Air Quality

Published on November 21st, 2016 | by Michael Barnard


How Real Is NET Power’s Zero-Carbon Gas Generation Tech?

November 21st, 2016 by  

A US startup that’s in a consortium with Toshiba, among others, NET Power is building what it claims is a no-carbon form of gas generation that’s better than all the rest. It has broken ground on a 10 MW Texas plant in a consortium with Exelon Generation and Chicago Bridge & Iron (CB&I) to prove its technology. How do its claims stand up to scrutiny?

First off, what is NET Power’s innovative technology?

screen-shot-2016-11-16-at-4-11-16-pmIt’s a variant of Brayton cycle generation, something that’s been around for well over a century. It has a couple of twists which aren’t fully explained in publicly available documents, but appears to have something to do with the how many things it runs through a heat exchanger. The big claim is that it automatically captures CO2 instead of venting it to the atmosphere. Secondary claims are about it being able to be scaled down and not emitting nitrous oxides.

The company is using supercritical CO2 as a heat exchange mechanism to drive turbines to generate electricity. This is instead of water. Combustion is of gasified coal or natural gas, and the publicly available material is unclear on which, although Net Power on its site talks only about natural gas and makes the interesting claim of zero emissions, which is demonstrably nonsense although in the range of hyperbole rather than bullshit.

The company uses pure oxygen to reduce a source of contaminants in the emissions.

They have branded it the Allam Cycle, but no one named Allam is associated with Net Power or its parent think tank, 8 Rivers, a company set up to spin off neat ideas with big potential revenue upside. It’s unclear where the name comes from. They don’t seem to publish, keep their work proprietary and so it’s pretty hard to actually evaluate their ideas. I’d assume they’ve got Toshiba and other partners referenced in various places under NDA on the specifics.

Is it alone in the space?

No, there are a handful of consortiums attempting to find crucial innovations to improve the efficiencies of gas generation above that of combined cycle generators. No one has managed it yet. GE is in the game, as one major example of an organization I would take more seriously in this space.

screen-shot-2016-11-16-at-4-14-25-pmIs it cheaper than normal gas or renewables?

Not according to the economic analysis performed by the IEA. It appears to be cheaper than nuclear, but that’s not hard. It is particularly susceptible to increased costs due to novel technology (unlike wind and solar).

Does it actually get greenhouse gases out of the atmosphere?

Well, maybe. Because it uses natural gas, there are always going to be methane leaks well-to-generator. It’s never going to be perfect, but it could be okay in well managed wells and distribution systems.

The big problem is carbon sequestration. There just isn’t anywhere to put the CO2. Net Power talks about enhanced oil recovery, the usual suspect when fossil fuel heads think about carbon sequestration, as it’s the only one that has a revenue stream. However, enhanced oil recovery (EOR) used about 48 million tons of CO2 in 2008, the year I have numbers for, and global CO2 emissions in 2015 were about 10 gigatonnes, about 200,000 times more. EOR is a rounding error on the necessary carbon capture. 48 million tons is about the annual emissions of 13 coal plants of the 400+ still operating in the USA.

z140407ogjsku01It’s worth pointing out where CO2 pipelines are and aren’t in the USA. There are a tiny number of pipelines and while CCS and EOR advocates have been pushing for more, it just hasn’t been worth building them. One thing they all have in common is that they go from sparsely populated areas to sparsely populated areas through sparsely populated areas. A theoretical advantage of the scalable natural gas generation plants which NET Power claims is that they can be put in cities due to low emissions. However, that doesn’t help their other advantage of ‘pipeline ready CO2’.

Other sequestration approaches have sequestered a tiny fraction of what is used for EOR. It’s greenwashing.

Are there other problems with it?

Well, yes. Using CO2 and other emissions are concerns.

Supercritical CO2 is neat stuff. As a solvent it dissolves stuff and it isn’t toxic. As a working fluid in moving equipment a whole bunch of material science has to be done to find alloys and materials that will survive for power plant lifetimes with its use. This isn’t insurmountable, but it’s a concern.

Natural gas isn’t just methane, aka CH4, which does combust cleanly with pure oxygen to create water and CO2. It’s only 88% to 92% methane. Depending on the source, the rest of it is nitrogen and hydrogen sulfide usually, along with other stuff like helium and various trace elements. For our purposes, the first two are important because they are sources of nitrous oxides and sulphur oxides, which are key pollutants. Net Power claims that by using pure oxygen instead of air, it gets rid of nitrogen and hence nitrous oxide pollutants, and maybe it does reduce them. I’m not enough of a chemist to prove it, and I’d need to see emissions tests on a variety of fuels before I was convinced.

The process has to separate oxygen from the atmosphere and separate CO2 from the emissions stream. Both of those take technology and energy. It’s a tradeoff which it seems to think is worthwhile, but it has yet to be proven to be economic. A variant would just put a little extra supercritical CO2 in the system occasionally and dump all of the CO2 as emissions at a cheaper price point, so if they can overcome the corrosion and durability concerns, someone is likely to do just that.

What is its status?

Well, the consortium it is working with is building a 10 MW prototype plant in Texas right now. If all goes well, in a decade it might have a product that’s licensed and in production. If the fiscal projections are right, the company will need a serious price on carbon in order for people to buy them instead of combined cycle gas plants, but perhaps it will exceed the IEA economic expectations. That’s unlikely as the IEA has a much better track record with gas generation than with wind and solar.

Is it worth doing?

screen-shot-2016-11-18-at-4-40-22-pmCertainly. If it builds a couple of GW of capacity of the things in the next 50 years instead of gas plants and the vast majority of CO2 was actually sequestered instead of pumping more oil out of the ground, then that would be better than a kick in the head with a frozen mukluk. But the IEA’s expectation that 20% of emissions reductions will come from CCS is highly suspect, so the assertion that this technology is a large part of the solution is also suspect.

Wind and solar are already cheaper and don’t have any of the ifs, buts, and maybes associated with them. Not burning fossil fuels at all is a better way to avoid CO2 emissions. By the time this technology is commercialized, I suspect it will be a niche play, not a primary play.

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About the Author

For the past several years Michael has been analyzing and publishing reports and articles on decarbonization technologies, business models and policies. His pieces on electrical generation transformation and electrification of transportation have been published in CleanTechnica, Newsweek, Slate, Forbes, Huffington Post, Quartz, RenewEconomy, RenewablesInternational and Gizmag, as well as included in textbooks. Third-party articles on his analyses and interviews with Mike have been published in dozens of news sites globally and have reached #1 on Reddit Science. Much of his work originates on, where Mike has been a Top Writer annually since 2012. He also has published a climate-fiction novel, Guangzhou Future Tense.

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