Vent sizing for phenolic reactors

First of all a reminder is given of the equations that describe the temperature increase with time of a reacting mass in adiabatic conditions. A discussion follows on the related plots, obtainable through tests with laboratory adiabatic calorimeters and pilot or industrial reactors, with particular reference to the problem of extrapolating to industrial reactors the results got through small apparatuses, primarily in the case of complex reactions as the phenol-formaldehyde one. The mechanisms of the two fundamental phases of this reaction (methylolation and condensation) are reminded, trying to correlate the total temperature increase (and therefore the overall heat of reaction) with the energy contributions of the single phases and with the molar ratio (formaldehyde/phenol) characterizing the reacting mixture. Then we report the calculation procedures suggested by DIERS for sizing emergency relief devices, with reference to the so-called “tempered” systems in which pressure and temperature are reciprocally correlated by the law of variation of the vapour pressure of the solvent (that is water in our case). For relief area evaluation we used the equation suggested by Leung supposing a two-phase homogeneous discharge flow (HEM). For determining the specific flow, including the reduction effect due to the pipe downstream the relief device, we used the “ω method” by the same Author. For the calculation of the reduction coefficient, which corrects the expression of flow through an ideal nozzle, we worked out some approximate simplified formulas, which apply to the most customary discharge configurations. An account follows of performed tests and used apparatuses, with the consequent working out of the results to obtain the thermokinetic constants (DH, E, K) characterizing the reaction of phenolic resins formation with basic catalysis. In particular we evaluated the influence of a variation of catalyst concentration around the values of normal use. At last we worked out a complete and detailed numerical example, studying the influence on the relief area both of rupture disk set pressure and reactor maximum allowable pressure, and of the possible inaccuracy which affects one of the thermokinetic parameters (DH). The example includes the evaluation of the thrust exerted on the discharge pipe and the preliminary sizing of the most suitable containment system for the emission. A mention is also made of the useful precautions to prevent or contain the quick temperature rise and so to avoid the rupture disk intervention.