Hamza Ahsan, Abbas Ahsan, Jason S. Olfert, Larry W. Kostiuk

Reacting Flow Laboratory, University of Alberta

Carbon Conversion Efficiency and Emissions Indices

from a Lab-Scale Air and Steam Assisted Methane Flare

Process Flaring Process flaring often occurs at facilities with access to steam or

compressed air, and are injected into the exiting fuel stream to enhance

combustion and are known as assisted flares.

These assisting fluids have been observed to have the benefit of reducing

soot emissions, luminosity, and thermal radiation.

Carbon Conversion Efficiency Carbon conversion efficiency (CCE) is the fraction of carbon in the

hydrocarbon flare gas that is converted to CO2.

A carbon mass balance is used to quantify the CCE.

Both air and steam provoked an abrupt collapse in CCE, although a higher

flow rate of air is required to provoke the collapse.

Steam was more effective in reducing emissions as compared to air.

Air- and steam-assisted flares have a regime of high CCE while

significantly lowering pollutant emissions.

Air

Steam

Visualization of an air- and steam-assisted methane flame indicates unique

combustion phenomena.

𝜂[%] =mass of carbon in produced CO2

mass of carbon in hydrocarbon fuel stream× 100

Emission Indices There is interest in various emission indices for species that could impact

climate change or have potential local health effects.

Emission indices (i.e., the mass of a particular species per kilogram of

methane flared) for CO2, soot, unburnt methane, and NOx were found.

Lab-Scale Assisted Methane Flare To understand the effects of either air- or steam-assist on industrial flares,

a generic lab-scale burner was built and tested.

The objectives were to quantify the effects of increasing amounts of air or

steam on the carbon conversion efficiency and emission indices of a

methane flame.

North Dakota’s largest natural gas planthttp://www.grandforksherald.com/news/business/3885801-north-dakotas-largest-natural-gas-plant-repairs-will-addflaring

John Zink Co. test facility in Tulsa, OklahomaThe John Zink Hamworthy Combustion Handbook, Chapter 11 - Flares

0 1 2 3 4 5

0

20

40

60

80

100

Air

Steam

Ca

rbo

n C

on

ve

rsio

n E

ffic

ien

cy (

%)

Coflow-Methane Mass Flow Ratio

0 1 2 3 4 5

1E-4

0.001

0.01

0.1

1

10

100

1000

10000

Em

issio

n In

dic

es (

g/k

g fu

el)

Coflow-Methane Mass Flow Ratio

Air EICH4

Air EICO2

Air EINOx

Air EISoot

Steam EICH4

Steam EICO2

Steam EINOx

Steam EISoot

Total emissions were expressed as a CO2 equivalent for a 100 year GWP.

0 1 2 3 4 5

0

20

40

60

80

100

Air CCE

Steam CCE

Air EICO2,eq

Steam EICO2,eq

Coflow-Methane Mass Flow Ratio

Ca

rbo

n C

on

ve

rsio

n E

ffic

ien

cy (

%)

0

5

10

15

20

25

30

CO

2 E

qu

iva

len

t E

mis

sio

ns (

kg

/kg

fu

el)

1.75kg coflow

kg methane

0.2 g/s methane