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Energy and exergy analyses of a Zero emission coal system

Yan, Linbo, He, Boshu, Pei, Xiaohui, Li, Xusheng, Wang, Chaojun
Energy 2013 v.55 pp. 1094-1103
calcium, carbon, carbon dioxide, coal, energy efficiency, exergy, fuel cells, hydrogen, recycling, steam, zero emissions
Energy and exergy analyses are used to evaluate the Zero emission coal (ZEC) system. Energy and exergy losses in each unit of the system are calculated and depicted with Sankey diagrams of energy flow and exergy flow when the system operates at a benchmark condition. Sensitivity analysis is carried out to investigate the effects of different operating parameters including H₂ recycling ratio (Rₕ), calcium to carbon ratio (Rcₜc) and fuel utilization factor (Uf) on the energy efficiency (Eₑₙ), exergy efficiency (Eₑₓ), total energy efficiency (Eₜₑₙ), total exergy efficiency (Eₜₑₓ) and carbon dioxide (CO₂) sequestration ratio (Rcₛ) of this system. The energy loss in the steam turbine (ST) is 35.2% which is the maximum among all the units and the maximum exergy loss of 37.0% occurs in the solid oxide fuel cell (SOFC). Rₕ at 0.75 and Uf at 0.8 are recommended as the optimum operation parameters of the system based on the sensitivity analysis. Rcₛ increases with increasing Rcₜc. Rcₜc at 1.5 is recommended to maintain a high CO₂ sequestration ratio with acceptable economic penalty. With these optimized parameters, Eₑₙ of 36.2%, Eₜₑₙ of 46.8%, Eₑₓ of 35.7%, Eₜₑₓ of 46.2% and Rcₛ of 87.4% can be achieved by the proposed system.