GB2190477A

GB2190477A - Production of oxygen by air separation

Info

Publication number: GB2190477A
Application number: GB08710895A
Authority: GB
Inventors: Dieter Siuka; Rainer Wawrina
Original assignee: Voestalpine AG
Current assignee: Voestalpine AG
Priority date: 1986-05-14
Filing date: 1987-05-08
Publication date: 1987-11-18
Anticipated expiration: 2007-05-08
Also published as: FR2598790A1; DE3714897C2; FR2598790B1; GB2190477B; GB8710895D0; AT387453B; DE3714897A1; JPS62272081A; ATA129086A

Description

1 GB 2 190 477 A 1 SPECIFICATION The invention now aims at providing an

economic process by means of which can be produced in a con Processforthe purification of gases as well as tinuous manner and with low energy consumption apparatus for performing this process oxygen of sufficient purity and, if necessary oxygen 70 of h ig h pu rity. For solving this task, the invention The invention refers to a process for purifying air by starts from an initia 1 ly mentioned cryogen ic rectif ica cryogenic rectification, in which process the air is tion process applying a maximum pressure of 7 bar.

compressed to a maximum pressure of 7 bar and at The invention essentially consists in that liquified least one liquified component is evaporated for ob- oxygen is evaporated in an isobaric mannerfor cool- taining a pre-purified gas, the invention further re- 75 ing compressed airto be separated into its com fers to an apparatus for performing this process. ponents and in that at least a partial amount of the Forthe purpose of producing argon, there has be- thus produced pressurized oxygen is subjected to an come known a combination of a rectification step adsorption process operated with changing pres and a subsequent adsorption step. In DD-A-1 26 953 sure and, optionally, is compressed in a gaseous there is disclosed a processfor obtaining argon of 80 condition. On account of the possibilityto applya high purity, in which process is obtained pure argon subsequent adsorption process operated under byan adsorption step and/or a distilling step aftera changing pressure besidethe cryogenic rectification firststep for separating air into its components and a processes, the purity of the oxygen obtained under double rectification step. The JP-13-84 030 646 shows application of low pressure can subsequently still es and describes a process in which argon of high 85 sentially be increased noting that, by putting intothe purity is obtained in a two-step adsorption process circuit a suitable and substantially smaller equip after a two-stage rectification step. From JP-A-54 061 ment for performing the adsorption process per 091 there can equally be taken a combination of a formed under changing pressure and by taking said plurai-stage rectification process and at least one equipment out of the circuit, a controllability of the adsorption step for the purpose of obtaining argon. 90 plant can be achieved which allows to produce For a number of technical plants it is an absolutely oxygen of high purity only in case of an existing de necessary premise to make provisions for a greater mand or, for example, if the major amount of oxygen amount of oxygen. In particular in steelworks, of lower purity is just not required. The combination oxygen is required for obtaining high combustion of the adsorption process performed under chan temperatures, on the one hand, and for refining 95 ging pressurewith a cryogenic rectification process steel, onthe other hand, noting that for different pu r- performed undera relatively low pressure provides posesthere isfrequently required oxygen of dif- the possibilityto control the process in viewof an ferent purity. Oxygen of high purity is in particular adaptation to the existing demand, on the one hand, required for refining purposes, whereas oxygen of and to perform the process in a substantially more lower purity is sufficientfor combustion plants. For 100 economic manner and atfavourable costs, on the the production of oxygen at a largetechnical scale, other hand. Such a procedure has the advantagethat cryogenic plants and, in particular, cryogenic rectific- pressurized oxygen can directly be derived from the ation processes represent most frequently the most cryogenic rectification stage and that any expensive economic solution. Such plants are scarcely con- and maintainance-intense equipments for com trollable with respeetto their production capacity 105 pressing oxygen can be omitted at least forthe major and must be operated with substantially nominal amount of the oxygen produced.

load when having started the operation. IfJorex- Within the scope of the process according to the ample, steel converters shall be given a fresh lining invention, the adsorption process performed under this means an interruption of the consumption of changing pressure can be performed directly with oxygen of high purity, but stopping of the oxygen 110 the pressurized oxygen extractable f rom the cryog plant is, even fortime intervals of 48 hours which are enic rectification plant and subsequently be cyclic usuallyfor giving the converter a new lining, not ally operated such that the adsorbers operated under economic on account of the long start-up times and changing pressure and containing molecularsieve on account of energetic considerations. material are, priorto again being charged, scaven- Cryogenic rectification plants are operable in a 115 ged by pure gas, in particular oxygen being com- particularly economic manner if they are operated at pressed as compared with the supply pressure, and J1 a comparatively low pressure and renouncing a high thatthe scavenging gas is, after having emerged purity of the oxygen. A pure gas containing upto 95 from the adsorber operated underchanging pres % oxygen can, forexample, be produced atoperat- sure, supplied into the discharge conduitfor pre- ing pressures of, at most, 7 bar, in particular 5 bar. A 120 purified gas. The oxygen compressor required in this more far-reaching purification of the oxygen to a type of procedure can be given substantially smaller purity ofJor example, 99 % requires substantially dimensions because it need only compressthat par higher pressures and a substantially greaterex- tial amount of gas which has been further purified, penditurewith respectto thetechnical plant. Forthe and by providing an oxygen compressor behindthe major part of consumers it is sufficientto have 125 adsorber operated undervarying pressure there is oxygen of lower purity, and known plants are, last not only put at disposal the desired operating pres not least, ineconomic becausethey produce, with sure for pure oxygen but also provided the pos corresponding expenditure, oxygen of high purity sibilityto use this pressurized oxygen of high purity also for applications forwhich could do also oxygen for purifying or, respectively, scavenging the molec oflowerpurity. 130 ular sieve material.

2 GB 2 190 477 A 2 The inventive apparatus for performing this pro- A branch conduit 7 leading to the adsorbers 8op- cess comprises an air compressor and a cryogenic erated under changing pressure is connected to the rectification plant, in which liquid oxygen is evapora- product gas conduit 4. The adsorbers 8 operated ted in an isobaric manner, and is essentially char- under changing pressure are filled with molecular acterized in thatto the product gas conduitforthe 70 sieve material, noting that controllable or, re gaseous pressurized oxygen there is connected a spectively, adjustable valves 9 are interconnected branch conduit leading to the adsorbers operated into the supply conduits and into the discharge con under changing pressure. The arrangement is duits of these adsorbers 8 operated under changing advantageously such that an oxygen compressor is pressure. If pre-purif ied oxygen is, via the branch interconnected into the discharge conduitfor pure 75 conduit7, passed through the adsorbers 8 operated gas connected to the adsorbers operated under under changing pressure, oxygen of high purity can changing pressure and that a recycling conduit for be extracted via the discharge condu it 10, which scavenging gas is, behind the compressor, connec- oxygen is supplied to an oxygen compressor 11 and ted with the adsorber operated under changing pres- can subsequently be delivered via a conduit 12 to the sure, noting thatthere can be made at disposal, on 80 consumer underthe desired operating pressure of, the one hand, oxygen of high purity and having the for example, 40 bar.

desired pressure and, on the other hand, scavenging A recycling conduit 13 for scavenging gas leads gas under a substantially higher pressure than the from this conduit 12 to corresponding connections operating pressure of the adsorber operated under 14 of the adsorbers operated under changing pres changing pressure. By recycling pressurized oxygen 85 sure, noting that again valves 15 are interconnected of high purityforthe purpose of scavenging the into this recycling conduit 13for scavenging gas.The adsorbers operated underchanging pressure,there scavenging gas can again be recycled intothe pro can be adjusted between the operating pressure and ductgas conduit4via adjustable throttle members the scavenging pressure a pressure differencewhich 16 after having purified the molecular sieve material allowsto omit evacuation of the adsorbers operated 90 and after having been expanded down to the lower under changing pressures, which evacuation is nec- pressure prevailing within said conduit.

essary in case of many adsorbers operated under

Claims

changing pressures forthe purpose of cleaning CLAIMS same.

Forthe purpose of further reducing any loss of 95 1. Process for purifying air by cryogenic rectifica- oxygen when operating the inventive apparatus, the tion, in which process the air is compressed to a arrangement can advantageously be such that an maximum pressure of 7 bar and at least one liquified adjustable throttling means or, respectively, pres- component is evaporated for obtaining a pre sure reducing member is interconnected into the purified gas, characterized in that liquified oxygen is conduit between pre-purified product gas and 100 evaporated in an isobaric mannerfor cooling com adsorber operated under changing pressure, in partpressed airto be separated into its components and icular into the conduitfor recycling scavenging gas in thatat least a partial amount of thethus produced into this produetconduit. In this manner,the gas of pressurized oxygen is subjected to an adsorption lower purity obtained after purifying the adsorber process operated with changing pressure and is opti operated underchanging pressure and, in particular, 105 onally compressed in a gaseous condition.

the produced oxygen now containing a substantially 2. Process as claimed in claim 1, characterized in greater amount of nitrogen can be recycled into the that the adsorbers operated under changing pres product gas conduit containing oxygen of lower sure and containing molecular sieve material are, purity and this oxygen can, for example, be used priorto again being charged, scavenged by using without hesitation forcombustion purposes. 110 pure gas being compressed relativeto the supply in the following, the invention is explained in grea- pressure and in thatthe scavenging gas is, afterhav terdetail with reference to a principal flowscheme of ing leftthe adsorber operated underchanging pres an apparatus according to the invention schematic- sure, supplied into the discharge conduitfor pre allyshown in the drawing. purified gas.

Inthe drawing, an aircompressor is designated by 115 3. Apparatus for performing the process accord 1 which can be followed by a first molecular sieve 2 ing to claim 1 or 2, comprising an air compressor and serving the purpose of pre-purifying the gas to be a cryogenic rectification plant in which liquid oxygen separated into its components. Within the cryogenic is evaporated under isobaric conditions, char rectification plant 3, oxygen is liquified and evapora- acterized in that a branch conduit (7) leading to the ted under isobaric conditions, so that pressurized 120 adsorbers (8) operated under changing pressure is oxygen can be extracted atthe outletvia a conduit 4 connected to the product gas conduit (4) forthe gas and pressureless nitrogen can be extracted via a con- eous pressurized oxygen.

duit 5.When adjusting an operating pressure of app- 4. Apparatus as claimed in claim 3, characterized roximately 7 bar it is possible to extract via the con- in that an oxygen compressor (11) is interconnected duit4 oxygen having substantially a purity of 95 %.A 125 into the discharge conduit (10), connected to the nitrogen compressor 6 can subsequently be inter- adsorber (8) operated under changing pressure, for connected into the nitrogen conduit for equally prod- pure gas and in that, behind said compressor (1 1),a ucing nitrogen under a pressure which is corn par- recycling conduit (13) for scavenging gas is connec able with the pressure prevailing within the oxygen ted with the adsorbers (8) operated under changing conduit. 130 pressure.

3 GB 2 190 477 A 3 5. Apparatus as claimed in claim 3 or4, characterized in that an adjustable throttle member or, respectively, throttle reducing means (16) is interconnected into the conduit between pre-purified product gas and adsorber (8) operated underchanging pressure, in particular into the conduit (13) for recycling scavenging gas into this product conduit (4).

6. A process for purifying air by cryogenic rectification, substantially as hereinbefore described.

7. Apparatus for purifying air by cryogenic rectification substantially as hereinbefore described with reference to the drawing.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,9187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies maybe obtained.