Process modeling and techno-economic analysis of a solar thermal aided low-rank coal drying-pyrolysis process

Abstract

This study investigated the feasibility of integration of concentrated solar power (CSP) to low-rank coal pyrolysis process from the economic and technical perspective. Victorian brown coal is generally used in local power plants with low efficiency and great greenhouse gas emissions. Therefore, the development of low-emission technologies for an efficient use of such vast resources is paramount. The principal objective of this process is to upgrade Victorian brown coal to alternative fuels through a solar-assisted pyrolysis process. Upon a robust design of four different scenarios for the process integration, the effects of a variety of key variables have been examined, including different types of solar collectors, heat transfer fluids (HTF) and pyrolysis temperature. The plant operation analysis showed that integrating solar tower (ST) to provide heat for both coal drying and pyrolysis within the plant can save an average of 12.8% of the annual thermal energy demand. For the optimum solar tower design, it requires a solar multiple of 2, using carbonate salts as HTF, a design point DNI of 750 W/m2 and a heat storage capacity of 8 h to maximize its total solar energy output over a year. However, from an economical perspective, the use of solar tower for both drying and pyrolysis is economically infeasible. Instead, the parabolic trough solar collectors (PTC) designed to cover the heat required for coal drying only is most economically viable. It even shows a slightly better economic performance than the conventional pyrolysis process. The parabolic trough solar assisted pyrolysis process has the potential to reach a high net present value (NPV) of $81.1 million and a short payback period of 4.9 years, relative to an NPV of $52.8 million and a payback period of 5.1 years for the conventional pyrolysis process.