Method and apparatus for separating air by cryogenic distillation

Abstract

An apparatus for separating air by cryogenic distillation comprises N air compressors (C1, C2, C3) connected so as to receive air at ambient pressure and designed to produce air at a first pressure above 12 bar absolute, N being at least 3, each of the compressors being driven by a single asynchronous motor (M1, M2, M3), the total power of the compressors being at least 10 MW.

Claims

1. A method for separating air by cryogenic distillation, the method comprising the steps of: i) sending N flows of air at approximately ambient pressure each to one of N air compressors; ii) compressing the air using each of the N compressors to a first pressure above 12 bar absolute and below 35 bar absolute, N being equal to or greater than 3 and the total power of the N compressors being greater than 10 MW; iii) sending the air at the first pressure from the N compressors to a single purification unit in order to remove water and carbon dioxide and cooling the air in the purification unit before sending the cooled air to a single system of columns in a single cold box where the cooled air is separated by cryogenic distillation; iv) extracting an enriched flow from the system of columns, wherein the enriched flow is selected from the group consisting of an oxygen-enriched flow, a nitrogen-enriched flow, and combinations thereof; v) sending the air from each of the N compressors to the system of columns through the purification unit, without sending the air at the first pressure to an air booster driven by a motor or a steam turbine; and vi) driving each of the N compressors by a single motor, these N motors being asynchronous and having a maximum power below 25 MW.

2. The method according to claim 1, in which all the air sent to the system of columns comes from the N compressors.

3. The method according to claim 1, in which N is equal to 4, 5, 6, 7, 8, 9 or 10.

4. The method according to claim 1, in which the N air compressors each send no more than 100%/N of the air that the N air compressors compress to the system of columns.

5. The method according to claim 1, in which each of the compressors sends at least 90% of the air that each compressor compresses to the system of columns, or to the same column in the system of columns.

6. The method according to claim 1, in which at least some of the air flow from each compressor is expanded before being sent to the system of columns.

7. The method according to claim 1, in which each of the motors is connected to a starter of a given type, the type of starter for each motor being either direct or by reactance or auto transforming.

8. The method according to claim 1, in which the total power of the N compressors is less than 25 MW.

9. The method according to claim 1, in which the total power of the N compressors is greater than 25 MW.

10. The method according to claim 1, in which the total power of the N compressors is greater than 40 MW.

11. An apparatus for air separation by cryogenic distillation, the apparatus comprising: a single system of columns in a single cold box; N air compressors configured to receive air at ambient pressure and designed to produce air at a first pressure above 12 bar absolute, N being at least equal to 3, wherein each of the compressors is configured to be driven by a single asynchronous motor, the total power of the compressors being at least 10 MW; a single purification unit configured to purify air at the first pressure coming from the N compressors; pipes configured to send purified air from the purification unit to the system of columns, a pipe for taking off a nitrogen-enriched flow from the system of columns; and a pipe configured to remove an oxygen-enriched flow from the system of columns, the apparatus comprising an absence of a motor or steam turbine driving an air booster.

12. An apparatus according to claim 11, in which each of the compressors comprises at least 4 stages.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 provides an embodiment of the present invention.

(3) FIG. 2 provides an embodiment of the present invention.

DETAILED DESCRIPTION

(4) An apparatus according to an embodiment of the invention will be described in more detail with reference to the figures, which show schematic drawings.

(5) In FIG. 1, a single cold box BF of an air separation apparatus contains a single system of columns and an exchanger for cooling the air to the distillation temperature. The air to be distilled 7 has previously been purified in a single purification unit E in order to remove the water and carbon dioxide.

(6) The apparatus produces at least one product 9 that may be gaseous oxygen and/or gaseous nitrogen and/or liquid oxygen and/or liquid nitrogen and/or gaseous argon and/or liquid argon.

(7) The air at atmospheric pressure is compressed in three compressors C1, C2, C3. Each of these compressors preferably has the same capacity. Each compressor compresses the air to the purification pressure, preferably equal to at least 12 bar absolute, preferably less than 35 bar absolute. The three flows of air 1, 2, 3 compressed in the compressors C1, C2, C3 are joined in a single flow 6 and purified together in the unit E.

(8) All the air sent to the single cold box comes from the compressors C1, C2, C3 and the compressors C1, C2, C3 send all their air 6 to the cold box BF.

(9) Each compressor C1, C2, C3 is driven by a single asynchronous motor M1, M2, M3. Each motor M1, M2, M3 has a respective starter D1, D2, D3, these starters being of the direct online, self or autotransformer type. None of the motors is started by a soft starter or a regulator, which enormously simplifies the installation.

(10) Each of the compressors C1, C2, C3 comprises at least 4 stages.

(11) The cold box, and therefore the three compressors, process air in order to produce at least 4000 tonnes per day of oxygen. Thus each compressor treats at least 6666 tonnes of air per day. The three compressors are driven by motors preferably at constant speed.

(12) The total power of the three compressors is greater than 10 MW or greater than 25 MW, or even greater than 40 MW, but less than 75 MW.

(13) The three compressors can each treat the same throughput, all a different throughput, or two the same throughput and the third a different throughput.

(14) Here each compressor compresses the air from atmospheric pressure to the same first pressure; however, a certain variation in pressure may be tolerated. For example, one compressor may have a pressure that differs by no more than 20% (or even by no more than 10%) from the pressure of the flow 6 formed by mixing the compressed flows.

(15) It will easily be understood that the invention can extend to appliances having four compressors, five compressors or six compressors in parallel. The precise case of five compressors is illustrated in FIG. 2.

(16) In FIG. 2, a cold box BF of an air separation apparatus contains a system of columns and an exchanger for cooling the air to the distillation temperature. The air to be distilled 7 has previously been purified in a purification unit E in order to remove the water and carbon dioxide.

(17) The apparatus produces at least one product 9 that may be gaseous oxygen and/or gaseous nitrogen and/or liquid oxygen and/or liquid nitrogen and/or gaseous argon and/or liquid argon.

(18) The air at atmospheric pressure is compressed in five compressors C1, C2, C3, C4, C5, connected in parallel. Each of these compressors preferably has the same capacity. Each compressor compresses the air to the purification pressure, preferably equal to at least 12 bar absolute, preferably less than 35 bar absolute. The five flows of air 1, 2, 3, 4, 5 compressed in the compressors C1, C2, C3, C4, C5 are combined in a single flow 6 and purified together in the unit E.

(19) All the air sent to the cold box comes from the compressors C1, C2, C3, C4, C5 and the compressors C1, C2, C3, C4, C5 send all their air to the cold box BF.

(20) Each of the compressors C1, C2, C3, C4, C5 comprises at least 4 stages.

(21) Each compressor C1, C2, C3, C4, C5 is driven by a single asynchronous motor M1, M2, M3, M4, M5. Each motor M1, M2, M3, M4, M5 has a respective starter D1, D2, D3, D4, D5, these starters being of the direct online, self or autotransformer type. None of the motors is started by a soft starter or regulator, which enormously simplifies the installation.

(22) The five compressors may each treat the same throughput, each a different throughput or there may be pairs of compressors having the same throughput.

(23) The total power of the five compressors is greater than 10 MW or greater than 25 MW, or even greater than 40 MW but less than 125 MW.

(24) The single cold box, and therefore the five compressors, process air in order to produce at least 4000 tonnes per day of oxygen. Thus each compressor processes at least 4000 tonnes per day of air. The five compressors are driven by motors preferably at substantially constant speed.

(25) Here each compressor compresses the air from atmospheric pressure to the same first pressure; however, a certain variation in pressure may be tolerated. For example, one compressor may have a pressure that differs by no more than 20% (or even by no more than 10%) from the pressure of the flow 6 formed by mixing the compressed flows.

(26) The air separation appliances according to the invention may comprise an air booster driven by an air turbine, for example sending the expanded air to a column of the cold box, or by a nitrogen turbine. On the other hand, the appliances do not comprise an air booster driven by a steam turbine or a motor since that would imply an input of energy into the system other than by the sending of compressed air from the N compressors.

(27) Compressors of products, for oxygen or nitrogen, may on the other hand be used, these being driven for example by motors.

(28) In general terms, the invention applies to methods where the total power of the compressors is less than 150 MW.

(29) 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.

(30) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(31) 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.

(32) 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 a range is expressed, it is to be understood that another embodiment is from the one.

(33) 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.

(34) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such particular value and/or to the other particular value, along with all combinations within said range.

(35) 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.