Editor & Publisher, Marcellus Drilling News (MDN)
A new zero-emissions natural gas power plant—the world’s first—is coming. It’s a complete game changer for multiplying the emissions benefits of shale gas.
We spotted an article that intrigued us with the headline, “A radical startup has invented the world’s first zero-emissions fossil-fuel power plant.” Most of the article–the first two-thirds of it–is obsequious genuflecting before the man-causes-global-warming gods. Whatever. Believe in fairy stories if you want to. The final one-third of the article is the real meat, which we highlight below.
It seems a group of smart people at a company called Net Power, located in Texas, have figured out a way to capture all, as in 100%, of the carbon dioxide that comes from burning natural gas to produce heat to turn a turbine. There are no CO2 emissions that escape into the atmosphere. We bring you details of this new technology because it’s neat and may one day change how electricity is generated in this country. What if (gasp!) natural gas became as “green” as solar or wind? That just doesn’t fit the narrow worldview of radical environmentalists.
…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.
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.
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.