Process equipment safety considerations

This chapter covers safety considerations in design, installation, operation, and maintenance of selected process equipment and auxiliary systems. The first section (3.1) briefly discusses the impact of material selection on process equipment safety. Section 3.2 introduces the subject of corrosion and its control. The following more specific topics are then covered ... 

The plutonium extracted by the Purex process usually has been in the form of a concentrated nitrate solution or symp, which must be converted to anhydrous PuF [13842-83-6] or PuF, which are charge materials for metal production. The nitrate solution is sufficientiy pure for the processing to be conducted in gloveboxes without P- or y-shielding (130). The Pu is first precipitated as plutonium(IV) peroxide [12412-68-9], plutonium(Ill) oxalate [56609-10-0], plutonium(IV) oxalate [13278-81-4], or plutonium(Ill) fluoride. These precipitates are converted to anhydrous PuF or PuF. The precipitation process used depends on numerous factors, eg, derived purity of product, safety considerations, ease of recovering wastes, and required process equipment. The peroxide precipitation yields the purest product and generally is the preferred route (131). The peroxide precipitate is converted to PuF by HF—O2 gas or to PuF by HF—H2 gas (31,132). 

Process Safety Considerations. Unit optimization studies combined with dynamic simulations of the process may identify operating conditions that are unsafe regarding fire safety, equipment damage potential, and operating sensitivity. Several instances of fires and deflagrations in ethylene oxide production units have been reported in the past (160). These incidents have occurred in both the reaction cycle and ethylene oxide refining areas. Therefore, ethylene oxide units should always be designed to prevent the formation of explosive gas mixtures. 

The fine chemicals business is characterized by a small volume of products manufactured. Therefore, batch production predominates and small-scale reactors are used. The need to implement fine chemistry processes into existing multiproduct plants often forces the choice of batch reactors. However, safety considerations may lead to the choice of continuous processing in spite of the small scale of operation. The inventory of hazardous materials must be kept low and this is achieved only in smaller continuous reactors. Thermal mnaways are less probable in continuous equipment as proven by statistics of accidents in the chemical industries. For short reaction times, continuous or semicontinuous operation is preferred. 

Equipments handling supercritical fluids and liquefied gases present important hazards that must be taken into account both for equipment design and construction and for operation and maintenance. Safety considerations must influence any technical choice and operation and a detailed analysis of potential hazards must be specifically conducted for any case. In this paper, we would try to list the different classes of hazards and how to cope with them, so that both the process designer and the operator be informed. 

As plants age there is a need for increased maintenance on the process equipment to ensure continued operability. To ensure safe and reliable operation, the maintenance practices used must follow suggested vendor recommendations or be defined internally to address technical and safety considerations. The continued operability of chemical agent stockpile incineration facilities is dependent in part on the effectiveness of the maintenance systems to proactively address obsolescence in their procedures and practices and to modify systems as required to process severely degraded stockpile items. 

There are other engineering factors that affect the fire and explosion hazard, e.g., engineering standards of the structural steel and foundations, process equipment, heat exchangers, feeding system, fan and blowers, storage vessels, electrical equipment, instruments, and fire protection and safety equipment. Considerable assistance in design also can be obtained from relevant codes of practice. The responsibility for safe operation rests with the manufacturers of equipment and products as required by national law (e.g.. Factories Act and Health and Safety at Work Act in the United Kingdom). 

In several industries (automobiles, semiconductors), failure modes and effects analysis has been the technique of choice by design engineers for reliability and safety considerations. They are used to evaluate (a) the ways in which equipment fails and (b) the response of the system to those failures. Although an FMEA is typically made early in the design process, the technique can also serve well as an analysis tool throughout the life of equipment or a process. 

Ensuring that a high level of risk avoidance, elimination, or control is achieved in new or altered facilities and equipment requires considerable effort. Ideally, safety practitioners should be a part of, and influential in, the design processes the earlier, the better. More specifically, organizations need to work toward... 

In some localities, adherence to national codes such as the ASME (American Society of Mechanical Engineers) Boiler and Pressure Vessel Code (ASME, 1992) is mandatory. Selection of containers, tubing, fittings, and other process equipment, along with the operational techniques and procedures, must adhere to the constraints necessary for high-pressure service. The proper selection and assembly of components in a pressure system are critical safety factors. Compatibility of materials, tools used for assembly, and the reliability of connections are all key considerations. 

Developing procedures begins with an analysis of the tasks or activities of an operation. One can use various forms of task analysis. Involved processes and complex equipment may have applied advanced engineering analysis during development. Engineers may have used analysis to make cost estimates or production planning. Those analyses may help when working on safety considerations. 

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