Physical-Chemical and Thermodynamic Analyses of Ethanol Steam Reforming for Hydrogen Production

Abstract

Steam reforming is the most usual method of hydrogen production due to its high production efficiency and technological maturity. The use of ethanol for this purpose is an interesting option because it is a renewable and environmentally friendly fuel. The objective of this article is to present the physical-chemical, thermodynamic, and exergetic analysis of a steam reformer of ethanol, in order to produce 0.7Nm3∕h of hydrogen as feedstock of a 1kW PEMFC. The global reaction of ethanol is considered. Superheated ethanol reacts with steam at high temperatures producing hydrogen and carbon dioxide, depending strongly on the thermodynamic conditions of reforming, as well as on the technical features of the reformer system and catalysts. The thermodynamic analysis shows the feasibility of this reaction in temperatures about 206°C. Below this temperature, the reaction trends to the reactants. The advance degree increases with temperature and decreases with pressure. Optimal temperatures range between 600 and 700°C. However, when the temperature attains 700°C, the reaction stability occurs, that is, the hydrogen production attains the limit. For temperatures above 700°C, the heat use is very high, involving high costs of production due to the higher volume of fuel or electricity used. The optimal pressure is 1atm., e.g., at atmospheric pressure. The exergetic analysis shows that the lower irreversibility is attained for lower pressures. However, the temperature changes do not affect significantly the irreversibilities. This analysis shows that the best thermodynamic conditions for steam reforming of ethanol are the same conditions suggested in the physical-chemical analysis.

Comparative Exergy and Environmental Assessment of the Residual Biomass Gasification Routes for Hydrogen and Ammonia Production

“…Compression and intercooling also require a significant amount of energy input per unit of hydrogen produced. In contrast, when liquid ammonia is expanded, energy can be harnessed through expansion, thus partially recovering the compression power [61,62]. The plantwide exergy efficiency (i.e., without considering the supply chain efficiency), shown in Figure 12, also exhibits this trend.…”

“…A way to help reduce the amount of exergy destroyed in Thomass-based production plants is to employ better technologies to remove bagasse moisture as well as implement hot catalytic cleaning of the syngas, thus avoiding the waste heat in the water scrubbing section. An increase in the gasifier pressures would also help avoid excessive compression power consumption [61].…”

“…Compression and intercooling also require a significant amount of energy input per unit of hydrogen produced. In contrast, when liquid ammonia is expanded, energy can be harnessed through expansion, thus partially recovering the compression power [61,62].…”

Towards automation of chemical process route selection based on data mining

“…9 and then the oxidation state of all such atoms at a given reaction step is summed (Ox i ) and the difference ΔOx i = Ox i − Ox target is found. Should both ΔOx i and ΔOx i−1 be positive (or both negative) and |ΔOx i | > |ΔOx i−1 | a penalty for step i will be applied according to eqn (13) as an oxidation or reduction that needs to subsequently be corrected has taken place. If, however both ΔOx i and ΔOx i−1 are of opposite signs an overshoot has taken place and the penalty will be given by eqn (14).…”

On the efficiency, exergy costs and CO 2 emission cost allocation for an integrated syngas and ammonia production plant

“…However, reported data on exergy costs and CO2 emission cost of various fuels [47][48][49][50][51] have shown that a small part of the cumulative unit exergy costs of natural gas and petroleum derivatives corresponds to renewable sources and, thus, it must be accounted for if a fair level playing field for comparative assessments with other syngas and ammonia production technologies is intended. For instance, other scenarios, including the syngas production by using the steam reforming of ethanol, have earned more attention in Brazil, mainly due to its well-established sugar cane ethanol economy [111][112][113][114][115]. Thus, apart from the fossil-based ammonia production process, future works on ethanol-based ammonia production may offer a more interesting opportunity to highlight the importance of the allocation of the renewable unit exergy costs and CO2 emission cost, including those associated to the upstream processing stages of the sugar cane.…”