Crude Oil Washing (COW) has been a longstanding practice in the tanker industry since the 1970s, despite being considered a high-risk operation. The process involves using heated cargo to clean tank residues, which poses fire and explosion hazards due to the potential for cargo atomization. It’s crucial to only conduct COW with trained personnel and adhere to strict safety protocols.
COW offers several benefits over alternative washing methods, such as water. The primary advantage is that the wash medium can be discharged simultaneously with the cargo, saving time, reducing costs, and improving cargo outturn efficiency. As a result, COW has become a widely expected practice during cargo discharge, with some charter parties even specifying the number of tanks to be washed during each port visit.
HISTORY OF CRUDE OIL WASHING
The History of Crude Oil Washing: A Shift from Expediency to Sustainability
In the early days of crude oil transport, speed and profit drove the industry. Vessels were quickly discharged and refilled, with little regard for the environmental impact of tank cleaning. Open-cycle tank washing, which used warm seawater to flush out residues, was the norm. However, this practice proved disastrous, as oil pollution became a significant problem.
The 1973/1978 MARPOL Convention marked a turning point, as regulations limited the discharge of oily water and oil prices soared. In response, the industry adopted closed-cycle tank washing, which retained oil residues for sale. However, this method still used seawater, requiring costly processing to remove water and reduce cargo value.
A breakthrough came when crude oil carriers discovered that warmed cargo could be used as a solvent to strip tank residues without adding water. This innovative approach, known as crude oil washing, retained the value of the cargo and improved discharge efficiency. Today, this method is a standard practice in the industry, striking a balance between economic viability and environmental responsibility.
REGULATIONS
ANNEX 1 REGULATION AND REQUIREMENT – After introduction of Marpol, No discharge is permitted except –
- Vessel is enroute.
- Tanker is not within special area.
- Tanker is more than 50NM from the nearest land.
- Instantaneous discharge rate should not exceed 30 Liters / Nautical mile.
- Total quantity of discharge should not exceed 1/30000 of the Cargo which form the residue.
Special Area
Special area defined under Annex 1 of MARPOL are :
- European Seas
- Mediterranean sea
- Black sea
- Baltic sea
- North West European water
- South of Equator
- Southern South African water
- The Antarctic Area
- Middle Eastern Areas
- Red Sea
- Gulf of Aden
- The “Gulfs” area and Oman area of the Arabian Sea
PSSAs defined under Annex 1
- Australasia
- The great barrier reef
- The Great Barrier Reef extension
- Torres Strait area
- Coral sea
- Jomard
- Asia
- Tubbatha Reefs national park (Philippians)
MARPOL Requirements for Crude Oil Washing
MARPOL has the following legal requirements for crude oil washing:
• Existing Crude tankers of 40,000 DWT and above, and new Crude tankers of 20,000 DWT and above, shall be fitted with Crude Oil Washing Systems.
• Sufficient tanks shall be washed with crude oil to preclude the ballasting of a cargo tank in an emergency without it having been crude oil washed.
• Ballast may only be placed into tanks that have been crude oil washed.
• Sufficient tanks must be Crude Oil Washed to permit ballast only to be carried in COWed tanks.
• Every COW fitted tanker must be fitted with an Inert Gas System.
• All crude oil washing systems must be fixed and not portable.
• The ship should be provided with manuals detailing the COW and IG systems and operational procedures to be followed.
Crude oil washing procedure
You must be familiar with Slop tanks, Pumps, Tank cleaning lines, Stripping system, Tank cleaning machine onboard, Blind sector or Shadow area to well understand the procedure. There are a number of different types of tank-mounted machines used for COW operation.
Crude oil washing should be done in accordance with the instructions in the COW manual. Some Operators prefer 2 stage (Top and Bottom) and some prefer 3 Stage (Top, Middle and Bottom). Both of these method are acceptable just the condition is all the area is covered.