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Industrial gases

Industrial TechnologyDr.-Ing. George Power Porto

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Industrial gases

02/04/2012 2Industrial Technology

Group of gases produced commercially for diverseapplications (metallurgy, oil refining, fertilizers,

medicine, etc.)

Manufactured by separation or synthesis processes,

and sold in gaseous (compressed), liquid or solid

state.

Important groups:

Air and its main components (O2, N2, Ar) Noble gases (He, Kr, Ne, Xe)

Other elementary gases (H2, Cl2, F2)

Compounds (NH3, CO2, N2O, CH4, C2H2, etc.)

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Earths atmosphere as a source of

industrial gases


Component Formula % vol.

Nitrogen N2 78,03

Oxygen O2 20,99

Argon Ar 0,94

Carbon dioxide CO2 0,03

Neon Ne 0,00123

Helium He 0,0004

Krypton Kr 0,00005

Xenon Xe 0,000006

Hydrogen H2 0,01

Methane CH4 0,0002

Nitrous oxide N2O 0,00005

Composition of atmospheric air at sealevel (dry basis)*:

*) Atmospheric air also contains variable amounts of water

vapor (humidity), ozone and suspended particles.

Average molar mass (g/mol):

97,2801,440003,094,390094,0

00,322099,002,287803,0

M

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History of cryogenic technology


In the past, the components of air wereconsidered permanent gases because they

couldnt be liquefied at high pressure.

In 1895 Carl von Linde developed and patented a

technical method for liquefaction of atmosphericgases and mixtures of gases like air.

The first air separation unit was built and put in

operation in 1902.

The original Linde process, modified withsubstantial improvements (regenerative cooling,

expansion turbines, cold box, etc.), is the basis of

industrialization of air and other cryogenic gases

(Tb

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Thermodynamic background


A gas can be liquefied only at atemperature below its critical point (O2

154.6 K, N2 126.2 K)

Necessary low temperatures for

liquefaction of air components (O2 90.2K, N2 77.4 K, Ar 87.3 K) can be reached

with application of the Joule-Thomson

effect (cooling due to expansion)

With the same principle other

industrial gases can be liquefied,

hydrogen and helium require pre-

cooling with liquid air.

Inlet valve

Outlet

valve

Compressor

200 bar

Heat exchanger

Expansion

valve

20 bar

Liquid air

Principle of the

Linde process

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Principle of cryogenic liquefaction


Compressor

Make-up

gas

Heat

exchanger

T

s

Expansion

valve

Scheme of Linde-Hampson process Temperature-Entropy diagram

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Process steps


Filtration of atmospheric air (dust and particleremoval)

Pre-compression and purification (removal of

water vapor, carbon dioxide, hydrocarbons) Main compression

Regenerative cooling

Expansion y liquefaction

Fractioning in double rectifier column

Separate purification of argon (optional)

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Generic Air Separation Unit (ASU)


GAR

GAN

GOX

PPU

(Mole

Sieve)

Rectifier

column

cold boxTruckloadingarea

LOX

LIN

LAR

Internalrefrigeration

orliquefier

coldbox

Main heatexchangers

cold box

Warm

Warm

ColdLocalpipelineusers

Airfeed Filter

Compressor Liquid

H2O

Gaseous

H2O, CO2, HC

Impurity removal

Argon

purifier

Vaporizer

Argon

Nitrogen

GAN

Oxygen

Partially

condensed air

Product

storage

Custom

ers

Product

compression

(By-) Product Gaseous Liquid

Oxygen GOX LOX

Nitrogen GAN LIN

Argon GAR LAR

Water H2O H2O

Carbon dioxide CO2

Hydrocarbons HC

Key:

f l d

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PFD filtration, pre-compression and

purification


CompressorFilterRefrigeration

unit

Separator

Molecular

Sieve

Air

6 7 atm

Heater

Waste nitrogen

from main heat

exchanger

Waste nitrogen

Purified air

to liquefaction

Condensed water

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Example PFD of LIN plant


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Examples


Largest air separation plant in Campeche (Mexico)

Capacity: 1.500 MMSCFD (50.000 t/d) of nitrogen

for enhanced oil recovery processes

Fractioning

column

Cold box

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Applications


Oxygen (100 million ton/y)

Metallurgy (production of iron, steel and other metals)

Welding and cutting (oxyacetylene torch)

Chemical processes

Oxidant for missile and rocket fuels

Medicine

Nitrogen Protecting inert gas (food industry, fuels)

Stainless steel manufacturing

Diode, transistor and integrated circuit manufacturing

Medicine, cryopreservation

Cryogenic coolant Argon

Inert gas for welding (MIG, TIG)

Lightning (incandescent lamps)

Protecting gas in food industry

Insulator (window panes)

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Hydrogen


Simplest, lightest and most abundantelement (75% of the universes mass,

and 93% of the solar system)

Represents only 0.12% of the earths

mass and 2.9% of the earths crust

and is never found in elementary

state

Together with carbon, oxygen and

nitrogen, hydrogen is an important

component of organic molecules

essential for lifeLarge gaseous planets like Saturn are

made mainly of hydrogen and helium

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Uses


More than 600 billion m3

(30 million tons) ofhydrogen are produced annually for:

Energy source: welding, rocket fuel, reaction and internal

combustion engines

Reducing agent for metallic oxides

Synthesis reactions (ammonia, methanol, hydrogen

chloride)

Petroleum refining and petrochemical industry

Liquid and gasous fuel manufacturing from coal

Food industry (hydrogenated fats, gas packaging)

Cryogenic technology

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Manufacturing methods


Hydrogen can be easily obtained byelectrolysis of water (concentrated KOH

soution for higher conductivity), however with

high energy costs:H2O (l) H2 (g) + O2 (g)

The most common industrial method is steam

reforming of natural gas (and other

hydrocarbons) :

CnHm + n H2O n CO (g) + (n+m)/2 H2 (g)

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Step 1: reforming


Methane (and other hydrocarbons) react with steam in asteam reformerat 800 900 C and 1.6 MPa, in ceramic tubes

impregnated with nickel catalyst and externally heated with

combustion of natural gas (endothermic reaction) :

CH4 + H2O CO + 3 H2 H = +191,7 kJ/mol

Conversion rate can be increased with a higher water vapor to

methane ration (up to 3:1), this also reduces undesired

products

Although reaction is favored by low pressure, higher

operation pressures (up to 20 atm) because of the desired

product state (pressurized hydrogen)

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Step 2: Shift reaction


More hydrogen can be obtained in the water gasshift reactor, by use of an iron oxide catalyst:

CO + H2O CO2 + H2 H =40,4 kJ/mol

This exothermic reaction is carried out in one or two

stages: a high temperature shift (HTS), at 350 C, anda low temperature shift (LTS), at 190 210 C

Carbon monoxide is converted in carbon dioxide,

which is easily separated during purification

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Step 3: Purification


Chlorine and sulfur must be removed from feed stream toextend catalyst life.

Product stream contains, apart from H2, H2O, CO2, CO, CH4 y

other impurities

Great part of H2O can be removed by condensation(compression and cooling)

CO2 can be removed by liquid absorption

In a final methanation step, residual traces of carbon oxides

are converted Modern plants use Pressure Swing Adsorption (PSA) to

produce high purity (99.99%) hydrogen.

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Flow diagram


Flow diagram for hydrogen production by steam reforming of

natural gasSource: http://www.alternative4energy.com

Steam reforming plant with HTS y PSA

in Texas City, TexasCapacity: 110.000 Nm3/h

Purity: 99.99% mol

Source: http://www.linde-process-

engineering.com/process_plants/hydrogen_syngas_plants/gas_generation/

steam_reforming.php

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Equipment detail


(Left) Modular reformerSource: Rttger Carbotech Engineering, 2003

(Right) PSA units

(Bottom) Skid with modular

reformer blockSource: Mahler IGS, 2003

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Carbon dioxide


Colorless and odorless gas, present inbiological processes and in the

atmosphere (385 ppm, increment

2 ppm/year)

Diverse uses:

Food industry (carbonated drinks,

fermentation, decaffeination, nutrient in

greenhouses)

Refrigerant (liquid, dry ice)

Technical uses: Lasers, polymers, fire

extinguishers, welding, semiconductor

manufacturing

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The global carbon cycle


Units: Flows GtC/a, Reservoirs GtCSource: GLOBE Carbon Cycle, 2007

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Production methods


Carbonate decompositionCaCO3 CaO + CO2

Fermentation

C6H12O6 2 CO2 + 2 C2H5OH Byproduct of hydrogen production

CH4 + 2 H2O CO2 + 4 H2

Combustion of carbon and hydrocarbonsCH4 + 2 O2 CO2 + 2 H2O

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Flow diagram


LIST OF EQUIPMENT1. Blower

2. CO2 generator

3. Stripping tower

4. Cooler/washer

5. Absorption tower

6. Exchanger

7. Cooler

8. Rich solution pump

9. Lean solution pump10. Recycler pump

11. Recycle cooler

12. Product cooler

Flue gas

Lean MEA solution

Rich MEA solution

CO2 vapor

Na2CO3 solution

Agua refrigeranteSource: The Wittemann Company, LLC

www.wittemann.com
http://www.wittemann.com/http://www.wittemann.com/

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Flow diagram (cont.)


KMnO4

WittFill

Cooling water

Activated carbon

Desiccant (silica gel)

Liquid CO2

Cold refrigerant

Hot refrigerant

LIST OF EQUIPMENT (cont.)

14. KMnO4 bubbler tanks15. Adsorption tower WittFill/activated carbon

16. CO2

compressor17. Intercooler

18. Aftercooler

19. High pressure precooler

20. Double CO2 drying tower21. CO2 condenser 22. Liquid CO2 stripper

23. Liquid CO2 reboiler

24. Liquid CO2 pump

25. Liquid CO2 storage tank

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Acetylene (ethine)


Is the simplest alkyne (C2H2) 80% of acetylene production goes in

organic synthesis reactions

The remainder 20% is used in

oxyacetylene torch (autogenous welding,

torch cutting T > 3300 C)

Highly inflammable and reactive, it must

be stored in acetone in pressurized bottlesfilled with porous material for stabilization

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Production methods


High-temperature hydrocarbon pyrolysis (2000 C) orin electric-arc furnace:

2 CH4 C2H2 + 3 H2

By-products: hydrogen, soot and other pyrolysis

gases

Reaction of calcium carbide with water:

CaC2 + 2 H2O C2H2 + Ca(OH)2

Obsolete method, high electrical energy

consumption in the production of calcium carbide,

product contaminated with raw material impurities.

Previously used gas lamps.

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PFD electric arc pyrolisis


CH4

Electric arc

reactor

Carbon

black (soot)

Cyclone Scrubber Electrostatic

precipitator

Water

Water with sootWater

Absorber Oil filter Condenser Phase separator

Oil

Oil

C2H2 with

pyrolysis gases

H2 withpyrolysis gases

C2H2 to

purification

83C

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Acetylene bottles

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