Natural Gas Usage and LNG Overview

Aug 19, 2024

Overview of Natural Gas Usage and Processing

Natural Gas Consumption in the U.S.

  • Daily Use: 80-85 billion cubic feet
  • Annual Use: ~30,000 billion cubic feet
  • Applications:
    • Cooking
    • Heating
    • Electricity generation
    • Manufacturing (fertilizers, pharmaceuticals)

Introduction to LNG (Liquefied Natural Gas)

  • Composition: Predominantly methane
  • Difference from LPG and NGL:
    • LPG: Primarily propane
    • NGL: General term for heavy hydrocarbons separated from natural gas
  • Volume Reduction: Liquefaction reduces volume by 600 times
  • Temperature of Liquefaction: -260°F

LNG Processing Chain

  1. Upstream Processing:
    • Separation from crude oil
    • Purification and dehydration
    • Removal of impurities (e.g., hydrogen sulfide)
  2. Pre-Treatment:
    • Remove heavy hydrocarbons to fractionation facility
  3. Liquefaction:
    • Uses cold boxes (heat exchangers)
    • Employs refrigeration cycle, Joule-Thomson effect

Cascade Refrigeration System

  • Multistage Process:
    • Each component (methane, ethylene, propane) has at least three stages for efficiency
  • Heat Integration:
    • Use of liquid propane to cool ethylene gas
    • Use of ethylene to condense methane
  • Efficiency: 93% or higher

LNG Trains and Storage

  • Types of LNG Plants:
    • Large units on waterways
    • Smaller peak shaving plants
  • Safety Considerations:
    • LNG vapors are heavier than air, posing explosion risks

Storage Design

  • Full Containment Tanks:
    • Inner tank: 9% nickel steel
    • Outer tank: carbon steel
    • Insulation to maintain cryogenic temperatures
    • Bottom heating system to avoid frosting

Safety Concerns in Storage

  • Stratification: Different density layers can lead to overpressure
  • Ball of Gas Phenomenon: Natural gas vapor due to heat leakage
  • Pressure Relief Systems: Essential to mitigate overpressure risks

Regasification Methods

  1. Submerged Combustion Vaporizer (SCV):
    • LNG heated through water bath
  2. Open Rack Vaporizer (ORV):
    • Sea water or river water used for heat exchange

LNG Transport

  • LNG Ships: 250-350 meters long, designed specifically for LNG
  • Leak Detection Technology: Ensures safe transport

Economic Considerations

  • Pipeline Costs: Higher for LNG due to low pressure maintenance
  • CNG: Less capital intensive equipment required

Conclusion

  • Climate Change: Increased use of LNG can reduce emissions and serve as a bridge to sustainable energy
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