Study on mass transfer property of oxygen molecules and kinetic regimes of pressured pulverized coal combustion
The ef fects of pres sure on dif fu sion of ox y gen mol e cules dur ing the coal com bus tion could not be ig nored. The com press ibil ity fac tor of real ox y gen is in ves ti gated to eval u ate the de vi a tion be tween real and ideal ox y gen, and ob tain the mean free path of real ox y gen. Com par ing the Knudsen pore di am e ter with the min i mum pore di am e ter, it is found that with the in crease of pres sure, Knudsen dif fu sion can not ex ist at low pres sure and may de lay to oc
... nd may de lay to oc cur at higher tem per a ture. When pres sure ex ceeds 3.5 MPa, no Knudsen dif fu sion oc curs within the whole tem per a ture range of our re search. Com par ing the dif fu sion rate at 1 MPa with the burn ing rate, one can con clude that the com bus tion mainly take place on the in ter nal and ex ter nal sur faces, and the re ac tion is con trolled by the chem i cal ki net ics be low 1400 K. When them per a ture is be tween 1400 K and 1600 K, the re ac tion is con trolled by both the dif fu sion and the chem i cal ki net ics. When the tem per a ture is more than 1600 K, the com bus tion pri mar ily hap pens on the ex ter nal sur faces and is controlled by the dif fu sion. In tro duc tion Now a days, coal has played and con tin ues to play a sig nif i cant role in meet ing the global de mand for en ergy ser vices and needs to be used more ef fi cient and en vi ron men tally friendly than ever be fore. Ad vanced clean coal tech nol o gies, such as pres sur ized com bus tion  and ox y gen-en riched com bus tion [2, 3] , have at tracted in creas ing in ter ests in re cent years. Coal is a com plex poly meric ma te rial which has a highly het er o ge neous and com pli cated pore struc ture. Pores in coal ac cord ing to the di am e ters may be di vided into: mi cro-pores (<2 nm), tran si tional pores (2-50 nm), and macro-pores (>10 nm)  . Pore vol ume dis tri bu tion is de pendent upon the rank of coal. For dif fer ent rank coals, pores with di am e ter of less than 10 nm account for the main por tion of the in ter nal coal sur face and the avail able sites for com bus tion. Many stud ies [5, 6] have also shown that the pore struc ture has a sig nif i cant ef fect upon the coal com bus tion. It is now es tab lished that pul ver ized coal (P. C.) com bus tion is con trolled both by ox y gen dif fu sion and chem i cal ki net ics  . While ex ten sive ex per i ments and mod el ing of atmo spheric coal com bus tion have been re ported , the cases of high pres sure are poorly ex am -Yue, F., et al.: Study on Mass Transfer Property of Oxygen Molecules and .