Operations area classification

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. 

Examples of electrical area classification for various operations... 

The European philosophy on area classification varies from that of the United. States and Canada. Specifically, in Europe and most other inter national areas, the Zone concept is utilized. An area in which an expio sive gas-air mixture is continuously present, or present for long perioiK of time, is referred to as Zone 0. The vapor space of a closed, but vented, process vessel or storage tank is an example. An area in which an explosive gas-air mixture is likely to occur in normal operations is designated Zone 1. An area in which an explosive gas-air mixture is less likely to occur, and if it does occur will exist only for a short time, is designated Zone 2. Zone 0 and Zone 1 correspond to Division 1 in the U.S. and Canada System. Zone 2 is equivalent to Division 2. 

Electrical switches, relays, and other devices are described for safety reasons by several general categories. Since these devices are potential sources of ignition during normal operation (for example, arcing contacts) or due to malfunction, the area classification limits the types of devices which can be used. 

Room classification tests in the at-rest condition should be carried out with the equipment operating where relevant, but without any operators. Because of the amounts of dust usually generated in a solid dosage facility most clean area classifications are rated for the at-rest condition,... 

These engineers do not normally contribute any power consumption data, but their input to the work of the electrical engineer is to advise on subjects such as equipment layout, access to equipment, maintainability, maintenance lay-down space, emergency exit routing, operational philosophies of plant and systems, hazardous area classification. 

Review of surrounding plants/facilities Existing pipe racks Maintenance and operations access Sewers and storm water drainage Existing fire and radiation circles Hazardous chemical releases from upwind locations Existing electrical area classification Close access to substations... 

For Case 2, each DVP requires 72.66 kWh of electricity, and operating cost savings due to this modification are US 257 801/year. Installed cost of two DVPs, based on vendor quotation, is US 400 000. So, payback period for this retrofit modification is 1.6 years. Thus, replacing the existing SJEs by DVPs is attractive for low capacities and non-hazardous applications such as a steam turbine s surface condenser vacuum system. DVPs are efficient, they require less electricity and so modification required at the substation is minimal. They are very compact and can be installed at ground level or on elevated platforms. Depending on the area classification of their location, explosion-proof motors may be required. 

Pumps are essential to the successful operation of a solvent storage tank. All pumps should be located in open areas outside the bunds, on an impervious base, such as concrete, and at least 4 m from buildings, boundaries and sources of ignition. Clearly the characteristics of the motor must match the flash point of the solvent and the area classification operating at the point of location. 

In all cases, the need for intrinsic safety barriers must be evaluated. Instrumentation must conform with the electrical classification of the operating area. 

Documentation during classification procedure The general documentations during area classification shall include but not be limited to the following. These are mainly based on ATEX directives but are generally applicable to others Identification of person responsible Stmctural and geographical details about plant site Description of process and operational details Material data... 

Many of the decisions to do with safe operations and maintenance depend on the area classification systems that is being used. Area classification is primarily to do with the design of electrical systems. However, the guidance provided can be used whenever flammable materials are present, regardless of the potential sources of ignition. Therefore, an overview of the topic is provided here. 

Processing costs include those for size reduction, size classification, minerals concentration and separations, soHd—Hquid separation (dewatering), materials handling and transportation, and tailings disposal. Size reduction, one of the most expensive unit operations in minerals processing, could account for as much as 50% of the total energy consumed. This cost varies considerably from deposit to deposit and quite often from one area of a deposit to another. Ore bodies are extremely heterogeneous and the associated minerals Hberation, complex. 

The selection of the motor enclosure type involves not only economics but also assessment of two factors area hazard classification and other area operation conditions. 

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