Computer simulation and performance evaluation of fixed-bed coal gasification processes

The present study concerns a performance analysis of an updraft moving bed gasifier, forming part of a small (700 kg/h, or 5 MWt) pilot gasification and gas treatment plant for hydrogen production under construction at the Sotacarbo Research Centre in Sardinia. The gasifier will be fed with imported, low sulphur coal and with Sardinian, high sulphur coal (Sulcis coal). Performance has been analysed by means of a computer simulation model developed at the DIMECA, which considers a “two zone” gasification process (coal drying and devolatilisation zone and char combustion and gasification zone), assuming thermodynamic equilibrium for the char combustion and gasification zone. The simulation model determines the mass and energy balance of the gasifier as well as the main characteristics of the syngas produced during gasification (composition, mass flow, temperature, lower heating value, etc.), for known composition and mass flow of coal, steam and oxidant (oxygen enriched air if required). The results have also been compared with a second simulation model developed using Aspen Plus 12.1 simulation software. This model enables to schematise, in more detail, the gasifier in different zones: coal preheating and drying, devolatilisation, gasification, combustion and oxidant preheating. However the results achieved with the two gasification models are very similar and compare favourably with the expected performance specified by the gasifier manufacturer