Start-up and safeguarding of an industrial adiabatic tubular reactor

The safeguarding methodology currently used in the chemical industry is based on controlling the instantaneous values of the process state variables within a certain operating window, the process being brought to shut-down when the operating constraints are exceeded. It is concluded from an analysis of runaways which occurred in industrial reactors that this safeguarding methodology does not necessarily prevent reactor systems suffering from a runaway because (a) excessive amounts of unreacted chemicals can still accumulate in the process, and (b) no means are provided to the operating personnel of identifying such hazardous process deviations during dynamic operations. Amodel-based start-up and safeguarding procedure is developed for an industrial adiabatic tubular reactor to improve process safety during start-up operations. The trajectories of the manipulated variables are optimized by minimizing the breakthrough of one of the main reactants in the reactor effluent. A maximum reactor temperature constraint is also taken into account. It is concluded that a proper control of the initial reactor temperature profile is critical for a safe reactor start-up while the impact of the other manipulated variables is relatively small in comparison to the effect of the initial reactor temperature profile.