Ni/Al_2O_3催化剂上CH_4三重整反应-催化剂床层温度分布

Tri-reforming of CH_4 to syngas over Ni/Al_2O_3—thermal distribution in catalyst bed

在连续流动的固定床反应装置上，考察了Ni／Al2O3催化剂上CH4三重整反应中催化剂床层的温度分布。实验在常压、750℃～950℃、2000h^-1～20000h^-1下进行，研究了外控炉温、空速和进料组成对催化剂床层温度分布的影响。结果表明，催化剂床层中的温度梯度较甲烷部分氧化反应平缓，在CH4／CO2／H2O／O2=50／12．5／12．5／25（摩尔比）、20000h^-1下，催化剂床层中入口处温度比炉温高约80℃，出口处温度与器壁温度相当。空速越低，催化剂床层入口处温度（tmax）与炉温之差△tmax越小（20000h^-1时，Δtmax=80℃；2000h^-1时，Δtmax=30℃）。当原料气中不含O2时，催化剂床层入口处没有观测到温度骤升的现象。催化剂床层温度分布出现“低谷”现象，温度最低点（tmin）比炉温低30℃～40℃。根据温度分布曲线，大体可将催化剂床层分为三个区域：富氧区、贫氧区和无氧区。富氧区内只发生燃烧反应，贫氧区内发生重整反应和部分氧化反应，无氧区内只发生重整反应。

Temperature profiles of fixed-bed with Ni/Al2O3 catalyst were studied during the tri-reforming of methane in the temperature range of 750 ℃ - 950 ℃, 1 atm, and space velocity from 2 000 h^-1 to 20 000 h^-1. The effects of the furnace temperature （ tf ）, space velocity, and the composition of feed stock on the thermal distribution were investigated. The results indicated that temperature grads of catalyst bed in the tri-reforming were lower than that in partial oxidation of methane. The temperature near the catalyst bed inlet （ tmax ） was 80 ℃ higher than tf at CH4/CO2/H20/O2 = 50/12.5/12.5/25 and 2 000 h^-1, whereas the temperature near the catalyst bed outlet was close to tf. Δtmax （ = tmax - tf ） decreased with the decrease of space velocity （ Atmax = 80 ℃ at 20 000 h^-1 ; Atmax = 30 ℃ at 2 000 h^-1 ）. No distinct temperature grads were found near the catalyst bed inlet when there was no oxygen in feed. Under specific condition, tmi. （the lowest temperature in the catalyst bed）, which was about 30 ℃ -40 ℃ lower than tf , can be observed in the bed. According to thermal distribution of the bed, the catalyst bed can be divided into three zones, oxygen adequate zone, oxygen inadequate zone, and oxygen absent zone. In oxygen adequate zone, methane combustion occurs only. In oxygen absent zone, methane reforming （carbon dioxide and steam reforming） takes places only. However, in oxygen inadequate zone, both reforming and partial oxidation of methane are present.