(47al) Inherently Safer Design Of Stirred Reactors and Visimix® Modeling Software

Stirred reactors are widely used for chemical process industry (CPI) and characterized by extremely diverse ranges of parameters (such as temperature, pressure, heat release/consumption) that, furthermore, vary substantially over time during each batch operation.  A wide variety of design solutions are necessary to accommodate this diversity, and any inadequacy of these design solutions to process requirements creates a risk of accidents caused by deviation of process parameters from their nominal specifications.  Therefore, software supporting real-time evaluation of current reactor and mixing device parameter adequacy to process requirements would be an essential tool for inherently safer design (ISD) of the corresponding chemical reactor/chemical process system.  This paper demonstrates an approach to creating such a tool for safety enhancement using VisiMix® software that combines computer simulations with expert assessments for various processes in stirred reactors governed by mixing.  Specifically, this software is capable to (i) utilize results of computer modeling for revealing inability of a particular mixing device to satisfy critical requirements of the process and (ii) generate respective messages alerting engineers on occurrence of potentially hazardous conditions.

In this paper, we demonstrate application of VisiMix® to ISD for a process where an available stirred reactor in used to run an exothermal two-stage reaction with solid catalyst, which includes (i) pre-heating that initiates the reaction, and (ii) subsequent cooling that removes heat generated during the reaction.

Predictive computer simulations for the reactor enable us to complete the following two tasks:

First, we evaluate degree of non-uniformity for solid catalyst concentration in the reactor and verify compliance with the critical requirement for mixing: prevention of solid particle sedimentation to the tank bottom that would cause local overheating and, in turn, can trigger a runaway reaction.  This hazard would be further exacerbated by clogging of the bottom outlet pipe by solid particles and, therefore, making emergency unloading virtually impossible.

Second, we define duration of and temperature restrictions for both the pre-heating and cooling reaction stages in order to obtain required product quality and prevent the runaway reaction.

VisiMix® potential at an ISD tool is clearly demonstrated through predicting hazardous situation and finding technical solution that prevents potential risks.