The greenhouse gases held in hydroelectric reservoirs can be captured to generate more energy, preventing them from turning into climate-changing emissions, according to Brazilian scientists.

The bubbles of reservoir water hold the energy potential of methane gas. - Photo Stock

Some hydroelectric plants in the Amazon hold an added energy capacity of 27 to 53 percent, making use of the methane bubbles released from the water as it passes through the turbines and spillways, says Fernando Ramos, based on a study he and two colleagues from Brazil's National Institute of Space Research (INPE) conducted at the Balbina, Samuel and Tucuruí dams.

But what his group proposes is to extract methane from the depths of the reservoirs, where there is a higher concentration of the gas.

With an investment of 100 million dollars, one million tons of methane a year could be captured at Tucuruí, Brazil's second largest hydroelectric dam, located in the eastern Amazon. The return, considering current prices of the gas, would reach 79 percent, much higher than the 25 percent expected in other Brazilian renewable energy projects.

A million tons of methane is the equivalent of 1,760 megawatts — the potential of a large hydroelectric dam — and more energy than what would be produced by the third nuclear plant under consideration for construction in this country.

As such, methane could replace several hydroelectric dams planned for the Amazon, and which are rejected by environmentalists because they would flood extensive areas of forest and cause other environmental and social problems.

The gas could be stored and transported for use in other areas, but the best option would be to build a thermoelectric plant at the site, taking advantage of the existing infrastructure of the dam to transmit the electricity, Ramos said in an interview for this report. Furthermore, it is a good way to avoid emissions of the gases that contribute to climate change, which could generate carbon credits and make the project more profitable.

“This technological idea would meet the criteria of the Clean Development Mechanism (CDM)” established in the 1997 Kyoto Protocol on climate change, and could enter the market of carbon credits, agreed Pablo Fernández, manager of CDM project implementation at EcoSecurities, though he admitted he is “not clear on how the methane would be captured.”

EcoSecurities is the company that put together the first Brazilian project that obtained carbon credits, NovaGerar, which extracts gas emissions from a huge garbage dump outside Rio de Janeiro to generate energy.

INPE's Ramos, a mechanical engineer, said “there is no doubt about the feasibility of the technique” for recovering methane from the dams, given that the gas is released when the water passes through the turbines and “pressure falls suddenly, producing bubbles,” in a process similar to opening a soda bottle.

The idea is to create a tubing system similar to a pool cleaner, installed on a barge that would move about the reservoir, seeking the areas of highest methane concentration.

The new task that the INPE group hopes to complete by the end of the year is a pilot project to verify its economic viability, he announced.

It is “a new idea, not yet made official in the CDM,” and needs to “mature” in technical details and an inventory of the methane held in the Brazilian reservoirs, Ramos acknowledged.

Other reservoirs, including those outside the Amazon region, could have high concentrations of gas from organic material as well, he noted.

The INPE scientists rule out trying to capture methane at the dam turbines, because the electric companies don't want to install anything that would affect the functioning of the dams. So the option is to collect the methane before the water reaches the turbines.

However, Alexandre Kemenes, researcher with the Large-Scale Biosphere-Atmosphere Experiment in the Amazon (LBA), proposes capturing the gas released from the water “during and after its passage through the turbines.” It is more feasible, he said in an interview, because the area will be limited and it would take advantage of existing installations, and is better for the environment because it would also permit carbon recovery.

Kemenes has already filed a patent request in Brazil and abroad for the “system and method of biogas exploitation” that he designed. It speaks of biogas because it makes use of the mix emitted in the turbines, predominantly methane and carbon. At the Balbina dam in the state of Amazonas, biogas is just 43 percent methane, and would have to be purified or enriched to be used in generating electricity, which requires a minimum of 45 percent methane.

Balbina has gigantic potential, given that it emits gases that represent 10 times what is contributed to global warming by a thermoelectric plant of equal capacity, run on fossil fuels, or 10 percent of the emissions of Sao Paulo, Brazil's largest and richest metropolis, says Kemenes.