1.introduction
DESCRIPTION
Gas process engineeringTRANSCRIPT
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Introduction
Gas Process Engineering
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Solar Energy
• Earth, Water, Air – oxygen-nitrogen • Volcanos, Oceans, Rain, Rivers, winds• Carbon Dioxide, water and Photosynthesis;
releases oxygen• life – trees, fish, animals, humans, waste
accumulation, fermentation, bio gas• Wood, Biomass,Carbohydrates• Peat, lignite, Coal, anthracite• Crude Oil and Natural Gas –hydrocarbons• Oxygen, Combustion – Carbon dioxide, water
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Crude Oil and Natural Gas
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Petroleum and Gas Fractions
•
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Oil & Natural Gas
• Oil and Natural Gas fields can be on-shore or off-shore and are generally in remote areas.
• Fluids produced from oil and gas wells generally constitute mixtures of crude oil, natural gas, salt water and solid particles.
• These mixtures are unsafe and very difficult to handle, meter, or transport to refineries and gas plants for processing.
• Hydrocarbon shipping tankers, oil refineries,and gas plants require certain specifications for the fluids that each receive.
• Also, environmental constraints exist for the safe and acceptable handling of hydrocarbon fluids and disposal of produced salt water.
• It is therefore necessary to process the produced fluids in the field to yield products that meet the specifications set by the customer and are safe to handle.
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Oil & Gas Resources
year OilX109 toe
GasX109 toe
1970 70 35
1980 85 70
1990 135 120
Proven Reserves 1000 m3 of NG = 0.85 toe (tons of oil equivalent)
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Oil vs Gas Marketed Production 1000 m3 of NG = 0.85 toe
(tons of oil equivalent)
year OilX109 toe
GasX109 toe
1970 2.5 0.8
1980 2.9 1.2
1990 3.2 1.7
2000 2.1
2010 2.6
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US Natural Gas Production, Trillion Cubic Feet per Year
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Natural Gas
• Natural gas produced along with oil is known as associated gas
• Natural gas produced from gas fields is known as non associated gas.
• Natural gas may contain liquid hydrocarbons (NGL) as well as undesirable components such as H2S,CO2, N2, water and water vapor.
• Field processing of natural gas implies the removal of undesirable components and recovery of higher hydro carbons before the gas can be sold in the market.
• The gas may undergo separation / condensation for the recovery of some hydrocarbon components.
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Gas CompositionSome Non-associated Gases
Component Frigg
(NOR)
Lacq
(FRA)
Kapuni
(NZL)
Uch
(PAK)
Methane 95.7 69 45.6 27.3
Ethane 3.6 3 5.8 0.7
Propane 0.9 5.3 0.3
Butanes 0.5 2.1 0.3
C5+ 0.5 0.2 0
N2 0.4 1.5 0.9 25.2
H2S 15.3 0
CO2 0.3 9.3 43.8 46.2
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Gas CompositionSome Associated Gases
Component Ekofisk
(NOR)
Parentis
(FRA)
Kirkuk
(IRQ)
Uthmaniyah
(SAU)
Methane 83.3 73.6 56.9 55.5
Ethane 8.5 10.2 21.2 18.0
Propane 3.4 7.6 6 9.8
Butanes 1.5 5 3.7 4.5
C5+ 1 3.6 1.6 1.6
N2 0.3 0.2
H2S 3.5 1.5
CO2 2 7.1 8.9
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Classification of Gases
Category 1 2 3 4
Standard Sweet dry gas
Sour Dry gas
Sweet wet gas
Sour wet gas
C2+ <10 <10 >10 >10
H2S <1 >1 <1 >1
CO2 <2 >2 <2 >2
% of fields
47 15.5 23 14.5
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% of Types of Natural Gas Available
Region Non Asso. Solution Gas Gas-Cap Gas
N.America 75.5 14.5 10
L.America 32.5 55 12.5
EU 73.5 15 11.5
CIS 94 2.5 3.5
Africa 61.5 19.5 9
Middle East 46 36 18
Aseana 82.5 11.5 6
Total 72 8.5 9
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Regions and Acidity factorsRegion Sour Gas
% of totalFrequency Of contam ination
H2S CO2 H2S+CO2
EU 9 7 93
CIS 10 62 38
Africa 5 100
Middle east
78 37 63
Aseana 75 6 94LAmerica 35 100
World 30 45
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Gas–Oil Separation Plant (GOSP)
• Crude oil–gas–water mixtures produced from wells are generally directed, through flow lines and manifold system, to a central processing and treatment facility normally called the Gas–Oil Separation Plant (GOSP).
• The first step in processing of the produced stream is the physical separation of the phases (oil, gas, and water) into separate streams.
• This takes place in two-phase gas–oil separators when the produced stream contains no water or three-phase separators when the produced stream contains water.
• The separators are used to relieve the excess pressure due to the gas associated with the produced crude and, consequently, separating it from the oil.
• Fig.1 describes further field treatment of each stream.
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An outline of the processing surface field operations
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Further treatment of Oil
• After separation also, Oil may contain water as emulsified water
• The presence of this salt water presents serious corrosion and scaling problems in transportation and refinery operations.
• Water remaining in the oil is known as the basic sediments and water (BS&W).
• A maximum of 1% BS&W and in some cases less than 0.5% BS&W is acceptable.
• The limit on the salt content of the remnant water in oils is usually in the range of 10 to 15 PTB (pounds of salt per thousand barrels of oil).
• Treatment involves emulsion treatment/dehydration and desalting processes.
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Crude Oil Specifications
Parameter Before Treatment After treatment
Water Emulsion 10%
Free Water 30%
0.3 vol% maximum
Salt 50,000-250,000 mg/L formation water
H2S 1000 ppm 70 ppm
Gas/vapor Pressure 600 scf/bbl crude oil 10 psig (4-5 psi RVP)
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Need for Gas dehydration• Water vapor is not objectionable as such;
however, the liquid or solid phase of water is very troublesome.
• This is experienced when the gas is compressed or cooled for the recovery of higher hydrocarbons.
• The liquid form of water accelerates corrosion of pipelines and other related equipment. It also reduces pipeline capacity, because it accumulates in low-point regions.
• Solid hydrates plug valves, fittings, and in some cases the pipe itself.
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Acid gas separation
• Acid gases basically imply hydrogen sulfide and carbon dioxide (H2S and CO2).
• Both H2S and CO2 are corrosive, especially in the presence of water.
• Hydrogen sulfide when combusted, produces sulfur oxides- atmospheric pollutants
• H2S could be commercially utilized to produce sulfur.
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Natural Gas Treatment
• It is desirable to remove hydrocarbons heavier than methane from natural gas, especially for fuel gasses.
• Heavier hydrocarbons, specifically C3+, on compression tend to condense,forming two-phase flow and thus creating pipeline operating problems.
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Natural Gas
Parameter
Natural Gas
Specification
Water Content 7 lbs/MMSCF (in a 1000-psia gas line)
Oxygen (air) 0.2% by volume
H2S 0.25–0.3 grain per 100ft3
(one grain¼64.799 mg)
Total Sulfur 20 grains per 100 ft3
Carbon dioxide 2% by volume
Liquefiable hydrocarbons 0.2 gal per 1000 ft3
Thermal heating value 1150 Btu/ft3
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Pipe Line Gas – Liquified Natural Gas