1 © Wärtsilä 01 October 2007 W50DF01V00BTM01A Rev. 01

00a Gas Properties & BehavioursWÄRTSILÄ W50DF

STANDARD ENGINE

2 © Wärtsilä 12.12.2006 taa001

Table of contents

– Gas general• Composition

– Natural gas

– Liquefied petroleum gas

– Different gases– Chemistry of gas

• Density• Ignition

• Burning

• Caloric values

– Liquefaction of gases– Safety

Source books:-Liquefied petroleum and natural gas Administrative stipulations and standardsHandbooks 58-1 and 58-2

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What is gas ?

� bìêçéÉ~å=råáçå=aáêÉÅíáîÉW

– Material is gas if it is in gaseous form at• 1 bar pressure (abs)

• +15°C temperature (59°F)

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Names of different gases

� cìÉä=Ö~ëÉë=~êÉ=åçêã~ääó=ÜóÇêç=Å~êÄçåë

– CnH2n+2

• NG = Natural Gas• LNG = Liquid Natural Gas• LPG = Liquid Petroleum Gas• CNG = Compressed Natural Gas• SNG = Synthetic Natural Gas

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Natural gas – Combination gas

– Natural gas is a combination gas and usually founded from gas field as finished product

– No need for further processing and it is finished product– Gas field are more or less similar as crude oil fields– All fields has its specific characteristic for both amount of gas

and quality – Even each drilling hole can have own specific characteristic– By mixing different gases from different wells, each production

field has typical composition and constant quality of that area gases

– Liquefied particles, condensates and crude oil will separate outfrom the gas and will be sent to further processing

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Natural gas – Combination gas

– On the gas field gas particles will be filter off and compressed to transportation pipeline

– Sulphur compound must be separate out from the gas before transportation pipeline

– From some fields can be recovered directly Liquefied petroleum gases and similar hydro carbon gases. These gases can be further process to Propane, Butane etc. of use without treatment for raw material of chemical industry

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Natural gas from Siberia

– The gas from Russia to Finland is 98% methane. The rest of gas is Ethane, Propane and small amount Nitrogen, Carbon oxide and Oxygen

– The gas has homogenous quality and doesn’t include mechanical impurities or condensates

– The imported gas to Finland is origin from West-Siberia. The field is locating in permafrost area approximately latitude of artic circle. Gas is locating in 1000-3000 m deep in earth surface

– The gas from Siberia has very high Methane content and low Nitrogen content. E.g. Dutch has 14% Nitrogen.

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Natural gas from Siberia

– The Siberian gas is not the best raw material of chemical industry

– Hydrogen from natural gas can be used e.g. in oil industry raw material for hydro cracking supply or hydrogen peroxide (H2O2)

Siberia Germany USA Holland Norway NorwayUrengoi Goldenstedt Kansas Gronningen Ekofisk Troll

% % % % % %

Methane CH 4 97,9 88,0 84,0 81,3 85,8 93,2

Ethane C 2H6 0,8 1,0 6,7 2,8 8,3 3,7

Propane C 3H8 0,2 0,2 0,3 0,3 2,8 0,4

Butane C 4H10 0,1 0 0 0,4 1,2 0,5

Nitrogen N 2 0,9 10,0 8,3 14,2 0,4 1,6

Carbon dioxide CO 2 0,1 0,8 0,7 0,9 1,5 0,6

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Use of methane

– The best use of methane is gas fuel. The methane is the best fossil fuel of all, because of its chemical composition.

– Because of methane burning properties it has exceptional wide using range from small stoves to large power plants

– Methane is suitable for process where exhaust gas will be supplied of touch directly to product

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Production of liquefied petroleum gas

– Liquefied petroleum gas will be get directly from gas fields as natural gas or crude oil refinery by-product

– The crude oil is a mixing of different hydro carbons– The chemical and physical methods are used for separation and

production of products. The most typical method is distilling– During the cracking process crude oil will be separated according

separate boiling points of hydro carbons

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Use of liquefied petroleum gases

– The most common liquefied petroleum gas is propane (C3H8). Propane is used similar as natural gas

– Liquefied petroleum gas is easier to transport and store as natural gas

– Liquefied petroleum gas bottles are filled with Propane– Butane (C4H10) is also used in industry processes The boiling point of

Butane is -1ºC, and therefore it is almost useless in normal use– Once use lighter gas is mixing of Butane and Propane

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Liquefied petroleum gases

– Liquefied petroleum gases are mixes of several hydro carbons. Main components are C3- and C4-hydro carbons

– Propane products are:• Components are propane (C3H8) also propene (C3H6)

• Also ethane can be added and C4- and C5-hydro carbons. Depend of trade marks

• Essential for gas blend is that gas properties mainly vapour pressure will follow Propane vapour pressure

• The vapour pressure of Propane is allowed to be at +70 ºC temperature maximum 31 bar abs. ( EU-directive 711/93)

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Liquefied petroleum gases

– Butane products are:• Components are mainly n- and I-butane

(C4H10)

• Depend of quality criteria Butane and mentioned heavier hydro carbons can be mixed to Butane.

• Typical the vapour pressure of Butane is 3,5-4,0 bar at +40 ºC temperature (dynamic pressure)

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Brand marks of liquefied petroleum gases

– Even liquefied petroleum gases are mixed from other products thecommon name of gases are Propane and butane or C3 –hydro carbon and C4 –hydro carbon

– Also mixing of Propane and Butane can be used. Then mixed gas 50/50 means volumetric concentrations of Propane and Butane

– The abbreviation “LPG” is common name of liquefied gases– Common abbreviations of natural gases are : CNG and LNG– Liquefied petroleum gases brand marks are not followed coherent

trade marks of natural gases

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City gas

– Earlier used process of gasification of coal. Mainly hydrogen– Gasoline or liquefied petroleum gas replaced coal. Both of

Gasoline and coal are still used as raw material for city gases.– Direct distribution of natural gas has replaced mainly city

gases– Still the name of “city-gas” or “town gas” is used– Properties of city gases are different as natural gases and

liquefied petroleum gases. Following properties are different:• Explosive levels (UEL, LEL)

• Combustion velocity• Wobbe-value

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Bio gases

– Bio gas is the product of micro biological process, there organic waste will rotten in oxygen-free space

– Bactrian will product methane or acids and carbon oxides– LFG (landfill gas) is collected from landfills and sewages cleaning

stations– Bio gas includes Methane 45-60 %, carbon oxides 35-45 % and also

small amounts hydrogen, solvents and fatty acids– Normally the caloric value of bio gas is approximately 5,0…5,5

kWh/m3n (Natural gas 10 kWh/m3n)– The density of bio gas is approximately 1,1 kg/m3n

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Hydro carbons

– All compounds which has only carbon (C) and Hydrogen (H) are so call hydro carbons

– Paraffin• The most common hydro carbon molecule is Methane

– CH4 methane– C2H6 ethane CH3 - CH3

– C3H8 propane CH3 - CH2 - CH3

– All above gases following formula CnH2n+2

– The generic name of Paraffin hydro carbons is saturated hydro carbons

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Hydro carbons

• Olefins

– If earlier page mentioned carbon atoms are going to regrouping together with “double unions”, will format new hydro carbon group, so call Olefins (Unsaturated hydro carbons)

– C2H4 ethane CH2 = CH2

– C3H6 propane CH2 = CH - CH3

– Olefins are following the formula CnH2n

– Olefins can be polymerized with Influence of temperature. Then liquefied compounds will be appeared from gas

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Density of gas

– Molecular mass distribution• The density and specific gravity depend on pressure and temperature

of gases

• In order to volumetric flows and densities can be between comparable the pressure and temperature must be agreed constant

• In Finland the standard values are gas absolute pressure 1,01325 bar and temperature 0 ºC

• In Russia the standard temperature is 20 ºC

• In USA the standard temperature is 15,6 ºC (60 ºF)

• According the Avogadro's law all gases includes in same pressure and temperature and equivalent volumes same amount of molecules

• The volume of one mole in standard conditions is 22,414 litres for all ideal gases

• The density of gas can be calculated by dividing mole weight of gas with volume of mole 22,414 litres

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Density of gas

– Relative density• Usually gas densities will

be compared to air density

• According this the gas behaviours can be evaluated during leakages and nozzle flows

• Relative density will get by dividing gas density by air density

• The density of air is in normal condition 1,293 kg/m3n

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Ignition borderlines and temperatures

– Typically gas fuels has narrow ignition area and relative high ignition temperature

– Natural gas ignition is more difficult than liquefied petroleum gas ignition, because its density is only half of air density

– Ignition of natural gas is only possible if gas is mixed to air minimum 5 %-vol and maximum 14 %-vol

– The ignition are will be wider if temperature will increase. E.g. ignition area of Methane is 3-20% at 500 ºC. The influence of temperature is smaller with Propane

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Ignition borderlines and temperatures

– The flashing point of natural gas is 600 -650 ºC. After this temperature the burning will continue regardless of gas/air mixing

– Regardless of high ignition temperature of gases the ignition spark energy is rather small (ignition areas must be on use)

IN AIR Lowe r Highe r Approximate79% -N2 borde rline borde rline ignition te mpe rature21% -O2 % % °C

Hydroge n 4,1 72,0 570

Carbon monoxide 19,6 73,0 610

Me thane 5,0 14,0 630

Ac e tyle ne 2,3 82,0 305

Propane 2,5 9,0 480

Butane 2,0 8,0 440

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Burning air/gas mix

Rich

Lean

Gas amount

inflammability

LEL

LEL UEL

LEL=LowerExplosiveLevel

UEL=UpperExplosiveLevel

UEL

Flammablemix

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Ignition borderlines and temperatures

Rich

Lean

Gas amount

inflammability

5 % vol

Methane CH4 / air mix

LEL UEL

LEL=LowerExplosiveLevel

UEL=UpperExplosiveLevel

15 %-vol

Flammablemix

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Gas content / inflammability

100 75 50 25 0

0 25 50 75 100

% Air

% Gas

H2 LEL UEL4 75

100 75 50 25 0

0 25 50 75 100

% Air

% Gas

CH4 LEL UEL5 15

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Lower Explosive Level (LEL)

– The lower explosive level has divided to percentual parts– E.g. Methane (LEL 5 % gas in air)

• Alarms controlled LEL 20 % (gas content in air 1 %)

• Trip usually LEL 60 % (gas content in air 3 %)

Gas content i n ai r (%) Content (ppm) LEL (%)

1 10000 20

2 20000 40

3 30000 60

4 40000 80

5 50000 100

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Methane/Wärtsilä/alarm levels

5 % vol

20%10%

1 % vol

0,5 % vol

100% LEL

Metaani / Wärtsilä / Hälytysrajat

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Perfumed gases

– The perfume of gas is (THT)– THT = C4H8S– 0,05…0,2 % minimum odour level– Will increase the level of sulphur up to 5,5 mg/m3

– Fuel without sulphur is 100 mg/m3

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Inert gases

– The ignition quality of gases can be changed by change air content– More oxygen will make ignition are more wider– Methane air mix can ignite if Methane content is 5 - 60 %. Propane

similar area is 2 - 55 %– Gases, Methane and Propane will lose their ignition quality if inert

gases, carbon oxides or nitrogen will be added to air– If air (21 % oxygen and 79 % nitrogen) will be mixed to nitrogen 37

% (air portion will be 63 %), methane can’t ignite. Air portion of mix will be then approximately 13 %. This number is so call oxygen index

– Oxygen index in propane is approximately 12 %. The idea of Inertis to be sure that the gas is not flammable. The maximum air content can be 10 % in atmosphere there used fuel will be mixed

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Burning of gases

– During the burning process of hydro carbons• hydrogen join to oxygen and forms water• carbon join to oxygen and forms carbon oxides

– Methane: CH4 + 2O2 →→→→ CO2 + 2H2O1 mol + 2 mol →→→→ 1 mol + 2 mol16 g + 64 g →→→→ 44 g + 36 g1 kg + 4 kg →→→→ 2,75 kg + 2,25 kg

– Propane: C3H8 + 5O2 →→→→ 4H2O + 3CO2

– Butane: C4H10 + 6,5O2 →→→→ 5H2O + 4CO2

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Minimum air demand for 1 kg methane

– Air composition• Oxygen 20,9 vol-% (=23,1 p-%)• Nitrogen 79,1 vol-% (=76,9 p-%)

• From this amount is 4 kg air and 13,3 kg nitrogen• Volumetric flows

– 1 m3 (0,72kg) methane needs air to theoretic burning:

• From this amount is 2 m3 air and 7,6 m3 nitrogen

)(/)(3,17231,0

4min methanekgairkg

kgL ==

33

6,9/293,1

3,1772,0 m

mkg

kg =×

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Minimum air demand

– Combustion gas will be carbon oxides and water steam. When burning 1 m3 methane by using theoretical air amount will get:• Carbon oxides 1 m3 (=2,0 kg)• Water steam 2 m3 (=1,6 kg)

• Additional nitrogen in exhaust gas from burned air 7,6 m3 (=9,5 kg)

– Complete burning can’t be newer reached if additional air amount will not be supplied to burning process

– Air formula λλλλ (Lambda) is ratio between real air amount and theoretical air amount

– Lambda must be minimum 1,1…1,3 in gas burning• Excess oxygen will be found from exhaust gas

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Minimum air demand

– It is impossible to evaluate exhaust gases according flame colour or shape

–Exhaust gas (burned fuel) must be evaluated always according excess air of exhaust gas or carbon monoxide content of exhaust gas

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CO2 in exhaust gas

– The maximum content of carbon dioxides will be reach when lambda will be one

– The maximum content of CO2 in natural gases is 11,7 % measured from dry exhaust gas or 9,5 % from wet exhaust gases

– Similar numbers in propane are 13,8 % and 11,6 % in butane 14,1 % and 12 %

– The carbon dioxide formation of gas burning is less than oil burning and approximately half of coal burning

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SULPHUR DIOXIDE EMISSIONS

0 200 400 600 800 1000 1200

NATURAL GAS

PEAT

LFO 0,2%-S

HFO 1,0%-S

HFO 2,1%-S

COAL+desulph.

COAL 0,8%-S

mg/MJ

Emissions

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Moisture of exhaust gases

– The exhaust gases of natural gas burning are more moisture than liquefied petroleum gas or oil burning exhaust gases

– This is because of high hydrogen content of the methane– This means that exhaust gases of methane burning dew

point is high – With Lambda number one the dew point of exhaust gases is

approximately 60 ºC – Liquefied petroleum gases the similar dew pints are 55 ºC

(butane) and 56 ºC (propane)– The LFO dew point is approximately 50 ºC

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Caloric value

– All fuels have to caloric values• Higher- so call calorimetric value,

Ho (gross caloric value)

• Lower – so call effective value, Hu (net caloric value)

– Lower value doesn't calculate steam energy of exhaust gases

– Difference between lower and higher caloric value is big in natural and liquefied petroleum gases

Effe c tive , lowe r c alorific valueMJ/m 3 MJ/kg kWh/m 3 kWh/kg

Natural Gas 36,0 49,3 10,0 13,70,73 kg /m3

City Gas 16,9 25,3 4,7 7,00,67 kg /m3

Propane 93,0 46,1 25,8 12,82,01 kg /m3

Butane 123,0 45,6 34,2 12,72,71 kg /m3

HFO * 40,6 * 11,30,96 kg /dm3

LFO * 42,7 * 11,90,85 kg /dm3

Coal * 25,5 * 7,1

Pe at * 7,1-12,5 * 2,0-3,5

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Liquefaction of gases

– Light hydro carbons have low boiling point, therefore the liquefaction of these gases needs• cooling • pressurizing

• or both

– In gas form the storing of gases is almost impossible or needs a lot of space or high pressures

Gas1 m3

0,72 kg CH4

0 ºC100 cm

Liquid1,7 l0,72 kg CH4

-162 ºC

12 cm

atmospheric 1000 litres

at 4 bar 200 litresat 40 bar 22.3 litres

at 300 bar 2.9 litres

liquefied 1.7 litres

Storing 0.72 kg natural gas

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The critical temperature

– The critical temperature is essential to know when Liquefaction gases – The critical temperature means the highest temperature, where gas can

be liquefied. The critical pressure is equivalent pressure– The critical temperature of methane is approximately -82 ºC and critical

pressure approximately 46 bar• In real life this kind of combination will be difficult to use

– Easiest is to cool methane directly to -162 ºC temperature, when the absolute vapour pressure of methane will be 1 bar (normal ambient pressure)

Methane Ethane Propane Butane

Crit ical temperature -82 47 97 152°C

Crit ical pressure 46 32 42 38bar

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Vapour pressure of liquefied petroleum gases

– Liquefied petroleum gases are easy to liquefy under of vapour pressure

– The critical temperature of propane is +97 ºC, so temperatures during store and handling are under of this

– When store gas in closed tank, the vapour pressure is depend only on gas composition and temperature

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Vapour pressure of liquefied petroleum gases

– Because of huge thermal expansion of liquefied petroleum gas, do not fill tank up to top

– When gas space will left to the tank, increase gas pressure onlyaccording gas vapour pressure

– If the tank will be filled up to top (full filling) one degrees increase of centigrade will increase the tank pressure 7 bar.

– For this reason e.g. tanks are allowed to fill only 80 % of total volume

– All parts of liquefied petroleum gas pipelines that can be closed by valves must be equipped with safety valves (thermal safety valves)

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Vaporization of liquefied petroleum gases

– Liquefied petroleum gases can move from liquid to gas by free evaporation, lowering pressure or heating it

– If gas will be used directly from tank or bottle gas space the energy of evaporation can be get from liquefied petroleum gas own caloric capacity

– Can be used only for propane– If temperature is under 0 ºC the butane will not evaporate– Natural evaporation method can’t be used for mixed gases,

because the composition of evaporated gases will be change

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Vaporization of liquefied petroleum gases

– The composition of mixed gas will not be changed if gas will be taken from tank as liquid and will be evaporated with separate evaporator of heat exchanger

Me thane Ethane Propane Butane

Boiling po int -162 -88 -42 -1°C

Evaporation he at 549 540 448 404(at c ritic a l te mp)

kJ/kg

De ns ity as gas 0,717 1,36 2,01 2,70kg /m3 (n)

De ns ity as liquid 421 546 585 600kg /m3

Re lative vo lume 587 402 291 222(gas /liquid)

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Handling of liquid methane

– The store of liquid methane at -162 ºC temperature needs effective cooling system (liquation by compressing the gas) and good insulation of gas tank

– To avoid high pressure of gas tank (because of increase of gas temperature) will gas be taken out from gas space of the gas tank. The liquefied petroleum gas inside of tank will evaporate and full fill the emptied space. For this will be needed energy and the temperature of gas tank will decrease

– If the need of gas use will exceed the amount of evaporated gas, must the consumption of gas be taken out as liquid

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Handling of liquid methane

– The energy is needed to evaporate methane is considerable big, because the temperature is low (-162 ºC ). Heating up the methane temperature up to +25 ºC the needed energy will be 910 kJ/kg, from there evaporation portion will be approximately half 510 kJ/kg

– The waste of liquid natural gas transportation chain is approximately 20 %• 15 % Liquefaction of natural gases

• transportation 5 %

• Final evaporation 2 % Storage tank

Evaporator

Freely evaporated gas

Evaporated gas

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Safety

– Natural gas is flammable and highly explosive in suitable conditions

– Natural gas is lighter than air -opposite to liquefied petroleumgases propane and butane

– Natural gas is odored to detect leakage

– Burning of natural gas gives water and carbon dioxide

– Incomplete burning gives toxic carbon monoxide

– Risk of freezing hazard– Safety clothes

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Aspects affecting the spreading of natural gas

– Gas pressure– Depth of transmission pipes– Placement of the pipes– State and property of the ground and soil– Terrain– Weather conditions– Placement in building and way of

construction

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Leakages

– Detecting leakage• By detector: fixed or portable

• By odour

• By sound

– Actions to follow detection• Main closing valves• Contact person in charge

• Alarm

– Contact local alarm centre and owner

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Action plan for emergency situations

– General• What is an ‘emergency situation’

– E.g. level of leakage• What is not considered as an ‘emergency

situation’• Action plan?

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Action plan for emergency situations

– Natural gas leakage in transmission pipes• Large quantities of gas (max 54 bar)

• Large risk zone for explosion• Not odored yet

– Natural gas leakage in distribution pipes and gas supply system outdoors• Does not necessary lead to an emergency

situation

• The amount of gas is usually smaller compared to a leakage in a transmission pipes, due to lower pressure (8 bar)

• Detectable by smell

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Action plan for emergency situations

– If the gas is not burning yet• Main valves• Only trained persons may restrict leakage

• Report the leak to the local alarm centre

• Stay away!

– If the gas is burning already• Gas fires should be put out by closing the valves

• Don’t extinguish the fire!

– A controlled fire is better than uncontrolled gas leakage!• Rescue people in danger

• Seal off the area

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Gas leakage in buildings

– Immediate danger of explosion!

– Shut the valves– Prevent the gas from igniting

– Evacuate

– Ventilate

– Report to the person in charge and alarm centre

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Health hazards

– Natural gas is non-toxic, but displaces air and may cause suffocation

– Small amounts inhaled (breath)-> no symptoms– Large amounts inhaled causes sleepiness, drowsiness or illness– Carbon monoxide, CO

• odourless, tasteless and heavier than air

• first symptom: cheerful feeling• second symptom: paralyzing

• third symptom: death

• more than 90% of fatal natural gas accidents are caused by CO