WEEK 6 Flashcards
5 examples of impurities
• water
• sulfur species
• mercury
• NORM
• oxygen
Most gas produced contains water, which must be removed. Concentrations range from trace amounts to saturation.
water
If the hydrogen sulfide (H2S)concentration is greater than 2%–3%, carbonyl sulfide (COS), carbon disulfide (CS2), elemental sulfur, organic sulfides, and mercaptans may be present
sulfur species
Can damage the brazed aluminum heat exchangers
mercury
what means NORM
Naturally occurring radioactive materials
A significant amount of corrosion in gas processing is related to oxygen ingress.
oxygen
Natural gases commonly are classified according to their _____
liquids content as either lean or rich
Apart from natural gases being classified according to their liquids content, they also commonly classified according to the _____
sulfur content as either sweet or sour
Gas plant processing includes:
• Dehydration of gas
• Carbon dioxide or nitrogen recovery
• Upgrading subquality gas
• Helium recovery
• Liquefaction
_____ to meet a specification, reduce corrosion, and prevent gas hydrate formation.
Dehydration of gas
for enhanced oil recovery (EOR)
Carbon dioxide or nitrogen recovery
To make the gas marketable, the undesired diluents N2, H2S, and CO2 are removed.
Upgrading subquality gas
Natural gas is the primary source of helium.
Helium recovery
For easier storage and transportation
Liquefaction
Gas and liquids entering the gas plant typically pass through emergency shutdown valves.
Inlet receiving
• _____ are critical because downstream gas processing units rely on a continuous gas stream free of liquids, even when surges of liquid enter the plant.
• It is a gas–liquid separator sized to hold the biggest slug a plant will experience.
Slug catchers
A _____ refers to a large volume of liquid that suddenly flows through a gas pipeline or processing system.
slug
The _____ occurs in a slug catcher.
initial gas–liquid separation
Pressure plays a major role in gas processing, as it moves gas from the field, through the gas plant, and into the sales gas line. Plant process streams that undergo compression include the gas leaving inlet receiving.
Inlet Compression
To maximize liquids recovery, the inlet gas is typically at _____ when it enters the hydrocarbon recovery section.
700–1,000 psi
Compressor types:
• Reciprocating Compressor
• Oil-Free Rotary Screw Compressors
Accurately calculating compressor power and capacity is critical in natural gas processing to ensure ______
efficiency, reliability, and cost-effectiveness
_____ with liquids present require either polytropic or more rigorous thermodynamic methods to be used.
Screw compressors
_____ require knowledge of displacement volumes to compute flow rates. If accurate calculations are needed, equation of state methods should be used, along with information about the compressor performance provided by the vendor.
Reciprocating compressors
Gas treating involves removal of the ______ to sufficiently low levels to meet contractual specifications, to minimize pipeline corrosion, or to permit additional processing in the plant without corrosion or plugging problems.
“acid gases” carbon dioxide (CO2) and hydrogen sulfide (H2S) along with other sulfur species
_____ is highly toxic, and in the presence of water it forms a weak, corrosive acid.
Hydrogen sulfide
_____ is nonflammable and, consequently, large quantities are undesirable in a fuel. Like H2S, it forms a weak, corrosive acid in the presence of water
Carbon dioxide
Four scenarios are possible for acid gas removal from natural gas:
- CO2 removal from a gas that contains no H2S
- H2S removal from a gas that contains no CO2
- Simultaneous removal of both CO2 and H2S
- Selective removal of H2S from a gas that contains both CO2 and H2S
Because the concentrations of CO2 and H2S in the raw gas to be processed and the allowable acid gas levels in the final product vary substantially, no single process is markedly superior in all circumstances and, consequently, many processes are presently used.
Purification Process
The reactions are reversible. In the regeneration (stripper) column, heat is applied to break the bonds and release the acid gases.
solvent absorption - amines
Approximately 93% of the sulfur produced in the United States goes into production of sulfuric acid, which is used extensively in a wide variety of industrial products.
Sulfur recovery
The ______ is an industrial method used to recover elemental sulfur (S₈) from hydrogen sulfide (H₂S).
Claus process
claus process 1st stage
Combustion:
H2S + (3/2)O2 → SO2 + H2O
claus process 2nd stage
Catalytic:
2H2S + SO2 → 3S + 2H2O
In the claus process, the catalysts used are generally
alumina(Al2O3) or titania (TiO2)
Presently, there are no comparable processes for turning CO2 into useful products, although research is underway. The discussion here deals only with using the acid gases in EOR operations or sequestering by injection into a suitable underground reservoir.
Acid Gas Injection
