Energy and exergy analyses of a Zero emission coal system

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 H-2 recycling ratio (R-h), calcium to carbon ratio (R-ctc) and fuel utilization factor (U-f) on the energy efficiency (E-en), exergy efficiency (E-ex), total energy efficiency (E-ten), total exergy efficiency (E-tex) and carbon dioxide (CO2) sequestration ratio (R-cs) 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). R-h at 0.75 and U-f at 0.8 are recommended as the optimum operation parameters of the system based on the sensitivity analysis. R-cs increases with increasing R-ctc. R-ctc at 1.5 is recommended to maintain a high CO2 sequestration ratio with acceptable economic penalty. With these optimized parameters, E-en of 36.2%, E-ten of 46.8%, E-ex of 35.7%, E-tex of 46.2% and R-cs of 87.4% can be achieved by the proposed system. (C) 2013 Elsevier Ltd. All rights reserved.