Thermodynamic analysis of hydrogen production from methane via autothermal reforming and partial oxidation followed by water gas shift reaction

摘要

Reaction characteristics of hydrogen production from a one-stage reaction and a two-stage reaction are studied and compared with each other in the present study, by means of thermodynamic analyses. In the one-stage reaction, the autothermal reforming (ATR) of methane is considered. In the two-stage reaction, it is featured by the partial oxidation of methane (POM) followed by a water gas shift reaction (WGSR) where the temperatures of POM and WGSR are individually controlled. The results indicate that the reaction temperature of ATR plays an important role in determining H_2 yield. Meanwhile, the conditions of higher steam/methane (S/C) ratio and lower oxygen/methane (O/C) ratio in association with a higher reaction temperature have a trend to increase H_2 yield. When O/C ≤ 0.125, the coking behavior may be exhibited. In regard to the two-stage reaction, it is found that the methane conversion is always high in POM, regardless of what the reaction temperature is. When the O/C ratio is smaller than 0.5, H_2 is generated from the partial oxidation and thermal decomposition of methane, causing solid carbon deposition. Following the performance of WGSR, it suggests that the H2 yield of the two-stage reaction is significantly affected by the reaction temperature of WGSR. This reflects that the temperature of WGSR is the key factor in producing H_2. When methane, oxygen and steam are in the stoichiometric ratio (i.e. 1:0.5:1), the maximum H_2 yield from ATR is 2.25 which occurs at 800 ℃. In contrast, the maximum H_2 yield of the two-stage reaction is 2.89 with the WGSR temperature of 200 ℃. Accordingly, it reveals that the two-stage reaction is a recommended fuel processing method for hydrogen production because of its higher H_2 yield and flexible operation.