$A$	area ${\mathrm{m}}^2$
$C_P$	molar constant-pressure heat capacity, $\mathrm{KJ}/\left(\mathrm{mol}·\mathrm{K}\right)$
$D_p$	catalyst pellet diameter, $\mathrm{m}$
F	molar flow rate, $\mathrm{mol}/\mathrm{s}$
$J_q$	heat flux density, W/m2
K	equilibrium constant
$L$	length, m
$P$	pressure, $\mathrm{bar}$
$R$	universal gas constant, $\mathrm{J}/(\mathrm{mol}·\mathrm{K})$
r	reaction rate, $\mathrm{mol}/\left(\mathrm{kg}·\mathrm{s}\right)$
$T$	temperature, K
v	flow velocity, $\mathrm{m}/\mathrm{s}$
$z$	length, $\mathrm{m}$
Greek letters
$\mathsf{\epsilon }$	catalyst bed porosity
$\mathsf{\eta }$	dynamic viscosity, $\mathrm{kg}/\left(\mathrm{m}·\mathrm{s}\right)$
$\kappa$	rate constant of chemical reaction
${\nu }_i$	the stoichiometric number of reaction component $i$
$\rho$	density, $\mathrm{kg}·{\mathrm{m}}^{-3}$
$\mathsf{\sigma }$	local EGR, J/K
$\Sigma$	total
${\Delta }_{r}G$	Gibbs free energy change of chemical reaction, J
${\Delta }_{r}H$	enthalpy change of chemical reaction, J
Subscripts
c	cross section of tubular plug-flow reactor
cr	chemical reaction
f	fluid flow
ht	heat transfer
i	component
in	inlet
j	reaction types (I) and (II)
out	outlet
$\mathrm{p}$	catalyst pellet
q	quantity of heat
r	reaction
tot	total
$\mathrm{w}$	wall of tubular plug-flow reactor
Abbreviations
EGR	entropy generation rate
FTT	finite-time thermodynamics
H-S	hybrid-Sulphur thermochemical cycle
NSGA-II	second generation non-dominated solution sequencing genetic algorithm
S-I	sulphur-Iodine thermochemical cycle