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Energy and the Environment

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  1. Introduction
  2. Transport Fuels
    5 Topics
  3. Energy Sources: Fossil Fuels
    8 Topics
  4. Energy Sources: Renewables
    10 Topics
  5. Electricity
    10 Topics
  6. Energy Sources: Nuclear
    6 Topics
  7. Demand Response
    6 Topics
  8. Energy/Emissions Policy
    15 Topics
  9. Energy Economics
    2 Topics
    1 Quiz
Lesson Progress
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  • 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
The cycle is shown for constant specific heats on P v, and T s diagrams

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


Are we underestimating natural gas emissions ?

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
Petroleum Plant with Flare Stack in Field, Aerial Shot, Oil and Gas Industry