Start up of an industrial adiabatic tubular reactor

The dynamic behaviour of an adiabatic tubular plant reactor during the startup is demonstrated, together with the impact of a feed-pump failure of one of the reactants. A dynamic model of the reactor system is presented, and the system response is calculated as a function of experimentally-determined, time-dependent, manipulated variables. The values of model parameters are estimated by using the SimuSolv (1991) computer program. The data set collected during the reactor start-up is used for the parameter estimation procedure. An excellent agreement is obtained between the experimental and the calculated system response. Many continuously-operated commercial reactors require a complete conversion of one of the main reactants at the reactor exit. It is shown that for an industrial tubular reactor a much higher initial reactor temperature is required during the startup, compared to the reactor inlet temperature during normal steady-state operation, to ensure a complete reactant conversion. Much more research is necessary to determine whether this is a generally valid rule

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

Start-up strategy design and safeguarding of industrial adiabatic tubular reactor systems

The safeguarding methodology of chemical plants is usually based on controlling the instantaneous values of process state variables within a certain operating window, the process being brought to shutdown when operating constraints are exceeded. This method does not necessarily prevent chemical reactors suffering from a runaway during dynamic operations because (a) excessive amounts of unreacted chemicals can still accumulate in the process, and (b) no means are provided to the operating personnel to identify hazardous process deviations. A model-based startup and safeguarding procedure is developed for an industrial adiabatic tubular reactor to improve process safety during startup. The trajectories of manipulated variables are calculated by minimizing the amount of one of the main reactants in the reactor effuent. It is concluded that proper control of the initial reactor temperature profile is critical for a safe startup while the impact of other manipulated variables is relatively smaller than that of the initial reactor temperature profile

Reactor operating procedures for start up of continuously operated chemical plants

Rules are presented for the startup of an adiabatic tubular reactor, based on a qualitative analysis of the dynamic behavior of continuously-operated vapor- and liquid-phase processes. The relationships between the process dynamics, operating criteria, and operating constraints are investigated, since a reactor startup cannot be isolated from an entire plant startup. Composition control of the process material is critical to speed up plant startup operations and to minimize the amount of offgrade materials. The initial reactor conditions are normally critical for a successful startup. For process conditioning, a plant should have an operating mode at which the reactor can be included in a recycle loop together with its feed system and downstream process section. Experimental data of an adiabatic tubular reactor startup and thermal runaway demonstrate some operational problems when such an intermediate operating stage is missing. The derived rules are applied to an industrial, highly heat-integrated reactor section, and the resulting startup strategy is summarized in an elementary-step diagram

Production of C(3)/C(4) Olefins from n-Hexane: Conceptual design of a catalytic oxidative cracking process and comparison to steam cracking

A conceptual design of the catalytic oxidative cracking (COC) of hexane as a model compound of naphtha is reported. The design is based on experimental data which are elaborated through a structural design method to a process flow sheet. The potential of COC as an alternative to steam cracking (SC) is discussed through comparing the key differences between the two processes. The presence of Li/MgO catalyst in the COC process (i) induces hexane cracking at lower operation temperatures (575 °C) than in SC (800 °C) and (ii) controls the olefin distribution by increasing the ratio of (butylene + propylene)/ethylene. The product distribution, and thus the separation train of both processes, is different. Catalytic oxidative cracking is designed to maximize propylene and butylene production, while steam cracking is designed to maximize ethylene production. In comparison to SC, the COC process is more energy efficient and consumes 53% less total duty for a production capacity of 300 kton/year of light olefins. However, a preliminary economic evaluation illustrates that the loss of valuable feedstock as a result of combustion of part of the naphtha feed makes the COC process economically less attractive than SC