Natural Gas

• Natural gas is versatile.
• It can make electricity, heat homes and fuel transportation.
• It produces fewer emissions, and much less carbon than coal or oil.

Gas Power (Open Cycle Gas)

Open Brayton Power Cycle (Gas Turbine)

• 1-2: isentropic compression
• 2 3: constant pressure combustion process (heat addition)
• 3 4: isentropic expansion combustion products at atmospheric pressure
• 4-1: constant pressure heat rejection until temperature returns to initial conditions

Combine Cycle Gas Power Station

• Natural gas is burnt in a mixture of compressed air after being drawn through filters and compressed
• Combustion produces high pressure, high temperature combustion gases that drive a turbine connected to a generator.
  • Generator spins an electromagnet (~50 revolutions a second), inside copper wire conductors
• Exhaust gases are sent to the Heat Recovery Steam Generator to boil water producing superheated steam.
  • remaining exhaust gas is released through a large chimney\
• Superheated steam directed to a steam turbine that drives another generator
  • producing more electricity
• The steam powered generator increases the overall efficiency >
• Spent steam is condensed and cooled back to liquid water for reuse
• Another water stream is pumped through the condenser and cooled using cooling towers

Conventional natural gas

• Crude oil wells ( associated gas)
  • traditionally flared as waste gas (Nigeria)
  • gas cap above crude /dissolved in crude
• Natural gas from gas wells ( non associated gas)
  • little or no crude oil
  • typically produce only raw natural gas
• Condensate wells ( non associated gas)
  • produce raw natural gas & some low MW HC
  • liquid at ambient conditions

Leakage

Waste gas flaring unwanted associated gas

• ~140 150 billion cubic meters (bcm) of natural gas is flared into the atmosphere annually
• translates into 270 290 million tons of CO₂