FALLY REGARDING SAVINGS ON OPERATIONAL COST BY USING HIGH VISCOSITY FUEL FOR SHIPBOARD DIESEL GENERATORS
Almost more than three decades back the engine builders offered to the ship owners the world over the substantial savings on the fuel cost by switching over the fuel grades from lighter fuel grades to more viscous, either straight or blended heavy grades. Ship owners obviously got attracted by this new concept & placed retrofit orders for their existing vessels & changed over their preference to burn Higher Viscous fuel while ordering new buildings. The immediate impact was naturally extremely encouraging with ship owners happy with the savings on account of fuel cost.
The engine builders must have carried out extensive study & research while arriving at the final conclusion of lower operational cost while convincing the owners the savings owners will derive on the fuel cost. This is only half the truth. The other half they did not reveal to the ship owners.
What is the other half?
The other half is the additional operational cost over the period to the owners. The technical advisers to the owners had not taken into consideration this dormant factor at the time of switching over to the new concept & only got carried away by saving in fuel cost.
The cleanest engine friendly fuel is, of course, the gas & thereafter in descending order MGO, MDO, blended high viscosity oil & last 380 CST viscosity oil. In true sense, MGO which is also known as HSD is most engine friendly. To certain extent MDO after passing through purification & filtration process can be considered an alternative source.
Rarely one comes across a failure of engine components while using cleaner fuels if periodic checks & maintenance is carried out to keep the spares inventory & operational cost low. Failure of major components such as pistons, liners, bearing shells & even crankshafts failures is rarely heard off.
In the crosshead type of engine design the crankcase is totally separated from power developing section such as piston/piston rings, liners, scavenge spaces & hence any blow pass along with impurities such as unburnt carbon, sulphur, phosphorous, vanadium etc. gets collected in the scavenge space & with the stuffing boxes functioning efficiently virtually there is no chance of any impurities passing in the lubricating system.
With the four-stroke medium & high-speed engine design such isolation is not possible between the power developing section & lube oil system hub & hence with the adoption of high viscosity fuel grades, impurities mentioned earlier are bound to deteriorate the quality of system oil & if the operational number of running hours is overlooked between the two changes of fresh replacement of sump oil, this may result in major damages leading to even crankshaft failures.
The system oil tends to create a sticky gummy deposits in the entire lube oil system such as lube oil coolers, filters, system pipes leading to camshaft bearing lubrication, spray nozzles, fuel pump roller guides & oil leading to cylinder head components such as rocker arm bushes, inlet / exhaust valve spindles & spindle guides, valve rotators etc. The size of these passages being small they get clogged easily thus starving the moving parts of oil. The increase in clearance in the way of valve spindles & spindle guides leads to valves not sitting properly on their valve seats thus leading to leakages leading to loss in compression pressure, improper & incomplete combustion leading to a creation of black smoke & most important that engine does not develop desired output. High exhaust temperatures, burnt valve seats, fouling of the turbochargers & exhaust gas silencers is the end result.
There has been a tremendous development of 2 stroke engines during past 2 to 3 decades. The periodic maintenance cycle of engine components intervals has increased many folds and with the adoption of closer checks on the quality of circulating lube oil & Cyl. oil system the modern main propulsion engines have proved reliable workhorses. Rarely one comes across with abnormal cyl. liner wear or piston ring failure which is solely due to the bad quality of bunker supplies & not the design or material failure. The workload of engine room staff is much reduced as far as main propulsion machinery is concerned.
On the contrary, the malfunctioning of electrical power generating sets with the adoption of high viscosity fuel grades, it is a constant mental worry & physical fatigue the engine room staff has to face.
There has been cases where many a owners suffered very heavily due to repeated failures of the power generating sets on series of their vessels with finally owners deciding to change the entire lot of generating sets with suitable alternatives causing heavy financial losses due to demurrages on account of generator failures & again additional cost of replacement (both purchase price & modifications) of the generator sets.
In one case when all four 2000 KW Gen. sets came to standstill on one of the 850 refer container vessel with 2 gen sets totally broken down with fractured crankshafts & remaining tow not developing beyond 25% output, it was a colossal loss to the owner both commercially & technical. The vessel had to be laid off for six months before all four gen-sets could be rebuilt with new OEM supplied spares to achieve the original rated output. Trials were conducted in the presence of Class & Insurance surveyor before the vessel could be put back into trade.
If once takes into consideration the losses suffered because of vessel’s earning capacity is lost with daily operating cost of vessel unchanged & added to that the insurance claims not settling 100% & with cost of insurance premium of the vessel going up; it certainly offsets the CLAIMS of GAINS out of saving over the fuel cost.
Time has come for the owners to rethink adoption of burning heavy viscous fuel oil for ship’s gen sets. Even the options of steam generation from exhaust gas economizer could be introduced to run turbo alternator at sea which will reduce the fuel cost during the sailing period. The steam turbo alternator is always very low-cost media where the steam is generated from the waste recovery unit. The three-fold gain:
- Power generation at no extra cost on account of nil fuel consumption.
- The number of diesel generator running hours reduce drastically with the result spares inventory is reduced considerably.
- The workload on ship staff both mentally and physically would reduce to minimal.
About the Author:
Mr. Suresh V Godbole
Steam & Motor 1st Class M.O.T. Certificate, C.Engr., F.I Mar. E C.E.O Marine Management Services Pvt. Ltd., Martek Engineering Works, Marman Engineering & Shipbuilding Pvt. Ltd.,
Passed out from D.M.E.T. in the year 1961 after completing 4 years course in Marine Engineering between 1957- 61.Commenced sea carrier joining The Great Eastern Shipping as Junior Engineer.
Bid Good Bye to sea carrier in the year 1971 after having served as Chief Engineer for 5 years. Sailed both on Motor as well as on Steam ships. Had an opportunity to closely observe New Building Construction as well as repair techniques adopted in Japanese Yards. Stepped ashore to start a new concept of repairs by FLYING SQUADS. Impressed by our work technique, the local service station engineer of Burmeister & wain arranged a special training programme for self at their Copenhagen works in the year 1974. Over the years built up the strength of our repair team by regular technical inputs to enhance their knowledge to keep up with latest innovations in repair techniques. Today we are 45 years old & proud to say that the leading Ship Owners & Technical Managers consider us as dependable work force.
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