Next Generation Steam Cracking Reactor Concept

Abstract

The steam cracking process is an important asset in the hydrocarbon processing industry. The main products are lower olefins and hydrogen, with ethylene being the world's largest volume organic chemical at a worldwide capacity of ~ 120 million tonnes per year. Feed stocks are hydrocarbons such as: ethane, LPG, naphtha's, gas condensates and gas oil. The research goal of this thesis is to search for the intrinsic optimal steam cracking reaction conditions, pushing the olefin yields to the maximum that the fundamental reaction kinetic models allow for. To get to that goal we have: firstly, identified and assessed alternative process concepts published in the literature. Secondly, developed the concepts and software for an equation based modelling tool suitable for optimisation of large scale reaction kinetic models. Thirdly, developed a new reactor concept, d-RMix for homogeneous reactions with distributed feed allocation, product removal and macro-mixing. Fourthly, applied the optimisation tool to the new reactor concept model and an advanced reaction kinetic model for steam cracking, SPYRO(r). For four different feed stocks optimisations of ethylene yield and of ethylene plus propylene yields have been carried out. For the cracking of ethane a linear-concave unconstrained temperature profile with a (free) maximum temperature of ~1260 K proves optimal. For propane and heavier feed stocks an isothermal profile at the upper temperature bound is optimal, with dips at the beginning and the middle of the reaction volume coordinate. For these heavier hydrocarbon feeds a distribution along the reactor volume coordinate does result in higher yields. Having established that the steam cracking chemistry offers a potential for significantly higher olefins yields, these equipment engineering considerations pose a significant challenge to actually realise this potential and arrive at a next generation steam cracking reactor.