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2.0 Natural gas processing• natural gas is gaseous form of petroleum
mostly methane (C1), some ethane(C2), propane (C3), butanes (C4), pentanes (C5), hexanes (C6) and C7+
Reserves at Year End: Natural Gas: 1.6 trillion m3 (56.5 trillion ft3)
Production: Natural Gas: 484 million m3/d (17.1 billion ft3/d)
Prices: Natural Gas – Nymex Henry Hub $8,300 US$/MJ (8.77 US$/mmbtu)
Exports: Natural Gas: 289 million m3/d (10.2 billion ft3/d)Share of Primary Energy
Consumption (2000):Natural Gas: 30%
Crude Oil: 38%
Coal: 11%
Electricity – Hydro: 10%
Electricity – Nuclear: 3%
Other: 10%
Inlet Separators
Condensate Stabilization
Acid Gas Removal
Sulphur Recovery
Dehydration/Compression
Propane/Butane Processing
e.g. deep cut, turboexpansion
C5+
C3 , C4
condensate (C2-C5+)
C1 , C2, H2S, CO2 etc..
C1 , C2, H2O
H2S, CO2 HC, SO2, CO2
S
Simplified PFD for Sour Gas Processing Plant
Point of processing is to meet pipeline/storage/use specifications
Pipeline Specification (Typical)Oxygen 10 ppmNitrogen 3 %CO2 2-3% pipeline to 100 ppm for LPG plant feedH2S low as 4 ppm (0.25grains/100 scf) for pipeline higher for fuel gasCS2, COS, RSH 20 grains/100 scf
H2S, Sulfurs Pass Copper Strip, ASTM D-2420
CO2varies – 0.35 LVP of Ethanecontent 1000 ppm orless, depends on application
Natural Gas Liquid (NGL) Specifications:
Inlet Separation
Gas Sweetening
Dehydration
Acid Gas Injection
Condensate Stabilization
Dewpoint Control and
Compression
gasfromwells
C2-C5+
light gases
C5+
natural gasto market
acid gas
Simplified PFD for Sable Island
Inlet Sep
Condensate stabilization/ fractionation
Amine plant
dehy comp
Claus Plant
C1, C2
some C3-C4
+contaminantsacid gas
C1, C2
some C3-C4
+H2O
C1, C2
some C3-C4
SO2, CO2, CO etc..
S
C5+,C3-C4C3-C4
C5+
Sour Gas Plant in AB
2.1 Auxiliary Equipmenta) fired equipment- heat exchangers throughout plant, furnaces used in utility and SRU2 types (figure 8-2)i. direct fired- combustion gases heat process stream which is contained in pipesii. fire tube- combustion gases are surrounded by a liquid that either is used as a heat transfer
medium or is the process stream itself
application characteristicsdirect fired regeneration gas heaters more equip/controls
amine reboilers higher ηthermal
lower spaceforced/natural combust
firetube line heaters low heat dutyC3+ vaporizers skid mountgly/am reboilers forced/natural combustlow P steam gen less hot spot
b) HE- discussed in section 1.3 c) cooling towers- detail in section 1.3- purpose cool process water by ambient air achieved by maximize
evaporation of H2O in droplets exposed to maximum air flow over longest time (picture)
- mech draft – fans move air and natural draft – use density d) pumps/turbines- mostly centrifugal type due to lower cost, smaller space, and low
maintenance e) compressors/expanders- compressors used inlet and sales gas to boost pressure
+ displacementdynamicthermal
f) refrigeration- used in:
NGL/LPG recovery HC dewpoint control reflux condensation for light HC fractions LNG plants
- refrigerant type selected by T requirements, availability, economics, previous experiencee.g. natural gas plant may use C2 and C3 while due availability and economics olefin plant may use ethylene and propylene
i. mech refrigeration- most common- simple cycle of expansion, evaporation, compression, condensation
ii. Absorption Refrigeration- if low cost of n.gas, low level heat source, and electricity rates
from GPSA Handbooks
2.2 Inlet Separators• discussed fractionators in general, separator is like one stage of a
fractionator where adjust P of incoming gas to separate v and la) 4 major sections
A. primary section – sep main portion of free l by abrupt change in momentum or direction (nozzle)
B. secondary or gravity sectn – use gravity to enhance sep of entrained droplets
• gas moves at low velocity w/ little turbulenceC. coalescing sectn – coalescer (wire, mesh, vane elements, cyclonic
passage) or mist extractor• removes droplets can’t be sep by gravity by impingement on surface• limits l carryover into gas (<0.013 mL/m3) D. sump/l collection – recover l from ii and iii – provides surge V for
degassing a slug catching b) orientation• vertical – high v:l ratio or total gas V low• horizontal – used large V total fluids and large amounts of dissolved gas in l• spherical – occasionally used where high P and compact size needed, l volumes
are small• new are small valve types on platforms
from GPSA Handbooks
2.5 Fractionation•separate gas mixtures into individual products•in next section discuss bulk separation of NGLs from gas which differs from this discussion
•absorption -type units also used use trays/packinga)types of fractionators at gas plants•demethanizer – product bottom is C2+, OH is C1•deethanizer - product bottom is C3+, OH is C1/C2
commercial C3, C3/C4 (LPG), C4, C4/gasoline, natural gasoline
e.g. at gas plant in AB deethan run depending price butane•depropanizer•debutanizer
from GPSA Handbooks
from GPSA Handbooks
b) Product specs• material balance around column is 1st step in design calcs need to
assume product stream compositions• defined in terms of
% recovery of component in OH or bottom OR composition of component in either product OR specify physical properties (Pvap) in either product
c) design• in fractionation there usually 2 components which are key in separation
lightest component in bottom (LK) heaviest component in OH (HK)
• these components are adjacent to each other in volatility• in hand calcs make the assumption all components heavier than than
heaviest in OH are in bottoms