Large (50 to 500 MW for instance):
• Commonly, oil is burnt to generate high pressure steam in a steam boiler. Power generator is steam turbine driven.
• It is mandatory to burn only very heavy fuel or residue, to avoid wasting money with unnecessary increase of operating costs.
Medium (3 to 30 MW for instance):
• Electricity generator may be driven by steam turbine or diesel engine.
• Once again, steam turbine means burning very heavy fuel-oil to avoid unnecessary waste in plant operating budget.
Diesel engine generator drive:
• Very often engine manufacturer has designed diesel engine to accept fuel specification up to bunker C.
• To reduce operating cost, the heaviest fuel oil acceptable to engine manufacturer must be supplied.
Fuel oil heating value
When generating thermal electricity, only recovered kilocalories or BTU are important: the additional qualities of the fuel oil are not improving the produced KWH quality. In other words, burning LPG , gas oil , domestic fuel or any oil product that could be better used, means burning its better properties… and wasting the differential part between thermal content value and total real cost .
If fuel was available at power plant fence door, it may be assumed every plant manager would decide buying the cheapest heaviest fuel offered.
Unfortunately usually fuel is imported from overseas and sea tanker tranported .
Here start transport limitations, whatever their name:
Pour point, freezing point, paraffins content.
High viscosity ( Redwood, Saybolt, furol, engler, ..) absolute or kinematic, centipoises or centistokes.
Each fuel has its own specific properties, but as first estimation:
Light fuel, such FO 180, is usually easy to transport
Heavy fuel, such FO 380, is usually difficult and may be impossible to transport
Extra heavy fuel , such pitch, is not intended to be transported
Thermal power plant usually burns fuel in a steam boiler to generate high pressure steam for the alternator steam turbine. Any fuel can be supplied to the boiler burners, provided the required viscosity is respected.
Typical example . Economical Feasibility
An excellent image of distillates and fuel prices correction with properties and specially viscosity is the spot price in various harbours where they are exported. In june 2003 for instance, an average range is:
Heavy fuel FO380 153 US $/T
Heavy fuel FO180 160 US $/T
GO cut MDO 240 US $/T
For the example , following is assumed:
Depending on imported heavy fuel characteristics, transport of FO180 is possible
but transport of FO380 not possible.
Power plant FO consumption: 400 000 T/Y
As shown on the simplified flow scheme hereafter, it is possible to import a fuel at 160 US $/T
and burn a transformed fuel costing only 153 US $/T:
Positif result # 400 000 T/Y * 7 $/T = 2.8 MM $/Y
A simple skid mounted distillation unit is necessary to achieve the gas-oil separation from the imported fuel.( mini-refinery type fractionation unit).
Pay-out time # 3 years