properties of natural gas - comenius project: energetic european
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Properties of Natural Gas
Knut-Olav Færaas
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Natural gas – different names
Naturgass: Energy rich gas found in underground oild fields, natural gas fieldsand in coal beds. Natural gas is normally found in a mix with heavier gases and liquids. The heavier components are separated on the oil rig or at a processingterminal.
LNG: Liquefied Natural Gas. Natural gas is cooled to liquid form at -162oC. Thisis done to facilitate bulk transport and storage. By doing this we are able to store 600 times the energi in the same volume compared to gas at standards conditions.
CNG: Compressed Natural Gas. Natural gas is compressed by increase ofpressure 2-300 Bar, also to facilitate bulk transport and storage. CNG has 2-300 times the energy in the same volume compared to gas at standard conditions.
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Tabell 3.1 Sentrale tekniske data for metan og etan
Gasstype Kjemisk
formel
Typisk andel i
naturgass, %
Kritisk
temperaturoC
Brennverdi,
nedre, kWh/kg
Antennelseste
mperatur, oC
Eksplosjonsgre
nser i luft,
vol.%
Metan CH4 85-95 -83 13.9 645 5.1-13.5
Etan C2H6 5-15 32 13.2 530 3.1-11.7
Tabell 3.1 Sentrale tekniske data for metan og etan
Gasstype Kjemisk
formel
Typisk andel i
naturgass, %
Kritisk
temperaturoC
Brennverdi,
nedre, kWh/kg
Antennelseste
mperatur, oC
Eksplosjonsgre
nser i luft,
vol.%
Metan CH4 85-95 -83 13.9 645 5.1-13.5
Etan C2H6 5-15 32 13.2 530 3.1-11.7
Gasstype Kjemisk
formel
Typisk andel i
naturgass, %
Kritisk
temperaturoC
Brennverdi,
nedre, kWh/kg
Antennelseste
mperatur, oC
Eksplosjonsgre
nser i luft,
vol.%
Metan CH4 85-95 -83 13.9 645 5.1-13.5
Etan C2H6 5-15 32 13.2 530 3.1-11.7
GasstypeGasstype Kjemisk
formel
Kjemisk
formel
Typisk andel i
naturgass, %
Typisk andel i
naturgass, %
Kritisk
temperaturoC
Kritisk
temperaturoC
Brennverdi,
nedre, kWh/kg
Brennverdi,
nedre, kWh/kg
Antennelseste
mperatur, oC
Antennelseste
mperatur, oC
Eksplosjonsgre
nser i luft,
vol.%
Eksplosjonsgre
nser i luft,
vol.%
MetanMetan CH4CH4 85-9585-95 -83-83 13.913.9 645645 5.1-13.55.1-13.5
EtanEtan C2H6C2H6 5-15 5-15 3232 13.213.2 530530 3.1-11.73.1-11.7
Properties of natural gas components
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Natural gass?
> Whats missing? What are the molecules called?
H
H H
HH H
HH
HH
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Important properties
> Combustible gas = combustible when mixed withair
> Propane is combustible in a 2-10% mix with air.
> Natural gas is combustible in a 4-14% mix with air.
> The cleanest of the fossil fuels
> Odourless and colourless
> The gas is originally odourlessand is for safety precautionsadded scent(Ethylmerkapthan).
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Natural gas properties
> Is the most applicable energy source today
> The cleanest fuel available today
> Able to compete with other energy sources
> Non-toxic – Lighter than air
> In Norway natural gas can quickly replace otherenergy sources which have greater impact onthe environment.
> Is a very safe and environmentally sound energysource
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Different phases of substances
Example: ice – water - steam
> Normal state – phase at normal pressureand temperature
> Energy gases are normally in gas phase
> A gas is not stable by form or volume
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Phase transitions
Drifter
Energigasser
Fast form
Væske
Gass
-
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Boiling point
> Boiling for a gas is the phase transition from
liquid to gas phase
Kokepunkt -162 °°°°CFordampningsvarme
Kokepunkt 100 °°°°CFordampningsvarme540 kcal/kg (2,26 MJ/kg)
Kokepunkt -42 °°°°CFordampningsvarme90 kcal/kg (0,4 MJ/kg)
LNG/naturgass VannPropan
Kokepunkt -162 °°°°CFordampningsvarme
Kokepunkt 100 °°°°CFordampningsvarme540 kcal/kg (2,26 MJ/kg)
Kokepunkt -42 °°°°CFordampningsvarme90 kcal/kg (0,4 MJ/kg)
LNG/naturgass VannPropan
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Vapor pressure - methane
> Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases.
> Methane has a steaper vurve than C3 and C4
> What is the pressure at –125°C?
Damptrykkurve for metan
0
5
10
15
20
25
30
35
40
-170 -160 -150 -140 -130 -120 -110 -100 -90
Temperatur, grd C
Metn
ing
str
ykk,
bar
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Mass and density
> Mass is the weight of all molecules in a
substance.
> Density is the mass devided by the volume
Fig. Samme antall molekyl (samme masse) – tetthet per volumenhet vil endres
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Relative density / Specific gravity
> Relative density is the ratio of the density relative to the density ofair or water
> Gas phase (temperature 15°C and atmospheric pressure)> Air = 1> Propane = 1,55> Natural gas = 0,6
> Liquids> Water = 1> LPG = 0,54> LNG = 0,45
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Explosion limits
Eksplosjonsgrenser for gasser i luft
Acetylen
Nafta
Butan
Propan
Etan
Metan
0 20 40 60 80 100 120
1
2
3
4
5
6
Volumprose nt gass i luft [%] UEL propane 10%
Butane 12%
Methane 14%
LEL propane 2%
Butane 2%
Methane 4%
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1 m3 Propane gas
Oxygen 22%
Nitrogen 78%25 m3 Exhaust
3 m3 CO2
4 m3 Water vapor24 m3 Air
19 m3 Nitrogen
27 kWh
Combustion