MDO/MGO cooling solutions in relation to compliance with the new SOx regulation26.10.2010
Operation of the Main Engines, Boilers and Auxiliary Machinery on distillate fuels constitutes a problem and so far there has been some confusion in the industry how to solve this issue in a feasible way.
Up to now the involvement of the marine industry has been limited and the available solutions are few undergoing still improvements. Although the current legislation call for operation of auxiliary machinery of ships on low sulphur distillate fuels 0.1% (MGO / MDO) at European ports from 1st of January 2010, very few applications have been completed.
The main problem of the low sulphur content of MGO fuel is the decrease of the viscosity of the fuel. According to ISO standards the MGO viscosity varies between 1.5-6cSt at 400 degrees Celsius. This has an effect on the operation of the fuel pumps, as well as on the boilers burners which results in leakages concerning the pumps and change from steam to air atomisation of the MGO at the burners.
Makers of boilers have already developed conversion kits for the burners, however concerning the auxiliary engines most of the makers have recommended cooling of the MGO.
Cooling of the MGO is a not a straight forward solution since several parameters should be considered before deciding the appropriate method of cooling.
There are three methods which can cool the MGO in order to increase its viscosity to at least 3 cSt in order to be handled by the pumps without leakages.
- Cooling by sea water coolers
- Cooling by refrigerating compressors of direct expansion connected by a cooler
- Cooling using water chillers in connection with coolers.
Cooling by sea water coolers:
This is the simplest solution, however does not provide always enough cooling capacity (unless the ship operates in very cold seas), and there the risk of contamination of sea water with fuel.
Cooling by refrigerating compressors of direct expansion connected by a cooler:
This is relatively simple solution, not so costly, however it is difficult to control accurately the cooling temperature of the Freon inside the cooler, which may result in cooling of MGO below its pour point (paraffin will be produced) and consequently blocking of the cooler. In addition, there is a limit of operation on low load (below 25%) and the risk of contamination of fuel with Freon.
Cooling using water chillers in connection with coolers:
Chiller units have been well known for many years and it seems that are well suited for the cooling of MGO too. They provide a trouble free operation at all loads, surface temperature in coolers can be controlled precisely, it safe regarding the leakages.
However it is more costly than the previous mentioned solutions.
Concluding, although cooling of MGO is the most recommended solution, there are still outstanding issues concerning this method, such as limited operational experience, uncertainty regarding the full classification of the systems, redundancy of chillers.