Petroleum Refining Chapter 4: Acid Gas Treatment
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Questions and Answers

What is the primary function of glycol in the glycol dehydration process?

  • To lower the boiling point of water
  • To increase the pressure of the natural gas
  • To absorb water vapor from the gas stream (correct)
  • To strip natural gas of its oil content

    • What happens to the glycol particles after they absorb water from the wet gas?

  • They become lighter and rise to the top of the contactor
  • They become heavier and sink to the bottom of the contactor (correct)
  • They remain unchanged and continue to circulate
  • They are removed from the system and replaced with new glycol

    • What is the purpose of the specialized boiler in the glycol dehydration process?

  • To vaporize the glycol solution
  • To vaporize only the water out of the glycol solution (correct)
  • To heat the natural gas to increase its pressure
  • To cool the natural gas to increase its density

    • What is the boiling point of glycol?

    <p>400°F</p> Signup and view all the answers

    What is the primary method of dehydrating natural gas using adsorption?

    <p>Solid-desiccant dehydration</p> Signup and view all the answers

    What is the purpose of the adsorption towers in solid-desiccant dehydration?

    <p>To allow the wet gas to pass through and absorb water</p> Signup and view all the answers

    What is typically used as a solid desiccant in solid-desiccant dehydration?

    <p>Both A and B</p> Signup and view all the answers

    Why is it possible to remove water from the glycol solution?

    <p>Because of the boiling point differential between glycol and water</p> Signup and view all the answers

    What is the primary function of a turbo-expander in an expander cycle liquefaction system?

    <p>To chill the incoming natural gas stream and liquefy a small portion of it</p> Signup and view all the answers

    What is the result of passing high-pressure natural gas through a turbo-expander?

    <p>A large decrease in pressure of the gas, resulting in a decrease in temperature</p> Signup and view all the answers

    What percentage of the incoming natural gas stream can be liquefied in an expander cycle?

    <p>No more than about 10%</p> Signup and view all the answers

    What is the primary component of a mixed refrigerant cycle?

    <p>A single refrigeration loop with a mixture of refrigerants</p> Signup and view all the answers

    What is the purpose of partially flashing the liquid at each pressure reduction step in a mixed refrigerant cycle?

    <p>To produce a colder liquid and vapor</p> Signup and view all the answers

    What is the significance of a separate refrigeration loop with propane as the refrigerant in a mixed refrigerant cycle?

    <p>It is used to pre-cool the gas feed before introducing it into the mixed refrigerant system</p> Signup and view all the answers

    What is the primary concern when acid gases are present in natural gas?

    <p>They cause corrosion in pipelines and equipment.</p> Signup and view all the answers

    What is the capacity of a typical LNG tanker?

    <p>Up to 33 million gallons of LNG</p> Signup and view all the answers

    What is the purpose of an Acid Gas Removal Plant?

    <p>To separate hydrogen sulfide from natural gas.</p> Signup and view all the answers

    What is the result of mixing acid gases with water?

    <p>They create a toxic and corrosive solution.</p> Signup and view all the answers

    What is the estimated impact of an explosion on a LNG tanker?

    <p>Similar to a small nuclear explosion</p> Signup and view all the answers

    What is the primary use of hydrogen sulfide in a refinery?

    <p>As a fuel in the refinery process.</p> Signup and view all the answers

    What is the minimum sulfur recovery required by regulations?

    <p>99% or more.</p> Signup and view all the answers

    What is the purpose of the modified Claus process and the Shell Claus Off-Gas Treatment (SCOT) process?

    <p>To recover sulfur from acid gases.</p> Signup and view all the answers

    What percentage of recovered sulfur is produced by the Claus process?

    <p>90 to 95 percent</p> Signup and view all the answers

    What is the purpose of the SCOT process?

    <p>To remove sulphur compounds from Claus tail gas</p> Signup and view all the answers

    Which of the following catalysts is more favourable in converting COS and CO2 to elemental sulphur?

    <p>Alumina catalyst</p> Signup and view all the answers

    What is the overall sulphur recovery efficiency of the SCOT process?

    <p>99.9%</p> Signup and view all the answers

    What is the purpose of acid gas treatment processes?

    <p>To obtain sweet, dry natural gas by removing acid gases and reducing water vapor</p> Signup and view all the answers

    Which of the following compounds brings problems in Claus operations?

    <p>CS2</p> Signup and view all the answers

    What is the reaction that occurs in the burner of the Claus process?

    <p>2H2S + 3O2 → 2H2O + 2SO2</p> Signup and view all the answers

    What is the type of absorption used in Amine Gas Treating?

    <p>Chemical Absorption</p> Signup and view all the answers

    What is the primary purpose of the RECTISOL process?

    <p>To physically absorb undesired compounds from the gas</p> Signup and view all the answers

    What is the effect of excess moisture in natural gas pipelines?

    <p>It can form hydrate compounds and cause blockages</p> Signup and view all the answers

    What is the purpose of a Gas Dehydration Plant?

    <p>To reduce the corrosion problem and prevent hydrate formation</p> Signup and view all the answers

    What is the role of the solvent in the RECTISOL process?

    <p>To physically absorb undesired compounds from the gas</p> Signup and view all the answers

    What is the purpose of molecular sieves in the RECTISOL process?

    <p>To physically adsorb H2S and CO2</p> Signup and view all the answers

    What is the effect of pressure drop on the gas stream in natural gas pipelines?

    <p>It can cause moisture to freeze and result in blockages</p> Signup and view all the answers

    What is the role of diethylene glycol (DEG) or triethylene glycol (TEG) in the Glycol Dehydration process?

    <p>To absorb water vapour from the gas stream</p> Signup and view all the answers

    Why is it necessary to remove water from natural gas pipelines?

    <p>To reduce the corrosion problem and prevent hydrate formation</p> Signup and view all the answers

    Study Notes

    Natural Gas Treatment

    • Acid gas: a gas that can form acidic solutions when mixed with water, including sulfurous gases (Hydrogen Sulfide, H2S, and Carbonyl Sulfide, COS) and Carbon Dioxide (CO2)
    • Properties of acid gases:
      • Corrosive to pipelines, reactors, and tanks
      • Toxic, flammable, and explosive
      • Contaminants for the environment
    • Hydrogen Sulfide (H2S):
      • Poisonous
      • Corrodes metallic equipment
    • Carbon Dioxide (CO2):
      • Reduces heating value
      • Solidifies under high pressure and low temperature

    Acid Gas Removal Plant

    • Sour water stripper (SWS) produces a sour water stripper acid gas stream (SWSAG) containing Hydrogen Sulfide (H2S) and Ammonia (NH3)
    • Sulfur Recovery Process:
      • H2S commonly used as a refinery fuel
      • Sulfur dioxide concentrations in flue gases must be within acceptable limits due to regulations
      • Recovery process requires ~99% or more efficiency, achieved through a 2-stage process:
        • Modified Claus Process
        • Shell Claus Off-Gas Treatment (SCOT)

    Modified Claus Process

    • Most practical method for converting H2S to elemental sulfur
    • First reported by Chance and Claus in 1885
    • Process depends on H2S concentrations in natural gas
    • 90-95% of recovered sulfur is produced by the Claus process
    • Best suited for acid gas containing 50% or more H2S

    Claus Sulfur Process

    • Reaction: 2H2S + 3O2 → 2H2O + 2SO2
    • Reaction: 2H2S + SO2 → 2H2O + 3S
    • Catalysts: Activated aluminum(III) or titanium(IV) oxide
    • Elemental sulfur is used as fertilizer and pesticide

    Carbon-Sulfur Compounds

    • Carbonyl sulfide (COS) and carbon disulfide (CS2) cause problems in Claus operations
    • These compounds cannot be completely converted to sulfur compounds and CO2
    • Formed during combustion through the reaction of HCs and CO2
    • Alumina catalyst is more favorable in converting COS and CO2 to elemental sulfur compared to bromide catalyst

    Shell Claus Off-Gas Treatment (SCOT) Process

    • Designed to remove sulfur compounds from Claus tail gas to comply with air emission regulations
    • Overall sulfur recovery efficiency of 99.9%
    • SCOT units are designed for minimum pressure drop to be easily added to existing Claus units

    Natural Gas Treatment Processes

    • Purpose: to obtain sweet, dry natural gas by removing acid gases and reducing water vapor
    • Amine Gas Treating: uses solvents like MDEA (Methyldiethanolamine), DEA (Diethanolamine), and MEA (Monoethanolamine)
    • RECTISOL Process: physically absorbs undesired compounds like CO2, H2S, COS, and other sulfur compounds from the gas using a solvent
    • Chemical Absorption: uses chemical reactions to absorb acid gases
    • Physical Adsorption: uses solid adsorbents with high surface areas, like molecular sieves, to adsorb acid gases

    Water Removal

    • Purpose: to reduce corrosion problems and prevent hydrate formation
    • In 1,000 cubic meters of gas, there can be 10-100 liters of water
    • Excess moisture in natural gas pipelines can cause:
      • Corrosion problems
      • Hydrate formation
      • Blockages
      • Reduced heating value
      • Liquid slugs can damage compressors

    Gas Dehydration Plant

    • Uses glycol dehydration to remove water vapor from the gas stream
    • Glycol: a liquid desiccant that absorbs water vapor from the gas stream
    • Process: glycol solution is contacted with wet gas, absorbs water, and is then regenerated through heating

    Solid Dessicant Dehydration

    • Uses solid desiccants like activated alumina or granular silica gel to adsorb water vapor from the gas stream
    • Process: wet gas is passed through adsorption towers, and water is retained on the surface of the desiccant particles

    Liquefaction Systems

    • Expander Cycle Liquefaction System:
      • Uses a turbo-expander to chill the incoming natural gas stream and liquefy a small portion of the stream
      • Generally, no more than 10% of the incoming natural gas stream can be liquefied
    • Mixed Refrigerant Cycle:
      • Uses a mixture of refrigerants (such as propane, ethane, methane, and nitrogen) within a single refrigeration loop
      • Produces a series of refrigeration loops at different temperatures
      • Can be used to pre-cool the gas feed before it is introduced into the mixed refrigerant system

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    Description

    This quiz covers the properties and effects of acid gases, including sulfurous gases and carbon dioxide, in natural gas treatment. Learn about their corrosive and toxic nature.

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