Characteristics of Dimethyl Ether Oxidation in a Preheated Pt-γ-Al₂O₃ Catalytic Reactor

ABSTRACT

An experimental study on the catalytic combustion of dimethyl ether under various oxidation conditions through a preheated tubular catalytic reactor filled with a lab-made Pt-γ-Al₂O₃ catalyst is presented in this paper. Both the transient variance of temperature distribution during the ignition process and the stationary results as the reactor reaches stable are delineated. The catalytic reactor is mounted in a tubular furnace to preheat and maintain an isothermal boundary. The reaction profiles and ignition processes are characterized by monitoring the temporal temperature traces, which is the steady-state axial distribution of temperature in the reactor. The average axial reaction temperature for different fuel quantities with various isothermal boundaries of the reactor was also evaluated. During the light-off process, the main exothermal reaction zone shift is found. The results demonstrate that a higher equivalence ratio of reactants produces a higher temperature, resulting in more heat transferring upstream and causes a higher conversion ratio. For the same equivalence ratio, a higher isothermal boundary temperature will result in a higher conversion ratio. The more extended reactor is required in one of the two conditions of a lower equivalence ratio of reactants and a lower isothermal boundary of the reactor. Finally, the energy balance and exergy analysis for the reactor was also performed; the results will be the basis for improving and optimizing designs.

KEYWORDS:

• Catalytic Combustion
• dimethyl ether
• Pt-γ-Al₂O₃ beads

Nomenclature

$c_p$	=	Isobaric specific heat capacity (kJ/kg-K)
$CR$	=	Conversion ratio
${\dot{E}}_{CV}$	=	Accumulation energy rate in a system (kJ/s)
$E{I}_i$	=	Emission index of species i
$e{x}_{ch,p}$	=	Specific chemical exergy of products (kJ/kg)
$e{x}_{ch,r}$	=	Specific chemical exergy of reactants (kJ/kg)
$e{x}_{ph,p}$	=	Specific physical exergy of products (kJ/kg)
$e{x}_{ph,r}$	=	Specific physical exergy of reactants (kJ/kg)
$e{x}_D$	=	Specific exergy destruction (kJ/kg)
$e{x}_p$	=	Specific exergy of products (kJ/kg)
$e{x}_q$	=	Specific exergy changes due to heat transfer (kJ/kg)
$e{x}_r$	=	Specific exergy of reactants (kJ/kg)
$LHV$	=	Low heating value of fuel
$M_i$	=	Molar mass of species i (kg/kmol)
${\dot{m}}_{total}$	=	Total mass flow rate (kg/s)
$m_i$	=	Mass of species i (kg)
${\dot{m}}_f$	=	Mass flow rate of fuel (kg/s)
$x_i$	=	Mass fraction of species i
$y_i$	=	Mass fraction of species i
${\dot{W}}_{CV}$	=	Energy transfer by work (kJ/s)
${\dot{Q}}_{CV}$	=	Heat transfer rate through system boundary (kJ/s)
${\dot{Q}}_p$	=	Energy output rate by products (kJ/s)
${\dot{Q}}_r$	=	Energy input rate by reactants (kJ/s)
$T_0$	=	Temperature of the reference environment (K)
$T_p$	=	Temperature of products at reactor exit (K)
$T_r$	=	Temperature of reactants at reactor entrance (K)
$p_0$	=	Pressure of the reference environment (101.325kPa)
$p_p$	=	Pressure of products at reactor exit (kPa)
$p_r$	=	Pressure of reactants at reactor entrance (kPa)
$\alpha$	=	The number of moles of carbon in 1 mole of fuel
$\mathrm{\Phi }$	=	Porosity
ϕ	=	Equivalence ratio
$\psi$	=	Exergy efficiency
${\rho }_B$	=	Bulk density (kg/m3)
${\rho }_P$	=	Particle density (kg/m3)

Additional information

Funding

This research was supported by the Ministry of Science and Technology, Taiwan, R.O.C. under Grant no. [MOST107-2221-E-244-003].