Knutsen VOC Technology
To reduce the emission of Volatile Organic Compounds (VOC) to the atmosphere Knutsen OAS Shipping AS has developed the KVOC® technology. This is a technology which reduces the emission of VOC from tankers during loading and transit. VOC are the mixture of low molecular weight organic compounds in crude oil that can be released from oil and oil products during production, processing, loading, transport, unloading and storage. The incentive to reduce the VOC emission worldwide is environmental protection and cost reduction by minimizing product losses.
When loading through a conventional drop line VOC is generated due to very low pressure in top of the drop line. Once VOC is generated it is carried with the oil into the cargo tanks where it is released and vented to air together with the inert gas. The low pressure in top of the drop line generating the VOC is caused by the suction created when the liquid flows down a vertical pipe. This mechanism for VOC generation will also occur in piping system at high elevations (upstream vertical down flow) and downstream throttling nozzles at premises also outside the vessel. The process where gas is released from the oil is called a flash process and is the main contributor to VOC generation during production, processing, loading, transport, unloading and storage.
The basic principle of KVOC® technology is to prevent generation of VOC during loading and transit by installing new drop lines specially designed for each tanker. These drop lines will have an increased diameter compared to a conventional drop line. The KVOC® drop line is designed to obtain maximum VOC reduction effect for all loading rates from zero up to the maximum design loading rate.
The KVOC® technology is based on feeding the oil at deck level tangentially into the specially designed drop line. Inside the KVOC®, the oil flows at the cylinder wall leaving and open space in the middle. The increased diameter compared to a conventional drop line reduces the velocity of the oil and therefore the drag forces of the loaded oil. Since the drag forces of the oil is reduced, the buoyancy forces of the oil together with the open space in the middle of the column allows the gas to rise inside the column.