Deep Dive

Refineries – You control some

Another big contributor to greenhouse gases and toxic chemical emissions are petroleum refineries. Companies have succeeded in controlling some but not all chemicals. Nitrogen compounds, which also show up as an area of concern in the monthly wastewater data published by the EPA, are particularly stubborn.

The four top groups of pollutants emitted by refineries are nitrogen compounds, ammonia, hydrochloric acid, and aromatic organic compounds.

The aromatics are particularly worrisome. Benzene is a known carcinogen and strictly regulated. Toluene and xylene contribute to smog and respiratory problems.

Refiners have been reducing their emissions of benzene, toluene, and xylene throughout this century. The top ten emitters by volume include all the major refiners, and all have reduced the release of aromatic compounds into the air and water.

Total releases of BTX for the top ten emitters by volume in millions of pounds

The group has moved mostly in lockstep toward the goal of reducing emissions of aromatics, with individual companies sometimes below and sometimes above the average reduction for the group in a particular year.

Difference in percentage points between the group average and the company reduction in the release of aromatic organic compounds for the last five years. Companies are in descending order by volume emitted

The industry has also gone a fair way toward controlling hydrochloric acid emissions. The rate of decline has decreased in the last decade. Still total volume over the last three years has averaged just above half of what it was in 2000, and about a quarter of the century’s peak of 2.5mn pounds per year in 2002.

Volatile organic compounds can be controlled by phasing out fixed roof tanks and installing better vapor recovery systems. Hydrochloric acid can be scrubbed out of flue stacks. Where the industry struggles is in controlling nitrogen.

Emissions of ammonia are down from the 2004 peak of 20mn pounds but have hovered around an average of 12.5mn pounds throughout the last decade. Nitrogen compounds are the biggest single toxic pollutant tracked by the EPA in the refining sector, and those emissions have gone up, not down. The drop in 2020 is almost certainly due to the decline in refinery utilization since nitrogen compound volume had been rising in the previous years.

Nitrogen compound releases from refineries (in millions of pounds) against average annual refinery throughput (in millions of barrels per day) for top ten emitters

These nitrogen compounds are released into the water, not into the air. Excessive nitrogen leads to algae blooms, which in turn create anaerobic dead zones in the ocean. The biggest contributor of nitrogen in waterways is agriculture through its use of fertilizer. But adding more than 20mn pounds per year from refineries certainly doesn’t help.