Latin
ab	specific area of the bed (m2/m3)
ac	activity of carbon
ct	total molar concentration of the gas (mol m−3)
cpg	molar specific heat of the gas (J mol−1 K−1)
cps	mass specific heat of the solid (J kg−1 K−1)
dp	pellet diameter (m)
D	diffusion or dispersion (Da, Dr) coefficient (m2/s)
h	heat transfer coefficient (W m−2 K−1)
H	height of the cylindrical section of the shaft (m)
Hfeed gas	height of the reducing gas inlet (m)
Hinf	height of the conical section of the shaft (m)
Keq	equilibrium constant
K	permeability coefficient (kg m−3 s−1)
k	mass transfer coefficient, or reaction rate constant
M	molar weight (kg mol−3)
p	gas pressure
Pi	partial pressure of component i (bar)
r	radius (m)
R	ideal gas constant (J mol−1 K−1)
S	source term
T	temperature (K)
u	velocity (m s−1)
v	reaction rate (mol m−3 s−1)
wj	mass fraction of solid j
X	degree of conversion
xi	molar fraction of i in the gas
z	height (m)
Greek
ΔrH	heat of reaction (J mol−1)
ε	porosity
τ	characteristic time (s)
λ	thermal conductivity (W m−1 K−1)
µg	viscosity of the gas (Pa s)
ρg	mass density of the gas (kg m−3)
ρb	mass density of the bed (kg ${\mathrm{m}}_{\mathrm{bed}}^{-3}$)
${\tilde{\rho }}_j$	molar density of species j in the bed (${\mathrm{mol}\mathrm{m}}_{\mathrm{bed}}^{-3})$
Subscripts
b	bed
c	catalyst
cryst	crystallite
chem	chemical
diff	diffusional
interg	intergranular
ini	initial
intrac	intra-crystallite
interc	inter-crystallite
∞	in the bulk gas
eff	effective (for the bed)
eq	at equilibrium
g	gas
grain	grain
p	pellet
r	radial
s	solid
z	axial