Thermodynamic Analysis Of Hydrogen Production Research Articles

Thermodynamic analysis of hydrogen production via steam reforming of selected components of aqueous bio-oil fraction

This work presents thermodynamics analysis of hydrogen production via steam reforming of bio-oil components. The model compounds, acetic acid, ethylene glycol and acetone, representatives of the major classes of components present in the aqueous fraction of bio-oil were used for the study. The equilibrium product compositions were investigated in a broad range of conditions like temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm). Any of the three model compounds can be fully reformed even at low temperatures producing hydrogen with maximum yield ranging from 80% to 90% at 900 K. Steam to fuel ratio positively affect the hydrogen content over the entire range of temperature studied. Conversely, higher pressure decreases the hydrogen yield. The formation of solid carbon (graphite) does not constitute a problem provided that reforming temperatures higher than 600 K and steam to fuel ratios higher than 4 for acetic acid and ethylene glycol and 6 for acetone are to be used. Thermal decomposition of the bio-oil components is thermodynamically feasible, forming a mixture containing C ( s ) , CH 4, H 2, CO, CO 2, and H 2O at various proportions depending on the specific nature of the compound and the temperature. Material and energy balances of complete reforming system demonstrated that the production of 1 kmol/s hydrogen from bio-oil steam reforming requires almost the same amount of energy as with natural gas reforming.

Thermodynamic analysis of hydrogen production from biomass gasification in supercritical water

Abstract A non-stoichiometric thermodynamic model based on minimum free energy is developed to predict the performance of hydrogen production from biomass gasification in SCW (supercritical water). Specially, we take glucose as a test sample of biomass and apply this model to analyze the processes of hydrogen production from glucose gasification in SCW. It is found that there is a “fast water–gas-shift-type pathway ”, and the product gases consist primarily of hydrogen and carbon dioxide with small amounts of methane and carbon monoxide. When the reaction temperature reaches a higher value, the equilibrium gases consist only of hydrogen and carbon dioxide. The gas yields, higher heating value, gasification efficiency and cold gasification efficiency are strongly affected by the reaction temperature and feedstock concentration and less affected by the pressure under the following range of conditions: a temperature of 650–1050 K, a pressure of 20–35 MPa and a concentration of 0.1–1.0 M. The higher the molar ratio of C/O, the higher are the maximum theoretical yields of hydrogen. The trend of the prediction results is in good agreement with the experimental data, especially as we take into consideration the carbon conversion efficiency.

04/02300 Thermodynamic analysis of hydrogen production by partial oxidation reforming: Lutz, A. E. et al. International Journal of Hydrogen Energy, 2004, 29, (8), 809–816

04/02300 Thermodynamic analysis of hydrogen production by partial oxidation reforming: Lutz, A. E. et al. International Journal of Hydrogen Energy, 2004, 29, (8), 809–816

Thermodynamic analysis of hydrogen production from ethanol using CaO as a CO2 sorbent

Abstract Ethanol steam reforming with and without the presence of CaO as a CO 2 sorbent is modeled. Potential advantages of the presence of CaO as CO 2 sorbent include higher energy efficiency, higher hydrogen production and lower CO content in the reformer gas exit. The presence of CaO eliminates the need of a WGS reactor for PEMFC application. Favorable operation conditions in the presence of CaO are (1) atmospheric pressure, (2) reactor temperatures around 700 °C, and (3) water/ethanol molar ratio of 4.

Thermodynamic analysis of hydrogen production by partial oxidation reforming

This paper presents thermodynamic analysis of hydrogen production by partial oxidation reforming. The analysis applies two approximations to the chemistry: global reaction balances and chemical equilibrium. The global reaction analysis provides theoretical upper limits on the process in the form of algebraic expressions involving the steam-to-carbon ratio and the oxygen-to-carbon ratio as process parameters. The equilibrium computations provide a more realistic estimate of the expected product composition and thermal efficiency of the process. The equilibrium predictions are compared to experimental data obtained using a first generation plasmatron reformer operated on diesel fuel. The efficiency of this compact reformer was considerably below the theoretical maximum.

Thermodynamic analysis of hydrogen production by steam reforming

This paper presents thermodynamic analysis of hydrogen production by steam reforming. The analysis treats the chemistry at two levels: a global species balance assuming complete reaction and solution of the equilibrium composition at the specified reformer temperature. The global reaction allows for an energy balance that leads to analytical expressions for the thermal efficiency. We use this to determine the maximum efficiency, and to distinguish between various definitions of efficiency. To obtain a more realistic estimate of the efficiency, the chemical equilibrium solution is combined with a system energy balance, which compares the energy required to vaporize and heat the fuel–steam mixture to the reformer temperature with the heat available from combusting the residual fuels in the reformate stream. The equilibrium solutions are compared to experimental measurements of the species and thermal efficiency of reforming diesel fuel, obtained with prototype compact steam reformers. The observed efficiency is significantly lower than the equilibrium prediction, indicating that both incomplete reaction and heat transfer losses reduce the performance.

Thermodynamic analysis of ethanol processors for fuel cell applications

A thermodynamic analysis of hydrogen production from ethanol has been carried out with respect to solid polymer fuel cell applications. Ethanol processors incorporating either a steam reformer or a partial oxidation reactor connected to water gas shift and CO oxidation reactors were considered and the effect of operating parameters on hydrogen yield has been examined. Employment of feeds with high H 2O/EtOH ratio results in reduced energy efficiency of the system. When hydrogen, non-converted in the fuel cell, is used to supply heat in the steam reformer, the effective hydrogen yield is essentially independent of the temperature of the reformer and the water gas shift reactor. Optimal operating conditions of partial oxidation processors have been determined assuming an upper limit for the preheat temperature of the feed. Results are discussed along with other practical considerations in view of actual applications.

A thermodynamic analysis of hydrogen production by steam reforming of ethanol via response reactions

The thermodynamics of ethanol steam reforming is considered in terms of response reactions (RERs). These have the property of being independent of the usually arbitrary initial choice of a set of independent reactions, and follow in a natural way from the fundamental equations of chemical thermodynamics. A simple algorithm is proposed for deriving a unique set of RERs, which can be used to rationalize the effect of process variables on steam reforming of ethanol to produce hydrogen. Further, from sensitivity analysis, the dominant reactions in the system can be identified and used in subsequent thermodynamic and kinetic analysis. These are usually arrived at through guess work. At or above 700–800 K, and high water/ethanol ratios the desired reaction of ethanol steam reforming can be made predominant and the effect of undesirable side reactions can be minimized.

Thermodynamic analysis of hydrogen production from biogas for phosphoric acid fuel cell

The utilization of low-cost biogas in stand-alone phosphoric acid fuel cells (PAFCs) offers a great potential for electric power generation. Digester biogas is processed via steam reformation and water-gas shift to generate H 2-rich gas for feeding the PAFC anodes. In this paper, the thermodynamics of steam reformation, shift and carbon deposition as a function of temperature are compared for a typical digester biogas feed (60% CH 4, 40% CO 2) and a pure methane feed. Equilibrium calculations are performed with identical steam-hydrocarbon ratios (1.54) for the two feeds at a total system pressure of 1 atm (0.1 MPa). The effect of CO 2 present in biogas on CH 4-conversion, H 2-yield and CO-content of the anode feed gas has been analysed. On this basis, optimum reformation and shift conditions for biogas feed have been identified. Threshold steam-hydrocarbon feed ratios for preventing carbon deposition in the reformer, shift converters and PAFC anodes have also been determined.