Fuel biomass in the liquid state

4.2.1 Vegetable oils

From sunflower seeds and rape seeds, oils are extracted which can, actually, be used without the need of further bio-fuels; therefore, they can be applied to the energy range just as combustibles of liquid fossil origin. Table 11 lists the main energy characteristics of combustible oils and compares them with the characteristics of gasoline.

Table 11: Comparison between the properties of vegetable combustible oil fuels and diesel [2].

Parameters

Measure unit

Vegetable combustible oils

Diesel

LCP

kcal/kg

9,000-9,500

10,200

Flashpoint

°C

230-290

60

Cetane number

30-40

54

Density

kg/m3

0.915

0.839

Viscosity at 38°C

mm2/s

27-53

2.7

The current energy applications of vegetable oils are relative to the use in diesel engines. Their use in energy production plants as a substitute for diesel poses some problems: the burners must be partially changed to cover the higher viscosity of the vegetable oils compared to diesel.

The high viscosity also excludes, at present, the application of vegetable oils for auto traction. In fact, in this case important changes would be necessary to the plans of engines [2, 14]. Vegetable oils are composed of 78% carbon, 12% hydrogen and 10% oxygen.

Oils are organic compounds, so they are highly biodegradable; these characteristics can represent an obstacle in their use as a combustible because they can undergo oxidation and polymerization in the storage reservoirs. For this reason, oils must be applied within 12 months from their production. Keeping in mind that the viscosity of the oils gradually increases as the temperature decreases (until solidification), such combustibles are not appropriate for use at temperatures below 5°C [1].

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