Numerical Analysis of a Solar Air Preheating Coal Combustion System for Power Generation

Abstract

A new type of solar-aided power generation plant has been proposed and numerically analyzed in this work. It is composed of a parabolic trough collector field, based on gas-phase nanofluid, coupled with a flameless coal burner. In this system, high-temperature solar thermal energy is used to preheat combustion air before it is sent to the burner. In the first part of this study, the solar field was sized in order to optimize its performance in coupling with the coal-fired power plant. The simulations, which resulted in 2,585 feasible solutions, explained the relationship between solar energy introduced into the burner, the parabolic trough collector field surface, and heat storage mass. In the second part of this work, a computational fluid dynamics analysis of the coal burner was carried out, in order to reach, as much as possible, a flameless operating condition, assuming provision of solar energy to the burner. At the same time, in order to keep the final flame temperature and the overall heat exchange conditions unchanged, it was considered useful to increase the external exhaust gas recirculation fraction in equal measure with the increase of the thermal input. The computational fluid dynamics analysis demonstrated that the increase in the temperature of the combustion air, due to solar input, intensifies the staging effect. In addition, the recirculation zone (more intense), resulting in flame shortening and rapid mixing of reagents and combustion products, yielded very uniform conditions in terms of chemical species and temperatures in the rest of the combustion chamber. All this contributed to a significant reduction in terms of NOx emission.