NITROGEN PRODUCTION SYSTEM FOR PRODUCING NITROGEN WITH DIFFERENT PURITIES AND NITROGEN PRODUCTION PROCESS THEREOF

Abstract

A nitrogen production system that can produce high purity nitrogen containing a desired concentration of oxygen and ultrahigh purity nitrogen containing a desired concentration of argon in a single rectifying column while restraining increase in electric power consumption, and a production process thereof are provided. The nitrogen production system includes a heat exchanger that cools material air, a nitrogen rectifying column including a rectifying unit into which the material air cooled by the heat exchanger is introduced and a condenser that is located in a column top, a first introduction pipe that introduces the material air from the heat exchanger into a buffer unit located at a lower part from a position of the rectifying unit, a second introduction pipe for introducing an oxygen-enriched liquefied gas into the condenser from the buffer unit of the nitrogen rectifying column, a first derivation pipe for deriving ultrahigh purity nitrogen from the rectifying unit and recovering the ultrahigh purity nitrogen, and a second derivation pipe for deriving high purity nitrogen from an intermediate plate of the rectifying unit and recovering the high purity nitrogen.

Claims

1. A nitrogen production system, comprising: a compressor that compresses material air; a removal unit that removes predetermined impurities from the material air compressed by the compressor; a heat exchanger that cools the material air from which the impurities are removed by the removal unit; a nitrogen rectifying column including a rectifying unit into which the material air cooled by the heat exchanger is introduced, and a condenser that is located at a column top; a first introduction pipe that introduces the compressed material air from the heat exchanger into a buffer unit located at a lower part from a position of the rectifying unit of the nitrogen rectifying column; a second introduction pipe for introducing an oxygen-enriched liquefied gas into the condenser from the buffer unit of the nitrogen rectifying column; a first derivation pipe for deriving ultrahigh purity nitrogen containing a first concentration of argon, from an upper plate or an uppermost plate of the rectifying unit of the nitrogen rectifying column, and recovering the ultrahigh purity nitrogen through the heat exchanger; and a second derivation pipe for deriving high purity nitrogen containing a second concentration of oxygen from an intermediate plate of the rectifying unit of the nitrogen rectifying column, and recovering the high purity nitrogen through the heat exchanger.

2. The nitrogen production system according to claim 1, further comprising: an oxygen concentration measurement unit that measures an oxygen concentration in the high purity nitrogen in the second derivation pipe downstream of the heat exchanger; and a flow rate control unit that controls a first flow rate adjustment unit provided in the first derivation pipe downstream of the heat exchanger, based on the oxygen concentration measured by the oxygen concentration measurement unit.

3. The nitrogen production system according to claim 1, further comprising a second flow rate adjustment unit provided in the second derivation pipe, wherein the second flow rate adjustment unit controls an extraction amount of the high purity nitrogen so as to achieve a desired flow rate specified in advance.

4. The nitrogen production system according to claim 1, wherein the condenser has a third introduction pipe that introduces liquid nitrogen for cooling as a cold heat source of the condenser.

5. The nitrogen production system according to claim 1, further comprising a waste gas introduction pipe that introduces waste gas extracted from the condenser into the heat exchanger via an expansion turbine.

6. A nitrogen production process, comprising: a compression step of compressing material air; a removal step of removing predetermined impurities from the material air compressed in the compression step; a cooling step of cooling the material air from which the impurities are removed in the removal step by a heat exchanger; a first introduction step of introducing the material air cooled by the heat exchanger into a lower part from the rectifying unit position of a nitrogen rectifying column including a rectifying unit and a condenser located in a column top; a second introduction step of introducing an oxygen-enriched liquefied gas into the condenser from the lower part from the rectifying unit position of the nitrogen rectifying column; a first derivation step of deriving ultrahigh purity nitrogen containing a first concentration of argon from an upper plate or an uppermost plate of the rectifying unit of the nitrogen rectifying column, and recovering the ultrahigh purity nitrogen through the heat exchanger; and a second derivation step of deriving high purity nitrogen containing a second concentration of oxygen from an intermediate plate of the rectifying unit of the nitrogen rectifying column, and recovering the high purity nitrogen through the heat exchanger.

7. The nitrogen production process according to claim 6, further comprising: an oxygen concentration measuring step of measuring an oxygen concentration in the high purity nitrogen downstream of the heat exchanger; and a flow rate control step of controlling a first flow rate adjustment unit that is provided downstream of the heat exchanger and adjusts a flow rate of ultrahigh purity nitrogen, based on the oxygen concentration measured in the oxygen concentration measuring step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 is a diagram illustrating concentrations of oxygen and Ar in a gas phase in respective theoretical plate numbers of a rectifying unit in a nitrogen rectifying column;

[0066] FIG. 2 is a diagram illustrating a configuration example of a nitrogen production system of embodiment 1;

[0067] FIG. 3 is a diagram illustrating a simulation result in the nitrogen rectifying column; and

[0068] FIG. 4 is a diagram illustrating total nitrogen recovery amounts based on the simulation result in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Hereinafter, several embodiments of the present invention will be described. The embodiments described as follows describe one example of the present invention. The present invention is not limited to the following embodiments in any way, and also includes various modified modes that are carried out in a range without changing the gist of the present invention. All of components described as follows are not always essential components of the present invention.

Embodiment 1

[0070] A nitrogen production system 1 of embodiment 1 will be described with use of FIG. 2. The nitrogen production system 1 has a heat exchanger H, a nitrogen rectifying column including a rectifying unit A and a condenser C located in a column top, a material air intake pipe 2 for feeding material air to cool the material air in the heat exchanger H, a material air introduction pipe 3 for feeding the cooled material air to the rectifying unit A, an oxygen-enriched liquefied gas introduction pipe 4 that derives an oxygen-enriched liquefied gas from the lower part of the rectifying unit A and introduces the oxygen-enriched liquefied gas into the condenser C to cool an inside of the condenser C, an ultrahigh purity nitrogen extraction pipe 5 that derives ultrahigh purity nitrogen from an upper plate of the rectifying unit A and introduces the ultrahigh purity nitrogen into the heat exchanger H, and a high purity nitrogen extraction pipe 6 that derives high purity nitrogen from an intermediate plate of the rectifying unit A and introduces the high purity nitrogen into the heat exchanger H. The respective components will be described in detail hereinafter.

[0071] The heat exchanger H cools the material air (for example, a material air amount is 1000 Nm.sup.3/h) that is compressed by a compressor (not illustrated), and has impurities such as carbon dioxide and water removed in a purification unit (corresponding to an impurity removal unit, not illustrated). The introduced material air exchanges heat with high purity nitrogen described later and ultrahigh purity nitrogen that will be described later in the heat exchanger H to be cooled to a vicinity of a liquefaction point. The cooled material air is in a state of a liquefied gas and is introduced into the rectifying unit A by the material air introduction pipe 3.

[0072] The material air in the liquefied gas state which is introduced into the rectifying unit A rises in the rectifying unit A and is rectified. A range of an operation pressure of the rectifying unit A is 5 barA to 20 barA, and the operation pressure can be set at 9 bar, for example. Further, the number of theoretical plates of the rectifying unit A is 40 to 100, and can be set at 60, for example. In a lower part of the rectifying unit A, oxygen-enriched liquefied gas is separated, whereas in an upper part of the rectifying unit A, high purity nitrogen gas is separated. At least part of the oxygen-enriched liquefied gas is derived from the lower part of the rectifying unit A, and is introduced into the condenser C through the oxygen-enriched liquefied gas introduction pipe 4, whereby the condenser is cooled.

[0073] From the upper plate of the rectifying unit A, ultrahigh purity nitrogen is derived. Here, high purity nitrogen is derived from an intermediate plate of the rectifying unit A through the high purity nitrogen extraction pipe 6. In the rectifying unit A, a reflux to lower plates from upper plates is performed, and by deriving high purity nitrogen from an intermediate plate, a reflux ratio among intermediate plates and upper plates can be made higher than in the case without performing the reflux. Thereby, as compared with the case where high purity nitrogen is not derived from the intermediate plate, an Ar content in nitrogen that is derived from the upper plate decreases, ultrahigh purity nitrogen with an extremely low Ar content can be extracted, and high purity nitrogen with an oxygen concentration that satisfies the product specifications although having a higher Ar content than the Ar content of ultrahigh purity nitrogen can be obtained from the intermediate plate.

[0074] In an upper part of the condenser C, waste gas including a lot of low boiling point impurities is separated. The waste gas passes through a waste gas introduction pipe 7, is introduced into the heat exchanger H to be fed to an expansion turbine T, is thereafter introduced into the heat exchanger H again through a waste gas pipe 8. The waste gas introduced into the expansion turbine T is expanded in the expansion turbine T and thereby a temperature of the waste gas is reduced. The waste gas which is introduced into the heat exchanger H again exchanges heat with the material air in the heat exchanger H, and thereafter is discharged.

[0075] The ultrahigh purity nitrogen which is derived from the rectifying unit A is introduced into the heat exchanger H through the ultrahigh purity nitrogen extraction pipe 5, exchanges heat with the material air in the heat exchanger H and rises in temperature, and is provided to a use point in a subsequent stage, or fed to a storage tank. The high purity nitrogen derived from the rectifying unit A is introduced into the heat exchanger H through the high purity nitrogen extraction pipe 6, exchanges heat with the material air and rises in temperature in the heat exchanger H, is provided to a use point in a subsequent stage or fed to a storage tank.

[0076] The oxygen content in high purity nitrogen and the Ar content in ultrahigh purity nitrogen are determined by a position of the high purity nitrogen extraction pipe (that is, the plate number of the rectifying unit A), and extraction amounts of high purity nitrogen and ultrahigh purity nitrogen to the amount of the material air which is taken in. Therefore, the high purity nitrogen extraction pipe is disposed in the position corresponding to the desired Ar content in advance.

[0077] For example, when the number of theoretical plates of the rectifying unit A is 60, the ultrahigh purity nitrogen extraction pipe 5 is located at a position corresponding to the 60.sup.th plate, and the high purity nitrogen extraction pipe 6 can be provided at the intermediate plate (a position corresponding to among the 40.sup.th to 49.sup.th plates, for example).

[0078] The material air intake amount and the high purity nitrogen extraction amount are respectively set at desired flow rates. Further, the extraction amount of ultrahigh purity nitrogen is set in accordance with the desired argon content in the ultrahigh purity nitrogen. Thereby, a fixed extraction amount of high purity nitrogen and a fixed extraction amount of ultrahigh purity nitrogen (containing a desired amount of Ar) can be produced in a single rectifying unit.

[0079] The Ar content in the ultrahigh purity nitrogen that is extracted from the upper plate of the rectifying unit A by the ultrahigh purity nitrogen extraction pipe 5 can be also set at less than a first concentration specified in advance, and the Ar content in the high purity nitrogen that is extracted from the intermediate plate of the rectifying unit A by the high purity nitrogen extraction pipe 6 can be also set at the first concentration or more.

[0080] The first concentration is 0.001 ppm to 100 ppm inclusive, and is preferably 0.1 volume ppm to 10 volume ppm inclusive. The first concentration can be determined in consideration of the requirement or the like of the application in which nitrogen to be a product is used, and can be set at, for example, 1 volume ppm or 100 weight ppb.

[0081] The nitrogen production system of embodiment 1 includes an impurity concentration measurement unit D that measures an impurity amount (oxygen concentration) in high purity nitrogen, a first flow rate adjustment unit 10 that controls a high purity nitrogen amount, a second flow rate adjustment unit 11 that controls ultrahigh purity nitrogen amount, and a flow rate control unit 12 that controls the second flow rate adjustment unit 11 based on an impurity concentration measurement result measured by the impurity concentration measurement unit D. The first flow rate adjustment unit 10 may or may not be present.

[0082] The second flow rate adjustment unit 11 is adjusted by the flow rate control unit 12 as to increase an amount of nitrogen that is extracted from the ultrahigh purity nitrogen extraction pipe 5 when an impurity measurement result (oxygen concentration) is less than a second concentration set in advance, and to decrease an amount of nitrogen that is extracted from the ultrahigh purity nitrogen extraction pipe 6 when the impurity measurement result (oxygen concentration) is the second concentration set in advance or more.

[0083] As the impurity concentration measurement unit D, for example, an oxygen content meter (capable of continuous analysis to which an oxygen concentration cell is applied) can be used. Measurement of the Ar concentration in nitrogen is difficult due to resemblance of the chemical and physical properties of nitrogen and Ar. The present inventors found that the Ar content in ultrahigh purity nitrogen and the oxygen content in high purity nitrogen are correlated. Thus, the flow rate control unit 12 obtains the Ar content in the ultrahigh purity nitrogen based on the oxygen content in high purity nitrogen, and controls the second flow rate adjustment unit 11 to adjust the derived amount of ultrahigh purity nitrogen.

EXAMPLE

[0084] The inventors calculate the derived amounts of high purity nitrogen (the oxygen concentration is 1 volume ppm) and ultrahigh purity nitrogen (the Ar concentration is 1 volume ppm) according to the change in the position of the intermediate plate, in the conditions of the rectifying unit of the number of theoretical plates of 60 and the material air amount of 1000 Nm.sup.3/h by simulation, and a result thereof is illustrated in FIG. 3. Further, FIG. 3 also illustrates an improvement efficiency in the case of being compared with the conventional art of extracting the same amount ultrahigh purity nitrogen (the Ar concentration is 1 volume ppm) from the rectifying column of the number of theoretical plates of 60, and extracting the same amounts of high purity nitrogen (the oxygen concentration is 1 volume ppm) from different rectifying columns of the numbers of theoretical plates of 49 to 40.

[0085] In the present simulation, an intermediate plate is within a range from a position of the theoretical plate number 49 to a position of 40. For example, when the intermediate plate is at the position of the theoretical plate number 44, the derived amount of ultrahigh purity nitrogen is 208 Nm.sup.3/h, and the derived amount of high purity nitrogen is 184 Nm.sup.3/h.

[0086] When ultrahigh purity nitrogen with the Ar concentration of 1 volume ppm is produced by the conventional process of extracting nitrogen from only the upper plate of the rectifying unit in the conditions that the number of theoretical plates is similarly set at 60, and the material air amount is similarly set at 1000 Nm.sup.3/h, the derived amount of ultrahigh purity nitrogen is 363 Nm.sup.3/h. A ratio of the material air amount and the derived amount of ultrahigh purity nitrogen is fixed, so that 1000:363=[the material air amount for obtaining 208 Nm3/h]:208 is established in the same conditions. That is, in the case of obtaining the ultrahigh purity nitrogen derived amount of 208 Nm.sup.3/h, the necessary material air amount is 1000208363=573 Nm.sup.3/h.

[0087] When high purity nitrogen with the oxygen concentration of 1 volume ppm is produced in the conditions that another rectifying unit with the number of theoretical plates set as 44 which is the same as the above described intermediate plate is used, and the material air amount is similarly set at 1000 Nm.sup.3/h, the high purity nitrogen production amount is 395 Nm.sup.3/h. The ratio of the material air amount and the derived amount of high purity nitrogen is fixed, so that 1000:395=[the material air amount for obtaining 184 Nm.sup.3/h]:184 is established in the same conditions. That is, in the case of obtaining the high purity nitrogen derived amount of 184 Nm.sup.3/h, the necessary material air amount is 1000184395=465.8 Nm.sup.3/h.

[0088] Accordingly, in order to obtain an ultrahigh purity nitrogen derived amount of 208 Nm.sup.3/h and a high purity nitrogen derived amount of 184 Nm.sup.3/h in the conventional art, material air of 1038.8 Nm.sup.3/h that is a total of 573 Nm.sup.3/h and 465.8 Nm.sup.3/h is necessary.

[0089] From the result of 1038.8 Nm.sup.3/h, an improvement rate of 3.88% is obtained as compared with the case of the material air amount being 1000 Nm.sup.3/h. In this way, from the simulation result, the position of the high purity nitrogen extraction pipe can be determined. Further, based on not only the simulation result, but also a pilot plant, or results of both of the simulation and pilot plant, the high purity nitrogen extraction position (the position of the intermediate plate of the rectifying unit) can be set.

[0090] From the result illustrated in FIG. 3, it became obvious that the highest improvement rate was achieved in the condition that high purity nitrogen is derived from the theoretical plate number 44, so that the inventors confirmed superiority over the conventional art in the nitrogen generation amount of the present invention in the condition. The result is illustrated in FIG. 4. In the present embodiment, the entire amount of nitrogen does not have to be refined to ultrahigh purity, so that evaluation can be made by the total recovery amount of nitrogen that can be recovered from the rectifying unit A. According to the present example, a total of 392 Nm.sup.3/h of nitrogen can be recovered with 208 Nm.sup.3/h of ultrahigh purity nitrogen that can be derived from NTP 60 of the single rectifying unit A combined with 184 Nm.sup.3/h of high purity nitrogen that can be derived from the NTP 40 of the rectifying unit A, with respect to 1000 Nm.sup.3/h of the material air. In contrast with this, in comparative examples 1 and 2, the ultrahigh purity nitrogen that can be derived from the rectifying unit of the maximum NTP of 44 of comparative example 1 is 314 Nm.sup.3/h with respect to 1000 Nm.sup.3/h of the material air. Further, the ultrahigh purity nitrogen that can be derived from the rectifying unit of the maximum NTP of 60 in comparative example 2 is 363 Nm.sup.3/h. Comparing the total nitrogen recovery amounts, it is found that the present example exhibits an effect of efficiency improvement of total nitrogen recovery amount of (392314)/314=25% as compared with the case of recovering nitrogen from the rectifying unit of the maximum NTP of 44 of comparative example 1, and an effect of efficiency improvement of the total nitrogen recovery amount of (392363)/363=8% as compared with the case of recovering nitrogen from the rectifying unit of the maximum NPT of 60 in comparative example 2.

[0091] The flow rate control unit 12 can control the derived amount of ultrahigh purity nitrogen by adjusting the second flow rate adjustment unit 11 as illustrated in FIG. 2 when the Ar concentration in the ultrahigh purity nitrogen is set at 1 volume ppm and the oxygen concentration in the high purity nitrogen is set at 1 volume ppm.

[0092] When the conditions deviate from the optimum conditions, for example, when the oxygen concentration decreases to less than the second concentration (1 volume ppm), the flow rate control unit 12 adjusts the first flow rate adjustment unit 11 so as to keep the second concentration (1 volume ppm) to control the derived amount of ultrahigh purity nitrogen, as illustrated in FIG. 2. When the oxygen concentration exceeds the second concentration (1 volume ppm), the flow rate control unit 12 adjusts the first flow rate adjustment unit 11 so as to keep the second concentration (1 volume ppm) to control the derived amount of ultrahigh purity nitrogen.

[0093] As another embodiment, a configuration can be also adopted, which has a liquid nitrogen introduction pipe for introducing liquid nitrogen to cool the condenser C.

[0094] In the case of introducing liquid nitrogen, liquid nitrogen is supplied from a liquid nitrogen supply decrease such as an external liquid nitrogen tank, and cools the condenser C.

[0095] In the case of a small nitrogen production system, the condenser can be cooled by only cooling by liquid nitrogen introduction without installing the expensive expansion turbine T. In a facility including the expansion turbine T, the liquid nitrogen introduction pipe does not have to be installed, but the liquid nitrogen introduction pipe can be also installed as backup equipment.

[0096] While in the present embodiment, the expansion turbine T that expands waste gas is installed, the present invention is not limited to this, but may adopt a configuration without having the expansion turbine T. In the case like this, a pipe that introduces liquid nitrogen for cooling the condenser C may be provided.

[0097] While in the present embodiment, the number of high purity nitrogen extraction pipe 6 is only one, a plurality of high purity nitrogen extraction pipes may be provided in accordance with the kinds of nitrogen to be produced as another embodiment. When the only one high purity nitrogen extraction pipe 6 is used, two kinds of products that are one kind of high purity nitrogen and ultrahigh purity nitrogen are obtained. When two or more of the high purity nitrogen extraction pipes 6 are used (respectively installed in different plate numbers), the high purity nitrogen extraction pipes are provided at heights corresponding to the different theoretical plate numbers. Thereby, three kinds or more products that are two kinds or more high purity nitrogen having different purities in accordance with the mounting positions of the high purity nitrogen extraction pipes 6, and ultrahigh purity nitrogen are obtained.

Embodiment 2

[0098] A process of producing nitrogen with different purities of embodiment 2 will be described. The process of embodiment 2 can be favorably executed by using the system of the above described embodiment 1.

[0099] A nitrogen production process of processing nitrogen by low temperature distillation includes

[0100] a compression step of compressing material air;

[0101] a removal step of removing predetermined impurities from the material air compressed in the compression step,

[0102] a cooling step of cooling the material air from which the impurities are removed in the removal step by a heat exchanger,

[0103] a first introduction step of introducing the material air cooled by the heat exchanger into a lower part from the rectifying unit position of a nitrogen rectifying column including a rectifying unit and a condenser located in a column top,

[0104] a second introduction step of introducing an oxygen-enriched liquefied gas into the condenser from the lower part from the rectifying unit position of the nitrogen rectifying column,

[0105] a first derivation step of deriving ultrahigh purity nitrogen containing a first concentration of argon from an upper plate or an uppermost plate of the rectifying unit of the nitrogen rectifying column, and recovering the ultrahigh purity nitrogen through the heat exchanger, and

[0106] a second derivation step of deriving high purity nitrogen containing a second concentration of oxygen from an intermediate plate of the rectifying unit of the nitrogen rectifying column, and recovering the high purity nitrogen through the heat exchanger.

[0107] Further, the above described process includes an oxygen concentration measuring step of measuring an oxygen concentration in the high purity nitrogen downstream of the heat exchanger, and a flow rate control step of controlling a first flow rate adjustment unit that is provided downstream of the heat exchanger and adjusts a flow rate of ultrahigh purity nitrogen, based on the oxygen concentration measured in the oxygen concentration measuring step.

[0108] Further, the oxygen concentration measuring step may measure the oxygen concentration in real time, or measure the oxygen concentration in a predetermined timing or in accordance with a measurement rule set in advance.

[0109] Further, the flow rate control step may control the first flow rate adjustment unit so that the oxygen concentration keeps a target value (or a predetermined range).

[0110] Further, the flow rate control step, for example, may control the first flow rate adjustment unit so as to increase the flow rate of the ultrahigh purity nitrogen when the oxygen concentration decreases below a target value (or a predetermined range), and control the first flow rate adjustment unit so as to decrease the flow rate of the ultrahigh purity nitrogen when the oxygen concentration increases more than the target value (or the predetermined range).

[0111] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0112] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0113] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0114] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0115] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0116] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0117] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.