The effects of gravity can be amplified by the use of centrifugal force to the extent that the separation process becomes rapid and continuous.

Transcription

1 Universidad Nacional Experimental Marítima del Caribe Vicerrectorado Académico Coordinación de Idiomas English VI. Maritime Engineering Marine facilities Unit VII.Marine purifiers and clarifiers Read the following text about the main processes of removing impurities from fuel for engines to work more efficiently. Separation Separation as a means of removing impurities from fuel can be undertaken by means of gravity in a settling tank or by means of centrifuging the fuel. Both methods work on the same principles that by subjecting the fuel to a constant force, the denser components of the fuel i.e. water and dirt will be separated from the lighter components i.e. the fuel itself. Gravity acting on the fuel as it passes slowly through the tank will separate the denser components from the fuel where they will accumulate at the bottom of the tank. The contaminants can then be removed by sludging the tank. Simple Gravity Separation Centrifuging The effects of gravity can be amplified by the use of centrifugal force to the extent that the separation process becomes rapid and continuous. The centrifugal separator is used to separate two liquids, for example oil and water, or liquid and solids as in contaminated oil. Where a centrifuge is arranged to separate two liquids, it is known as a 'purifier'. Where a centrifuge is arranged to separate impurities and small amounts of water from oil it is known as a 'clarifier'.

2 Reading comprehension. Write True or False. 1. The process of removing impurities from the fuel can be done by means either of gravity separation or centrifuging the fuel. 2. Gravity separation and centrifuging are based on a different principle. 3. Centrifuging is the process by which the effects of gravity can be amplified by the use of centrifugal force. 4. Centrifuging accelerates the process of separating impurities from the fuel. Answer these questions. 1. What is a centrifugal separator used for? 2. What is the difference between a purifier and a clarifier? Vocabulary Complete the following text with the words in the box. breakdowns - water - centrifuging - combustion - impurities The separation of and from fuel oil is essential for good. The removal of contaminating impurities from lubricating oil will reduce engine wear and possible. The of all but the most pure clean oils is therefore an absolute necessity. Grammar Complete this chart by inserting words found in the previous reading and exercises. separate centrifuge remove contaminate Separator, separation Unscramble the words to form meaningful sentences. as separators are known of two liquids centrifugal used for purifiers - of different densities the separation

3 speeded up separation the use is a centrifuge by of How does a centrifuge work? A centrifuge consists of an electric motor drive to a vertical shaft on the top of which is mounted the bowl assembly. Centrifuges work by rapidly spinning a bowl containing the liquid, thus producing the required centrifugal force to produce separation. When a bowl containing impure fuel is rotated, centrifugal forces will throw any item with density greater than the fuel oil density (solids and free water) to the periphery of the bowl The centrifugal separation of two liquids, such as oil and water, results in the formation of a cylindrical interface between the two. The positioning of this interface within the centrifuge is very important for correct operation. The setting or positioning of the interface is achieved by the use of dam rings or gravity discs at the outlet of the centrifuge. Various diameter rings are available for each machine when different densities of oil are used. As a general rule, the largest diameter ring which does not break the 'seal' should be used. Cleaning oil which contains little or no water is achieved in a clarifier bowl where the impurities and water collect at the bowl periphery. A clarifier bowl has only one outlet. No gravity disc is necessary since no interface is formed; the bowl therefore operates at maximum separating efficiency since the oil is subjected to the maximum centrifugal force

4 Answer these questions. 1. What does a centrifuge consist of? 2. How does a centrifuge work? 3. What occurs when a bowl containing impure fuel is rotated? Label the parts of this centrifugal separator Heavy duty motor - Spinning bowl - Centrifuge body - Clean outlet - Dirty supply inlet Maintenance The bowl and the disc stack will require periodical cleaning whether or not an ejection process is in operation. Care should be taken in stripping down the bowl, using only the special tools provided and noting that some left-hand threads are used. The centrifuge is a perfectly balanced piece of equipment, rotating at high speeds: all parts should therefore be handled and treated with care. For a prolonged safe, trouble free and efficient operation of machinery and system on board ship, it is important that there is proper maintenance, record of correct parameters and prevention of impurities from entering the systems. The first and second points are a part of routine duties; however for preventing impurities from entering, it is important that every system is incorporated with filters and strainers which help in removing contamination from the system.

5 Filters. A filter is a fine mesh screen which is used to remove impurities from oil, water and air on ship. Filters are mounted in pairs as a duplex system so that one can be used and other is kept on standby at a time. Filter can be used both in low pressure (suction) and discharge (high pressure) side of the system and is used to remove the smallest part of dirt which is carried away in the system. The cleaning frequency of filters depends upon the type of the filter. The schedule is normally included in the planned maintenance system on board. Types of filters Hydraulic Filter: Hydraulic filters are very useful for removing solid contamination from lube and fuel oil systems of marine machinery. Without filters in the lube or fuel oil system, the machinery internal parts, bearings, piston, rings, liners etc. can get damaged, which will result in inefficient working of the machinery. Water Filter: The sea water and fresh water systems on board ship are provided with line filters in order to trap the solid impurities flowing in the system. Normally the sea water side has more numbers of filters incorporated in the line as compared to the fresh water system as the latter is a closed system. Air Filter: These filters are used on board so that the compressed air supplied to different machinery and systems get pure air for efficient operation of the same. Special filters