Effect of Coal Type and Oxyfuel Combustion Parameters on Pulverised Fuel Ignition

摘要

Oxyfuel combustion is currently one of the principal technological options being considered for capturing carbon dioxide from pulverized coal power plants. In oxyfuel combustion, coal is burnt in a mixture of recycled flue gases and added oxygen instead of in air. In principle this yields a flue gas containing only carbon dioxide, water vapor and small amounts of other impurities. Oxyfuel combustion is superficially similar to combustion in air, but there are inevitable differences. This paper describes ignition tests on pulverized coal suspensions using a suite of coals of different rank and from different countries of origin and over a range of oxygen and coal concentrations of interest for oxyfuel combustion. The ignition tests were carried out using the National Institute for Occupational Safety and Health (NIOSH) 20-litre explosion chamber. The purpose was to determine how easily the various coals ignite and burn in mixtures of O2 and CO2 compared to their combustion in air. The residual char volatile and ash contents for the ignition residues were measured using a thermogravimetric analyzer (TGA), allowing Q factors (i.e., enhancement in apparent volatile yield due to higher heating rates and/or heterogeneous reactions) to be determined and compared. An ignition index has been derived from the explosion and char data. This index has been used to rank low volatile coals for ignition propensity in air.