Conceptual design and techno-economic analysis for a coal-to-SNG/methanol polygeneration process in series and parallel reactors with integration of waste heat recovery

The coal-based polygeneration is identified as a promising manner to enhance the overall energy-efficiency and cost-effectiveness via rational energy utilization and efficient resources sharing. Within this paper, a novel conceptual design for a coal-to-SNG/methanol polygeneration process (CTSM) with integration of waste heat recovery steam cycle (WHRSC) is proposed. A series scheme (S-CTSM) and a parallel scheme (P-CTSM) of the conceptual design are investigated and analyzed based on rigorous process modelling and simulation. In this process, a part of unshifted syngas without entering Rectisol is mixed with H-2-rich syngas directly to reduce energy consumption and flexibly adjust H/C. Sensitivity analysis in terms of mechanism model is carried out to recognize the key parameters and explore their effects on process performance improvements. An enhanced Duran-Grossmann (D-G) model for WHRSC optimization is proposed by conducting heat integration among the whole reaction units. A comprehensive techno-economic analysis is performed. The results indicate that exergy saving ratio of P-CTSM is 2.36% while that of S-CTSM is 2.14%, and their cost saving ratios are 9.06% and 7.08% respectively when compared to that of the single coal-to-SNG/coal-to-methanol process. Furthermore, according to the fact that the production cost of P-CTSM and S-CTSM is 4.63 $/GJ and 4.71 $/GJ, respectively, P-CTSM is a preferable scheme to improve economic performance and global energy efficiency. The major contributions derived from this work is of significant aid in highlighting strong potentials for overall performance enhancement via polygeneration optimization and providing guidelines for future development of a heat/power-integrated system combined with the conceptual design of polygeneration.