(529e) A One-Dimensional Transient Model of a Single-Stage, Downward-Firing, Entrained-Flow Gasifier

The integrated gasification combined cycle (IGCC) technology has emerged as an attractive alternative to conventional coal-fired power plant technology due to its higher efficiency and cleaner environmental performance especially with the option of CO₂ capture and sequestration. The core unit of this technology is the gasifier whose optimal performance must be understood for efficient operation of IGCC power plants. This need has led a number of researchers to develop gasifier models of varying complexities.

Whereas high-fidelity CFD models can accurately predict most key aspects of gasifier performance, they are computationally expensive and typically take hours to days to execute on high-performance computers.  Therefore, faster one-dimensional (1D) partial differential equation (PDE)-based models are required for use in dynamic simulation studies, control system analysis, and training applications.  A number of 1D gasifier models can be found in the literature, but most are steady-state and have limited application in the practical operation of the gasifier. As a result, 1D PDE-based dynamic models are needed to further study and predict gasifier performance under a wide variety of process conditions and disturbances.

In the present study, a 1D transient model of a single-stage downward flow GE/Texaco-type gasifier has been developed. The model comprises mass, momentum and energy balances for the gas and solid phases. The model considers the initial gasification processes of water evaporation and coal devolatilization. In addition, the key heterogeneous and homogeneous chemical reactions have been modeled. The resulting time-dependent PDE model is solved using the well-known method of lines approach in Aspen Custom Modeler®, whereby the PDEs are discretized in the spatial domain and the resulting differential algebraic equations (DAEs) are then solved to obtain the transient response. The transient response of various gasifier performance parameters to certain disturbances commonly encountered in the real world operation of commercial IGCC plants will be presented. These 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. Comparison of gasifier model predictions to available dynamic data will also be discussed.