17th July 2008. With their broad insensitivity to fuel quality, large medium speed diesel engines designed for heavy fuel oils (HFO) can cope readily with a wide range of other fuels. Currently, a major emphasis at MAN Diesel is renewable, carbon dioxide (CO₂) neutral fuels like treated and untreated plant oils, animal fats, waste oils – fuels which cause considerable problems in high speed engines with their more sensitive injection systems. Accordingly, the company has won a number of major contracts for cogeneration plants operating on these types of fuels in recent times.

Crude Oils
At a very different point on the fuel quality spectrum, four-stroke medium-speed engines from MAN Diesel are well proven in operation on crude oil taken direct from oil wells and conditioned on site. MAN Diesel’s crude oil technology and experience date back to 1986, since when the company has sold over 65 crude oil engines of various sizes to all parts of the world.

In an interesting application, since 2005 two engines from MAN Diesel operating on crude have been saving a Libyan oilfield operator fuel costs for while also significantly reducing CO₂ emissions on a “well to wheel basis”.

Mabruk Oilfield
The Mabruk oil field is one of Libya’s most important, producing around 17,000 barrels of crude oil per day (2006). It is operated by Mabruk Oil, formerly known as Compagnie Des Pétroles Total Libye (CPTL) and one of the TOTAL S.A. group’s affiliates operating in Libya.

The field’s development started in 1994 and has required innovative technologies like horizontal and multilateral drain drilling to achieve economic production from a tight and complex field. As part of plans to double the crude oil output from the Mabruk field, a new power plant was constructed in 2004 and 2005 in the “GOSP” area of the oil field to supply electricity for all the oil field and the associated camp. CPTL selected a main contractor for the extension of the whole oilfield including the erection of the new power plant. MAN Diesel’s scope-of-supply was two generator sets plus all mechanical and electrical equipment required in the plant The construction of the power plant lasted 13.5 months from contract award to start of power generation. It is based on two of the largest, eighteen cylinder, vee configuration versions of MAN Diesel’s well proven medium speed type 32/40 engine adapted to burn crude oil from the adjacent wells. The two 18V 32/40 engines each produce a mechanical output of 8,640 kW and drive 50 Hz generators at 750 rpm.

Interestingly, as well as enabling the Mabruk oilfield expansion programme, the MAN Diesel generator sets replaced smaller gen-sets running on distillate fuel oil which previously had to be transported by road to the site. As such, the new power plant is instrumental in saving a considerable quantity of distillate fuel - i.e. the fuel used in by the road tankers delivering the fuel. In terms of the greenhouse gas CO₂, this saving is compounded by the elimination of CO₂ emissions associated with refining the distillates consumed both in the earlier gen-sets and during transportation.

Fuel analysis
As a first step in the Mabruk project, crude oil from the field was analysed by the Petroleum Research Center of the Libyan NOC at the Petroleum Research Center in Tripoli. A paraffin wax content of 2.57% by weight was established, pointing to possible injection nozzle blockages. However, tests made at the MAN Diesel Laboratory in Augsburg confirmed Mabruk crude’s suitability for injection in MAN Diesel engines.

Further, a filtration test revealed particles of approximately 0.1 mm in the crude oil, leading to the requirement that it be cleaned in centrifugal separator modules prior to injection.

Finally a flash point of <1° C was established, indicating the fuel’s highly explosive nature. As a result, MAN Diesel took special precautions with the generator sets and engines and overall plant to ensure operational safety. One set of measures involves effective ventilation of the powerhouse in view of the low flash point. It entails feeding the generator sets a copious volume of cooling air from outside the machine hall.

The GOSP Area
GOSP stands for Gas-Oil Separation Process. All crude oil is processed in the GOSP. The processed crude oil is then pumped to the main storage tanks nearby. The crude oil for the diesel power plant is pumped from the main storage tanks into the storage tank of the diesel power plant for settling. From here it is further cleaned in separator modules to remove small particles before being fed to the injection system of the MAN Diesel 32/40 engines.

Plant in operation
Since the plant is required to run in stand alone mode and on crude oil, the high reliability of engines from MAN Diesel and their crude oil fuel capability were decisive factors in their selection to provide power for all the oil field and associated camp MAN reports that the plant has a very favourable operating record.

See the pictures in our picture gallery.