快猫短视频

IT SOUNDS too good to be true. How can a bunch of pipes in a huge lake provide electric power for much of Rwanda, help revive its devastated forests and quell the danger of a bizarre natural disaster?

The answer is sitting on Rwanda鈥檚 north-western border, where the deep waters of Lake Kivu are brimming with vast quantities of three dissolved gases: carbon dioxide, hydrogen sulphide and methane. The CO₂ and hydrogen sulphide come mainly from volcanic activity, while the methane comes from lake bed bacteria. Engineers are now planning to suck out the methane and burn it to produce electricity.

The gas reserve should be enough to supply the country鈥檚 electricity needs for 400 years. Using it will mean far less logging since Rwanda currently gets 90 per cent of its energy from wood burning. And tapping the gas will reduce the risk of a massive gas explosion killing people who live near the lake.

There is a precedent. In 1986, Lake Nyos in Cameroon released a vast cloud of carbon dioxide that had slowly been building upin the water 鈥� suffocating more than a thousand people. For safety, an elaborate system of pipework is draining away the lake鈥檚 CO₂ output (快猫短视频, 24 March 2001, p 36).

Now Michel Halbwachs from the University of Savoie in Chamb茅ry, France, the engineer behind the Nyos pipework, has an ambitious plan to harvest Kivu鈥檚 methane for energy production. He is proposing using a single 360-metre-long pipe (see Graphic) that will hang down into the depths of the lake from a raft a few kilometres from the shore.

In his scheme, a small pump starts sucking gas-filled water up from the bottom of the lake. The higher the water goes up the pipe, the lower its pressure gets, forcing the three gases to bubble out of solution. These bubbles rise, pulling up water behind them in a process called entrainment. You can then stop the pump as no further energy is needed to keep drawing water up the pipe. So the scheme is cheap and self-sustaining.

To separate out the methane, the gases are bubbled through a chamber of fresh water 20 metres below the surface. Here the pressure is such that the unwanted hydrogen sulphide and CO₂ dissolve back into the water. The methane output in tests was 85 per cent pure 鈥� more than good enough to burn. Because Kivu is so much bigger than Nyos there is little danger of a similar CO₂ cloud developing.

The Rwandan government has applied to the European Community for cash to fund Halbwachs鈥檚 scheme and expects to install the first system by the end of the year, assuming no rows break out over rights to the methane between Rwanda and the Democratic Republic of Congo, which also borders the lake. To begin with, the scheme should be able to fuel a small 1-megawatt power station 鈥� with several industrial groups interested in expanding the idea to 20 megawatts.

Rwanda鈥檚 forests should benefit enormously. The country鈥檚 annual deforestation rate is 4 per cent. 鈥淚t鈥檚 a very big problem. I hope this will solve it,鈥� says Emmanuel Nsanzumuganwa, coordinator of the project at the Ministry of Infrastructure.