The Characteristics of Methane

Methane has chemical formula of CH4 and often also called as carbon tetrahydride (in context of their systemic naming convention) means the compounds consist of one carbon substance and four hydrogen substance. However, most scientist and engineer called CH4 as methane for easier spelling and pronounciation.

Each chemical compounds has different characteristics because of the substances combination that formed them. Methane has following properties: one carbon atom on the center and four hydrogen atom arround it in form of tetrahedral arrangement.

      H
      |
  H - C - H
      |
      H

due to those properties, methane has following characteristics that might affect operations & HSSE aspect in oil and gas industry (especially at downstream/refinery facilities):

  1. Flammability - Highly flammable means substance is can get burnt easily if it contacted with ignition sources plus oxygen. Even a hot surface can ignite methane and make fire.
  2. Odor - pure methane is odorless, make it harder to get smelled by human. Require special technique to detect methane.
  3. Density (how tight is the particle towards the container volume) - ligher than air. If methane leaked either from the pipeline or tank, it tends to move upwards (rise up) to the atmosphere and dilustes with air.
  4. Greenhouse gas level - Methane is known as strong greenhouse gas which can easily trap earth’s outgoing heat and re-radiating it back to earth.
  5. Corrosivity - pure methane is benign to the pipeline integrity (non corrosive).

Methane Leak on Refinery System

Downstream facilities main responsibility to process crude oil into consumed ready product or often called as FG(final goods) like gasoline, diesel, jet fuel and petrochemicals (plastics and rubber). By nature, crude oil contains alkanes compounds methane, ethane and propane. When crude oil is heated on distillation unit, all compounds inside the crude oil will be separated based on its boiling unit. Light gas such as methane will be vaporized and separated.

Methane gas can get leaked on the whole crude distillation system and connected gas handling equipment. Following process: thermal cracking process (high temperature breakdown), catalytic cracking, catalytics reforming can leak methane as these refining process will break hydrocarbon molecule into smaller one.

In otherhand, equipment can potentialy leak methane as well. Below are the usual equipment which can leak methane.

  1. Pump Seal
  2. Compressor Seal
  3. Valves
  4. Flanges
  5. Piping Connector

Leak on those equipment is considered as fugitive emissions (unintended and uncontrolled leak). Apart from equipment, methane can also get “vented” during startup ,shutdown or maintenance activities.

Impact of Methane Leak

Methane leak is harmful to the facilities. a small methane ignition can blow up the entire refinery if the explosion happened at confined places near the dangereous area within the facilities. Hence, it is important to ensure no methane leak and no ignition soureces on the facilities that could produce methane. Hazardous area often classified based on the potential methane gas appearances. Those area will require special work permits and intensive safety procedures.

The mixture between methane+air (oxygen, carbon dioxide) can become explosive at certain concentrations range or limits. Leak location can affect the level of impact. Methane leak on enclosed space can rise the concertraion and reaching its explosive range. Hence, building ventilation is critical.

Methane on confined place can dilute oxygen (reducing oxygen concentration) which may reduce oxygen level to a point where it can affect human respiratory system (lack of oxygen can lead human into unconsciousness or even death).

below are the impact on HSSE

No Properties Impact on HSSE
1 Flammability Fire & Explosion Risk. All equipment/asset hot surfaces must be closely monitored especially the one that close with methane producer
2 Gas Form / State Methane in gas form can easily be transported through pipeline. However, it also means that i could easily get leaked.
3 Density Methane can dilute oxygen on confined places. Methane concentration level must be considered when releasing permit to work.

Methane Gas on Plume

Plume is visible or invisble cloud of gases which spread out to the air once its released. Methane considered as invisible plume as it cant be seen by naked eyes and often called as methane plume. The spread level of methane plume will be dependent on following parameter

  1. wind parameter (speed)
  2. temperature (sunny day / night time)
Parameter Horizontal Spread Vertical Spread
Sunny Day Moderate-high High
Night time Moderate Low
High windspeed High Moderate-High
Slow windspeed Low Low

High windspeed will cause methane plume to be spreaded in horizontal manner (increasing the area of effect) as it dilute the air concentration faster and move the plumb faster. Sunny day tends to heat air which cause strong vertical mixing between the plume and air while night time has low vertical spread level. The most catastropic methane plume spreading event is occured during sunny day with high wind speed.

Due to the invisibility, methane plume need to be detected with special tools such as FGD (fire gas detector) and satellite.