Equipment Safety Subindex

For the Equipment Safety Subindex the process plant area is divided into two different areas, which have different safety properties. The onsite area is the area where the raw materials are converted into the products. This is referred as the inside battery limits area (ISBL). This area is characterized by large number of equipment and piping located in a concentrated way in a small area. The rest of the plant is referred as the offsite or outside battery limits area (OSBL). The offsite area is characterized by large inventories of fluids, which are often flammable and/or toxic. The number of equipment in OSBL area is smaller but their size larger than in the ISBL area. The layout is much more scattered in OSBL than in ISBL which is to enhance safety. 

For the generation of the equipment safety subindex the data discussed in the previous chapters were evaluated ... 

Table 23. The scores of Equipment Safety Subindex Ieq/ot ISBL. 

The Process Structure Subindex does not describe the safety of process items as such or their interaction through nonprocess route (i.e. through layout), since this is described by the Equipment Safety Subindex (Ch. 11.4). 

The chemical and most process factors affecting the index are quite straightforward to estimate. More problematic are the equipment safety and the safety of process structure. The equipment safety subindex was developed based on evaluation of accident statistics and layout information. The evaluation of the safe process structure subindex is based on case-based reasoning, which requires experience based information on accident cases and on the operation characteristics of different process configurations. 

The fitness function was based on the inherent safety index, which was simplified It was noticed that there are only minor differences in the safety properties of the compounds in the process. Therefore most subindices are the same for all configurations. The equipment type used in all the configurations is the same (i.e. distillation). Therefore the subindex of equipment safety is constant too. Also the safety of process structures is quite the same since the distillation systems used are rather similar in configuration. Therefore the subindex for process structure was not evaluated and case-based reasoning was not needed. 

In Eqs. [6.14] and [6.15] Me is the flow rate of chemical C Icj is the score of the chemical inherent safety subindex of chemical C Np is the number of equipment P and Ipi is the score of the process inherent safety subindex of equipment P. Again the dry grind process is found to be superior. In summary, it is observed that the dry grind process is superior to the wet milling process for aU three sustainability measures. 

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