Zero-Emissions Combined Cycle and Beyond

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").

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

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.

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.

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. 

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.