POWER July 2016 - 8

Rwanda's Power
Production Triumph over a
" Killer Lake "
Lake Kivu, the 1,040-square-mile " killer
lake " that stretches over the border between
Rwanda and the Democratic Republic
of Congo (DRC), has long been a source
of trepidation.
Because it sits between two volcanic
regions in the western branch of the Great
Rift Valley, the deep, perpetually stratified
lake's bottommost waters absorb
high concentrations of carbon dioxide
(CO2
)
from magma-heated springs deep
to methane. These dissolved
underground, and microbes convert much
of the CO2
gases are held in solution by pressures
in the depths of the lake but can emerge
if zones of high concentration move toward
the surface, a process known as a
limnic eruption, or " overturn. " Because
the region is regularly subject to largemagnitude
seismic events and volcanic
discharges-and considering that methane
has a high partial pressure-Lake
Kivu is known to experience violent overturns.
Geologists believe they occur at
Lake Kivu about every 1,000 years-and
that the lake is ripe for another.
Limnic eruptions occurred at much
smaller Lakes Monoun and Nyos across the
continent in Cameroon in 1984 and 1986
respectively, killing more than 1,700 people
by asphyxiation. But an overturn at
Kivu could be catastrophic and endanger
millions of people living around its shores
on both sides of the border because it
contains far more dissolved gases than
those two lakes.
Rwanda's government has for years
sought to extract the methane from Kivu's
depths, both to mitigate the risk of such
a calamity and to generate power. Its efforts
first came to fruition in 2008, when
the country's first methane-extracting and
power-producing plant, a 3-MW pilot project,
started operations.
Since then, the government has negotiated
several methane gas concessions.
Later in 2008, U.S.-based ContourGlobal,
a firm that owns about 4,000 MW of capacity
in 20 countries, including in Africa,
entered into a partnership with the Rwandan
government to transform the menace
of the lake's gas deposits into a 25-MW
power plant, dubbed KivuWatt. The project
subsequently garnered financial backing
from the African Development Bank,
the Emerging Africa Infrastructure Fund,
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POWER | July 2016
the Netherlands Development Finance Co.,
and the Belgian Investment Co. for Developing
Countries. In 2011, ContourGlobal
contracted Finnish energy technology firm
Wärtsilä to supply an engine-based plant
with full engineering, procurement, and
construction delivery.
The plant, which has been operational
since December 2015 but was inaugurated
in May, relies on two processes: methane
extraction and power production. The gas
extraction process, performed on a barge
anchored 13 kilometers (km) offshore in
Lake Kivu (Figure 1), brings gas-rich waters
from a depth of 300 meters (m) and
35-bar pressure, reducing pressure to 2 bar
in a gas separator, where gas bubbles are
extracted from the water. Raw gas is then
washed in four wash towers, ContourGlobal
explained.
1. A killer lake reformed. Methane is drawn from Rwanda's Lake Kivu at a depth of 300
meters by a special barge anchored 13 kilometers offshore. Courtesy: Werner Krug
2. Harnessing lake methane. Rwanda's KivuWatt power plant runs on methane gas
that is lifted from the depths of Lake Kivu, an " exploding lake. " The plant comprises three 20-cylinder
34SG gas-powered engines supplied by Wärtsilä. Courtesy: Werner Krug

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POWER July 2016

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