Tri-reforming of methane to syngas over Ni/Al2O3 — Thermal distribution in the catalyst bed

Thermal distribution in catalyst bed was investigated for the fixed-bed tri-reforming of methane over Ni/Al2O3 under atmospheric pressure, 750 – 950°C, and space velocity (SV) of 2000 – 20000 h−1. The effects of the furnace temperature (tf), the space velocity, and the feed stock composition on the thermal distribution were examined. The results indicated that the temperature gradient of the catalyst bed in methane tri-reforming is smaller than that in methane partial oxidation. The temperature near the inlet of the catalyst bed (tmax) is 80°C higher than tf when the feed composition n(CH4)/n(CO2)/n(H2O)/n(O2) = 50/12.5/12.5/25 (by mol) and the space velocity SV = 20000 h−1, whereas the temperature near the outlet of the catalyst bed is close to tf. The temperature difference between the inlet and the furnace Δtmax = tmax – tf) increases with the space velocity Δtmax = 30°C at 2000 h−1, Δtmax = 80°C at 20000 h−1). No distinct hot spot is observed near the catalyst bed inlet when there is no oxygen in feed. Under specific condition, the lowest temperature in the catalyst bed (tmin) is about 30 – 40°C lower than tf. According to the thermal distribution, the catalyst bed can then be divided into three zones: oxygen adequate zone, oxygen inadequate zone, and oxygen absent zone. Methane reforming proceeds in the first and second zones, while methane combustion proceeds only in the first zone and partial oxidation of methane proceeds only in the second zone.