The Allam Cycle is a new, high-pressure, oxy-fuel, supercritical CO2 cycle that generates low-cost electricity from fossil fuels while producing near-zero air emissions; all CO2 generated by the system is produced as a high-pressure, pipeline-ready by-product for use in enhanced oil recovery, industrial processes, or sequestration.
The base cycle was developed by 8 Rivers Capital and is being commercialized by NET Power, LLC in partnership with Toshiba Corporation, Exelon Corporation, and CB&I. The four parties are currently developing a natural gas-fired power plant to demonstrate this system. Target net efficiencies for the natural gas and coal versions of this cycle, based on current process modeling, are 59% and 52% (LHV) respectively, both with full carbon capture and no other air emissions. Detailed designs indicate that NET Power plants, with full carbon capture, will produce lower-cost electricity than state-of-the-art fossil fuel plants without CCS.
8 Rivers Capital continues to develop on top of the Allam Cycle platform. Building upon the original single turbine design, 8 Rivers has developed a two-turbine design that combines the benefits of the original, high-pressure Allam Cycle with a low-pressure reheat cycle. This new design can enable Allam Cycle-based plants to greatly increase power output with only a moderate increases in capital cost, substantially lowering the overall plant $/kW cost. Such a configuration would enable Allam Cycle plants to produce even lower-cost electricity than the single turbine Allam Cycle design currently being commercialized by NET Power, CB&I, Toshiba and Exelon. This paper outlines the design considerations utilized for the base Allam Cycle development and then details this new cycle design and its potential benefits.
The Allam Cycle is a semi-closed, recuperated, oxy-fuel, supercritical carbon dioxide (sCO2) Brayton power cycle, offering advantages over simple cycle and combined cycle arrangements. The Allam Cycle uniquely combines oxy-combustion with a substantially elevated operating pressure, high sCO2 recirculation flow, high gross turbine efficiency, and inventive low- and high-grade heat recuperation. As a result, the core Allam Cycle meets or exceeds the achievable net efficiencies of existing high efficiency combined cycle plants not equipped for carbon capture, while capturing substantially all CO2 emissions at purities and pressures necessary for downstream CO2 reuse and/or sequestration. Additionally, with minor alterations, the core cycle can operate with a variety of organic fuels. A 50MWt natural gas-fired demonstration of the core cycle is currently under development by 8 Rivers, NET Power, CB&I, Exelon, and Toshiba.
This paper addresses the coal syngas-fired variant of the Allam Cycle system, extending beyond high-level feasibility analyses conducted in previous studies. The paper explores in detail the unique considerations, possible hurdles, and advantages of integrating a commercially-available coal gasifier with the Allam Cycle. In particular, the paper analyzes five (5) primary technical optimizations that drive the Allam Cycle’s advantages in efficiency and cost over conventional baselines. These include: (1) a simpler overall process, requiring fewer critical integration points while still providing for efficient high- and low-grade heat recuperation; (2) high efficiencies regardless of coal rank and type used — further, the efficiency drop when using low-rank coal in an Allam Cycle arrangement is smaller than IGCC arrangements; (3) high efficiencies regardless of syngas composition (such as H2:CO ratio), particularly when compared to gasification in the chemical industry and IGCC with carbon capture and sequestration; (4) the ability to utilize a singular, cost-effective post-combustion SOX/NOX removal mechanism; and (5) considerable water savings versus IGCC and SCPC baselines, with the ability to run substantially water free with only minor impacts to overall efficiency.
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