new developments in flaring - deerparkcac · flare operators have been trained to add sufficient...
TRANSCRIPT
Flare Operation
Primary function is as a safety deviceProtect equipment from catastrophic failure (pressure relief)Protect employees/community from exposure to pollutantsDesigned with safety in mind: big enough to handle the largest release
Over the years, flare operations have evolvedInitially designed only for emergencies (safety devices)Then became “dump” for waste gases, off-spec materials, etc.Later used as alternative to venting directly to atmosphereToday used as emissions control devices for most process vents
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Flare Operation
In addition to process gases, purge gas and assist gas are often routed to flares
Purge gas (usually natural gas) sweeps the flare header of oxygen, corrosives, reactives, and inerts
Assist gases (usually steam or air) improve mixing for better combustion, help protect the flare tip from heat damage, and help minimize visible emissions
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Flare Operation
Flare operators have been trained to add sufficient steam (or air) to prevent visible emissions
Over the years this has translated into “more is better”
Many facilities have reduced continuous flaring, resulting in flares that operate well below their design capacities
Operating at <1% of design capacity is known as “high turndown”
Some recent study data indicate that this combination of high flare turndown + increased assist rate may be contributing to lower flare destruction efficiency (DRE)
DRE = how well a flare destroys the materials being burned
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“Over-steamed” Flare
Good looking flare? Here’s what’s really going on!!
Video Source: TCEQ Houston Office
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“Over-steamed” Flare
Qualitative Test with IR Camera Shows Significant Flare Hydrocarbon EmissionsIn the Presence of Visible Steam
Video Source: TCEQ Houston Office
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TCEQ R12 oversteam video.wmv
Background16
EPA regulates flares through a rule called “60.18”Visible emissions limited to 5 minutes in 2 hoursFlame must be present at all timesLimits on minimum net heating value and maximum gas exit velocityMonitor to ensure the above conditions are met
Flares meeting all 60.18 requirements assumed to have a 98% destruction and removal efficiency (DRE)
For every 100 pounds VOCs fed to the flare, 98 pounds will be destroyed and only 2 pounds will be emitted
Air quality studies raised questions about differences in measured air quality vs. estimated emissions
Texas 2000 Air Quality Field Study2006 Texas Air Quality Study (TexAQSII) Numerous Houston-area flyovers2009 Study of Houston Atmospheric Radical Precursors (SHARP)
Some skepticism about flare DRE arose
TCEQ Flare Study
$2.2 million study conducted in Sept. 2010
Objective to measure DRE at very low turndownNot emergency flare scenarios
Limited test conditions Vent gas was simple mixture of propylene, natural gas, and nitrogen Test conditions met 60.18 requirementsAssist gas rates varied from zero to point of snuffing out flare flame
Emissions sampler & remote sensing instruments
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Extractive Sampler Parts
Elevation Chain
PositioningChains
ExtractiveSample
Inlet
Pitot
Flue GasEductor
GPS
SampleLines
Forced Air Device Positioned with Crane while Extracting Samples of Flare Emissions
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Test Results at Incipient Smoke Point
Test Point A4.6
Vent Gas Btu/scf DRE (%)937 lb/hr 350 Btu 99.4
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Effect of Small Increase in Steam
Test Point S4.2 Test Point S4.7 Test Point S4.3
Visible Flare and Invisible Steam Result in >99% DREVisible Steam Results in Rapidly Falling DRE
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Why is High DRE Important?
Test Point S4.2 Test Point S4.7 Test Point S4.3
At 99.2% DRE, 20,000 pounds of flare gasresults in (0.008 x 20000) =
160 pounds of unburned flare gas
At 90.6% DRE, 20,000 pounds of flare gasresults in (0.094 x 20000) =
1880 pounds of unburned flare gas
At 27.3% DRE, 20,000 pounds of flare gasresults in (0.727 x 20000) =
14,540 pounds of unburned flare gas
Third photo has almost 100 times higher emissions compared to first photo
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TCEQ Flare Test Results Summary
The flares tested were able to achieve greater than 99% DRE for vent gas streams at low flow rates (high turndown) under certain conditions
For the conditions tested, the highest DRE was achieved at or near the point when smoke first appeared (incipient smoke point)
Low DRE occurred with invisible flames
Operating the flare within legal requirements of 60.18 and no visible emissions may or may not minimize emissions
Proper assist rates appear to be key to good DRE under high turndown conditions
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Flares in your Area
Plant Managers have provided a brief summary of the number & types of flares they have
Emergency-only flaresProcess-only flaresCombination emergency & process flares
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Flares in your Area
Summary of DPCAC Flare Survey
7 of 14 DPCAC plants have flares 50 flares among the 7 plants3 of the 50 flares are emergency only flares24 of the 50 flares are process only flares, with continuous flow10 of the 50 flares are process only flares, with intermittent flow13 of the 50 flares are combination flares13 of the 50 flares are steam-assisted5 of the 50 flares are air-assisted12 of the 50 flares have no assist1 plant of 7 (Shell) has flare gas recovery
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Next Steps
TCEQ, EPA, and Industry are working to better understand flare performance
Industry is examining its current flare operating practices to find improvements
Looking at manual assist rates Exploring better controls, monitoring equipment, and alternative emissions control technology that might be implemented in some cases
TCEQ is developing flare operator guidance
EPA is developing new flare rules
Flare vendors are reassessing their designs and operating recommendations
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