Incorporation of statistical distribution of particle properties in chemical reactor design and operation: the cooled tubular reactor

Pellet heat and mass transfer coefficients inside packed beds do not have definite deterministic values, but are stochastic quantities with a certain distribution. Here, a method is presented to incorporate the stochastic distribution of pellet properties in reactor design and operation models. The theory presented is illustrated with a number of examples. It is shown that pellet-scale statistics have an impact on cooled tubular reactor design and operation. Cooled tubular reactor design is determined to a large extent by the objective that run away inside the reactor tubes be avoided. We obtain the highest conversion if conditions in the tubes are such that the pellet and reactor run-away mechanisms are in balance. This determines an optimum amount of particles on a diameter inside a cooled tubular reactor. This optimum is influenced by the distribution of transport coefficients over the pellets. Because of the pellet-scale statistical behaviour, a certain percentage of the tubes will always suffer run away if we operate close to the run-away region. If we have certain fluctuations in the coolant temperature, reactor pressure or load, any of these can damage a certain amount of tubes. As these fluctuations occur often, the performance of the cooled tubular reactor will deteriorate with time. The effects, as shown in this study, may cause an increase in inherent reactor instability. Therefore, if these effects are taken into account, a more conservative reactor design emerges

Safe design of cooled tubular reactors for exothermic, multiple reactions; parallel reactions—I: Development of criteria

Previously reported design criteria for cooled tubular reactors are based on the prevention of reactor temperature run away and were developed for single reactions only. In this paper it is argued that such criteri a should be based on the reactor selectivity, from which eventually a maximum allowable temperature can be derived. To this end and for the pseudo-homogeneous, one dimensional model of a cooled tubular reactor in which two parallel, irreversible first order exothermic reactions are carried out, two criteria are developed for the safe design and operation of the reactor. The criteria enable us to choose tube diameters and operating conditions, which are safe in view of the derived selectivity and of possible runaway as well. The method outlined can be used in the initial design stage and requires kinetic information on both the desired and the undesired reaction

Digital computer study of nuclear reactor thermal transients during startup of 60-kWe Brayton power conversion system

A digital computer study was made of reactor thermal transients during startup of the Brayton power conversion loop of a 60-kWe reactor Brayton power system. A startup procedure requiring the least Brayton system complication was tried first; this procedure caused violations of design limits on key reactor variables. Several modifications of this procedure were then found which caused no design limit violations. These modifications involved: (1) using a slower rate of increase in gas flow; (2) increasing the initial reactor power level to make the reactor respond faster; and (3) appropriate reactor control drum manipulation during the startup transient

Safe design of cooled tubular reactors for exothermic, multiple reactions. Consecutive reactions

The model of the pseudo-homogeneous, one-dimensional, cooled tubular reactor is applied to two consecutive, irreversible first order reactions. A criterion is derived to obtain a desired integral yield. Based on this criterion three requirements are formulated, which enable us to choose the relevant design and operating conditions. If any of the requirements are met, the reactor is also safe with respect to runaway. In an illustration the results are applied to the production of phthalic anhydride via the oxidation of naphthalene. It is shown that the requirements formulated can be used for the design of the reactor and for its immediate adjustment to a change in operating conditions. In view of the special behaviour of consecutive reactions in a tubular reactor a fine tuning of the operating conditions remains necessary after this adjustment

Ultrasonic wave propagation in cylindrical vessels and implications for ultrasonic reactor design

Reactors in which processes are enhanced by ultrasound are hampered by the lack of a theoretical framework on their design. Simulation results of ultrasonic wave propagation in a cylindrical geometry are presented in this work, which are then used to develop guidelines for the design of ultrasonic reactors. These guidelines are used to design a new type of reactor with a novel geometry, operating at a frequency of 27kHz, 39kHz and 82kHz. This reactor is characterized using Weissler's reaction dosimetr