NITROGEN GENERATING DEVICE AND NITROGEN GENERATING METHOD

Abstract

A nitrogen generating device comprises: a main heat exchanger; a nitrogen distillation column; at least one nitrogen condenser; a compressor; an expansion turbine; a rotation control unit for controlling rotation with respect to a rotating shaft connecting the compressor and the expansion turbine; a pressure measuring unit for measuring a pressure value of product nitrogen gas; and an optimum rotational speed calculation command unit which inputs the pressure value measured by the pressure measuring unit into a pre-installed rotational speed calculation function to calculate the rotational speed of the rotating shaft, and issues a command to the rotation control unit.

Claims

1. A nitrogen generating device comprising: a main heat exchanger into which feed air is introduced; a nitrogen distillation column having a lower portion into which the feed air discharged from the main heat exchanger is introduced; at least one nitrogen condenser configured to condense the nitrogen gas discharged from a column top portion of the nitrogen distillation column; a compressor into which first gas discharged from column top portion of the nitrogen condensers is introduced; a first gas recycling pipeline configured to cause the first gas compressed by the compressor to pass through a portion of the main heat exchanger and configured to introduce the same into the lower portion of the nitrogen distillation column; an expansion turbine into which second gas discharged from the column top portion of the nitrogen condenser is introduced after passing through a portion of the main heat exchanger; a second gas discharge pipeline configured to cause the second gas used by the expansion turbine to pass through the main heat exchanger and be expelled; a rotation control unit configured to control rotation with respect to a rotating shaft connecting the compressor and the expansion turbine; a product nitrogen gas extraction pipeline configured to cause the nitrogen gas discharged from the column top portion or an upper distillation portion of the nitrogen distillation column to pass through the main heat exchanger, and for then configured to extract product nitrogen gas; a pressure measuring unit configured to measure a pressure value in an arbitrarily defined part of the nitrogen distillation column or to measure a pressure value of the product nitrogen gas; and an optimum rotational speed calculation command unit configured to use the pressure value measured by the pressure measuring unit in a pre-installed rotational speed calculation function to calculate a rotational speed of the rotating shaft, and configured to issue a command to the rotation control unit.

2. The nitrogen generating device as claimed in claim 1, provided with: a feed air compressor configured to control the supply pressure of the feed air upstream of the main heat exchanger; and a feed air supply pressure control unit configured to control a discharge pressure set value of the feed air compressor on the basis of a demand pressure value of the product nitrogen gas or a pressure value measured by the pressure measuring unit.

3. The nitrogen generating device as claimed in claim 1, wherein a liquid level measuring unit for measuring an amount of oxygen-enriched liquid in a bottom portion of the nitrogen distillation column, and the optimum rotational speed calculation command unit and/or the rotation control unit may restrict the rotational speed such that a liquid amount measured by the liquid level measuring unit lies within a predetermined set range.

4. The nitrogen generating device as claimed in any one of claim 1, provided with a flow rate measuring unit which is provided on the upstream side or the downstream side of the main heat exchanger in the product nitrogen gas extraction pipeline to measure a flow rate value of the product nitrogen gas, wherein the optimum rotational speed calculation command unit adjusts the rotational speed obtained by the rotational speed calculation function in accordance with the flow rate measured by the flow rate measuring unit.

5. A method for generating nitrogen with at least a main heat exchanger, a nitrogen distillation column, at least one nitrogen condenser, a compressor, and an expansion turbine, the method including: a rotation control step for controlling rotation with respect to a rotating shaft connecting the compressor and the expansion turbine; a pressure measuring step for measuring a pressure value in an arbitrarily defined part of the nitrogen distillation column or measuring a pressure value of product nitrogen gas; and an optimum rotational speed calculation command step for using the pressure value measured in the pressure measuring step in a pre-installed rotational speed calculation function to calculate a rotational speed of the rotating shaft connecting the compressor and the expansion turbine, and for issuing a command for the rotation control step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Further developments, advantages and possible applications of the invention can also be taken from the following description of the drawing and the exemplary embodiments. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-references.

[0066] FIG. 1 is a configuration example of a nitrogen generating device (air separating device) according to embodiment 1.

[0067] FIG. 2 is a configuration example of a nitrogen generating device (air separating device) according to embodiment 2.

[0068] FIG. 3 is a configuration example of a nitrogen generating device (air separating device) according to embodiment 3.

[0069] FIG. 4 is a configuration example of a nitrogen generating device (air separating device) according to embodiment 4.

DETAILED DESCRIPTION OF THE INVENTION

[0070] Several embodiments of the present invention will be described below. The embodiments described below are examples of the present invention. The present invention is in no way limited by the following embodiments, and also includes a number of variant modes which are implemented within a scope that does not alter the gist of the present invention. It should be noted that not all the configurations described below are necessarily essential configurations of the present invention.

[0071] (Definition of Technical Terms) In this specification, “upstream” and “downstream” are based on a flow of gas (for example, feed air, first gas, second gas, nitrogen gas).

[0072] In the specification, “pressure value in an arbitrarily defined part of the nitrogen distillation column” means, for example, a pressure value in a column top portion of the nitrogen distillation column, or in a distillation portion or bottom portion of the nitrogen distillation column.

Embodiment 1

[0073] A nitrogen generating device 100 of embodiment 1 illustrated in FIG. 1 is a single-column rectification type air separating device.

[0074] The nitrogen generating device 100 comprises, as a basic configuration, a main heat exchanger 1, a nitrogen distillation column 2, a first nitrogen condenser 3, a second nitrogen condenser 4, a recycled gas compressor 6, and an expansion turbine 7.

[0075] The main heat exchanger 1 exchanges heat between feed air and another gas. The feed air discharged from the main heat exchanger 1 is introduced into a lower portion 22 of the nitrogen distillation column 2. The nitrogen distillation column 2 includes a bottom portion 21, a lower distillation portion 22, an upper distillation portion 23, and a column top portion 24. Nitrogen gas discharged from the column top portion 24 of the nitrogen distillation column 2 is sent to both the first nitrogen condenser 3 and the second nitrogen condenser 4, is cooled by means of cold energy of an oxygen-enriched liquid, and then returns to the nitrogen distillation column 2. The oxygen-enriched liquid discharged from the bottom portion 21 of the nitrogen distillation column 2 is introduced via a circulating pipeline L21 into the second condenser 4 to be utilized as a cold energy source, and is sent from the second condenser 4 to the first condenser 3 to be utilized as a cold energy source.

[0076] In the present embodiment, the recycled gas compressor 6 and the expansion turbine 7 are interlocked using a common rotating shaft, and are configured as a booster expander provided with an oil brake 8 for braking the rotating shaft. The oil brake 8 has a function (rotation control function) of controlling the rotation with respect to the rotating shaft.

[0077] A second gas discharged from a column top portion 32 of the first nitrogen condenser 3 passes via a second gas discharge pipeline L32 through a portion of the main heat exchanger 1, is then sent to the expansion turbine 7 and is utilized, and then passes through the main heat exchanger 1 again and is expelled as waste gas.

[0078] A first gas (recycled gas) discharged from a column top portion 42 of the second nitrogen condenser 4 is sent via a first gas recycling pipeline L42 to the recycled gas compressor 6 to be compressed, then passes through a portion of the main heat exchanger 1 and is sent to the lower distillation portion 22 of the nitrogen distillation column 2.

[0079] Nitrogen gas discharged from the column top portion 24 or the upper distillation portion 23 of the nitrogen distillation column 2 is sent via a product nitrogen gas extraction pipeline L24 to the main heat exchanger 1 for heat exchange, and is then supplied as product nitrogen gas to a supply point.

[0080] A pressure measuring unit 91 is provided on the downstream side of the main heat exchanger 1 in the product nitrogen gas extraction pipeline L24 to measure a pressure value of the product nitrogen gas. Furthermore, an optimum rotational speed calculation command unit 9 inputs the pressure value measured by the pressure measuring unit 91 into a pre-installed rotational speed calculation function to calculate the rotational speed of the rotating shaft of the booster expander, and issues a command to the oil brake 8. In the present embodiment, the optimum rotational speed calculation command unit 9 controls a flow rate control valve 94 provided in an oil introduction pipeline for supplying oil to the oil brake 8, to control the amount of oil that is supplied. A rotation angle measuring unit 93 for measuring a rotation angle of a motor of the flow rate control valve 94 is provided, and the optimum rotational speed calculation command unit 9 reads the rotation angle measured by the rotation angle measuring unit 93 and performs control (feedback control) such that the rotational speed obtained by the rotational speed calculation function is achieved.

[0081] As another embodiment, the pressure measuring unit 91 may be provided on the upstream side of the main heat exchanger 1 in the product nitrogen gas extraction pipeline L24 to measure the pressure value of the product nitrogen gas, and may measure the pressure value in an arbitrarily defined part of the column top portion or the distillation portion of the nitrogen distillation column 2.

[0082] The rotational speed calculation function is stored in a memory, which is not shown in the drawings.

[0083] In the present embodiment, the rotational speed calculation function is the following formula (1).

y=a×x+b  (1) [0084] Rotational speed set value: y [0085] Coefficient: a [0086] Product nitrogen gas pressure: x [0087] Correction value: b

[0088] The coefficient a and the correction value b are set in advance from the results of simulations corresponding to the equipment specifications and from device implementation experiments. The rotational speed calculation function is not limited to formula (1), and may be a polynomial expression of a non-linear function, set in accordance with the device specifications.

Embodiment 2

[0089] The nitrogen generating device 100 according to embodiment 2 illustrated in FIG. 2 is provided with a feed air compressor 5, in addition to the configuration of embodiment 1. The same component reference numbers indicate the same functions, and components having additional functions will, in particular, be described.

[0090] The feed air compressor 5 controls the supply pressure of the feed air upstream of the main heat exchanger 1. A feed air supply pressure control unit 95 controls a discharge pressure set value of the feed air compressor 5 on the basis of a demand pressure value of the product nitrogen gas or a pressure value measured by the pressure measuring unit 91.

[0091] In the present embodiment, the feed air supply pressure can be optimized in accordance with the product nitrogen gas pressure, allowing the energy consumption related to feed air compression to be optimized. Specifically, power applied to the feed air compressor 5 is adjusted by changing the discharge pressure set value of the feed air compressor 5, for example. An air cleaning device (53) may be provided between the feed air compressor 5 and the main heat exchanger 1.

[0092] The optimum rotational speed calculation command unit 9 or the feed air supply pressure control unit 95 may obtain the discharge pressure set value. The discharge pressure set value may be obtained using the following arithmetic expression (2).

z=d×x+e  (2) [0093] Feed air pressure set value: z [0094] Coefficient: d [0095] Product nitrogen gas pressure: x [0096] Correction value: e

[0097] The coefficient d and the correction value e are set in advance from the results of simulations corresponding to the equipment specifications and from device implementation experiments.

Embodiment 3

[0098] The nitrogen generating device 100 according to embodiment 3 illustrated in FIG. 3 is provided with a liquid level measuring unit 211, in addition to the configuration of embodiment 2. The same component reference numbers indicate the same functions, and components having additional functions will, in particular, be described.

[0099] The liquid level measuring unit 211 measures the amount of oxygen-enriched liquid in the bottom portion 21 of the nitrogen distillation column 2. The optimum rotational speed calculation command unit 9 restricts the rotational speed such that the liquid amount measured by the liquid level measuring unit 211 lies within a predetermined set range (upper limit value and lower limit value).

[0100] As a result, adjustments can be made to the rotational speed control of the booster expanders (6, 7) in accordance with the liquid level in the bottom portion 21 of the nitrogen distillation column 2. Enthalpy is released to the outside from process gas by means of a braking system, through a medium such as heat or electric power, and the process gas is cooled correspondingly. This is referred to as supplying coldness to the process gas. For a cryogenic air separating device such as the nitrogen generating device 100, it is important to obtain liquefied air as a reflux liquid, and to this end, a sufficient supply of coldness is essential. Since it is normally desirable to maintain a certain amount of liquefied air in the device in order to maintain the operation of the nitrogen generating device, a certain liquid level is maintained in a space in the bottom portion 21 of the nitrogen distillation column 2. Meanwhile, if the rotational speed control of the booster expander is changed in conjunction with a change in the pressure of the product nitrogen gas in the present embodiment, there is a concern that the coldness supplied to the process may be insufficient (when increasing the rotational speed, for example). Consequently, as in the present embodiment, a configuration is adopted in which an operation management liquid level is set in advance, and a deflection amplitude of a control rotation speed is limited to prevent deviation from the management range. By so doing, continuous operation of the device can be maintained without causing a shortage of coldness, even with respect to larger demand pressure changes.

Embodiment 4

[0101] The nitrogen generating device 100 according to embodiment 4 illustrated in FIG. 4 is provided with a flow rate measuring unit 97, in addition to the configuration of embodiment 3. The same component reference numbers indicate the same functions, and components having additional functions will, in particular, be described.

[0102] A pressure measuring unit 97 is provided on the downstream side of the main heat exchanger 1 in the product nitrogen gas extraction pipeline L24 to measure a flow rate value of the product nitrogen gas. The optimum rotational speed calculation command unit 9 adjusts the rotational speed obtained by the rotational speed calculation function in accordance with the flow rate measured by the flow rate measuring unit 97.

[0103] According to the present embodiment, the rotational speed can be adjusted in accordance with (in proportion to) the flow rate of the product nitrogen gas, with respect to the rotational speed obtained from the pressure of the product nitrogen gas.

[0104] The rotational speed set value obtained using the rotational speed calculation function is adjusted using the following formula (3).

y′=w×Y  (3) [0105] Rotational speed set value after adjustment: y′ [0106] Rotational speed set value: y (obtain using formula (1) above) [0107] Coefficient: w (adjustment coefficient based on flow rate value of product nitrogen gas)

[0108] The coefficient w is set in advance from the results of simulations corresponding to the equipment specifications and from device implementation experiments.

[0109] The optimum rotational speed calculation command unit 9 and the feed air supply pressure control unit 95 may be implemented through a collaborative action between a computer provided with a processor and a memory, and a software program stored in the memory, or may be implemented using a dedicated circuit or firmware, for example, and may be provided with an input/output interface and an output unit.

[0110] (Nitrogen Generating Method)

[0111] The nitrogen generating method may employ the nitrogen generating device described hereinabove to generate nitrogen, or may be executed using other equipment.

[0112] In one embodiment, the nitrogen generating method according to the present disclosure is a method for generating nitrogen with at least a main heat exchanger, a nitrogen distillation column, at least one nitrogen condenser, a compressor, and an expansion turbine, the method including: a rotation control step for controlling rotation with respect to a rotating shaft connecting the compressor and the expansion turbine; a pressure measuring step for measuring a pressure value in an arbitrarily defined part of the nitrogen distillation column or measuring a pressure value of product nitrogen gas; and an optimum rotational speed calculation command step for using the pressure value measured in the pressure measuring step in a pre-installed rotational speed calculation function to calculate a rotational speed of the rotating shaft connecting the compressor and the expansion turbine, and for issuing a command for the rotation control step.

[0113] Feed air discharged from the main heat exchanger may be introduced into a lower portion of the nitrogen distillation column.

[0114] The nitrogen condenser may condense the nitrogen gas discharged from a column top portion of the nitrogen distillation column.

[0115] First gas discharged from the column top portion of the nitrogen condenser may be introduced into the compressor.

[0116] Second gas discharged from the column top portion of the nitrogen condenser may be introduced into the expansion turbine after passing through a portion of the main heat exchanger.

[0117] The rotation control step may be executed by means of a rotation control unit for controlling the rotation with respect to the rotating shaft connecting the compressor and the expansion turbine.

[0118] The pressure measuring step may be executed by means of a pressure measuring unit for measuring a pressure value in an arbitrarily defined part of the nitrogen distillation column or measuring a pressure value of the product nitrogen gas.

[0119] The optimum rotational speed calculation command step may be executed by means of an optimum rotational speed calculation command unit for using the pressure value measured by the pressure measuring unit in a pre-installed rotational speed calculation function to calculate the rotational speed of the rotating shaft, and for issuing a command to the rotation control unit.

[0120] A product nitrogen gas extraction pipeline may be a pipeline for causing the nitrogen gas discharged from the column top portion or an upper distillation portion of the nitrogen distillation column to pass through the main heat exchanger, and for then extracting product nitrogen gas.

[0121] A first gas recycling pipeline may cause the first gas compressed by the compressor to pass through a portion of the main heat exchanger and may introduce the same into the lower portion of the nitrogen distillation column.

[0122] A second gas discharge pipeline may be a pipeline for causing the second gas used by the expansion turbine to pass through the main heat exchanger and be expelled.

[0123] In the nitrogen generating method, in the optimum rotational speed calculation command step and/or the rotation control step, a rotational speed measured by a rotation measuring unit which measures the rotational speed of the rotating shaft may be controlled (feedback control) so as to become the rotational speed obtained by the rotational speed calculation function.

[0124] The nitrogen generating method may include a feed air supply pressure control step for controlling a discharge pressure set value of a feed air compressor for controlling the supply pressure of the feed air upstream of the main heat exchanger, on the basis of a demand pressure value of the product nitrogen gas or a pressure value measured in the pressure measuring step.

[0125] In the nitrogen generating method, in the optimum rotational speed calculation command step and/or the rotation control step, the rotational speed may be restricted such that a liquid amount measured by a liquid level measuring unit for measuring an amount of oxygen-enriched liquid in the bottom portion of the nitrogen distillation column lies within a predetermined set range (upper limit and lower limit values).

[0126] In the nitrogen generating method, in the optimum rotational speed calculation command step, the rotational speed obtained by the rotational speed calculation function may be adjusted in accordance with a flow rate measured by a flow rate measuring unit for measuring a flow rate value of the product nitrogen gas on the upstream side or the downstream side of the main heat exchanger.

OTHER EMBODIMENTS

[0127] (1) The nitrogen generating device may be provided with a first distillation column (high pressure distillation column) for distilling liquefied air, and a second distillation column (low pressure distillation column) to which crude oxygen from which high boiling-point components (such as methane) have been removed is discharged from the high pressure distillation column for further distillation. The high pressure distillation column may be a nitrogen producing distillation column. Nitrogen can be extracted from the nitrogen producing distillation column. The low pressure distillation column may be an oxygen producing distillation column. [0128] (2) In embodiments 1 to 4, the oil brake is used to adjust the rotational speed, but the present invention is not limited thereto, and the rotational speed may essentially be controlled by driving an electricity generator connected to the expansion turbine to recover electrical energy.

[0129] 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.

[0130] The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

[0131] “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.

[0132] “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.

[0133] 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.

[0134] 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.

[0135] 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.

LIST OF ELEMENTS

[0136] 100 Nitrogen generating device (air separating device) [0137] 1 Main heat exchanger [0138] 2 Nitrogen distillation column [0139] 3 First condenser [0140] 4 Second condenser [0141] Feed air compressor [0142] 6 Compressor [0143] 7 Expansion turbine [0144] 8 Rotation control unit (oil brake) [0145] 9 Optimum rotational speed calculation command unit [0146] 91 Feed air compressor [0147] 93 Air cleaning device [0148] 95 Feed air supply pressure control unit [0149] 97 Flow rate measuring unit [0150] 211 Liquid level measuring unit [0151] L21 Circulating pipeline [0152] L24 Product nitrogen gas extraction pipeline [0153] L32 Second gas discharge pipeline [0154] L42 First gas recycling pipeline