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Zero-Emissions Combined Cycle and Beyond

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John Benson's picture
Senior Consultant, Microgrid Labs

PROFESSIONAL EXPERIENCE: Microgrid Labs, Inc. Advisor: 2014 to Present Developed product plans, conceptual and preliminary designs for projects, performed industry surveys and developed...

  • Member since 2013
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  • Oct 15, 2019

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This paper has a proposal that will keep combined cycle power plants running by converting them to (nearly) zero greenhouse gas (GHG) emission operation. Ultimately these can be converted to negative emissions technology to offset other GHG sources.

Bob Meinetz's picture
Bob Meinetz on Oct 15, 2019

John, you claim

"Ultimately these can be converted to negative emissiona technology to offset other GHG sources."

Do you have any evidence that suggests carbon capture and sequestration is remotely practical, economical, or verifiable? Without it, your scenario might be accurately termed a "pipe dream".

Matt Chester's picture
Matt Chester on Oct 15, 2019

Bob-- I know you're always keen on quoting Bill Gates's opinions on renewable energy, so maybe his investment in a company to sequester CO2 from the air and convert it to synthetic fuels will be of interest

Bob Meinetz's picture
Bob Meinetz on Oct 23, 2019

Matt, capturing carbon from the air and using it to synthesize liquid hydrocarbon fuels using the Fischer-Tropsch process requires significant energy inputs. Producing net-zero fuels would be viable only using nuclear as an energy feedstock; renewables would be capable of generating methyl/ethyl alcohol a drop at a time; producing useful quantities of diesel or gasoline from solar and wind would be impractical.

Both are far better employed generating electricity straight to the grid. High-Temperature Gas Reactors (HTGRs) can efficiently electrolyze water while generating electricity, thanks to the availability of abundant high-temperature gas. I spoke to Geoff Holmes of Carbon Engineering last year about the possibility of converting coal plants in the southeastern U.S. to HTGR plants for production of zero-carbon electricity and hydrogen. With CE's carbon-from-air all the ingredients for net-zero gasoline would be available at one facility.

A former Chinese coal plant as been converted to an HTGR facility for just that purpose. Though the technology could reinvigorate the economies of areas of the U.S. hardest hit by coal plant closures, obtaining regulatory approval for innovative nuclear approaches like HTGR fuel synthesis is next to impossible in the U.S. (GE-Hitachi describes how design license applications to the NRC disappear into a "Valley of Death").

John Benson's picture
John Benson on Oct 16, 2019

Off the top of my head I do not know what "proof" of CCS has been done (future post?). I do know some methods that can be used to do this. I believe the only function that cannot be modeled and measured directly is the "S" (sequestration).

Several types of strata are considered secure for sequestration by geologists. Each of these would need to be verified by one of (at least) two methods: (1) modeling and long-term measurement (for instance, of subsurface temperature and pressure) or (2) injecting tracer isotopes with the carbon dioxide and sampling possible escape routes.

I'll add a survey of work done on this subject to my list of possible future papers.


Matt Chester's picture
Matt Chester on Oct 16, 2019

Always appreciate your eagerness to turn knowledge gaps into opportunity to educate the rest of the community, John!

Bob Meinetz's picture
Bob Meinetz on Oct 22, 2019

John, I have no doubt it's possible to sequester some CO2 underground in salt caverns or porous voids leftover from extraction wells. There is one project in Decatur, IL which (as of May 2018) had reportedly sequestered 640,000 metric tonnes of CO2 in a saline reservoir at a cost of $208 million.

640,000 metric tonnes represents one five-thousand seven-hundred eightieth (1/5780) of the 37 billion tonnes of CO2 emitted by the burning of fossil fuels each year worldwide. To capture 100% of emitted CO2 would cost $1.2 trillion - but it will never happen for many, many reasons, only some of which include:

• construction of a CO2 collection pipeline network in every country of the world, including those where residents are considerably less affluent and self-entitled than Americans
• CCS is impossible to verify, thus any profit available to practitioners will promptly be exploited by venting collected CO2 back into the atmosphere
• inavailability of suitable saline reservoirs of unlimited volume
• the only profitable implementations thus far are Enhanced Oil Recovery (EOR) projects, used to extract even more carbon than that being sequestered
• oil / coal companies recognize the simpleminded fantasies of both CCS and renewables can be usefully employed to justify business-as-usual extraction indefinitely.


Roger Arnold's picture
Roger Arnold on Oct 21, 2019

Projects I know of that have been explicitly been aimed at testing and measuring long term efficacy of geological CO2 sequestration are Norway's Sleipner project in the North Sea, the Wyburn project between the US and Canada, and a recent project in Iceland. The latter, whose name I don't recall, was notable in that CO2 was injected into a volcanic basalt formation and was rapidly mineralized. The Sleipner and Wyburn projects have been ongoing for about 20 years, as I recall, and have included regular monitoring of migration of injected CO2 through the fields.

There are other projects as well, but they're either too new to be used as evidence of long term efficacy, or are still in planning. You might want to check out this recent article at GTM:

Of course, if one considers CO2 injection for enhanced oil recovery, experience is widespread and goes back several decades.

The official scientific position of the IPCC is that, while proposed sequestration sites must be carefully evaluated, capacity for safe geological sequestration is ample. There's a detailed IPCC report on the issue.

You didn't raise this issue, but I know that among advocates for nuclear power, there is sometimes opposition to CCS rooted in a feeling that it will be used as an argument that "we don't need nuclear". No doubt there are some anti-nuclear activists who would say that, but not many. The "small village, decentralized economy" ideology that gave rise to the anti-nuclear movement finds CCS equally abhorrent.

If new generation nuclear reactors succeed in a big way, they will reduce the need for massive CCS. That will be good, not because of largely bogus safety considerations, but just from a practical standpoint of cost and resource use. The issues that are nuclear power must overcome are regulatory burden and perception of risk, not real competition from inferior technologies.

Michael Keller's picture
Michael Keller on Oct 24, 2019

I have little faith in anything the IPCC claims as their reports are heavily biased to justify a pre-determined outcome.

The idea of rountinely pumping massive amounts of CO2 sludge into the ground has only poorly understood environmental risks. Further, the economic merits are very poor. The power production cycle also becomes significantly less efficient which produces more CO2 emissions on an energy output basis.

Far better to more efficiently use natural gas which inherently reduces CO2 emissions. This approach is driven by economics. That same economic approach applies to nuclear energy.

Fixation on zero CO2 emissions is out of touch with reality while stemming from an unsound initial assumption. Namely, a religious-like act of faith belief that CO2 emissions are an existential threat. They are not.

Gary Hilberg's picture
Gary Hilberg on Oct 22, 2019

John - it would seem that carbon capture will be required in the future, but while there are higher emission technologies still being added to grid, would it not be a better choice to displace coal and oil vs. adding costs to existing facilities?  California being zero carbon will make no difference if the rest of world does not reduce emissions.  Califoronia would be better served to keep their nuclear plants running and investing in much lower cost carbon reduction efforts like combined cycle plants to reduce coal emission even if those plants are not physically in California since so much of their electricity is imported from surrounding states.     

Michael Keller's picture
Michael Keller on Oct 22, 2019

The idea of zero CO2 emissions from gas turbine power plants is financially and environmentally nonsensical.
The long-term impacts, if any, of man's CO2 emissions are unknown. Similarly, our ability to meaningfully curb CO2 emissions is highly doubtful. Simple mathematics demonstrates that any actions on the part of Western countries are overwhelmed by Asia's increased use of coal. The only thing accomplished by green energy is to make everyone poorer while lining the pockets of the elite, utilities and Wallstreet investors

Roger Arnold's picture
Roger Arnold on Oct 23, 2019

If you're thinking of post-combustion CC from a conventional gas turbine power plant, then I agree that it's at least financially non-viable. The CO2 would have to be extracted from the flue gas stream, and that makes for a high parasitic load on the plant's output. In addition, that type of capture is never complete. Amine scrubbing might remove 80% of the CO2 from coal plant flue gas, but for a gas fired plant, it would remove only 60%. The CO2 content for the gas-fired plant is only half that from a coal-fired plant to begin with, but amine scrubbing will leave the same residual concentration of CO2 in both streams.

That said, oxy-fueled combustion is just as applicable for gas-fired plants as it is for coal-fired plants. In fact t's even better for a gas-fired plant, because the flue gas stream in then nearly pure CO2 and water vapor. After the water vapor is condensed out, the CO2 stream is "pipeline ready". For a coal-fired plant, the flue gas in mostly CO2, but there are significant fractions of sulfur dioxide, nitrous oxides, and nasty metal carbonyls. There's standard technology for scrubbing those, but it raises the capital cost for the system.

Of course, if one is going to do oxy-fueled combustion in a new gas-fired power plant, then it's better to go with an Allam cycle supercritical CO2 arrangement, rather than a conventional gas combustion turbine. Better efficiency, and more felxibility.

Something not often mentioned: tha Allam cycle -- and oxy-fueled combution in general -- requires a high volumen source of pure oxygen. That's usally an ASU (air separation unit). However, with intermittent renewables getting so cheap, it would make economic sense to use the oxygen stream from an electrolytic hydrogen production facility. That saves the cost of an ASU, and would make for an efficient and economical way to provide flexible backing power for intermittent renewables.

Michael Keller's picture
Michael Keller on Oct 24, 2019

Creating oxygen using air separation units requires a significant amount of energy because air has to be compressed. Also, the output of a gas turbine relies on the mass of the fluid going thru the machine and the machine's firing temperature. If nitrogen is discarded, about 70% of the turbine's output is gone.

With today's gas turbines moving past 64% LHV efficiency  (GE HA 7.03 in combined cycle mode), there is no financial reason to use expensive oxy-fueled combustion processes. Further, the merits of near zero CO2 emissions are near zero in the broader scheme of world-wide CO2 emissions.

H2 and O2 produced by green energy electrolysis has no economic merit, particularly when considering that natural gas is so cheap in the U.S. There is also no market for the H2 and O2 products nor is there a distribution system. Further, the land requirements necessary to provide the gases from green energy are stunningly large. 

Roger Arnold's picture
Roger Arnold on Oct 26, 2019

I'm afraid you're wrong about a couple of things, Michael. ASUs do require a "significant" amount of energy, but it's not huge. Modern units are regenerative, and use counterflow heat exchange to do the heavy lift of cooling air to near-liquid temperatures. The liquefied oxygen and nitrogen give back most of the energy used for compression when they are warmed and expanded. Capital costs are high, however, because the market for ASUs is currently small. They are custom built from stock components, which is always expensive.

It's also not true that removing nitrogen from the combustion mixture has an adverse effect on power output. Quite the contrary. The nitrogen is replaced by recirculated CO2 to keep the flame temperature at the turbine's optimum design level. (Fuel combustion in pure oxygen would melt any turbine.) A recuperated Brayton cycle turbine operating with supercritical CO2 is both highly compact and highly efficient. It's also highly flexible. It can be throttled over a broad range without significant loss of efficiency. That's because supercritical CO2 is so dense that radial turbines (i.e, centrifugal) can be used instead of axial flow turbines. Gas flow can be regulated by wicket gates, in the same manner as it is in Francis turbines for hydroelectric power generators.

None of this is speculation on my part. The Allam cycle has been validated in physical prototypes and implemented it a moderately large demonstration unit. Its measured efficiency and performance live up to theoretical predictions. You can find it on google.

John Benson's picture
John Benson on Oct 22, 2019

Roger, Gary and Michael. Thanks for your responses.

Roger - thanks for the leads. As I indicated to Bob, I've added CCS "proofs" to my future paper lists, and your information will help me get started.

Gary - I understand very well the limitation of what we are doing in California. It will take major international agreements with real teeth to get all major nations to start playing by the "net zero" rules. I posted a paper a few months ago where I suggested a possible route for this (linked below, Section 4), but I'm sure there are others.

Also economics seem to be doing a pretty good job of eliminating coal in the U.S.

Michael - you could be right that keeping any of the combined cycle plants running in the long run is not viable, but in the short run they will be necessary for their dispatchable power during certain times of the year, in certain constrained locations on the grid and under certain weather conditions. Only time will tell if wind, PV, storage and other renewables will be able to completely displace these in several decades. Also, as described in my paper, these may be the most cost-effective way to provide negative emission technology, and I believe this will be required to offset many emission sources that will be very difficult to eliminate (cars, airplanes, ships, etc.).



Michael Keller's picture
Michael Keller on Oct 24, 2019

I seriously doubt any sane nation will commit economic harakari by actually having zero CO2 emissions.

While dishonest and feckless politicians may make grandiose claims of future zero CO2 emissions, folks will revolt long before their standards of living plummet.

Pretty gutless to commit future generations to poverty while the political class lives in a life of hypocritical luxury.

Matt Chester's picture
Matt Chester on Oct 24, 2019

While dishonest and feckless politicians may make grandiose claims of future zero CO2 emissions, folks will revolt long before their standards of living plummet.

Pretty gutless to commit future generations to poverty while the political class lives in a life of hypocritical luxury.

You bring up the great challenge that leaders (and all of us) are facing right now. Down one path there are people making claims that committing to net zero carbon and other ambitious (perhaps overly so) are committing future generations to poverty while reaping wealth now; the other path will be people making claims that not committing to drastic action is committing future generations to a ruined environment and an inhospitable climate. 

Michael Keller's picture
Michael Keller on Oct 26, 2019

You are conflating facts versus an unsubstantiated act of faith.

There is no doubt that 100% renewables will cost trillions of dollars. There is considerable doubt as to whether or not CO2 is a problem.

Further, large scale green energy necessarily requires using vast areas of the planet. That directly ruins the environment and directly threatens species with extinction. All this damage created by the self serving hype generated by green energy religious zealots. The green energy motto "We had to destroy the environment to save the environment"

Matt Chester's picture
Matt Chester on Oct 28, 2019

There is considerable doubt as to whether or not CO2 is a problem.

Well if that's the basis of your arguments, then I'm not sure we'll end up seeing eye to eye on the solutions then. 

Michael Keller's picture
Michael Keller on Oct 28, 2019

That would be correct. CO2 emissions are not an existential threat. No need to panic.

John Benson's picture
Thank John for the Post!
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