Process vents, equipment safety

The safety criteria for a forging operation is the next section. Operation, inspection, and maintenance requirements are covered. The requirements for venting special processes and equipment that needs to be guarded are included. 

Although the ethyleneamines ate water soluble, soHd amine hydrates may form at certain concentrations that may plug processing equipment, vent lines, and safety devices. Hydrate formation usually can be avoided by insulating and heat tracing equipment to maintain a temperature of at least 50°C. Water cleanup of ethyleneamine equipment can result in hydrate formation even in areas where routine processing is nonaqueous. Use of warm water can reduce the extent of the problem. 

Noronha, J. A., R. J. Seyler, and A. J. Torres, "Simplified Chemical and Equipment Screening for Emergency Venting Safety Reviews Based on the DIERS Technology," in Proceedings of the International Symposium on Runaway Reactions, Center for Chemical Process Safety/AIChE, New York, NY (1989). 

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... 

If the plant safety shutdown is not rapid enough and an overpressure situation develops, then the pressure relief system is activated. Pressure vessel design codes such as the ASME Boiler and Pressure Vessel Code require relief devices to be fitted on all pressure vessels (see Section 13.17). If the relief system has been properly designed and maintained, then in the event of an overpressure incident, the plant contents will be vented via relief valves or bursting disks into the relief system, where liquids are recovered for treatment and vapors are sent to flare stacks or discharged to the atmosphere if it is safe to do so. The pressure relief system should allow the plant to be relieved of any source of overpressure before damage to process equipment (leaks, bursting, or explosion) can occur. 

The process requirements for both temperature and pressure should also be evaluated against the production equipment capabilities as part of the production equipment assessment. Normal operating conditions are used as a base case, but upset conditions should also be included as part of the evaluation. If venting is chosen to control unintended reactions, vent sizing calculations must be performed and peripheral equipment selected as needed. Experiments and simulations to determine consequences of unintended reactions and the interpretation of these experiments are documented as part of the production process safety review. 

Liquid drains, manifolded and taken to a heater for vaporizing, process safety valves, vents and thaw lines, together with the major casing vents, all culminate in a vent stack to the atmosphere. This stack should have its exit point well above surrounding equipment to prevent it from being a hazard to personnel in the event of a fire. A continuous flow of nitrogen at a velocity of 1 ft/sec can be supplied at the bottom of the vent stack to blanket all process and casing equipment from air. A check valve placed in this line provides added protection. 

P IDs show all the process lines in a unit, including valves, material specs, and insulation detail. The P ID may or may not include minor piping such as vent and drain lines and tubing. They provide a pictorial representation of all equipment, instmmentation, and piping in a facility. They are crucial documents in almost all types of safety study and analysis. 

Relief valves are designed to respond automatically to sudden increases in pressure. A relief valve opens at a predetermined pressure. In a relief valve, a disc is held in place by a spring that will not open until system pressure exceeds its operating limits. Tremendous pressures can be generated in process units. When a system overpressurizes, safety valves respond to allow excess pressure to be vented to the flare header or atmosphere. This prevents damage to equipment and personnel. Relief valves are designed to open slowly, and thus are best for pressurized liquid service. They do not respond well in gas service, where quicker pressure reduction is needed. 

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