FLASHCHAIN THEORY FOR RAPID COAL DEVOLATILIZATION KINETICS .6. PREDICTING THE EVOLUTION OF FUEL NITROGEN FROM VARIOUS COALS

The release of fuel nitrogen during the primary devolatilization of an y bituminous coal involves only two mechanisms, the shuttling of nitro gen as an element in tar molecules and the conversion of char-N into H CN. This modeling study characterizes these processes for heating rate s from 5 to 10(4) K/s, temperatures to 1550 K, and pressures from vacu um to atmospheric. Evaluations against a database compiled from the be havior of 40 coals of rank from lignite through low-volatile bituminou s demonstrates that predicted evolution histories of tar-N, HCN, and c har-N and the nitrogen contents of tar are within experimental uncerta inty throughout this domain, Under conditions of rapid heating, tar sh uttling is the only mechanism for nitrogen release as long as tar is b eing expelled, but for slower heating conditions it is overlapped by H CN production from char-N, With FLASHCHAIN, no additional parameters o r rate expressions are required to quantitatively predict the contribu tions from tar shuttling from any bituminous coal at any operating con ditions, including the nitrogen contents of tar. The data evaluations also show that tar shuttling imparts the familiar dependences of tar e volution on coal rank, heating rate, and pressure onto the evolution o f the nitrogen species distributions, Conversion of char-N into HCN is analogous to the release of Hz during the graphitization of char at h igh temperatures, Only one reaction rate expression is needed to predi ct the yields and evolution rates of HCN during the primary devolatili zation of any coal, provided that it is based on an extremely broad di stribution of activation energies. The nominal rates of HCN production must also be reduced for coals of progressively higher rank in propor tion to their O/N ratios,