Air separation unit and air separation method

Abstract

To provide an air separation device capable of preventing a pretreatment adsorber from becoming an overload state along with a rise of a raw material air temperature during quantity reduction operation in the air separation device.SOLUTION: An air separation device 1 includes: a product nitrogen gas flow rate detector 22; a temperature detector 51 for a gas introduction passage to a pretreatment adsorber 12; a computing unit 52 for computing a maximum product nitrogen gas flow rate that can be generated from a temperature detected by the temperature detector 51; a guide vane 24 that is provided in a raw material air compressor 11 and controlling a discharge flow rate of the raw material air compressor 11 on the basis of a pressure measurement value detected by a product nitrogen gas pressure detector 20; and a product nitrogen gas flow rate instruction regulator 53 that instructs a product nitrogen gas flow rate control valve 25 to regulate a product nitrogen gas flow rate to the maximum product nitrogen gas flow rate computed by the computing unit 52 when a measurement value obtained by the product nitrogen gas flow rate detector 22 becomes larger than the maximum product nitrogen gas flow rate computed by the computing unit 52.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an air separation unit and an air separation method, and more particularly to the configuration of an air separation unit that uses a rectification column to perform rectification separation of feed air to produce product nitrogen gas, and an air separation method using the unit. [Background technology]

[0002] Conventionally, in an air separation unit that separates and produces product nitrogen gas from feed air using a single rectification column, when the required flow rate of product nitrogen gas falls below the rated flow rate, a so-called turn-down operation is performed, and the feed air flow rate is reduced to reduce the product nitrogen gas flow rate to match demand. As a result, the pressure loss between the feed air compressor and the product nitrogen outlet decreases, and the product nitrogen gas pressure increases. This has led to a demand for improved power, and an air separation unit with this improved power and a control method thereof have been disclosed (for example, Patent Document 1).

[0003] In the air separation unit and control method thereof described in Patent Document 1, when the required flow rate of product nitrogen gas decreases, the feed air flow rate is decreased and the feed air pressure (discharge pressure of the feed air compressor) is adjusted (particularly reduced) so that the product nitrogen gas pressure becomes a predetermined pressure. According to the air separation unit described in Patent Document 1, even if the flow rate of product nitrogen gas decreases, it is possible to obtain the optimal flow rate and pressure of feed air for the feed air. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4091388 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the feed air compressor and its control method described in Patent Document 1 have the following problems remaining, and further improvements are required.

[0006] That is, the feed air that has been pressurized to a predetermined pressure is cooled by cooling water in the aftercooler and introduced into the pretreatment adsorber, where the water vapor, carbon dioxide, and the like inside are adsorbed and removed. The amount of water vapor contained in the feed air is determined by the feed air temperature at the aftercooler outlet. For example, if the feed air temperature at the aftercooler outlet is 40°C, the feed air will contain saturated water vapor at that temperature. When the feed air temperature rises, the amount of water vapor contained in the feed air increases relatively, and the load on the adsorbent that adsorbs and removes water vapor in the pretreatment adsorber increases. In an air separation unit, if the adsorbent in the pretreatment adsorber is overloaded and the load is continued for a long period of time, the amount of moisture that can be adsorbed by the adsorbent in the pretreatment adsorber will exceed (overloaded state), and the moisture that should be removed will pass through the pretreatment adsorber and clog the downstream heat exchanger, making it impossible to continue operation. In addition, if the adsorbent layer that adsorbs carbon dioxide in the pretreatment adsorber absorbs moisture, it will not be able to be regenerated by heating and will need to be replaced.

[0007] Therefore, an object of the present invention is to provide an air separation unit and an air separation method that can prevent the pretreatment adsorber from becoming overloaded due to an increase in the feed air temperature during turn-down operation in an air separation unit. [Means for solving the problem]

[0008] In order to achieve the above object, an air separation unit of the present invention comprises a feed air compressor for compressing feed air, a pretreatment adsorber for removing impurities in the feed air compressed by the feed air compressor, a main heat exchanger for cooling the feed air from which impurities have been removed by the pretreatment adsorber, a rectification tower for rectifying the feed air cooled by the main heat exchanger to separate a product nitrogen gas, and a product nitrogen gas outlet path for exchanging heat with the feed air in the main heat exchanger and discharging the product nitrogen gas separated in the rectification tower after raising its temperature, wherein the air separation unit comprises a temperature detector for detecting the temperature of a gas introduction path to the pretreatment adsorber, a calculator for calculating a maximum product nitrogen gas flow rate that can be generated from the temperature detected by the temperature detector, and a product nitrogen gas extractor provided in the product nitrogen gas outlet path and detecting the pressure in the product nitrogen gas outlet path. The nitrogen gas pressure detector is provided with a product nitrogen gas flow rate detector that is provided in the product nitrogen gas discharge path and detects the flow rate of the product nitrogen gas; a product nitrogen gas flow rate control valve that is provided in the product nitrogen gas discharge path and controlled to change the flow rate of the product nitrogen gas based on the flow rate detected by the product nitrogen gas flow rate detector; a guide vane that is provided in the raw air compressor and controls the discharge flow rate of the raw air compressor based on the pressure measurement value detected by the product nitrogen gas pressure detector; and a product nitrogen gas flow rate indicating regulator that, when the measurement value of the product nitrogen gas flow rate detector becomes greater than the maximum product nitrogen gas flow rate calculated by the calculator, instructs the product nitrogen gas flow rate control valve to adjust the product nitrogen gas flow rate to the maximum product nitrogen gas flow rate calculated by the calculator.

[0009] Furthermore, the air separation unit of the present invention preferably further comprises a product nitrogen gas compressor that is provided downstream of the product nitrogen gas pressure detector in the product nitrogen gas discharge path and compresses the product nitrogen gas.

[0010] Furthermore, in the air separation unit of the present invention, the rectification column is preferably a single rectification column or a plurality of single rectification columns.

[0011] Furthermore, in the air separation unit of the present invention, the guide vane is preferably an inverter or a control valve.

[0012] Furthermore, the air separation unit of the present invention may further include a pretreatment adsorber flow rate detector that detects the flow rate of gas discharged from the pretreatment adsorber, and the guide vane may control the discharge flow rate of the feed air compressor further based on the gas flow rate detected by the pretreatment adsorber flow rate detector.

[0013] The air separation method of the present invention is an air separation method for separating product nitrogen gas from feed air using an air separation unit including a feed air compressor for compressing feed air, a pretreatment adsorber for removing impurities in the feed air compressed by the feed air compressor, a main heat exchanger for cooling the feed air from which impurities have been removed by the pretreatment adsorber, a rectification column for rectifying the feed air cooled in the main heat exchanger to separate a product nitrogen gas, a product nitrogen gas outlet path for exchanging heat with the feed air in the main heat exchanger, raising the temperature of the product nitrogen gas separated in the rectification column, and outletting the product nitrogen gas after being discharged, and a product nitrogen gas flow rate control valve provided in the product nitrogen gas outlet path and controlled to change the flow rate of the product nitrogen gas, detecting a pressure change in the product nitrogen gas outlet pathway associated with the increase in pressure of the nitrogen gas product, controlling the discharge flow rate of the feed air compressor so as to maintain the product nitrogen gas at a predetermined pressure based on the detected pressure change in the product nitrogen gas outlet pathway, detecting a temperature in the gas introduction pathway to the pretreatment adsorber, calculating a maximum product nitrogen gas flow rate that can be generated in the air separation unit from the detected temperature of the gas introduction pathway and outputting the calculated maximum product nitrogen gas flow rate as a flow rate set value, and controlling the product nitrogen gas flow control valve to limit the flow rate of the product nitrogen gas according to the output flow rate set value, thereby increasing the pressure of the product nitrogen gas, thereby reducing the air processing volume of the pretreatment adsorber and preventing the pretreatment adsorber from becoming overloaded. Effect of the Invention

[0014] According to the present invention, when the detected temperature of the temperature detector that detects the temperature of the gas introduction path to the pretreatment adsorber rises, the product nitrogen gas flow rate and the feed air compressor throughput are reduced, thereby making it possible to reduce the power of the feed air compressor while preventing the pretreatment adsorber from being overloaded. Therefore, even if the temperature of the air introduced into the pretreatment adsorber rises due to an abnormality such as deterioration of the cooler performance of the feed air compressor or an increase in the cooling water temperature, the throughput of the feed air compressor is automatically reduced, making it possible to continue operating the air separation unit without damaging the adsorbent in the pretreatment adsorber. [Brief description of the drawings]

[0015] [Figure 1] 1 is a system diagram of an air separation unit showing a first embodiment of the present invention. [Diagram 2] FIG. 2 is a system diagram of an air separation unit showing a second embodiment of the present invention. [Diagram 3] 4 is a graph showing the relationship between the feed air temperature at the inlet of a pretreatment adsorber and the throughput of the pretreatment adsorber and the product nitrogen gas flow rate in an air separation unit of an example. [Figure 4] 4 is a graph showing the results of a simulation in which the present invention is employed in an air separation unit according to an embodiment of the present invention. [Diagram 5] 4 is a graph showing the results of a simulation in which the present invention is not employed in the air separation unit of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Fig. 1 is a system diagram of an air separation unit 1 showing a first embodiment of the present invention. The air separation unit 1 shown in Fig. 1 is a so-called single rectification column type nitrogen production unit, and is capable of producing product nitrogen gas by separating and purifying feed air.

[0017] This air separation unit 1 comprises a feed air compressor 11 that compresses feed air, a pretreatment adsorber 12 that removes impurities such as moisture and carbon dioxide from the feed air compressed by the feed air compressor 11, a main heat exchanger 13 that cools the feed air from which impurities have been removed by the pretreatment adsorber 12, a single rectification tower 14 that rectifies and separates the feed air cooled in the main heat exchanger 13, a condenser 15 that produces rectification tower reflux liquid, an expansion turbine 16 that generates the refrigeration required to operate the unit, and a product nitrogen gas discharge path 17 that exchanges heat between the product nitrogen gas separated in the single rectification tower 14 and the feed air in the main heat exchanger 13, raises the temperature, and then discharges it.

[0018] Furthermore, the air separation unit 1 is provided in the product nitrogen gas outlet path 17 as devices for controlling the pressure and flow rate of the product nitrogen gas to be supplied to a destination, and is equipped with a product nitrogen gas pressure detector 20 for detecting the pressure in the product nitrogen gas outlet path 17, a product nitrogen gas flow rate detector 22 for detecting the flow rate of the product nitrogen gas, and a product nitrogen gas flow rate control valve 25 that is controlled to change the flow rate of the product nitrogen gas based on the flow rate detected by the product nitrogen gas flow rate detector 22. In addition, the liquefied air path 18 connecting the bottom of the single rectification column 14 and the condenser 15 is provided with a flow rate indicating regulator 26 and a flow rate control valve 27 for controlling the flow rate of the oxygen-enriched liquefied air.

[0019] The air separation unit 1 also includes a temperature detector 51 (TI1) that detects the temperature of the gas introduction path to the pretreatment adsorber 12, and a calculator 52 (TX1) that calculates the maximum product nitrogen gas flow rate that can be generated from the temperature detected by the temperature detector 51 (TI1). The feed air compressor 11 is further provided with a guide vane 24 that controls the discharge flow rate of the feed air compressor 11 based on the pressure measurement value detected by the product nitrogen gas pressure detector 20, and is provided with a product nitrogen gas flow rate indicating regulator 53 that controls the product nitrogen gas flow rate control valve 25 so that the product nitrogen gas flow rate becomes the maximum product nitrogen gas flow rate calculated by the calculator 52 (TX1) when the measurement value of the product nitrogen gas flow rate detector 22 becomes greater than the maximum product nitrogen gas flow rate calculated by the calculator 52 (TX1).

[0020] The air separation unit 1 also has other components, which should be understood in light of FIG. 1 and the description of the process for producing product nitrogen gas from feed air using the air separation unit 1 described in detail below.

[0021] The feed air sucked through the filter 11a is pressurized to a predetermined pressure by the feed air compressor 11, and is cooled to about 100°C by the heat of compression. The high-temperature feed air is heat exchanged with cooling water in the aftercooler 11b, and is cooled to about 40°C. The feed air is then introduced into the pretreatment adsorber 12, where impurities such as water vapor and carbon dioxide in the feed air are adsorbed and removed, and the feed air is introduced into the cold box 19. The feed air introduced into the cold box 19 is heat exchanged with the product nitrogen gas and waste gas in the main heat exchanger 13, and is cooled to near the liquefaction temperature, and is introduced into the lower part of the single rectification column 14.

[0022] The feed air introduced into the single rectification tower 14 is separated by a rectification operation into nitrogen gas at the top of the tower and oxygen-enriched liquefied air at the bottom of the tower. The oxygen-enriched liquefied air is extracted from the bottom of the tower into the liquefied air line 18 and introduced into the condenser 15, where it exchanges heat with nitrogen gas extracted from the top of the tower into line 31 and introduced into the condenser 15, and the entire amount of the oxygen-enriched liquefied air is vaporized to become waste gas. This waste gas is introduced into the main heat exchanger 13 through line 32, where it is heated to an intermediate temperature, extracted through line 33, and introduced into the expansion turbine 16, where it generates refrigeration by adiabatic expansion. The expanded waste gas is introduced into the main heat exchanger 13 again through line 34, where it is heated to room temperature and discharged through line 35.

[0023] The entire amount of the nitrogen gas introduced into the condenser 15 is liquefied to become liquefied nitrogen, which is introduced from a line 36 into the upper part of the single rectification column 14 and becomes a reflux liquid. Then, a part of the nitrogen gas extracted into the line 31 is branched off into a line 37, introduced into the main heat exchanger 13, heated to room temperature, and supplied to a destination via the product nitrogen gas discharge line 17 and the product nitrogen gas flow control valve 25.

[0024] When the consumption of nitrogen gas at the destination decreases compared to normal operation, the pressure in the product nitrogen gas outlet path 17 rises accordingly, and this pressure rise is detected by the product nitrogen gas pressure detector 20, and the guide vane 24 is controlled by the pressure indicating regulator 21 (PIC_C) in accordance with the detected pressure value to adjust the amount of intake air to the feed air compressor 11. At this time, the guide vane 24 is controlled so that the pressure of the product nitrogen gas that is led out to the product nitrogen gas outlet path 17 and supplied to the destination becomes a predetermined pressure.

[0025] Here, the pretreatment adsorber 12 is filled with an adsorbent, which adsorbs and removes impurities such as moisture (water vapor) and carbon dioxide in the raw air. The adsorbent is divided into a layer that adsorbs moisture and a layer that adsorbs carbon dioxide. If the layer that adsorbs moisture becomes overloaded, the moisture reaches the layer that adsorbs carbon dioxide, irreversibly damaging the adsorbent that adsorbs carbon dioxide, and the adsorbent must be replaced. The adsorbent has an upper limit on the amount of raw air that can be processed / adsorption time. Even if the processing amount of the pretreatment adsorber 12 is the same, if the adsorption temperature becomes higher than the design temperature or the adsorption pressure becomes lower than the design pressure, the load on the adsorbent becomes large (overloaded), and it is not possible to process a specified amount of raw air even within the designed adsorption time. As a result, water vapor, carbon dioxide, etc. are mixed into the raw air introduced from the pretreatment adsorber 12 to the main heat exchanger 13. In this case, it would be necessary to regenerate the pretreatment adsorber 12, replace the adsorbent, or fully heat the downstream fractionator, etc. (an operation to raise the temperature of the low-temperature parts of the air separation unit and remove moisture and carbon dioxide), which could cause major problems in the operation of the air separation unit.

[0026] To address this, in the air separation unit 1, a temperature detector 51 (TI1) measures the temperature of the feed air introduced into the pretreatment adsorber 12, a calculator 52 (TX1) calculates the maximum air amount that can be processed by the pretreatment adsorber 12 from the feed air temperature and the maximum product nitrogen gas flow rate corresponding to that air amount, and this maximum product nitrogen gas flow rate is set as the flow rate set value SP of the product nitrogen gas flow rate indicating regulator 53 (FIC_C). A control signal is output from the product nitrogen gas flow rate indicating regulator 53 (FIC_C) to the product nitrogen gas flow rate control valve 25 via a low selector 54 (FY-A) so that the product nitrogen gas flow rate becomes the flow rate set value SP.

[0027] On the other hand, a pressure regulator 23 (PIC_A) is provided adjacent to the pressure indicating regulator 21 (PIC_C) to adjust the product nitrogen gas to a specified pressure, and a control signal is sent to the product nitrogen gas flow control valve 25 via a low selector 54 (FY-A) so that the pressure of the product nitrogen gas becomes the set value.

[0028] Then, the low selector 54 (FY-A) compares the control signal from the product nitrogen gas flow rate indicating regulator 53 (FIC_C) with the control signal from the pressure regulator 23 (PIC_A) and selects the signal with the smaller value, and the product nitrogen gas flow rate control valve 25 is controlled by the selected signal.

[0029] In other words, in the conventional air separation unit described in Patent Document 1, when the required product nitrogen gas flow rate decreases and the feed air compressor is operated at a reduced rate in response to this, the pressure and flow rate of the feed air compressor 11 are basically controlled based only on the pressure loss and flow rate from the feed air compressor to the product nitrogen gas flow control valve, that is, the guide vane 24 is controlled by the pressure indicating regulator 21 (PIC_C) to minimize the power of the feed air compressor 11. However, in the air separation unit 1 in this embodiment, if there is a concern that the pretreatment adsorber 12 will become overloaded due to a rise in the temperature of the feed air introduced into the pretreatment adsorber 12, it is possible to immediately perform control that prioritizes avoiding overload operation of the pretreatment adsorber 12, that is, control that switches to control of the product nitrogen gas flow rate control valve 25 by the product nitrogen gas flow rate indicating regulator 53 (FIC_C).

[0030] That is, in the air separation unit 1 of this embodiment, the flow rate of the product nitrogen gas is restricted by the product nitrogen gas flow control valve 25 so that the pretreatment adsorber 12 does not become overloaded. As a result, the detection value of the product nitrogen gas pressure detector 20 rises, so that a signal in the direction of decreasing the pressure is output from the pressure indicating regulator 21 (PIC_C) in order to maintain the product nitrogen gas at a predetermined pressure, and the guide vane 24 of the feed air compressor 11 is controlled to reduce the amount of feed air.

[0031] As described above, the air separation method for separating product nitrogen gas from feed air using the air separation unit 1 includes detecting a pressure change in the product nitrogen gas outlet path 17 associated with a change in the flow rate of the product nitrogen gas outlet from the product nitrogen gas outlet path 17, controlling the discharge flow rate of the feed air compressor so as to maintain the product nitrogen gas at a predetermined pressure based on the detected pressure change in the product nitrogen gas outlet path 17, detecting the temperature of the gas introduction path to the pretreatment adsorber 12, calculating the maximum product nitrogen gas flow rate that can be generated in the air separation unit 1 from the detected temperature of the gas introduction path and outputting it as a flow rate set value, and controlling the product nitrogen gas flow control valve 25 to limit the flow rate of the product nitrogen gas using the output flow rate set value, thereby increasing the pressure of the product nitrogen gas, thereby reducing the air processing volume of the pretreatment adsorber 12 and preventing the pretreatment adsorber 12 from becoming overloaded.

[0032] The air separation unit 1 of this embodiment is equipped with a product nitrogen gas flow rate detector 22 that detects the flow rate of the product nitrogen gas, a temperature detector 51 (TI1) that detects the temperature of the gas introduction path to the pretreatment adsorber 12, a calculator 52 (TX1) that calculates the maximum product nitrogen gas flow rate that can be generated from the temperature detected by the temperature detector 51 (TI1), a guide vane 24 provided in the raw air compressor 11 that controls the discharge flow rate of the raw air compressor 11 based on the pressure measurement value detected by the product nitrogen gas pressure detector 20, and a product nitrogen gas flow rate indicating regulator 53 that instructs the product nitrogen gas flow rate control valve 25 to adjust the gas flow rate. In the air separation unit 1, when the measured value of the product nitrogen gas flow detector 22 becomes larger than the maximum product nitrogen gas flow rate calculated by the calculator 52 (TX1), the product nitrogen gas flow rate indicating regulator 53 adjusts the product nitrogen gas flow rate control valve 25 so that the product nitrogen gas flow rate becomes the maximum product nitrogen gas flow rate calculated by the calculator 52 (TX1), and therefore, when there is a concern that the pretreatment adsorber 12 will be overloaded due to a rise in the temperature of the feed air introduced into the pretreatment adsorber 12, control immediately switches to one that prioritizes avoiding overload operation of the pretreatment adsorber 12. Therefore, with an air separation unit configured like the air separation unit 1, it is possible to prevent the pretreatment adsorber 12 from being overloaded due to a rise in the feed air temperature during turndown operation.

[0033] In the air separation method, a pressure change in the product nitrogen gas outlet path 17 associated with a change in the flow rate of the product nitrogen gas discharged from the product nitrogen gas outlet path 17 is detected, the discharge flow rate of the feed air compressor is controlled so as to maintain the product nitrogen gas at a predetermined pressure based on the detected pressure change in the product nitrogen gas outlet path 17, the temperature of the gas introduction path to the pretreatment adsorber 12 is detected, the maximum product nitrogen gas flow rate that can be generated in the air separation unit 1 is calculated from the detected temperature of the gas introduction path and output as a flow rate set value, the product nitrogen gas flow control valve 25 is controlled to limit the flow rate of the product nitrogen gas according to the output flow rate set value, the pressure of the product nitrogen gas is increased, and the air throughput of the pretreatment adsorber 12 is reduced, thereby preventing the pretreatment adsorber 12 from becoming overloaded. Therefore, according to the air separation method, it is possible to prevent the pretreatment adsorber 12 from becoming overloaded due to an increase in the feed air temperature during the reduction operation of the air separation unit 1.

[0034] According to the air separation unit 1 and air separation method of this embodiment, even if the temperature of the air introduced into the pretreatment adsorber 12 rises due to an abnormality such as deterioration of the cooler performance of the feed air compressor 11 or an increase in the cooling water temperature, the processing volume of the feed air compressor 11 is automatically reduced, making it possible to continue operation without damaging the adsorbent in the pretreatment adsorber 12.

[0035] Fig. 2 is a system diagram of an air separation unit 101 showing a second embodiment of the present invention. In the following explanation, the same components as those of the air separation unit shown in the first embodiment are given the same reference numerals and detailed explanations are omitted. The air separation unit 101 of the second embodiment shown in Fig. 2 basically has the same configuration as the air separation unit 1 of the first embodiment shown in Fig. 1 and applies an air separation method with the same control, but differs in the following points.

[0036] That is, compared to the air separation unit 1 of the first embodiment, the air separation unit 101 of the second embodiment further includes a pretreatment adsorber flow rate detector 60 which detects the flow rate of gas derived from the pretreatment adsorber 12, and the guide vanes 24 are adjusted based on the pressure measurement detected by the product nitrogen gas pressure detector 20 and the gas flow rate detected by the pretreatment adsorber flow rate detector 60, thereby controlling the discharge flow rate of the feed air compressor.

[0037] In the air separation unit 101, a calculator (FX_2) 62 performs calculations based on the output value of the pressure indicating regulator 21 (PIC_C), and the set value of the pretreatment adsorber outlet flow rate indicating regulator 61 (FIC_2) can be changed. In other words, the flow rate of the feed air introduced into the pretreatment adsorber 12 can be controlled so that the pretreatment adsorber 12 is not overloaded.

[0038] Even if the setting value of the pretreatment adsorber outlet flow rate indicating regulator 61 (FIC_2) is directly changed when the inlet air temperature of the pretreatment adsorber 12 rises, the product nitrogen gas pressure will drop if there is no change in the amount of product nitrogen gas used. However, in the air separation unit 101, this is avoided by a control configuration in which the product nitrogen gas flow rate is limited by measuring the inlet temperature of the pretreatment adsorber 12 and the resulting pressure increase is used to adjust the setting value of the inlet flow rate of the pretreatment adsorber 12, indirectly operating the guide vanes 24 via the product nitrogen gas flow rate and pressure.

[0039] According to the air separation unit 101 of this embodiment, as described above, by directly controlling the flow rate of the feed air introduced into the pretreatment adsorber 12, it is possible to prevent the pretreatment adsorber 12 from becoming overloaded.

[0040] In the above-mentioned first and second embodiments, the guide vane 24 is provided as a flow rate controller for controlling the discharge flow rate of the feed air compressor 11, but an inverter or a control valve can be used as the guide vane 24. In addition, a suction valve may be used, and a method of adjusting the flow rate by controlling the rotation speed of the compressor driving motor and other various flow rate control means may be used. In addition, a pressure indicating regulator is exemplified as the pressure detector, but pressure detection and discharge flow rate control can be performed using any device. In addition, an example of performing rectification separation using a single rectification column has been given, but similar control can be performed in an air separation unit that uses multiple single rectification columns to improve the product yield. In addition, an air separation unit that produces only product nitrogen has been given as an example, but an air separation unit that also produces oxygen may also be used. In addition, a product nitrogen gas compressor 41 can be provided at a position downstream of the product nitrogen gas pressure detector 20 in the product nitrogen gas discharge path 17, and the product nitrogen gas can be pumped as necessary. At this time, since the pressure in the product nitrogen gas discharge path 17 is kept constant, disturbances to the product nitrogen gas compressor 41 can be reduced, and the product nitrogen gas can be stably supplied at a predetermined pressure.

[0041] The air separation units (nitrogen production units) shown in the first and second embodiments are merely examples, and the drawings do not necessarily reflect all configurations. For example, in each embodiment, an expansion turbine is used to generate the refrigeration required to operate the unit, but the air separation unit may be one in which liquefied nitrogen is injected from the outside to obtain the refrigeration required to operate the unit. The pressures and temperatures described above are merely examples, and may take different values ​​depending on the unit specifications. EXAMPLES

[0042] 800kPaG nitrogen gas at 3500Nm 3 A simulation was carried out using an air separation unit having a similar configuration to the air separation unit 1 in Fig. 1 that produces 1000 ml / h (hereinafter referred to as the "air separation unit used in the simulation" or simply the "air separation unit") as an example. In the following description, the symbols in Fig. 1 will be used.

[0043] In the air separation unit 1 used in this simulation, the required air compressor throughput is 6190 Nm 3 / h and its discharge pressure is 875 kPaG. In this air separation unit 1, the product nitrogen gas consumption is 2584 Nm 3 / h (operating at approximately 74% of the rated capacity), the required throughput of the feed air compressor 11 is 5270 Nm 3 / h, and the discharge pressure will be 860kPaG, reducing power consumption by approximately 94kW.

[0044] Fig. 3 is a graph showing the relationship between the feed air temperature at the inlet of the pretreatment adsorber 12 and the pretreatment adsorber throughput and product nitrogen gas flow rate in an air separation unit used in the simulation. Fig. 4 is a graph showing the simulation results when the present invention is adopted in the air separation unit used in the simulation. Fig. 5 is a graph showing the simulation results for an air separation unit when the present invention is not adopted, as in Patent Document 1.

[0045] 3, in this air separation unit, when the temperature of the feed air at the inlet of the pretreatment adsorber 12 rises, the amount of entrained water vapor increases, and therefore, in order to remove the entrained water vapor, the throughput that can be processed by the pretreatment adsorber 12 decreases. Furthermore, the amount of product nitrogen decreases as the throughput that can be processed by the pretreatment adsorber 12 decreases.

[0046] As described above, the calculator 52 (TX1) calculates the maximum amount of air that can be processed by the pretreatment adsorber 12 and the maximum value of the product nitrogen gas flow rate corresponding to that amount of air based on the temperature of the raw air introduced into the pretreatment adsorber 12 measured by the temperature detector 51 (TI1), and outputs this as the flow rate setting value SP of the product nitrogen gas flow rate indicating regulator 53 (FIC_C).

[0047] Using this air separation unit, a simulation was performed to see how the feed air flow rate, the CO2 concentration at the outlet of the pretreatment adsorber 12, the feed air temperature at the inlet of the pretreatment adsorber 12, and the amount of moisture (amount of moisture brought in) entrained in the pretreatment adsorber 12 change over time in cases where the present invention is adopted and where the present invention is not adopted. In the simulation, the pretreatment adsorber 12 was assumed to be an adsorber consisting of two towers, with a 120-minute switching system, and with an introduced feed air temperature of 38°C. In addition, a case was assumed in which the feed air temperature rose by 2 to 3°C for some reason 40 minutes after the start of the adsorption operation of the pretreatment adsorber 12 (A in FIG. 4 and A in FIG. 5). Accordingly, the amount of water vapor entrained in the pretreatment adsorber 12 together with the feed air increases by 11 to 17%. Therefore, it is necessary to reduce the amount of feed air in consideration of the increased amount of water vapor and the decrease in adsorption performance due to the increase in temperature.

[0048] In the case where the present invention is adopted, when the product nitrogen gas flow rate set value in the product nitrogen gas flow rate regulator 53 (FIC_C) falls below the maximum product nitrogen gas flow rate calculated by the calculator 52 (TX1) as the raw air temperature at the inlet of the pretreatment adsorber 12 rises, the product nitrogen gas flow rate set value in the product nitrogen gas flow rate regulator 53 (FIC_C) is rewritten to the value calculated by the calculator 52 (TX1). As a result, in the case where the present invention is adopted, as shown in FIG. 4, when the raw air temperature at the inlet of the pretreatment adsorber 12 rises by 2 to 3°C (A in FIG. 4), the raw air flow rate is reduced (B in FIG. 4), and the amount of moisture (moisture carried in) entrained in the pretreatment adsorber 12 becomes constant (C in FIG. 4). As a result, in the case where the present invention is adopted, no breakthrough of carbon dioxide and water vapor is observed until the end of the adsorption operation of the pretreatment adsorber 12 (D in FIG. 4).

[0049] On the other hand, when the present invention is not adopted, as shown in Fig. 5, even if the feed air temperature at the inlet of the pretreatment adsorber 12 rises (Fig. 5A), the amount of water entrained in the pretreatment adsorber 12 (amount of water brought in) increases (Fig. 5F), as shown in Fig. 5. As a result, breakthrough of carbon dioxide is observed immediately before the end of operation (Fig. 5G).

[0050] These simulation results also show that, by adopting the present invention, the air separation unit can automatically reduce the air treatment volume in accordance with the inlet air temperature of the pretreatment adsorber 12, and continue to operate without damage, even if an abnormality such as deterioration of the cooler performance of the feed air compressor 11 or an increase in the cooling water temperature occurs. [Explanation of symbols]

[0051] 1,101...air separation unit, 11...feed air compressor, 11a...filter, 11b...aftercooler, 12...pretreatment adsorber, 13...main heat exchanger, 14...single rectification column, 15...condenser, 16...expansion turbine, 17...product nitrogen gas outlet path, 18...liquefied air path, 19...cold box, 20...product nitrogen gas pressure detector, 21...pressure indicating regulator, 22...product nitrogen gas flow detector, 23...pressure regulator, 24...guide vane, 25...product nitrogen gas flow control valve, 31-37...path, 41...product nitrogen gas compressor, 51...temperature detector, 52...computing unit 53...product nitrogen gas flow indicating regulator, 54...low selector, 60...pretreatment adsorber flow detector, 61...pretreatment adsorber outlet flow indicating regulator

Claims

1. an air separation unit having a feed air compressor for compressing feed air, a pretreatment adsorber for removing impurities from the feed air compressed by the feed air compressor, a main heat exchanger for cooling the feed air from which the impurities have been removed by the pretreatment adsorber, a rectification column for rectifying the feed air cooled by the main heat exchanger to separate a product nitrogen gas, and a product nitrogen gas discharge path for discharging the product nitrogen gas separated in the rectification column after heat exchange with the feed air in the main heat exchanger and raising its temperature, a temperature detector for detecting a temperature of a gas introduction path to the pretreatment adsorber; a calculator that calculates a maximum possible product nitrogen gas flow rate from the temperature detected by the temperature detector; a product nitrogen gas pressure detector provided in the product nitrogen gas outlet path for detecting a pressure in the product nitrogen gas outlet path; a product nitrogen gas flow rate detector provided in the product nitrogen gas outlet path for detecting a flow rate of the product nitrogen gas; a product nitrogen gas flow rate control valve provided in the product nitrogen gas discharge path and controlled to change the flow rate of the product nitrogen gas based on the flow rate detected by the product nitrogen gas flow rate detector; a guide vane provided in the feed air compressor for controlling a discharge flow rate of the feed air compressor based on a pressure measurement value detected by the product nitrogen gas pressure detector; an air separation unit comprising: a product nitrogen gas flow rate indicating regulator that, when the measurement value of the product nitrogen gas flow detector becomes greater than the maximum product nitrogen gas flow rate calculated by the calculator, instructs the product nitrogen gas flow rate control valve to adjust the product nitrogen gas flow rate to the maximum product nitrogen gas flow rate calculated by the calculator;

2. 2. The air separation unit according to claim 1, further comprising a product nitrogen gas compressor for compressing the product nitrogen gas, the product nitrogen gas compressor being provided downstream of the product nitrogen gas pressure detector in the product nitrogen gas discharge path.

3. 2. The air separation unit of claim 1, wherein the rectification column is a single rectification or a multiple single rectification column.

4. 2. The air separation unit according to claim 1, wherein the guide vane is an inverter or a control valve.

5. a pretreatment adsorber flow rate detector for detecting a flow rate of the gas discharged from the pretreatment adsorber; 5. The air separation unit according to claim 1, wherein the guide vane controls the discharge flow rate of the feed air compressor based on the gas flow rate detected by the pretreatment adsorber flow rate detector.

6. an air separation method for separating product nitrogen gas from feed air using an air separation unit comprising: a feed air compressor for compressing feed air, a pretreatment adsorber for removing impurities in the feed air compressed by the feed air compressor, a main heat exchanger for cooling the feed air from which impurities have been removed by the pretreatment adsorber, a rectification column for rectifying the feed air cooled in the main heat exchanger to separate a product nitrogen gas, a product nitrogen gas discharge path for exchanging heat with the feed air in the main heat exchanger, raising the temperature of the product nitrogen gas, and discharging the product nitrogen gas, and a product nitrogen gas flow rate control valve provided in the product nitrogen gas discharge path and controlled to change the flow rate of the product nitrogen gas, detecting a pressure change in the product nitrogen gas outlet path associated with a change in flow rate of the product nitrogen gas outlet from the product nitrogen gas outlet path; controlling a discharge flow rate of the feed air compressor so as to maintain the product nitrogen gas at a predetermined pressure based on the detected pressure change in the product nitrogen gas outlet path; Detecting a temperature of a gas introduction path to the pretreatment adsorber; calculating a maximum product nitrogen gas flow rate that can be generated in the air separation unit from the detected temperature of the gas introduction path, and outputting the calculated maximum product nitrogen gas flow rate as a flow rate setting value; and controlling the product nitrogen gas flow control valve to limit the flow rate of the product nitrogen gas in accordance with the output flow rate set value, thereby increasing the pressure of the product nitrogen gas, thereby reducing the air processing volume of the pretreatment adsorber, thereby preventing the pretreatment adsorber from becoming overloaded.

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