TRACTEBEL TECHNOLOGY

A pilot plant built in 1963 at Cape Rubona on the Rwandan shore of the Lake has perfectly demonstrated the technical and commercial feasibility of gas exploitation from the Lake. To date, some 18 million standard cubic meters of methane gas have been produced. Nearly all of the gas has been used as a boiler fuel in the nearby Bralirwa brewery.

The gas production process used in the Cap Rubona pilot plant is straightforward. Water from the bottom is brought to the surface through two large pipes. As water rises it reaches zones where the water column pressure is progres-sively lower so that the gas comes out of the solution. Rising gas bubbles then exert enough upward force on the water to avoid the need for pumps once the process is started. The liberated gas and the partially degassed water are passed through a water-gas separator, operating at a pressure slightly higher than the atmospheric pressure, where more gas is liberated and separated from the water. The gas separated from the water, "crude gas", is essentially a mixture of about 70% carbon dioxide (CO2) and 30% methane (CH4). This crude gas is then put through a series of gas washing "scrubbing" tanks where water from shallow depth in the Lake, having relatively little amount of gas in solution, is circulated. Coming in contact with the crude gas, the circulating water dissolves and removes the major part of the carbon dioxide fraction from the crude gas. The resulting gas at the outlet of the scrubbing tanks has approximately 80% methane, 18% carbon dioxide and 2% of nitrogen. This gas "sales gas" is then dried, compressed and evacuated through a 3" flow line to the brewery to be used as fuel. The degassed residual water from the water-gas separator is mixed with the scrubbing tank water and disposed of into the Lake below the surface.

In 1989, TRACTEBEL realized, with a grant from the Kingdom of Belgium to the Rwandan Government, one of the most com-prehensive financial and economical study. They recommend an extension of the existing plant up to five times its original production capacity using a technology similar to that of Cape Rubona. The very high investment cost remains the primary handicap of this technology.

TECHNIP Modular technology

At the same time in 1986, a French Consulting Firm, TECHNIP carries out a feasibility study with EEC as a financial backer (through the European Bank of Investment and European Development Fund); it proposes an original process of extraction and purification called "modular". A module is a compact set of separator and washing vessel that can be located either on or off shore. This technology was developed in order to cover the energy needs of the regional market. For the same quantity ( 25 million cum/year i.e. 5 times the current production capacity of the pilot plant) of purified gas, the investment cost of TECHNIP technology is substantially lower than the TRACTEBEL-ENGINEERING one and it can be easily exported to and implemented at any other site on the lake where methane extraction is possible. Unfortunately, the technical studies were not further developed to lead on to the Bid Packages allowing an immediate execution of the project. On a EDF (European Development Fund) investment, a Consulting group TECNITAS produced a synthesis study containing the modular concept of TECHNIP with some adjustments. Yet it is not a detailed engineering of an extracting module as such.

Pipings

Rwanda has a unique energy resource in the form of methane gas dissolved in the deep water of lake Kivu. The amount of methane is estimated at about 55 billion cubic meters two thirds of which are estimated to be economically recoverable. The resource is at least partially renewable as the volume of methane generated is estimated to be in the range of 100 to 150 million cubic meters per annum. Methane resources can sustain large-scale production sufficient to satisfy the equivalent of the current hydrocarbon and electricity consumption in Rwanda for at least one century. The technical and economic feasibility of methane gas exploitation has beenclearly demonstrated by the small methane extraction 'pilot' unit at Cape Rubona since 1963.

Most of the issues relative to the design, choice of materials and operating conditions have been identified and resolved. For the time being power generation constitute potentially the biggest and economically the most favorable utilization for Lake Kivu methane gas. Gas would be the least-cost alternative for producing electricity in Rwanda, and its development for power generation would encourage its utilization in the commercial and industrial sectors

Rwanda is currently consuming imported fuel from abroad and large volumes of wood and charcoal. Natural gas is a much higher efficiency fuel than either, is much more environmentally friendly in both the burning and emissions as well as the reduction of deforestation which has reached an alarming level in the country. The successful conversion from these sources of fuel would greatly improve both economic and environmental conditions in Rwanda.

The environmental risks associated with large-scale exploitation of gas from Lake Kivu are insignificant.Recent analyses and simulation of Lake Kivu behavior, under production rates of methane up to one billion cubic meters per year, have shown the lake to remain remarkably stable with infinitely small probability that spontaneous liberation of carbon dioxide and methane into the atmosphere would occur.