丙烯腈尾气段间取热式流向变换催化燃烧

Catalytic Combustion of Acrylonitrile Off-Gas in a Reverse Flow Reactor with a Heat Extractor

丙烯腈吸收塔尾气浓度较高,传统的流向变换催化燃烧反应器无法维持正常操作。在中间带换热器的立升级流向变换催化燃烧反应装置上对高浓度的丙烯腈尾气进行处理,考察了换向周期、进料空速和浓度等操作条件对尾气中各组分的转化率、床层热波特性和轴向温度分布的影响以及床层的"飞温"和"熄火"特性。结果表明,换向周期、进料浓度和空速对反应器温度分布影响明显。经过第一段催化床层后,丙烯腈尾气中的可燃物基本转化完全,经过中间换热器后,气体温度迅速降低,在到达第二段催化床层后,由于没有可燃物供给,温度会进一步下降,从而形成了不对称的"M"型温度分布。换向周期延长,将使两催化床层的温度差加大,可能导致高温段床层"飞温"和低温段床层"熄火"。空速和进料浓度增加都会使两段催化床层的温度上升,但进料段催化床层的温升更为明显。进料浓度是导致床层"飞温"或"熄火"的主要因素。

The concentration of acrylonitrile off-gas in the absorption tower was high and the traditional reverse flow reactor could not maintain normal operation. The high concentration acrylonitrile off-gas was treated in a reverse flow reactor with a heat extractor in the middle. The factor of cycle period, space velocity and feed concentration on operation performance of the reactor with a heat extractor were investigated. At the same time, the “temperature run-away” and “extinction” behavior of the reactor were observed to find out the reasonable range of the operation parameters. The experimental results showed that the cycle period, space velocity and feed concentration had important effects on the temperature distribution of the reactor. The combustible reactants in the off-gas were mostly oxidized in the first catalytst bed, and the temperature of the off-gas decreased rapidly after it flew through the heat extractor and would decrease further when it flew into the second catalyst bed because there were no combustible reactants in the off-gas, so an asymmetric “M” temperature distribution in the reactor was formed. When the cycle period became longer, the temperature difference between the two catalyst beds became larger and could result in “temperature run-away” in the catalyst bed with high temperature and “extinction” in the catalyst bed with low temperature. The temperature of two catalyst beds would increase with the increasing of space velocity and feed concentration, but the temperature of the feed catalyst bed increased more obviously than that of the effluent catalyst bed. The feed concentration was the major factor which resulted in the “temperature run-away” and “extinction” behavior of the reactor.