Patent Application
20230296314
The present invention relates to cryogenic air separation process and apparatus, in particular such process and apparatus relating to argon production.
As is well known, double column air distillation plants typically include a medium-pressure distillation column operating at about 6 bars, a low-pressure distillation column operating slightly above atmospheric pressure, and a condenser-vaporizer. After an initial purification, the inlet air is sent to the bottom of the medium-pressure column. A “rich liquid” (air enriched in oxygen) collected in the bottom of the medium-pressure column is sent to reflux at an intermediate point in the low-pressure column. At the same time, the “lean liquid”, consisting almost entirely of nitrogen, collected at the head of the medium-pressure column is sent in reflux at the head of the low-pressure column.
Below the inlet of the rich liquid, the low-pressure column often includes an “argon-tapping” location for the production of this gas. The low-pressure column is generally provided with gaseous oxygen and liquid oxygen withdrawal lines. And the medium-pressure column is generally provided at the head with gaseous nitrogen and liquid nitrogen withdrawal lines. The vapor at the top of the low-pressure column (“impure nitrogen”) consists of nitrogen containing a few percent oxygen and is generally released to the atmosphere.
In installations intended essentially to produce gaseous oxygen supplied directly to a user by pipeline, it sometimes happens that the oxygen production can temporarily become surplus. This is particularly the case during periods of shutdown of the end user's factories. In conventional distillation installations the gaseous oxygen is then simply vented into the atmosphere, and the energy expended for the separation of this oxygen is lost.
One solution to this is described in French patent 2550325, which is herein incorporated by reference. The idea of the 2550325 patent is to take advantage of the temporary drop in oxygen demand to increase one or more of the other productions of the installation. Such other productions may be one or more of the productions of argon, liquid oxygen, liquid nitrogen or nitrogen gas.
To this end, the process described in the 2550325 patent utilizes the distillation of air by means of a double column comprising a first distillation column, called a medium-pressure column, operating under a relatively high pressure, and a second distillation column, said low-pressure column, operating under a relatively low-pressure. A liquid withdrawn from one of the two columns is sent to the top of an auxiliary column operating substantially at the pressure of the low-pressure column. A gas less rich in oxygen than this liquid and taken from the low-pressure column is sent to the base of this auxiliary column. The liquid collected at the base of the auxiliary column is sent under reflux into the low-pressure column, substantially at the level of the sampling of said gas. The term “auxiliary column” means a column having the structure of a distillation column, that is to say comprising a lining or a number of trays of the type used in distillation.
Maximum efficiency is obtained when the liquid supplying the auxiliary column is liquid oxygen collected in the bottom of the low-pressure column and said gas is the overhead vapor of this low-pressure column.
An air separation apparatus is provided, including an air separation unit including a low-pressure column, a mixing column, and a pure nitrogen column, wherein the low-pressure column has a first nominal diameter, the pure nitrogen column has a second nominal diameter which is smaller than the first nominal diameter, wherein the mixing column has an open cylindrical shape, with the inner diameter nominally greater than the second nominal diameter, with the pure nitrogen column located within the mixing column interior.
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present idea resides in adding a column on the waste nitrogen which will operate in parallel with the pure nitrogen column. This additional column will act as a mixing column which will, with the help of the liquid oxygen reflux sent to the top of this column, produce additional reflux at the top of the low-pressure column.
Turning to
At least a portion of this overhead vapor is condensed in condenser 127 and collected in column 125. A portion of this lean liquid 108, is subcooled in sub-cooler 104, and then subcooled lean liquid 109 is expanded in lean liquid reflux valve 122 into a pressure slightly above atmospheric pressure. This expanded, sub-cooled liquid is injected substantially at the top of low-pressure column 101 as reflux.
Liquid oxygen 106 is removed from the low-pressure column and is increased in pressure by pump 105, and the pressurized liquid oxygen stream is subcooled in sub-cooler 104. Thus producing sub-cooled liquid oxygen stream 107.
It may happen that, for a limited period of time, the gaseous oxygen becomes surplus, for example due to the temporary shutdown or turndown of a user. In such an instance, sub-cooled liquid oxygen stream 107 may be split into liquid oxygen stream to storage 116, and liquid oxygen reflux stream 117. Pump 105 is adjusted to produce a flow of oxygen in line 117 equal to the excess oxygen.
It has to be noted that the liquid oxygen reflux 117 might also not be sub-cooled in the sub-cooler 104 and then be sent directly to the mixing column 103 from the stream 110.
At the distil end 130 of the low-pressure column is pure nitrogen column 102 and mixing column 103. As indicated in
During such times of surplus oxygen, liquid oxygen 117, which may pass through liquid oxygen reflux valve 121, is introduced into the top of mixing column 103 and undergoes a countercurrent exchange with the impure nitrogen stream arriving at the bottom of mixing column 103. Mixing column 103 is supplied at the top by liquid oxygen by stream 117. This leads to the evacuation of rich oxygen waste stream 114 and the removal of a rich nitrogen liquid stream 118 consisting of nitrogen containing a few percent of oxygen. Rich oxygen waste stream 114 may be combined with waste nitrogen stream 112 from the low-pressure column, after passing through waste nitrogen balancing valve 123.
The combined rich oxygen waste stream 114 and waste nitrogen stream 112 may then be introduced into argon column 133. At least a portion of the combined stream 131 may be introduced into argon column 133 prior to having passed through sub-cooler 104. At least a portion of the combined stream 132 may be introduced into argon column 133 after having passed through sub-cooler 104.
The double column 125/101 is equipped with an additional column 102, called a “minaret”, or pure nitrogen column, for the production of pure nitrogen under low-pressure. Column 102 is supplied at the bottom with impure nitrogen 120, and at the top by the sub-cooled liquid nitrogen reflux 111 taken from the top of the column 125, by conduit 110, sub-cooled in sub-cooler 104 and controlled a liquid nitrogen reflux valve 124. The pure nitrogen leaves at the head of the column 102 by conduit 115, and rich nitrogen liquid 119 is removed from the bottom of pure nitrogen column 102.
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.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“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.
“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.
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.
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.
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.
This application is a § 371 of International PCT Application PCT/CN2020/103506, filed Jul. 22, 2020, which is herein incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2020/103506 | 7/22/2020 | WO |
