OCR Text |
Show -11- where $ is the mass flow parameter [15] m <J> = 2(m. + rajc /kd , (34) m 1 IJ p p m and c is the specific heat of the gas at the mean temperature of the gas and m the particles. E. Chemical Reactions Following devolatilization, the volatiles and other gaseous species in the system are gradually mixed, and have the opportunity to react chemically. In the CONCHAS-SPRAY code chemical reactions are divided into two groups: the kinetic reactions, which proceed relatively slowly compared to the fluid flow time scales, and the equilibrium reactions, which are assumed to proceed sufficiently fast that they are always at equilibrium. The reaction progress of the kinetic reactions is described by conventional chemical kinetics rate equations, while the end states of the equilibrium reactions are described by the equilibrium constants . The gas phase kinetic reactions presently incorporated into the code are 0 + 2N -• 2N + 2N0 , (35) 20 + N -> 20 + 2N0 , (36) N + 20H -• 2H + 2N0 , (37) CH4 + 202 -• C02 + 2H20 , (38) 2C H + 30 -• 2H 0 + 4C0 , (39) and 0£ + 2H2 > 2H20 . (40) The reactions, (35)-(37), comprise the extended Zel'dovich mechanism for nitric oxide production, as discussed in the CONCHAS-SPRAY documentation [1]. Equations (38) and (39) represent the burning of methane and acetylene, which are generated in the coal devolatilization and subsequent cracking and reforming processes. Equation (40) is added to allow for the burning of any hydrogen formed in these processes. Kinetic rate data for oxidation of the volatiles have been taken from the compilation of Westbrook and Dryer [16]. |