In these evaluations, the following energy equivalents
are assumed :
- PCI of a M3 of methane = 34 000 Kj
- PCI of a litre of
fuel oil = 42 000 Kj
- I litre of fuel equals 1.25 Nm3 of methane (Nm"
at 0°C and at atmospheric pressure)
- 1 MNm3 of methane = 800 tep (tonne
The calorific energy of wood (generally eucalyptus in
Rwanda) is more difficult to estimate. According to what has been written, the
weight/volume ratio for a cubic metre (stere) of wood varies between 300kg per
stere and 500 kg per stere. We believe that a value of about 350 kg/stere is close
The PCI of wood will amount to 15 000 Kj/kg. The comparison
between wood and gas on the level of energy works out at : 1 stere of wood is
equivalent to 150 Nm3 of gas - that is about 5 GJ.
Prices in Rwanda in August
2004 were as follows :
- 1 stere of wood = 5 000 FRW, that is 7.15 euros or
- 1 litre of fuel oil = 350 FRW, that is 0.5 euros or US$0.6 (1 euro
= 700 FRW = US$1.2)
Comparison of the price of wood and the price of fuel
oil in energy terms
- Fuel oil : 1 GJ = 12 euros = US$14
- Wood : 1 GJ =
1.36 euros = US$1.65
Note that the price of fuel oil is currently 8
or 9 times higher than wood, a fact which cannot be discounted in looking at the
economic reality of the country : it would be difficult for methane to be cost
competitive with wood. Methane would however be exceptionally competitive as a
substitute for fuel oil.
Prices given above may vary considerably with time.
One can foresee a continuous exponential increase in the price of wood with the
decrease in reserves and the increase in need. On the other hand it is difficult
to foresee the future concerning the price of fuel oil (a barrel of oil cost around
US$ 45 at the beginning of September 2004)
of energy needs of the Pfunda tea factory
Tea production is a seasonal
occupation : so production at the Pfunda factory varies throughout the year. Energy
consumption shows this clearly, with a peak in March (178% of the monthly average)
and a low point in August (32% of the monthly average). The capacity for supplying
methane should thus be calculated on the period when most wood is used. Currently,
during March, in the middle of the rainy season, wood consumption for drying the
tea is about 20 steres per day.
Thus the methane extraction unit should be
proportioned so as to supply 20x150 = 3000 Nm3 of methane a day, that is about
1.1 MNm3 of gas per year. The present management of Pfunda have told us that there
are plans for the tea drying plant to expand in the coming years. We envisage
the setting up of an extraction station with a capacity of 1.5 MNm3 of methane,
thus replacing the use of 27 steres of wood per day during the rainy season.
to the wide variation in tea production over a year (see figure below) there will
be a surplus of methane available during the dry season. This gas could be sold
by UPEGAZ to Bralirwa, replacing fuel oil (in current conditions which is 90%of
the price of fuel oil, equivalent PCI)
Annual wood consumption of wood
by Pfunda was of about 4300 steres in 2003. This quantity would take the equivalent
of 650 000 Nm3 of methane, thus leaving an excess of 950 000 Nm3 of gas, the equivalent
of 760 000 litres of fuel oil.
Figures for wood consumption 2004 - 2009
are even higher, because provisions envisage 5800 steres of wood per year (which
would correspond to a maximum consumption of 27 steres per day). Thus the quantity
of methane which could be sold to Bralirwa would be 730 000 Nm3 per year, the
equivalent of 585 000 litres of fuel oil.
Calculating on the basis of the
present price of fuel oil of 0.5 euros a litre and taking into account the reduction
of 90% compared to fuel oil, the sale to Bralirwa would bring UPEGAZ : - in the
present situation 760 000 x 0.5 X 0.9 = 342 000 euros a year; - in the hypothesis
of expansion : 585 x 0.5 x 0.9 = 263 000 euros a year.
floor at the Pfunda factory
Furthermore, for other parts of the production process, the Pfunda factory uses
about 1 950 000 KWh of electricity per year (information obtained from the management
in October 2003, with an average consumption of 1 500 000 KWh in 2002 for tea
production of 1 020 tonnes and an electricity bill of 63 M FRW, or US$ 105 000),
a consumption unequallty spread over the year. The factory also has a 450 Kva
generator which goes into service during power cuts or when the grid is not available,
(periods which account for 2 or 3 % of the time in 2003 (and probably much more
at present, in a period of electricity shortage). This amount of energy corresponds
to an additional consumption of about 58 000 KWh by the generator and a fuel oil
consumption of about 1.7 M FRW or US$ 2 800.
One can thus suggest adding further
value to the project by integrating a gas powered electricity generator, the factory
thus profiting from the advent of cheap fuel. This could be accomplished - either
by transforming the diesel generator into one powered by gas (at a cost of between
US$ 50 000 and 60 000 if it were done on site) - or by installing a new 300 KW
generator (which could moreover be equipped with a heat retrieval system, usable
for preheating the boiler) - and by conserving as a back up the link to the grid
(to which excess capacity could moreover be sold, on the condition that a legal
arrangement for this reselling could be found during the feasible limits of the
The consumption of gas for a 450 KW generator (or 300 KW if new)
to supply electricity to the factory would be about 25 000 GJ or 750 000 Nm3 per
for substituting methane for wood
Extraction of methane from Lake Kivu.
The process of extracting gas from the deep waters of Lake Kivu, then the
enrichment of the methane has been treated elsewhere (cf. Data Environment Report
"Exploitation of Lake Kivu's methane : pilot station project", June
2003°. A synthesis is included as an Appendix. A preliminary study was done
for an extraction plant of a size able to produce 1.5 MNm3 per year. Compared
with the previously studied pilot station, which had a capacity of 3.5 to 4 MNm3
per year, the proposed project would allow us to validate our calculations and
to determine parameters which remain uncertain.
Remember that our previous
experiments at Lake Nyos in Cameroon never used an extraction column with a larger
diameter than 140 mm.
The pilot station proposed in the 2003 document foresees
a diameter of 440 mm. The diameter of the Pfunda station column will be 280 mm,
which would act as a 'half-way house', always desirable in a largely unexplored