Page 271 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 7 Gasification Theory 247

G total total Gibbs free energy (kJ)
2
g acceleration due to gravity, 9.81 (m/s )
ΔH k heat of reaction of kth reaction at char surface (kJ/mol)
ΔH enthalpy change (kJ)
0
h ; h 0 f heat of formation at reference state (kJ/mol)
i
2
gas-wall convective heat transfer coefficient (kW/m K)
h conv
2
2
mass-transfer coefficient (kg carbon/m bar s)
h m
21
k first-order reaction rate constant (s )
21
preexponential factor (s )
k 0
21
rate constant for the liquid yield of pyrolysis (s )
k liq
bubble emulsion mass exchange coefficient (m/s)
k BE
21
rate constant for the char yield of pyrolysis (s )
k c
21
rate constant for the gas yield of pyrolysis (s )
k g
21
rate constant of three primary pyrolysis reactions taken together (s )
k 1
K number of element in Eq. (7.77)
s )
rate constants in Eq. (7.70) (7.72) (bar 21 21
K e1 , k e2 , k e3
2
K sk surface reaction rate constant for kth reaction, mol/m bar n
equilibrium constant ( )
K e , K equilibrium
l number of gaseous reactants ( )
L r length of the reactor (m)
L Lagrangian function ( )
m b mass of the biomass in the primary pyrolysis process (kg)
m 0 initial mass of the biomass (kg)
m c mass of the biomass remaining after complete conversion (kg)
m reaction order with respect to carbon conversion in Eq. (7.42) ( )
m, n, p, q stoichiometric coefficients in Eqs. (7.27) (7.29)
n reaction order with respect to the gas partial pressure, Eq. (7.44) ( )
N number of species present ( )
N c number of char particles in unit gas volume ( )
number of orifices in a bed of area (A r )
N or
partial pressure of gasifying agent outside the char particle (bar)
P g
partial pressure of the species i (bar)
P i
P total pressure of the species (bar)
2
Q char gasification rate (kg Carbon/m s)
Q gasification , energy transfer due to gasification, convection, radiation, and mass trans-
3
Q conv , fer, respectively (kW/m of bed)
Q rad , and
Q mass
3
R gas constant (8.314 J/mol K or 8.314 3 10 25 m bar/mol K)
2
2
chemical kinetic reaction rate (kg carbon/m bar s)
R c
3
rate of production or consumption of gas species j (kg/m s)
R m,j
21
r i reaction rate of the ith reaction (s )
char particle radius (m)
r c
T temperature (K)
T s surface temperature of char particles (K)
T g gas temperature (K)
T w wall temperature (K)