Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

Transcription

1 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

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3 Contents Fuel Oil Quality... 5 Analysis Data... 6 Fuel Oil Stability... 8 Fuel Oil Treatment... 8 Centrifuging Recommendations... 9 Fuel Sampling Supplementary Fuel Oil Treatment Fuel Oil System Operational Aspects Low-sulphur Fuel Operation Off-spec. Fuels Lube Oil Blending on Board Cylinder Oil, Low Speed Diesels Performance Verification of Cylinder Oils Fuels and Lubes for Stationary Two-stroke MAN B&W Engines List of References Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 3

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5 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels MAN B&W Two-stroke Engines Fuel Oil Quality MAN Diesel s engines are designed to operate in accordance with the unifuel principle. For specific guidelines for fuel and lube oils for gensets, contact MAN Diesel in Augsburg, Germany. For guidance on purchase, reference is made to ISO 8217, BS6843 and to CIMAC recommendations regarding requirements for heavy fuel for diesel engines, edition According to these, the maximum accepted grades are RMH 55 and K55. The mentioned ISO and BS standards supersede BS MA 100, in which the limit is M9. For reference purposes, an extract from the relevant standards and specifications is shown in Table I. Based on our general service experience, and as a supplement to the abovementioned standards, MAN Diesel issues a guiding fuel oil specification, shown in Table I. Residual marine fuel standards Category ISO-8217 (Class F) Characteristic Unit Limit RMA 30 RMB 30 RMD 80 RME 180 RMF 180 RMG 380 Density at 15 ºC kg/m 3 max. 960,0 975, RMH 380 RMK 380 RMH 700 RMK 700 Test method reference ISO 3675 or ISO (see also 7.1) Kinematic viscosity at 50 ºC mm 2 /s a max. 30, ISO 3104 Flash point ºC min ISO 2719 (see also 7.2) Pour point (upper) b - winter quality - summer quality ºC max. max ISO 3016 ISO 3016 Carbon residue %(m/m) max ISO Ash %(m/m) max ISO 6245 Water %(v/v) max ISO 3733 Sulphur c %(m/m) max ISO 8754 or ISO (see also 7.3) Vanadium mg/kg max ISO or IP 501 or IP 470 (see also 7.8 Total sediment potential %(m/m) max Aluminium + Silicon mg/kg max Used lubricating oil (ULO) - Zinc - Phosphorus - Calcium mg/kg max. max. max. The fuel shall be free of ULO d ISO (see also 7.6) ISO or IP 501 or IP 470 (see also 7.9) IP 501 or IP 470 (see 7.7) IP 501 or IP 500 (see 7.7) IP 501 or IP 470 (see 7.7) a Annex C gives a brief viscosity/temperature table for information purposes only. (1 mm 2 /s = 1 cst) b Purchasers should ensure that this pour point is suitable for the equipment on board, especially if the vessel operates in both the northern and southern hemispheres. c A sulphur limit of 1.5 % (m/m) will apply in SO x emission control areas designated by the International Maritime Organization, when its relevant protocol comes into force. There may be local variations. d A fuel must be considered to be free of ULO if one or more of the elements zinc, phosphorus and calcium are below or at the specified limits. All three elements must exceed the same limits before a fuel shall be deemed to contain ULO. Table I Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 5

6 In both tables the data refers to fuel oils as delivered to the ship, i.e. before onboard cleaning. Fuel oils within the limits of this specification have, to the extent of their commercial availability, been used with satisfactory results in MAN B&W two-stroke low speed diesel engines. It should be noted that current analysis results do not fully suffice for estimating the combustion properties of fuel oils. This means that service results could depend on oil properties which are not known beforehand. This applies especially to the tendency of the fuel oil to form deposits in combustion chambers, gas passages and turbochargers. As mentioned, the data refers to the fuel as supplied, i.e. before the treatment. If a fuel oil exceeding the data in Table I is to be used, the engine builder or MAN Diesel should be contacted for advice. Analysis Data Viscosity Viscosity cannot be considered a quality criterion in its own right for fuel oils, and is stated only for handling reasons (pumps, preheaters and centrifuges). Density Density is related to the fuel quality because fuels derived from extensive refinery processing are left with a higher carbon content, are more aromatic and thus heavier. Therefore, fuels with a high density are also high in carbon residue and asphaltenes. The water separation ability of the fuel oil is ensured by limiting the density for reasons of centrifuging, as stated in the specification. Density is normally measured at higher temperatures, and the density at 15 C is calculated on the basis of tables which, depending on their origin, date of issue, and the data on which they are based, could give slightly differing densities at 15 C. Whereas the limit of 991 kg/m 3 must be observed when traditional centrifuges (before 1985, purifier clarifier) are used, 1010 kg/m 3 is accepted provided that modern centrifuges capable of handling fuels of such density are installed. Flash point The flash point limit is set as a safeguard against fire only. Pour point The pour point indicates the minimum temperature at which the fuel should be stored and pumped. Temperatures below the pour point results in wax formation. Sulphur The corrosive effect of sulphuric acid during combustion is counteracted by adequate lube oils and temperature control of the combustion chamber walls. The cylinder lube oil feed rate must be according to the MAN Diesel recommendation. The sulphur content has a negligible effect on the combustion process. Carbon residue The carbon residue is measured as Conradson Carbon or Microcarbon. Fuels with a high carbon residue content could cause increased fouling of the gasways, necessitating more frequent cleaning, especially of the turbocharger and exhaust gas boiler. Some changes in combustion, requiring adjustment of maximum pressures for reasons of economy, could also be attributed to a high carbon residue content. Part of the carbon residues represents asphaltenes. The effect of asphaltenes on the combustion process is similar to that of the carbon residue. Asphaltenes also affects the fuel oil lubrication properties. Fuels with a high content of asphaltenes may tend to emulsify with water. Water Water in the fuel should be removed by centrifuging the fuel before use. This applies especially to salt water, the sodium content of which can result in deposits on valves and turbochargers. If the water cannot be removed online, homogenising after centrifuging is recommended. Ash Ash represents solid contaminants as well as metals bound in the fuel (e.g. vanadium and nickel). Part of the ash could be catalyst particles from the refining process. Catalyst particles are highly abrasive. Solid ash should be removed to the widest possible extent by centrifuging, and cleaning can be improved by installing a fine filter after the centrifuge (e.g. 50 μm). 6 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

7 Vanadium, magnesium and sodium Vanadium is bound in chemical complexes in the fuel and, consequently, cannot be removed. Vanadium deposits can be very hard, and may cause extensive damage to the turbocharger nozzle ring and turbine wheel. The only way to remove vanadium deposits is to disassemble the components and erase the deposits mechanically. Sodium is normally present in the fuel as a salt water contamination and may, as such, be removed by centrifuging. Sodium can also reach the engine in the form of airborne sea water mist. Vanadium, in combination with sodium, may lead to exhaust valve corrosion and turbocharger deposits. This can occur especially if the weight ratio of sodium to vanadium exceeds 1:3, and especially in the case of a high vanadium content. MAN Diesel has limited data to show that the level of sodium and vanadium in combination, and in this ratio, has led to the above-mentioned complications on MAN B&W engines. For lower contents of sodium and vanadium, the weight ratio is considered of less importance (for a vanadium content less than 150 mg/kg). Aluminium and silicon The limit to aluminium and silicon has been introduced in order to restrict the content of catalytic fines, mainly Al 2 O 3 and SiO 2, in the oil. 80 mg Al and Si corresponds to up to 170 mg Al 2 O 2 and SiO 2. Catalytic fines give rise to abrasive wear, and their content should, therefore, be reduced as much as possible by centrifuging the fuel oil before it reaches the engine. MAN Diesel recommends that 80 ppm of catalytic fines before the centrifuge is reduced as much as possible by the fuel centrifuge and, as a guideline, the level should in any case not exceed 15 ppm after the centrifuge, see Ref. [1] and Ref [2]. Ignition quality Normally applied analytical data for fuel oil contain no direct indication of ignition quality, neither do current specifications and standards. However, this is not an important parameter for engines with high compression ratios. In a few cases (less than five), we have observed that the fuel had such poor ignition quality that the engines could not operate properly. Analysis of the fuel in question revealed that these fuels had all been contaminated by chemical waste. at a number of fuel laboratories and builders of marine diesel engines worldwide. The test presents the Rate of Heat Release, reflecting the actual heat release process and, thus, the combustion quality of the fuel tested. By the use of calibration fuels, a recorded ignition delay in combination with the combustion quality can be converted into an instrument-related Cetane number. The test results reflect the differences in ignition and combustion properties of diesel engine fuels resulting from variations in the chemical composition of the fuels being tested. However, these test results do not reflect the functions of the actual combustion in the diesel engine, because the tests are conducted at different conditions/mechanisms than exist in the engine. With the modern high compression ratio engines, the denoted differences in the fuel, both good and bad, are not at the level indicated by the test results. The cetane number in an ignition quality test might, as such, only provide an indication of the difference in the fuels, but not whether this will have an influence on the engine performance. Magnesium, either present in the fuel, in salt water contamination or introduced via additives can, to some extent, increase the melting point of the vanadium, thus preventing the formation of deposits. Tests performed together with fuel analysing institutes give indications of the ignition and combustion qualities of the different fuels. Test instruments utilising a constant volume combustion technology have been developed and are currently being used for marine fuel testing Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 7

8 Fuel Oil Stability Fuel oils are produced on the basis of widely varying crude oils and refinery processes. Due to incompatibility, such fuels can occasionally tend to be unstable when mixed, for which reason mixing on board should be avoided to the widest possible extent. A mixture of incompatible fuels in the tanks can result in rather large amounts of sludge being taken out by the centrifuges or even lead to centrifuge blocking. Inhomogeneity in the service tank can be counteracted by recirculating the contents of the tank through the centrifuge. This will have to be carried out at the expense of the benefits derived from a low centrifuge flow rate as described below. With the introduction of new IMO emission regulations and the fuel sulphur limit in SECAs (sulphur emission control areas), more blending of fuels to comply with the regulations is taking place. For this reason, the risk of incompatibility of fuels is also higher. Fuel Oil Treatment Fuels supplied to a ship must be treated on board before use. Detailed information on fuel oil system layout can be found in the CIMAC Recommendations issued in 2005, Volume 9, concerning the design of heavy fuel treatment plants for diesel engines. Practically all fuel specifications refer to fuel as supplied and, as such, serve primarily as purchasing specifications. Furthermore, the data in a standard fuel analysis serves to adjust the onboard treatment and is actually of little use to the operator when referring to the engine operational data. Hence the basic design criterion is that engines must be capable of accepting all commercially available fuel oils, provided that they are adequately treated on board. For this purpose, a well-designed fuel oil treatment system is a must. General minimum recommendations for the layout of such a system have been speci- From centrifuges Deck Diesel oil service tank Heavy fuel oil service tank Automatic de-aerating valve Venting box Overflow valve adjusted to 4 bar Common fuel oil supply unit Full flow filter Booster pump Supply pumps Circulating pumps Heater Main engine Auxiliary engines Auxiliary engines Auxiliary engines Diesel oil Heavy fuel oil Heated pipe with insulation To fresh water cooling pump suction Fuel oil drain tank Fig. 1: Pressurised uni-fuel oil system for both main engine and gensets 8 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

9 fied and should be complied with in order to ensure proper treatment of the fuel permitted by the guiding specification. The operation of the fuel preparation system is the responsibility of the operator. Good results require both the correct system and the correct operation of the system. The fuel oil system consists of a cleaning plant (comprising centrifuging) and a pressurised fuel oil system. Fig. 1 shows the pressurised fuel oil system common for MAN B&W main and GenSet engines. utmost importance that the centrifuge is operated with as low a fuel oil viscosity as possible, and that the fuel oil is allowed to remain in the centrifuge bowl for as long as possible. Temperature of HFO before centrifuges It is often seen that the HFO preheaters are too small, or the steam supply of the preheater is limited, or that they have too low a set point in temperature. Often the heater surface is partly clogged by deposits. These factors all lead to reducing the separation temperature and hence the efficiency of the centrifuge. should always be operated with an inlet temperature of 98 C. A temperature decrease has to be followed by a reduced throughput to ensure the same cleaning efficiency, see Fig. 2. The fuel is kept in the centrifuge as long as possible by adjusting the flow rate through the centrifuge so that it corresponds to the amount of fuel required by the engine without excessive recirculation. Consequently, the centrifuge should operate for 24 hours a day except during necessary cleaning. Centrifuging Recommendations Fuel oils, whether HFO or DO, should always be considered as contaminated upon delivery and should therefore be thoroughly cleaned to remove solid as well as liquid contaminants before use. The solid contaminants in the fuel are mainly rust, sand, dust and refinery catalysts. Liquid contaminants are mainly water, i.e. either fresh water or salt water. Impurities in the fuel can cause damage to fuel pumps and fuel valves, and can result in increased cylinder liner wear and deterioration of the exhaust valve seats. Also increased fouling of gasways and turbocharger blades could result from the use of inadequately cleaned fuel oil. Effective cleaning can only be ensured by using a centrifuge. We recommend that the capacity of the installed centrifuges should, at least, be according to the centrifuge maker s specifications. To obtain optimum cleaning, it is of the In some cases, the temperature of the HFO from the preheater is unstable and fluctuates, which again results in improper cleaning of the fuel. In order to ensure that the centrifugal forces separate the heavy contaminants in the relatively limited time that they are present in the centrifuge, the centrifuge Capacity for same separation (%) cst 300 cst 700 cst Centrifuges with separate feed pumps with a capacity matched to the engine output are to be preferred. Taking today s fuel qualities into consideration, the need for maintenance of the centrifuges should not be underestimated o cst at 50 C Fig. 2: Relationship of throughput and temperature Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 9

10 On centrifuges equipped with adjusting throughput, i.e. longer retention time in the screws and/or gravity disks, their correct choice and adjustment is of special instructions should be followed. centrifuge. However, the maker s specific importance for the efficient removal of water. In this context, see section on high density fuels. If the centrifuge capacity The centrifuge manual states which installed is on the low side, in relation disk or screw adjustment should be to the specific viscosity of the fuel oil chosen on the basis of the density of used, and if more than one centrifuge is the fuel. available, parallel operation should be considered as a means of obtaining an The normal practice is to have at least even lower flow rate. However, in view two centrifuges available for fuel clean- of the above results and recommendations, serious consideration should be ing purposes, operating in serial or parallel mode. given to installing new equipment in compliance with today s fuel qualities For old type centrifuges, results from and flow recommendations. experimental work on the centrifuge treatment of today s residual fuel qualities have shown that the best cleaning capacity, we generally advise that the For determination of the centrifuging effect, particularly in regard to removal recommendations of the centrifuge of catalytic fines, is achieved when the maker be followed, but the curves in centrifuges are operated in series, i.e. Fig. 3 can be used as a guide. in purifier/clarifier mode. It is recommended that new centrifuges For the automatically operating centrifuges delivered from the mid-1980s, mance standard test according to the in- have gone through a separation perfor- suitable for treating fuels with densities higher than 991 kg/m 3 at 15 C, it dustry standard CWA is recommended to operate the centrifuges in parallel, as this results in reduced the centrifuge, fuel samples taken reg- In order to check the performance of % Rate of flow, related to rated capacity of centrifuge ularly before and after the centrifuge should be analysed. High Density Fuels In view of the fact that some fuel oil standards incorporate fuel grades without a density limit, and also the fact that the traditional limit of 991 kg/m 3 at 15 C is occasionally exceeded on actual deliveries, some improvements in the centrifuging treatment have been introduced to enable treatment of fuels with higher density. Since the density limit used so far is, as informed by centrifuge makers, given mainly to ensure interface control of the purifier, new improved clarifiers, with automatic desludging, have been introduced, which means that the purifier can be dispensed with. With such equipment, adequate separation of water and fuel can be carried out in the centrifuge, for fuels up to a density of 1010 kg/m 3 at 15 C. Therefore, this has been selected as the density limit for new high density fuel grades. Thus we have no objections to the use of such high density fuels in our engines, provided that these types of centrifuges are installed. They should be operated in parallel or according to the centrifuge maker s instructions sec RI/100 o F Fig. 3: Centrifuge makers capacity specification 10 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

11 Fuel Sampling Sampling To be able to check whether the specification indicated and/or the stipulated delivery conditions have been complied with, we recommend that a minimum of one sample of each bunker fuel lot be retained. In order to ensure that the sample is representative for the oil bunkered, the sample should be continuously taken at the ship manifold throughout the bunkering period. This is done by a continuous collection of drip sample during the bunker delivery, see Ref. [3]. This is without including the BDN (bunker delivery note) for compliance with IMO Annex VI. Analysis of samples The samples received from the bunkering company are frequently not identical with the heavy fuel oil actually bunkered. It is also appropriate to verify the heavy fuel oil properties stated in the bunker documents, such as density, viscosity and pour point. If these values deviate from those of the heavy fuel oil bunkered, there is a risk that the heavy fuel oil separator and the preheating temperature are not set correctly for the given injection viscosity. Supplementary Fuel Oil Treatment In a traditional system, the presence of large amounts of water and sludge will hamper the functioning of a clarifier, for which reason a purifier has been used as the first step in the cleaning process. With the new automatic desludging clarifiers, the purifier can, as mentioned, be dispensed with. We consider the removal of solids to be the main purpose of fuel treatment. Although not necessarily harmful in its own right, the presence of an uncontrolled amount of water and sludge in the fuel makes it difficult to remove the solid particles by centrifuging. Therefore, the following additional equipment has been developed: Homogenisers Homogenisers are used to disperse any sludge and water remaining in the fuel after centrifuging. A homogeniser placed after the centrifuge will render fresh water (not removed by centrifuging) harmless to the engine. Homogenising may also be a means to cope with the more and more frequently occurring incompatibility problems, which are not really safeguarded against in any fuel specification. Both ultrasonic and mechanical homogenisers are available. Homogenisers can also be used for moderate emission control in conjunction with emulsification of freshwater into the fuel. Homogenisers installed before the fuel centrifuge can, when considering the full range of the ISO 8217 fuel specification, reduce the efficiency of the centrifuge and, thus, the cleanliness of the fuel delivered to the engine. The sodium will not be removed from the fuel in the form of salt water. The cat fines and other abrasive material might be split up into very small particles, which are difficult for the centrifuge to separate and which will still have a harmful wear effect on the engine components. Installation of homogenisers before the centrifuge, see Fig. 4, is therefore not advisable. Sampling equipment Several suppliers of sampling and fuel test equipment are available on the market, but for more detailed and accurate analyses, a fuel analysing institute should be contacted. Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 11

12 Suggested location of homogeniser by some suppliers. Not acceptable for engine performance Deck Automatic de aerating valve Venting tank Centrifuges Fuel storage tank Heavy fuel oil service tank Diesel oil service tank From diesel centrifuges TSA TE To drain tank F.O. drain tank To F.W. cooling pump suction Main engine PI PI VSA 303 PT PSA TI TI Pre heater VT 8004 Full flow filter Circulating pumps Supply pumps Acceptable location of homogeniser Diesel oil Heavy fuel oil Heated pipe with insulation Fig. 4: Pressurised fuel oil system, with homogeniser In order to reduce the NO x level in the engine exhaust gas, water can be added to the fuel oil to create an emulsion. Clean freshwater should be used, and this is homogenised into the fuel oil at a maximum ratio of approx. one part of water to two parts of fuel oil. The water emulsion can be stable with HFO but with lighter fuels, such as gas oil and diesel oil, it may be necessary to add an emulsifier to the fuel oil before homogenising the fuel and water. The homogeniser is located between the HFO service tank and the engine, i.e. after the fuel oil purifiers. Fine filters Fine filters are placed directly after the centrifuge, or in the supply line to the engine, in order to remove any solid particles not taken by centrifuging. The mesh is very fine, i.e. down to 5 μm. Homogenising before a fine filter can reduce the risk of fine filter blocking by the agglomeration of asphaltenes. 12 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

13 Temperature after heater o C Normal heating limit Approximate viscosity after heater cst Sec RW In most installations, heating is carried out by means of steam, and the viscosity is kept at the specified level by a viscosity regulator controlling the steam supply. Depending on the viscosity/temperature relationship of the fuel oil (the viscosity index), an outlet temperature of up to 150 C might be necessary, as indicated on the guidance curves shown in Fig. 5, which illustrate the expected heating temperature as a function of the specific fuel oil viscosity in cst/50 C Approximate pumping limit cst/100 C cst/50 C sec. RW/100 F Viscosity of fuel The recommended viscosity meter setting is cst. However, service experience has shown that the viscosity of the fuel before the fuel pump is not a too critical parameter, for which reason we allow a viscosity of up to 20 cst after the heater. In order to avoid too rapid fouling of the heater, the temperature should not exceed 150 C. Fig. 5: Heating chart for heavy fuel oil Fuel Oil System A pressurised fuel oil system, as shown in Fig. 1, is necessary when operating on high viscosity fuels. When using high viscosity fuels requiring high preheating temperatures, the oil from the engine fuel oil system to the return line will also have a relatively high temperature. The fuel oil pressure measured on the engine (at fuel pump level) should be about 8 bar, which is equivalent to a circulating pump delivery pressure of up to 10 bar. This maintains a pressure margin against gasification and cavitation in the fuel system, even at 150 C preheat. In order to ensure correct atomisation, the fuel oil temperature must be adjusted according to the specific fuel oil viscosity used. An inadequate temperature can influence the combustion and could cause increased wear on cylinder liners and piston rings, as well as deterioration of the exhaust valve seats. Too low a heating temperature, i.e. too high viscosity, could also result in a too high injection pressure, leading to excessive mechanical stresses in the fuel oil system. Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 13

14 Operational Aspects All low speed engines from and including the K-GF types (from around 1973) are equipped with uncooled, allsymmetrical lightweight fuel injection valves. These allow constant operation on heavy fuel, due to the built-in possibility of circulating heated heavy fuel through the high-pressure fuel pipes, and fuel valves during engine standstill. In view of the emission regulations and the increased use of low-sulphur fuels, a special procedure is made to protect the engine when changing between fuels (see the chapter: Low-sulphur Fuel Operation ). If a change to diesel oil is necessary as a result of, for instance, the need for a major repair of the fuel oil system, a prolonged stop, or the use of very lowsulphur fuels, as required by environmental legislation, the heavy fuel in the system can be changed with diesel oil at any time, provided the change-over procedure is followed, even when the engine is not running. See also the engine instruction book. The temperature should be raised to the recommended service value, as illustrated in Fig. 5, about 30 minutes before starting-up is expected. As previously mentioned, the heating temperature must not exceed 150 C, and during operation it is not necessary to apply pipe heating by means of heat tracing. When running on diesel oil, the Compatibility of mixed fuels! Tank system considerations! High S% Low S% Fuel change-over unit Engine heat tracing system must not be used at all. However, it should be noted that the pipe heating system on drain pipes should remain in operation when running on heavy fuel. Fig. 6: Considerations to be made to before changing between high/low sulphur fuels Oil Viscosity! BN ! During engine standstill, the heated fuel oil circulating through the fuel system does not require the same low viscosity as recommended for injection. Thus, in order to save steam, the heating temperature may be lowered by some 20 C, giving the circulating oil a viscosity of up to 30 cst. Fig. 7: Recommended cylinder oil feed rates depending on the fuel sulphur level 14 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

15 Low-sulphur Fuel Operation Today, there are ECAs (emission control area, based on EU and IMO regulations) in the Baltic Sea, the North Sea and the English Channel. And more such areas are expected to come. In the USA, the EPA (Environmental Protection Agency) is considering to designate Long Beach an ECA very soon. The sulphur content has an impact on the sulphur acid emission to the air, sea and land, as well as a major impact on the particle level in the exhaust gas. Even though MAN B&W two-stroke engines are largely insensitive to the fuel quality, changing between fuels with different levels of viscosity is an important consideration to make. The cylinder lube oil base number must be considered. Operating on normal BN70 cylinder oil for too long when burning low-sulphur fuel will prevent controlled corrosion on the cylinder liners. The mechanism is a creation of an excess of deposits originating from the cylinder oil s additives. Low-BN oil is available from the major oil companies, and recommendations on the use of low and high-bn oils are also available. The fuel change-over process must follow the thermal expansion of both the fuel pump plunger and the barrel, and a procedure has been created to avoid causing damage to the fuel pumps. An automatic change-over unit will be available in In order to ensure the creation of a hydrodynamic oil film between the fuel pump plunger and barrel, a viscosity of 2 cst is required at the engine inlet. This may be difficult to achieve for some DO and GOs, and some operators may have to introduce a cooler in the fuel oil system to ensure a satisfactory viscosity level. The ignition quality of a fuel oil is not an issue for MAN B&W two-stroke engines. MAN Diesel has conducted a number of research tests showing that the MAN B&W two-stroke engine is insensitive to the poor ignition combustion quality fuels on the market today. A separate booklet called Low-sulphur fuel operation is available from MAN Diesel, Ref. [4]. Off-spec. Fuels Several selected off-spec. fuels (i.e. beyond ISO 8217) have been tested on MAN B&W s two-stroke research engine: Natural gas Bitumen Orimulsion Tallow Our research facility in Copenhagen is available for such testing. In the event that off-spec. fuels are considered for use on MAN B&W engines, it is recommended that MAN Diesel is contacted for further information regarding operational experience and any necessary precautions. Table II shows the guiding biofuel specification for MAN B&W two-stroke low speed diesel engines. MAN Diesel can be contacted for further recommendations on the use of biofuels. Guiding Biofuel Specification for MAN B&W Two-stroke Low Speed Diesel Engines 1) Designation Density at 15 o C kg/m Kinematic viscosity at 10 o C 2) cst 55 Flash point o C >60 Carbon residue % (m/m) 22 Ash % (m/m) 0.15 Water % (m/m) 1.0 Sulphur 3) % (m/m) 5.0 Vanadium ppm (m/m) 600 Aluminium + Silicon mg/kg 80 Sodium plus potassium ppm (m/m) 200 Calcium ppm (m/m) 200 Lead ppm (m/m) 10 TAN (Total Acid Number) mg KOH/g 4) <25 SAN (Strong Acid Number) mg KOH/g 0 1) Valid at inlet to centrifuge plant 2) Pre-heating down to 15 cst at engine inlet flange is to be ensured 3) Lodene, phosphorus and sulphur content according to agreement with emission controls maker 4) Experience shows that a high Total Acid Number has influence on the time between overhaul of the engine fuel system and, therefore, need to be adjusted accordingly Table II Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 15

16 Lubricating Oil Qualities Low speed diesel rust and oxidation inhibited alkaline engine oils of the SAE 30 viscosity grade should be chosen for circulating oil. The oils should have adequate dispersancy/detergency to keep the crankcase and the piston cooling spaces free from deposits. For engines with an integrated gear driven Power Take Off (PTO), a minimum FZG load level (Foursquare gear oil test) of 8 should be observed. For electronically controlled engines, a minimum FZG load level of 10 is required. Contamination of system lube oil Increase of BN (Base Number) and viscosity of the system lube oil during operation is unavoidable. The piston rod stuffing box separates the combustion and scavenge air spaces from the crankcase. Therefore, lube oil will not be severely contaminated with combustion products and used cylinder lube oil. However, some cylinder lube oil leaks through the stuffing box, down into the system lube oil sump. This is revealed by increasing BN and viscosity levels of the system lube oil. Normally, the increase will stop after some time and remain at a stable level where topping up with new system lube oil, to make up for normal consumption, will balance the degree of contamination of the system oil with cylinder lube oil. Water may also contaminate system oil. Excess water levels may harm tin-aluminum bearings, for which reason MAN Diesel recommends that the water level does not exceed 0.2% (0.5% water allowed for shorter periods of time), Ref. [5]. In some cases, fuel has been seen leaking through the fuel pump umbrella sealings into the system oil. Fuel is known to form deposits on hot spots, i.e. in the piston undercrown space. It is therefore important to keep the recommended overhaul intervals on fuel pumps to secure that the pump packings/sealings are replaced. BN level consideration The increase in BN can influence the ability of the oil to reject water by the usual centrifuging. Water together with calcium compounds from oil additives may form calcium hydroxide recommended to ensure calcium carbonate and build up a deposit of lacquer on the bearings. Another risk is the increased sludge formation when water is present. Experience shows, however, that many engines are operating with up to 30 BN (starting from approx. 6 BN) without any operational problems, and without any changes in the lube oil performance that give reason for renewing the oil. International brands of lubricating oils which have been applied with satisfactory results on MAN B&W engines, on a large number of vessels Lubricating oils - Low speed main engines Type Circulating oil Cylinder oil Requirement SAE 30, BN 5-10 SAE 50, BN SAE 50, BN Oil company BP Energol OE-HT 30 Energol CLO-50M/CL 605 Energol CL 505/CL-DX 405 Castrol CDX 30 Cyltech 70/80 AW Cyltech 40 SX/50 S Chevron (Chevron, Texaco, Caltex) Veritas 800 Marine 30 Taro Special HT 70 Taro Special HT LS 40 Total Atlanta Marine D 3005 Talusia HR 70/Talusia Universal Talusia LS 40 Exxon Mobil Mobilgard 300 Mobilgard 570 Mobilgard L540 Shell Melina 30/30S Alexia 50 Alexia LS * depending on load profile and sulphur content, see MD recommendation for cylinder feed rate Table III 16 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

17 An increase in BN to an equilibrium value of up to 25 in BN and in viscosity from SAE 30 to SAE 40 is considered normal, and no action is called for. An increase beyond that is not really harmful and can, in most cases, be counteracted by new low-bn topping oil. The circulation oil consumption on the MC/ME/ME-B/C/S engines is very low because the engines are designed to have fewer leaks and because of the much reduced stuffing box oil drain, compared to previous engine types, causing a higher increase in BN and viscosity. Therefore, it may be necessary to add some new oil to the lube oil sump at times to ensure a proper quality and BN level of the lube oil. This is done by exchanging part of the circulation oil in the sump based on an analysis of the oil. Lube Oil Blending on Board A new blending-on-board (BoB) concept makes it possible to add additives to the engine system oil and then utilise it as cylinder lube oil. By topping up the thereby used system oil, a steady renewal of the oil is ensured as well as improved viscosity control and cleanliness. The oil suppliers get the advantage of supplying only one oil and a limited amount of additives. The traditionally consumed cylinder oil is replaced with the blended lube oil. Furthermore, the idea with the BoB concept is that the operator will ultimately be able to adjust the cylinder oil BN to the current fuel sulphur level by changing the blending ratio. In 2007, MAN Diesel issued a No Objection Letter (NOL) on a BN70 blend. The NOL applies to a specific additive in a specific system oil. Testing of a BN60 blend on is ongoing, on an engine in service, and the condition is so far found to be satisfactory. Some considerations must be made in this respect: System oil condition prior to blending must be acceptable Quality control of the additives must be ensured Technical performance of additive package in different concentrations (BN40, BN50, BN60 ) must be clarified MAN Diesel shares a common interest with the oil companies to keep the lube oil expenses predictable and optimal. Therefore, also in this field it is of the utmost importance to ensure the reliable performance of the blended products. This requires continuous verification tests. No-objection letters will be issued as the tests with BoB and lower BN oils are successfully concluded. MAN Diesel can be contacted for information on the test status. Technically, it is currently being investigated how the blending-on-board concept could cover all BN levels on just the same additive package. Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 17

18 Cylinder Oil, Low Speed Diesels For engines operating on heavy residual fuel oil, a cylinder oil with a viscosity of SAE 50 and BN of 70 is recommended. In most cases the high BN cylinder lubricant will also be satisfactory during temporary operation on diesel oil/gas oil. In general, changing the cylinder oil type to correspond to the fuel type used (i.e. bunker fuel or diesel oil/gas oil) is considered relevant only in cases where operation on the respective fuel type is to exceed two weeks. However, cylinder oil feed rate adjustments might be required. There is a high risk when using BN70 cylinder oils in connection with frequent bunkering of low-sulphur fuels, with a sulphur content of below to 1.5%, see Ref. [6] The main problem has been the accumulation of unused cylinder oil additives, resulting in excessive deposits on the piston topland. This has led to high wear, and to a situation where increased lubrication does not improve the condition. On the contrary, increased lubrication increases the formation of deposits, leading to acceleration of the problem. It has been established that a certain degree of controlled corrosion enhances lubrication, in that the corrosion generates small pockets in the cylinder liner running face from which hydrodynamic lubrication from the oil in the pocket is created. The alternative, no corrosion, could lead to bore polish and, subsequently, hamper the creation of the necessary oil film on the liner surface, resulting, eventually, in accelerated wear. Controlled corrosion not avoiding corrosion is therefore crucial, and adjusting the BN to the fuel oil sulphur content is essential. Low alkaline cylinder lubricants are therefore available on request from the major lubricating oil suppliers. Table III shows typical lube oils used on marine applications together with the fuel oils specified in Table I. In order to control and prevent uncontrolled sulphur corrosion, it has become the industry standard for marine engines to use cylinder lubricants with a BN of 70 in combination with the average marine fuels, i.e. 380 cst and 2.7% sulphur content. Special running conditions because of frequent bunkering of low-sulphur fuels and environmental fuel regulations (by the authorities or self imposed), requiring the use of low-sulphur fuel and special running conditions, might call for a lowering of the total alkaline additive content. This can be done by lowering the dosage towards our minimum feed rate or, alternatively, by using one of the specially designed cylinder oils with a lower BN and with full detergency. Service tests with such specially designed low-bn oils have shown good results. However, it may be difficult to determine whether changing to a BN40 or BN50 cylinder oil will be adequate for operation of ultra-low sulphur fuels. A lower BN than might be the future oil for low-sulphur operation. For this reason, we recommend that you contact MAN Diesel, or the engine builder, before operation on ultra-low sulphur fuel. General It should be considered that, irrespective of the sulphur content being high or low, the fuels used in low speed engines are usually low quality heavy fuels. Stationary applications Ambient conditions Stationary engines Marine engines Tropical Design Maximum Average Minimum Cooling water temp. yearly site yearly site yearly site 32 C 25 C Air inlet temp. climatic cond. climatic cond. climatic cond. 45 C 25 C Blower inlet pressure Depends on height above sea level 1000 mbar 1000 mbar Table IV 18 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

19 Therefore, the cylinder oils must have full capacity in respect of detergency and dispersancy, irrespective of the BN specified. This is a technology which has to be mastered by the lube oil suppliers, who can individually tailor a cylinder lube oil to the relevant fuel. Breaking-in cylinder lube oils for testbed running In addition to determining the optimum oil design for normal operation of the two-stroke MAN B&W engines, we also investigate and test various lube oil designs in cooperation with the oil companies to find the optimum cylinder lube oils for testbed running. Most builders of MAN B&W two-stroke engines are using low-sulphur DO fuels, primarily for environmental reasons. This, in combination with a relatively high running-in lube oil dosage, requires a high detergency level in the oil. Therefore, we generally recommend the use of a BN70 cylinder oil, irrespective of the sulphur content of the fuel oil. When introducing alucoating on piston rings and semi-honed cylinder liners, we also introduced a shorter runningin period which, furthermore, limits the period in which excess cylinder lube oil is supplied, and improves the runningin conditions. This means that the entire running-in period, up to 100 hours, is fully acceptable for using BN70 cylinder lube oils. Performance Verification of Cylinder Oils All oils listed have gone through a performance test for about 4,000 running hours on a relevant engine type in service and have, during the test, been inspected by engineers from MAN Diesel, in cooperation with the oil supplier. When satisfactory results have been achieved, MAN Diesel issues a Letter of No Objection for the use of the oil on MAN B&W two-stroke engines. However, MAN Diesel does not assume responsibility for any damage caused due to the quality of an oil mentioned in a Letter of No Objection. The performance of the oil is the responsibility of the oil supplier. It is up to the operator to obtain guarantees from the oil supplier that the oil is suitable for operation on the plant in question in conjunction with the currently used fuel. If an oil on the list fails to provide acceptable performance, then MAN Diesel will work together with the oil company to clarify the reasons and, if needed, have a better oil introduced. If an oil fails, the Letter of No Objection will be withdrawn. The list should not be considered com- plete, and oils from other companies may be equally suitable. Upon request, MAN Diesel will inform whether a given oil has been tested and whether the test results were acceptable. Further information about the oil test and Letter of No Objection can be obtained by contacting MAN Diesel in Copenhagen. Fuels and Lubes for Stationary Twostroke MAN B&W Engines Stationary engines operate at load patterns and ambient conditions which differ widely from those of their marine counterparts. This is illustrated in Fig. 8 and Table IV showing the typical operating conditions for both applications. Thus, Fig. 8 shows that for stationary engines, the average load is % during 8,000 hours, or more, per year in operation, whereas for marine engines the average load is around 80% and, furthermore, often only for 6,000 hours per year in operation. This means that stationary engines typically have a more than 60% higher load factor than marine engines. Stationary engines are exposed to widely varying ambient conditions, i.e. higher and lower air and cooling water temperatures, see Table IV. Furthermore, stationary engines are frequently exposed to fuel oils of non-marine qualities. The fuel is often delivered from one permanent supplier, meaning that the quality from this supplier, good or bad, will prevail. % load 110 Stationary Marine ,000 4,000 6,000 8,000 hours Time in service over one year Fig. 8: Typical load profile during a year in operation Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels 19

20 Therefore, lube oils, especially cylinder oil, have to be individually selected and, at times, even individually specified and optimised in order to match the fuel oil available. Table III shows typical lube oils to be used for marine applications together with the fuel oils specified according to ISO In order to control/prevent sulphur corrosion, it has become the industry standard for marine engines to use cylinder lubricants with a BN of 70 for use with the average marine fuels. This simple rule does not apply to stationary engines, where the sulphur level in the fuel usually remains constant, i.e. at the level set by the supplies available, or, when regulated by local legislation, often shows a decreasing tendency over the lifetime of the plant. Hence, temperatures are high in the combustion chamber, and the need to counteract cold corrosion with alkaline additives is lower, thus reducing the BN requirement. List of References [1] Heavy Fuel Oil Treatment, Service Letter SL05-452, Kjeld Aabo, MAN Diesel, Copenhagen, Denmark [2] Marine diesel engines, catalytic fines and a new standard to ensure safe operation, by Alfa Laval, BP Marine and MAN B&W Diesel [3] Guidelines for the sampling of fuel oil for determination of compliance with Annex VI of MARPOL 73/78, Resolution by the IMO Marine Environment Protection Committee, MEPC 96 [4] Operation on Low-sulphur Fuel, by Kjeld Aabo, MAN Diesel, Copenhagen, Denmark, publication no.: ppr, January 2006 Hence, the constant use of a higher than average sulphur content, possibly even higher than that found in the marine specification, will call for the use of a higher BN, and for this situation lube oils with a BN of up to 100 are available. Correspondingly, long-term use of lower-than-average sulphur fuels will call for the use of lower BN lube oils, as described for low-sulphur marine fuels. In addition, the engine load for stationary engines is usually very high, and the ambient temperature is often higher as well, ref. Fig. 8 and Table IV. [5] Cylinder Lubrication Guidelines Operation on Fuels with Varying Sulphur Contents All MC/MC-C and ME/ME-C type engines Mk 6 and higher, with Alpha ACC System, and Cylinder Lubrication New ACC Guidelines All MC/MC-C and ME/ME-C type engines Mk 6 and higher, with Alpha ACC System, Service Letters SL and SL07-479, Henrik Rolsted, MAN Diesel, Copenhagen, Denmark 20 Guidelines for Fuels and Lubes Purchasing Operation on Heavy Residual Fuels

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24 All data provided in this document is non-binding. This data serves informational purposes only and is especially not guaranteed in any way. Depending on the subsequent specific individual projects, the relevant data may be subject to changes and will be assessed and determined individually for each project. This will depend on the particular characteristics of each individual project, especially specific site and operational conditions. Copyright MAN Diesel & Turbo ppr Aug 2014 Printed in Denmark MAN Diesel & Turbo Teglholmsgade Copenhagen SV, Denmark Phone Fax MAN Diesel & Turbo a member of the MAN Group