Influence of necking configuration of a methanol steam reformer on catalyst amount and reforming performance

ABSTRACT

A reformer applied in a PEM (proton exchange membrane) fuel cell, which is a clean power source, is becoming a future trend as it employs catalyst to produce hydrogen. If some of the catalyst can be saved, the saved catalyst can be used to produce the extra hydrogen to generate the increased power of PEM fuel cell. The main objective of this study is then to investigate the saved catalyst amount in the cylindrical methanol reformer by the necking configuration through the non-isothermal transport processes and the estimated net power of PEM fuel cell produced by the saved catalyst. The results show that the used catalyst compared with the original reformer is saved by about 23.44%, and the saved catalyst can be used to produce additional amount of hydrogen to increase about 14.78% estimated net power of PEM fuel cell. The results of calculation were also compared with those of experiments, and achieved very good approximation.

KEYWORDS:

• Hydrogen production
• methanol reforming
• energy conversion
• necking effect
• saving of catalyst amount

Nomenclature

a, b, d, e, f, g, x, y, z	=	coefficients of chemical equilibrium reaction equation
ci	=	concentration of species i (mol m−3)
CP	=	specific heat at constant pressure (kJ kg−1 K−1)
D	=	flow channel diameter of reformer chamber (m)
Deff	=	effective diffusivity(m2s−1)
Dk	=	mass diffusion coefficient (m2s−1)
Dp	=	diameter of the catalyst particles (m)
Ea1, Ea2, Ea3	=	activation energy (kJ mol−1)
hi0	=	enthalpy of species i (kJ mol−1)
HT	=	necking depth
k1	=	pre-exponential factor for steam reforming
k2	=	pre-exponential factor for reverse water-gas shift
k3	=	pre-exponential factor for water-gas shift
Keff	=	effective thermal conductivity (W m−1 K−1)
Kf	=	thermal conductivity of fluid (W m−1 K−1)
KS	=	thermal conductivity of solid(W m−1 K−1)
L	=	flow channel length of reformer reactor (m)
LC	=	distance between inlet and catalyst bed (m)
LCB	=	catalyst bed thickness (m)
Mi	=	mole fraction of species i
Mw,i	=	molecular weight of species i (kg mol−1)
n	=	normal vector along the reformer wall
$({\dot{\mathrm{n}}}_{\mathrm{C}{\mathrm{H}}_3\mathrm{O}\mathrm{H}}{)}_{\mathrm{R}}$	=	molar flow rate of the actual reacted methanol
$({\dot{\mathrm{n}}}_{\mathrm{C}{\mathrm{H}}_3\mathrm{O}\mathrm{H}}{)}_{\mathrm{i}\mathrm{n}}$	=	molar flow rate of the input methanol
N	=	number of species in the chemical reaction
p	=	pressure (N m−2)
r, $\theta$, z	=	coordinates
R	=	universal gas constant (J mol−1 K−1)
RC	=	radius of catalyst bed (m)
${\mathrm{R}}_{\mathrm{i},\mathrm{r}}$	=	Arrhenius reaction mole rate of creation and destruction of species i in the reaction r (mole m−3 s−1)
RN	=	necking ratio (${\mathrm{R}}_{\mathrm{N}}$)
${\mathrm{R}}_{\mathrm{S}\mathrm{R}}$	=	Arrhenius reaction mole rate for the steam reforming reaction (mole m−3 s−1)
${\mathrm{R}}_{\mathrm{r}\mathrm{W}\mathrm{G}\mathrm{S}}$	=	Arrhenius reaction mole rate for reverse water-gas-shift reaction (mole m−3 s−1)
${\mathrm{S}}_{\mathrm{t}}$	=	energy source term for chemical reaction
T	=	temperature (°C)
${\mathrm{T}}_0$	=	inlet fuel temperature (°C)
${\mathrm{T}}_{\mathrm{W}}$	=	heated-wall temperature (°C)
$\vec{\mathrm{u}}$	=	velocity vector (m s−1)
${\mathrm{u}}_{\mathrm{r}},{\mathrm{u}}_{\theta },{\mathrm{u}}_{\mathrm{z}}$	=	velocity components in the r, $\theta$ and z direction (m s−1)
${\dot{\mathrm{V}}}_{\mathrm{i}\mathrm{n}}$	=	inlet volume flow rate for reforming
WT	=	distance between necking position and catalyst bed (m)

Greek symbols

$\beta$	=	inertial loss coefficient
${\eta }_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{v}}$	=	methanol conversion efficiency
$\epsilon$	=	porosity of the catalyst bed (volume of fluid region/total volume of catalyst)
$\kappa$	=	permeability of the catalyst bed
$\mu$	=	dynamic viscosity (kg m−1 s−1)
${\mu }_{\mathrm{m}\mathrm{i}\mathrm{x}}$	=	viscosity of the gas mixture (kg m−1 s−1)
${\varphi }_{\mathrm{i}\mathrm{j}}$	=	a term used in calculating the viscosity of the gas mixture
${\theta }_{\mathrm{T}}$	=	necking angle
${\rho }_{\mathrm{f}}$	=	fluid density (kg m−3)
$\tau$	=	tortuosity of the catalyst bed

Subscript

in

=

inlet

Additional information

Funding

This work was supported by the Ministry of Science and Technology of the Republic of China [grant number MOST 103-2221-E-168-021-MY2].