Technical Review on Thermochemical Conversion Based on Decoupling for Solid Carbonaceous Fuels

The thermochemical conversion process of solid fuels is explicitly shown as the processes of pyrolysis (including coking and carbonization), gasification, and combustion. These processes actually involve a similar complex reaction network. The so-called “decoupling” refers to the optimization approach of process performance through controlling the interactions between or among the involved individual reactions. Our previous article in Energy & Fuels (2010, 24, 6223–6232) has analyzed how the approach of decoupling applies to the gasification technologies and justified the realized effects from decoupling. This successive report is devoted to understanding the applications of decoupling to the other types of thermochemical conversion technologies (mainly including pyrolysis and combustion) so as to generalize the “decoupling” methodology for innovations of thermochemical conversion technologies. After a reiteration of the principle and implementation approaches (isolating and staging) for decoupling, reanalysis of the process design principle and its consequent technical superiorities based on decoupling is performed for a few well-known or emerging novel conversion technologies developed in the world. The concrete technologies exemplified and their realized beneficial effects include the high-efficiency advanced coal coking processes with moisture control or gentle pyrolysis of feedstock in advance, coal pyrolysis in multiple countercurrent reactors for producing high-quality tar, gasification of caking coal in fluidized bed through adopting jetting preoxidation of coal, low-NO x decoupling combustion of coal by developing the in-bed NO x reduction capabilities of pyrolysis gas and char, and coal topping combustion for the coproduction of tar and heat. These highlights further justified that the decoupling would be a viable technical choice for achieving one or more of the technical advantages among polygeneration, high efficiency, high product quality, wide fuel adaptability, low pollutant emissions in thermochemical conversions of solid carbonaceous fuels.