USEPA Petroleum Refinery Enforcement Emerging Issues February 22, 2011

New Directions Flare Efficiency Concerns – Excess Assist Gas Addition Delayed Coker Emissions – Coke Drum Steam Vent Emissions – Quench Water Emissions 2

Flare Efficiency Excess addition of steam or air to assisted flares reduces heating value in the combustion zone (CZNHV) and causes a reduction in flare combustion efficiency (CE), often well below the 98% CE typically assumed. Reduced CE results in increased VOC emissions. Passive FTIR has been used to measure flare plume emissions concentrations and calculate combustion efficiency: – THC term is the sum of hydrocarbon concentrations weighted by carbon content (e.g., 2 × ethane concentration, 3 × propane concentration); – Soot term is assumed to be zero for smokeless flaring. 3

Steam-Assisted Flare Tip 4

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Case Study: Flare Emissions Inventories Prior to 2009, a US refinery reported flare VOC emissions assuming a VOC emission factor of 0.14 lb/mmBTU. In 2009, the refinery revised its estimates based on an assumed 98% combustion efficiency, resulting in VOC emissions that were on average 7 times greater than previous estimates. Using the Marathon Texas City test results, and the refinery’s flare vent gas and steam flow rates, EPA calculated combustion efficiencies and estimated VOC emissions that were up to 15 times higher than the refinery’s revised estimates for some flares. 9

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Delayed Coker Steam Vents After the quench period of a decoking cycle, a coke drum vent is opened to allow the drum to come to atmospheric pressure. The steam released from the vent contains significant amounts of VOC, particulate matter, and reduced sulfur compounds. Steam vent testing has shown emissions can be reduced by first reducing the drum pressure prior to venting. 11

Coke Drum Steam Vent Diagram 12 Blowdown Off-gas Compressor Steam Quench Water Blowdown Settling Drum Blowdown Condenser Blowdown Tower To Main Fractionator Coke Drum Steam Vent Coke to Pit To Wet Gas Compressor Light Slop Oil to Main Frac Sour Water to Sour Water Stripper

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Delayed Coker Quench Water VOC and reduced sulfur compounds dissolved in quench water can be emitted when quench water is drained from the coke drums, and especially when recycled quench water is stored in open or vented tanks. Injection of oily waste at the beginning of the quench period is believed to increase the emissions from quench water. Depending on coker operating conditions (e.g., drum pressure, quench duration) and waste handling practices, quench water emissions may vary from negligible to several hundred tons per year. 15

For More Information EPA National Petroleum Refinery Initiative (NPRI) Website: EPA Headquarters Contact: Patrick Foley Senior Environmental Engineer (202)