Title of Invention	AIR SEPARATION UNIT WITH REBOILER, BUFFER VESSEL AND BOOSTER AIR COMPRESSOR WITH ENGINE
Abstract	The conventional air separations units (ASU) for production of compressed oxygen and compressed nitrogen gases entail multiple (3 or more) rectification columns, a main heat exchanger, a pre-treatment auxiliary column and a combination of these features. They (ASUS) yield oxygen levels of around 29% in liquefied air prior to separations. The present invention incorporates a damper to an expansion engine to dually serve as an improvised column, fitted with 6-8 sieve trays and air coil reboiler in bottom section of high pressure rectification column to liquefy process air prior to enrichment in the buffer vessel. The twin features yield oxygen concentrations of 39%, thereby substantially reducing column size for high-pressure and high pressure rectifications and offering substantial savings in overall operating costs.

Title of Invention

AIR SEPARATION UNIT WITH REBOILER, BUFFER VESSEL AND BOOSTER AIR COMPRESSOR WITH ENGINE

Abstract

The conventional air separations units (ASU) for production of compressed oxygen and compressed nitrogen gases entail multiple (3 or more) rectification columns, a main heat exchanger, a pre-treatment auxiliary column and a combination of these features. They (ASUS) yield oxygen levels of around 29% in liquefied air prior to separations. The present invention incorporates a damper to an expansion engine to dually serve as an improvised column, fitted with 6-8 sieve trays and air coil reboiler in bottom section of high pressure rectification column to liquefy process air prior to enrichment in the buffer vessel. The twin features yield oxygen concentrations of 39%, thereby substantially reducing column size for high-pressure and high pressure rectifications and offering substantial savings in overall operating costs.

Full Text	FORM 2 THE PATENT ACT 1970 (39 of 1970) & The Patents Rules, 2003 COM PLETE SPEFICIATION (See Sec tion 10 and rule 13) 1. TITLE OF THE INVENTION : Air separation unit with reboiler, buffer vessel and booster air compressor with engine 2. APPLICANT (a) NAME : (b) NATIONALITY (c) ADDRESS: Artefact Technologies Private Limited An Indian Private Ltd. Company A-4, Trishul, Mahakali Caves Road, Andheri (E), Mumbai - 400 093. M. S. India 3. PREAMBLE TO THE The following specification particularly DESCRIPTION COMPLETE describes the invention and the manner SPEFICIATION in which it is to be performed. 1.0 Title of Invention Air separation unit with reboiler, buffer vessel and booster air compressor with engine 2.0 Field of Invention The invention pertains to the field of air separation units (ASU) for manufacture of compressed nitrogen and oxygen gases, and more particularly to refinements and improvements to conventional air separation units to enhance rated capacity of the ASUs to yield higher oxygen volumes of production, while lowering overall production costs. 3.0 Background of Invention 3.1 There are numerous prior works of art reported in the field. A separate discussion on each of these works is beyond the scope of this work apart from drawing out the major and substantive dissimilarities between the cited works and the present invention. The dissimilarities are highlighted in the following paragraphs. 3.2 The US Patent 5379598 relates to an air separation apparatus that relies on operating a low temperature rectification column without disturbing thermodynamic irreversibility of a main heat exchanger. The present invention has no such reliance on a main 2 heat exchanger and its thermodynamic irreversibility and instead employs a buffer vessel that dually functions as a damper to expansion engine and enriches rich liquid oxygen stream from conventional 30% levels to 39-40% levels. The cited work differs from the present invention. The U.S. Patent 5,697,229 relates to an auxiliary column that pre-treats crude oxygen from bottom of high pressure column. The present invention employs a buffer vessel in conjunction with an air coil reboiler - the buffer vessel substituting auxiliary column -to pre-treat crude liquid oxygen. The buffer vessel instead handles liquid air resulting from condensation of air in air coil reboiler. The present invention bears substantial dissimilar features. The British Patent No. GB 2245961- also published as US Patent No. 146756 - entails operating a low pressure column at a pressure of 2.5 bar, whereas the present invention operates low pressure column at a low pressure of 0.6 bar only. In the cited invention, product nitrogen gas is utilized to cool air, whereas the present invention rather relies on cooling or liquefying air by means of rich liquid oxygen. The present invention employs the buffer vessel, which is a damper to the expansion engine. The 3 present invention effectively meets the requirement of a damper for the expansion engine in the form of the buffer vessel, while enriching liquid oxygen in condensed liquid air. The present invention carries several dissimilarities to the cited invention. The European Patent No. EP 0709632 - also published as JP 8210771, EP 0709632 and AU 700591B - pertains to producing nitrogen as a product, whereas the present invention facilitates production of compressed nitrogen and oxygen gases. In the cited invention, liquid oxygen exchanges heat with nitrogen rich stream to liquefy nitrogen for reflux requirement of the air fractionation column, whereas in the present invention, liquid oxygen rich stream exchanges heat with air and liquefies the air for pre-treatment in the buffer vessel. In the cited invention, the incoming air is merely chilled but undergoes no enrichment in respect of liquid or gaseous oxygen level, whereas the present invention -by means of a buffer vessel - achieves enrichment of rich liquid oxygen even before it is introduced into high pressure rectification column. The present invention bears substantial dissimilarities to the cited invention. 4 3.6 The prior works US Patent No. 6,564,581, US No. 6,536,234 and US No.6,230,519 rely on 3-column low temperature air fractionation, whereas the present invention relies on oxygen-enriched 2-column air separation. 4.0 Objects of Invention 4.1 A primary object of this invention is to substantially improve rich liquid oxygen concentration in crude oxygen prior to fractionation of air to achieve higher oxygen production rates for a given rated plant capacity. 4.2 Another object of this invention is to reduce power costs and the corresponding overall costs by significantly reducing load on air fractionation double columns, operating on low and high column pressures, 4.3 Another object of this invention is to achieve substantial improvement in rich liquid oxygen concentrations - without adding another column - by means of improvising the damper of expansion engine as a small diameter column, called 'buffer vessel'. 4.4 Another object of this invention is to pre-treat process air to cryogenic cooling by means of both heat exchange with rich liquid oxygen stream and expansion in expansion engine* 5 liquid oxygen stream and expansion in expansion engine. 5.0 Summary of Invention The invention successfully meets requirements of air separation units (ASU) for manufacture of compressed nitrogen and oxygen gases, and more over provides low-cost refinements and improvements to conventional air separation units to enhance rated capacity of the ASUs to yield higher oxygen volumes of production, while lowering overall production costs. 6.0 Description of Drawings: 6.1 Drawing # 1 illustrates process flow chart of Air Separation Unit (ASU) with buffer vessel on downstream end of Expansion Engine and Air Coil Reboiler in high pressure bottom column. 6.2 Following nomenclature, as illustrated in drawing # 2, is used in the accompanying drawing # 2: Air - green Defrost Air - Blue W. Nitrogen - mustard yellow Oxygen - Red Poor Liquid - Saffron Rich Liquid - Pink HP Nitrogen- Light Red 6 7.0 Description of Invention 7.1 Atmospheric air is compressed by a multi-stage compressor through a filter (not shown) to the required pressure and is then passed through inter-coolers, industrial refrigerator, moisture separators and molecular sieve battery to remove carbon dioxide, hydrocarbons and moisture from the compressed air. The purification equipment is not shown in the accompanying diagram. 7.2 Purified air compressed to 32-40 bars pressure (hereafter called process air) (01) enters heat exchanger HE-1, where it is mechanically expanded through cross current copper foils and is cooled through indirect heat exchange with countercurrent flows of nitrogen and oxygen. At the outlet end of heat exchanger (HE-1), the chilled air (02) is available at - 120 degree C temperature and pressure of 32-40 bars and is passed through a Distribution Piece (DP-42), where one part of the chilled process air (03) is taken to an Expansion Engine (EE-45) for further expansion, as illustrated in the accompanying drawing # 1. The other part (04) of the chilled process air coming out from the 7 Distribution Piece (DP-42) is further chilled in Heat Exchanger (HE-2). 7.3 The expansion engine (EE-45) - a vertical, single acting, reciprocating type engine, expanding incoming chilled air (03) in its downward stroke and ejecting out the said expanded chilled air in its upward stroke - expands and cools the chilled air (03) to the air having -170 degree C temperature and pressure 5 bars (05) at the point of exit from the Expansion Engine (EE-45). 7.4 The second heat exchanger HE-2, like its counterpart HE-1, cools the incoming chilled air (04) in indirect heat exchange with countercurrent flow of oxygen and nitrogen streams. The chilled air (06) exits the heat exchanger (HE-2) at - 160°C degree C temperature and 32-40 bars. 7.5 The chilled process air (06) leaving the heat exchanger (HE-2) is passed through a coil (AC-10) - provided in the reboiler section of the high pressure lower column (C-20) - where it is condensed and liquefied (08) completely in indirect heat exchange with oxygen rich liquid (07) present in the bottom end of the lower column (FC-60). The crude oxygen - termed as rich liquid (07) - due to 8 heat exchange, boils off nitrogen present in rich liquid as vapour (10). 7.6 The condensed, liquefied process air (08) is taken to top end of buffer vessel (BV-40), where the condensed, liquefied air (08) is expanded on the 6th uppermost tray. The vapourized air (05) leaving the Expansion Engine (EE-45) at - 170 degree C temperature and 5 bars pressure is introduced into the Buffer Vessel (BV-40) through a dummy tray, situated between 3rd and 4th trays from bottom of the Buffer Vessel (BV-40). The Buffer Vessel (BV-40) effectively dampens pulsations from the Expansion Engine (EE-45). 7.8 The Buffer Vessel (BV-40) is a damper on the downstream end of the Expansion Engine (EE-45), improvised to additionally function as a small diameter column and is fitted with 6 to 10 number sieve trays. Vapourized process air (05), entering the Buffer Vessel between the 3rd to 6th trays, is condensed by the falling liquids of the condensed, liquefied process air (08) in the Buffer Vessel (BV-40). The temperature of liquid air and vapour air are equalized in the buffer vessel which acts as a dampener to the Expansion Engine that takes part of the bottom columm load. 9 7.9 The oxygen-rich liquid process air (11), leaving the Buffer Vessel (BV-40) from the bottom end is introduced on 6th tray - from -bottom - of high pressure lower column (FC-60) and chilled vapourized air (10) is introduced on 3rd tray of the high pressure lower column (FC-60). The lower column (FC-60) operates at a pressure of 5 bars. 7.10 In between the lower column (FC-60) and upper low pressure column (FC-70) is provided a condenser (C-100), which provides reflux for the lower column (FC-60) and acts as a reboiler for the upper column (FC-70). The liquid air (11) falling from the 6th tray separates nitrogen vapour to yield crude oxygen (12), collected at bottom end of the lower column (FC-60), while 0.5% pure nitrogen (13) -termed as poor liquid - leaves top end of the lower column (FC-60). 7.11 Crude oxygen (12) - termed as rich liquid leaving from bottom end of the lower column (FC-60) - is expanded through expansion valve (R-2) and is introduced to middle of the upper low pressure column (FC-70). The low-pressure, upper column (FC-70) 10 operates at 0.5 bar pressure. 7.12 Nitrogen (13), termed as poor liquid leaving the top of the lower column (FC-60), is passed in Sub-Cooler (SC-80) and is introduced to top end of the upper column (FC-70) after expansion through the expansion valve (R-3). Due to difference in boiling points, pure nitrogen (15) boils over and collects at top end of the upper column (FC-70), while pure oxygen (14) accumulates in the condenser (CN-85). 7.13 Pure oxygen (14) is cooled in Sub-Cooler (SC-90) by exchanging heat with pure nitrogen stream, is expanded through expansion valve (R-6) and is pumped by liquid oxygen pump (PO-110) through heat exchangers (HE-2) and (HE-1) to cool incoming process air (01) and is compressed into high pressure oxygen cylinders by means of a high pressure compressor (CO-200). 7.14 Pure vapourized nitrogen (15), from condenser at the top end of the upper column (FC-70), is expanded after passing through Sub-Coolers-in-series (SC-80), (SC-90) and (SC-100) and heat exchangers (HE-2) and (HE-1) before being either vented to atmosphere as waste nitrogen or is alternatively compressed by 11 means of an independent compressor into compressed nitrogen of high purity for bottling . 7.15 Pure nitrogen (16), after expansion in the Sub-Cooler (SC-80) is taken through expansion valve (R-5) to Nitrogen Buffer Vessel (N-300) from where liquid nitrogen (16) is pumped to heat exchanger (HE-2) and (HE-1) for indirect heat exchange with incoming process air (01), before being filled as compressed nitrogen at outlets NP1 and NP2. 7.16 The invention offers following advantages over the standard plants as described in the table below : StandardOxygenPlant ModifiedOxygenPlant Rich Liquid 31%+69%(N2) 40+60 (N2) Total quantity of rich liquid 65% 50% Nitrogen generated 35% 50% 02 carried in waste nitrogen 2.5% Less than 1% Recovery of oxygen frominput air 18.5% 20% i) Quantity extra produced for same air is greater than 7.5%. The reason is more liquid nitrogen (poor liquid) is available for condensing oxygen in the waste nitrogen stream, ii) Quantity of nitrogen is 40% more i.e. 50% of nitrogen is generated for whole air. 12 iii) In Air Separation Unit, Nitrogen and Oxygen have to be separated. Since more nitrogen is separated in the bottom column itself, top column load is reduced. A plant designed for 130 M3/Hr. of Oxygen can produce 170 M3/Hr. in the modified plant with extra air. iv) Due to the air going through coil in the bottom column and buffer vessel with trays, air is sub cooled to - 172 degree C. Hence more air can be passed through Expansion Engine and more power is available to run the booster compressor. This also brings down the working pressure of plant. 7.17 Booster Air Compressor As stated in the paragraph above, the additional air can be boosted into the Air Separation Unit with the help of a booster compressor shown in the drawing # 1 with small addition of power cost. The booster compressor is incorporated and coupled with the existing Expansion Engine as shown in the drawing # 1. The compressed air available from the system will be added to the process air through the second stage of the existing main air compressor, thus adding to the overall quantity of compressed air available to the Air Separation Column. These additions have been operated satisfactorily for over five years and can assist in saving 9 to 11% of production cost by saving power and by adding to the volume of production. 13 Expansion Engine is the reverse of a compressor. Whole power is available by expanding the process air from 3 5 bar to 5.5 bar pressure. To control the speed of the Expansion Engine, one running motor is continuously coupled to the Expansion Engine.The unutilised power of the Expansion Engine is now used to power the booster compressor. 8.0 Best Operation of the Invention: 8.1 The invention is best operated by performing the following operations, namely: 8.2 Post-purification air is compressed to 35 bars pressure, 8.3 The Expansion Engine (EE) receives 30 to 35%% of the chilled process air (02) and the balance 65 to 70% of the chilled process air (02) is fed to the second stage heat exchanger (HE2), 8.4 the second stream of chilled process air is cooled to - 160°C temperature, pressure 35 bars in heat exchanger (4E-2), 8.5 6 no. sieve trays in the buffer vessel (BV-40) are provided, 8.6 the super-chilled process air (05) is introduced in the buffer vessel between 3rd and 4th trays, 8.7 vapourized process air (10) leaving top of buffer vessel is introduced on 3rd tray of high-pressure fractionation column (FC-60), 8.8 liquid - oxygen - enriched process air (11) is introduced onto 6th tray of the said high-pressure lower rectification column (FC-60), 14 8.9 the high-pressure lower column (FC-60) is operated with 35 sieve trays and the upper low pressure column with 62 sieve trays. 9.0 The Applicant claims 1 A process for separation of air into compressed nitrogen and oxygen gases, is comprised of: 2 (i) cooling process air (01) - atmospheric air freed off hydrocarbon and other impurities and compressed to 32 to 40 bar pressure - in first stage heat exchanger (HE-1) to process air at - 120 degree centigrade temperature (02) by indirect heat exchange with product oxygen (100) and nitrogen (110) streams; (ii) introducing the said chilled process air (02) to a Distribution Piece (DP) to divide into one stream of chilled process air (03) to be fed to Expansion Engine (EE) and into the other stream of the chilled process air (04) to be fed to a second stage heat exchanger (HE2); (iii) expanding and cooling further the said one stream of chilled process air (03) in the said Expansion Engine to super-chilled process air (05), having a pressure of 5 bars and a temperature of- 170 degree Centigrade; (iv) cooling the said second stream of chilled process air (04) in the said heat exchanger (HE-2) to chilled air (06) of pressure 32-40 bars and temperature - 160°C degree Centigrade; (v) feeding the said chilled process air (06) exiting the said heat exchanger (HE-2) to air coil (AC-10) for condensation and liquefaction of the said chilled process air (06) into condensed and liquefied process air (08) by indirect heat exchange with rich liquid oxygen (07); 15 (vi) introducing the said condensed and liquefied process air (08) to 6th to 9th plate at top of a Buffer Vessel (BV-40); (vii) introducing into middle region of the said Buffer Vessel (BV-40) the said super-chilled process air (05) - exiting the said Expansion Engine (EE-45) - on a dummy tray situated between 2nd to 5th trays of the said Buffer Vessel (BV-40); (viii) condensing the said super-chilled process air (05) in the said Buffer Vessel (BV-40) in direct contact with falling liquids of the said condensed and liquefied air (06); (ix) directing vapourized process air (10) exiting the said Buffer Vessel (BV-40) at top end onto 2nd to 5th tray of a high pressure lower fractionation column (FC-60); (x) introducing the said liquid oxygen-enriched liquid process air (11) onto a 5th to 8th tray of the said high-pressure lower rectification column (FC-60); (xi) fractionating the said liquid oxygen enriched process air into (a) crude oxygen fraction (12) - termed as rich liquid -collected from bottom end of the said lower rectification column (FC-60 and (b) crude nitrogen fraction (13) - termed as poor liquid - collected from top end of the lower column (FC-60); (xii) cooling the said crude oxygen fraction (12) in a sub-cooler (SC-100) in indirect heat exchange and thereafter expanding from lower column pressure of 5 bars to upper column (FC-70) pressure of 0.5 bar in an expansion valve (R2) to yield crude oxygen fraction (14); 16 (xiii) introducing the said condensed and liquefied process air (08) to 6th to 9th plate at top of a Buffer Vessel (BV-40); (xiv) introducing into middle region of the said Buffer Vessel (BV-40) the said super-chilled process air (05) - exiting the said Expansion Engine (EE-45) - on a dummy tray situated between 2nd to 5th trays of the said Buffer Vessel (BV-40); (xv) condensing the said super-chilled process air (05) in the said Buffer Vessel (BV-40) in direct contact with falling liquids of the said condensed and liquefied air (06) and enriching the liquid oxygen content of the resultant liquid process air (11), exiting the said Buffer Vessel (BV-40); (xvi) directing vapourized process air (10) exiting the said Buffer Vessel (BV-40) at top end onto 2nd to 5th tray of a high pressure lower fractionation column (FC-60); (xvii1) introducing the said liquid oxygen-enriched liquid process air (11) onto a 6th to 8th tray of the said high-pressure lower rectification column (FC-60); (xviii) fractionating the said liquid oxygen enriched process air into (a) crude oxygen fraction (12) - termed as rich liquid -collected from bottom end of the said lower rectification column (FC-60 and (b) crude nitrogen fraction (13) - termed as poor liquid - collected from top end of the lower column (FC-60); (xix) cooling the said crude oxygen fraction (12) in a sub-cooler (SC-100) in indirect heat exchange and thereafter expanding from lower column pressure of 5 bars to upper column (FC-70) pressure of 0.5 bar in an expansion valve (R2) to yield crude oxygen fraction (14); 17 (xx) cooling the said nitrogen fraction (13) in a sub-cooler (SC- 80), dividing the said nitrogen stream into (a) one part (15) for expansion through an expansion valve (R3) from initial pressure of 5 bars into final pressure of 0. 5 bar to yield liquid stream (17), and (b) the other part (16) for expansion through an expansion valve (R5) from the initial and final pressures of 5 bars and 0.5 bar respectively to yield liquid nitrogen (18), which is introduced at top end of the said low-pressure upper column (FC-70). (xxi) introducing the said crude oxygen fraction (14) onto middle of the said low pressure, upper column (FC-70) and fractionating the said crude oxygen fraction (14) - utilizing difference in boiling points of oxygen and nitrogen - into (a) pure oxygen fraction (100), collected at bottom end of the said upper column (FC-70) in a condenser (CN-85), and (b) pure nitrogen (110), collected at top end of the said upper column (FC-70), (xxii) cooling in a sub-cooler (SC-90) the said pure oxygen stream (100), expanding through an expansion valve (R6), pumping through liquid oxygen pump (P1000) and cooling the incoming process air (01) in indirect heat exchange through the said twin heat exchanger (HE-2) and (HE-1) before being filled as compressed oxygen gas at outputs 03 and 04, 18 (xxiii) taking oxygen vapour, exiting the said pump (P-1000) through a valve (R7) for pressure reduction from the said pressure of 5 bars to 0.5 bar and introducing the said expanded oxygen vapour at bottom end of the said low-pressure upper column (FC-70); (xxiv) cooling the vapourized pure nitrogen (19) leaving top end of the said low-pressure upper column (FC-70) at a pressure of 0.5 bar in indirect heat exchange in series through sub-coolers (SC-80), (SC-90) and (SC-100) and through the said heat exchangers in series HE-2 and HE-1 to cool the incoming process air (01) and optionally either venting as waste nitrogen or compressing the said vented pure nitrogen (WN2) in an independent compressor and bottling it as pure compressed nitrogen; (xxv) introducing the said low pressure pure liquid nitrogen stream (18) to liquid nitrogen buffer vessel (LN-1100), pumping the said pure liquid nitrogen (18) leaving the nitrogen buffer vessel (LN-1100) via firstly expansion cum isolation valve (R8) and then through pure, liquid nitrogen pump (P-1100), warming the said pure, liquid nitrogen (18) by indirect heat exchange with the said incoming process air (01) in the said twin heat exchanger (HE-2) and (HE-1) and filling the said pure liquid nitrogen exiting the said heat exchanger (HE-1) into cylinders; 2. A process for separation of air into compressed nitrogen and oxygen gases according to claim 1, wherein the said buffer vessel (BV-40), which is a small diameter vessel on the 19 downstream line of the said Expansion Engine (EE-45) to dampen pulsations from the said Expansion Engine (EE-45), has 6-9 number sieve trays to dually enrich the said condensed air (08) by mass transfer - on the said sieve trays - of pure vaporized oxygen from the chilled expanded air (05) to the said condensed air (08) to yield higher liquid oxygen concentrations of 39% in the condensed air (11), exiting the said Buffer Vessel (BV-40) at bottom for being introduced as feed steam to the said high-pressure lower rectification column (FC-60); A process for separation of air into compressed nitrogen and oxygen gases according to claim 1, wherein (i) the said high-pressure, lower column (FC-60) - operating at the column pressure of 5 bars - has 35 to 40 sieve trays, (ii) the said low-pressure, upper column (FC-70), operating at the column pressure of 0.5 bar has 61- 64 sieve trays and (iii) the oxygen rich liquid (14) is introduced on 38th –41st tray of the said low-pressure column (FC-70); 4. A process for separation of air into compressed nitrogen and said lower, high-pressure column (FC-60) is fitted internally at the bottom end of the said lower, high-pressure column (FC-60) by being immersed in rich liquid oxygen - termed as rich liquid - and is a simple coil through which chilled air (06) exiting the said heat exchanger (HE-2) is condensed into the said liquefied air (08); 20 5. A process for separation of air into compressed nitrogen and oxygen gases according to claim 1, wherein the said expansion engine (EE-45) is coupled to a motor (M-47) to regulate speed of the said expansion engine (EE-45) and to power a booster compressor (CP-48) to compress the said process air to second stage or third stage compression pressures; 6. A process for separation of air into compressed nitrogen and oxygen gases, a dual function buffer vessel (BV-40) to enrich liquefied process air with liquid oxygen and an air coil reboiler (AC-10) substantially described herein above and illustrated in the accompanying drawings Date : 22nd March , 2007 21 ABSTRACT Drawing - 2 Air separation unit with reboiler, buffer vessel and booster air compressor with engine The conventional air separations units (ASU) for production of compressed oxygen and compressed nitrogen gases entail multiple ( 3 or more) rectification columns, a main heat exchanger, a pre-treatment auxiliary column and a combination of these features. They (ASUS) yield oxygen levels of around 29% in liquefied air prior to separations. The present invention incorporates a damper to an expansion engine to dually serve as an improvised column, fitted with 6- 8 sieve trays and an air coil reboiler in bottom section of high pressure rectification column to liquefy process air prior to enrichment in the buffer vessel. The twin features yield oxygen concentrations of 39%, thereby substantially reducing column size for high-pressure and high pressure rectifications and offering substantial savings in overall operating costs. 22

Full Text

FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COM PLETE SPEFICIATION
(See Sec tion 10 and rule 13)
1. TITLE OF THE INVENTION : Air separation unit with reboiler, buffer
vessel and booster air compressor with engine

2. APPLICANT
(a) NAME :
(b) NATIONALITY
(c) ADDRESS:

Artefact Technologies Private Limited
An Indian Private Ltd. Company
A-4, Trishul, Mahakali Caves Road, Andheri (E), Mumbai - 400 093. M. S. India

3. PREAMBLE TO THE The following specification particularly
DESCRIPTION COMPLETE describes the invention and the manner
SPEFICIATION in which it is to be performed.

1.0 Title of Invention
Air separation unit with reboiler, buffer vessel and booster air compressor with engine
2.0 Field of Invention
The invention pertains to the field of air separation units (ASU) for manufacture of compressed nitrogen and oxygen gases, and more particularly to refinements and improvements to conventional air separation units to enhance rated capacity of the ASUs to yield higher oxygen volumes of production, while lowering overall production costs.
3.0 Background of Invention
3.1 There are numerous prior works of art reported in the field. A separate discussion on each of these works is beyond the scope of this work apart from drawing out the major and substantive dissimilarities between the cited works and the present invention. The dissimilarities are highlighted in the following paragraphs.
3.2 The US Patent 5379598 relates to an air separation apparatus that relies on operating a low temperature rectification column without disturbing thermodynamic irreversibility of a main heat exchanger. The present invention has no such reliance on a main
2

heat exchanger and its thermodynamic irreversibility and instead employs a buffer vessel that dually functions as a damper to expansion engine and enriches rich liquid oxygen stream from conventional 30% levels to 39-40% levels. The cited work differs from the present invention.
The U.S. Patent 5,697,229 relates to an auxiliary column that pre-treats crude oxygen from bottom of high pressure column. The present invention employs a buffer vessel in conjunction with an air coil reboiler - the buffer vessel substituting auxiliary column -to pre-treat crude liquid oxygen. The buffer vessel instead handles liquid air resulting from condensation of air in air coil reboiler. The present invention bears substantial dissimilar features. The British Patent No. GB 2245961- also published as US Patent No. 146756 - entails operating a low pressure column at a pressure of 2.5 bar, whereas the present invention operates low pressure column at a low pressure of 0.6 bar only. In the cited invention, product nitrogen gas is utilized to cool air, whereas the present invention rather relies on cooling or liquefying air by means of rich liquid oxygen. The present invention employs the buffer vessel, which is a damper to the expansion engine. The
3

present invention effectively meets the requirement of a damper for the expansion engine in the form of the buffer vessel, while enriching liquid oxygen in condensed liquid air. The present invention carries several dissimilarities to the cited invention. The European Patent No. EP 0709632 - also published as JP 8210771, EP 0709632 and AU 700591B - pertains to producing nitrogen as a product, whereas the present invention facilitates production of compressed nitrogen and oxygen gases. In the cited invention, liquid oxygen exchanges heat with nitrogen rich stream to liquefy nitrogen for reflux requirement of the air fractionation column, whereas in the present invention, liquid oxygen rich stream exchanges heat with air and liquefies the air for pre-treatment in the buffer vessel. In the cited invention, the incoming air is merely chilled but undergoes no enrichment in respect of liquid or gaseous oxygen level, whereas the present invention -by means of a buffer vessel - achieves enrichment of rich liquid oxygen even before it is introduced into high pressure rectification column. The present invention bears substantial dissimilarities to the cited invention.
4

3.6 The prior works US Patent No. 6,564,581, US No. 6,536,234 and US No.6,230,519 rely on 3-column low temperature air fractionation, whereas the present invention relies on oxygen-enriched 2-column air separation.
4.0 Objects of Invention
4.1 A primary object of this invention is to substantially improve rich liquid oxygen concentration in crude oxygen prior to fractionation of air to achieve higher oxygen production rates for a given rated plant capacity.
4.2 Another object of this invention is to reduce power costs and the corresponding overall costs by significantly reducing load on air fractionation double columns, operating on low and high column pressures,
4.3 Another object of this invention is to achieve substantial improvement in rich liquid oxygen concentrations - without adding another column - by means of improvising the damper of expansion engine as a small diameter column, called 'buffer vessel'.
4.4 Another object of this invention is to pre-treat process air to cryogenic cooling by means of both heat exchange with rich
liquid oxygen stream and expansion in expansion engine*
5

liquid oxygen stream and expansion in expansion engine.
5.0 Summary of Invention
The invention successfully meets requirements of air separation units (ASU) for manufacture of compressed nitrogen and oxygen gases, and more over provides low-cost refinements and improvements to conventional air separation units to enhance rated capacity of the ASUs to yield higher oxygen volumes of production, while lowering overall production costs.
6.0 Description of Drawings:
6.1 Drawing # 1 illustrates process flow chart of Air Separation Unit (ASU) with buffer vessel on downstream end of Expansion Engine and Air Coil Reboiler in high pressure bottom column.
6.2 Following nomenclature, as illustrated in drawing # 2, is used in the accompanying drawing # 2:
Air - green
Defrost Air - Blue
W. Nitrogen - mustard yellow Oxygen - Red
Poor Liquid - Saffron
Rich Liquid - Pink HP Nitrogen- Light Red
6

7.0 Description of Invention
7.1 Atmospheric air is compressed by a multi-stage compressor through a filter (not shown) to the required pressure and is then passed through inter-coolers, industrial refrigerator, moisture separators and molecular sieve battery to remove carbon dioxide, hydrocarbons and moisture from the compressed air. The purification equipment is not shown in the accompanying diagram.
7.2 Purified air compressed to 32-40 bars pressure (hereafter called process air) (01) enters heat exchanger HE-1, where it is mechanically expanded through cross current copper foils and is cooled through indirect heat exchange with countercurrent flows of nitrogen and oxygen. At the outlet end of heat exchanger (HE-1), the chilled air (02) is available at - 120 degree C temperature and pressure of 32-40 bars and is passed through a Distribution Piece (DP-42), where one part of the chilled process air (03) is taken to an Expansion Engine (EE-45) for further expansion, as illustrated in the accompanying drawing # 1. The other part (04) of the chilled process air coming out from the
7

Distribution Piece (DP-42) is further chilled in Heat Exchanger (HE-2).
7.3 The expansion engine (EE-45) - a vertical, single acting,
reciprocating type engine, expanding incoming chilled air (03) in
its downward stroke and ejecting out the said expanded chilled air
in its upward stroke - expands and cools the chilled air (03) to the
air having -170 degree C temperature and pressure 5 bars (05) at
the point of exit from the Expansion Engine (EE-45).
7.4 The second heat exchanger HE-2, like its counterpart HE-1, cools
the incoming chilled air (04) in indirect heat exchange with countercurrent flow of oxygen and nitrogen streams. The chilled air (06) exits the heat exchanger (HE-2) at - 160°C degree C temperature and 32-40 bars.
7.5 The chilled process air (06) leaving the heat exchanger (HE-2) is
passed through a coil (AC-10) - provided in the reboiler section of
the high pressure lower column (C-20) - where it is condensed
and liquefied (08) completely in indirect heat exchange with
oxygen rich liquid (07) present in the bottom end of the lower
column (FC-60). The crude oxygen - termed as rich liquid (07) -
due to
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heat exchange, boils off nitrogen present in rich liquid as vapour (10).

7.6 The condensed, liquefied process air (08) is taken to top end of buffer vessel (BV-40), where the condensed, liquefied air (08) is expanded on the 6th uppermost tray.
The vapourized air (05) leaving the Expansion Engine (EE-45) at - 170 degree C temperature and 5 bars pressure is introduced into the Buffer Vessel (BV-40) through a dummy tray, situated between 3rd and 4th trays from bottom of the Buffer Vessel (BV-40). The Buffer Vessel (BV-40) effectively dampens pulsations from the Expansion Engine (EE-45).

7.8 The Buffer Vessel (BV-40) is a damper on the downstream end of the Expansion Engine (EE-45), improvised to additionally function as a small diameter column and is fitted with 6 to 10 number sieve trays. Vapourized process air (05), entering the Buffer Vessel between the 3rd to 6th trays, is condensed by the falling liquids of the condensed, liquefied process air (08) in the Buffer Vessel (BV-40). The temperature of liquid air and vapour air are equalized in the buffer vessel which acts as a dampener to the Expansion Engine that takes part of the bottom columm load.

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7.9 The oxygen-rich liquid process air (11), leaving the Buffer Vessel (BV-40) from the bottom end is introduced on 6th tray - from -bottom - of high pressure lower column (FC-60) and chilled vapourized air (10) is introduced on 3rd tray of the high pressure lower column (FC-60). The lower column (FC-60) operates at a pressure of 5 bars.
7.10 In between the lower column (FC-60) and upper low pressure column (FC-70) is provided a condenser (C-100), which provides reflux for the lower column (FC-60) and acts as a reboiler for the upper column (FC-70). The liquid air (11) falling from the 6th tray separates nitrogen vapour to yield crude oxygen (12), collected at bottom end of the lower column (FC-60), while 0.5% pure nitrogen (13) -termed as poor liquid - leaves top end of the lower column (FC-60).
7.11 Crude oxygen (12) - termed as rich liquid leaving from bottom end of the lower column (FC-60) - is expanded through expansion valve (R-2) and is introduced to middle of the upper low pressure column (FC-70). The low-pressure, upper column (FC-70)
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operates at 0.5 bar pressure.
7.12 Nitrogen (13), termed as poor liquid leaving the top of the lower column (FC-60), is passed in Sub-Cooler (SC-80) and is introduced to top end of the upper column (FC-70) after expansion through the expansion valve (R-3). Due to difference in boiling points, pure nitrogen (15) boils over and collects at top end of the upper column (FC-70), while pure oxygen (14) accumulates in the condenser (CN-85).
7.13 Pure oxygen (14) is cooled in Sub-Cooler (SC-90) by exchanging heat with pure nitrogen stream, is expanded through expansion valve (R-6) and is pumped by liquid oxygen pump (PO-110) through heat exchangers (HE-2) and (HE-1) to cool incoming process air (01) and is compressed into high pressure oxygen cylinders by means of a high pressure compressor (CO-200).
7.14 Pure vapourized nitrogen (15), from condenser at the top end of the upper column (FC-70), is expanded after passing through Sub-Coolers-in-series (SC-80), (SC-90) and (SC-100) and heat exchangers (HE-2) and (HE-1) before being either vented to atmosphere as waste nitrogen or is alternatively compressed by
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means of an independent compressor into compressed nitrogen of high purity for bottling .
7.15 Pure nitrogen (16), after expansion in the Sub-Cooler (SC-80) is
taken through expansion valve (R-5) to Nitrogen Buffer Vessel
(N-300) from where liquid nitrogen (16) is pumped to heat
exchanger (HE-2) and (HE-1) for indirect heat exchange with
incoming process air (01), before being filled as compressed
nitrogen at outlets NP1 and NP2.
7.16 The invention offers following advantages over the
standard plants as described in the table below :

StandardOxygenPlant ModifiedOxygenPlant
Rich Liquid 31%+69%(N2) 40+60 (N2)
Total quantity of rich liquid 65% 50%
Nitrogen generated 35% 50%
02 carried in waste nitrogen 2.5% Less than 1%
Recovery of oxygen frominput air 18.5% 20%
i) Quantity extra produced for same air is greater than 7.5%. The reason is more liquid nitrogen (poor liquid) is available for condensing oxygen in the waste nitrogen stream, ii) Quantity of nitrogen is 40% more i.e. 50% of nitrogen is generated for whole air.
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iii) In Air Separation Unit, Nitrogen and Oxygen have to be separated. Since more nitrogen is separated in the bottom column itself, top column load is reduced. A plant designed for 130 M3/Hr. of Oxygen can produce 170 M3/Hr. in the modified plant with extra air.
iv) Due to the air going through coil in the bottom column and buffer vessel with trays, air is sub cooled to - 172 degree C. Hence more air can be passed through Expansion Engine and more power is available to run the booster compressor. This also brings down the working pressure of plant.
7.17 Booster Air Compressor
As stated in the paragraph above, the additional air can be boosted into the Air Separation Unit with the help of a booster compressor shown in the drawing # 1 with small addition of power cost. The booster compressor is incorporated and coupled with the existing Expansion Engine as shown in the drawing # 1. The compressed air available from the system will be added to the process air through the second stage of the existing main air compressor, thus adding to the overall quantity of compressed air available to the Air Separation Column.
These additions have been operated satisfactorily for over five years and can assist in saving 9 to 11% of production cost by saving power and by adding to the volume of production.
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Expansion Engine is the reverse of a compressor. Whole power is available by expanding the process air from 3 5 bar to 5.5 bar pressure. To control the speed of the Expansion Engine, one running motor is continuously coupled to the Expansion Engine.The unutilised power of the Expansion Engine is now used to power the booster compressor.
8.0 Best Operation of the Invention:
8.1 The invention is best operated by performing the following operations, namely:
8.2 Post-purification air is compressed to 35 bars pressure,
8.3 The Expansion Engine (EE) receives 30 to 35%% of the chilled process air (02) and the balance 65 to 70% of the chilled process air (02) is fed to the second stage heat exchanger (HE2),
8.4 the second stream of chilled process air is cooled to - 160°C temperature, pressure 35 bars in heat exchanger (4E-2),
8.5 6 no. sieve trays in the buffer vessel (BV-40) are provided,
8.6 the super-chilled process air (05) is introduced in the buffer vessel between 3rd and 4th trays,
8.7 vapourized process air (10) leaving top of buffer vessel is introduced on 3rd tray of high-pressure fractionation column (FC-60),
8.8 liquid - oxygen - enriched process air (11) is introduced onto 6th tray of the said high-pressure lower rectification column (FC-60),
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8.9 the high-pressure lower column (FC-60) is operated with 35 sieve trays and the upper low pressure column with 62 sieve trays.
9.0 The Applicant claims
1 A process for separation of air into compressed nitrogen and oxygen gases, is comprised of:
2 (i) cooling process air (01) - atmospheric air freed off
hydrocarbon and other impurities and compressed to 32 to 40
bar pressure - in first stage heat exchanger (HE-1) to process
air at - 120 degree centigrade temperature (02) by indirect heat exchange with product oxygen (100) and nitrogen (110) streams; (ii) introducing the said chilled process air (02) to a Distribution Piece (DP) to divide into one stream of chilled process air (03) to be fed to Expansion Engine (EE) and into the other stream of the chilled process air (04) to be fed to a second stage heat exchanger (HE2); (iii) expanding and cooling further the said one stream of chilled process air (03) in the said Expansion Engine to super-chilled process air (05), having a pressure of 5 bars and a temperature of- 170 degree Centigrade; (iv) cooling the said second stream of chilled process air (04) in the said heat exchanger (HE-2) to chilled air (06) of pressure 32-40 bars and temperature - 160°C degree Centigrade;
(v) feeding the said chilled process air (06) exiting the said heat exchanger (HE-2) to air coil (AC-10) for condensation and liquefaction of the said chilled process air (06) into condensed and liquefied process air (08) by indirect heat exchange with rich liquid oxygen (07);
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(vi) introducing the said condensed and liquefied process air (08) to 6th to 9th plate at top of a Buffer Vessel (BV-40);
(vii) introducing into middle region of the said Buffer Vessel (BV-40) the said super-chilled process air (05) - exiting the said Expansion Engine (EE-45) - on a dummy tray situated between 2nd to 5th trays of the said Buffer Vessel (BV-40);
(viii) condensing the said super-chilled process air (05) in the said Buffer Vessel (BV-40) in direct contact with falling liquids of the said condensed and liquefied air (06);
(ix) directing vapourized process air (10) exiting the said Buffer Vessel (BV-40) at top end onto 2nd to 5th tray of a high pressure lower fractionation column (FC-60);
(x) introducing the said liquid oxygen-enriched liquid process air (11) onto a 5th to 8th tray of the said high-pressure lower rectification column (FC-60);
(xi) fractionating the said liquid oxygen enriched process air into (a) crude oxygen fraction (12) - termed as rich liquid -collected from bottom end of the said lower rectification column (FC-60 and (b) crude nitrogen fraction (13) - termed as poor liquid - collected from top end of the lower column (FC-60);
(xii) cooling the said crude oxygen fraction (12) in a sub-cooler (SC-100) in indirect heat exchange and thereafter expanding from lower column pressure of 5 bars to upper column (FC-70) pressure of 0.5 bar in an expansion valve (R2) to yield crude oxygen fraction (14);
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(xiii) introducing the said condensed and liquefied process air (08) to 6th to 9th plate at top of a Buffer Vessel (BV-40);
(xiv) introducing into middle region of the said Buffer Vessel (BV-40) the said super-chilled process air (05) - exiting the said Expansion Engine (EE-45) - on a dummy tray situated between 2nd to 5th trays of the said Buffer Vessel (BV-40);
(xv) condensing the said super-chilled process air (05) in the said Buffer Vessel (BV-40) in direct contact with falling liquids of the said condensed and liquefied air (06) and enriching the liquid oxygen content of the resultant liquid process air (11), exiting the said Buffer Vessel (BV-40);
(xvi) directing vapourized process air (10) exiting the said Buffer Vessel (BV-40) at top end onto 2nd to 5th tray of a high pressure lower fractionation column (FC-60);
(xvii1) introducing the said liquid oxygen-enriched liquid process air (11) onto a 6th to 8th tray of the said high-pressure lower rectification column (FC-60);
(xviii) fractionating the said liquid oxygen enriched process air into (a) crude oxygen fraction (12) - termed as rich liquid -collected from bottom end of the said lower rectification column (FC-60 and (b) crude nitrogen fraction (13) - termed as poor liquid - collected from top end of the lower column (FC-60);
(xix) cooling the said crude oxygen fraction (12) in a sub-cooler (SC-100) in indirect heat exchange and thereafter expanding from lower column pressure of 5 bars to upper column (FC-70) pressure of 0.5 bar in an expansion valve (R2) to yield crude oxygen fraction (14);
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(xx) cooling the said nitrogen fraction (13) in a sub-cooler (SC-
80), dividing the said nitrogen stream into (a) one part (15) for
expansion through an expansion valve (R3) from initial
pressure of 5 bars into final pressure of 0. 5 bar to yield liquid
stream (17), and (b) the other part (16) for expansion through
an expansion valve (R5) from the initial and final pressures of
5 bars and 0.5 bar respectively to yield liquid nitrogen (18),
which is introduced at top end of the said low-pressure upper
column (FC-70).
(xxi) introducing the said crude oxygen fraction (14) onto middle of the said low pressure, upper column (FC-70) and fractionating the said crude oxygen fraction (14) - utilizing difference in boiling points of oxygen and nitrogen - into (a) pure oxygen fraction (100), collected at bottom end of the said upper column (FC-70) in a condenser (CN-85), and (b) pure nitrogen (110), collected at top end of the said upper column (FC-70),
(xxii) cooling in a sub-cooler (SC-90) the said pure oxygen stream (100), expanding through an expansion valve (R6), pumping through liquid oxygen pump (P1000) and cooling the incoming process air (01) in indirect heat exchange through the said twin heat exchanger (HE-2) and (HE-1) before being filled as compressed oxygen gas at outputs 03 and 04,
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(xxiii) taking oxygen vapour, exiting the said pump (P-1000) through a valve (R7) for pressure reduction from the said pressure of 5 bars to 0.5 bar and introducing the said expanded oxygen vapour at bottom end of the said low-pressure upper column (FC-70);
(xxiv) cooling the vapourized pure nitrogen (19) leaving top end of the said low-pressure upper column (FC-70) at a pressure of 0.5 bar in indirect heat exchange in series through sub-coolers (SC-80), (SC-90) and (SC-100) and through the said heat exchangers in series HE-2 and HE-1 to cool the incoming process air (01) and optionally either venting as waste nitrogen or compressing the said vented pure nitrogen (WN2) in an independent compressor and bottling it as pure compressed nitrogen;
(xxv) introducing the said low pressure pure liquid nitrogen stream
(18) to liquid nitrogen buffer vessel (LN-1100), pumping the
said pure liquid nitrogen (18) leaving the nitrogen buffer
vessel (LN-1100) via firstly expansion cum isolation valve
(R8) and then through pure, liquid nitrogen pump (P-1100),
warming the said pure, liquid nitrogen (18) by indirect heat
exchange with the said incoming process air (01) in the said
twin heat exchanger (HE-2) and (HE-1) and filling the said
pure liquid nitrogen exiting the said heat exchanger (HE-1)
into cylinders;
2. A process for separation of air into compressed nitrogen and
oxygen gases according to claim 1, wherein the said buffer
vessel (BV-40), which is a small diameter vessel on the
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downstream line of the said Expansion Engine (EE-45) to dampen pulsations from the said Expansion Engine (EE-45), has 6-9 number sieve trays to dually enrich the said condensed air (08) by mass transfer - on the said sieve trays - of pure vaporized oxygen from the chilled expanded air (05) to the said condensed air (08) to yield higher liquid oxygen concentrations of 39% in the condensed air (11), exiting the said Buffer Vessel (BV-40) at bottom for being introduced as feed steam to the said high-pressure lower rectification column (FC-60);
A process for separation of air into compressed nitrogen and oxygen gases according to claim 1, wherein (i) the said high-pressure, lower column (FC-60) - operating at the column pressure of 5 bars - has 35 to 40 sieve trays, (ii) the said low-pressure, upper column (FC-70), operating at the column pressure of 0.5 bar has 61- 64 sieve trays and (iii) the oxygen rich liquid (14) is introduced on 38th –41st tray of the said low-pressure column (FC-70);
4. A process for separation of air into compressed nitrogen and

said lower, high-pressure column (FC-60) is fitted internally at the bottom end of the said lower, high-pressure column (FC-60) by being immersed in rich liquid oxygen - termed as rich liquid - and is a simple coil through which chilled air (06) exiting the said heat exchanger (HE-2) is condensed into the said liquefied air (08);
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5. A process for separation of air into compressed nitrogen and oxygen gases according to claim 1, wherein the said expansion engine (EE-45) is coupled to a motor (M-47) to regulate speed of the said expansion engine (EE-45) and to power a booster compressor (CP-48) to compress the said process air to second stage or third stage compression pressures;
6. A process for separation of air into compressed nitrogen and oxygen gases, a dual function buffer vessel (BV-40) to enrich liquefied process air with liquid oxygen and an air coil reboiler (AC-10) substantially described herein above and illustrated in the accompanying drawings

Date : 22nd March , 2007
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ABSTRACT
Drawing - 2 Air separation unit with reboiler, buffer vessel and booster air compressor with engine
The conventional air separations units (ASU) for production of
compressed oxygen and compressed nitrogen gases entail multiple ( 3
or more) rectification columns, a main heat exchanger, a pre-treatment
auxiliary column and a combination of these features.
They (ASUS) yield oxygen levels of around 29% in liquefied air prior to
separations. The present invention incorporates a damper to an
expansion engine to dually serve as an improvised column, fitted with 6-
8 sieve trays and an air coil reboiler in bottom section of high pressure
rectification column to liquefy process air prior to enrichment in the
buffer vessel. The twin features yield oxygen concentrations of 39%,
thereby substantially reducing column size for high-pressure and high
pressure rectifications and offering substantial savings in overall
operating costs.

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AIR SEPARATION UNIT WITH REBOILER, BUFFER VESSEL AND BOOSTER AIR COMPRESSOR WITH ENGINE

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