(273e) Heat Transfer From Hot Particles to Cold Particles in Downward-Flow Binary Solids Systems

Coal is the major source of energy for the generation of electricity throughout the world, however burning of coal in conventional coal-fired power plants is one of the major contributors to climate change and global warming. To cope with this issue, various Clean Coal Technologies (CCTs) such as integrated coal gasification combined cycle (IGCC) have been widely developed. IGCC can increase the efficiency of power generation from coal, and hence reduce the pollutants emissions.

For further improvement of the energy efficiency of IGCC, Advanced IGCC (A-IGCC) system, which makes use of the exergy recuperation concept; utilizing the exhausted heat from the gas turbine for steam gasification, has been proposed. For the A-IGCC system, a triple-bed combined circulating fluidized bed (TBCFB) gasifier, composed of a downer pyrolyzer of coal, a bubbling fluidized bed gasifier of char, and a riser combustor of unreacted char to produce heat, has been considered to replace the conventional high temperature gasifiers. The TBCFB gasifier is expected to enhance the efficiency of char gasification by separating the volatiles from coal soon after rapid pyrolysis process to avoid inhibition effects of volatiles to char gasification. In this system, it is essential to transfer the heat carried by inert particles from the riser combustor immediately and effectively to the coal particles injected into the downer pyrolyzer.

For the TBCFB gasifier, the design of the downer coal pyrolyzer with high performance is necessary. For this purpose, it is important to investigate the changes of heat transfer coefficients in binary solids systems (inert particle and coal particle) with different flow structures in the downer. In this work, an novel experimental technique was developed to measure the temperatures of coal particles in the binary solids systems via heat balance method. Simultaneously, local solids holdup and particle velocities were also measured. The relationship between heat transfer coefficient and flow structure was analyzed and discussed.