Chemical plant design explosions

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 ha2ard 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 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). 

More detailed check lists are given by Carson and Mumford (1988) and Wells (1980). Balemans (1974) gives a comprehensive list of guidelines for the safe design of chemical plant, drawn up in the form of a check list. A loss prevention check list is included in the Dow Fire and Explosion Index Hazard Classification Guide, Dow (1987). 

Process industry has used the Dow Fire and Explosion Hazard Index (DOW, 1987) and the Mond Index (ICI, 1985) for many years. These indices deal with fire and explosion hazard rating of process plants. Dow and Mond Indices are rapid hazard-assessment methods for use on chemical plant, during process and plant development, and in the design of plant layout. They are best suited to later design stages when process equipment, chemical substances and process conditions are known. 

The chemical reactor is the most hazardous unit in any chemical plant because most accidents occur by uncontrolled reaction, either within the reactor or after reactants have escaped the reactor and perhaps reacted with oxygen in air. Obviously no reactor or piping can withstand the temperatures and pressures of total combustion unless designed specifically for these conditions. We will consider the energy balance and temperature variations in continuous reactors in more detail in Chapters 5 and 6, while flames and explosions will be considered in Chapter 10. 

In the propellant field new chemical engineering designs were being evolved to improve economics and safety safety was particularly important in the case of NG which has had the dubious record of at least one major explosion per year since manufacture started (2). The Schmid continuous process (15), the first successful continuous process which appeared in 1927, was installed at Holton Heath and was adopted also for the Ransldll plant. 

Any process heat plant design implies piping through the containment to connect the reactor vessel with the chemical plant. The fracture of a pipe could result in the accumulation of a flammable gas mixture in the containment. Precautions must be taken to minimize the risk of a fire or gas explosion such as avoidance of explosive gas ingress, proper detection devices, inerting, sufficient safety distances, appropriate layout of secondary coolant boundary, explosion-proofed wall, plant isolation valve. For the PNP-500, the use of two concentric pipes for the process gas carrying lines were recommended. Alternatives are concrete channels around the gas lines or inerting of the containment [10]. 

It is hardly affordable to design the entire plant for the worst-case scenario. Therfore, a chemical plant is divided into different explosion-hazard zones (Table 2.9-2). 

This paper will focus upon Germany s - and to a lesser extent, Austria s -wartime experience. The story is a familiar one of military unreadiness and belated administrative leadership, coupled with a less familiar history of industrial flexibility in plant design and apparatus, a capacity to survive losses of raw materials and intermediates, and an ability to improvise and innovate in a domain of chemicals needed for explosives production. The war was also to expose stark contrasts between Germany s privately-owned research-intensive dyestuffs industry, and the less sophisticated Austrian chemical industry, in which state-owned or controlled factories played a dominant but less efficient role. 

Whilst operational (fire and explosion) hazards are not the main subject of this guide. Chapter 7 discusses them in outline. Such hazards arise when, for example, a flammable gas mixture is present at the same time as a source of ignition. It is important to understand how the plant design interacts with the chemical process. 

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