What’s Propelling Marine Lubes?

2012-06-08   来源：润滑油情报网 网友评论 0 条

 More than 3,000 years ago, a small group of cities in the eastern Mediterranean began trading their most precious commodity (purple dye) by sea. Known as the Phoenicians, they ventured in classic oar-and-sail powered   vessels throughout the Mediterranean, establishing trading posts in Spain, France, Italy, Sicily, Greece, North Africa and ultimately, even the British Isles. For their dye and other products such as timber and fine glass objects, they received copper, gold, tin and other materials.

   The Phoenicians could rightfully be called the creators of maritime commerce, maintaining their trade for nearly 700 years before being overthrown by the Persians and then the Greeks. Their marine lubricants probably consisted of nothing more than some animal fat to lubricate oarlocks, rudders or sail rigging.

   Today, not just the Mediterranean but every ocean on Earth has extensive maritime traffic moving   cargo and people. Sails and oars have given way to engines and turbines, and the lubricants now include stern tube lubes, hydraulic fluids, greases, gear oils, cylinder oils, trunk piston engine oils and conventional heavy-duty engine oils.  

   The scope of modern maritime operations is massive. In addition to passenger travel by ship, cargo is carried in three primary modes: tanker, bulk shipment and containers. The last of these is the fastest-growing, having increased in traffic by 83 percent since 2000. Annual container movements for 2007 were estimated at 420 million TEU, or twenty-foot equivalent units. If that number seems a bit obscure, try this: 420 million TEU is about 4.9 billion cubic feet.

   According to the International Maritime Organization, the global merchant fleet (including all types 100 gross tons and larger) was just under 100,000 ships at the end of 2008. The cargo-carrying fleet — tankers, bulk carriers, container ships and   multipurpose — counted 52,944. Until choked off by the recession, this number was steadily increasing over the last 15 years.

   In the Engine Room

   Marine engines are either two-stroke cycle (large, slow speed) diesel or crosshead engines, or four-stroke cycle (medium or high speed) trunk piston diesel engines. Both types are often turbocharged. Heavy-duty diesel engines are also used as auxiliary engines and in smaller vessels.

   Both engine types require unique lubricants, due in part to the use of residual or bunker fuels. Bunker fuels are derived from crude   residuum (“the bottom of the barrel”) and are supplied in a number of grades based on viscosity. They contain up to 5 percent sulfur as well as a great deal of ash and metals, including vanadium which is notoriously corrosive at high temperatures. The carbon residue and asphaltene content is high, leading to sludge and deposit formation.

   The two cycle crosshead engine employs separate lubricants for the cylinder liner and the crankcase, while the trunk piston models use a common lubricant (trunk piston engine oil, or TPEO) for the entire engine. Both engine designs deliver very high horsepower per cylinder. Horsepower is essential, because the engines either drive generators which provide electric power for the propellers or directly drive the prop through a gear box, moving ships of up to 200,000 deadweight tons.

   A small number of major manufacturers supply most of these engines and include such names as MAN Diesel & Turbo in Germany, Finland’s Wartsila, and Mitsubishi in Japan. Wellknown auxiliary engine suppliers include Caterpillar, Cummins, Detroit Diesel and MAN; their powerplants are more like commercial four-stroke cycle automotive or locomotive engines.  

   Lubricant Needs

   The question is how to lubricate these engines. Four-stroke auxiliary engines are often lubricated with conventional automotive engine oils or railroad engine oils, although marine lubricants can also be used. On board, these engines provide electrical and hydraulic pump power to the various systems on the ship but do not directly drive the vessel. However, auxiliary engines are often powered by bunker fuel and     therefore require TPEO. There are applications for inland marine using railroad or heavy-duty engine oil, but engines such as some fishing vessels use TPEO (with a base number of 12 to 20) where the fuel sulfur is higher and the application more demanding.

   Marine cylinder lubricants (MCL) are used in large-bore, slow-speed two-cycle engines to lubricate the cylinder walls   and minimize blowby into the crankcase. These oils are designed to deal with the normally very high sulfur content of bunker fuel. The MCL components provide sealing capability, lubricity for the cylinder liner and protection against the corrosive effects of the acids formed in combustion.

   Separately, the crankcase is lubricated with oils that provide protection against wear and corrosion. These oils also provide lubricity, corrosion protection, antiwear and anti-scuff protection, hightemperature stability, antioxidancy and detergency. An unusual aspect of these oils is that their viscosity is lower than one might expect. This   is due to the fact that MCL blowby causes an increase in crankcase oil viscosity. SAE 20 and SAE 30 are preferred for this application. Both oils — the MCL and crankcase lubricant — must be compatible with each other due to the cross contamination that occurs.

   TPEO is used in four-cycle, medium-speed trunk piston engines, and lubricate the entire engine. They also   must provide lubricity, corrosion protection, antiwear and anti-scuff protection, high temperature stability and antioxidancy, as well as superior detergency and dispersency to reduce ring deposits. SAE 40 and SAE 50 grades are the most commonly recommended. Many of these oils carry the nowobsolete API CF category designation.

   In addition, there is also a berth for more common API CH-4 diesel engine oils. There are a large number of four-cycle, high-speed engines used in auxiliary applications and for smaller vessels. Typically, SAE 40 and SAE 15W-40 oils are used in these situations.  

   Globally, marine lubes are a big market — an estimated 3 million metric tons a year pre-recession. More recently, additive maker Infineum pegged 2009’s volume at just 1.45 million tons of cylinder oil and 772,000 tons of TPEO. Since the trade is global, so are the top suppliers: The major marketers are the giants of the oil industry and include BP, Chevron, ExxonMobil and Shell.  

   Oil Approvals

   Marine engine builders each have their own process for oil approvals and don’t rely on industry standard tests such as those used by U.S. heavyduty engine manufacturers. Because engine builders will not fully honor their warranties unless approved oils are used, most ship owneroperators want approved oils even after the warranty has expired. There are no industry recognized test procedures, and the OEMs generally require field trials. As with North American heavy-duty engine oils, approvals are granted to oil companies on finished lubricants, and not simply to additive packages.    

   A typical approval process involves presenting the OEM with available bench and engine test data, finished oil and base oil properties. If the OEM decides the data are satisfactory, it will issue a letter of “no objection” for field testing. From there, the OEM will conduct an initial inspection of 2 to 4 cylinders of a test engine. Then fresh oil, fuel and used oil must be monitored during the test, which can last for 4,000 to 6,000 hours of operation. A final test inspection for deposits and wear is conducted by an OEM engineer.

   All of this can cost an oil company $50,000 to $100,000. Approval is granted by the OEM after the oil company submits a report of the field test and a   request for the oil to be approved

   Regulatory Realities

   The big issues for marine engines are the same as for land-based ones: fuel consumption and emissions reduction.

   Fuel economy is a crucial issue for ship operators. Costs for bunker fuel essentially track the price of crude oil, which continues to rise. However, new ship and engine designs can offer major improvements in fuel economy. Current container vessels, for example, consume bunker fuel at the rate of about 360 metric tons per day. Newer designs, operating at speeds of about 25 knots, have lowered that to 260 tons. That’s a 28 percent improvement — meaning   greater profits to the ship operator and/or lower prices to customers.

   Emissions are another major hurdle. Reducing fuel emissions is necessary to control emissions of nitrogen oxides, sulfur oxides and CO2 , but the drive to clean the air has spawned serious new regulations, and created economic and technical headaches for ship owners, operators and port authorities.

   Certain areas of the world, but not all, have restricted the amount of sulfur in bunker fuel. For instance, the North Sea & English Channel area created a SO x Emissions Control Area (SECA) which imposed a 1.5 percent maximum for sulfur in bunker fuel in August 2007. A SECA in the Baltic     has the same restriction, in force there since 2006.

   This is particularly troublesome to ships arriving from other areas of the world, since they may be operating on higher sulfur fuels and may need to put into port at great cost to change to the lower-sulfur product, if it’s not already aboard.

   Meanwhile, the California Air Resources Board (CARB) has decreed that all ships operating in California waters and in port must operate on distillate fuel. CARB also ordered that no auxiliary engines be run in port after a ship has been berthed for one hour; they can only start up in order to leave port.

   In October 2008, member states of the IMO adopted new international standards for marine diesel engines   and their fuels (2008 Amendments to MARPOL Annex VI) that apply globally as of July 1, 2010. The amendments establish additional, more stringent emission requirements for ships that operate in designated coastal areas where air quality problems are acute.

   On April 30, 2010, the U.S. Environmental Protection Agency published final emission standards under the Clean Air Act for new marine diesel engines with per-cylinder displacement at or above 30 liters installed on U.S.-flagged vessels. These standards are equivalent to those adopted in the amendments to MARPOL Annex VI. The emission standards apply in two stages: Near-term standards for new-built engines will apply beginning in 2011,   and long-term standards requiring an 80 percent reduction in nitrogen dioxides (NO x ) will begin in 2016.

   The Future

   The search for ships that are more fuel efficient and less polluting has led to some new innovations in ships propulsion. One novel approach is the so-called “Sky Sail” which is a large parachute tethered to the ship’s bow, supplying additional power to move the vessel. Other ventures are looking at fuel cell technology to move ships. This is much further down the road, and cost and efficiency are still the two major stumbling blocks.

   In the world of present-day ships, there is a great deal of interest in extended drain oils for marine applications.   The volume of oil used annually represents a significant cost, not to mention a logistics challenge. By extending drains through improved oil quality, the ship operator may gain on product and logistic costs as well as performance. This especially applies to TPEO and particularly to power generating, where the application is very severe and TBN loss can reach condemning limits before an engine is due for overhaul.

   Marine commerce has come a long way in 3,000 years. The Phoenicians would hardly recognize it, but would be very impressed with the scale and power of the ships that today move global trade. And in another 3,000 years, who knows what they’ll look like?