Inherent safety intensification

Table 5 illustrates inherent safety parameters and the selection of them by Edwards and Lawrence (1993) and Heikkila et al. (1996). E.g. inventory has been chosen by both. It is relative to the capacity of a process and residence times (hold-up s) in vessels. It has a large effect on the degree of hazard and it should be kept small by intensification. 

Additional discussion and more examples of these strategies can be found in books by Kletz (6) and CCPS (4,5). The remainder of this discussion will focus on minimization (process intensification) as an inherent safety strategy. 

A single-number overall index characterizing the inherent safety of the overall process is generated by both proposed inherent safety indices. Process intensification will lower the value of the index (indicating an inherently safer process) because it will reduce the penalty for inventory. If the alternative process results in an increase in the inherent hazard due to other factors, the index will be useful in understanding the inherent safety characteristics of the different alternatives. The relative contributions of the various components of the index to the total value may also be useful in understanding process safety characteristics. Table 3 summarizes the application of this proposed inherent safety index to a number of alternative routes for the manufacture of methyl methacrylate. 

However, the integration of PIM also creates synergy in the development of intensified processes, novel product forms, and size dependent phenomena, which in turn provides novel intensified processes. Process intensification-miniaturization is seen as an important element of sustainable development because it can deliver 1) at least a 10-fold decrease in process equipment volume 2) elimination of parasitic steps and unwanted by-products, thus eliminating some downstream processing operations 3) inherent safety because of reduced reactor volume 4) novel product forms 5) energy, capital, and operating cost reduction, and an environment friendly process 6) plant mobility, responsiveness, and security and 7) a platform for other technologies. 

Although there are many advantages of applying process intensification, there are some aspects that will invariably need to be managed. Some of these issues to be managed are a potential for decreased inherent safety as there will be less incentive to ehminate hazardous materials, given that the inventories are minimized a potential for reaction runaway if heat transfer is not sufficient, given a reduction of solvent used a potential for... 

Green chemistry has introduced several new terms and new research frontiers, including "eco-efficiency," "sustainable chemistry," "atom efficiency or economy," "process intensification and integration," "inherent safety," "product life-cycle analysis," "ionic liquids," "alternate feedstock," and "renewable energy sources."... 

The primary philosophy is to follow the principles of inherent safety. This implies a systematic effort to apply the principles of hazard elimination, minimization/ intensification, hazard substitution, moderation/attenuation, and simplification. However, additional controls will still be required to control a hazardous situation, prevent escalation, and mitigate the risk to people, to the environment, asset, and reputation. Preferably, these safeguards will be passive- or active-engineered controls rather than administrative controls (i.e., dependent on direct human intervention). 

The best way to deal with a hazard in a flowsheet is to remove it completely. The provision of safety systems to control the hazard is much less satisfactory. One of the principal approaches to making a process inherently safe is to limit the inventory of hazardous material, called intensification of hazardous material. The inventories we wish to avoid most of all are flashing flammable liquids or flashing toxic liquids. 

Many of the incidents in this book were the result of leaks of hazardous materials, and the recommendations describe ways of preventing leaks by providing better equipment or procedures. As we have seen, equipment can fail or can be neglected, and procedures can lapse. The most effective methods, therefore, of preventing leaks of hazardous materials are to use so little that it hardly matters if it all leaks out (intensification or minimization) or to use a safer material instead (substitution). If we cannot do this and have to store or handle large amounts of hazardous material, we should store or handle it in the least hazardous form (attenuation or moderation). Plants in which this is done are said to be inherently safer because they are not dependent on added-on equipment or procedures that might fail the hazard is avoided rather than controlled, and the safety is inherent in the design. 

Many of the advances required for development of practical alternatives to today s chemicals and chemical processes are fundamental and pre-competitive. The economic incentives for industrial funding are frequently absent, which leads to the need for either a government investment in research or government-provided financial incentives for industrial investments. Inherently safer chemistry, such as process intensification, just-in-time chemical manufacturing, and the use of smaller-scale processes, offers the potential for improved safety at chemical facilities. While applications show promise and have found use within the chemical industry, these applications at present are stiU quite limited in scope. 

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