Technology to tame the killer lake8 July 2016
Lake Kivu in Rwanda has a reputation as a “killer lake”. Trapped beneath the deeper water washed out of the nearby volcanoes there is a large volume of methane gas. When the concentration rises too high, or the lake is hit by one of the region’s regular earthquakes, the gas can be released in a great bubble that poses a threat to the people living in the vicinity.
The KivuWatt project is intended to alleviate this problem, while at the same time creating a new power supply for the national grid, by extracting the methane and burning it in gas powered generators. The project came to fruition on 16 May when it was inaugurated, at a special ceremony, by Rwanda's president Paul Kagame.
The power plant
The 25 MW power plant has been supplied by Wärtsilä for the owner ContourGlobal from its Smart Power Generation range. It is powered by three 34SG engines running on methane gas that is lifted by a specially equipped barge anchored 13 km offshore.The methane is lifted from a depth of 300 metres, purified on the barge and transported to the shore through an underwater pipeline. The gas is then supplied directly to the power plant's engines, providing low-cost renewable energy to the local community and to the country.
Wärtsilä was contracted in 2011 to supply the plant with a full engineering, procurement and construction delivery, and it has been operational and running on the extracted methane since December. Currently, ContourGlobal is preparing to extend the plant with one more Wärtsilä 34SG engine.
Wärtsilä says that its 34SG engine offers the highest simple cycle efficiency in the market, showing no derating at the altitude of 1500 metres. The engines are optimised to run on Lake Kivu's gases that have a lower heating value than normal natural gas. This has helped to downsize the size of the extracting barge and optimise the costs of producing electricity.
Wärtsilä has previously delivered two other EPC projects to ContourGlobal in Africa: a 100 MW plant in Togo, and a 53 MW plant in Senegal. Wärtsilä's installed capacity in Rwanda is now 46 MW, about
50 % of the country's available capacity.