A new information paper by OCIMF presents the technologies and methods that are currently available for controlling or treating Volatile Organic Compound (VOC) emissions from oil tanker loading and during vessel transit.
The paper includes information on regulations, equipment, safety concerns, training and other design and installation considerations that will help operators better understand the technologies and methods available for controlling these emissions.
VOCs in cargo tanks are caused by a build-up of positive pressure that occurs during loading, the loaded voyage to the discharge port and transit from discharge to the next load port.
During loading, the amount of VOCs into the inert gas tank atmosphere is linked to the oil’s volatility, which is the tendency of a substance to vaporise. VOCs can be methane and non-methane (NMVOC).
As OCIMF informs, there are two generic approaches to VOC recovery, known as:
- Active: Active systems include a compression steb followed by condensation, absorption and/or adsorption, and
- Passive: Passive systems use vapour-balanced loading and unloading with VOC as blanket gas.
The VOC emissions control methods, systems and procedures available for limiting VOC emissions from oil tankers while loading and during vessel transit are:
- Reduced volatility
- Vapour balancing
- Thermal oxidation
- Absorption
- Adsorption
- Membrane separation
- Cryogenic condensation
- Cargo pipeline partial pressure control
- Sequential transfer of tank atmosphere
- VOCON procedure.
However, as there are several types of VOC control methods on the market, and in view of the diversification of the cargoes, the paper recommends a robust risk assessment with the manufacturer. The risk assessment namely should:
- encompass all the conditions that the installed VOC control methods will be certified to operate under, based on the potential safety hazards,
- include the specific cargo operations the vessel may undergo, including fail safe conditions
- determine personnel training requirements.
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