Thermodynamic Analysis Of Ethanol Steam Reforming System For Hydrogen Production

A thermodynamic analysis of ethanol-steam reforming system which involves 9 species in total including ethanol, aldehyde, ethylene, methane, carbon dioxide, carbon monoxide, solid carbon, water and hydrogen is carried out in this thesis using the method of Gibbs free energy minimization. Different temperatures, pressures and ethanol-water mole ratios are taken into account over the ranges of 400~1200K, 1~5atm, 0~10 respectively and equilibrium mole numbers of each species are calculated.It is shown by the calculation that the conversion of ethanol is always 100%. High temperature and high water-ethanol mole ratio favor the hydrogen yield of unit mole ethanol, while high temperature and low water-ethanol ratio are conducive to raising the hydrogen mole fraction on a wet basis. The compact of water-ethanol ratio upon hydrogen concentration on a dry basis is negligible. Concentration of hydrogen over a dry basis can be largely influenced by temperature, the higher the temperature, the larger the concentration. Carbon monoxide is numerousely formed under conditions of high temperatures and low water-ethanol ratios. The amount arrives at it maximum of 1.9mol/molEtOH for water-ethanol ratio being 1 and temperature being 1200K. Low water-ethanol ratio mainly accounts for the carbon formation, which can be amplified by lower temperatures. For temperatures lower than 650K, carbon formation can be attributed to decomposition of methane. For temperatures between 650K and 950K, carbon formation should be attributed to all of the three carbon containing components: methane, carbon dioxide and carbon monoxide. For temperatures higher than 950K, carbon monoxide becomes the dominant factor accounting for carbon formation. It is also displayed by the calculation that low pressure favor hydrogen production, while high pressure is conducive to inhibiting carbon monoxide formation. Considering factors related to increasing hydrogen productivity and efficiency as well as preventing carbon and carbon monoxide formation, it is suggested that the thermodynamic favorable condition should be 850K or more for temperature, atmosphere pressure, and 8:1 for water-ethanol ratio.Additionally, a method called response reactions for sensitivity analysis is employed in this thesis. It is shown in the results that the steam reforming of methane predominantly contributes to the system response at low temperatures. For higher temperatures, the water gas shift reaction becomes predominant.