Abstract
Hydrogen could be a promising source fuel, and is often considered as a clean energy carrier as it can be produced by ethanol. The use of ethanol presents several advantages, because it is a renewable feedstock, easy to transport, biodegradable, has low toxicity, contains high hydrogen content, and easy to store and handle. Reforming ethanol steam occurs at relatively lower temperatures, compared with other hydrocarbon fuels, and has been widely studied due to the high yield provided for the formation of hydrogen. A new computational fluid dynamics (CFD) simulation model of the ethanol steam reforming (ESR) has been developed in this work. The reforming system model is composed from an ethanol burner and a catalytic bed reactor. The liquid ethanol is burned inside the firebox, then the radiative heat flux from burner is transferred to the catalytic bed reactor for transforming the ethanol steam mixture to hydrogen and carbon dioxide. The proposed computational model is composed of two phases—Simulation of ethanol burner by using Fire Dynamics Simulator software (FDS) (version 5.0) and a multi-physics simulation of the steam reforming process occurring inside the reformer. COMSOL multi-physics software (version 4.3b) has been applied in this work. It solves simultaneously the fluid flow, heat transfer, diffusion with chemical reaction kinetics equations, and structural analysis. It is shown that the heat release rate produced by the ethanol burner, can provide the necessary heat flux required for maintaining the reforming process. It has been found out that the mass fractions of the hydrogen and carbon dioxide mass fraction are increased along the reformer axis. The hydrogen mass fraction increases with enhancing the radiation heat flux. It was shown that Von Mises stresses increases with heat fluxes. Safety issues concerning the structural integrity of the steel jacket are also addressed. This work clearly shows that by using ethanol which has low temperature conversion, the decrease in structural strength of the steel tube is low. The numerical results clearly indicate that under normal conditions of the ethanol reforming (The temperature of the steel is about 600 °C or 1112 °F), the rupture time of the HK-40 steel alloy increases considerably. For this case the rupture time is greater than 100,000 h (more than 11.4 years).
Highlights
In recent decades, there has been a continuous effort to reduce global environmental pollution and fossil oil consumption [1]
Hydrogen production from ethanol has advantages compared to other H2 production techniques, including steam reforming of methanol and hydrocarbons
Amongst the various processes and primary fuels that have been proposed for hydrogen production in fuel cell applications, steam reforming of ethanol is very attractive
Summary
There has been a continuous effort to reduce global environmental pollution and fossil oil consumption [1]. Fuel cells are electrochemical devices described as continuously operating batteries and are considered as a clean source of electric energy, containing high energy efficiency, and its resulting emission is just water [3] It can be produced from different kinds of renewable feedstocks, such as ethanol. Ethanol steam reforming (ESR) proceeds at temperatures in the range of 300–600 ◦C, which is significantly lower than those required for CH4 or gasoline reforming This is an important consideration for the improved heat integration of fuel cell vehicles. The CFD computational study shows that high reforming temperatures (above 625 ◦C) should be avoided This is because the decomposition of ethanol competes effectively with the dehydrogenation of the alcohol to acetaldehyde, which is the key intermediate of the ESR process, and results in a reduced hydrogen yield and an increased content of CO in the reformate stream.
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