Process equipment enclosures

Combined construction, process-related, and ventilation measures include air locks between two zones (Fig. 7A09f) and process equipment enclosures with air exhaust from the enclosures (Fig, 7.109g). 

The effect of turbulent exchange l>etween the contaminated air in the process equipment enclosure and the room air (Fig. 7.11 lb) is described by Elter-nian. According to Elterman, the air velocity in the process equipment enclosure opening assuring contaminant concentration Q at the distance / from the opening can be calculated from... 

Instrumentation, controls, valves and chemical addition points should be located, as much as practicable, outside the process equipment enclosures unless the anticipated radiation level within the enclosure is not signiEcant. 

A. B. Shuck and R. M. Mayfield, The Process Equipment and Protective Enclosures Designedfor the Fuel Fabrication Facility, Facility No. 350, ANL-5499, Argonne National Laboratory, Argonne, lU., 1956. 

The compressor or blower installation in a typical refinery or chemical process unit is not out-of-doors completely. Some form of shelter often is provided, ranging from only a roof to a completely closed building. When process equipment such as a centrifugal gas compressor, which is not hazardous in normal operation, is present in the shelter, the hazard classification depends on the extent to that which the shelter restricts ventilation. The extent of the shelter provided determines the area classification and the type of motor enclosure that should be applied. 

Air curtains are local ventilation devices that are used in industrial buildings to reduce leakage of airflow through apertures in building enclosures and process equipment. Their operation is based on the damping effect of air jets that are supplied into the area of the open aperture. The advantages of air curtains include... 

Except for conduit or cable entries into explosion-proof enclosures containing arcing or high-temperature devices (as described in Item I above), cables that will leak gas through the core at a rate of less than 0.007 ft /hr at 6 in. of water pressure need not be sealed if they are provided with a continuous gas/vapor-tight sheath. Cables with such a sheath that will transmit gas at or above this rate must be sealed if connected to process equipment that may cause a pressure of 6 in. of water at the cable end. 

Exposure to dust or other pollutants that may exist in certain industrial processes will dictate requirements for such aspects as equipment enclosures and air filtration. For the same reasons, it may be prudent to avoid air-cooled heat transfer surfaces. 

A confined explosion occurs when there is a rapid combustion of a fuel and an oxidizer inside an enclosure (e.g., building, vessel, or duct), developing sufficient pressure to cause the enclosure to rupture. Examples of confined explosions include gas or dust explosions inside buildings, storage tanks, or process equipment. 

Process equipment and ancillary support or utility equipment are often placed in either partial or complete enclosures for ... 

Where there is exposure from surrounding flammable or combustible process equipment, external fire protection of the enclosure may be needed, based on the importance or value of the protected equipment or instruments. In addition, the interior of the enclosure may require electrical classification, unless the enclosure is purged or pressurized as described in NFPA 496. 

Applications. The kinds of motors that are being used successfully with particular kinds of. chemical process equipment are identified in Table 4.1. As many as five kinds of AC motors are shown in some instances. The choice may be influenced by economic considerations or local experience or personal preference. In this area, the process engineer is well advised to enlist help from electrical experts. A checklist of basic data that a supplier of a motor must know is in Table 4.2. The kind of enclosure may be specified on the last line, operating conditions. 

Medical Sources. All medical encapsulations are done in a facility which consists of a series of five interconnected stainless steel boxes which provide primary containment of process equipment and materials. Interconnections include transfer ports, drop-through tubes, and ventilation ducts. Each containment enclosure has a floor area of 1.52 m x 0.91 m the floor level is 0.76 m above the building floor. A pair of master-slave manipulators serve each containment box. A closed circuit television system and a telescope are provided for close-up viewing of incell operations and can be moved from cell to cell as needed. General arrangement of the facility is shown in Figures 13 and 14. 

There are two types of process equipment to feed hypochlorite solution (a) basic system and (b) complex systems. Both basic and complex systems are electrically and hydraulically activated. The basic liquid hypochlorination systems include two metering pumps (one serving as a standby), a solution tank, diffuser, and appropriate quantities of tubing. The more complex system adds a diffuser corporation cock, antisiphon backflow preventer, a safety housing enclosure, a flow pacing system, and a flow meter and signal. 

Secondary containment serves to provide a back-up in the event of failure of the primary barrier and most commonly takes the form of a physical enclosure, although secondary containment can also be achieved by engineering improvements to the primary containment unit itself." Some do not make this distinction between primary and secondary containment, describing both as primary containment." However, in our opinion it is important to distinguish between the inherent containment properties of process equipment and those features that need to be added in order to cope with the failure of primary containment barriers. 

It is significant that manufacturers increasingly are seeking to incorporate containment features into the design of process equipment such that physical enclosure may not be necessary, except at the highest containment levels. Particular examples of containment design for centrifuges and cell disruptors are described elsewhere in this book (see chapter 9) but the... 

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

Understanding of the technological process and identification of subprocesses are essential for proper ventilation design, especially when designing process ventilation but also in enclosure air technology. The purpose of process description is to identify possible emission sources, occupational areas, the effects of environmental parameters on production, needs for enclosure and ventilation equipment, etc. One purpose is to divide the process into parts such that their inputs and outputs (e.g., process, piping and duct connections, electricity, exposure) to environment can be defined. Parts here can he different departments, and inside them, subprocesses. See Fig. 3.4. 

The more enclosed a process is, the easier it is to keep a low concentration in the workroom. It is usually necessary for the workers or for some equipment to have physical contact with the process, w hich could make it difficult to use complete enclosures. If it is possible to enclose the contaminant source and the tool, a total enclosure is recommended, especially if the workers only need to access the process during pauses in operation. Total enclosures may also be necessary for processes that generate highly toxic contaminants. Where total enclosures are not practicable, partial enclosures may be used. F xterior hoods are the least effective exhaust hood. 

Figure All Purged enclosure for operation of laboratory HPLC equipment in process area.

A laminar flow enclosure provides a means for environmental control of a confined area for aseptic use. Laminar flow units utilize HEPA filters, with the uniform movement of air along parallel lines. The air movement may be in a horizontal or vertical direction and may involve a confined area, such as a workbench, or an entire room. Laminar flow modules are suspended above filling lines, vial- and stopper-washing equipment, and other processes to provide an aseptic and particulate-free environment. 

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