6 (part 2) Flashcards
Water needs to be removed to reduce pipeline corrosion and prevent line blockage caused by hydrate formation.
Dehydration
Hydrate formation in natural gas processing occurs when water and light hydrocarbons (such as methane, ethane, and propane) form ______ under high-pressure and low-temperature conditions.
solid, ice-like crystalline structures
Water levels in natural gas can be reduced to the 10 ppmv range in a _____ in which the gas is contacted with a liquid that preferentially absorbs the water vapor.
physical absorption process
The solvent used for the absorption should have the following properties:
• A high affinity for water and a low affinity for hydrocarbons
• A low volatility at the absorption temperature to reduce vaporization losses
• A low viscosity for ease of pumping and good contact between the gas and liquid phases
• A good thermal stability to prevent decomposition during regeneration
• A low potential for corrosion
In practice, the glycols, ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG) and propylene glycol are the commonly used absorbents. _____ is the most frequently used because it offers the best compromise between solvent losses and initial cost.
TEG
Hydrocarbon recovery in a natural gas processing plant involves separating valuable hydrocarbons (such as natural gas liquids, NGLs) from raw natural gas to improve its _____
quality, meet pipeline specifications, and maximize economic value
The process ensures the removal of heavier hydrocarbons (ethane, propane, butane, and natural gasoline) while delivering dry sales gas.
Hydrocarbon recovery
A _____ system plays a major role in many hydrocarbon recovery processes, as it is used to cool the gas stream to recover a significant amount of C2+ and to lower gas temperatures as the gas goes into other stages of hydrocarbon recovery.
refrigeration
usually uses propane as the refrigerant and reciprocating or centrifugal types of compressors to move the refrigerants from the low- to high-pressure operating conditions
MECHANICAL REFRIGERATION (PROPANE-BASED)
involves extracting liquids like ethane, propane, and butane from natural gas
NGL RECOVERY PROCESS
When a natural gas has excessive nitrogen levels, three options are available:
- Gas blending to meet pipeline specifications
- Accepting a reduced price for the gas
- Removing sufficient nitrogen to meet sales specifications
Nitrogen (N₂) is often removed (rejected) from natural gas because it is an inert, non-combustible gas that reduces the energy value of the gas and can cause operational issues.
Nitrogen Injection
The most common methods for removing nitrogen from natural gas are:
• Cryogenic distillation
• Pressure swing adsorption (PSA)
• Membrane separation
_____ is the most efficient and widely used method for removing nitrogen (N₂) from natural gas when nitrogen content is high (above 6-8%). It uses low temperatures to separate nitrogen from hydrocarbons based on their different boiling points.
Cryogenic distillation
_____ is a valuable, non-renewable gas used in medical, industrial, and scientific applications. It is often found in natural gas reservoirs, especially those with high nitrogen content.
Helium (He)
Helium is recovered because:
• It is lightweight and non-reactive
• It is rare
• Demand is high, especially in medical, electronics, and scientific fields.
After nitrogen (N₂) is removed from natural gas using a Nitrogen Rejection Unit (NRU), helium (He) is recovered through cryogenic distillation. This process takes advantage of the large difference in boiling points between helium and nitrogen to separate them effectively.
Helium recovery process
_____ (also called “condensate” or “natural gasoline”) is a liquid hydrocarbon mixture that separates from natural gas when it undergoes pressure and temperature changes
Natural gas condensate
Processing the condensate involves two steps:
water washing and condensate stabilization
Water received with the inlet gas often contains methanol or ethylene glycol, added in the field to prevent ______
hydrate formation
After free water removal, the condensate goes to the _____, where remaining lighter hydrocarbons are removed, compressed, and recombined with the gas from the inlet receiver.
stabilizer
______ makes condensate safer for storage and transport.
Stabilization
Natural Gas Liquids (NGLs) are hydrocarbon components separated from natural gas during processing. They include:
Ethane (C₂H₆)
Propane (C₃H₈)
Butane (C₄H₁₀) & Isobutane (i-C₄H₁₀)
Liquid processing: NGLs
Sweetening (removal of H2S & CO2)
Dehydration
Fractionation
