IG and Crude Oil Washing
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Transcript of IG and Crude Oil Washing
Inert gas systemInert gas system
What is inert gas?Ans:Inert gasAn inert gas is any gas that is not reactive under normal circumstances.In marine applications, inert gas refers to gases with a low content of oxygen that are used to fill void spaces in and around tanks for explosion protection. There are two types of inert gas which are either based on nitrogen or on flue gas.
Fire and explosion are among the greatest threats to the mariner; a tankship carrying crudeoil, refined petroleum, or chemicals is an even greater threat. Fortunately, a properlydesigned, installed, operating, and maintained inert gas system (IGS) will completelyprevent fire and explosion in an intact ship tank. Since the late 1970's, inerting has been required for most U.S. and foreign tankships. As of1 June 1983, inert gas (IG) systems are required aboard all U.S. crude oil carriers over20,000 deadweight tons (DWT) and all U.S. product carriers over 40,000 DWT.
When did IG system start?
Typical arrangement for an inert gas system
Scrubbera. Where feasible, all access plates and internal components such
as demisterpads and scrubber trays shall be removed. Soot and scale deposits shall beremoved prior to the inspection. The following
areas and internal componentsshould be given close attention:(1) Internal coatings should be completely intact. Check for signs of
chipping or cracking, particularly around internal fastenings.(2) Inspect gas inlet pipe in the scrubber water seal for corrosion and holesor leaking flanges, especially above the water level, that would
allow gasto bypass the seal and render it ineffective.(3) Closely inspect the internal area at the bottom of the scrubber forcorrosion, especially in way of the effluent discharge line. Check the
discharge line for clogging.(4) Inspect float switches, temperature sensors, Venturi slots,
impingement plates, packed trays, and demisters (as applicable) for damage, wastage,and corrosion.
(5) Ensure that the water heater (used to prevent water freezing) and itscontrol system are in good condition.
(6) Inspect fresh and saltwater inlet piping for corrosion or wastage, and
especially for holes or leaking flanges. Check spray nozzles for clogging
and intact condition.
BlowersThe inspection ports and access plates on all blowers shall be
opened. Blowerimpellers, bearings, and casings shall be checked for corrosion or excessivebuildup of deposits that may
cause blade failure. If accessible, fresh waterflushing spray nozzles shall be checked for intactness or clogging; the
blowerdrain piping, for corrosion or clogging.
Valves Boiler uptake (or IGG) valves, blower inlet and discharge valves, recirculatingvalves, pressure regulating valves, deck mechanical
nonreturnvalves, deckisolating valves, and IGS isolating valves shall be disassembled for inspection.Valve internals shall be inspected for cleanliness,
and for signs of corrosion orerosion. Careful attention should be given to "butterfly" mechanisms to ensurefree, smooth operation and proper seating. Check nonreturnvalve seals. Ifaccessible, either through inspection ports or
disassembled components, theinternal areas of the inert gas main and branch lines shall be checked forexcessive scale buildup or soot deposits, which could
result in a critical gaspressure drop between the IGS blowers and the cargo tanks.
Deck Water SealThis shall be disassembled. Internal
coatings shall be inspected for intactness;housing and heating coils, for corrosion; gas inlet pipes, for corrosion,
holes, orleaking flanges (especially above the water level) that would permit gas to
bypass the seal; and drain lines, for clogging or corrosion. The demister
padsmust be clean and free of soot and scale deposits. Check that the heater(used
to prevent water freezing) and its control system are in good condition.
Only the wet type of water seal is permitted; in this type there is always
waterpresent in the device and the inert gas flowing through the seal always bubblesthrough a layer of
water. Semidry seals, in which water is not always present,are approved for U.S. vessels on a casebycase
basis. "Dry" water seals andthe double blockandbleed
assemblies are not permitted aboard U.S. vessels.
P/V ValvesP/V valves shall be disassembled and inspected for corrosion and the chokingof flame screens from soot, oil entrainment, and rust.
The forward pressurerelease valve shall be disassembled and the butterfly mechanism inspected forfree, smooth operation and
proper seating. If feasible, the liquidfilled,pressure/vacuum breaker shall be drained and inspected for sludge, sediment,or
soot deposits that could render the component ineffective. Highvelocityventinstallations shall be inspected for internal
deposits or corrosion that mayreduce venting capacity or prevent tight closure.
IG GENERATOR
Gia Nitrogen System (psa) on Tankers
In case of Ig System failure on tankers , Nitrogen is used to inert the Cargo tanks. It works on the Pressure Swing
Adsorption Principle.
Suggested Maintenance Programme
Component Preventive maintenance Maintenance interval
Flue gas isolating valves
Operating the valveCleaning with compressed or steam
Before start-up and one weekBefore operating valve
Dismantling for inspection and cleaning
Boiler shutdown
Flue gas scrubber
Water flushing After use
Cleaning of demister Three months
Dismantling of level regulators and temperature probes for inspection
Six months
Opening for full internal inspection Dry docking
Overboard pipes and valve from flue gas scrubber
Flushing with scrubber water pump for about one hour
After use
Dismantling of the valve for overhaul, inspection of pipeline and overboard end
Dry-docking/regular period
Blowers Vibration checking While running
Flushing After use
Internal inspection through hatches After flushing and six months
Dismantling for full overhaul of bearings, shaft tightenings and other necessary work
Two years or more frequently if required/dry-docking
Deck water seal
Dismantling of level regulators/float valves for inspection
Six months
Opening for total internal inspection One year
ComponentPreventive maintenance Maintenance interval
Overhaul of auto-valves One year
Deck mechanical non-return valve
Moving and lubricating the valve if necessary
One week and before start
Overhaul of auto-valves One year/18 months
Pressure-vacuum valves
Operating and lubricating the valves Six months
Opening for full overhaul and inspection One year
Deck isolating valve
Opening for overhaul One year
Gas pressure regulating system
Removal of condensation instrument, air supply
Before start
Opening of gas pressure regulating valves for overhaul.
As appropriate
Liquid filled pressure-vacuum breaker
Checking liquid level when system at atmospheric pressure
When opportunity permits and every six months
I.g. system Panel
Crude oil washingCrude oil washingCrude 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.
COW is mandatory on new tankers under the International Convention for the Prevention of Pollution by Ships (MARPOL 73/78).
1)The problem – pollution from oil cleaning operations
2)Development of Load on Top
3)Development of Crude Oil Washing
Crude Oil Washing
Development of Load on Top Under load on top, tanks were cleaned as previously using high-
pressure hot-water cleaning machines. However, instead of pumping the resulting oily mixtures overboard, they were pumped
into a special slop tank. During the course of the return voyage to the loading terminal this mixture separates. Oil, being lighter than water, gradually floats to the surface leaving the denser water at the bottom. This water is
then pumped into the sea, leaving only crude oil in the tank. At the loading terminal fresh crude oil is then loaded on top of it.
The process had advantages for the owner of the oil, since the oil normally lost during tank cleaning can be saved (as much as 800
tons of oil on a large tanker), but the main beneficiary was the environment. Some experts believe that without load on top the
amount of oil being dumped into the sea as a result of tank cleaning could have reached more than 8 million tons a year.
Development of Crude Oil WashingThe introduction of load on top was a great contribution to the fight
against marine pollution but it did not completely eliminate pollution resulting from tank cleaning operations. Although the amount and rate of discharge is carefully regulated the process
still resulted in some pollution occurring. In the late 1970s an improvement was introduced. Instead of
using water, the tank cleaning machines used crude oil - in other words, the cargo itself.
When sprayed onto the sediments clinging to the tank walls, the oil simply dissolved them, turning them back into usable oil that could be pumped off with the rest of the cargo. There was no
need for slop tanks to be used since the process left virtually no slops. The process became known as Crude Oil Washing (COW).Crude oil washing meant that the mixture of oil and water which
led to so much operational pollution in the past was virtually ended. At the same time, the owner is able to discharge far more of this cargo than before, since less of it is left clinging to the tank
walls and bottoms.
Crude oil washing regulations Crude oil washing was made mandatory for new tankers by the 1978 Protocol
to the MARPOL Convention.MARPOL Annex I Regulation 13 (6) 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.Regulation 13B states that COW installation and arrangements should comply with at least all of the
provisions of the Specifications for the Design, Operation and Control of Crude Oil Washing Systems adopted by IMO in 1978, as may be revised. In 1999,
IMO adopted revised specifications for COW by resolution A. 897(21) Amendments to the revised Specifications for the Design, Operation and
Control of Crude Oil Washing Systems (Resolution A.446(XI), as amended by resolution A.497(XII).
Crude oil washing regulations and specification
The problem – pollution from oil cleaning operationsTankers carry their cargo in a number of tanks or compartments within the hull of the ship. Before the introduction of segregated
ballast tanks, tanks were cleaned after the oil was discharged and about one third of them filled with seawater so that the ship's
propeller is properly immersed and it has correct handling and sea‑keeping characteristics. This process is known as ballasting.
In the 1950s, there were no alternative ways of cleaning tanks. The OILPOL Convention, adopted in 1954, tried to alleviate the pollution from this process by prohibiting the discharge of oil or oily mixtures within 50 miles of land. This limit was extended to
100 miles in certain areas which were regarded as being particularly endangered.
In the late 1960s, concern about the waste of oil and pollution caused by this process led the industry to look for an alternative.
The result was to become known as "load on top".