Method for operating nitrogen gas production equipment

Abstract

To provide an operation method of a nitrogen gas manufacturing apparatus that can obtain product gas with required purity and reduce power consumptions.SOLUTION: An operation method of a nitrogen gas manufacturing apparatus, which has a plurality of adsorption towers filled with adsorbent and is configured so that the adsorption towers repeatedly perform at least an adsorption process, a pressure equalization process and a regeneration process to separate nitrogen from compressed air which is raw material gas and supply the gas as product gas, comprises a pausing process in which an implementation time of the adsorption process is extended as flow volumes of the extracted product gas reduce, and supply of the raw material gas to the adsorption towers and extraction of the product gas from the adsorption towers are paused, after the adsorption process is completed.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for operating a nitrogen gas production apparatus. [Background technology]

[0002] In the pressure swing adsorption gas separation method, a raw mixed gas is supplied to an adsorption tower that repeatedly performs an adsorption step and a regeneration step, and the strongly adsorbable components are adsorbed onto various adsorbents packed in the adsorption tower, thereby separating the strongly adsorbable components from the weakly adsorbable components in the raw mixed gas. For example, a device that uses molecular sieve carbon as an adsorbent and produces nitrogen gas from air by the pressure swing adsorption gas separation method (nitrogen gas production device, hereinafter simply referred to as a "nitrogen PSA device") is widely used in practice.

[0003] A known feature of nitrogen PSA units is that when the flow rate (product flow rate) of the product nitrogen (product gas) is high, the purity of the product nitrogen (product purity) decreases, and when the flow rate of the product nitrogen is low, the purity of the product nitrogen increases. Nitrogen PSA units are also designed to be able to supply product nitrogen of the required purity at the required flow rate during rated operation. Therefore, when the required flow rate of product nitrogen is low, the nitrogen PSA unit will supply product nitrogen of excessive purity.

[0004] Therefore, Patent Document 1 proposes an operating method for a nitrogen gas production device in which, when the actual flow rate (supply amount) of product nitrogen becomes lower than the flow rate (design value) of product nitrogen during rated operation, the operation of the nitrogen PSA device is stopped during the pressure equalization process carried out between multiple adsorption towers between the adsorption process and the regeneration process, and product nitrogen is supplied at the internal pressure of the product tank.

[0005] In the method of operating a nitrogen gas production apparatus disclosed in Patent Document 1, during the pressure equalization process, when the operation of the nitrogen PSA unit is stopped (hereinafter simply referred to as the "pause process"), the nitrogen PSA unit does not require compressed air from the compressor, and the compressor motor is put into an unloaded state (unloaded operation), thereby reducing power consumption. In other words, the smaller the flow rate (supply amount) of product nitrogen, the longer the time that product nitrogen can be supplied using only the internal pressure of the product tank, resulting in a significant energy-saving effect. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3781187 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of operating a nitrogen gas production apparatus disclosed in Patent Document 1 has the problem that, due to the characteristics of a PSA apparatus, the product purity in the adsorption tower in the adsorption step increases when the product flow rate is low, and therefore there is a tendency to supply a product gas of higher purity than during rated operation, which produces a product gas of the required specifications. Also, there has been a demand for an operating method of a nitrogen gas production apparatus that can further reduce power consumption compared to conventional methods.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for operating a nitrogen gas production apparatus that can obtain a product gas of a required purity and reduce power consumption. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention employs the following configuration. [1] A method for operating a nitrogen gas production apparatus having a plurality of adsorption towers filled with adsorbents, the adsorption towers repeatedly performing at least an adsorption step, a pressure equalization step, and a regeneration step to separate nitrogen from compressed air as a raw material gas and supply the nitrogen as a product gas, extending the adsorption step in response to a decrease in the product gas extraction flow rate; A method for operating a nitrogen gas production apparatus, comprising, after completion of the adsorption step, providing a pause step in which the supply of raw material gas to the adsorption tower and the withdrawal of product gas from the adsorption tower are stopped. [2] The method for operating the nitrogen gas production apparatus according to [1], wherein the compressed air is supplied using an inverter air compressor. [Effects of the Invention]

[0010] According to the method for operating a nitrogen gas production apparatus of the present invention, a product gas of a required purity can be obtained and power consumption can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a system diagram schematically illustrating a nitrogen gas production apparatus to which a method of operating a nitrogen gas production apparatus according to an embodiment of the present invention is applied. [Figure 2] 3 is a diagram illustrating the open / closed state of each switching valve during rated operation in the method for operating the nitrogen gas production apparatus of the present embodiment. FIG. [Figure 3] 3 is a diagram illustrating the open / closed state of each switching valve during a reduction operation in the method for operating the nitrogen gas production apparatus of the present embodiment. FIG. [Figure 4] FIG. 2 is a diagram showing a time chart of each adsorption tower during rated operation in the method of operating the nitrogen gas production apparatus of the present embodiment. [Figure 5] FIG. 2 is a diagram showing a time chart of each adsorption tower during a decrease operation in the method of operating the nitrogen gas production apparatus of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a method of operating a nitrogen gas production apparatus according to one embodiment of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for convenience in order to make the characteristics easier to understand, and the dimensional proportions of the components may not necessarily be the same as those in reality.

[0013] First, a method for operating a nitrogen gas production apparatus according to an embodiment of the present invention will be described together with the nitrogen gas production apparatus used therein, with reference to Fig. 1. Fig. 1 is a system diagram showing a nitrogen gas production apparatus to which the method for operating a nitrogen gas production apparatus according to an embodiment of the present invention can be applied.

[0014] <Nitrogen gas production equipment> As shown in FIG. 1, a nitrogen gas production apparatus (hereinafter also simply referred to as a "nitrogen PSA apparatus") 1 applicable to the method for operating a nitrogen gas production apparatus of this embodiment is a PSA apparatus that produces nitrogen from air. The nitrogen PSA unit 1 is generally configured with an air compressor 2 for supplying raw air, two adsorption towers 3A and 3B, a product tank 4 for storing the product nitrogen gas extracted from the adsorption towers 3A and 3B, and multiple selector valves AV1A-AV5A, AV1B-AV5B, and AV6 for switching the adsorption towers 3A and 3B between the adsorption process, the pressure equalization process, and the regeneration process. Note that check valves can be used for the selector valves AV2A and AV2B.

[0015] It is preferable to use an inverter-type air compressor, in which the rotation speed of the motor can be controlled by an inverter according to the pressure, etc., as the air compressor 2. In this way, the rotation speed of the motor can be controlled by varying the operating frequency, and compressed air can be supplied to the adsorption towers 3A, 3B while performing constant pressure control so that the pressure in the adsorption towers 3A, 3B during the adsorption process approaches the set pressure (so that it falls within the target pressure).

[0016] The adsorption towers 3A and 3B are filled with an adsorbent such as molecular sieve carbon that preferentially adsorbs oxygen in air that mainly contains oxygen and nitrogen.

[0017] The selector valve AV6 is used to prevent a decrease in pressure in the adsorption tower due to the outflow of purge gas from the adsorption tower on the purge gas supply side when the operation of the nitrogen PSA system 1 includes a purge operation during the regeneration step and the purge operation overlaps with the shutdown step of the nitrogen PSA system 1 of this embodiment. Closing the selector valve AV6 can completely isolate the adsorption tower.

[0018] Furthermore, in the nitrogen PSA system 1, during the shutdown step described below, the product nitrogen gas in the product tank 4 is continuously supplied to the user, so the pressure in the product tank 4 gradually decreases. However, when molecular sieve carbon is used as the adsorbent, during the shutdown step after the adsorption step, the gas in the towers is adsorbed by the molecular sieve carbon, and the pressure in the adsorption towers also gradually decreases. Therefore, depending on the size relationship between the product tank 4 and the adsorption towers 3A and 3B, the pressure drop in the adsorption towers 3A and 3B may be greater than that in the product tank 4, and the pressure in the adsorption towers 3A and 3B may become lower than the pressure in the product tank 4, causing the product nitrogen gas in the product tank 4 to backflow into the adsorption towers 3A and 3B. Therefore, by using check valves as the switching valves AV2A and AV2B in the nitrogen PSA system 1, backflow of nitrogen gas from the product tank 4 to the adsorption towers 3A and 3B can be reliably prevented.

[0019] Furthermore, the nitrogen PSA unit 1 preferably includes, as operation control devices, an air pressure gauge (not shown) that measures the pressure in the supply path that supplies compressed feed air from the air compressor 2 to the adsorption towers 3A and 3B, a nitrogen pressure gauge (not shown) that measures the pressure in the product tank 4, a nitrogen flow meter (not shown) that measures the flow rate (product extraction flow rate) in the product gas supply path that supplies product nitrogen gas from the product tank 4 to the destination (user), and a valve control device (not shown) that performs various calculations based on the flow rate signal of the nitrogen flow rate measured by the nitrogen flow meter and the pressure signals from the air pressure gauge and the nitrogen pressure gauge, and controls the opening and closing of each switching valve based on the results of the calculations.

[0020] <Method of operating nitrogen gas production equipment> Next, the method of operating a nitrogen gas production apparatus of this embodiment is a method of operating a nitrogen gas production apparatus that has a plurality of adsorption towers filled with adsorbent, and the adsorption towers repeatedly perform at least an adsorption process, a pressure equalization process, and a regeneration process to separate nitrogen from compressed air, which is a raw material gas, and supply it as a product gas, and the method extends the execution time of the adsorption process in accordance with a decrease in the extraction flow rate of the product gas, and provides a pause process after completion of the adsorption process to stop the supply of raw material gas to the adsorption towers and the extraction of product gas from the adsorption towers. In the method for operating the nitrogen gas production apparatus of this embodiment, it is preferable to supply compressed air using an inverter type air compressor.

[0021] Hereinafter, the method for operating a nitrogen gas production apparatus of this embodiment will be described using the nitrogen PSA apparatus 1 described above as an example. Here, FIG. 2 is a diagram illustrating the open / close states of each switching valve during rated operation in the method for operating a nitrogen gas production apparatus of this embodiment. FIG. 3 is a diagram illustrating the open / close states of each switching valve during turndown operation in the method for operating a nitrogen gas production apparatus of this embodiment. FIG. 4 is a diagram illustrating a time chart for each adsorption tower during rated operation in the method for operating a nitrogen gas production apparatus of this embodiment. FIG. 5 is a diagram illustrating a time chart for each adsorption tower during turndown operation in the method for operating a nitrogen gas production apparatus of this embodiment.

[0022] (at rated operation) In the operating method of the nitrogen PSA system 1 of this embodiment, when supplying 100% of the specified product nitrogen gas from the product tank 4 to the destination (user), both adsorption towers 3A and 3B repeatedly perform the conventional adsorption, regeneration, and pressure equalization processes shown in FIG. 4 in addition to the operation of the switching valves shown in FIG. 2.

[0023] As shown in adsorption tower 3A in FIG. 2(A) and adsorption tower 3B in FIG. 2(C), the adsorption step includes a pressurization operation of increasing the pressure in the adsorption tower while supplying feed air or product gas to the adsorption tower, and an operation of removing the product gas from the adsorption tower while supplying feed air.

[0024] As shown in adsorption tower 3B in Fig. 2(A) and adsorption tower 3A in Fig. 2(C), the regeneration step involves reducing the pressure in adsorption towers 3A and 3B to desorb the highly adsorbable component from the adsorbent and regenerating the adsorption towers to prepare for the next adsorption step. Simultaneously with or subsequent to reducing the pressure in the adsorption towers, an operation of purging the adsorption towers with product gas or other operations may be performed.

[0025] As shown in Figures 2(B) and 2(D), the pressure equalization step is a step of recovering pressure by communicating adsorption tower 3A with adsorption tower 3B and transferring gas within the towers. The two towers may be communicated via the upper (product outlet side) of the adsorption tower, the lower (raw material inlet side) of the adsorption tower, or both the upper and lower towers, and the pressures in both towers do not need to be completely equal.

[0026] (When operating at reduced power) In the operating method of the nitrogen PSA unit 1 of this embodiment, when product nitrogen gas is supplied from the product tank 4 to the destination (user) at less than 100% of the specification, both adsorption towers 3A and 3B repeat the operations shown in Figure 5, adding a pause step to the conventional adsorption step, regeneration step, and pressure equalization step.

[0027] During turndown operation, the adsorption process time is extended according to the decrease in the amount of product nitrogen gas supplied from the product tank 4 to the user (the extraction flow rate of product nitrogen gas). For example, if the product nitrogen gas supply rate is 70% of the specification, it is preferable to extend the adsorption time by 200%. However, the optimal extension time for the adsorption time is determined based on the product flow rate and product tank capacity. For example, the rated adsorption time is used when the product nitrogen gas supply rate is 100% to 90%, and the adsorption time is 1.2 times the rated time when the product nitrogen gas supply rate is 90% to 80%. The relationship between the product nitrogen gas supply rate and the adsorption time is determined based on the equipment specifications. In addition, it is preferable to use an inverter-type air compressor that can be controlled by an inverter according to the pressure of the adsorption tower. Specifically, the adsorption process can be extended to the specified time by controlling the motor rotation speed by varying the operating frequency and supplying compressed air to the adsorption towers 3A and 3B while maintaining constant pressure control so that the pressure of the adsorption towers 3A and 3B during the adsorption process approaches the set pressure (so that it falls within the target pressure).

[0028] The pause step is performed after the completion of the adsorption step, as shown in Fig. 5. During the pause step, the supply of raw gas to the adsorption towers 3A, 3B and the withdrawal of product gas from the adsorption towers 3A, 3B are stopped. That is, during the pause step, as shown in Fig. 4, all of the selector valves AV1A to AV5A, AV1B to AV5B, and AV6 are closed, and no gas flows into or out of the adsorption towers 3A, 3B.

[0029] During the shutdown step, the inlet valves AV1A and AV1B to the adsorption towers 3A and 3B are closed, and therefore the air compressor 2 is in unloaded operation.

[0030] Because the user is still using product gas even during turndown operation, the duration of the pause step is determined according to the degree of turndown operation so that the pressure in the product tank 4 meets the specified pressure. In other words, the pause step is completed while the pressure in the product tank 4 remains at or above the specified pressure, and the pause step duration is set so that product nitrogen can be supplied to the product tank 4 from the adsorption tower that has started the adsorption step.

[0031] (When operating in an increase or decrease mode) When the operation switches from turn-down operation to normal operation, or when the supply rate of product nitrogen gas increases, the adsorption time is varied based on the relationship between the supply rate of product nitrogen gas and the adsorption time, as explained above for turn-down operation. Furthermore, when the nitrogen gas product supply rate is further reduced from the rate reduction operation, the adsorption time is also varied based on the relationship between the nitrogen gas product supply rate and the adsorption time.

[0032] The nitrogen PSA device 1 can smoothly switch between normal operation (rated operation) when the product extraction flow rate is the specified flow rate, reduced operation to reduce the product extraction flow rate to a desired level, and increased operation to return the reduced product extraction flow rate to the specified flow rate, depending on the product extraction flow rate.This allows the user to freely change the product extraction flow rate within the specified flow rate.

[0033] As described above, according to the operating method of the nitrogen PSA unit 1 of this embodiment, the duration of the adsorption step is extended in response to a decrease in the product gas extraction flow rate, and after completion of the adsorption step, a pause step is provided in which the supply of raw material gas to the adsorption towers 3A, 3B and the extraction of product gas from the adsorption towers 3A, 3B are stopped. This makes it possible to obtain a product gas of the required purity and reduce power consumption.

[0034] Furthermore, according to the operating method of the nitrogen PSA unit 1 of this embodiment, the number of times switching to unload operation per unit time can be made much smaller than in the conventional method, thereby suppressing breakdowns in the air compressor 2.

[0035] The technical scope of the present invention is not limited to the above-described embodiments, but includes designs within the scope that do not deviate from the gist of the present invention. [Example]

[0036] The effects of the present invention will be specifically described below, but the present invention is not limited to the following description.

[0037] <Verification test> As an example, using the nitrogen PSA unit 1 shown in Figure 1, the power consumption and oxygen concentration in the product gas were investigated when the flow rate of the product gas was reduced from rated operation (100%) to 70%, 50%, and 30%. As a comparative example, the nitrogen PSA apparatus described in the prior art was used, and the power consumption and oxygen concentration in the product gas were investigated when the flow rate of the product gas was reduced from rated operation (100%) to 70%, 50%, and 30%, in the same manner as in the above example. Table 1 shows the power consumption and oxygen concentration in the product for each product flow rate in the nitrogen PSA apparatus 1 of the present invention and in the prior art nitrogen PSA apparatus (when the adsorption time is constant).

[0038] [Table 1]

[0039] As shown in Table 1, in the nitrogen PSA unit of the comparative example, the idle time increased and power consumption decreased as the product flow rate decreased from 100% to 70%, 50%, and 30%. However, the oxygen concentration in the product decreased as the product flow rate decreased, so it was confirmed that excessive purity was being supplied. In contrast to this, it was confirmed that the nitrogen PSA apparatus 1 of the example can reduce power consumption even more than the comparative example, and the oxygen concentration in the product does not become excessive. [Explanation of symbols]

[0040] 1. Nitrogen PSA equipment (nitrogen gas production equipment) 2. Air compressor 3A,3B Adsorption tower 4 Product tank AV1A~AV5A, AV1B~AV5B, AV6 Switching valve

Claims

1. A method for operating a nitrogen gas production apparatus having a plurality of adsorption towers filled with adsorbents, the adsorption towers repeatedly performing at least an adsorption step, a pressure equalization step, and a regeneration step to separate nitrogen from compressed air as a raw material gas and supply the nitrogen as a product gas, comprising: extending the adsorption step in response to a decrease in the product gas extraction flow rate; A method for operating a nitrogen gas production apparatus, comprising, after completion of the adsorption step, providing a halt step of stopping the supply of raw material gas to the adsorption tower and the withdrawal of product gas from the adsorption tower.

2. 2. The method for operating a nitrogen gas production apparatus according to claim 1, wherein the compressed air is supplied using an inverter type air compressor.

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