Oil refineries control emissions with different systems for different pollutants and process units. Sulfur recovery plants capture hydrogen-sulfide-rich gas and produce elemental sulfur; other approaches include using lower-sulfur fuels, scrubbing flue gas, and applying unit-specific controls for nitrogen oxides, particulate matter, carbon monoxide, and hazardous air pollutants. No single device removes every refinery emission, and the controls that apply depend on the unit, its operation, and the relevant regulation.
How do refineries reduce sulfur emissions?
It helps to distinguish sulfur in process gas from sulfur dioxide (SO₂) released by combustion. Hydrogen sulfide (H₂S) is a sulfur-bearing gas generated by refinery processes, including coking and catalytic cracking. SO₂ can form when sulfur-containing fuel or gas is burned. These are related problems, but controlling one stream does not automatically control the other.
| Emission or source | Control approaches described by EPA | Scope and qualification |
|---|---|---|
| Hydrogen-sulfide-rich process gas | Sulfur recovery plants process the gas and recover elemental sulfur, which can be sold. An EPA enforcement alert reports that these plants convert 95 percent or more of the hydrogen-sulfide gases to elemental sulfur. | The 95-percent-or-more figure is from the EPA alert; it is not a verified current average for all refineries. EPA enforcement alert on flaring and uncontrolled SO₂ releases; EPA 2015 economic impact analysis. |
| SO₂ from fuel combustion or flue gas | Use lower-sulfur fuel, desulfurize fuel before use, or scrub high-sulfur flue gas. | These are control options described in EPA’s historical 1981 technical guidance, not a complete summary of current requirements or a claim that every refinery uses all three. EPA environmental impact guidelines for new petroleum refineries. |
| Acid gas and flare systems | Route acid gas through sulfur recovery where applicable; flare-gas recovery and measures to prevent process upsets are also cited as controls. | Flares serve pressure-relief and upset functions. Recovery and flare-management measures are not interchangeable, and settlement measures cited by EPA are facility-specific. EPA enforcement alert; EPA Conoco refinery settlement. |
| Nitrogen oxides (NOₓ) | Combustion adjustments and low-nitrogen fuels are among the approaches in EPA’s historical guidance. A refinery settlement also describes ultra-low-NOₓ boilers and selective noncatalytic reduction. | These examples do not establish a universal technology or limit for every refinery unit. EPA technical guidance; EPA Conoco settlement. |
| Particulate matter, SO₂, NOₓ, and carbon monoxide from covered cracking or coking units | EPA’s New Source Performance Standards (NSPS) include pollutant-specific standards for relevant new fluid catalytic cracking units (FCCUs) and fluid coking units, with monitoring options for demonstrating particulate-matter compliance. | The standards’ applicability depends on the source category and rule; they should not be read as one set of limits for every existing refinery unit. EPA petroleum refinery NSPS information. |
| Hazardous air pollutants (HAPs) | EPA’s National Emission Standards for Hazardous Air Pollutants (NESHAP) address covered catalytic cracking, catalytic reforming, and sulfur recovery sources. | HAP controls are a distinct regulatory program; they are not the same as SO₂ controls. EPA petroleum refinery NESHAP information. |
Why is sulfur recovery different from flaring?
A sulfur recovery plant treats a process gas stream to recover sulfur as a product. A flare burns gas to dispose of it during pressure relief or upset conditions; it does not perform the same recovery function. EPA’s enforcement alert warns that flaring acid gas instead of sending it through sulfur recovery can cause very large uncontrolled SO₂ releases. The agency describes a sulfur recovery plant as “a refinery process for producing elemental sulfur for sale but is also a part of the refinery’s air pollution control systems.”
That distinction matters because emissions depend not only on installed equipment but also on how gas is routed and how the plant is operated. EPA enforcement material describes flare-gas recovery and measures to prevent process upsets, while the Conoco settlement documents measures at the covered refineries. Those examples illustrate possible approaches; settlement terms at one company are not universal requirements.
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How do refinery air-pollution rules apply?
EPA’s refinery NSPS materials cover several categories of equipment, including cracking and coking units, combustion devices, and sulfur recovery plants. Requirements can differ by unit and source category, so the NSPS page is a starting point for determining scope—not evidence that every refinery unit has identical standards.
NESHAP addresses hazardous air pollutants from the covered catalytic cracking, catalytic reforming, and sulfur recovery sources. EPA’s refinery-sector rule page identifies final amendments in 2024; the rules and their applicability should be checked for the specific source and provision rather than generalized to every refinery operation.
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For context on the rule pages and amendments, see EPA’s petroleum refinery sector rule information alongside the agency’s NSPS and NESHAP pages.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What determines whether a control is appropriate?
There is no supported universal ranking of refinery control technologies. A meaningful comparison has to specify the pollutant and unit, operating conditions, expected performance, monitoring and compliance method, and whether a system recovers a useful material or transfers pollutants into another stream. EPA’s emissions-estimation protocol provides technical context for refinery emissions estimates, but a facility’s applicable standards and operating circumstances still matter.
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EPA Emissions Estimation Protocol for Petroleum Refineries, Version 3.0.
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