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FT diesel is a superior fuel for compression ignition engines.  It contains virtually no sulfur or aromatics.  Its cetane number is 75 compared to 50 for high quality diesel fuels.  Both sulfur and aromatics are related to particulate production in diesel engines, while a high cetane number generally results in lower NOx emissions.

Table 2-3:  Composition and Properties of Gaseous Fuels

Property

Pipeline Natural Gas

LPG from Petroleum

LPG from Natural Gas

Carbon (wt %)

73.6

82.0

81.8

LHVb (Btu/lb)

20,300

19,770

19,770

        (Btu/gal

92,800c

83,200

82,600

Density (lb/gal)

4.6c

4.21

4.18

Composition

(vol %)

(wt %)

(vol %)

(wt %)

(vol %)

(wt %)

N2

1.6

2.6

0

0

0

0

CO2

1.0

2.5

0

0.0

0

0

CH4

93.2

86.4

0.05

0.03

0.1

0.06

C2H6

3.1

5.4

0.5

0.37

2.0

1.48

C3H8

0.7

1.8

94.15

93.9

97.0

97.5

C3H6

0

0

2.3

2.3

0

0

C4H10

0.4

1.3

3.0

3.4

0.9

1.0

C5H12

0

0

0

0

0

0

aLPG = Liquefied petroleum gas.

bLHV = Lower heating value.

cper 100 scf

Source:  Unnasch 1994.

The volumetric heating value of FT diesel is slightly lower than that of conventional diesel fuel since it has higher hydrogen to carbon ratio.  Similarly, it has a higher energy content than conventional diesel fuels on a Btu/lb basis.  The fuel is colorless and odorless and miscible with conventional diesel fuels.

South Africa and Russia have been operating coal based FT plants since the 1950’s.  Typical units produce 5,000 to 13,000 bbl/day of synthetic fuel and provide a substantial portion of South Africa’s fuel.

More recently, major oil companies have been constructing FT plants that operate on remote natural gas.  Shell Malaysia completed at 10,000 bbl/day plant that produces middle distillates and paraffins in 1994.  In 1997, ARCO announced plans to build a small-scale gas to liquids plant on the West Coast of the United States.  Texaco also announced plans to build a mobile plant that will produce synthetic diesel on a commercial basis.  Exxon is expected to site a 100,000 bbl/day plant in Qatar.  FT plant capacity could be over 2 millions bbl/day by 2005.  Plants operating on both remote natural gas as well as North American gas are possible.  An FT diesel plant in Alaska could produce fuels that could be sent to market down the 800-mile trans-Alaska pipeline.  The production of such fuels could make up for declining oil production.  In 1997, Tosco and Paramount Petroleum also blended Shell’s FT diesel to produce clean diesel for sale in California.

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