L06 - Volatile Organic Compounds (VOC)

Question 1

What are VOCs?

Answer 1

Volatile Organic Compounds are the lighter hydrocarbons that vaporise during the ship oil product loading process.

VOCs also include the unburnt hydrocarbons (from fuel) that may enter the atmosphere.

Question 2

From where are VOCs emitted?

Answer 2

• VOCs in shipping are mainly polluting the port of oil loading.
• They could be discharged as part of tank washing / tank purging
  processes as well.
• Other sources of VOC: From other oil-based products or industries
  (chemical, petroleum, petrochemical, paint, … industries).
• Generally, VOC are associated with production and use of fossil fuels
  (oil wells, refineries, petrochemical industry, oil-based process
  industries, fuel storage areas, discharges from fuel tanks, etc.)

Question 3

What are the sources of VOCs?

Answer 3

• A variety of sources
• Fuel sources (transport and other
  industries).
• Chemical industries (oil-based
  products)

Question 4

how are VOCs emitted from tankers when loading cargo?

Answer 4

1. Displacement of Vapors:

• Loading Process:
  When oil is loaded into the cargo tanks of a tanker, it displaces the air and vapors already present in the tank. This displaced mixture of air and hydrocarbons, which includes VOCs, is expelled through the tank’s venting system to prevent over-pressurization.
• Vapor Composition:
  The expelled vapors contain hydrocarbons that are part of the oil being loaded. These hydrocarbons are typically in a gaseous state at the tank’s temperature and pressure and are released as VOCs.

2. Evaporation from the Oil Surface:

• Volatilization:
  As oil is loaded, the surface area of the liquid oil in the tank increases, leading to the evaporation of lighter hydrocarbons from the oil into the vapor phase. This evaporation process contributes additional VOCs to the vapor being displaced.
• Temperature Influence:
  Higher temperatures can increase the rate of volatilization, resulting in higher VOC emissions.

3. Breathing Losses:

• Thermal Expansion:
  After loading, as the temperature of the oil increases (due to solar heating or other factors), the vapor pressure of the oil increases, causing more hydrocarbons to evaporate. This thermal expansion can result in further emissions of VOCs through the tank’s venting system.
• Pumping Operations:
  During oil transfer operations, changes in the tank’s liquid level can also cause “breathing” emissions as the tank’s vapor space volume changes.

Question 5

What is the impact of VOCs?

Answer 5

1. They are carcinogenic. (can cause cancer)
2. Supports the smog formation

NOx + VOC + PM + other air
pollutants + water vapour +
sunlight = smog

Question 6

How to mitigate VOC?

Answer 6

1. Reduction at source (avoid leakage, collect back to ports, etc.)
2. Absorption
3. Combustion (e.g. flaring)
4. In shipping, the main case is VOC at ports of loading for oil tankers and there are specific regulations for this purpose.
5. All other cases has no regulation (VOC from bunker tanks, due to
   tank washing and tank purging, etc.)

Question 7

Name two chemical compound that you consider as a VOC.

Answer 7

Alcohols:
Methanol (CH₃OH)
Ethanol (C₂H₅OH)
Propanol (C₃H₇OH)
Butanol (C₄H₉OH)

Aliphatic Hydrocarbons:
Methane (CH₄)
Ethane (C₂H₆)
Propane (C₃H₈)
Butane (C₄H₁₀)

Question 8

What are the two main impacts of VOCs?

Question 9

In shipping, which type of ships send highest level of VOCs to the
atmosphere?

Question 10

An oil tanker causes most VOC pollution in which of the following
modes of operation? Give your reasons.
– During discharge of oil
– During loading of oil
– During passage operation

Question 11

Name two other industries that in your view emit significant levels
of VOCs?