FLASHCHAIN Theory for Rapid Coal Devolatilization Kinetics. 11. Tar Hydroconversion during Hydrogasification of Any Coal

摘要

This paper introduces a FLASHCHAIN-based reaction mechanism for oils production during tar hydroconversion with any coal for any hydrogasification conditions. Oils are generated by the hydrogenation of tar monomers in two stages. In the first stage, the tar monomers released as primary tars are rapidly hydrogenated into oils at the monomer hydrogenation rate. Since elevated pressures always shift primary tar molecular weight distributions toward lighter species, monomers constitute substantial fractions of primary tar, and as much as one-half the ultimate oils yield is produced soon after the onset of tar hydroconversion. In the second stage, additional tar monomers are gradually released by hydrocracking of larger tar molecules and then hydrogenated into oils, while control of the oils production rate shifts from monomer hydrogenation to hydrocracking. Oil yields are uniform with H-2 pressures higher than 1 MPa because rates of monomer hydrogenation and hydrocracking accelerate for progressively higher H2 pressures to compensate for diminishing primary tar yields. Predicted oil yields grow for progressively hotter temperatures. The analysis shows that aliphatic tar components must be incorporated into oils along with their aromatic nuclei during monomer hydrogenation and constitute one-half or more of the oils yield at the highest H2 pressures. Primary tar composition and, especially, their structural components determine the maximum oil yields from different coals. The sample-to-sample variability in primary tar yields is apparent in their associated oil yields. In combination, the mechanisms for hydropyrolysis, tar hydroconversion, and char hydrogasification accurately interpreted a database representing coals of rank from lignite to anthracite, heating rates from 1 to 10(4) degrees C/s, temperatures from 475 to 900 degrees C, coal contact times from 1 to 900 s, gas contact times from 2 to 42 s, and H2 pressures from 0.3 to 15 MPa.