Thermodynamic analysis of the Allam cycle and its pressure sensitivity

Abstract

The Allam cycle is a novel system which operates the oxy-combustor at a high pressure under supercritical conditions, uses a single gas turbine, circulates carbon dioxide as the working fluid in a semiclosed-loop and utilizes low-pressure-ratio recuperated Brayton cycle. These properties of the Allam Cycle enable to reach high efficiencies. This system was simulated using Chemcad software for a methane feed flow rate of 1 kmol/s. The pressure at the inlet of turbine was taken as 285 bar. The net power generation rate was estimated considering the generation in the turbine and the usage in the compressors for circulating carbon dioxide and for oxygen and natural gas feeds. The calculations using energy balance for the process gave 388 MW net power output, whilst Chemcad software gave 392 MW. The thermal energy recovered by lowering the temperature of the flue gas before condensing its water content was also considered in the overall efficiency of the system. The net power cycle efficiency was determined as 48.89%. The second law analysis of the cycle was also made. Entropy generation rate, Sgen, was determined as 965.79 kW/K and exergy destroyed, ψdestroyed, was found as 287.81 MW from entropy balance for the process. The exergy balance for the process was also made and the results were compared with the findings from the entropy balance. The second law efficiency of the process was found as 62.54%. Working at high pressure, naturally, affects the material of construction and consequently the fixed capital investment as well as operating and maintenance costs. Therefore, in this work, a sensitivity analysis is also made to see the effect of pressure on power generation and efficiency. The sensitivity analysis was made using Chemcad software simulation. It was found that the optimum pressure range for operation of the system was between 250 and 350 bar.

Keywords

• Allam cycle
• Efficiency
• Entropy
• Pressure sensitivity

References

1. [1] Ahn Y, Bae SJ, Kim M, Cho SK, Baik S, Lee JI, et al. Review of supercritical CO2 power cycle technology and current status of research and development. Nucl Eng Techn 2015;47:647-61. https://doi.org/10.1016/j.net.2015.06.009.
2. [2] Lockwood T. A compararitive review of next-generation carbon capture technologies for coal-fired power plant. Energy Procedia 2017;114:2658-70. https://doi.org/10.1016/j.egypro.2017.03.1850.
3. [3] Allam RJ, Palmer MR, Brown Jr GW, Fetvedt J, Freed D, Nomoto H, et al. High Efficiency and low cost of electricity generation from fossil fuels while eliminating atmospheric emissions including carbon dioxide, Energy Procedia (GHGT-11) 2013;37:1135-49. https://doi.org/10.1016/j.egypro.2013.05.211.
4. [4] Allam RJ, Palmer M, Brown Jr GW. System and method for high efficiency power generation using a carbon dioxide circulating working fluid. USA Patent 03 December 2013;8:596, 075 B2.
5. [5] Allam RJ, Fetvedt JE, Forrest BA, Freed DA. The Oxy-Fuel, Supercritical CO2 Allam Cycle: New Cycle Developments to Produce Even Lower-Cost Electricity from Fossil Fuels Without Atmospheric Emissions, in Proceedings of ASME Turb Expo 2014: Turbine Technical Conference and Exposition, June 16-20 2014 Dusseldorf, Germany. https://doi.org/10.1115/GT2014-26952.
6. [6] Allam RJ, Martin S, Forrest B, Fetvedt J, Lu X, Freed D, et al. Demonstration of the Allam Cycle: An update on the development status of a high efficiency supercritical carbon dioxide power process employing full carbon capture, Energy Procedia 2017;114:5948-66. https://doi.org/10.1016/j.egypro.2017.03.1731.
7. [7] Sifat NS, Haseli Y. A critical review of CO2 capture technologies and prospects for clean power generation. Energies 2019;12:4143-76. https://doi.org/10.3390/en12214143.
8. [8] Khallaghi N, Hanak DP, Manovic V. Techno-economic evaluation of near-zero CO2 emission gas-fired power generation technologies: a review. Journal of Natural Gas Science and Engineering 2020;74:103095. https://doi.org/10.1016/j.jngse.2019.103095. [9] Laumb JD, Holmes MJ, Stanislowski JJ, Lu X, Forrest B, McGroddy M. Supercritical CO2 cycles for power production. Energy Procedia 2017;114:573-80. https://doi.org/10.1016/j.egypro.2017.03.1199.

9. [10] Scaccabarozzi R, Gatti M, Martelli E. Thermodynamic analysis and numerical optimization of the NET Power oxy-combustion cycle. Appl Energy 2016;178:505-26. https://doi.org/10.1016/j.apenergy.2016.06.060.
10. [11] Tosun İ. Thermodynamics-Principles and Applications. Singapore: World Scientific Publishing Co; 2015. https://doi.org/10.1142/9670.
11. [12] Bejan A. Advanced Engineering Thermodynamics. 4th Ed. New Jersey: John & Wiley; 2016. https://doi.org/10.1002/9781119245964.
12. [13] Yüncü H. Ekserji Analizi-İkinci Kanun Verimi ve Termoekonomi. Ankara: ODTÜ Basım İşliği; 2010.
13. [14] Yüncü H. Termodinamik. Ankara: ODTÜ Basım İşliği; 2016
14. [15] Hasan A, Dincer I. Assessment of an Integrated Gasification Combined Cycle using waste tires for hydrogen and fresh water production. International Journal of Hydrogen Energy 2019;44:19730e19741, https://doi.org/10.1016/j.ijhydene.2019.05.075.
15. [16] Hervás GR, Petrakopoulou F. Exergoeconomic analysis of the allam cycle. Energy Fuels 2019;33:7561-8. https://doi.org/10.1021/acs.energyfuels.9b01348.
16. [17] Zaryankin A, Rogalev A, Osipov S, Kindra V. Supercritical carbon dioxide gas turbines for high-power generation. AIP Conference Proceedings 2018;2047:020026. https://doi.org/10.1063/1.5081659.