Abstract
The performances for both the tube reactor for CO methanation and the small tubular reactor of methanol-steam reforming for hydrogen production are investigated numerically in this study. For the CO methanator using Ni/Al2O3 as catalyst, the effects of temperature, flow rate, catalyst loading, and inlet gas composition in isothermal process are studied. The results show that both the CO conversion and the CH4 selectivity can reach 99% under optimum operating condition. For fixed catalyst loading and inlet gas composition, the result from the variation of flow rate shows that there exists a peak value of the CO conversion and CH4 selectivity. The temperature plays an important effect in the reactor performance. Furthermore, the higher molar H2/CO ratio is, the better CO conversion is. When adding H2O at inlet gas, the CO methanation reaction speed is reduced for the higher molar H2O/CO ratio. In the tubular methanol reformer integrating with methanol reforming, CO removal, and methanol catalytic combustion, the CuO/ZnO/Al2O3 catalyst in the inner tube is used for methanol steam reforming and the Pt/Al2O3 catalyst in the outer tube is used for methanol catalytic combustion to supply the thermal energy for reforming. The reformed syngas contains about 1~5% CO, the CO methanation with Ni/Al2O3 as catalyst is used to lower the CO concentration. The effects of the operating parameters of methanol-water flow rate, methanol-oxygen flow rate, Ni/Al2O3 filling length and the heat loss from the outside wall on the reactor performance are studied. The numerical results show that under appropriate condition, the methanol conversion rate can over 98% and CO conversion can over 95%. Under the conditions that the methanol-steam flow rate and catalyst fillings are fixed, there exists a methanol-oxygen flow rate range where both the methanol conversion and CO conversion can reach the optimum value. There also exists an optimum catalyst filling length for CO methanation with higher methanol conversion and CO conversion when the methanol-water and methanol-oxygen flow rates are fixed.