gas. , an increased pressure adsorption process that selectively adsorbs nitrogen and extracts oxygen-rich gas, a vacuum regeneration process that evacuates in a countercurrent direction, and a process in which parts are evacuated in a countercurrent direction simultaneously with oxygen-rich gas from other columns. 9- Pressure fluctuation consisting of sequentially carrying out a cycle with different phases including a step and a pressure equalization step in which the pressure inside the column is equalized by introducing oxygen-rich gas from another column. In the adsorption method, after the end of the pressure equalization step, the amount of oxygen-rich gas flowing out during at least one period during which the oxygen-rich gas is withdrawn from the adsorption tower from which oxygen-rich gas is continuously withdrawn. monitoring at least one oxygen-enriched gas flow characteristic, including velocity, concentration, and pressure, and not advancing the process cycle to the next step until said characteristic reaches a predetermined value, while said pressurization is being performed. The supply of the pressurized mixed gas to the adsorption tower is stopped at the same time as the internal pressure of this tower reaches a predetermined pressure or the pressure equalization step is completed, and the supply of the pressurized mixed gas to the adsorption tower that is being The method is characterized in that exhaust gas from the adsorption tower is stopped at the same time as the internal pressure of the adsorption tower reaches a predetermined vacuum pressure or the pressure equalization step is completed.

Detailed Description of the Structure of the Invention In the present invention, three adsorption towers filled with beds of adsorbent are used, and the adsorbent is synthetic zeolite, e.g.
Molecuiler Sheeps 5A or 13X1 and natural zeolite, such as mordenite, are used. Adsorption and desorption are repeated in the following cycle using these three adsorption towers A, B and C'.

For example, a cycle including two pressure equalization steps in one step cycle per adsorption tower is according to the following embodiment.

Step I A pressurized mixed gas is supplied from the mixed gas supply port at the bottom of the A column. At the same time, the internal pressure of the column has already been increased to a predetermined pressure in the previous step, and the product outlet at the upper part of the C column, which is releasing oxygen-rich gas, is communicated with the upper part of the A column.
Equalize the pressure between the column and C column (first pressure equalization). On the other hand, the nitrogen-saturated column B is depressurized countercurrently and nitrogen is desorbed.

Step 2 The A column is gradually pressurized by supplying pressurized mixed gas and at the same time releases the product oxygen-rich gas. On the other hand, concentrated oxygen from the upper part of the C tower is supplied to the upper part of the B tower, and is discharged outside the system by a vacuum pump while countercurrently cleaning the inside of the B tower (vacuum/sage). The C column discharges the oxygen-rich gas for 9-di by cocurrent depressurization, and the pressure inside the column further decreases.

Step 3 In column A, the product oxygen-rich gas is released while the pressure inside the column rises and reaches a predetermined pressure.Meanwhile, the oxygen-rich gas remaining in the upper part of column C is transferred to the lower or upper part of column B. The pressure between the B column and the C column is equalized by supplying the same to the above (second pressure equalization).

The above process is repeated up to step 9 by changing the phase in the 6 towers to complete one complete cycle.

Similarly, in a cycle that includes only one pressure equalization step, the mode consisting of steps 1 and 2, excluding the above-mentioned sten f3, is changed in phase in 6 columns to perform ster f6.
Repeat until 1 complete cycle.

According to such a pressure fluctuation adsorption cycle, oxygen-enriched sludge can be continuously obtained by switching over a certain period of time. However, there is no problem when the accumulated gas is removed from the product at a constant rate, but there are many cases where the required amount of product oxygen-rich gas changes, and even in such cases, mixing The power consumed by the gas pressurizing compressor and the exhaust vacuum pump is not reduced, and exactly the same power is consumed. - Thus, the present invention monitors the flow characteristics of the exiting oxygen-rich gas, stops the step until this characteristic reaches a preset predetermined value, and turns off the compressor and vacuum pump for at least a period of time. This makes it possible to reduce power by placing it in an unloaded state. The flow characteristics mentioned here include, for example, the amount, velocity, concentration, and pressure of the oxygen-rich gas flowing out.

There are the following ways to unload the compressor and exhaust vacuum pump. That is, in one embodiment, after the aforementioned pressure equalization step (in the cycle consisting of the nine steps, the first pressure equalization step) is completed, the adsorption tower is pressurized by supplying the pressurized mixed gas. When the internal pressure of the adsorption tower reaches a predetermined pressure (the highest pressure in the cycle), the pressure & i machine is unloaded, and on the other hand, when the internal pressure of the evacuated adsorption tower reaches the predetermined vacuum pressure (the lowest pressure in the cycle), the vacuum The pumps are unloaded. At this time, each unloading of the compressor and vacuum pump is performed by, for example, a pressure switch activated by sensing the pressure inside each column or the pressure of the supply mixed gas line and the vacuum exhaust line. You can do it.

In other embodiments, the compressor and vacuum pump are both unloaded upon completion of the pressure equalization step described above and loaded again upon initiation of the next step. In this case, the loading and unloading of these compressors and vacuum pumps are pressurized by supplying a pressurized mixed gas, for example, also after the above-mentioned pressure equalization step is completed. When the internal pressure of the adsorption tower reaches a predetermined pressure (the maximum pressure in the cycle), the compressor is unloaded, while the vacuum pump is unloaded at the same time as the pressure equalization process is completed. In this case, for example, , the compressor can be unloaded by a pressure switch, and the vacuum pump can be unloaded at the same time as the step is stopped.In addition, in the case of this third aspect, the vacuum pump can be unloaded during the Since ON-OF does not occur, there is an advantage that the attachment/desorption operation can be performed stably.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, an example will be explained in which the outflow amount of oxygen-rich gas is measured and monitored as a flow characteristic.

FIG. 1 is a system diagram of a specific apparatus for explaining the method of the present invention. FIG. 2 is a schematic diagram showing the process operation sequence of the method of the present invention in the case of 9 steps. FIG. 3 is a schematic diagram showing the process operation sequence of the method of the present invention in the case of six steps.

A flow meter 25 is provided in the product oxygen-enriched waste line, and the @ number is converted into a frequency pulse and sent to a counter 27 with a setting device. The set flow rate of oxygen-rich gas of 9 per adsorption group is 1
00%, for example, when the oxygen-rich gas flow rate is 50 cm, it takes twice as long to reach the set value. on the other hand,
When the product gas flow rate is 100%, for example, counting starts from Stella f2 in FIG.
This is done in seconds, and the process advances to the next Stella f5. However, when the product gas flow rate is, for example, 50%, it will take twice as long, 120 seconds, to count out against the set value in step 4', which is newly provided according to the present invention. Then, the process does not proceed from step 4' to step 5 until it is counted out.

In step 4' or step 5, since the B column has already reached a predetermined pressure, by detecting the adsorption pressure of this adsorption column or the pressure of the supplied mixed gas line with the pressure switch 29, the mixed gas compressor on the pressurizing side is 20 is unloaded. On the other hand, in Stella f4', when the evacuation of the C tower is completed and a predetermined vacuum pressure is reached, the valve 5 is closed and the valve 7 is opened, so that the vacuum pump 19 draws directly from the atmosphere. Therefore, the following equation (1), (
In the formula, La is the shaft horsepower (kW), △P is the differential pressure between the discharge pressure and the suction pressure (moan/cm"), and Q8 is the theoretical suction air volume (-7
(min) and η is efficiency), as a result of a decrease in ΔP, the power is significantly reduced.

The same is true for the pressure fluctuation adsorption cycle starting from 6 steps. That is, as shown in FIG.
Counting starts from , and the product sludge flow rate during the period when only tower A is releasing oxygen-rich gas is counted. At the point where the set value is reached, in step 3', which is newly provided according to the invention, the stop ml so/T% -y = -, -I
II J ry Jh-h -a, +-For example, when the product gas flow rate is 50% of the set value, the A column reaches the predetermined pressure at Stella f3', and the adsorption pressure of the adsorption column or the supply mixed gas line increases. By detecting the pressure with the pressure switch 29, the compressed mixed gas 4120t on the pressurizing side is unloaded. On the other hand, when the B tower is evacuated and reaches a predetermined vacuum pressure, the valve 5 is closed and the valve 7 is opened, so that the suction into the vacuum bomb 7''19 is performed directly from the atmosphere, and the vacuum pump is in an unloaded state.

In this way, as the flow rate of the product oxygen-rich gas decreases, the unmead time becomes longer and the power consumption decreases.

In addition, in FIG. 1, IA to IC, 2A to 2C.

3A-3C, 4A-4C15, 6A-6C17, 9, 1
0, 11, 17 are valves, 18 is an aftercooler,
19 is a vacuum pump, 20 is a compressor, 21 is a minutocenogulator, 22 is an outflow of oxygen-rich gas as a product, 23 is an outflow of a gas mainly composed of separated and removed nitrogen, 24 is a suction silencer, 9Ru Fang rifusu? l/F tatami needle 9
Is 6 trance? 27 is a counter, 28 is a control panel, and 29 and 30 are pressure switches.3 From the control panel 28, control signals are sent to 6 valves, a compressor, and a vacuum bonder.

FIG. 4 is a graph showing an example of pressure fluctuations and nine turns in each adsorption tower when turndown control is not performed in a cycle consisting of nine steps. Figure 5 shows 6
Similar pressure fluctuations in the case of a cycle consisting of steps No. 4
' is a graph showing an example of a turn.

Figure 6 is a graph showing changes in the power of the compressor and vacuum pump when pressure fluctuations in the pattern shown in Figure 5 are applied. A case where turndown control is performed according to the invention is also shown. In this way, in the present invention, the power can follow changes in accordance with changes in the outflow amount of the product oxygen-rich gas, and control for energy saving can be performed.

When turndown control is performed as described above, as shown in Figure 7 (in the case of 9 steps), the longer the waiting time during turndown, the greater the decrease in the concentration of the product oxygen-rich gas. . This means that the longer the waiting time is,
This is because the moving speed of the nitrogen adsorption front becomes slow, and conversely, nitrogen diffusion occurs, making it impossible to obtain a sharp adsorption front.

Therefore, in order to prevent the oxygen concentration of the product gas from decreasing as much as possible, the ideal cycle time (for example, if the cycle time per adsorption tower is 60 seconds, the ideal time is (set flow rate / product gas flow rate) x 60 seconds). seconds),
As the waiting time is extended, it is necessary to significantly shorten it.

FIG. 8 is a graph showing the relationship between the ratio of the product gas flow rate to the set flow rate and the cycle time for each adsorption tower.

X is the ideal cycle time, and Y is the actual cycle time required to suppress the decrease in the concentration of the product oxygen-rich gas. Therefore, in actual operation, it is necessary to control the progression of steps by programming so that the Y relationship is obtained.

In the above embodiment, power reduction of the compressor and vacuum pump is performed by an unloading method using a pressure switch, but it is performed by controlling the mixed gas amount of the compressor and the suction amount of the vacuum pump by controlling the rotation speed. It is also possible.

[Brief explanation of drawings]

FIG. 1 is a system diagram for explaining the method of the present invention, FIG. 2 is a schematic diagram showing the process operation order in the case of 9 steps, FIG. 3 is a schematic diagram showing the process operation order in the case of 6 steps, and FIG. 4
The figure is a graph showing an example of a pressure fluctuation pattern in the case of 9 steps, Figure 5 is a graph showing an example of pressure fluctuations and turns in the case of 6 steps, and Figure 6 is a graph of the compressor and vacuum pump in the case of 6 steps. A graph showing an example of a change in the power of
Figure 7 is a graph showing the change over time in the oxygen concentration of the product gas in each adsorption tower in the case of 9 steps, and Figure 8 shows the relationship between the ratio of the product gas flow rate to the set flow rate and the cycle time for each adsorption tower. It is a graph. In the figure, A, B%C are adsorption towers, IA to IC. 2A~2C, 3A~3C14A~4C15, 6A~6C
17, 9, 10, 11% 17 is a valve, p118 is an aftercooler, 19 is a vacuum pump, 2° is a compressor, 21 is a mist separator, 22 is an outflow of the product oxygen-rich scum, 23 is separation and removal 24 is a suction silencer, 25 is an orifice flowmeter, 26tj:) a radiator, 27 is a counter,
28 is a control panel, and 29.3o is a pressure switch. Patent applicant Showa Denko Co., Ltd. Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Yoshi 1) Takeo Patent attorney Akira Yamaguchi Patent attorney Masaya Nishiyama 3rd

Claims (1)

[Claims] 1. Filled with a bed of adsorbent that selectively adsorbs nitrogen 3.
In each adsorption tower, a mixed gas mainly containing oxygen and nitrogen is passed through the adsorption tower to adsorb and remove nitrogen to produce oxygen-rich gas. An increased pressure adsorption process in which the internal pressure of the column is increased by supply, selectively adsorbing nitrogen, and extracting oxygen-rich gas, a vacuum regeneration process in which the vacuum is evacuated in the countercurrent direction, and purging with oxygen-rich gas from other columns. At the same time, a cycle including a purge process in which the vacuum is evacuated in the countercurrent direction, and a pressure equalization process in which the pressure inside the column is equalized by introducing oxygen-rich gas from another column is performed sequentially with different phases. In the pressure fluctuation adsorption method, which is carried out in The amount and speed of oxygen-rich gas flowing out,
an adsorption column in which at least one oxygen-enriched gas flow characteristic, including concentration and pressure, is monitored, and the process cycle is not advanced to the next step until said characteristic reaches a predetermined value, while said pressurization is being carried out; The supply of the pressurized mixed gas to the adsorption tower is stopped at the same time as the internal pressure of this tower reaches a predetermined pressure or the pressure equalization step is completed, and the supply of the pressurized mixed gas from the other adsorption tower where the evacuation is being performed is stopped. A turndown control method in a pressure fluctuation adsorption method, characterized in that the evacuation of the column is stopped at the same time as the internal pressure of the column reaches a desired vacuum pressure or the pressure equalization step is completed.