The problem with consistency of heavy fuel oils, and they have been with us since the 1970's (the fuel crisis resulted in secondary processing; secondary processing means an increasing proportion of heavy fuel oils are a blend and not straight run products: today 65% of fuels out of the ARA ports and Singapore are blended) is that it is currently only in the refinery that the blend quality can be assured (almost always) That's not quote true, some leading independents can now offer far better consistency in barge and terminal blended fuels (see below).
Samples of the feedstocks (residual oil, cutter stock) are analysed and the fuel calculator (obtainable from the oil companies or DNV PS on request) is used to determine the required volume or mass ratio to produce a fuel of the target specification.
Viscosity is an excellent indicator of quality. If the viscosity is right the other parameters will conform to the fuel calculator predictions.
In the refinery the industry standard instrument is the process capillary viscometer. This is not practical for use elsewhere in the marine fuel industry.
In terminals and in barges they blend by controlling the volume flow rate ratio to the value predicted by the calculator. Many of the methods used are vulnerable.
The problem is that the system depends on the integrity of the samples and the accuracy of the blending equipment. Ensuring a representative sample can be a problem; for example, fuel in storage can stratify. This problem also affects the refiners; many blend into storage tanks, take top middle and bottom samples and then calculate any corrections required. In one Siberian refinery they now use modern digital viscometers which allow them to pipeline blend without subsequent correction; obtaining much improved consistency.
If the samples are wrong, the fuel calculation result gives the wrong ratio. Even with the right ratio there are some uncertainties in the accuracy of many mechanical blenders.
These are the problems that beset ethical suppliers who often compensate by adding excess cutter stock (the expensive component) and this excess is referred to as the "give-away" and can vary from around $1-$7 a ton according to estimates.
Chalmers Lindholmen (Sweden) monitored fuel supplied to a vessel over a two year period. It was supposed to be 380cst. It actually varied from 150cSt to 415cSt but mostly was lower viscosity rather than higher.
This does not consider corrupt practise. In order to try and ensure that fuel is correctly supplied bunker surveyors can be retained to witness the blending or transfer of fuel during bunkering.
According to the Singapore authorities some surveyors were earning nearly 5 times salary in bribes when associated with fraudulent fuel supply. The problem can be serious. Fuel is around 70% of the operating cost of a ship.
Without proper instrumentation the parties to the bunker supply are dependent on sample taking and analysis. The results are not available during bunkering but 24-48hrs later by which time the cost of returning to port and re-bunkering are punative and the cost of litigation is also a serious issue.
The instrumentation is now available for refiners, terminals, barges and receiving ships. Many of the problems can be identified and resolved/improved but it is early days yet. So far this equipment is only being used by some independent bunker suppliers. Similar instruments are used with some engines but not on many ships yet.
Some estimates say that as many as 40% of bunker operations are not sampled, though they should be, and of those sampled something like 17% of samples are not sent for test. In many cases the ships engineer can compensate by careful management of the fuel treatment system on board and by relying on the fuel heaters to compensate for excessive viscosity. So this is preferable to discovering you need to go back to port. Chances of fuel out of spec: 1 in 10; of being out enough to damage engiens: 1 in 120... you see the odds.
However, at least one major engine company has been using digital viscometers for fuel heater control for some years now and uses similar instruments to check bunkers as they are delivered. These instruments can inform about density (at operating temp, at 15degC and at 98degC), dynamic and kinematic viscosity (and kinematic viscosity at 100deg C or 50degC), ignition index (CCAI and CII to BS MA 100)and can inform the engineer as he is bunkering the answers to two quesions: "Can i clean it?" and "Can i burn it?".
Without these technologies the option is to depend more and more on refinery controlled quality.
The result of this is only refnery blends will be supplied. This may guiarantee better consistency but may lead to fewer grades available and only from the major ports.
It isn't going to make fuels cheaper.
Already the independant bunker suppliers are fewer. In Rotterdam only the major oil companies now supply fuel, the independents being forced out into the smaller ports.
It may soon not be possible to obtain competitively priced fuels.
The independents can operate from the smaller ports and can buy feedstocks competitively. If they adopt the new technologies they can blend accurately on line in the terminal or on the barge. Some few have already taken these steps.
For them and for the ship owners modern viscometers can enable them to control cosnistency, can enable them to continue to provide fuels from small ports and to exploit availability of lower cost bunkers.
Ship owners and barge operators can see quality as the fuel is delivered.
The solution is there, just very few people have it yet.
Anyone interested in the new methods can see articles in the December 2003 issue of Bunker News, the April 2002 issue of bunker News and various article in Hyrocarbon Engineering in 2000, 2001 and 2002 where they have run articles on viscosity measurement.
JMW