Automatic control of soot and unburnt hydro carbons from flares in oil and gas industry

Abstract

Flaring is a high-temperature oxidation process used to burn waste gases from industrial operations. Smoke results from combustion, depends on waste gas components, quantity and distribution of combustion air. Flares stacks are used in industries are often assisted with steam to ensure complete combustion and to avoid any unburnt hydro carbons. In this process, flares are often sooty due to insufficient steam. This results in black carbon from flares. Soot particles in the air are a contributing factor in respiratory diseases. The fine particles less than 3micron are the worst causes of lung damage due to their ability to penetrate into the deep air passage. This paper explains the health effects of soot and particulate matter. New scientific evidence has led to recognition of the significant role of black particles (black carbon – BC) as one of the short-lived climate forcers. Measures focused on BC and methane is expected to achieve a significant short-term reduction in global warming. The black carbon or soot from flares can be minimized by controlling steam to flare by automation. Flare gas flow measurement by ultrasonic flow meter gives a high turn down ratio of 2000:1. This paper explains the methodology of control of soot from flares by steam to hydro carbon ratio control and how the combustion efficiency varies with the amount of steam. The economical benefit of saving steam by automation is not only credit to the company but also carbon credit to the world.

Full text

International Conference and Utility Exhibition 2014 on Green Energy for Sustainable Development (ICUE 2014)
Jomtien Palm Beach Hotel and Resort, Pattaya City, Thailand, 19-21 March 2014
Abstract--Flaring is a high-temperature oxidation process used
to burn waste gases from industrial operations. Smoke results
from combustion, depends on waste gas components, quantity and
distribution of combustion air. Flares stacks are used in industries
are often assisted with steam to ensure complete combustion and
to avoid any unburnt hydro carbons. In this process, flares are
often sooty due to insufficient steam. This results in black carbon
from flares. Soot particles in the air are a contributing factor in
respiratory diseases. The fine particles less than 3micron are the
worst causes of lung damage due to their ability to penetrate into
the deep air passage. This paper explains the health effects of soot
and particulate matter. New scientific evidence has led to
recognition of the significant role of black particles (black carbon
– BC) as one of the short-lived climate forcers. Measures focused
on BC and methane is expected to achieve a significant short-term
reduction in global warming. The black carbon or soot from
flares can be minimized by controlling steam to flare by
automation. Flare gas flow measurement by ultrasonic flow meter
gives a high turn down ratio of 2000:1. This paper explains the
methodology of control of soot from flares by steam to hydro
carbon ratio control and how the combustion efficiency varies
with the amount of steam. The economical benefit of saving steam
by automation is not only credit to the company but also carbon
credit to the world.
Index Terms--Absorption, Automatic Control, Gas
Chromatography, Global Warming, Hydrocarbons, Pollution..
I. NOMENCLATURE
BC Black Carbon
GC Gas Chromatograph
HC Hydro Carbon
PAH Poly cyclic Aromatic Hydrocarbons
PM Particulate Matter
II. INTRODUCTION
n many oil refineries, the flare is manually observed by the
operator for any abnormality. Manual observation of the
flare on a 24×7 basis is a difficult job, and is not a reliable way
to detect abnormalities. In case of plant shut down/emergency
or pressure relief valves pops up, sudden flaring causes smoky
1Research Scholar at Jawaharlal Nehru Technological University,
Kakinada, Andhra Pradesh, India-533003.
(e-mail: rekhapalli_sri@yahoo.co.in)
2Professor in Civil Engineering, at Jawaharlal Nehru Technological
University, Kakinada, Andhra Pradesh, India-533003
(e-mail: kvsg.muralikrishna@gmail.com).
flare. It may take some time to operator to respond to inject
steam as process operator’s manual action. During this time,
often flares are smoky. According to government legislation
(Ministry of Environment), if waste gases venting with black
smoke and its opacity is above Ringlemann no#2 and smoky
flare is more than 5 minutes, it should be reported as flare
incident.
So during this 5 minutes crucial period of process plant upset,
it is difficult to adjust steam to flare manually. Ringlemann
chart method is out dated now a days and it will take
15minutes to check the correct flare opacity. This results
increases number of flare incidents.
III. TECHNICAL WORK PREPARATION
Flaring is a technique used extensively in the oil and gas
industry to burn unwanted flammable gases. Oxidation of the
gas can preclude emissions of methane (a potent greenhouse
gas); however flaring creates other pollutant emissions such as
particulate matter (PM) in the form of soot or black carbon
(BC) [1]. Smoke forms when C-C bonds in hydrocarbon crack
and aromatic structures grow in to multi ring molecules [>3
ring=primary soot particle]. Other Polyaromatic hydrocarbons
[PAH] form a long reaction route to soot. As of the end of
2011, 150 × 109 cubic meters of associated gas are flared
annually. That is equivalent to about 25 per cent of the annual
natural gas consumption in the United States or about 30 per
cent of the annual gas consumption in the European Union [2].
As of 2010, 10 countries accounted for 70% of the flaring,
and twenty for 85%. The top ten leading contributors to world
gas flaring in 2010, were (in declining order): Russia (26%),
Nigeria (11%), Iran (8%), Iraq (7%), Algeria (4%), Angola
(3%), Kazakhstan (3%), Libya (3%), Saudi Arabia (3%) and
Venezuela (2%) [3].
The amount of flaring and burning of associated gas from oil
drilling sites is a significant source of carbon dioxide (CO2)
emissions. Some 400 × 106 tons of carbon dioxide are emitted
annually in this way and it amounts to about 1.2 per cent of the
worldwide emissions of carbon dioxide [4]
Unlike carbon dioxide and other greenhouse gasses, which can
survive in the atmosphere for decades and centuries, black
carbon has a relatively short life span of approximately one to
two weeks. Black carbon is part of a group of pollution
sources known as Short-Lived Climate Forcers (SLCFs),
including methane gas and ozone, which are produced on
earth. Polycyclic aromatic hydrocarbons (PAH) are important
components of organic particulate matter because of their
carcinogenic nature. Some typical PAH compounds are: benzo
alpha pyrene, Chrysene, benzofluoranthene. PAH compounds
Automatic Control of Soot and Unburnt Hydro
Carbons from Flares in Oil and Gas Industry
R. Srinivasarao1 and K.V.S.G. Murali Krishna2
I

International Conference and Utility Exhibition 2014 on Green Energy for Sustainable Development (ICUE 2014)
Jomtien Palm Beach Hotel and Resort, Pattaya City, Thailand, 19-21 March 2014
occur in urban atmospheres at levels of about 20 μg/m3. They
are mostly found in the solid phase. It is known that most PAH
compounds are sorbed onto soot particles. Soot itself is a
highly condensed product of PAH compounds. A soot particle
consists of several thousand interconnected crystallites which
are made up of graphitic platelets. The latter (platelets) consist
of roughly 100 condensed aromatic rings.
Soot consists of 1-3% H and 5-10% O trace metals such as Be,
Cd, Cr, Mn, Ni, and V and also toxic organic such as benzo
alpha pyrene adsorbed on its surface. During their lifetime,
black carbon particles are coated with airborne chemicals,
Fig. 1 TEM graph of soot particles. [5]
Emission factors:
For a very rough order of magnitude estimate, considering gas
flared volumes of 139 billion m3/year as estimated from
satellite data [6] and estimating a single valued soot emission
factor of 0.51 kg soot/103 m3, flaring might produce 70.9 Gg
of soot annually. This amounts to 1.6% of global black carbon
emissions from energy related combustion, based on estimates
of 4400 Gg for the year 2000[7].
Soot in concentration values [8]:
Non smoking flares, 0μg/l;
Lightly smoking flares, 40μg/l;
Average smoking flares, 177 μg/l; and
Heavily smoking flares, 274μg/l.
Methodology:
Required steam will be injected as calculated into the flame
zone with the help of Steam/Carbon ratio controller by feed
forward signal. Ultrasonic flow meter measures the gas flow to
the flare. Different molecular weight gases having different
carbon numbers. Gaschrometography measures the carbon
numbers of different gases. Sum of all different carbon
numbers gives total number of hydro carbon to flare. Carbon
flow in kg/hr can be achieved as follows,
Carbon flow (kg/hr) = hydrocarbon flow (N m3/hr)* total
carbon no./22.414
Gas Chromatography takes 15-20minutes to calculate the
complete gas composition. Feed forward signal compensates
this time lag. Steam flow required to achieve smokeless
flame will be calculated as follows
Required Steam flow (kg/hr) = S/C * Carbon flow (kg/hr)
Combustion efficiency:
Flare gases of different compositions and same heating value
can have different stable flame operating envelopes when
flared from the same flare. But with different quantities of
steam to hydrocarbon ratio will change the combustion
efficiency.
Steam to HC ratios of 3.5 to 1 or less had 98% plus
Combustion efficiency.
Steam to HC ratios of 5.8 to 1 or less had 82% plus
Combustion efficiency.
Steam to HC ratios of 6.7 to 1 or less had 69% plus
Combustion efficiency.
Fig. 2 Impact of steam injection and combustion efficiency
Ringlemann chart:
The Ringelmann Smoke Chart [9], giving shades of gray by
which the density of columns of smoke rising from stacks may
be compared, was developed by Professor Maximilian
Ringelmann of Paris. The Ringelmann system is virtually a
scheme whereby graduated shades of gray, varying by five
equal steps between white and black, may be accurately
reproduced by means of a rectangular grill of black lines of
definite width and spacing on a white background.

International Conference and Utility Exhibition 2014 on Green Energy for Sustainable Development (ICUE 2014)
Jomtien Palm Beach Hotel and Resort, Pattaya City, Thailand, 19-21 March 2014
The rule given by Professor Ringelmann by which the charts
may be reproduced is as follows:
Card 0— All white.
Card 1—Black lines 1 mm thick, 10 mm apart, leaving white
spaces 9 mm square.
Card 2— Lines 2.3 mm thick, spaces 7.7 mm square.
Card 3— Lines 3.7 mm thick, spaces 6.3 mm square.
Card 4— Lines 5.5 mm thick, spaces 4.5 mm square.
Card 5— All black.
The chart, as distributed by the Bureau of Mines, provides the
shades of cards 1, 2, 3, and 4 on a single sheet, which are
known as Ringelmann No. 1, 2, 3, and 4, respectively.
Use of Chart:
Although the chart was not originally designed for regulatory
purposes, it is presently used for this purpose in many
jurisdictions where the results obtained are accepted as legal
evidence. The apparent darkness or opacity of a stack plume
depends upon the concentration of the particulate matter in the
effluent, the size of the particulate, the depth of the smoke
column being viewed, natural lighting conditions such as the
direction of the sun relative to the observer, and the colour of
the particles. Since unburned carbon is a principal colouring
material in a smoke column from a furnace using coal or oil,
the relative shade is a function of the combustion efficiency.
To use the chart, it is supported on a level with the eye, at such
a distance from the observer that the lines on the chart merge
into shades of gray, and as nearly as possible in line with the
stack. The observer glances from the smoke, as it issues from
the stack, to the chart and notes the number of the chart most
nearly corresponding with the shade of the smoke, then records
this number with the time of observation. A clear stack is
recorded as No. 0, and 100 percent black smoke as No. 5.
To determine average smoke emission over a relatively long
period of time, such as an hour, observations are usually
repeated at one-fourth or one-half minute intervals. The
readings are then reduced to the total equivalent of No. 1
smoke as a standard. No. 1 smoke being considered as 20
percent dense, the percentage "density" of the smoke for the
entire period of observation is obtained by the formula:
Equivalent units of No. 1 smoke × 0.20 × 100
_____________________________________
Number of observations
= percentage smoke density.
20% smoke density equals to Ringlemann no#1
40% smoke density equals to Ringlemann no#2
60% smoke density equals to Ringlemann no#3
80% smoke density equals to Ringlemann no#4
100% smoke density equals to Ringlemann no#5

International Conference and Utility Exhibition 2014 on Green Energy for Sustainable Development (ICUE 2014)
Jomtien Palm Beach Hotel and Resort, Pattaya City, Thailand, 19-21 March 2014
Limitations of Ringlemann Chart:
The chart shall be used under day light conditions. Clear back
ground should be there when an observer takes observations.
If the weather is dusty, foggy and rainy, Ringlemann chart
cannot be used.
Health Effects of Soot:
Soot particles in the air are a contributing factor in
respiratory diseases. The fine particles (<3μ) are the worst
causes of lung damage due to their ability to penetrate into the
deep air passage. Larger particles (>3 μ) are trapped in the
nose and the throat from which they are easily eliminated, but
finer particles can stay intact for years in the inner most
regions of the lungs, which have no effective mechanism for
particle removal. The lodged particles in the lungs can cause
severe breathing trouble by physical blockage and irritation of
the lung capillaries.
Emissions of fine particulate matter (PM and ultra fines)
in diesel exhaust have been of growing community, industry
and government concern. Their combination of extremely
small size and chemical composition increases the likelihood
that particles will carry irritants and toxic compounds into the
deepest and most sensitive areas of the lungs. This can lead to
severe bronchial problems and increased susceptibility to
respiratory infection, such as pneumonia, bronchitis, and
asthma. Carbon soot particles from diesel engines adsorb onto
their surfaces other metals and toxic substances produced by
diesel engines such as cancer-causing aldehydes (like
formaldehyde) and polycyclic aromatic hydrocarbons (PAH).
Occupational health studies link cancers, particularly lung
cancer to diesel exhaust exposures. Traffic studies suggest
increased rates of respiratory and cardiovascular disease and
risk of premature death near busy urban streets or highways
and thus must be addressed by industry and government.
Conclusions:
Ringlemann Chart is used to identify the opacity of the flare.
But as it is out dated and is not a continuous method to find out
the opacity, it is obsolete. So automatic control of soot by ratio
controller keeps always zero soot formation from the flare stack
in any emergency situation.
Meet or exceed government legislation, and eliminate risk of
non-compliance, as flare opacity is always less than
Ringlemann index#2
Economical benefits by adopting automatic control of soot
from flares are:
1) $70 per hour saving by reducing excess steam to flares,
consider that Natural gas price is $1/mmbtu and Raw water
price is $5/ m3
2) Due to reduction of excess steam, total CO2 reduction to
atmosphere is 7.45ton/day
International Carbon Trade: 1Carbon Credit = 1ton CO2
removed = $12 in today’s market
The above cost savings will be different from different
countries due to raw materials cost is different.
3) US Environmental Protection Agency proposal would
strengthen the annual health standard for harmful fine particle
pollution (PM2.5) to a level within a range of 13μg/ m3 to
12μg/m3. The current annual standard is 15μg/ m3. By
proposing a range, the agency will collect input from the
public as well as a number of stakeholders, including industry
and public health groups, to help determine the most
appropriate final standard to protect public health.
IV. ACKNOWLEDGMENT
I express my profound gratitude and sincere thanks to my
research supervisor Dr. KVSG Murali Krishna, Professor of
Civil Engineering, JNTUK, Kakinada, Andhra Pradesh, for his
valuable and dynamic supervision throughout the progress of
this work.

International Conference and Utility Exhibition 2014 on Green Energy for Sustainable Development (ICUE 2014)
Jomtien Palm Beach Hotel and Resort, Pattaya City, Thailand, 19-21 March 2014
V. REFERENCES
Periodicals:
[1] Black Carbon Particulate Matter Emission Factors for Buoyancy Driven
Associated Gas Flares”-James D.N. McEwen and Matthew R. Johnson.
[2] Estimated Flared Volumes from Satellite Data, 2006-2010.
http://web.worldbank.org/
[3] http://en.wikipedia.org/wiki/Low-carbon_economy
[4] http://www.pbl.nl/sites/default/files/cms/publicaties/pbl-2013-trends-in-
global-co2-emissions-2013-report-1148.pdf
[5] www.worldbank.org/html/fpd/ggfrforum06/berg/johnson.ppt
[6] http://www.mdpi.com/1996-1073/2/3/595
[7] Bond, T. C.; Bhardwaj, E.; Dong, R.; Jogani, R.; Jung, S.; Roden, C.;
Streets, D. G.; Trautmann, N. M. Historical emissions of black and
organic carbon aerosol from energy-related combustion, 1850–2000.
Global Biogeochemical Cycles 2007, 21, 1-16.
[8] Flare Efficiency Study, EPA-600/2-83-052, U. S. Environmental
Protection Agency, Cincinnati, OH, July 1983.
[9] IC information circular 8333 RINGELMANN SMOKE CHART
(Revision of IC 7718) By Staff, Bureau of Mines