Goar, Allison & Associates
licensed technology


> Oxygen Enrichment and Sulfur Recovery featuring COPE®
(Claus Oxygen-based Process Expansion)

Superior Solutions for your Sulfur Processing Needs
Oxygen enrichment of Sulfur Recovery Units (SRUs) is a popular, economic, reliable and safe method for addressing the dual needs of providing additional sulfur removal capacity while conserving capital for more profitable operations. Goar, Allison & Associates offer a full range of oxygen enrichment technologies that provide capacity increases from 10% to 100% or more.

Key Benefits of Oxygen Enrichment Include:

  • Increasing the acid gas processing capacity of the SRU to process heavier and more sour crudes.
  • Significant capital cost savings of 75% to 85% on retrofit installations, and 25% to 35% on grassroots installations as compared to the cost of building a new SRU.
  • Operational flexibility and reliability, allowing the refinery to tailor the SRU capacity to match the acid gas processing requirements at any given time and to run sour crude campaigns.
  • Quick implementation into your existing processes in as little as a few days for low-level oxygen enrichment and during a SRU turnaround for COPE installations.
  • Improved sulfur recovery efficiency and reduced emissions.
  • Effective destruction of ammonia and heavy hydrocarbons as SRU oxygen enrichment results in higher reaction furnace temperatures.
  • Higher furnace temperatures for lean acid gas streams, often eliminating the need for supplemental fuel gas firing, resulting in increased SRU capacity.
  • Improved amine unit operation. As oxygen enrichment reduces the pressure drop in the SRU, the upstream amine unit can operate at a lower, optimal design pressure, potentially reducing corrosion problems and amine degradation.

sulfur recovery unitOxygen Enrichment Technologies
Nitrogen contributes significantly to the pressure drop in the SRU. Replacing some or all of the combustion air with oxygen using oxygen enrichment technology decreases the nitrogen content, allowing an increase in the acid feed rate while operating within the hydraulic constraints of the existing SRU. As illustrated in the table below, the feed to a SRU can be more than doubled while keeping the total flow to the SRU (a proxy for pressure drop) the same.

Why Oxygen Enrichment Increases SRU Capacity

Oxygen Enrichment (%) 20.9 (Air) 25 50 100
Acid Gas (kmol/h) 100 113 170 226
Oxygen (kmol/h) 50 57 85 113
N2 + Ar (kmol/h) 189 169 84 0
Total Flow to RF (kmol/h) 339 339 339 339
Total Flow to TGCU (kmol/h) 293 286 261 235
Total Flow Constant
Acid Gas Flow Increases as O2% Increases

We offer three distinct SRU oxygen enrichment technologies specifically designed for the level of capacity increase desired. These technologies, ranging from low-level oxygen enrichment to our patented COPE oxygen enrichment process technology, have been implemented or licensed at over 50 SRU trains worldwide since 1985. The table below defines each technology and the associated attributes.

Low-Level Oxygen Enrichment
  • Minimum capital investment & process modification
  • Oxygen enrichment levels up to 28%
  • 15% to 25% SRU capacity increases (typical)
  • Mid-Level Oxygen Enrichment
    (COPE Phase I)
  • Special high-intensity COPE® burner designed for
        multiple gas streams, safe oxygen handling, and
        effective ammonia destruction
  • Oxygen enrichment levels up to 45%
  • SRU capacity increases up to 60% (typical)
  • High-Level Oxygen Enrichment
    (COPE Phase II)
  • Employs the COPE® burner in conjunction with a
        recycle process to implement temperature moderation
        in the furnace
  • Oxygen enrichment levels up to 100%
  • SRU capacity increases up to 100% or higher (typical)
  • > The COPE® Oxygen Enrichment Process

    A Sulfur Recovery Unit retrofit with the patented COPE process may operate in air-based mode, Phase I mode or Phase II mode, depending on the processing capacity requirements. The control system for the ratio of oxygen to air is designed to provide the most effective ratio for each process, thereby minimizing the consumption of purchased oxygen.

    The COPE process can increase the existing SRU and tail gas unit processing capacity to as high as 150% of the air-based capacity at 15% to 20% of new construction costs while fitting into the existing process footprint. Utilization of the COPE process can result in a capital cost reduction of 25% to 35% for new construction projects.

    The graph below provides a snapshot of the capacity increases for each of our SRU oxygen enrichment technologies.

    SRU capacity increase with oxygen enrichment

    The patented COPE technology was first commercialized for SRU oxygen enrichment at a major refinery in 1985. Since then, Goar, Allison & Associates has implemented or licensed oxygen enrichment technologies in over 50 refineries worldwide.

    For a list of installed and operating COPE units, or to learn more about SRU oxygen enrichment, COPE technology and how it can benefit your operation, please contact us.

    Environmental Advantages
    The addition of oxygen in the SRU significantly improves the performance of the SRU and Tail Gas Cleanup Unit (TGCU). The efficiency and emissions benefits improve as the level of oxygen is increased. An increase of 0.5% to 1% in overall sulfur recovery may be realized with oxygen enriched processes when compared to air-based operations. Downstream tail gas cleanup processing units can typically process the SRU tail gas with little or no modification. The relative SRU tail gas flow rate, defined as the ratio of the tail gas volumetric flow to the volume of acid gas feed, is progressively reduced as the level of oxygen enrichment is increased.

    As less nitrogen enters the tail gas cleanup unit, higher partial pressures in the selective amine absorber result in better absorption by the selective amine and less H2S being sent to the absorber off-gas and downstream incinerator. The greatly reduced flow rates in the tail gas cleanup unit result in a significant reduction in SO2 emissions. The table below shows a comparison of an operation with 65% oxygen enrichment to an air-based operation. In this example, the SO2 emissions are reduced by 62% even while the capacity of the SRU is doubled!

    Comparison of Air-based Operation versus COPE® Process Operation at 62% Oxygen

    Rich Acid Gas Feed
    (93.7% H2S)
    100 LTPD
    (65% O2
    200 LTPD
    COPE vs
    % Increase
    SRU Acid Gas Feed, MSCFH 128 256 100%  
    Contained S in Feed, LTPD 100 200 100%  
    SRU Tail Gas Flow, MSCFH 353 322 –9%  
    Contained S in Tail Gas, LTPD 2.7 4.2 56%  
    Feed Gas to TGCU
    Amine Absorber, MSCFH
    257 104 –60% Feed to absorber
    60% lower despite
    2X capacity
    Absorber Off-Gas to Incinerator,
    255 98 –62% Feed to incinerator
    62% lower despite
    2X capacity
    H2S Level in Absorber Off-Gas,
    80 80 0%  
    Contained S in Gas to
    Incinerator, lb/hr
    1.72 0.66 –62%  
    SO2 Emissions from Incinerator
    Stack, TPY
    15.05 5.78 –62% SO2 emissions
    62% lower despite
    2X capacity!

    Low-Level Oxygen Enrichment
    Low-level oxygen enrichment is implemented by injecting oxygen into the SRU combustion air line through a custom designed diffuser that promotes good mixing (see figure below). This technology typically allows for maximum enrichment levels of 28% due to limitations relating to oxygen compatibility and cleanliness of the combustion air piping. This technology requires minimal capital investment and process modification and typically offers an SRU capacity increase of 15% to 25%.

    The equipment required for low level oxygen enrichment is a custom designed diffuser that injects oxygen into the combustion air header and an oxygen supply skid. Normal installation time is a few days and does not require a shutdown of the SRU. The diffuser may be hot-tapped into the combustion air header through a packing gland while the air blower and the sulfur plant are in operation.

    standard Claus unit with low level oxygen enrichment

  • Equipment required:
  • – Customized diffuser
    – Oxygen flow control system
  • Oxygen enrichment levels up to 28%
  • Increased processing capacity of 15% to 25%
  • COPE Phase I: Mid-Level Oxygen Enrichment
    Oxygen enrichment levels exceeding 28% require the use of a special burner with discrete oxygen port(s) to safely handle oxygen. The COPE burner is a high-intensity burner that can safely handle the multiple incoming gas streams and has excellent ammonia destruction capability. COPE Phase I provides SRU capacity increases of up to 60% at oxygen enrichment levels of up to 45% for typical refinery acid gas streams. The upper oxygen enrichment limit of this technology is set by the maximum allowable furnace refractory temperature.

    The COPE Phase I process requires the addition of a patented, special high-intensity COPE burner designed for multiple gas streams, safe oxygen handling and effective ammonia destruction. The figure below shows the SRU process schematic with the COPE Phase I technology.

    COPE Phase I process

  • Equipment required:
  • – Proprietary high-intensity COPE® burner designed for multiple gas streams,
       safe oxygen handling, and effective ammonia destruction
    – Oxygen flow control system
  • Oxygen enrichment levels up to 45%
  • Increased processing capacity up to 60%
  • COPE Phase II: High-Level Oxygen Enrichment
    The high reaction furnace temperatures typically encountered when oxygen enrichment exceeds 40% to 45% for rich acid gas streams require the implementation of special temperature moderation technology to attain further capacity gains. COPE Phase II is a patented technology in which a portion of the cooled gas from downstream of the first sulfur condenser is recycled back to the reaction furnace to achieve temperature moderation. This technology can be deployed at oxygen enrichment levels up to 100% to more than double the capacity of an existing SRU. The COPE technology allows an SRU to operate over the entire range of oxygen enrichment levels, from an air-based mode to 100% oxygen, for the greatest possible operational flexibility.

    The COPE Phase II process requires the addition of equipment: the COPE burner, a recycle compressor, and acid gas pre-heater(s). The figure below shows the SRU process schematic with the COPE Phase II technology.

    COPE Phase II process with recycle ejector

  • Equipment required:
  • – Proprietary high-intensity COPE® burner designed for multiple gas
       streams, safe oxygen handling, and effective ammonia destruction
    – Recycle ejector
    – Acid gas preheater(s)
    – Oxygen flow control system
  • Oxygen enrichment levels up to 100%
  • Increased processing capacity up to 100% or more
  • Recycle stream provides temperature moderation: regulated recycle stream is used
    to control the reaction furnace temperature
  • Cope Burner
    The COPE® burner, fabricated by Duiker Combustion Engineers for Goar, Allison & Associates, is a high intensity, swirl vane burner that produces a short, highly turbulent flame. Pure oxygen is introduced at the burner tip into the center of the flame.

    • The oxygen-rich zone in the center of the flame produces a short, localized high temperature zone, which maximizes the dissociation of H2S into hydrogen and sulfur and enhances the dissociation/cracking of NH3 and other components.
    • The highly endothermic reactions reduce reaction furnace operating temperatures, allowing additional oxygen enrichment while reducing the total oxygen requirement.
    • The short flame allows for retrofit of the COPE burner to existing reaction furnaces.

    legal notice
    © 2019 by Goar, Allison & Associates, LLC. COPE and D'GAASS are registered service marks of Fluor Corporation.

    Goar, Allison & Associates