From twilight zone to a clear standard
For the first time, purchasers of fuel treatment systems for ships have access to a standardized test method that enables them to compare different separators and choose the correct size based on separation performance rather than throughput capacity.
Alfa Laval is one of the parties behind the development of the Separation Performance Standard. Based on a reproducible test method approved by Det Norske Veritas (DNV), this is now becoming a unified standard for independent verification of separation performance in centrifugal separators for marine fuel oils. The standard is expressed as Certified Flow Rate (CFR), and DNV already offers a voluntary Type Approval of separators with CFR as part of its new Class Notation FUEL. The next step is the establishment of an International Standard on separation performance in cooperation with major players in the marine industry.
Residual fuels contain contaminants such as water, sediment and catalytic fines all of which have to be reduced to acceptable levels prior to entering the engine. Of these, the most damaging to the engine are catalytic fines, which are hard, abrasive, irregularly-shaped particles of aluminium silicate and are a residue from the refinery process. If catalytic fines are not removed before the fuel oil is injected into the engine, they can lodge in injection pumps, piston rings and cylinder liners and cause serious wear that can, in time, lead to breakdowns.
According to the ISO 8217 fuel standard, the maximum allowable catalytic fines in bunkered fuel is 80 ppm. The engine builder typically stipulates a reduction to a maximum of 15 ppm in the fuel oil when it is injected into the engine.
To achieve satisfactory reduction of contaminants, minimise breakdowns, and prolong service intervals and engine lifetime, the oils are typically cleaned onboard ship by centrifugal separation before being fed to the engine.
However, in the absence of an approved test method for separation performance, the stipulated reduction of cat fines from 80 ppm to 15 ppm is a grey area. To date, the shipping industry has placed no specific demands on makers of centrifugal separators to prove that the equipment they recommend can achieve this level of performance.
Today, an important milestone has been reached in the history of centrifugal separation as a technology for cleaning marine fuel oils. A model test method for separation performance is now becoming a de facto standard. In cooperation with classification societies and other major players in the shipping industry, an international standard on separation performance is now being drafted.
Separator manufacturers have been under pressure to deliver more cost-effective equipment to shipyards. As a result, purifiers have been adjusted to provide higher throughput capacities, sometimes without corresponding improvements in bowl design to maintain safe and consistent cleaning levels.
This capacity race is a negative trend for the shipping industry. It can lead to excessive engine wear, costing ship operators large sums in maintenance and replacement parts. It can also lead to claims against engine builders with regard to excessive wear in engines.
Classification societies have seen it as a potential threat to the safety of sea transportation.
Changing the situation
Alfa Laval, in cooperation with a number of classification societies, has already gone a long way towards changing this unsatisfactory situation. The company’s efforts have resulted in a de facto standard for independent verification of separation performance. It is based on the DNV-approved Dyno Test Method developed in conjunction with Alfa Laval.
The new standard is expressed as Certified Flow Rate (CFR) and is an alternative to Max Recommended Capacity (MRC) as a way of specifying separator performance.
DNV’s definition for CFR is a separator’s throughput rate at which 85% of 5 micron Dyno particles (simulating harmful catalytic fines) are removed from the test oil (simulating a high viscosity fuel oil). The CFR represents a SAFE level for continuous, efficient separation.
This gives the industry independent verification and makes it possible to compare fuel oil separators based on separation performance rather than throughput capacity.
With CFR measured for every separator, the customer can specify a unit of the correct size for the task, in the knowledge that the installed unit will be fit for the intended purpose and eliminate the risk of installing an undersized unit.
The method utilizes 5 micron Dyno particles added into a particle-free synthetic fuel oil of defined viscosity. The Dyno particles are identically-sized, homogeneous, spherical plastic particles, normally used for the calibration of instruments. The selected Dyno particles size is in the critical size range of catalytic fines and their density is similar to catalytic fines. The Dyno test represents the most effective method for simulating the separation of catalytic fines from fuel oil.
A standard means clear benefits
Catalytic fines are not available in any standard size distribution. Fuel oils also vary in terms of both chemical characteristics, which affect the polarity, and in physical characteristics like density and viscosity. Due to these wide variations, it is impossible to obtain repeatable and comparable results from tests made on actual bunkers. There is hence a need for a standardized test method using well-defined oil and particles.
The development of the Separation Performance Standard is positive for the shipping industry as a whole. For the ship-owner, the overall benefits are clear. Different separators can be compared on equal terms before deciding on purifiers for new-buildings. The ship-owner no longer needs to trust the claims of the supplier when there is an independent international performance standard he can rely on.
The ship-owner may find that he needs to invest in a larger separator when he makes his selection according to CFR. This, however, can be compared with buying a separator based on MRC, plus paying an insurance fee against damage to the engine caused by inadequate separation. Analyses indicate that a reduction in engine wear of as little as 2% makes the selection of separators according to CFR a profitable investment. A larger separator will always give higher separation performance than a smaller one at a given flow rate.
Ship-owners have been quick to recognize the benefits and have already begun specifying HFO separators for new-buildings according to “the DNV certified flow rate method (CFR)”. By doing so, they ensure a safe margin against wear and problems due to inadequate cleaning of the fuel. The margin is important in cases where fuel characteristics and operating parameters are substandard. Also, with separation performance specified, purifiers of different types and from different suppliers can be compared more easily in terms of price / flow rate ratio.
Representatives of classification societies, ship-owners, engine builders and oil companies have agreed that a standardised method for testing separation efficiency will benefit the shipping industry and contribute to enhanced reliability and safety in sea transports.
Catalytic fines are hard, abrasive, irregularly shaped particles of aluminium silicate, here embedded in a piston ring, that can cause serious wear and lead to breakdowns.
Based on the response received from the shipping industry, the first step towards an ISO standard has been taken. Thus, one given separator will have two alternative throughputs: Maximum Recommended Capacity according to the separator maker’s assessment (separation performance unspecified), and Certified Flow Rate according to Class (specified separation performance), i.e., ensuring a safe cleaning level of HFO with regard to removal of catalytic fines and other contaminants.
Go to Index of # 3(29) 2009