Modeling for simple process analysis in a dry-feeding entrained bed coal gasifier

Abstract

A dry-feeding entrained bed coal gasifier was numerically modeled to analyze the process in this thesis. The Shell type up-flow gasifier was modeled in the view of reverse engineering and by simultaneously solving the rate equations for the solid and gas phases. It was modeled considering own reactivity of a case of coal introduced into the gasifier. According to the heterogeneous characteristics of coal, this model describes the simplified physical and chemical processes occurring in the entrained bed coal gasifier. The gasification phenomena can be separated into devolatilization, gas phase, and solid phase reactions by difference of reaction time of coal. The coal gasifier shape is also simplified to 1-D PFR and pseudo 2-D reactor models for simple analysis. As an indicator of the gasifier performance, carbon conversion and cold gas efficiency (CGE) are determined. Oxygen/coal mass ratio, steam/coal mass ratio, and pressure are selected as operating parameters. As a result of simulation, carbon conversion, CGE, gas composition, temperature, and velocity distributions are obtained along with the reactor. The oxygen/coal ratio at which maximum CGE was achieved ranged from 0.5 to 0.6 kg/kg. However, the higher oxygen/coal ratio is, the higher carbon conversion rate is. Therefore, proper operating conditions are changeable on operating objectives. For validation, the results are compared with data obtained in Shell gasifier and it shows a little difference for CGE. That is because the kinetic data applied in this research is to incorporate the incoherent rate constants from different experimental conditions and coal type. In addition, this model does not consider the physical phenomena such as turbulence and radiative heat transfer. The model prediction may be best used to evaluate trends in process analysis of the Shell gasifier and may give useful information for the designing and operation of the coal gasifier.