Chemical plant design hazardous material

The concept of inherently safer plant has been with us now for many years. But in spite of its clear potential benefits related to safety, health and the environment (SHE), as well as the costs, there has been few applications in chemical plant design. But as Kletz (1996) has written there are hurdles to be overcome. Inherently safer design requires a basic change in approach. Instead of assuming e.g. that we can keep large quantities of hazardous materials under control we have to try and remove them. Changes in belief and the corresponding actions do not come easily. 

Often, chemical plant design is informed by laboratory and pilot-scale experimentation. While the initial chapters in this book will inform the reader of the most important design parameters that need to be measured and determined from such experiments, how to then ensure that these parameters perform in the same way in a large-scale plant is the subject of Chapter 6. Although it is desirable to conduct the experimental work in the system for which the results are required, this is not always easy. The system of interest may be hazardous or expensive to build and run, while the fluids involved may be corrosive or toxic. In this case scale models are used, which overcome the above problems and allow extensive experimentation. In the majority of cases the model will be smaller in size than the actual, desired plant, but sometimes, due to the nature of the materials to be handled, the fluids involved may also be different. Scale-up is only possible if the model and plant are physically similar and, hence, the procedure is based on dimensionless groups. How to develop and use these groups is described in Chapter 6. 

Raw material and in-process storage tanks and pipelines often represent a major portion of the risk of a chemical plant. Attention to the design of storage and transfer equipment can reduce hazardous material inventory. 

The first step in minimizing accidents in a chemical phuit is to evaluate the facility for potential fires, explosions, and vulnerability to other liazards, particularly those of a chemical miture. This calls for a detailed study of plant site and layout, materials, processes, operations, equipment, and training, plus an effective loss prevention program. The technical nature of industry requires detailed data and a broad range of experience. Tliis complex task, today becoming the most important in plant design, is facilitated by the safety codes, standiu ds, and practice information available. The technical approach to evaluating die consequences of hazards is discussed later in tliis cliapter and in Part V (Chapters 20 and 21). 

All chemicals to be handled in a process plant must be evaluated during the design phase. Once an accident lias occurred, knowledge of properties of any hazardous materials will allow appropriate handling. 

Fire and Explosion Prevention. Prevention of fire and explosion takes place in the design of chemical plants. Such prevention involves the study of material characteristics, such as those in Table 1, and processing conditions to determine appropriate hazard avoidance methods. Engineering techniques are available for preventing fires and explosions. Containment of flammable and combustible materials and control of processes which could develop high pressures are also important aspects of fire and explosion prevention. 

The technical part of the feasibility study considers the alternative processes, and the equipment that constitutes the chemical plant in each case. At this stage it is necessary to identify any items of equipment that pose particular or unusual design problems, or which are very expensive or hazardous. The feasibility study should determine whether it is possible to design and build a chemical plant for a particular manufacturing process. Any external factors that may influence the operation of the plant should be noted, e.g. discharge levels, stability of raw materials supply, etc. 

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