Study on coal gasification with soot formation in two-stage entrained-flow gasifier

Concerning the global warming due to large CO₂ emission, the efficient use of coal becomes important for getting sustainable energy production. Coal gasification under CO₂-rich condition is expected to be an effective way to produce a concentrated and pressurized carbon dioxide stream, resulting in reduction in separation energy of CO₂ for CCS. Moreover, the soot formation, which is of significant environmental concern, is still being neglected in the past studies of coal gasification. A one-step soot formation reaction mechanism is proposed in this study and implemented in numerical simulations of coal gasification with the aim of describing the gasification behaviors in a two-stage entrained-flow gasifier. In addition, the effects of O₂ ratio and CO₂ concentration on soot concentration, syngas heating value and carbon conversion are numerically studied in an effort to increase the syngas production. The Eulerian–Lagrangian approach is applied to solve the Navier–Stokes equation and the particle dynamics. Finite rate/eddy dissipation model is used to calculate the rate of nine homogeneous gas-to-gas phase reactions including soot formation and soot oxidation. While only finite rate is used for the heterogeneous solid-to-gas phase reactions. It is found that formation of soot enhances the H₂ production in the gasifier. Carbon conversion gradually increases with an increase in O₂ ratio, while producing a low heating value syngas beyond a certain limit of O₂ ratio. In contrast, an increase in CO₂ concentration in the gasifier increases heating value of product syngas.