Cryogenic Air Separation History and Technological Progress
2
Contents. 3
Introduction
4
Rerigeration
5
Liqueaction o air
6
Air separation by rectifcation
7
The principles o air separation
8
Column design
9
Technological developments
10
Structured packings Pure argon production by rectifcation Internal compression Advanced condenser/reboiler design
Carl von Linde Berndor 11. June 1842 Munich 16. November 1934
13
Supply chain
14
Typical cryogenic air separation process
16
Historical data
17
Reerences
20
Contact Title-page: Vresova, Czech Republic
3
Introduction. Design and construction o air separation plants is part o Linde’s traditional scope o activities, which led to the establishment o Linde’s Engineering Division at the turn o the 19th century. In 1902, the start-up o the world’s irst air separation plant initiated the development o the cryogenic industry. Today, several hundred engineers and specialists work at Linde or the worldwide sale and contract execution o plants recovering the air constituents oxygen and nitrogen as well as the various rare gases. Over 2,800 air separation plants in 80 countries - 500 o them have been built in the last 15 years bear witness to Linde´s pre-eminent market position in this ield o technology.
4
Rerigeration. In May 1895, Carl von Linde performed an experiment in his laboratory in Munich which led to his invention of the first continuous process for the liquefaction of air based on the Joule-Thomson refrigeration effect and the principle of countercurrent heat exchange. This was the breakthrough for cryogenic air separation.
Air was compressed rom 20 bar to 60 bar in the compressor P and cooled in the water cooler K to ambient temperature (t1). The pre-cooled air was ed into the countercurrent heat exchanger G, urther cooled down and expanded in the expansion valve E (Joule-Thomson valve) to liqueaction temperature. The gaseous content o the air was then warmed up again in the heat exchanger G and ed into the suction side o the compressor (p1). The hourly yield rom this experiment was approx. 3 liters o liquid air.
The above described experiment was based on indings discovered by J. P. Joule and W. Thomson (1853). They ound that compressed gases expanded in a valve cool down by approx. 0.25°C with each bar pressure drop. This proved that real gases do not ollow the Boyle-Mariotte principle, according to which no temperature decrease is to be expected rom expansion. An explanation or this eect was given by J. K. van der Waals (1873) who discovered that the molecules in compressed gases are no longer reely movable and the interaction among them leads to a temperature decrease ater decompression.
K
p2t5
P
Composition o dry air
O2 N2 Ar Ne He Kr Xe
Vol % 20.95 78.08 0.93 0.0018 0.0005 0.00011 0.000009
p2t1
Boiling point -183.0 °C -195.8 °C -185.9 °C -246.1 °C -268.9 °C -153.2 °C -108.0 °C
p1t4 G
t2p2
p1t3
E
N2
tt33
O2
F
5
Liqueaction o air. To enable air to be separated into its constituents by means o rectiication - the actual separation process - a large part o the air volume used must be liqueied. A gas can only be transormed into a liquid state at temperature and pressure conditions below those o its critical point.
The critical point o air is Tcrit = -140.7ºC (= ^ 132.5 K) Pcrit = 37.7 bar, in other words, air can be liqueied only at temperatures below -140.7ºC (132.5 K).
– Air below atmospheric pressure (1 bar) must be chilled to -192ºC (81.5 K) beore condensation sets in. – Air below a pressure o 6 bar must be chil led to -172ºC (101 K) beore condensation begins.
The vapor pressure curve illustrates the allocation o temperatures and pressures at which a gas condenses or a liquid evaporates.
The boiling point and condensation conditions o gas mixtures such as air are not identical. There is a condensation line and a boiling point line which delineate the boiling point range.
Vapor pressure curves o atmospheric gases 100
Crit. point
50
Ar N2
r a b n i e r u s s e r P
O2
LIQUID 10
6 5
AIR V = Start o evaporation K = Start o condensation
VAPOR
1
0.5
81.5 60
80
Temperature in K
101 100
120
140
160
6
Air separation by rectiication. Rectiication is synonymous with countercurrent distillation. This special distillation separation process enables the individual components o a mixture to be separated with a high purity combined with a good yield, even when their boiling points are relatively close to each other.
Vapor pressure o N 2 pN2=1.55 at Ts=81.5K
r a b n i e r u s s e r P
Due to the dierent vapor pressures o the individual components (pN2 >pO2) the composition o the vapor diers rom that o the liquid mixture. Correspondingly, a higher proportion o the component with the greater pressure vaporizes during the evaporation process.
The vapor produced rom a boiling liquid mixture o O2/N2 will thus have a higer N2 concentration than the liquid mixture rom which it originates. Accordingly, the condensate produced when an O2/N2 vapor mixture is liqueied will display a higher O2 concentration because the component with the lower partial pressure tends to transorm into liquid.
Boiling point pressure P S at TS = 81.5K
p*N2 Partial pressure o N2 Condensation pressure PS at TS = 81.5 K
PO2=0.36 vapor pressure o O2 at TS=81.5K
p*O2 partial pressure o O 2 0
100
O2 concentration in O2/N2 mixture % by volume
Condensation temperature TS at PS = 1 bar
90
90
Vapor
K77 n i e r u t a r e p m e T
Liquid
0
O2 concentration in O2/N2 mixture % by volume
Boiling point temperature TS at PS = 1 bar
100
7
The principles o air separation. Air separation by rectification in a single/double column: Based on his air liqueaction principle Carl von Linde constructed the irst air separation plant or oxygen production in 1902, using a single column rectiication system. In 1910, he set the basis or the cryogenic air separation principle with the development o a double-column rectiication system. Now it was possible to produce pure oxygen and pure nitrogen simultaneously:
Nitrogen with 7% O2
Pure oxygen Below the low pressure column a pressure column was installed. At the top o this column pure nitrogen was drawn o, liqueied in a condenser and ed to the low pressure column serving as relux. At the top o this low pressure column pure gaseous nitrogen was withdrawn as product while liquid oxygen evaporated at the bottom o this column to deliver the pure gaseous oxygen product. This principle o double column rectiication combining the condenser and evaporator to orm a heat exchanger unit is stil l used today.
Process air Single column
Liquid N2
Pure nitrogen
Condenser Pure oxygen
Process air Liquid with 35-40% O2 Double column
Condenser/reboiler The principle o double-column rectiication is characterized through the combination o condenser and evaporator to orm a common heat exchanger unit. By this means the rectiication is divided into two separate areas with dierent pressures.
1.5 1,5 bar
5,6 bar 5.6
Condenser reboiler
8
Column design. Any tray o the rectiication column ollows this principle: The O2 concentration o the boiling O2/N2 liquid mixture F is greater than the O2 concentration o the vapour D. A certain volume o liquid corresponding to the same volume o relux constantly lows rom the tray above into the liquid mixture below with an equivalent volume lowing down over a weir onto the tray below. The vapour Du coming rom the bottom tray penetrates the liquid mixture F and has a higher O2 content than the vapour mixture D. The O 2 concentration o the vapour Do rising rom the upper tray is in turn less than that o the vapour D. Thus a product rich in nitrogen is obtained in the head o the column and a liquid rich in oxygen in the sump o the column.
Do Fo D F Trays
Du Fu
Sieve tray column
9
Technological developments. Structured packings A signiicant progress in air s eparation technology was made in the mid-eighties. For the irst time, structured packings were used in cryogenic rectiication. Packed columns work according to a similar principle as sieve trays. The intensive contact between liquid and vapour required or the rectiication takes place on the huge surace area o the packing material. Liquid lowing down becomes increasingly richer in oxygen, whereby the ascending vapour is enriched with nitrogen. The main beneits o packed columns compared to tray sieves are a lower pressure drop and consequently a lower power consumption or the air separation process. This also set the basis or a new process or argon separation.
Packed column
10
Structured packings. waste
Pure argon production by rectification Modern process Within the so-called „ argon belly“ – the area in the low pressure column, where the argon concentration is at a maximum (approx. 10 %) – a gas stream is ed into the raw argon column or urther rectiication. The remaining oxygen in this gas stream is completely removed in the raw argon column which is also a packed column. Due to the very low pressure drop in the packing, it is possible to install a suicient number o “theoretical trays” required or the rectiication. In the adjoining pure argon column the remaining nitrogen is removed by rectiication and the pure argon is liqueied.
Argon 99.5% (free of oxygen)
(0.5% N2 O2 <1 ppm)
LAR 99.9996%
Pure argon production by catalytic converter Conventional process Beore the technological progress in the orm o structured packings was applied, a signiicantly more complex, alternative process or the production o pure argon had been used.
At that time, it was not possible to remove the oxygen in the raw argon column completely by means o rectiication. A percentage o 2.5 remained. This was due to a higher pressure loss through the trays which consequently resulted
in a lower oxygen concentration that was insuicient or a complete rectiication. An additional process step was required to remove the remaining oxygen by means o a catalytic converter using hydrogen.
Argon 99.5% (free of oxygen) (0.5% N2; O2 < 1ppm, H2, H2O, CO2, CO, CnHm)
waste
raw argon 97% (2.5% O2 0.5% N2 )
H2
LAR 99.999%
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Internal compression The internal compression (or liquid pumping) process allows or oxygen, nitrogen as well as argon to be compressed within the cold box by means o liquid pumps, to be evaporated and warmed up in heat exchanger sand to be inally supplied to the enduser at the required pressure. In order to evaporate and warm up the compressed liquid a countercurrent stream o nitrogen (or air) with a higher pressure than the required liquid is required or thermodynamic reasons.
M
For plants, which produce pressurized nitrogen, the booster and/or recycle nitrogen compressor also provide the countercurrent stream or evaporation. With this method a complex external oxygen compression is no longer required, thus plant operation and maintenance have become considerably easier and more reliable. Furthermore, the risk o dangerous hydrocarbon enrichment in the condenser is avoided because liquid oxygen is continuously withdrawn rom there and pumped into the heat exchanger where it evaporates. Compared to the external compression system a considerably higher level o saety has been achieved.
HDGAN 80 bar
Process Air 6 bar
HDGOX 100 bar
Heatexchanger -
.
RektificationRectiication/ column
Turbine
Oxygen pump
External compression (conventional) High pressure gaseous oxygen is required or the storage in pressure vessels or in high pressure gas bottles and or the application o oxygen in certain chemical processes. For oxygen storage pressures o up to 200 bar are us ed. For chemical processes such as partial oxidation o residual oil oxygen at a pressure o up to 100 bar is required. A signiicant increase in applications in the chemical and petrochemical industry and the high requirement o plants with high capacities lead to alternative concepts with regard to the risks involved with high oxygen pressures.
In particular, the compression o oxygen in external compressors created problems due to the reduction o ignition temperature o organic and inorganic materials with increasing temperatures (e.g. the ignition temperature o iron/steel is reduced by more than 100°C with a pressure increase rom 50 to 100 bar). Furthermore, the required saety measures or external compression have an impact on the overall investment costs.
Nitrogen compressor
M
M
HDGAN 80 bar M
Process Air 6 bar
HDGOX 100 bar Oxygen compressor
Condenser/ Evaporator
12
LOX
Advanced condensor/reboiler design Down flow condenser – Used instead o two-storied or multi-storied bath condensers – No condenser vessel – LOX recycle pump or relux is necessary – Oxygen pipework is necessary – Suitable ASUs with internal LOX compression – Suitable or large size ASUs – Energy saving solution
1.5 bara
GAN
5.4 bara
PLIN
M
LOX Product
Combi condenser – Combination o bath condenser plus down low condenser – No oxygen pipework – No LOX recycle pump in connection with Kr/Xe production – LOX recycle pump or relux is necessary without Kr/Xe production – Suitable or ASUs with internal LOX compression – Suitable or large size ASUs
LOX from LP column
PGAN
PLIN GOX+LOX
PGAN PLIN
PGAN
Linde multi-stage bath condenser This latest invention patented by Linde is using in principle a cascade o bath-type condensers. It combines all advantages e.g. power saving, improved wetting o the evaporator surace, urther improved saety and avoidance o LOX recycle pump. The Linde Cascade Condenser package needs less space, can be integrated into the LP column, leads to lower installation costs and enhances the design o very large mega-ASUs.
LOX Product
Top of Pressure column
PLIN
13
Supply chain. Transport of liquefied gas
Filling station
Gas production cente r
Cylinder transport
Pipeline Retailer
Cylinder transport
Transport of liquefied gas
On-site supply
Cylinder transport
Pipeline
Trieste, Italy
Rauha, Finland
Leuna, Germany
14
Cryogenic air separation process for the production of gaseous pure oxygen and nitrogen with internal compression and the production of liquid oxygen, liquid nitrogen and liquid argon Air compression
Air cooling and & puriication
Compression o ambient air by a multi -stage turbo compressor with intercoolers at a supply pressure o approx. 6 bar. Removal o dust particles by a mechanical air ilter at the inlet o the compressor.
Cooling o process air with water in a direct contact cooler and removal o soluble air impurities. Chilling o cooling water in an evaporation cooler against dry nitrogen waste gas rom the rectiication process.
Removal o CO2, water vapour and hydrocarbons rom the process air in periodically loaded/regenerated molecular sieve adsorbers.
air booster compressor
GOX
GAN
HP-heat exchanger heat exchanger molecular sieve unit
expansion turbine
liquid separator
impure GAN
direct contact cooler
evaporation cooler
air compressor filter AIR water pump air compression
air cooling & purification
coldbox
heat exchange
cryo pumps for int. compression
refrigeration & int. compression
15
Low temperature heat exchange
Cold production & internal
product compression
Cooling o process air in heat exchangers down to nearly liqueaction temperature by means o countercurrent with nitrogen waste gas rom the rectiication process.
Further compression o a si destream o process air by an air booster compressor. Expansion and cold production o the boosted air stream in an expansion turbine.
Expansion and liqueaction o a sidestream o the boosted air in a liquid separator. Evaporation and warming to ambient temperature o the pumped oxygen and nitrogen product in high pressure heat exchangers. Cryogenic rectiication o air
LOX
LIN
GOX
gaseous Oxygen
GAN
gaseous Nitrogen
LOX
liquid Oxygen
LIN
liquid Nitrogen
LAR
liquid Argon
Pre-separation o the cooled and liqueied air within the pressure column into oxygen enriched liquid in the column sump and pure nitrogen gas at the column top.
ATM
crude argon column
Liqueaction o the pure nitrogen gas in the condenser/reboiler against boiling oxygen in the sump o the low pressure column. Liqueied nitrogen provides the relux or the pressure column and (ater sub-cooling) or the low pressure column. Further separation in the low pressure column o the oxygen enriched liquid within the low pressure column into pure oxygen in the sump and nitrogen waste gas at the top.
pure argon column
Cryogenic rectiication o argon
Argon enriched gas rom the low pressure column is transormed into oxygen ree crude argon by means o separation within the crude argon column.
low pressure column Sub-cooler
Pumping back o liquid oxygen rom the crude argon column sump into the low pressure column. Removal o the remaining nitrogen in the pure argon column.
condenser/ reboiler
LAR
pressure column
rectification
cryogenic separation of pure Argon
16
Historical data. 1902 World‘s irst air separation plant or the recovery o oxygen.
1968 Introduction o the molecular sieve technology or pre-puriication o air.
1904 World‘s irst air separation plant or the recovery o nitrogen.
1978 Internal compression o oxygen is applied to tonnage air separation plants .
1910 World‘s irst air separation plant using the doublecolumn rectiication process.
1981 The „elevated pressure“ process is introduced.
1930 Development o the Linde-Fränkl process or air separation.
1984 World‘s largest VAROX® air separation plant with variable oxygen demand adjustment.
1950 First Linde-Fränkl oxygen plant without pressure recycle and stone-illed reactors.
1990 World‘s irst telecontrolled air separation plant with unmanned operation. Pure argon production by rectiication.
1954 World‘s irst air separation plant with air puriication by means o adsorbers.
1991 World‘s largest air separation plant with packed columns.
1992 Air separation plants produce megapure gases. 1997 Linde sets a new milestone in air separation history. Four nitrogen generation trains are provided, each individually constituting the largest air separation plant ever built. Nitrogen capacity 40,000 t/d. 2000 Development o the advanced multi-stage bathtype condenser. 2006 Largest TKLS contract in the history o air separation. Capacity 30,000 MTPD o oxygen or the “Pearl” GTL project in Qatar.
1902 5 kg/h
17
Reerences Air separation plants or the Pearl GTL project in RAS Laan, Qatar Customer Qatar Shell GTL Ltd. (QSGTL Ltd.) Design eatures Cryogenic air separation, ront-end air puriication with MS, elevated process pressure, double column system, internal compression o oxygen Capacity Total 30,000 MTD oxygen, ~860,000 Nm 3/h (eight trains) Scope o work Turnkey-lumpsum, basic and detail design, manuacture, delivery, construction, erection, commissioning and start-up Contract signature in 2006
2007 8 x 156,250 kg/h
Shell “Pearl” GTL project 140,000 bpd
18
Reerences. One of the largest steelworks in China supplied with oxygen, nitrogen and argon from Linde air separation plants. Customer: Wuhan Iron and Steel Company Plant
Status
Oxygen tpd
Nitrogen tpd
A/B
Other products
commissioned in 1975
690
600
-
C/D
commissioned in 1982
690
605
argon
E/F
commissioned in 1992
2,100
1,810
argon, krypton, xenon
G/H
commissioned in 2004
4,190
4,860
argon, krypton, xenon, helium, neon
I/J
commissioned in 2006
4,190
4,860
argon, krypton, xenon, helium, neon
19
The largest multi-train air separation plant in the world supplying nitrogen for enhanced oil recovery in Mexico. Customer: Pemex – Turnkey project – 5 trains in operation – Product capacity o 63,000 t/d nitrogen (17,500 t/d oxygen equivalent) – Comissioned in 2000
Designing Processes - Constructing Plants. Linde´s Engineering Division continuously develops extensive process engineering know-how in the planning, project management and construction o turnkey industrial plants.
The range o products comprises:
− − − − − − − − − −
Petrochemical plants LNG and natural gas processing plants Synthesis gas plants Hydrogen plants Gas processing plants Adsorption plants Air separation plants Cryogenic plants Biotechnological plants Furnaces or petrochemical plants and refneries
Linde and its subsidiaries manuacture:
− − − − − −
Packaged units, cold boxes Coil-wound heat exchangers Plate-fn heat exchangers Cryogenic standard tanks Air heated vaporizers Spiral-welded aluminium pipes
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