Introduction
· Requirements for COW system (REG 33 of MARPOL)
· I.G system shall be provided in every tanker having COW
· Only those cargo tanks can be ballasted that have been COW
· Not following the above is a contravention of the International rules
· All ships with COW must have a “Operations and equipment manual” approved by the Administration
· Every new crude oil tanker above 20,000 DWT and every existing tanker above 40,000 DWT shall be fitted with cow system
· To comply with requirements within 1 year after first engaged in the crude oil trade or by the third voyage carrying crude oil suitable for washing, whichever later
· Compliance of cow specifications to be shown in IOPP certificate
· Advantages of COW
§ Increased cargo out turn
§ Reduced sludge accumulation
§ Reduced gas freeing time
§ Reduced manual cleaning
· Disadvantages of COW
§ Does not eliminate water washing
§ Need for additional equipment
§ Specialized man power required
§ Increased stay in the discharge port
§ Increased work load
§ Increases corrosion rate inside the tank
Design of COW system
· Parts of a COW system
o Pumps
o Piping
o Fixed washing machines
o Stripping system
· Factors influencing the effectiveness of COW
o Characteristics of the crude oil
§ Wax content
§ Specific gravity
§ Dissolved sediments
o Temperature of oil
o System pressure
o Nozzle rotation
o Shadow sectors in the tank
o Stripping effectiveness
o Location & number of washing machines
· Number & Location of washing machines is governed by the regulations in MARPOL
o 85% of the VERTICAL surface area inside a tank must be covered by the direct impingement of the jet
o 90% of the HORIZONTAL surface area inside a tank must be covered by the direct impingement of the jet
· Jet length is governed by the washing pressure & nozzle diameter
· Jet length should be such as to be effective in fulfilling the requirements of MARPOL
· Number of machines that can be run simultaneously is given in the COW operations manual
· Running more than above machines causes a drop in system pressure and thereby washing effectiveness
· Minimum system pressure to be maintained is given in the COW operations manual
· Minimum recommended trim during washing given in the COW operations manual
· The given conditions of the COW operations manual must be complied with for a effective wash
· Diameter of piping, Number of machines & fluid velocity in the pipe have a relationship that goes into the designing of the system to satisfy MARPOL constructional & operational requirements
Crude oil washing (COW) is a system whereby oil tanks on a tanker are cleaned out between voyages not with water, but with crude oil - the cargo itself. The solvent action of the crude oil makes the cleaning process far more effective than when water is used. There is usually a final water rinse but the amount of water involved is very low. The system helps prevent pollution of the seas from operational measures ¹.
Crude oil washing was made mandatory for new tankers by the 1978 Protocol to the MARPOL Convention. Regulation 33 of MARPOL Annex I requires every new crude oil tanker of 20,000 tons deadweight and above to be fitted with a cargo tank cleaning system using crude oil washing .
Some benefits of crude oil washing include a substantial reduction in air pollution capacity since less oil remains aboard after discharge and also much less oil-contaminated water is handed throughout the ballast passage. It also leads to an increased cargo out turn, decreased storage tank rust caused by water washing, and a reduction in time and cost of tank cleaning .
Crude oil washing (COW) is a system whereby oil tanks on a tanker are cleaned out between voyages not with water, but with crude oil - the cargo itself. The solvent action of the crude oil makes the cleaning process far more effective than when water is used. There is usually a final water rinse but the amount of water involved is very low.
Crude oil is pumped back and preheated in the slop tanks, then sprayed back via high pressure nozzles in the cargo tanks onto the walls of the tank .
Crude oil washing was made mandatory for new tankers by the 1978 Protocol to the MARPOL Convention. Regulation 33 of MARPOL Annex I requires every new crude oil tanker of 20,000 tons deadweight and above to be fitted with a cargo tank cleaning system using crude oil washing .
