JPH067899B2 - Turndown control method by pressure fluctuation adsorption method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to production of oxygen-rich gas by a pressure swing adsorption method, and more specifically, a period or turn during which the characteristics such as outflow rate during outflow of oxygen-rich gas decrease. A method of controlling a system of pressure swing adsorption during down.

BACKGROUND ART It is known to produce oxygen-rich gas by separating a nitrogen / nitrogen mixed gas such as air by pressure fluctuation adsorption by utilizing selective adsorption of nitrogen to an adsorbent such as synthetic zeolite or natural zeolite. (For example, Japanese Patent Publication No. Sho 51-405
49, JP-A-53-96987 and JP-A-58-84.
No. 020). In producing oxygen-rich gas by such a method, in each of a plurality of adsorption towers containing a bed of adsorbent, oxygen / nitrogen mixed gas is introduced to adsorb and remove nitrogen, thereby making it difficult to adsorb oxygen that is hard to adsorb. The gas enriched in is extracted from the adsorption tower and used as a product gas. Then, the steps of decompressing, purging, exhausting, etc. for regenerating the adsorbent in the adsorption tower and the adsorption separation step are sequentially switched in each adsorption tower.

A turndown control method in such a pressure fluctuation adsorption system is disclosed in Japanese Patent Laid-Open No. 54-16375. In this method, turndown control is performed for a pressure fluctuation adsorption system in a pressurization cycle at a specific atmospheric pressure or higher. 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. Then, after the pressure in the tower reaches the maximum pressure, the introduction of the feed gas is transferred to another adsorption tower, but the product gas from the first adsorption tower is taken out as a product by cocurrent depressurization, and at the same time the other adsorption is carried out. It is also used for pressure equalization and purging in the column. Next, the internal pressure of the first adsorption tower is countercurrently reduced to atmospheric pressure, thereby desorbing the adsorbed substance, and further regenerating the adsorption bed by countercurrent purging. The adsorption tower is composed of two or more pieces, and the product gas can be continuously obtained. In such a pressure fluctuation adsorption cycle, the amount of product gas generated per adsorption bed per cycle is set, and the amount of product gas generated is reduced when the required usage amount of the product gas decreases. Do not advance the cycle to the next step until the set amount is reached,
On the other hand, in the adsorption tower where the supply gas is pressurized, when the maximum adsorption pressure is reached, the compressor is unloaded (no load), the introduction of the supply gas is stopped, and the power is reduced. . Thus, this turndown control is performed in a pressure type pressure fluctuation adsorption cycle, and an example of performing turndown control in a vacuum type pressure fluctuation adsorption cycle in which the pressure fluctuation range extends to the vacuum side at a pressure lower than atmospheric pressure. Has never existed.

OBJECT OF THE INVENTION The main object of the present invention is to provide a method for effectively reducing the power of this system by performing turndown control in a system for producing oxygen-rich gas by pressure fluctuation adsorption method including constant pressure adsorption and vacuum desorption. To do.

The present invention provides a turndown control method in a pressure swing adsorption method, which uses three adsorption columns packed with a bed of an adsorbent that selectively adsorbs nitrogen. When a mixed gas containing oxygen and nitrogen is passed through the adsorption tower to adsorb and remove nitrogen to produce an oxygen-rich gas, the raw material end portion in the first adsorption tower pressurized to a constant pressure by the oxygen-rich gas. From the end of the product, while at the same time introducing a pressurized mixed gas from the end of the product, a part of this oxygen-rich gas is used to pressurize the second adsorption tower.
The step of supplying to the product end of the adsorption tower, exhausting from the raw material end, and purging the inside of the tower by introducing oxygen-rich gas from the second adsorption tower from the product end, or performing this purging The steps of reducing the internal pressure to a pressure lower than atmospheric pressure and introducing the oxygen-rich gas from the third adsorption column from the end of the product to increase the internal pressure to a constant pressure. In the pressure fluctuation adsorption method, in which the process cycle is performed while changing the phase in each of the second and third adsorption towers during that time, the adsorption cycle from one adsorption tower from which the oxygen-rich gas is derived is Monitoring at least one oxygen-rich gas flow characteristic selected from the amount, velocity, concentration and pressure of the oxygen-rich gas flowing out for at least one period between the derivation of the oxygen-rich gas until the characteristic reaches a predetermined value. Said process cycle Of the adsorbed column is introduced and stopped from the end of the raw material of the adsorbing column so that the adsorbing column holds the predetermined pressure without advancing the adsorbing column. When the pressure is reduced to a predetermined pressure lower than the atmospheric pressure, the exhaust from the raw material end of the adsorption tower is stopped.

Detailed Description of the Structure of the Invention In the present invention, three adsorption columns packed with a bed of adsorbent are used, and as the adsorbent, a synthetic zeolite, for example,
Molecular sieves 5A or 13X and natural zeolites such as mordenite are used. An oxygen / nitrogen mixed gas such as pressurized air is supplied to an adsorption tower filled with this adsorbent, nitrogen is adsorbed on the adsorbent, and oxygen is concentrated to obtain an oxygen-rich gas. The supply of the pressurized mixed gas is stopped before the adsorption front of nitrogen breaks through in the adsorbent bed, and the tower of the adsorbent bed saturated with nitrogen is sucked to the vacuum pressure in the mixed gas supply direction and the countercurrent direction. Desorption of nitrogen and regeneration of the adsorbent bed. Further, during this regeneration, a part of the product-rich oxygen gas may be purged in the countercurrent direction.

According to such a pressure fluctuation adsorption cycle, oxygen-rich gas can be continuously obtained by switching in a fixed time. However, when the oxygen-rich gas of the product is taken out at a constant rate, there is no problem, but in many cases, the required usage amount of the product-rich oxygen gas changes, and even in such a case, the mixed gas pressurizing compressor and The power consumed by the exhaust vacuum pump is not reduced, but exactly the same power is consumed. Thus, the present invention monitors the flow characteristics of the outgoing oxygen-rich gas and stops the steps until this characteristic reaches a predetermined preset value, during which the compressor is unloaded or the number of revolutions is increased. It is possible to reduce power consumption by lowering the vacuum pump and further unloading the vacuum pump.

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

FIG. 1 is a systematic diagram of a concrete apparatus for explaining the method of the present invention, and FIG. 2 is a schematic diagram showing a sequence of process operations of the method of the present invention.

The product oxygen-rich gas line is equipped with a flow meter 25, and its signal is sent to a counter 27 with a setting device. Assuming that the set flow rate of oxygen-rich gas per adsorption tower is 100%, for example, when the flow rate of oxygen-rich gas is 50%, until the set value is reached,
It takes twice as long. On the other hand, when the product gas flow rate is 100%, as shown in step 1 of FIG. 2, constant pressure adsorption in the tower A, pressurization with the product gas in the tower B and vacuum desorption in the tower C are performed for 60 seconds, for example. Then, proceed to Step 3. However, when the product gas flow rate is, for example, 50%, step 2 is entered, and step 3 is not proceeded for 60 to 120 seconds, that is, until the outflow product gas flow rate is counted out with respect to the set value.

When step 2 is entered, the valve 4C is closed and the valve 7 is opened, so that the suction pressure of the vacuum pump 19 becomes close to the atmospheric pressure, and the following equation (1), (Where P _s is the theoretical horsepower (kW), ΔP is the differential pressure between discharge pressure and suction pressure (kg / cm ² ), and Q _s is the theoretical suction air volume (m ³ / mi)
As shown in (n)), as a result of the decrease in ΔP, the power is drastically reduced, resulting in an unload state.

On the other hand, in the compressor 20 on the pressurizing side, ON-OFF is repeated via the pressure switch or rotation speed control is performed in order to maintain the pressure of the tower A at a predetermined pressure by the unload setting.

Incidentally, in FIG. 1, 1A to 1C, 2A to 2C, 3A to
3C, 5, 6A to 6C, 7, 9, 17 are valves, 18
Is an aftercooler, 19 is a vacuum pump, 20 is a compressor, 21 is a mist separator, 22 is an outflow amount of oxygen-rich gas as a product, 23 is an outflow amount of a gas mainly composed of separated and removed nitrogen, and 24 is a suction A silencer, 25 is an orifice flow meter, 26 is a transmitter, 27 is a counter, and 28 is a control panel. An open / close signal is sent from the control panel 28 to each valve.

FIG. 3 is a graph showing an example of a pressure fluctuation pattern in each adsorption tower.

FIG. 4 is a graph showing changes in the power of the compressor and the vacuum pump when the pressure fluctuation of the pattern shown in FIG. 3 is applied. This graph is when the pressure fluctuation is given by the operation and stop of the compressor.When this pressure fluctuation is given by the rotation speed control of the compressor, the change in the power of the compressor and the vacuum pump is The graph is as shown in FIG.
In the present invention, as described above, the power is changed and followed in accordance with the change in the outflow amount of the product-rich oxygen gas, and the control for energy saving can be performed.

When the turndown control is performed as described above, as shown in FIG. 5, the longer the standby time during the turndown, the greater the decrease in the concentration of the product-rich oxygen gas.
This is because when the waiting time becomes long, the moving speed of the nitrogen adsorption front in the column A in step 2 becomes too slow, and conversely, diffusion of nitrogen occurs and a sharp adsorption front cannot be obtained. Therefore, in order to prevent the oxygen concentration of the product gas from decreasing as much as possible, the ideal time of the cycle time (for example, assuming that the cycle time per adsorption tower is 60 seconds, the ideal time is (set flow rate / product gas flow rate) × 6.
0 seconds) is required to be shortened more greatly according to a predetermined increasing function as the waiting time is extended.

FIG. 6 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 represents the ideal cycle time, and Y represents 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 progress of steps by programming so that the relationship of Y is obtained.

The compressor on the pressurizing side will disturb the constant pressure adsorption by turning on and off by the operation of the pressure switch connected to each adsorption tower, but this will not affect the performance of the system at all. Also,
During step 2, depending on the type of compressor used (eg, reciprocating type or screw type), rotation speed control is performed to adjust the supply of the pressurized mixed gas regardless of ON-OFF control. It is possible to maintain the pressure of the adsorption tower at a constant pressure.

[Brief description of drawings]

FIG. 1 is a system diagram for explaining the method of the present invention, FIG. 2 is a schematic diagram showing a process operation sequence of the method of the present invention, FIG. 3 is a graph showing an example of a pressure fluctuation pattern in each adsorption tower, and FIG. FIG. 5 is a graph showing changes in power of the compressor and the vacuum pump when the pressure fluctuations of the pattern shown in FIG.
The figure is a schematic diagram showing the change over time in the product gas broth concentration in each adsorption tower, and FIG. 6 is a graph showing the relationship between the ratio of the product gas flow rate to the set flow rate and the cycle time per adsorption tower. Further, FIG. 7 is a graph showing changes in the power of the compressor and the vacuum pump when the pressure fluctuation of the pattern shown in FIG. 3 is given by the rotation speed control of the compressor. In the figure, A, B, C are adsorption towers, 1A-1C, 2A-
2C, 3A to 3C, 5, 6A to 6C, 7, 9, 17 are valves, 18 is an aftercooler, 19 is a vacuum pump, 20
Is a compressor, 21 is a mist separator, 22 is an oxygen-rich gas outflow, 23 is a gas mainly containing nitrogen, 24 is a suction silencer, 25 is an orifice flow meter, 26 is a transmitter, 27 is a counter, 28 is It is a control panel.

Claims (1)

[Claims] 1. A three-gas adsorption column packed with a bed of an adsorbent that selectively adsorbs nitrogen, and a mixed gas containing oxygen and nitrogen is circulated through the adsorption column to adsorb and remove nitrogen to obtain oxygen-rich oxygen. In producing the gas, the pressurized mixed gas is introduced from the end of the raw material in the first adsorption tower pressurized to a constant pressure by the oxygen-rich gas, and at the same time, the oxygen-rich gas is discharged from the end of the product, and in the meantime. A step of supplying a part of this oxygen-rich gas to the product end of the second adsorption tower for pressurizing the second adsorption tower, exhausting from the raw material end, and from the product end to the second adsorption tower Purging the inside of the column by introducing oxygen-rich gas from the column or without depressurizing the column pressure to a pressure lower than atmospheric pressure, and from the end of the product from the third adsorption column Introducing oxygen-rich gas and increasing the pressure in the tower to a constant pressure, In the pressure fluctuation adsorption method, which is performed by changing the phase in each of the second and third adsorption columns during the process cycle, At least one oxygen-rich gas flow characteristic selected from the amount, velocity, concentration, and pressure of the oxygen-rich gas flowing out during at least one period between the derivation of the oxygen-rich gas, and the characteristic reaches a predetermined value. Without advancing the process cycle up to, the introduction of the pressurized mixed gas from the raw material end of the adsorption tower and the stop or adjustment of the supply amount are performed so that the one adsorption tower holds a predetermined pressure. And, when the pressure of one of the other adsorption columns is reduced to a predetermined pressure lower than the atmospheric pressure, the exhaust from the raw material end of the adsorption column is stopped. Down control method.