Effects of sewage sludge blending on techno-economic performance of Integrated Gasification Combined Cycle (IGCC) system

Municipal sewage sludge (SS) can be used as an alternative carbon-neutral feedstock for energy utilization owing to its considerable higher heating value compared with lignite coal. It is potential to efficiently co-utilize SS by coal-sludge-slurry gasification technology avoiding the energy consumption for SS drying process. In this study the effects of SS blending on the techno-economic performance of Integrated Gasification Combined Cycle (IGCC) systems based on different kinds of gasification technology and coal are analyzed. The results show that the overall energy efficiency of the system based on dry gasifier is more sensitively affected by the blending of SS than the one based on wet gasification due to the energy consumption during drying process. For wet gasification technology, the overall energy efficiency for coal A first increases from 45.17% to 45.26% and then reduces to 44.77% with the SS mix ratio, while the overall energy efficiency for coal C declines from 38.58% to 38.03%. The results indicate the overall energy efficiency has positive correlation with the cold gas efficiency instead of ash fusion temperature and the effects of SS addition on the overall energy efficiency can be qualitatively estimated by analyzing the cold gas efficiency. In most cases the blending of SS in IGCC systems benefits the economic performance and the net present value of the system based on wet gasification and coal A could be increased by 88% due to the increasing power output and the SS treatment subsidy.