>
Loading...

FLARING : Another Road to Success

Objective: To identify the most efficient and safest method of flaring and familiarize ourselves with the different flaring methods.

Definition: FLARE

  • To flame up with a bright, wavering light.
  • To burst into intense, sudden flame.
  • To cause to flame up.
  • To burn or cause to burn with an unsteady or sudden bright flame


What is Flaring?

Flaring is the open-air burning of natural gas. Flaring disposes of the gas and releases emissions into the atmosphere. Most of the flaring involves sweet natural gas, although flaring is also used to dispose of some sour gas.

Natural Gas
Natural gas is a combustible mixture of hydrocarbon gases. While natural gas is formed primarily of methane, it can also include ethane, propane, butane and pentane. The composition of natural gas can vary widely, but below is a chart outlining the typical makeup of natural gas before it is refined.


Typical Composition of Natural Gas
     

Methane

CH4

70-90%

Ethane

C2H6

0-20%

Propane

C3H8

Butane

C4H10

Carbon Dioxide

CO2

0-8%

Oxygen

O2

0-0.2%

Nitrogen

N2

0-5%

Hydrogen sulphide

H2S

0-5%

Rare gases

A, He, Ne, Xe

Trace

Sweet and Sour Gas
"Sour gas" is natural gas or any other gas containing significant amounts of hydrogen sulfide (H2S). And natural gas that does not contain significant amounts of hydrogen sulfide is called "sweet gas".

 Types of Flare

Open or Elevated Flares

asdf- most widely used in the petroleum industry and in chemical plants thanks to its capacity to handle higher loads. The elevated refinery flare system consists of flare header collecting the waste gas and entrained condensates from all over the plant. Condensates are removed using a 'Condensate Knock Out Drum (KOD)'. The gases to be burned are then sent to a vertical flare stack the height of which can range from 32 to 320 feet. Backflow of gases from stack to the Knock Out Drum is usually prevented by having a water seal at the gas inlet to the flare stack. Proper elevation of the flare tip can ensure adequate and safe dispersion of toxic or smelly gases resulting from combustion. The gases are finally burned in the elevated flare tip located at the top of the gas flare stack. Commonly the flame is open at the top of the gas flare stack and hence the name. Due to the open flame, this type of flare system can be a source of noise pollution. Also the radiation from open flame renders some area around the stack unsuitable for installation of any equipment.



Enclosed Ground Flares


asdf
-conceal the flame from direct view, and reduce noise and thermal radiation to the surrounding community.

-commonly this type of flame close to the ground has to be enclosed in a refractory lined enclosure to contain the radiation and gases originating from the flame.
ground flare has lower or no problems related to noise pollution and heat radiation. But because the flame is close the ground, gases are also released quite close to the ground and the dispersion of gases is not as effective as with the elevated refinery flare. Hence ground flare can have problems in case the combustion products are toxic in nature or in case of flame-out. Due to these limitations, the enclosed or ground flare system is preferred in case of clean burning gases and when noise pollution is a critical factor. But it should be kept in mind that enclosed or ground flare systems have limited capacity compared to elevated flare systems and it may be desirable to use the ground flare system in combination with an elevated flare system.

 





Methods, Software and Equipment

asdf

  • Flare System:

  • Relief, safety and depressuring valves(which relieve the fluid to be flared)
  • Pressure-relieving headers that convey discharges from safety valves and pressure control valves in the process unit to the flare.
  • Knock out drum located before the flare stack in order to separate any condensate or liquid from the relieving vapours
  • Flare stack consisting of riser structure, molecular seal and burner tip
  • Riser Structure- consists of two or more sections. The flare header enters at the bottom section which can also serve as a flare stack knock out drum where any condensate carried over from the main knock out drum is collected.
  • Molecular seal- provides a seal against entrance of air into the flare stack and minimizes the possibility of an explosive mixture forming in the flare system.
  • Flare Burner Tip-sealed to the molecular seal outlet.
  • Steam or air-assist

  • Plume Real-Time System (Plume-RT)

Plume-RT is the only air quality management system that integrates

  • on-site meteorology,
  • air quality data,
  • site-specific weather forecasts, and
  • advanced dispersion models

asdf-A web-based system that models airborne pollutants in real-time by integrating regulatory-approved air dispersion models, site-specific meteorology, weather forecasts, and environmental monitoring. Plume-RT has been used to model sour gas flaring events, facility emissions, visibility from fires, and to assist with emergency response/incident command.

 

C.) Software
FLARES -a software for sizing industrial flares, for the evaluation of their thermal and acoustic impact and for the calculation of the flue gas composition.
Features:
*Sizing (i.e. calculation of height and diameter) of subsonic industrial flares according to a specified allowable radiation
*Calculation of thermal radiation of subsonic, sonic flares and flue gas composition
*Calculation of the effective stack parameters for atmospheric dispersion modelling according to the US-EPA SCREEN3 and TCEQ (Texas Commission on Environmental Quality) methodologies
*Works with SI (International Standard) and USC (United States Customary) units
*Flame tilting calculated with the Simple approach and with the Brzustowski and Sommer approach
*Allows to load and georeferentiate a base map
*Georeferentiation done automatically if the base map file has an associated world file
*Thermal radiation levels and noise levels can be exported in KML format for Google Earth.

Environmental Consideration

Many of the substances emitted by flaring, incineration and venting can affect humans, animals, plants and the environment. Effects depend on the magnitude, duration and frequency of exposure, as well as the susceptibility of the individual organism or environment. Air monitoring data in Alberta indicate that most emissions from flaring, incineration and venting in the oil and gas industry occur in areas that are within the Canada-wide standards for air quality, including the standards for particulate matter and ozone in ambient air.However, there is no question that high enough concentrations of petroleum-related emissions could affect the respiratory health, vision and skin of humans and animals. Exposure to some VOC and PAH substances increases the likelihood of cancers. VOCs, NOx and particulate matter can cause smog. Sulphur dioxide and oxides of nitrogen can acidify soils and lakes and affect the growth of crops and forests. Acid deposition can even cause wire fences to rust.

Rules and Regulations

Temporary Flaring/Incineration Permits

Figure below shows the temporary flaring/incineration permit process.
asdf

The ERCB(now called AER) may suspend well flaring or incineration for noncompliance with conditions of the permit. The licensee must comply with the conditions of the temporary flaring permit.

 

Permit Requirements for Temporary Flares and Incinerators

General Permit Requirements

1) Requests for temporary permits must be submitted to the ERCB Technical Operations Group via paper copy and e-mail (Directive060Inbox@ercb.ca) and must include complete information on the proposed activity, as requested in the ERCBflare.xls and ERCBincin.xls spreadsheets (available on the ERCB website under Regulations & Directives : Directives : Directive 060) and summarized as follows:
a) a cover letter requesting a permit and informing the ERCB Technical Operations Group of any public objections to or concerns about the proposed flaring/incineration
b) information about the site on which flaring/incineration will occur, including location, Lahee classification, and related National Topographical System 1:50 000 scale maps
c) an evaluation of the most feasible option for in-line testing
d) information on planned flaring/incineration, including reasons (e.g., well testing, completions, pipeline depressuring), H2S content, flow rates, total volumes, and type of combustion device to be used (i.e., flare or incinerator)
e) information on the licensee's assessment of effects on ambient air quality, including results of dispersion modelling for SO2
f) in situations with potential to exceed the risk-based criteria for SO2, information on the licensee's proposed air quality management plan to prevent exceedances
2) Any inconsistencies in the request or modelling will result in the request being rejected and returned to the licensee. Permit requests are processed in the order received, and resubmissions will be treated as new permit requests.
3) Temporary permit requests can be submitted electronically by the licensee. A permit will be in the name of the licensee.

Sources

http://people.clarkson.edu/~wwilcox/Design/FlareSel.pdf

http://siteresources.worldbank.org/EXTGGFR/Resources/578068-1258067586081/FlaringQA.pdf

http://www.enggcyclopedia.com/2011/06/flare-system-types/

http://www.scribd.com/doc/159091027/Flare-System

http://www.aer.ca/documents/directives/DraftDirective060.pdf

http://www.flaring.ca/flaring/plumert.htm

http://software.rwdiair.com/product/plumert/