Process equipment design safety

Introduction Review and audit processes are used in the chemical process industry to evaluate, examine, and verify the design of process equipment, operating procedures, and management systems. These processes assure compliance with company standards and guidelines as well as government regulations. Reviews and audits can encompass the areas of process and personnel safety, environmental and industrial hygiene protection, quality assurance, maintenance procedures, and so on. 

For any proposed suppression system design, it is necessary to ascribe with confidence an effective worst-case suppressed maximum explosion overpressure Pred.max- Provided that the suppressed explosion overpressure is less than the process equipment pressure shoclc resistance and provided further that this projected suppression is achieved with a sufficient margin of safety, explosion protection security is assured. These two criteria are mutually independent, but both must be satisfied if a suppression system is to be deployed to provide industrial explosion protection. 

CCPS G-39. Guidelines for Design Solutions for Process Equipment Eailures. American Institute of Chemical Engineers, Center for Chemical Process Safety, New York. 

Guidelines for Design Solutions to Process Equipment Eailures Safety (1997)... 

When designing a plant, every piece of process equipment should be specified as large enough to do its job, and no larger. We should minimize the size of all raw material and in-process intermediate storage tanks, and question the need for all in-process inventories, particularly of hazardous materials. Minimizing the size of equipment not only enhances inherent process safety, but it can often save money. 

To develop a safe design, it is necessary to first design and specify all equipment and systems in accordance with applicable codes and standards. Once the system is designed, a process safety shutdown system is specified to assure that potential hazards that can be detected by measuring process upsets are detected, and that appropriate safety actions (normally an automatic shutdown) are initiated. A hazards analysis is then normally undertaken to identify and mitigate potential hazards that could lead to fire, explosion, pollution, or injury to personnel and that cannot be detected as process upsets. Finally, a system of safety management is implemented to assure the system is operated and maintained in a safe manner by personnel who have received adequate training. 

Because of the magnitude of the task of preparing the material for this new edition in proper detail, it has been necessary to omit several important topics that were covered in the previous edition. Topics such as corrosion and metallurgy, cost estimating, and economics are now left to the more specialized works of several fine authors. The topic of static electricity, however, is treated in the chapter on process safety, and the topic of mechanical drivers, which includes electric motors, is covered in a separate chapter because many specific items of process equipment require some type of electrical or mechanical driver. Even though some topics cannot be covered here, the author hopes that the designer will find design techniques adaptable to 75 percent to 85-1- percent of required applications and problems. 

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. 

During the plant design the safety of process equipment is also recognized by layout. The objectives of layout are to minimize risk to personnel, to minimize escalation (both within the plant and to adjacent plants), and to ensure adequate emergency access. It is also essential to ensure adequate access for maintenance and operations. Plant layout is a crucial factor in the safety of a process plant because of e.g. segregation of different risks, containment of accidents and limitation of exposure. Safe plant layout is designed on the basis of design... 

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. 

Rupture Disks A rupture disk is a non-reclosing device designed to function by the bursting of a pressure-retaining disk. This assembly consists of a thin, circular membrane usually made of metal, plastic, or graphite that is firmly clamped in a disk holder. When the process reaches the bursting pressure of the disk, the disk ruptures and releases the pressure. Rupture disks can be installed alone or in combination with other types of devices. Once blown, rupture disks do not reseat thus, the entire contents of the upstream process equipment will be vented. Rupture disks of nonfragmented type are commonly used in series (upstream) with a safety relief valve to prevent corrosive... 

Inherently design safety features at facilities provides for adequate spacing, arrangement and segregation of equipment from high hazard to low hazard. The least hazardous process systems should be used for obtaining the desired product or production objectives. Protective systems are provided to minimized the effects that may occur from a catastrophic incident. 

Relatively small marine vessel motions have a significant effect on the process equipment design. For example, three degrees of pitch can cause a forty percent Increase in gas velocity due to the spirit level effect, combinations of pitch and heave can cause resonant waves, further reducing the dedicated phase areas and causing primary turbulence roll and sway motions, although of lesser conse quence, add to turbulent fluid conditions Inside the vessel. In addition all motion adversely affect level control and level safety systems. 

In addition to the need to consider human reactions in designing plants, processes, and equipment, the chemical engineer always will be dealing with people in plant operations. In the chemical industry, most chemical engineers apply their skills in operations, management, safety, loss prevention, and other related activities. 

Factors relating to the safety of a chemical plant have so far been ignored. This is mainly because it is impossible to discuss all the aspects of plant design initially in a set of notes. The designer will obviously design items of equipment, and perform other tasks in process design, in... 

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