Argon enhancement method and apparatus

Abstract

An air separation plant comprising: an air separation unit comprising a lower pressure column (101), a mixed column (103), and a pure nitrogen column (102), wherein the lower pressure column (101) has a first nominal diameter (D1), the pure nitrogen column (102) has a second nominal diameter (D2) that is smaller than the first nominal diameter (D1), the mixed column (103) has an open cylindrical shape, the mixed column has an interior (129) having an inner diameter (D3) that is nominally larger than the second nominal diameter (D2), and the pure nitrogen column (102) is located within the interior (129) of the mixed column (103).

Description

Technical Field

[0001] This invention relates to a method and apparatus for cryogenic air separation, and particularly to a method and apparatus for generating argon gas. Background Technology

[0002] As is well known, a typical dual-tower air distillation system includes a medium-pressure distillation column operating at approximately 6 bar, a low-pressure distillation column operating at slightly above atmospheric pressure, and a condenser-vaporizer. After initial purification, the feed air is sent to the bottom of the medium-pressure column. The "oxygen-enriched liquid" (oxygen-enriched air) collected at the bottom of the medium-pressure column is sent to the midpoint of the low-pressure column as reflux. Simultaneously, the "lean liquid nitrogen," which consists almost entirely of nitrogen and is collected at the top of the medium-pressure column, is sent to the top of the low-pressure column as reflux.

[0003] Below the inlet of the oxygen-enriched liquid, low-pressure towers typically include an "argon outlet" location for generating this gas. Low-pressure towers are usually equipped with gaseous and liquid oxygen extraction lines. Medium-pressure towers typically have gaseous and liquid nitrogen extraction lines at the head. The vapor at the top of the low-pressure tower ("impure nitrogen") consists of nitrogen containing a few percent oxygen and is usually released into the atmosphere.

[0004] In facilities primarily designed to produce gaseous oxygen for direct pipeline supply to users, temporary excess oxygen production can sometimes occur. This is especially true during plant shutdowns for end users. In conventional distillation facilities, the gaseous oxygen is simply released into the atmosphere, resulting in the loss of the energy expended in separating it.

[0005] French Patent 2550325 describes a solution to this problem, which is incorporated herein by reference. The idea behind Patent 2550325 is to utilize a temporary decrease in oxygen demand to increase one or more of the facility's other products. These other products may be one or more of argon, liquid oxygen, liquid nitrogen, or nitrogen.

[0006] To this end, the method described in patent 2550325 utilizes distillation of air through a dual-tower system, comprising: a first distillation tower, referred to as the medium-pressure tower, operating at a relatively high pressure, and a second distillation tower, referred to as the low-pressure tower, operating at a relatively low pressure. Liquid extracted from one of these towers is fed to the top of an auxiliary tower, which operates substantially at the pressure of the low-pressure tower. Gas with an oxygen content lower than that of the liquid, taken from the low-pressure tower, is fed to the base of the auxiliary tower. Liquid collected at the base of the auxiliary tower is then refluxed back into the low-pressure tower, substantially at the location where the gas was sampled. The term "auxiliary tower" refers to a tower having a distillation tower structure, that is, a tower including linings or multiple trays for distillation-type processes.

[0007] Maximum efficiency is achieved when the liquid supplied to the auxiliary tower is liquid oxygen collected at the bottom of the low-pressure tower and the gas is the vapor at the top of the low-pressure tower. Summary of the Invention

[0008] An air separation device is provided, comprising: an air separation unit including a low-pressure tower, a mixing tower, and a pure nitrogen tower, wherein the low-pressure tower has a first nominal diameter, the pure nitrogen tower has a second nominal diameter smaller than the first nominal diameter, the mixing tower has an open cylindrical shape, the mixing tower has an inner diameter nominally larger than the second nominal diameter, and the pure nitrogen tower is located inside the mixing tower. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of one embodiment of the present invention.

[0010] Figure 2 This is a schematic diagram of the upper portion of a distillation column according to an embodiment of the present invention, showing details of the pure nitrogen column and the mixing column.

[0011] Figure 3 This is a schematic diagram showing details of a pure nitrogen tower and a mixing tower according to an embodiment of the present invention.

[0012] Figure 4 This is a schematic diagram illustrating an associated argon tower according to an embodiment of the present invention.

[0013] Component reference numerals

[0014] 100 = A method scheme with a crude argon tower and a concentric mixing tower and a pure nitrogen tower.

[0015] 101 = Low-pressure tower

[0016] 102 = Pure Nitrogen Tower

[0017] 103 = Mixing Tower

[0018] 104 = Subcooler

[0019] 105 = Liquid oxygen pump

[0020] 106 = Liquid oxygen from the low-pressure tower

[0021] 107 = supercooled liquid oxygen

[0022] 108 = Lean liquid nitrogen 5

[0023] 109 = Supercooled lean liquid nitrogen

[0024] 110 = Liquid nitrogen

[0025] 111 = Supercooled liquid nitrogen reflux stream

[0026] 112 = Sludge nitrogen from the low-pressure tower

[0027] 113 = Sludge nitrogen gas to the mixing tower

[0028] 114 = Oxygen-enriched waste stream from the mixing tower

[0029] 115 = Pure nitrogen gas from the pure nitrogen tower

[0030] 116 = Liquid oxygen in the storage tank

[0031] 117 = Liquid oxygen reflux stream to the mixing tower

[0032] 118 = Nitrogen-rich liquid flow from the mixing tower

[0033] 119 = Nitrogen-rich liquid flow from the pure nitrogen tower

[0034] 120 = Waste nitrogen gas going to the pure nitrogen tower

[0035] 121 = Liquid oxygen reflux valve to the mixing tower

[0036] 122 = Lean nitrogen reflux valve at the top of the low-pressure tower

[0037] 123 = Sludge nitrogen balance valve

[0038] 124 = Liquid nitrogen reflux valve at the top of the pure nitrogen tower

[0039] 125 = Medium-pressure tower

[0040] 127 = Condenser / Vaporizer

[0041] 128 = Feed air inlet

[0042] 129 = Inside the mixing tower

[0043] 130 = Distillation end of the low-pressure column

[0044] 131 = The oxygen-rich waste stream from the mixing tower and the sludge nitrogen from the low-pressure tower combined before entering the subcooler.

[0045] 132 = The oxygen-rich waste stream from the mixing tower and the sludge nitrogen from the low-pressure tower combined after passing through the subcooler.

[0046] 133 = Argon Tower Detailed Implementation

[0047] The following describes illustrative embodiments of the invention. While the invention may have various modifications and alternatives, specific embodiments thereof have been shown by way of example in the accompanying drawings and described in detail herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the specific forms disclosed, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0048] Of course, it will be understood that in the development of any such practical embodiment, many implementation-specific decisions must be made to achieve the developer’s specific goals (e.g., compliance with system-related and business-related constraints), which will vary depending on the implementation. Furthermore, it will be understood that such development efforts can be complex and time-consuming, but remain a routine endeavor for those skilled in the art who will benefit from this disclosure.

[0049] The idea is to add a tower above the waste nitrogen tower, which operates in parallel with the pure nitrogen tower. This additional tower will serve as a mixing tower, which will generate additional reflux at the top of the low-pressure tower by means of a liquid oxygen reflux stream sent to the top of this tower.

[0050] exist Figures 1 to 4 The present invention provides a method scheme 100 having a crude argon column and a mixing column concentric with a pure nitrogen column. This includes a medium-pressure column 125, a low-pressure column 101, and a condenser-vaporizer 127. The low-pressure column 101 has a first nominal diameter (D1) and a distillation end 130. Feed air 128, after being appropriately purified (not shown), is injected into the low-pressure column 101, thereby producing an oxygen-rich liquid consisting almost entirely of oxygen and a column overhead vapor consisting almost entirely of nitrogen.

[0051] At least a portion of the vapor at the top of the column is condensed in condenser 127 and collected in column 125. A portion of the lean liquid nitrogen 108 is subcooled in subcooler 104, and then the subcooled lean liquid nitrogen 109 expands to a pressure slightly above atmospheric pressure in lean liquid nitrogen reflux valve 122. This expanded, subcooled liquid is essentially injected as reflux at the top of low-pressure column 101.

[0052] Liquid oxygen 106 is removed from the low-pressure tower and pressurized by the liquid oxygen pump 105, and the pressurized liquid oxygen is subcooled in the subcooler 104. This produces subcooled liquid oxygen 107.

[0053] It is possible that, for a limited period of time, gaseous oxygen may become excessive, for example, due to a temporary shutdown or reduction by the user. In this case, the supercooled liquid oxygen 107 can be divided into liquid oxygen 116 to a storage tank and liquid oxygen reflux stream 117. The liquid oxygen pump 105 is adjusted to generate liquid oxygen reflux stream 117 in the pipeline equal to the excess oxygen.

[0054] It should be noted that the liquid oxygen reflux stream 117 may not be subcooled in the subcooler 104 and may be sent directly to the mixing tower 103.

[0055] The pure nitrogen column 102 and the mixing column 103 are located at the distillation end 130 of the low-pressure column. For example... Figure 2 As indicated in the document, in at least one embodiment, the mixing tower 103 is concentric with and surrounds the pure nitrogen tower 102.

[0056] The mixing tower 103 has an open cylindrical shape, or an annular shape with a rectangular cross-section. The mixing tower 103 has an interior 129 with an inner diameter D3. The pure nitrogen tower 102 has a second nominal diameter D2. The inner diameter D3 is nominally larger than the second nominal diameter D2. This concentric arrangement of the mixing tower 103 and the pure nitrogen tower 102 results in lower capital expenditure because no additional independent pressure vessels are required.

[0057] During the period of oxygen excess, the liquid oxygen reflux stream 117, which can pass through the liquid oxygen reflux valve 121 to the mixing tower, is introduced into the top of the mixing tower 103 and undergoes countercurrent exchange with the impure nitrogen stream reaching the bottom of the mixing tower 103. Liquid oxygen is supplied to the top of the mixing tower 103 by the liquid oxygen reflux stream 117. This results in the discharge of the oxygen-rich waste stream 114 and the removal of the nitrogen-rich liquid stream 118, which consists of nitrogen containing a few percent oxygen. After passing through the waste nitrogen balancing valve 123, the oxygen-rich waste stream 114 can be combined with waste nitrogen 112 from the low-pressure tower.

[0058] The combined oxygen-enriched waste stream 114 and polluted nitrogen gas 112 are then introduced into the argon tower 133. At least a portion of the combined stream 131 may be introduced into the argon tower 133 before passing through the subcooler 104. At least a portion of the combined stream 132 may be introduced into the argon tower 133 after passing through the subcooler 104.

[0059] The twin towers 125 / 101 are equipped with an additional tower 102, referred to as a "spike" or pure nitrogen tower, for producing pure nitrogen at low pressure. Tower 102 is supplied with impure nitrogen gas 120 at its bottom and with a subcooled liquid nitrogen reflux stream 111 at its top. This subcooled liquid nitrogen reflux stream 111 is taken from the top of tower 125, subcooled in a subcooler 104, and controlled by a liquid nitrogen reflux valve 124. Pure nitrogen gas 115 exits from the head of tower 102, and a nitrogen-rich liquid stream 119 is removed from the bottom of the pure nitrogen tower 102.

Claims

1. A method for enhancing argon recovery, characterized in that, include: An air separation unit includes a low-pressure tower (101), a mixing tower (103), and a pure nitrogen tower (102), wherein the low-pressure tower (101) has a first nominal diameter (D1), and the pure nitrogen tower (102) has a second nominal diameter (D2), which is smaller than the first nominal diameter (D1). The mixing tower (103) has an open cylindrical shape and an interior (129) with an inner diameter (D3) that is nominally larger than a second nominal diameter (D2). The pure nitrogen tower (102) is located inside the mixing tower (129). The mixing tower (103) and the pure nitrogen tower (102) are in fluid contact with the distillation end (130) of the low-pressure tower (101). Among them, the mixing tower (103): Receive liquid oxygen return stream (117). Oxygen-rich waste stream (114) is generated. The waste nitrogen gas (113) from the low-pressure tower (101) to the mixing tower is received, and The nitrogen-rich liquid stream (118) from the mixing tower is returned to the low-pressure tower (101). Among them, the pure nitrogen tower (102): Receives supercooled liquid nitrogen reflux (111). Pure nitrogen gas (115) is produced. The waste nitrogen gas (120) from the low-pressure tower (101) to the pure nitrogen tower is received, and The nitrogen-rich liquid stream (119) from the pure nitrogen tower is returned to the low-pressure tower (101). The oxygen-rich waste stream (114) from the low-pressure tower (101) and the waste nitrogen gas (112) from the low-pressure tower are introduced into the argon tower (133).

Images