Maloperation scenario

The same concept can also be transferred to any other maloperation scenario. For instance, the same diagram can be supplemented by a curve representing the effect of a different concentration and the additional occiurence of a cooling failure. For this purpose the corresponding MTSR curve must be calculated for a different Da -value and the related adiabatic temperature increase value and subsequently compared with the original curve. 

Fig. 4-85. Classes of maloperation scenarios for the BR with increasing criticality according to Stoessel [75]...

This very plausible and easy to follow approach to an evaluation of a cooling failure scenario for the batch reactor can in numerous ways be transferred to other reactor types as well as the assessment of the consequences of other maloperation scenarios. 

However, if the thermokinetic evaluation procedure is applied, which was explained in Section 4.3.3.3, very reliable kinetic models can be obtained from adiabatic measurements. The parameters thus determined can reliably be used for the prediction of the reactor behaviour in other maloperation scenarios. In a first approximation, other adiabatic induction times may be estimated with the help of the following equation... 

The procedure to determine both the basis of safety for the reactor (see Annex 1) and the worst case scenario for that basis of safety is iterative. The same screening tests which help determine the worst case for pressure relief sizing may lead to the conclusion that pressure relief is not the best basis of safety. The results of screening tests may also indicate that it is worthwhile to seek a more inherently safe solution by designing out the possibility of certain maloperations or system failures (for example, if the screening indicates that a very large relief system would be required). 

At this stage, a number of credible maloperations will have been defined that can lead to vessel over-pressurisation. In order to cope with all the credible runaway scenarios, the relief system will need to be sized for the "worst case runaway" reaction that can occur, and this is normally the maloperation that will give rise to the highest rate of temperature and/or pressure rise over the relief range. 

For the purposes of the Workbook, the worst case scenario is the credible combination of equipment failures and maloperations that gives rise to the largest calculated relief size compared with other credible scenarios. See Chapter 3. The worst case scenario is the basis for the relief system design. 

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