Hybrid clean energy technologies for power generation from sub-bituminous coals:a case of 250MW unit

摘要

Major re-thinking is required on the conventional pulverized fuel conversion route of power generation wherein the ash and mineral burden in coals is transported through the entire flow passage of the boiler. For high-ash fuels, this has to be contained and the boiler must be clear of all mineral matter. The two independent clean coal candidate technologies for efficiency enhancement and emission controls - ultrasupercritical cycle (USC) and integrated gasification with combined cycle (IGCC) - both have limitations in adaptation to high-ash coals. While the USC is limited by the steam temperature up to 600?C (commercial scale) (700?C pilot scale) and boiler tube failure risks, IGCC is limited to high-quality fuels like diesel, naphtha, etc. (commercial scale) and high-grade coals (pre-commercial scale). The hybridization of the two technologies in their current form (ultra-supercritical cycle with gasification conversion) and carbon capture and storage (CCS) together with solar energy (solar thermal and solar photovoltaic) integration presents possibilities for immediate application to low-grade sub-bituminous coals to achieve the clean technology goals. The energy efficiency of the hybrid system is around 44.45%, which is of the order of the USC with pulverized coal combustion. But the predominant benefits of a clean operation override. The benefits are reduction in CO_2 generation from 0.86 to 0.70 kg/kWh and reduction in ash expelled from 0.20-0.24 to 0.12-0.18 kg/kWh besides elimination of dispersion of ash around the power station and facilitating CCS.