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