From the top of the Sam Houston Ship Channel Bridge, more than 50 meters (160 ft) above Buffalo Bayou, in every direction you look, you can see huge oil tankers, massive piles of coal, and uncountable smokestacks. This small corner of Houston is home to some of the world’s most valuable businesses, which turn fossil fuels into the products that have powered the development of our civilization. But the 21st century has brought with it an existential problem for these companies.
Ever-growing carbon emissions fuel the ever-growing risk of catastrophic climate change. The trouble is that, like a smoker to his cigarettes, humans are addicted to the luxuries fossil fuels have brought to our lives. The International Energy Association, an inter-governmental think tank, believes we’ll keep burning these fossil fuels for decades to come. Net Power, a North Carolina-based energy startup, is betting on that prediction. At its pilot plant in Houston, the company is making a $150-million investment in a new approach to deploy carbon-capture technology that it believes could completely change the way we use natural gas to generate electricity.
Carbon capture has been in commercial use in some form since the 1970s. Ironically, it was first developed to help oil companies extract more oil from their depleting fields, a process called “enhanced oil recovery.” But now it’s being touted as the means to avoid dangerous climate change.
The foremost global body on the issue, the Intergovernmental Panel on Climate Change, has modeled the most economically viable routes to meeting the emissions goals set under the Paris climate agreement. These models show that, without the mass deployment of carbon-capture technology, there is no way to keep the global average temperature from rising above 2°C compared to pre-industrial levels. In fact, 101 of the 116 options modeled by the IPCC say the world needs to not only capture emissions from fossil-fuel power plants and industries, but also to suck it out of the air to produce “negative emissions,” a technology yet to be commercialized.
There are only 17 large-scale carbon capture and storage (CCS) plants in operation today, and, annually, they stop less than 40 million metric tons of carbon dioxide from entering the atmosphere. That’s less than 0.01% of the 40 billion metric tons we emit each year.
There’s currently no financial incentive to cut emissions in most of the world. Where there is a price on carbon emissions, such as in Norway, carbon-capture technologies have been given a boost. But in most places, without a penalty to their bottom line, companies won’t stop dumping carbon dioxide in the atmosphere. Cleaning up comes with costs, too: A typical power plant would have to use as much as 20% of the energy it produces to power today’s carbon-capture technology.
To make it work, you need to either charge more for your electricity, which would likely be self-sabotage in a hyper-competitive market, or find another revenue source, such as a paying customer for the captured carbon dioxide. The only two fossil-fuel power plants currently operating a carbon-capture unit—Boundary Dam in Canada and Petra Nova in the US—cover the cost by selling the carbon dioxide for enhanced oil recovery. (Each of the projects is also partially supported by government grants.) But there aren’t many buyers out there for the human-produced greenhouse gas.
An energy company launching today needs to look at the future in much longer terms. If we assume that down the road, all new fossil-fuel plants will have no choice but to include carbon capture—and we should, given the IPCC’s models—then a new energy company’s first goal should be to develop a way to eliminate carbon emissions without raising the cost of electricity. Net Power seems to have figured one out, thanks to an unusual group of three inventors.
This article is part of The Race to Zero Emissions series investigating carbon-capture technology. You can also read our feature laying out the case for using the technology to fight climate change.
Change is good
In 2008, as the stock markets were melting, Bill Brown decided to quit his Wall Street job and “make something good for a change.” He founded 8Rivers, an investment firm focused on new technologies, with Miles Palmer, a friend from his undergraduate years at the Massachusetts Institute of Technology. They thought the energy industry seemed ripe for disruption. The risk of failure was high, but so was the reward for success.
After their first few ideas failed to take off, Brown and Palmer realized they needed someone with process-engineering knowledge on the team. Through friends of friends, they were introduced to Rodney Allam, a retired chemical engineer whose last job was as the head of research and development for a speciality gas supplier in Europe. After just a few months with 8Rivers, Allams presented them with a radically new design for a natural-gas power plant.
The core of Allam’s solution is a new type of gas turbine, an update to a technology that hadn’t changed much since its invention 150 years ago. The job of a turbine is to convert heat energy into mechanical energy, which can then be turned into electricity. All turbines today use either steam or a mixture of hot gases to transfer energy from one form into another, but the process is inefficient. Allam’s system uses carbon dioxide to achieve heat transfer and gets much higher efficiencies as a result.
“He did it old-school style—with just pen, paper, and an engineering calculator,” says Walker Dimmig, a principal at 8Rivers. “We had to hire an engineering firm to redraw Rodney’s drawings on the computer, and verify whether what he claimed would be feasible.” The numbers checked out.
Not all evil
Most people know carbon dioxide for its greenhouse-gas effect, but the colorless, odorless gas isn’t, on its own, much of a problem. In fact, without any greenhouse gases in our atmosphere, the Earth would basically be a ball of snow and ice, with an average global temperature of -18°C (0°F). The natural carbon cycle is essential to the maintenance of life as we know it.
The problem is humans have become so dependent on fossil fuels and so unwilling to cut emissions that we’ve overloaded the atmosphere with carbon dioxide. The last time there was so much atmospheric CO2 was more than 800,000 years ago, when sea levels were 10 meters (30 ft) higher than they are today.
Beyond the greenhouse-gas effect, carbon dioxide has some fascinating properties. At high pressure and temperature, for instance, it enters a state of matter where it’s neither a gas nor a liquid but has properties of both. It’s called a “supercritical fluid.” If you’ve ever had decaf coffee, you’ve likely been an unwitting customer of supercritical carbon dioxide, which is often used to extract caffeine from coffee beans with minimal changes to the taste.
For Net Power, supercritical carbon dioxide holds a different promise: the ability to convert heat more efficiently into electricity.
Currently, the most efficient natural-gas power plants use a “combined cycle.” Oxygen-containing air is supplied to a chamber where natural gas is burned. As the gases heat up, the pressure in the chamber increases. The energy generated by this increasing pressure turns a mechanical shaft in the turbine. This shaft is connected to an electrical generator, which converts the mechanical energy into electricity. The hot gases lose some energy in the process, but the remaining heat is enough to convert water into high-pressure steam in a heat exchanger. The steam is then passed through a steam turbine also connected to a generator, which produces additional electricity.
However, even the most efficient combined-cycle systems of this sort are not all that efficient. At best, for each unit of energy trapped in natural gas, these systems produce 0.6 units of electricity. (And, if you were to capture emissions from this system, you would lose another 20% in the extra energy needed to power current carbon-capture technology.) The efficiency problem is primarily due to the fact that neither the gas turbine nor the steam turbine are all that good at extracting heat. Replacing gas or steam with a better medium, like supercritical carbon dioxide, could solve the problem.
The Allam cycle
Net Power’s pilot plant site in Houston is surprisingly small, no bigger than a soccer field. After putting on the standard safety gear, I got the tour; it soon became clear to me why the plant wasn’t bigger.
After looking at compressors, gas pipes, and more compressors, we arrived at the heart of the power plant: its gas turbine. The Japanese company Toshiba partnered with Net Power to convert some of Toshiba’s own high-pressure steam turbines into ones fit for what’s now called the “Allam cycle.” Because it uses the highly effective heat transfer of supercritical carbon dioxide, the new gas turbine can be less than one tenth the size of a normal one—small enough to fit in a 60-sq-ft room—yet just as powerful.
In the small turbine, a combustor burns natural gas and pure oxygen—producing only carbon dioxide and water—in a chamber that’s already full of supercritical carbon dioxide at high pressure and temperature. That’s no small feat; it’s like trying to light a match while someone else is doing their best to put it out with an extinguisher. The combustion produces additional carbon dioxide, some water, and lots of heat. This hot, high-pressured mixture is then passed through a gas turbine, where the pressure turns a shaft to generate electricity.
The cooled mixture exits the turbine, then is separated into parts. The necessary amount of carbon dioxide is compressed to become supercritical again and added back to the initial chamber, keeping a steady amount of the gas circulating through the system. The remaining, pure stream of CO2 can be buried underground. And the (clean) water is dumped. The heat transfer in this process is so efficient that for each unit of energy trapped in natural gas, the Allam cycle produces 0.8 units of electricity.
There are some additional energy costs, though, that bring the final efficiency down. To get the oxygen necessary for the first step in the Allam cycle, Net Power has to run an air-separation unit, which as the name suggests, separates air into its components: nitrogen (78%), oxygen (21%), and argon (1%). Running the air-separation unit reduces overall energy efficiency by about 10%. And before the carbon dioxide is reinjected at the end of the cycle, it has to be put through a separate compressor to turn it back into supercritical CO2. That reduces efficiency by an additional 10%.
In the end, the Allam cycle is only slightly more efficient than typical combined-cycle systems. But it has the major added benefit of capturing all potential carbon dioxide emissions essentially for free.
A big bet
Net Power has already finished construction on the pilot plant. It will begin supplying electricity to the grid in 2018, Dimmig told me, when final tests have been completed on each part of the system and the last few wrinkles ironed out. When it starts, it will produce 50 MW of electricity, enough to power over 40,000 homes.
The company hopes to license the technology, instead of building and operating its own power plants. That way, Net Power can keep its capital investments low and not take on all the risks that come with building anything that expensive. Even so, it’s a tricky market. Other turbine makers, such as Siemens and GE, are struggling. In November, Siemens announced it will cut 6,900 jobs in its power division, because there isn’t enough demand for new turbines.
But Net Power believes, as do many international bodies and think tanks, that natural gas has a long future. There has been huge growth in the renewable sector in recent years, but Net Power thinks demand will peter out as government subsidies get cut. Moreover, regulations have focused on energy efficiency, which has stymied growth in electricity demand in wealthy countries. That’s likely to change as electric cars become cheaper, and more car owners are able to “refuel” at a charging point rather than at a gasoline station.
There’s no guarantee Net Power will succeed, but there are good reasons it’s a strong bet. In my year of reporting on carbon-capture technology, I’ve consistently heard the same thing from experts from all over the world: Net Power is the next big thing in the energy industry. A power plant that burns fossil fuels with no greenhouse-gas emissions, and produces electricity that doesn’t cost more—what’s not to like? The $150 million Net Power has raised in investments is the most of any startup in the field that I’m aware of.
Choosing natural gas over coal as a fuel of choice means Net Power can ride the current wave of fuel-switching, where coal power plants are transitioning to cheaper and cleaner natural gas. The glut of natural gas in the US is so huge that the analytics firm IHS Markit predicts there will be plentiful, inexpensive global supplies for the next 30 to 40 years.
Net Power will also have customers for the carbon dioxide it captures: oil companies looking for enhanced oil recovery. To get the fossil fuel out of the ground, oil companies pump water into the fields to push out the oil. However, because oil and water don’t mix, the process leaves behind oil in hard-to-reach pockets. If you in pump supercritical carbon dioxide, it can dissolve this oil and force it up to the surface. Currently, the US uses about 68 million metric tons of carbon dioxide to recover oil from depleted fields.
The trouble is that more than 80% of that CO2 comes from naturally occurring carbon-dioxide fields, and not from fossil-fuel burning emissions. In effect, these companies are pumping carbon dioxide from under one part of the US and to under another, usually hundreds and sometimes even thousands of miles apart, while allowing other forms of carbon dioxide to enter the atmosphere and wreck havoc on the global climate. If Net Power can provide human-made carbon dioxide for a lower price, oil companies would have no reason to continue using geological sources. That would be more than a good start in the world’s efforts to really make a dent in global emissions.
You can sign up for our newsletter to be informed when new stories in the series are published. The reporting was supported by a fellowship from the McGraw Center for Business Journalism at the City University of New York Graduate School of Journalism.