Design process INDEX

It is worthwhile estimating the F El index at an early stage in the process design, as it will indicate whether alternative, less hazardous, process routes should be considered. 

In this thesis an Inherent Safety Index for conceptual chemical process design is presented. This is required, since inherent safety should be considered in the early phases of design when the major decisions on the chemical process are made. The presented methodology allows such a consideration since the index is based on the knowledge available in the preliminary process design stage. 

Edwards and Lawrence (1993) have developed a Prototype Index of Inherent Safety (PIIS) for process design. The inherent safety index is intended for analysing the choice of process route i.e. the raw materials used and the sequence of the reaction steps. This method is very reaction oriented and does not consider properly the other parts of the process even they usually represent the majority of equipment. 

Also indices such as the Dow Fire and Explosion Hazard Index and the Mond Index have been suggested to measure the degree of inherent SHE of a process. Rushton et al. (1994) pointed out that these indices can be used for the assessment of existing plants or at the detailed design stages. They require detailed plant specifications such as the plot plan, equipment sizes, material inventories and flows. Checklists, interaction matrices, Hazop and other hazard identification tools are also usable for the evaluation, because all hazards must be identified and their potential consequences must be understood. E.g. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop-study requires final process plans with flow sheets and PIDs. 

In the Chapter 7 the selected inherent safety parameters for conceptual process design were presented. From these parameters an inherent safety index is formed in this Chapter. There is a straight link between inherent safety principles and the inherent safety index as discussed earlier (see Figure 5). 

Process temperature for the Inherent Safety Index (ISI) is determined on the basis of the maximum temperature in the process area under investigation. This is feasible since in the early stage of process design preliminary estimates of temperatures and pressures are available. 

In this thesis an inherent safety index for evaluating inherent safety in preliminary process design was presented. The inherent safety of a process is affected by both chemical and process engineering aspects. These have been dealt separately, since the index was divided into the Chemical Inherent Safety Index and the Process Inherent Safety Index. These two indices consist of several subindices which further depict specific safety aspects. The Chemical Inherent Safety Index describes the inherent safety of chemicals in the process. The affecting factors are the heat of the main reaction and the maximum heat of possible side reactions, flammability, explosiveness, toxicity, corrosiveness and the interaction of substances present in the process. The Process Inherent Safety Index expresses safety of the process itself. The subindices describe maximum inventory, maximum process temperature and pressure, safety of equipment and the safety of process structure. 

Heikkila, A-M. Hurme, M. 1998a. Equipment Safety as a Part of Inherent Safety Index for Preliminary Process Design. Proceedings of 9th International Symposium (EFCE) Loss Prevention and Safety Promotion in the Process Industries, 4—8 May 1998, Barcelona, pp. 770-779. 

Swaney, R. E., and Grossmann, I. E., An index for operational flexibility in chemical process design. Part II Computational algorithms. AIChEJ. 31, 631 (1985b). 

The Dow Fire and Explosion Index (FEI) (12) and the Dow Chemical Exposure Index (CEI) (14) are two commonly used tools that measure inherent safety characteristics. Gowland (25) reports on the use of the FEI and CEI in the development of safety improvements for a urethane plant. Tables 1 and 2 illustrate the application of the FEI and CEI in measuring inherent safety characteristics of process design options. These indices measure the inherent safety characteristics of processes in only two specific areas—fire and explosion hazards and acute chemical inhalation toxicity hazards. Other indices would be required to evaluate other types of hazards. 

A process design is flexible if it can tolerate uncertainties in parameters and can handle disturbances. A flexibility index is a measure of the amount of uncertainty that can be tolerated with the desired process operation remaining feasible. A schematic of the flexibility index, 5, is shown in Fig. 8. Here, the two degrees of freedom represent uncertain parameters or disturbance variables, which have assumed upper and lower bounds. The feasible operating region lies within the cross-hatched area. The flexibility index is the fraction of the parameter range that still results... 

Predictive hazard evaluation procedures may be required when new and different processes, designs, equipment, or procedures are being contemplated. The Dow Fire and Explosion Index provides a direct method to estimate the risks in a chemical process based upon flammability and reactivity characteristics of the chemicals, general process hazards (as exothermic reactions, indoor storage of flammable liquids, etc.) and special hazards (as operation above the flash point, operation above the auto-ignition point, quantity of flammable liquid, etc.). Proper description of this index is best found in the 57-page Dows Fire and Explosion Index, Hazard Classification Guide, 5 th ed., AIChE, New York, 1981. 

Editorial support. Dirk De Weerdt text processing, correspondence, lay-out, figure design, index, cover design, cover illustration. Contact ddwdesign telenet.be... 

The DIPPR databases were developed in the United States by the Design Institute for Physical Properties of the American Institute of Chemical Engineers. The DIPPR projects are aimed at providing evaluated process design data for the design of chemical processes and equipment (www.aiche.org/TechnicalSocieties/ DIPPR/index.aspx). The DIPPR Project 801 has been made available to university departments see Rowley et al. (2004). 

Areas of application of reaction calorimetry include determination of calorimetric data for reactions and process design, for the kinetic characterization of chemical reactions and of physical changes, for on-line monitoring of heat release and other analytical parameters needed in subsequent process development as well as for the development and optimization of chemical processes with the objective, for instance, to increase yield or profitability, control the morphology or degree of polymerization and/or index of polydispersity, etc. 

D. R. Woods, Data for Process Design and Engineering Practice. Englewood Cliffs, NJ Prentice Hall, 1994. Gives order of magnitude values of properties for more than 1200 compounds and a guide to sources for more accurate data. This includes the PDEP Corrosion Index referred to in Table 13.16. 

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