Reactor vent size design

This chart was prepared to be a guide to insurance inspectors and not a design technique. Experience indicates, however, it is often used by designers to estimate a reactor vent size. 

Many methods have been used to size relief systems area/volume scaling, mathematical modeling using reaction parameters and flow theory, and empirical methods by the Factory Insurance Association (FIA). The Design Institute for Emergency Relief Systems (DIERS) of the AIChE has performed studies of sizing reactors undergoing runaway reactions. Intricate laboratory instruments as described earlier have resulted in better vent sizes. 

Boyle [15] and Huff [16] first accounted for two-phase flow with relief system design for runaway chemical reactions. A computer simulation approach to vent sizing involves extensive thermokinetic and thermophysical characterization of the reaction system. Fisher [17] has provided an excellent review of emergency relief system design involving runaway reactions in reactors and vessels. Fauske [18] has developed a simplified chart to the two-phase calculation. He expressed the relief area as ... 

In 1967 a paper by Boyle IJ provided a more quantitative method for designing vents for polymer reactors. It was based on reaction rate, heat of reaction, and vapor pressure data. Boyle assumed that the venting of a system can be approximated by sizing to discharge the entire batch contents as a liquid. 

For steady-state design scenarios, the required vent rate, once determined, provides the capacity information needed to properly size the relief device and associated piping. For situations that are transient (e.g., two-phase venting of a runaway reactor), the required vent rate would require the simultaneous solution of the applicable material and energy balances on the equipment together with the in-vessel hydrodynamic model. Special cases yielding simplified solutions are given below. For clarity, nonreactive systems and reactive systems are presented separately. 

The vent was sized for the peak batch requirement of displacement from the reactor during the initial reaction boil-up. For the remainder of the reaction and ECH distillation stages, the design basis was no normal flow . 

The two-step system design shown in Figure 21.5c is used when 90% recovery of hydrocarbons from the vent gas is not enough, and a higher recovery of hydrocarbons is desired. In the example calculation shown, the recovery is 99%. Two membrane units are used in series. The permeate from the first membrane step is recycled to the reactor, and the permeate from the second membrane step is recycled to the front of the first step. To minimize mixing losses, it is desirable to size each membrane unit so that the second-step permeate... 

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