NetPower | Technology

We need a new approach to clean energy

Despite growing urgency to reduce emissions of carbon dioxide and other pollutants from power plants, producing cleaner power that remains low cost, reliable and easy to integrate into the grid has proven difficult. Traditional fossil fuel systems – such as natural gas combined cycle, integrated combined cycle, and supercritical coal – are reaching both theoretical and practical efficiency limits, and “add-on” environmental control systems – such as post-combustion carbon capture equipment – are expensive and energy intensive.

Net Power's Novel Approach

Rather than developing environmental control equipment for existing power systems to make them cleaner (which inevitably leads to increased electricity costs), the NET Power team decided to develop an entirely new power cycle from the ground up. By stepping outside the traditional power technology box, NET Power was able to design a process that inherently addresses the emissions clean-up challenges faced by traditional power plants.

WITH A FRESH LOOK, THE SOLUTION BECAME OBVIOUS

Net Power’s Allam Cycle

NET Power invented and is commercializing a novel power system that produces electricity from natural gas that is cost competitive with current technologies and generates zero atmospheric emissions – eliminating the smokestack altogether. This system is based on a new thermodynamic cycle, the Allam Cycle, named for its lead inventor, Rodney Allam.

Regarded as a breakthrough in power generation technology, the Allam Cycle uses a high-pressure, highly recuperative, oxyfuel, supercritical CO₂ cycle that makes carbon capture part of the core power generation process, rather than an afterthought. The result is high-efficiency power generation that inherently produces a pipeline-quality CO₂ byproduct at no cost to the system’s performance.

how is net power different?

The Allam Cycle vs. Existing Thermal Power Cycles

The majority of power plants today – including combined cycle gas turbine (CCGT) and supercritical coal plants – rely on thermal power cycles for energy production. These systems operate by combusting ambient air with a fossil fuel (natural gas, coal, or coal “syngas”) to create heat. In traditional coal plants, this takes place in a large boiler, which boils water to create steam. This expansion from water to steam causes a turbine to turn, creating power. In CCGT power plants, natural gas or coal syngas are ignited in a combustor, where they “explode” and drive a turbine. The turbine exhaust is extremely hot, so it is then used to boil water and drive a second set of turbines (hence the name “combined cycle”). In both cases, steam-based working fluids are essential to the process.

THESE APPROACHES HAVE TWO MAJOR FLAWS

Major Problem 1: Continued reliance on steam as a working fluid

Most modern power plants still rely on steam as a primary means for generating power. Unfortunately, steam is an inefficient working fluid. In power plants, a small volume of water is heated, turning it into a large volume of steam. The resulting expansion drives a turbine to create power.

On the back end of the turbine, however, the steam must turn back into water outside of the system; otherwise, the expansion that drove the turbine forward would be reversed when the steam condensed into water. During this condensing process, heat is “rejected” up cooling towers and into the atmosphere, resulting in a loss of 30% to 40% of the original energy created by the system.

Major Problem 2: Air-Emissions are addressed as an afterthought

Fossil fuel-based power plants produce large quantities of harmful air emissions. Natural gas power plants produce large quantities of nitrous oxides (NO_x) and carbon dioxide (CO₂). Coal plants add sulfur dioxides, mercury, and fine particulate matter to the mix. Each of these have major impacts on the health of people and our environmental. In order to address these emissions, power plants have traditionally taken an “add-on” or Band-Aid^TM approach: they begin adding expensive, energy intensive equipment to reduce emissions production or clean-up the emissions once they’ve been produced. These systems degrade the economic performance and reliability of power plants because they are costly to build, complex to design, and energy intensive to operate.

Net Power overcomes these flaws

The CO₂ produced by combustion in the Allam cycle is recycled back to the combustor multiple times, producing a working fluid that is mostly pure, high-pressure CO₂. By using a CO₂ working fluid at very high pressures as opposed to steam, NET Power can avoid the “phase changes” that cause steam cycles to be so inefficient. Instead of driving a steam cycle and losing heat energy up a stack, NET Power keeps heat within the system, meaning less fuel is needed for the turbine to reach the required operating temperature.

Additionally, because NET Power uses a mostly pure, high-pressure stream of CO₂ as its primary means of producing power, it has turned a major problem for other power systems – the energy and processes needed to capture, cleanup, and compress carbon dioxide emissions – into a solution. NET Power plants produce “carbon capture-ready” CO₂ as a function of how they efficiently operate, not as an extra, costly process.

NET Power plants employ a process called oxy-combustion, where fuel is burned with pure oxygen instead of ambient air. Oxygen is preferable to air because air is nearly 80% nitrogen. When combusted, nitrogen creates NOx, a harmful pollutant. Oxy-combustion enables NET Power plants to virtually eliminate all NOx production.

NET Power plants require an Air Separation Unit (ASU) to separate oxygen out of ambient air for oxy-combustion. ASUs are well-known technologies, but their application in the power industry has been hampered by high capital costs and energy requirements. NET Power overcomes these challenges in several ways. NET Power plants do not require all the equipment associated with a steam cycle, and so they can use this “saved” capital cost to add an air separation unit without breaking the bank. Further, NET Power has a higher starting efficiency, or “gross” efficiency, than traditional systems since steam-based energy losses have been eliminated; this means NET Power plants can absorb an ASU’s energy consumption while remaining highly efficient.

The net power advantage

High efficiency

A power system’s efficiency is key to its economic competitiveness. NET Power natural gas plants are directly competitive with the best-in-class natural gas combined cycle plants, which have been optimized for decades and are reaching their practical and theoretical efficiency limitations. In all cases, NET Power plant efficiencies include full emissions capture and are being compared to current technologies that do not have carbon capture. (All efficiencies are LHV.)

NET Power Gas Cycle:

Natural Gas Combined Cycle without Carbon Capture:

Natural Gas Combined Cycle with Carbon Capture:

Supercritical Coal without Carbon Capture

Supercritical Coal with Carbon Capture

Integrated Gasification Combined Cycle (IGCC) without Carbon Capture:

Integrated Gasification Combined Cycle (IGCC) with Carbon Capture:

simpler, smaller plants

NET Power plants have low capital costs because they are smaller and simpler than traditional combined cycle and supercritical coal plants. NET Power’s high pressure means the system has a higher power density, and therefore the components can be smaller. And while NET Power plants do have new components that other technologies do not, they also eliminate the entire steam process, and the associated equipment, that is common to traditional power plants.

Plants at scale with the same power capacity

vastly superior environmental performance

No Air Emissions

As a semi-closed loop, NET Power has precise control over the emissions streams from the plant. The only byproducts are clean, liquid water and high-pressure, high-purity CO₂ for pipeline removal. No carbon dioxide, NO_X, SO_X, mercury or particulates are released to the atmosphere.

Oxy-combustion

Because NET Power plants utilize oxycombustion, they do not require NO_x cleanup equipment and processes. And by eliminating NO_x production, NET Power plants can be built in areas where other plants cannot, such as many major US metropolitan regions, because NO_x is a highly-regulated pollutant that causes ozone and health issues.

Inherent CO₂ Capture

NET Power is designed to capture carbon as a function of how it most-efficiently operates, not as an afterthought. This means expensive, add-on carbon capture systems are not required to virtually eliminate carbon emissions. In addition, unlike traditional carbon capture technologies, NET Power is able to capture almost 100% of its carbon.

Low water use

Because NET Power plants do not run on a steam based working fluid, they are able to actually eliminate water usage. The only place water is used in a NET Power plant is for cooling; by switching to air cooling, NET Power plants actually become net producers of water while only seeing a minor efficiency reduction of about 2.5%

Pipeline-ready Carbon Dioxide Byproduct

NET Power produces a high-pressure, high-quality CO₂ byproduct that is pipeline-ready. This CO₂ can be sequestered or used for enhanced oil recovery (EOR), a decades-old process that uses carbon dioxide to extract significantly more oil from mature oilfields while permanently storing CO₂ underground. In the United States alone, 85 billion barrels of oil are recoverable using EOR. Most industrial CO₂ capture technologies cannot produce cost-effective, EOR-ready CO₂, despite the fact that the industry is tremendously CO₂-starved. NET Power will have both the capacity and economics to enable the EOR industry to unlock this vast resource while simultaneously sequestering carbon dioxide from thousands of power plants below ground.

THE FIRST NET POWER PLANTS ARE UNDER DEVELOPMENT

Development status

NET Power, CB&I, Toshiba, and Exelon have partnered to develop a 50MWth NET Power natural gas demonstration plant. NET Power is responsible for overall project development and systems engineering; Toshiba is developing a new combustor and turbine for the NET Power system, and they successfully tested the combustor in July 2013; CB&I is providing engineering, procurement, and construction services; and Exelon is providing development, permitting, siting, and commissioning services and support. Following successful demonstration at the 50MWth level, the system will be scaled up and the first 500MWth commercial natural gas plant will be built.

On March 9th, 2016, NET Power announced that the company has broken ground on its demonstration plant.

Check in on our progress