One-Dimensional Dynamic Modeling of a Single-Stage Downward-Firing Entrained-Flow Coal Gasifier

Abstract

In the current paper, a one-dimensional partial differential equation (PDE)-based dynamic model and its simulation results are presented for a single-stage down-fired entrained-flow gasifier. The gasifier model comprises mass, momentum, and energy balances for the gas and solid phases. The initial gasification processes of water evaporation and coal devolatilization and the key heterogeneous and homogeneous chemical reactions have also been modeled. The resulting coupled system of PDEs and algebraic equations is solved using the well-known method of lines in Aspen Custom Modeler. In addition to the dynamic gasifier model, efficient control strategies that can satisfactorily perform both servo and disturbance rejection functions have been developed for the entrained-flow gasifier. The dynamic variations of key gasifier output variables in response to the disturbances commonly encountered in industrial operation are presented. Output variables of interest include gas and solid phase temperatures, synthesis gas compositions, and carbon conversion, while disturbances include ramp and step changes in input variables such as coal flow rate, oxygen-to-coal ratio, and water-to-coal ratio among others. Feedstock switchovers have also been studied by simulating transitions from one coal type to another. The gasifier model results are also compared to the dynamic data available in the literature.