Question 1

What is the Allam-Fetvedt cycle?

Accepted Answer

It is a natural gas power cycle that burns fuel in pure oxygen rather than air, using supercritical CO₂ as the working fluid that drives the turbine. Because there is no nitrogen from the air in the combustion, the exhaust is essentially pure CO₂ and water instead of flue gas. The water is condensed out and the CO₂ is recirculated, with the surplus leaving the plant at pipeline pressure. It was developed by 8 Rivers and commercialised by NET Power.

Question 2

How does it capture 100% of its CO₂ without a scrubber?

Accepted Answer

It never dilutes the CO₂ in the first place. Conventional plants burn fuel in air, which is 78% nitrogen, so the CO₂ leaves as a few per cent of a large exhaust stream and has to be chemically separated back out — that separation is what makes post-combustion capture expensive and energy-hungry. Oxy-combustion removes the nitrogen at the start, so the CO₂ is already concentrated and pressurised. There is no scrubber because there is no exhaust stack.

Question 3

Has the Allam-Fetvedt cycle actually been built, or is it theoretical?

Accepted Answer

It has been built and run. NET Power operates a 50 MW thermal demonstration facility at La Porte, Texas, which first fired in 2018 and in 2021 became the first zero-emission natural gas plant to deliver electricity to a grid. That is a genuine milestone, but it is a demonstration plant — the first utility-scale units, at roughly 250 MW each, are still in development. Proven at demonstration scale is not the same as commercially routine.

Question 4

How efficient is it compared with a combined cycle gas turbine?

Accepted Answer

Around 59% net, against roughly 60–64% for a modern H-class combined cycle. The important part is that the 59% already includes the capture. Bolting post-combustion capture onto a conventional CCGT typically costs seven to twelve efficiency points, so the fair comparison is 59% with capture against roughly 50% with capture — which is where the cycle's advantage actually sits.

Question 5

What happens to the captured CO₂?

Accepted Answer

It leaves the plant as a supercritical stream at pipeline pressure and high purity, which is the form sequestration and utilisation both want. That is also the constraint: the cycle only makes sense where there is somewhere for the CO₂ to go — a pipeline, a sequestration site, or an industrial offtaker. Without that, you have a plant producing a product with no buyer.

Question 6

Does GRECO use the Allam-Fetvedt cycle today?

Accepted Answer

No. GRECO builds solid oxide fuel cells below roughly 20 MW and combined cycle above it, because those are proven at the scale our campuses need and permittable now. We track the Allam-Fetvedt cycle as a capture-ready option for larger sites where CO₂ transport and storage exist, and we would rather say that plainly than imply a deployment we have not made. Scale and permitting decide the machine, not novelty.

テクノロジー	正味効率	回収率	成熟度	コスト構造
Post-Combustion Capture	~50%	85-95%	Commercial	High retrofit cost
Pre-Combustion Capture	~45%	90-95%	Demonstration	Medium
Oxy-Combustion	~45%	95-99%	Pilot	Medium-High
Allam-Fetvedt Cycle	~59%	~100%	Commercial 2026	Low (inherent)

Allam-Fetvedtサイクル:炭素100%回収

Allam-Fetvedtサイクルの仕組み

炭素回収技術の比較

開発の経緯

NET Power実証プラント

初の系統同期

カリフォルニアでの提携

商業運転

主要な技術パートナー

NET Power

8 Rivers Capital

Greco Energyのアプローチ

Allam-Fetvedtサイクル:よくあるご質問

回収レディはロードマップです。こちらが実際のプラントです。

出典と参考資料

NET Power:カリフォルニアで最大1 GWの低炭素ベースロード電源

8 RiversとWoodによるワイオミング州炭素回収プロジェクトのPre-FEED契約

Allam-Fetvedtサイクル技術

NET Power、系統に接続された初の排出ゼロ天然ガス発電所