Definitions used in Plant Layout Levels

This article is about definitions used for plant layout level in petrochemical industries. Every engineer must have knowledge of these definition and terms. We have collected large number of definitions to understand clearly.

Definitions for Plant Layout

1. Battery Limits. Exact definition is the boundaries of a process unit establishing outer limits for its equipment.
2. Boilover. The expulsion of crude oil or certain other liquids from a burning tank. The light fractions of the crude oil distill, burn off, and produce a heat wave in the residue, which on reaching a water stratum results in the violent expulsion of a portion of the contents of the tank.
3. Central Control House (CCH). A control house that controls a significant portion of a facility such that its loss would result in a major shutdown and/or adversely affect the safe shutdown of the facility during an emergency.
4. Dimensions. Measurements that apply to spacing between equipment, or from equipment to defined lines, and which are “edge-to-edge” dimensions (not “centerline” dimensions).
5. Fire Fighting Access. A clear path with at least one alternate secondary accessway for fire fighters or mobile equipment, or both, to safely enter or leave a fire area.
6. Fire Seal. A means of providing a liquid trap to prevent fire passage in a piping or drainage system. A fire seal provides 150 mm of submergence below the liquid level of an inlet or outlet pipe opening.
7. Fire Stop. A closed drain section at least 9 m long in an open drainage ditch, with a fire seal at the upper end.
8. Flammable and Combustible Liquids. Flammable liquids are those having flash points below 37.8 °C. Combustible liquids are those having flash points at or above 37.8 °C. When heated above their flash points, combustible liquids should be treated as flammable liquids. Detailed definitions of flammable and combustible liquids will be found in NFPA 30.
9. Flash Point. The temperature at which a liquid gives off vapor sufficient to form an ignitable mixture with air near the surface of the liquid or within a vessel as determined by the appropriate test procedure and apparatus (see NFPA 321):
   • The flash point of liquids having a viscosity less than 45 SUS at 37.8 °C and a flash point below 93.4 °C shall be determined in accordance with ASTM D56.
   • The flash point of liquids having a viscosity of 45 SUS or more at 37.8° and a flash point 93.4 °C or higher shall be determined in accordance with ASTM D93.
10. Foam. A stable aggregation of small bubbles of lower density than oil or water, which shows tenacious qualities in covering and clinging to vertical or horizontal surfaces. Foam flows freely over a burning liquid surface, forming a tough, air-excluding continuous blanket to seal volatile combustible vapors from access to air. Foam resists disruption due to wind and draft, or to heat and flame attack, and is capable of resealing in case of mechanical rupture.
11. Foam Concentrate. A foaming agent in concentrated liquid form, as received from the foam manufacturer.
12. Foam Solution. A homogeneous mixture of water and foam concentrate in the proper proportions.
13. Frothover. A steady, slow foaming of an oil-water-steam conglomerate over the tank rim, without fire. It is caused by the presence of water in a slop oil, hot oil, or asphalt tank.
14. High Hazard Chemical Process Class. Processes, operations or materials having a high explosion hazard and a moderate to heavy fire hazard. This class involves highly exothermic or potential runaway reactions and high hazard products handling. Examples include: Acetic acid, Acetaldehyde (oxidation), Acetone (cumene oxidation), Acrolein, Acrylic acid, Acrylonitrile, Butadiene, Caprolactum, Cumene hydroperoxide, Dimethyl Terephtalate, Ethylene, Ethylene oxide, Hydrocracking, Maleic anhydride, Methyl methacrylate, Phenol (cumene oxidation), Phtalic anhydride, Polyethylene LD (high pressure), Polyethylene HD (large units), Propylene oxide, Vinyl acetate, Vinyl chloride (VCM-EDC).
15. Immediately Dangerous to Life or Health (IDLH) Level. The IDLH level is that maximum concentration from which, in the event of respirator failure, one could escape within 30 minutes without experiencing any escape-impairing or irreversible health effects. IDLH levels are listed in various documents, including the NIOSH Pocket Guide to Chemical Hazards (available from U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Washington, D.C).
16. Intermediate Hazard Chemical Process Class. Processes, operations or mateerials having an appreciable explosion hazard and a moderate fire hazard. This class involves mildly exothermic reactions. Examples include: Acetic anhydride (from acetic acid), Alkylation (refinery), Benzene (from toluene-xylene), Benzene-Toluene-Xylene (BTX), Cumene, Cyclohexane, Ethyl benzene, Methanol (reforming), Polyethylene HD (small units), Polypropylene, Polystyrene, Polyvinylchloride, reforming (refinery),Terephtalic acid.
17. Moderate Hazard Chemical Process Class. Processes, operations or materials having a limited explosion hazard and a moderate fire hazard. This class involves highly endothermic reactions and nonreactive operations such as distillation, absorption, mixing and blending of flammable liquids. Exothermic reactions with no flammable liquids or gases also fit in this hazard class. Examples include: Acetic anhydride (carbolaytion of methyl acetate), Acetone (dehydrogenation of alcohol), Adiponitrile, Ammonia, Crude distillation, Choloromethanes, Ethanol (from methanol), Ethylene glycol, Formaldehyde (methanol oxidation), Methyl amine, Methyl Ethyle Ketone (dehydrogenation of alcohol), solvent extraction, Styrene, Urea, Visbreaking.
18. Multi-Unit Control House. A control center that serves several process units. Loss of a multi-unit control house would curtail operation of the facility but would not result in a total shutdown.
19. Main Pipeway. Pipeways, at grade or elevated on pipe supports, that contain utility lines and product lines for a number of process units and that are connected to process unit pipeways.
20. Operator Shelter. A substantial enclosed structure used by multiple operators for activities such as limited monitoring, breaks, inclement weather protection, lunch.
21. Process Equipment. Any components of an operating facility such as vessels, tanks, fired heaters, heat exchangers, rotating equipment, and piping that are part of a process train used in processing material into a given product or products.
22. Process or Processing. An integral sequence of operations. The sequence can be inclusive of both physical and chemical operations, unless the term is modified to restrict it to one or the other. The sequence can involve, but is not limited to, preparation, separation, purification, or change in state, energy content, or composition.
23. Process Unit. A complete train of equipment in which a material or product is processed and then sent either to the next unit for further processing or to storage. Process units can be separate or can be integrated with other units. Integrated process units are part of a continuous operation such that they are not operated independently.
24. Process Unit Control House. A control center for one process unit (single-unit).
25. Process Unit Pipeway. Pipeways that are at grade or elevated on pipe supports and contain feed, recycle, and rundown lines, as well as utility lines within a battery limit.
26. Remote Instrument Enclosures (RIE). Structures that contain instrument and process control equipment for one (single) or more (multi) process units. The structure is separate from the central control house.
27. Slopover. The rapid expulsion of a portion of the tank contents, usually occurring during fire fighting operations when water applied from foam or cooling water streams expands into steam as it passes through the hot oil layer.
28. Storage Tanks. Any vessel having a liquid capacity that exceeds 2.27 m3, is intended for fixed installation, and is not used for processing. Following are several types of storage tanks:
    • a. Atmospheric tank. A storage tank designed to operate at any pressure from atmospheric up to 3.45 kPa gage.
    • b. Cone roof tank. A storage tank with a fixed cone-shaped roof.
    • c. Cone roof tank with internal floating cover. A storage tank with a fixed cone-shaped roof and an internal floating cover of one of the following designs:
      • (i) Metal (steel or aluminum) pan-type cover.
      • (ii) Thin-skin metal deck on floats.
      • (iii) Aluminum honeycomb sandwich panel cover.
      • (iv) Any combustible (nonmetal) cover.
    • d. Covered Floating Roof Tank. A storage tank with a fixed roof and steel internal floating roof of the single-deck pontoon or double-deck design.
    • e. Open-Top Floating Roof Tank. A storage tank with a steel floating roof of the pontoon, buoy, or double-deck design and without a fixed roof.
    • f. High-pressure tank. A storage vessel designed as a pressure vessel; see definition (h).
    • g. Low-pressure tank. A storage tank designed to operate at pressures above 3.45 kPa gage but not to exceed 103.4 kPa gage.
    • h. Pressure vessel. A vessel designed to operate at pressures above 103.4 kPa gage in accordance with Section VIII of the ASME Boiler and Pressure Vessel Code.
29. Vapor Pressure. The pressure, measured in kPa abs (psia), exerted by a volatile liquid as determined by ASTM D323.