Process intensification Safety

Minimization goes much further than storage, however. For many processes the largest inventory of hazardous materials is in the reactor. If, through radical reactor design, inventories and equipment size can be reduced whilst throughput is maintained, then this presents opportunities for improved safety and possibly reduced capital costs. This is the concept behind Process Intensification which is discussed more fully below. 

The philosophy of process intensification has been traditionally characterized by four words smaller, cheaper, safer, slicker. And indeed, equipment size, land use costs, and process safety are among the most important PI incentives. But process intensification can (and should) also be placed in a broader context—the context of sustainable technological development. Several years ago DSM published a picture symbolizing its own vision of process intensification (32), in which skyscraping distillation towers of the naphtha-cracking unit are replaced by a compact, clean, and tidy indoor plant (see Figure 3). The importance of PI for sustainable development and its role in the company s responsible business has been further stressed in a recent publication by the company s CEO, Peter Elverding (33). Here,... 

From this general philosophy of process intensification follow concrete opportunities that PI offers to chemical enterprises, as shown in Figure 4. These opportunities exist primarily in four areas costs, safety, time to market, and company image. 

Process intensification drastically increases the safety of chemical processes. It is obvious that smaller is safer. In Table 2 some of the more severe chemical disasters of the past century are listed. The table shows clearly how disastrous consequences may arise from the large inventories when something goes wrong. And of course, one may not claim that process intensification would have prevented all those tragedies. Yet a study done at AIChE showed that methyl isocyanate (MIC),... 

Examples of strategies for safe designs are prevent large volumes, intensify contact, reduce the need for aids (like solvents), use little intermediate storage. One can immediately see the similarities between intrinsically safe design and process intensification. This also means that applying process intensification techniques is beneficial for process safety. 

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. 

Because the material inventory is considered in these indices, process intensification will result in a lower value (greater safety) for either index. However, the indices do also consider other factors, such as temperature and pressure, that... 

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. 

Figure 3.3 PI provides radically innovative principles in process and equipment design that can benefit process and chain efficiency, capital and operating expenses, quality, wastes, process safety and more, and align perfectly with the Triple-P philosophy of sustainable industrial chemistry. Source adapted from EU Roadmap for Process Intensification (www.creative-energy.org).

Basically, process intensification aims at replacing large, expensive, energy-intensive equipments or processes with ones that are smaller, cheaper and more efficient. At the same time, they have to minimize environmental impact, increase safety, improve remote control and automation and ensure a better product quality. 

Undoubtedly, this new kind of integrated approach is well representative of what should be membrane engineering, with final objectives clearly defined, the right hypothesis and choice of simple equations for modeling, a realistic representation of real complex solutions and the set-up of efficient simulation tools involving successive intra- and extrapolation steps. It appears to be easily extended to other membrane operations, in other fields of applications. It should provide stakeholders with information needed to make their decision costs, safety, product quality, environment impact, and so on of new process. Coupled with the need to check the robustness of the new plant and the quality of final output, it should constitute the right way to develop the use of membranes as essential instruments for process intensification with industrial units at work. 

Micro-processing will be another paradigm. Micro-reactors, micro-heaters, microexchangers and the lab-on-a-chip will be developed to provide industrial scale production, especially for liquid and gaseous phase reactions. Process intensification will also offer new opportunities for industrial safety and pollution control [3],... 

These hmitations, which are associated with the use of molecular oxygen, might be overcome by the use of microreactor technology [7-15]. Due to their small inner dimensions, microreactors provide both high safety and enhanced process intensification [16-18]. The high surface-to-volume ratio properties of microchannels (inner diameter 100-1000 pm) are highly beneficial, especially for multiphase reactions. In addition to enhanced gas-hquid interfacial transfer, intense recirculation within the hquid slugs allows for fast renewal of the interfaces... 

The selection of a reactor, from those described above as an alternative to the STR, depends on the heat reaction, the nature of the phases involved and the rate of production. The safety, reliability, energy consumption and cost have to be considered. The volumetric heat- and mass-transfer coefficients can be viewed as measures of process intensification. The attainable coefficients in the reactors dictate the yield, selectivity and size reduction. 

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... 

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