A new project in western Ghana, however, could help tame the flames. GE Power has teamed up with local electricity producer Marinus Energy to capture the “waste” gas and burn it to generate electrons.
The waste fuel is isopentane. It is one of several heavier hydrocarbons naturally occurring in the raw gas produced from Ghana’s giant offshore fields. Energy companies strip off these heavier hydrocarbons during processing to leave pipeline-quality dry natural gas, which can be burned safely in the country’s power plants.
Some of these compounds are useful. For example, ethane, butane and propane can be easily pressurized in steel cylinders and Ghanaians use them for cooking. Even isopentane found industry applications as a component in cosmetics, shaving creams and hair conditioners. “It is highly flammable, so it can also be used in the fuel for Formula 1 racing cars,” says Fred Asamany, a strategic adviser to Marinus Energy.
But the isopentane was going to waste in Ghana, which is not known for beauty products or Grand Prix. With no market for the fuel, the state-run Ghana Gas Company had no choice but to flare it.
Burning off the isopentane was not just wasteful — it also polluted the local area. Flaring the fuel emits nitric oxide and nitrogen oxide gases, which increase the concentration of ground-level, or ‘bad’, ozone, in the air. “Flaring isopentane was also leaving a residue on the skin, which is mildly irritable and also leaves a pungent smell,” Asamany says. Burned isopentane has a strong gasoline-like odor. Depending on the gas processing plant’s operational parameters, the smell may have residual sulfur-containing components that contribute to a rotten eggs-like smell.
In 2012, GE and Marinus decided to break the cycle of waste and pollution. “We put our heads together and came up with a proposal to put the isopentane to good use,” Asmany says.
The result is the Atuabo Waste to Power Independent Power Project. It captures the isopentane and uses it to fuel GE’s latest TM2500 gas turbines to generate up to 25 megawatts of electricity — enough for more than 100,000 Ghanaian households.
The turbines, which are based on a design GE originally developed for jet engines, are like power plants on wheels. The trailer-mounted machines fit inside cargo planes and on trucks and barges, and can be easily and quickly deployed in remote locations. They are already working in the Algerian desert and in Angola, Indonesia and even in Ghana.
Once the turbines are on the ground, operators need to connect them to fuel supply and electrical grid. They can ramp up to full power in just 10 minutes, and they can be up and running within a month of the contract signing.
Atuabo’s gas turbines will start burning pure natural gas but gradually switch to an isopentane mix. The operators plan to add extra turbines to build capacity up to 100 MW. “We are in pole positon to take greater volumes of isopentane,” Asamany says.
But capturing the isopentane and making it power plant-ready is not a straightforward task — especially in Ghana’s tropical climate. Isopentane is extremely volatile and flammable, with a boiling point of 27.8 Celsius, which is similar to Ghana’s average air temperature. “You’re constantly monitoring temperature, pressure and fuel composition,” Asamany says.
Workers first chill the isopentane gas down from approximately 87 Celsius until it condenses completely. Next, they pump it to holding tanks designed to keep the fuel in liquid form at local ambient conditions, says Jesus Daniel Castillo, a lead systems engineer at GE Power. Fuel nozzles then atomize the pressurized fuel and inject it into the combustion chamber. The thermal energy released by the ignition spins the turbine, which powers the generator and completes the waste-gases recycling process.
The pipes, pumps and tanks along the way all need to be robust. For example, the project will use special holding tanks for the isopentane to prevent rupture or explosion, says Asamany.
The benefits of capturing the isopentane are huge. Flaring the gas emits 297 parts per million (ppm) of the highly polluting nitrogen oxide (NOx) gases. However, stripping out the isopentane reduces NOx emissions from flaring at Atuabo to just 97 ppm, says Wilmot Asumeng, a senior sales manager at GE Power.
Capturing isopentane also boosts the efficiency levels of the gas processing plant itself, allowing the increased throughput of natural gas, as well as the other heavier hydrocarbons that can be sold is Ghana. This wins the processing plant operator additional revenues of $50,000 per day, Asamany says.
Additional revenue comes from the extra isopentane-fired electricity that operators sell to Ghana’s grid. The power generated from the isopentane is cheap, coming in at $0.11/kWh, which is around half the price of Ghana’s gas-fired electricity. That is purely because of feedstock prices. Natural gas prices are just shy of $8.5/MMBtu in Ghana, while isopentane is $4/MMBtu.
Isopentane isn’t the only source of this quick-fix, cheap power. The TM2500 turbine-on-wheels can burn natural gas, isopentane and other hydrocarbons. For example, it can handle natural gas condensate, which is normally a mix of raw natural gas plus liquid propane, butane or pentane. It can also generate power by burning pure propane and butane, as either a gas or liquid.
Atuabo could be the first of many such projects, with several African countries flaring gas or other fuels that could instead be burned for power. Nigeria fits the bill, according to Asamany.
“When we originally made the proposal to capture the isopentane flare and convert it into electricity, many people were very skeptical,” he said. “But Atuabo shows you can mix GE’s global reach with innovation to solve local problems.”