(356f) Thermodynamic Study and Energy Optimization of Bioethanol Steam Reforming and Autothermal Reforming: A Comparative Analysis

In 2018, approximately 81% of the world's energy consumption was supplied by processes that uses fossil fuels (IEA, 2020). The concerns about environmental impacts caused by using such fuels, mainly due to the emissions of gases that cause the greenhouse effect, renewable sources of energy have been studied and developed. For countries with a large production of ethyl alcohol, such as Brazil, the production of hydrogen from the ethanol reforming is a viable alternative fuel option, due to its high combustion power and lower environmental impacts. The purpose of this work is to carry out a thermodynamic study and energy optimization of the steam and autothermal reforms of ethanol, with possible application in internal combustion engines. Thus, a fraction of ethanol from the fuel tank is directed to an embedded reformer to produce hydrogen, which is mixed with unreformed ethanol, allowing an increase in the calorific value (heat of combustion) of the fuel mixture and a reduction of pollutants emission (GARCIA; LABORDE, 1991). The production of unwanted compounds and the selectivity of the reaction depend on the catalyst employed and the process conditions used. Previous studies in the literature indicate that the temperature of 1100 K led to a maximum production of hydrogen with practically no carbon production. In the present study, different reactions conditions were simulated using the Gibbs reactor developed by the commercial simulator Aspen Plus^®. A strategy of adding oxygen to the ethanol combustion reaction was proposed to raise the temperature of the reformer and decrease the formation of unwanted products, such as methane, acetone, ethylene, acetaldehyde and coke. The analysis was carried out in the temperature range from 400 K to 1200 K, with pressure from 1 to 7 bar, water/ethanol feed molar ratio between 0 and 9 and oxygen/ethanol between 0 and 1.5 under ideal conditions. The results show that the production of hydrogen in the steam reforming is enhanced at atmospheric pressure, by increasing the temperature and the water/ethanol feed ratio, and the formation of by-products is reduced, except for carbon monoxide. In the autothermal reforming, the increase in the oxygen/ethanol feed ratio does not favors the formation of hydrogen at temperatures above 800 K, however, undesirable products such as coke also have their production reduced.

References

IEA - International Energy Agency. World Energy Balances: Overview. 2020. Available in: <https://www.iea.org/reports/world-energy-balances-overview&gt;.

GARCÍA, E. Y.; LABORDE, M. A. Hydrogen Production by the Steam Reforming of Ethanol: Thermodynamic Analysis. International Journal of Hydrogen Energy, 16 (1991) 307-312.