8 Rivers - We Can Build Coal & Natural Gas Power Plant Without Greenhouse Gases/CO2 Emissions

NET Power has developed a novel power system that produces electricity from natural gas. NET Power plants are cost competitive with current technologies but generate zero atmospheric emissions – eliminating the smokestack altogether. This system is based on a new thermodynamic cycle called the Allam Cycle.

The Allam Cycle is a breakthrough in power generation technology. It uses a high-pressure, highly recuperative, oxyfuel, supercritical CO2 cycle that makes emission capture a 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 additional cost to the system’s performance.

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 burning fossil fuel (natural gas, coal, or coal “syngas”) using the oxygen in air to create heat.  In traditional coal plants,  this takes place in a large boiler, where coal is burned and water is boiled to create high pressure steam.  This high pressure steam then expands through a steam turbine, creating power.  In CCGT power plants, natural gas or coal syngas is burned in a combustor with compressed air. The heated gases then expand and drive a gas turbine.  The turbine exhaust is extremely hot, so it is then used to boil water to create high pressure steam and drive a steam turbine (hence the name “combined cycle”).  In both systems, steam (i.e. water) is essential to the process 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.

Fossil fuel-based power plants produce large quantities of harmful air emissions.  Natural gas power plants produce large quantities of nitrogen oxides (NOX) and carbon dioxide (CO2).  Coal plants add sulfur oxides (SOX), mercury, and fine particulate matter to the mix.  Each of these have major impact on the health of people and our environment. In order to address these emissions, traditional power plants have taken the tack-on approach: they add expensive, energy-intensive equipment to help reduce emissions or clean-up emissions once they’ve been produced.  These systems degrade the performance, reliability, and cost of power plants because they are costly to build, complex to design, and energy intensive to operate.

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 burned, nitrogen can convert to NOX, a precursor to acid rain. Oxy-combustion enables NET Power plants to eliminate all NOX production and air emissions.

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 is limited due to capital cost and energy requirements. NET Power overcomes these challenges in several ways. NET Power plants do not require the additional equipment associated with a steam cycle, and so they can use this avoided capital cost to add other processes without breaking the bank. Further, NET Power has a higher starting efficiency, or “gross” efficiency, than traditional systems. This means NET Power plants can absorb an ASU’s energy consumption and retain net-efficiency.

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.

A power system’s efficiency is key to its economic competitiveness. NET Power natural gas plants with full carbon capture are directly competitive with best-in-class natural gas combined cycle plants that do not capture any carbon emissions.

Because NET Power plants utilize oxy-combustion, they do not produce NOx. This greatly improves environmental performance, enables plants to operate more flexibly, eliminates the need for complex NOx emissions reduction equipment, and allows plants to be built in areas where others cannot due to strict regulations.

Using a patented thermodynamic cycle called the Allam Cycle, NET Power is able to generate lower-cost power from fossil fuels than existing power plants while eliminating all air emissions, including carbon dioxide. Additionally, the CO2 that NET Power plants generate from burning fuel is produced as a high-pressure, high-quality byproduct, ready for pipeline transportation and storage.  In many places, this CO2 can be sold for use in enhanced oil recovery (EOR), permanently sequestering the CO2 and providing significant added value for NET Power plant owners.

NET Power produces a high-pressure, high-quality CO2 byproduct that is pipeline-ready. This CO2 can be sequestered or used in industrial processes, such as enhanced oil recovery (EOR), which is a decades-old process that uses CO2 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 CO2 from thousands of power plants below ground.

In tandem, 8 Rivers is also developing a 300-MW Allam Cycle coal plant. The company this October garnered the Department of Energy’s (DOE’s) backing as part of its Coal FIRST initiative to perform a pre-FEED study for a project to integrate coal gasification and the Allam Cycle core technology currently being proven at the La Porte facility. 

According to the DOE, 8 Rivers’ design could boost the net efficiency percentage of a coal plant to the mid-to-high 40s. It also promises “higher heating value with carbon capture; ramping speeds in-line with natural gas combined cycle technology, with the potential to exceed that performance; significant water savings (50% to 60%) compared with integrated gasification combined cycle technology; fuel flexibility; and the ability to store electricity as chemicals when power is in low demand.”

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