ABSTRACT
The vast majority of all diesel driven ships and power plants have cleaning systems based on high-speed centrifugal separators for cleaning of fuel oil and lubrication oil.
Surprisingly the performance effectiveness in terms of separation efficiency is seldom part of the negotiation during the purchasing process, either to ensure that an effective system is installed or to compare competing systems on equal conditions. Why?
The answer to this question is that there is no adequate method to measure separation efficiency on the market. Attempts have sometimes been made to use complicated methods of analysis, measuring the presence of harmful substances in oil samples taken before and after the cleaning system. The result of these methods has always proved to be too dependent on parameters related to the specific bunker or to the lubrication oil used.
Alfa Laval has developed a laboratory method that accurately and with a very good repeatability can be used to measure the separation efficiency versus the flow rate for centrifugal separators. Comparisons between the new method and other tests using actual heavy fuel oil have shown that the correlation between separators is maintained but on different efficiency levels. The efficiency levels with actual fuel oil differs from bunker to bunker. If this new Alfa Laval laboratory method can be accepted by classification societies, engine builders, oil companies etc., the market would have an excellent tool to classify separation equipment and to compare different brands of equipment on equal conditions.
Key Words: ISME2000, Alfa Laval, Separators, Separation efficiency, Separation curve, KQ, Areaequivalent, Monodispers, Recommended capacity,
1. INTRODUCTION
The vast majority of all diesel driven ships and power plants have cleaning systems for cleaning of fuel oil and lubrication oil based on high-speed centrifugal separators.
These cleaning systems are very much focused upon during the design phase of the ship/power plant as they are considered to be essential equipment for the protection of the engines and injection pumps from abrasive solids and for maintaining the quality of the lubricating oil within allowed limits of impurities.
Considering the importance of these systems and that they are in fact doing a cleaning job that is dependant on both the design and size of the separators it is astonishing how little attention is given to the actual performance of the cleaning process. During the purchasing process the main parameters that are considered are separator throughput and price of the cleaning system. The performance effectiveness in terms of separation efficiency is seldom part of the negotiation, either to ensure that an effective system is installed or to compare competing systems on equal conditions. Why?
The answer to this question is that no adequate method to measure the separation efficiency has been available on the market. Attempts have sometimes been made to use complicated laboratory methods measuring the presence of harmful substances in the oil before and after the cleaning system but the result of these methods has always proved to be too dependent on parameters related to the specific bunker or type of lube oil. If, for example, Aluminium and Silicon are used as indicative substances for the presence of catalyst fines, no knowledge of the catalyst size distribution is obtained or, if particle counting is used the instrument can not discriminate between catalyst particles and other less harmful particles.
In case of lube oil there are a number of established analyses used to judge the condition of the oil but unfortunately none of these analyses is developed to measure particles separable by centrifugal force. The most common analyses to judge the content of sludge forming substances are those designed to measure the solubility in different organic solvents, such as n-pentane, which is completely irrelevant as measure of the separable sludge in the oil. Neither of these two cases will be possible to use as base for judging the process effectiveness, or comparing equipment of different makes on the market.
2. NEW METHOD TO MEASURE SEPARATION EFFICIENCY
Alfa Laval has developed a method that accurately measures separation efficiency versus flow rate for centrifugal separators. This method can be used to closely approximate normal operating conditions and with ability to provide accurate and reproducible results.
2.1. Comparison with other test methods
Comparisons between this new laboratory method and other tests using actual heavy fuel oil have shown that the differences in performance between tested separators are maintained but on different efficiency levels. The efficiency levels with actual fuel or lube oil differs from bunker to bunker or lube oil to lube oil respectively. Furthermore, the accuracy of existing methods using real HFO or LO is far from good.
