JPH05277322A - Pressure fluctuation adsorption device reducing operation method - Google Patents

Abstract

(57) [Summary] [Purpose] In a pressure fluctuation adsorption device in which the adsorption tower is vacuum-regenerated, it is possible to stably produce a product gas of a predetermined concentration even in the reduction operation state and to reduce power consumption. Provide a driving method that can be done. [Structure] When the pressure fluctuation adsorption device performing the vacuum regeneration step is operated in a reduced amount, the purge gas amount introduced into the adsorption tower performing the vacuum regeneration is increased according to the reduction amount of the product gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the pressure of a pressure fluctuation adsorption device, and more particularly, to a pressure fluctuation adsorption device in which an adsorption tower is operated by a vacuum regeneration method. The present invention relates to an operating method capable of stably manufacturing a vehicle and reducing power consumption.

[0002]

2. Description of the Related Art A pressure fluctuation adsorption device (hereinafter referred to as PSA device) is widely used as a method for separating or purifying various gases. Particularly, an adsorbent such as zeolite that preferentially adsorbs nitrogen is used in the feed air. It is widely used as an oxygen production device that separates and produces oxygen gas from water.

FIG. 5 shows an example of a PSA oxygen production apparatus using three adsorption towers (JP-A-2-784).
(See Japanese Patent Publication No. 15).

This PSA apparatus 1 comprises three adsorption towers 2a,
2b, 2c, a blower 3 for supplying a raw material gas, a compressor 4 for delivering a product gas, flow rate adjusting mechanisms 5a, 5b used for regeneration and charging steps of an adsorption tower, and a vacuum pump 6 for performing vacuum regeneration and each. Adsorption and regeneration of the adsorption towers 2a, 2b, 2c,
It is composed of a large number of valves for sequentially switching to each step of charging.

Here, the case where the first adsorption tower 2a is in the adsorption step, the second adsorption tower 2b is in the charging step, and the third adsorption tower 2c is in the regeneration step will be described.

The raw material gas is introduced into the adsorption tower 2a from the blower 3 through the switching valve 7a, and the adsorption separation in which the nitrogen is adsorbed by the adsorbent is performed in the adsorption tower 2a, and the product gas is discharged from the outlet of the adsorption tower 2a. Some oxygen gas flows out. This product oxygen gas is sent to the compressor 4 via the switching valve 8a and the valve 9, and is pressure-fed to the consumer.

At this time, the second adsorption tower 2b is subjected to a pressure equalizing step in which the gas in the third adsorption tower 2c is introduced from the switching valves 10b and 11b at both ends of the second adsorption tower 2b.
b and 11b are closed, and the outlet side switching valve 12
b is opened, oxygen gas is introduced from the flow rate adjusting mechanism 5a at a predetermined flow rate, and pressurized to a predetermined pressure.

In the third adsorption tower 2c, each step constituting the regeneration step, that is, the pressure equalizing step, and the switching valve 13c is opened after the pressure equalizing step is completed and the vacuum pump 6 exhausts the inside of the tower. A vacuum regeneration step of decompressing, and when the inside of the tower reaches a predetermined vacuum degree, the switching valve 15c is opened to open the flow rate adjusting mechanism 5.
A purge regeneration step of introducing a predetermined amount of product gas into the tower from the tower outlet side is sequentially performed from b.

Hereinafter, the sequential switching valves 7a, 7b, 7c, 8
a, 8b, 8c, 10a, 10b, 10c, 11a, 1
1b, 11c, 12a, 12b, 12c, 13a, 13
b, 13c, 14, 15a, 15b, 15c are respectively opened and closed in a predetermined order to open and close the first adsorption tower 2
a is a regeneration step, the second adsorption tower 2b is an adsorption step, the third adsorption tower 2c is a charging step, and the first adsorption tower 2a is a charging step, and the second adsorption tower 2b is a regeneration step. The cycle in which the third adsorption tower 2c is in the adsorption step is repeated.

In the PSA apparatus 1 thus constructed, the time of each cycle is determined based on the time required for the adsorption process of the adsorption tower 2a in the adsorption process, and the adsorption, regeneration, and charging are performed in a cycle of 60 seconds, for example. The pressure is switched to each tower in sequence. At this time, in the adsorption tower 2c in the regeneration step, for example, the pressure equalizing step is performed for 10 seconds, the vacuum regeneration step is performed for 20 seconds, and the page regeneration step is performed for 30 seconds. In the adsorption tower 2b in the charging step, the pressure equalizing step is performed for 10 seconds as described above, and then the charging with the product gas is performed for 50 seconds.

As described above, in the oxygen production apparatus using PSA, a plurality of adsorption towers filled with an adsorbent such as zeolite are sequentially switched to respective steps of adsorption, vacuum regeneration and charging, so that product oxygen is continuously produced. Gas is produced, but in such an oxygen production apparatus, it is necessary to increase or decrease the production amount of oxygen according to the operating state of the apparatus that consumes oxygen.

Generally, the adjustment of the oxygen production amount is performed by controlling the product oxygen derivation amount and controlling the switching time of each of the steps of adsorption, regeneration and charging.
For example, when a 50% reduction operation is performed, the oxygen derivation amount is reduced to 1/2 and the switching time (cycle time) of each process is doubled.

As one means for reducing the power cost during the reduction operation according to the quantity of products, Japanese Patent Laid-Open No. 60-1935.
In the turndown control method by the pressure fluctuation adsorption method described in Japanese Patent Publication No. 20, the flow characteristics of the oxygen-rich gas derived from the adsorption tower in the adsorption step (amount, velocity of oxygen-rich gas, velocity,
(Concentration, pressure, etc.) is monitored, and steps (steps) other than the adsorption step are stopped until this flow characteristic reaches a predetermined value set in advance, while adjusting the capacity of the compressor that supplies the raw material air, It is shown that the vacuum pump used in the vacuum regeneration process is in an unloading state.

Further, Japanese Patent Laid-Open No. 2-78415 discloses that
A method is described in which during the regeneration process, a standby process for a predetermined time corresponding to the reduction operation is provided to bring the vacuum pump into an unloading state, thereby reducing the power consumption.

[0015]

However, in the above-described turndown control method, the operation state is not stable because the gas flow rate in the adsorption tower in the adsorption step is greatly different, and the adsorption pressure fluctuates greatly. It also adversely affects the adsorption capacity.

For example, in the case of normal operation, the product gas amount is 1
Then, generally, the ratio of the raw material air amount is 10, and the amount of the pressurized gas is 5. Then, when a 50% reduction operation is performed, the product gas amount becomes 0.5, and in the adsorption tower during the charging step, the outflow amount is 5.5 with respect to the inflow amount of 10. ..

Then, when the charging is completed and the standby process is started,
Since pressurizing gas is not required, the outflow amount is only the product gas, and it rapidly drops to 0.5.

As described above, when the outflow rate sharply decreases with respect to the inflow rate, the column pressure rapidly rises. Therefore, in the above method, the compressor is turned on and off by a pressure switch that operates according to the pressure in the tower to keep the inside of the tower at a predetermined pressure.

However, such a pressure switch requires a certain pressure difference for switching the contacts, and the pressure in the adsorption tower frequently repeats pressure fluctuations by this pressure difference. Although it is stated in the above-mentioned specification that this pressure fluctuation does not cause any hindrance to system performance, it is known that such pressure fluctuation affects system performance. Is.

Further, it is described that depending on the type of compressor, the feed gas supply amount can be adjusted by controlling the rotation speed of the compressor, but the control system becomes complicated and the cost of the device increases. Invite.

Further, in the above method, at least one of the flow characteristics of the oxygen-rich gas as a product, such as the amount, velocity, concentration and pressure of the oxygen-rich gas, is monitored, and this characteristic reaches a predetermined value. The conditions are to accelerate the process. However, when the usage amount of the product changes frequently, the time until the above characteristics reach the predetermined value changes from time to time, so in extreme cases, the switching time differs for each cycle. May come. Therefore, the position of the gas concentration distribution zone in the adsorption tower is different each time, and it becomes difficult to operate with a stable product concentration.

The latter, which is provided with the standby step, does not cause the above-mentioned inconvenience, but is used especially in a large PSA apparatus because the valve is closed to stand by when the inside of the adsorption tower is in a vacuum state. Since the valve has a large diameter, it is difficult to completely seal the gas. For example, when the degree of the volume reduction operation is 50% or more, the standby time becomes long, and the gas leakage may be a non-negligible amount.

Further, as a problem when the cycle time is extended, in the adsorption process for a longer time than usual, the raw material air passes through the adsorbent layer and oxygen is taken out little by little. Becomes slower, and the film resistance in adsorption cannot be ignored.

Since this acts to lengthen the so-called adsorption zone, the relationship between the time and the amount in extending the cycle time is disturbed, and the cycle must be switched in a time shorter than the originally extendable time. This means that the rate at which power consumption can be reduced decreases.

Therefore, in the present invention, in the PSA for performing vacuum regeneration using the above-mentioned vacuum pump, the weight reduction operation is efficiently performed by considering the characteristics of the vacuum pump and the characteristics of the operating method of the PSA, and during the weight reduction operation. It is an object of the present invention to provide a reduction operation method of a pressure fluctuation adsorption device capable of reducing the power consumption of the device.

[0026]

In order to achieve the above-mentioned object, the method for reducing the amount of pressure fluctuation adsorption device of the present invention comprises a plurality of adsorptions filled with an adsorbent which preferentially adsorbs a specific component in the raw material gas. The amount of purge gas to be introduced into the adsorption tower performing the vacuum regeneration when the pressure fluctuation adsorption device for continuously producing the product gas by sequentially switching the adsorption step, the vacuum regeneration step, and the charging step to the volume reduction operation is performed. Is increased according to the amount of decrease in the product gas.

[0027]

[Operation] As described above, the load on the vacuum pump is reduced and the power consumption is reduced by increasing the amount of purge gas to the adsorption tower performing vacuum regeneration during the reduction operation.

That is, as shown in FIG. 1, in a three-column PSA with a cycle time of 60 seconds, the pressure inside the column during the adsorption process was 760 Torr and the regeneration pressure during normal operation was 230 T.
In the case of orrr, for example, when performing a 75% reduction operation, the amount of purge gas introduced into the adsorption tower during vacuum regeneration is increased so that the internal pressure during vacuum regeneration, that is, the regeneration pressure is about 340 Torr. To

Generally, a large vacuum regenerative PSA (hereinafter referred to as V
The vacuum pump used in (SA) is of the roots type, but this type of vacuum pump has the characteristics shown in FIG. 2, that is, the power consumption decreases as the pressure decreases and the degree of vacuum increases. It has the property of increasing.

Therefore, it can be seen that the power consumption of the vacuum pump can be reduced by increasing the regeneration pressure. Note that V
In SA, since the pressure of the raw material gas is slightly higher than the atmospheric pressure, the power consumption of the blower for feeding the raw material air into the adsorption tower is small, and most of the power consumption of VSA is the power consumption of the vacuum pump. It can be said that there is.

In the VSA operation, the regeneration pressure and the product recovery rate have a relationship that the lower the regeneration pressure, the higher the product recovery rate, as shown in FIG. The relationship between the two is substantially linear when the product recovery rate is higher, and when the product recovery rate at a regeneration pressure of 230 Torr during normal operation is taken as a reference amount, the regeneration pressure is about 460 Torr.
When this is set, the product recovery rate will be about 50% of the standard amount.

Further, in the above-mentioned regeneration process in the VSA cycle, the adsorbent is washed by using not only the vacuum pump but also a part of the product oxygen gas.

The effect of the above cleaning is that by increasing the oxygen partial pressure in the atmosphere of the adsorbent, nitrogen adsorbed on the adsorbent in the adsorption step is desorbed from the adsorbent and oxygen is adsorbed instead, so-called substitution desorption. The action of is used.

If the oxygen purge amount at this time is small, the above-mentioned substitution and desorption will be performed only for the adsorbent near the inlet of the purge gas at the upper part of the adsorption tower. Conversely, if the purge amount is too large, the adsorbent will be completely replaced. It can be desorbed, but it causes a loss of oxygen flowing out to the vacuum pump side.

Therefore, there is an optimum value for the purge gas amount, and in normal operation, the optimum value is maintained.

On the other hand, when the amount of purge gas is increased, the degree of vacuum at the time of regeneration tends to deteriorate at the same time. By consciously implementing this tendency, the above-mentioned regeneration pressure and product recovery rate are reduced. From the relationship, it becomes possible to perform the reduction operation without changing the cycle time.

That is, when the product flow meter detects that the product usage amount has decreased from the normal operating condition, the purge gas is increased to increase the regeneration pressure and the product recovery rate to decrease the product amount. You can reduce the dose according to.

As for the increase rate of the purge gas, for example, as shown in FIG. 4, when the product generation rate ratio becomes 0.7, the purge rate increase rate is set to 1.3 and the product generation rate ratio becomes 0.5. Then, the increase rate of the purge amount can be set to 1.5.

The control of the purge amount is carried out by detecting the product amount with a flow meter, inputting the detected product flow rate into a calculator to calculate the corresponding purge amount or valve opening, and based on this, the flow rate adjusting mechanism. That is, a signal for adjusting the opening of the flow rate control valve that controls the flow rate of the purge gas may be output.

By increasing the amount of purge gas and increasing the regeneration pressure in this way, it becomes possible to reduce the power consumption of the vacuum pump, as is clear from the characteristics of the vacuum pump shown in FIG.

The period of increasing the purge gas in the vacuum regeneration process may be the entire vacuum regeneration process,
As shown by the broken line in FIG. 1, the amount may be increased when the inside of the adsorption cylinder reaches a predetermined degree of vacuum.

Further, the VSA can have an optimal structure depending on the type and amount of the product gas, and the number of columns is arbitrary.

[0043]

[Example] Using the PSA oxygen production apparatus having the configuration shown in FIG. 5, a standard product amount operation and a weight reduction operation in which the product amount is reduced to 75% are performed, and the weight reduction amount is simply reduced. The electric power consumption per unit product amount was compared between the operation and the reduction operation by the method of the present invention.

The cycle time is 60 seconds, the regeneration pressure during normal operation is 230 Torr, and in the volume reduction operation according to the method of the present invention, the amount of purge gas introduced into the adsorption cylinder during vacuum regeneration is 1.28 times the normal amount. And the regeneration pressure was 340 Torr.

As a result, when the power consumption amount per unit product amount when the reference product amount is generated is 100, in the method of the present invention, this can be 82, whereas the product amount is simply reduced. In the weight reduction operation of No. 133, it was 133.

[0046]

As described above, the method for reducing the pressure fluctuation adsorption device according to the present invention introduces the pressure fluctuation adsorption device which performs the vacuum regeneration step into the adsorption tower which is performing the vacuum regeneration when the pressure fluctuation adsorption device performs the volume reduction operation. The amount of purge gas to be used is increased according to the reduction amount of the product gas.Therefore, the pressure in the adsorption cylinder during the regeneration process during the reduction operation increases and the power consumption of the vacuum pump decreases. Product cost can be reduced.

That is, according to the method of the present invention, during the reduction operation, the product recovery rate can be lowered to correspond to the product amount and the power consumption of the vacuum pump can be reduced at the same cycle time as in the normal operation. Therefore, the inconvenience that occurs when the cycle time is extended does not occur, and efficient weight reduction operation can be performed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a change in column pressure.

FIG. 2 is a diagram showing a relationship between pressure and power consumption in a roots type vacuum pump.

FIG. 3 is a diagram showing a relationship between a regeneration pressure and a product recovery rate.

FIG. 4 is a diagram showing a relationship between a product generation amount ratio and an increase ratio of a purge amount.

FIG. 5 is a system diagram showing an example of a pressure fluctuation adsorption device that performs vacuum regeneration.

[Explanation of symbols]

2a, 2b, 2c ... Adsorption tower 3 ... Blower 6 ... Vacuum pump

Claims (1)

[Claims] 1. A product gas is continuously produced by sequentially switching a plurality of adsorption towers filled with an adsorbent that preferentially adsorbs a specific component in a raw material gas to an adsorption step, a vacuum regeneration step and a charging step. In reducing the pressure fluctuation adsorption device, the amount of purge gas introduced into the adsorption tower performing the vacuum regeneration is increased according to the reduction amount of the product gas. ..