Semester

Fall

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Chemical and Biomedical Engineering

Committee Chair

Richard Turton

Abstract

Numerous gasifier models of varying complexity have been developed to study the various aspects of gasifier performance. These range from simple one-dimensional (1D) models to rigorous higher order 3D models based on computational fluid dynamics (CFD). Even though high-fidelity CFD models can accurately predict many key aspects of gasifier performance, they are computationally expensive and typically take hours to days to execute even on high-performance computers. Therefore, faster 1D partial differential equation (PDE)-based models are required for use in dynamic simulation studies, control system analysis, and training applications.;In the current study, a 1D transient model of a single-stage downward-firing entrained flow General Electric Energy (GEE)/Texaco-type gasifier has been developed. The model comprises mass, momentum and energy balances for the gas and solid phases. A detailed energy balance across the wall of the gasifier has been incorporated in the model to calculate the wall temperature profile along the gasifier length. This balance considers a detailed radiative transfer model with variable view factors between the various surfaces of the gasifier and with the solid particles. 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 method of lines in Aspen Custom ModelerRTM, whereby the PDEs are discretized in the spatial domain and the resulting differential algebraic equations (DAEs) are then integrated over time using a variable step integrator.;Results from the steady-state model and parametric studies have been presented. These results include the gas, solid, and wall temperature profiles, concentrations profiles of the solid and gas species, effects of the oxygen-to-coal ratio and water-to-coal ratio on temperature, conversion, cold gas efficiency, and species compositions. In addition, the dynamic response of the gasifier to the disturbances commonly encountered in real-life is 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. The results from the steady-state and dynamic models compare very well with the data from pilot plants, operating plants, and previous studies.

Download

Share

COinS