Zero-emission natural gas power

The Allam-Fetvedt Cycle: 100% Carbon Capture

Exploring the breakthrough supercritical CO₂ technology that captures all emissions at source without efficiency penalties. Unlike traditional post-combustion capture, the Allam-Fetvedt Cycle produces pipeline-ready CO₂ as an inherent byproduct—no expensive retrofits required.

~100%
CO₂ Captured
~59%
Net Efficiency
250 MW
Per Modular Unit
Zero
NOx/SOx Emissions

How The Allam-Fetvedt Cycle Works

The Allam-Fetvedt Cycle, developed by 8 Rivers Capital and NET Power, represents a fundamental reimagining of thermal power generation. Instead of using steam as a working fluid like conventional power plants, it uses supercritical CO₂—carbon dioxide at temperatures and pressures where it behaves like both a liquid and gas simultaneously.

The process works as follows: Natural gas is combusted with pure oxygen (not air) in a high-pressure combustor. This oxy-combustion produces only CO₂ and water vapor—no nitrogen oxides (NOx) or sulfur oxides (SOx). The resulting hot, high-pressure CO₂ drives a specialized turbine to generate electricity.

After expansion through the turbine, the CO₂ is cooled and water is condensed out. Most of the CO₂ is recirculated as the working fluid, while the excess—exactly matching the carbon content of the burned natural gas—is captured at pipeline pressure, ready for sequestration without additional compression. This inherent capture achieves near-100% CO₂ removal with minimal efficiency penalty.

Carbon Capture Technology Comparison

TechnologyNet EfficiencyCapture RateMaturityCost Profile
Post-Combustion Capture~50%85-95%CommercialHigh retrofit cost
Pre-Combustion Capture~45%90-95%DemonstrationMedium
Oxy-Combustion~45%95-99%PilotMedium-High
Allam-Fetvedt Cycle~59%~100%Commercial 2026Low (inherent)

Development Timeline

2018

NET Power Demonstration Plant

First-of-its-kind 50 MW thermal demonstration facility in La Porte, Texas successfully proves the Allam-Fetvedt Cycle technology.

2021

First Grid Synchronization

NET Power achieves global first: zero-emission electricity from natural gas delivered to the power grid in Texas.

2025

California Partnership

NET Power and Carbon TerraVault sign MOU to develop up to 1 GW of zero-emission power capacity in Northern California.

2026

Commercial Operations

First utility-scale NET Power plants expected to begin commercial operations, each generating up to 250 MW.

Key Technology Partners

NET Power

Commercializing the Allam-Fetvedt Cycle technology. First utility-scale plants expected 2026, with a backlog including the California partnership for up to 1 GW capacity. Each modular plant requires less than 20 acres and generates up to 250 MW.

NYSE: NPWR

8 Rivers Capital

Inventor of the Allam-Fetvedt Cycle. Leading decarbonization technology developer with projects including the Wyoming carbon capture facility with PacifiCorp, currently in Pre-FEED engineering phase.

Durham, NC

Greco Energy's Approach

Led by Leo Paskalidis, all Greco Energy facilities are designed with CCUS integration capability from the ground up. Our North American developments will incorporate carbon capture infrastructure to achieve net-zero emissions.

CCUS-Ready DesignNet-Zero PathwayTechnology Flexibility

The Allam-Fetvedt cycle: common questions

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.

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.

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.

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.

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.

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.
What GRECO builds today

Capture-ready is a roadmap. This is the plant.

GRECO generates behind the meter so a campus energizes in months rather than waiting years in an interconnection queue — solid oxide fuel cells below roughly 20 MW with no combustion and near-zero NOx, combined cycle above that, and over 90% total efficiency once the heat is recovered and sold into district energy.

How the generation worksOfftake compute or heatHeat export at 50 °C

Sources & Further Reading

Power Engineering• January 2025

NET Power: Up to 1 GW of Low-Carbon Baseload Power in California

8 Rivers Capital• March 2025

8 Rivers and Wood Pre-FEED Agreement for Wyoming Carbon Capture

8 Rivers Capital• 2024

The Allam-Fetvedt Cycle Technology

Power Engineering• 2021

NET Power First Grid-Connected Zero-Emission Natural Gas Plant