Unit Two. Different liquids in marine use. Fuel oil, lube oil and water treatment.
Any future motorman should know that there are several liquids that are essential for efficient engine room operation. He studies their main properties and the basic ways of treatment for gaining higher efficiency and, of course, finds out about some liquids that are produced by a ship and her crew that should be also treated before the discharging. Let’s enumerate them in brief.
Ship’s marine diesel engines run on heavy fuel oil (HFO) nowadays with low sulfur content, or on marine diesel oil (MDO). The lube oil is widely used for lubricating different machinery. For efficient operation of the engine room it is necessary to have sufficient volume of fresh water that can be achieved by seawater treatment. Every ship produces bilge water and sludge that should be treated in accordance of their type.
Part One. HFO and MDO. Treatment of Fuel Oil
Both HFO and MDO have four main properties, such as density, viscosity, flash point and pour point. The latest one is of certain concern because fuel must be stored at a temperature above that of its pour temperature to avoid wax formation and for ease of transfer via pumps for treatment and intermediate storage in settling tanks and day tanks. HFO has some more properties that should be taken into account. They are ash and sulphur content, specific gravity and carbon residue. Heavy fuel combustion products remain high in NOx, SOx, and CO2 in the exhaust gases. It’s one of the main disadvantages and the reason for MDO usage. HFO contains a lot of contaminants that are removed from the lighter oils. This makes it much cheaper than other lighter marine fuels.
In daily operation, diesel or heavy fuel oils are contaminated with water and solids. To enable the propulsion engines to work with the minimum wear possible, these oils have to undergo continuous treatment.
Treatment of fuel oil
| Answer the following questions: 1.What is the difference between MDO and HFO? 2.What is the reason of the usage MDO/HFO? 3.What is flash point/pour point? 4.Why should any fuel be treated? 5.What do you know about fuel oil treatment? *** The words in italics and their meanings can be found in the vocabulary section on the 5th page. |
Part Two. Lubricating Oil.
Lubrication is necessary to dissipate heat caused by friction, reduce friction and combat wear and tear between the surfaces of two moving components. The lube oil has the following properties: viscosity, volatility, alkalinity, detergent and oiliness. The viscosity must be calculated by taking into consideration the application and operating temperature range. Volatility should be taken into account to prevent crankcase explosions. Alkalinity is especially important for the cylinder lubrication, as it acts as a neutralizer to the acidic sulphur residues from combustion of HFO. Detergents are added to the lube oil to inhibit (замедлять) the formation of deposits of the moving components, also it helps to keep the oil clean.
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To maintain the lubricating oil's operating parameters and properties, the temperature and pressure must be controlled. The solids and water should be removed from the oil through centrifuging. The use of low quality lubricating oil can lead to several problems:
1. Less amount of lube oil in circulation causes rise in temperature thus reducing the viscosity leading the failure of boundary lubrication due to decrease in oil film thickness.
2. Lubrication oil properties can be lost or the oil viscosity will increase.
3. Increase in friction, wear, heat corrosion, contamination and noise and it reduces the engine performance.
The purifying of the oil is also necessary to maintain the original properties of the oil. Knowing the quantity of engine oil, the rule states that the amount of system oil depends on the type of engine. It should be 1lit/bhp and lube oil should not circulate more the 15 times/hr.
In daily operation, the lube oils of diesel engines are continuously contaminated. All rotating or sliding parts deposit metal impurities. Added to this are residues of the combustion process, condensed water decomposition products which settle in the lube oil sump. The oils themselves can also contain acids which, in combination with catalyzing foreign substances, can result in premature ageing of the oil. At the same time, on diesel engines, residues of the combustion process and incombustible constituents from the cylinder can also reach the lube oil circuit. These residues can lead to considerable symptoms of wear at bearing points, pistons and cylinders.
Lube Oil Treatment
| Answer the following questions: 1. What is the main property of oil? Why? 2. What can the quality of the oil be worsen? 3. What are the problems caused by using the low quality of oil? 4. How is lube oil contaminated? 5. What do you know about lube oil treatment? |
Exercise I. Put the verbs from the brackets in the correct form.
1. If the viscosity of the oil is too great, it ___ (to affect) the operation of the moving components against each other-offering greater resistance to motion.
2. If the viscosity is too low it ____ (to be able, to flow) too freely between the surfaces of the components, failing to lubricate them properly.
3. If the oil’s flash point ___ (to be) low, it ___ (to ignite) due to the high temperature of a hot spot causing an explosion of crankcase. The flash point of a marine diesel engine lube oil ____ (should, to be) above 200°C.
4. The proper treatment ____ (to achieve) aboard ship by maintaining the optimum temperatures and pressures of both the fuel and lube oil through the use of pumps, heaters, and coolers.
5. Cleanliness as well as the regular maintenance and inspection of the lube and fuel oil cleaning components __ (to be) very important and ___ (to carry out) by means of centrifuges and filters.
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6. The supply of good quality low sulfur heavy fuel oil ___ (to be) essential to the marine diesel engine combustion process.
7. Due to its properties HFO __ (to require) to be kept at high temperature for storage and usage, it __(to achieve) by use of low steam coils in the bunkers and storage tanks and a series of heaters between here and the engine fuel pumps and injectors to keep the oil between 104°F in the main bunkers and 250°F at the main engine injectors.