Absorption - The process of contacting a vapor and gas stream with an absorbing liquid to remove specific materials from the gas stream.

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1 Sufe Design and Optvation ofpi-oc.ess Vents and Emission Contid $wteins by Center for Chemical Process Safety Copyright John Wiley & Sons, Tnc. APPENDIX B GLOSSARY Absorption - The process of contacting a vapor and gas stream with an absorbing liquid to remove specific materials from the gas stream. Adsorption - The process of contacting a vapor and gas stream with the surface of a solid adsorbent material. Adiabatic Flame Temperature - The temperature developed by the combustion of a fuel and oxidizer mixture in conditions where there are no heat losses. In practice this value is difficult to measure experimentally and most published figures are the results of theoretical calculations. Atmospheric Storage Tank - A storage tank designed to operate at any pressure between ambient pressure and 0.5 psig (3.45kPa gage). Autoignition Temperature - The minimum temperature at which combustion can be initiated without an external ignition source in a standardized test apparatus. Blowdown Drum - A separate collection vessel intended to receive a periodic or emergency discharge of liquids, liquid reaction mass, or slurries from a number of process vessels, reactors, or equipment items. Blowdowns may be initiated automatically, i.e., depressuring a batch reactor, or manually for other applications. Blowdown drums are usually maintained at a low level or essentially empty. The collected liquids are pumped elsewhere for recovery, recycle, or disposal. Gases and any uncondensed vapors are vented through relief devices or an open line into a vent header system for appropriate treatment and disposal. 207

2 Safe Design and Operation of Process Vents and Emission Control Systems Catch Tank - A separate containment vessel intended to receive an emergency discharge from relief devices in the process vessel's vapor space. Catch tanks are usually employed where substantial two-phase relief flow, entrained solids, or reaction mass carryover is expected to occur. Combustion - An exothermic reaction between a fuel and an oxidizer (usually but not necessarily oxygen) that results in a significant temperature rise and usually a visible flame or glow. Corrosivity - A complex series of reactions between water and metal surfaces and materials in which the water is stored or transported. Combustible Liquid - A liquid having a flash point at or above 100'F (37 C). Combustible liquids are subdivided as follows: Class I1 liquids include those having flash point at or above 100 F (37 C) and below 140 F (60 C). Class IIIA liquids include those having flash points at or above 140 F (60 C) and below 200 F (93 C). Class IIIB liquids include those having flash point at or above 200 F (93 C). Deflagration - A combustion that propagates by heat and mass transfer through the un-reacted medium at a velocity less than the speed of sound. Design Case - Conditions to be used for the design of a vent system to ensure it will meet safety, health, environmental, and commercial objectives. For emergency vent headers, this will normally be based on the "worst credible case" scenario. For normal process vents, the design should take into consideration all non-emergency situations unless they will be addressed by some other means, such as by providing a temporary vent system for maintenance operations. Detonation - A combustion that propagates by adiabatic compression heating caused by a shock wave, and which travels through the unreacted medium at a velocity equal to or greater than the speed of sound. 208

3 Appendix B - Glossary Dispersion Modeling - A technique that can be used to confirm that the residual or converted products from a normally operating end-of-pipe treatment system do not present any residual hazards to plant personnel, community, or environment. In addition, modeling could be employed to assess the impact on plant personnel, community, or environment if the treatment system malfunctions and releases the collected vent streams untreated. Dump Tank - A separate collection and containment vessel intended to receive an emergency discharge of liquids, liquid reaction mass, or slurries originating from the bottom of a process vessel or reactor. The "dump" is usually automatically triggered by a process safety interlock, but may also be initiated manually. An uncontrolled, exothermic, or other runaway reaction can be controlled by discharging the process vessel contents to the dump tank. This may allow the process vessel to be returned to service in a shorter time. Entrainment - To draw in and transport (as solid particles, liquid droplets, or gas) by the flow of a fluid. Equipment - A term used in this book to describe any form of process vessel, storage tank, or any other items that may be connected to a vent system. Explosion - A sudden increase in the atmospheric pressure perceptible to an observer as a bang or boom, Explosions can be caused by several scenarios, including: A deflagration or detonation inside equipment causing it to rupture. Detonations involving high explosives. Physical explosions, such as a vessel failing as a result of it being subjected to pressures above its ultimate strength. Explosion Prevention - Where the gas composition is maintained outside the flammable region. Explosion Protection - Where devices are provided to minimize pressure development if ignition occurs. Fire Triangle - Three basic conditions are required for fire to take place. These are fuel, oxygen, and heat. Fuel - the reducer; any combustible material, solid, liquid or gas. Most solids and liquids must vaporize before they will burn. Oxygen - the oxidizer; sufficient oxygen must be present in the atmosphere surrounding the fuel for fire to bum. 209

Safe Design and Operation of Process Vents and Emission Control Systems Heat - sufficient energy must be applied to raise the fuel to its ignition temperature.

4 Safe Design and Operation of Process Vents and Emission Control Systems Heat - sufficient energy must be applied to raise the fuel to its ignition temperature. Fire can only occur when all three of the above elements are present and in the proper conditions and proportions. These three basic conditions are often represented as a fire triangle shown in 0. The combustion reaction itself is often included as a fourth central element of the fire triangle. Figure B-1. The Fire Triangle If one of the sides of the fire triangle is missing, the fire will not start. If one side is removed, the fire will be extinguished. The fire triangle forms the foundation for all methods of fire prevention and firefighting (NFPA, 1997). Flame Arrester - A device fitted to the opening of an enclosure or to the connecting piping of a system of enclosures and whose intended function is to allow flow but prevent the transmission of flame from either a deflagration or detonation. Flame Speed - The speed of a flame relative to a fixed reference point. Flammable Gas - A gas that, if mixed with a gaseous oxidizer such as air or chlorine and ignited, can burn with a flame. The term flammable gas includes vapors from flammable or combustible liquids above their flash points. In this book the term "flammable gas" generally includes vapors from liquids that are above their flash points, as well as combustible materials that are gases at normal temperature and pressure. Flammable Limits - The minimum (LFL) and maximum (UFL) concentration of combustible gas, vapor, mist, or dust, (or a combination of these materials), mixed with a gaseous oxidizer, that if ignited can burn. These limits are equipment specific and different test methods can produce significantly different values. The terms upper or lower flammable limits are synonymous with the terms "upper or lower explosive limits". 210

5 Appendix B - Glossary Flammable Liquids - A liquid having a flash point below 100 F (37 C) and a vapor pressure not exceeding 40 psia. NFPA further classifies flammable liquids as follows: Class 1A liquids have a Reid vapor pressure that does not exceed 4Opsi (2068.6mm Hg) at 100 F (373 C) and have a closed-cup flash point below 73 F (223 C) and a boiling point below 100 F (373 C). Class 1B liquids have a closed-cup flash point below 73 F (223 C) and a boiling point at or above 100'F (37.8"C). Class 1C liquids have a closed-cup flash point at or above 73 F (223 C) but below 100 F (37.8"C). Flammable Vapor - A vapor that is above its lower flammable limit (LFL) concentration. A zone of flammable vapor will exist in equilibrium with a flammable or combustible liquid any time it is above its flash point. In this book the term "flammable gas" generally includes vapors from liquids that are above their flash points, as well as combustible materials that are gases at normal temperature and pressure. Flashback Arrester - A device to limit damage from a flashback by preventing propagation of the flame front beyond the location of the arrester. Flashback Prevention - Prevention of a recession of the flame into or back of the mixing chamber. Flashpoint - The temperature at which a liquid develops sufficient vapor pressure to form a vapor/air mixture capable of undergoing combustion after ignition from an external energy source. (Fire point is the temperature at which the reaction will be sustained). Frequency - The number of occurrences of an event per unit of time. Hazard and Operability Study (HAZOP) - A technique to identify process hazards and potential operating problems using a series of guidewords to study process deviations. Hybrid Mixture - A mixture of flammable gas and combustible dust or mist. Incident - An unplanned event with the potential for undesirable consequences. Inherently Safer - A term applied to a component, system, or facility in which potential dangers have been removed or reduced. Inherent safety is incorporated during development, design, or engineering. 21 1

Safe Design and Operation of Process Vents and Emission Control Systems Limiting Oxidant Concentration (LOC)- Is the concentration of oxidant, e.g. oxygen, air, chlorine, etc.

6 Safe Design and Operation of Process Vents and Emission Control Systems Limiting Oxidant Concentration (LOC)- Is the concentration of oxidant, e.g. oxygen, air, chlorine, etc. below which the combustion reaction can no longer generate sufficient energy to produce a propagating flame. The LOC is synonymous with the term Minimum Oxygen Concentration (MOC). Minimum Oxygen Concentration (MOC) - See Limiting Oxidant Concentration. Plume - A visible or measurable discharge of a contaminant from a given point of origin that can be measured according to the Ringelmann scale. Quench Drum - A vessel with internal liquid sprays supplied by an external recirculation pump loop with a quenching liquid sprayed directly into the vapor space to contact, cool, and condense at least part of the hot vented gas or vapor stream before these gases enter the main vent header system. Quench Pool - A closed vessel containing a relatively large volume of liquid. The emergency vent stream is sparged subsurface through the liquid volume at high velocity, resulting in vigorous agitation and circulation of the pool contents in order to maximize cooling and condensation or reaction with the pool liquid. Most or all of the vented stream can be captured; residual vapor and non-condensable gas may be released to the vent header system for further treatment or disposal. Risk - A measure of economic loss or human injury in terms of both likelihood and the magnitude of the loss or injury. Risk Analysis - The development of a quantitative estimate of risk-based engineering evaluation and mathematical techniques for combining estimates of incident consequences and frequencies. Risk Assessment - The process by which the results of a risk analysis are used to make decisions either through a relative ranking of risk reduction strategies or rhrough comparison with risk targets. Risk assessment is often defined as the qualitative estimation of probability and consequence of an incident or incidents. Runaway Reaction - An exothermic reaction where the heat evolved from reacting materials exceeds the heat being removed from the equipment. The imbalance between the heat of reaction and the heat removal causes the temperature to rise, which in turn greatly increases the reaction rate. This can create a positive feedback loop that results in rapidly accelerating reaction rates referred to as a runaway reaction. 212

7 Appendix B - Glossary Safeguards or Protective Features - Design features, equipment, procedures, etc. in place to decrease the probability or mitigate the severity of a causeconsequence scenario. Severity - The maximum credible consequences or effects, assuming no safeguards are in place. Stoichiometric Mixture - A balanced mixture of fuel and oxidizer such that no excess of either remains after combustion. Stoichiometry - Calculations about masses or volumes of reactants and products involved in a chemical reaction. Tempered - A term that describes an exothermic reaction involving a volatile reaction mass where the heat losses due to the latent heat of vaporization balances the heat of reaction. In this situation, the temperature and reaction rates do not increase, and hence the reaction does not runaway. Toxic Gases - Materials that can cause physiological harm other than asphyxiation and that are immediately dangerous to life and health and can be fatal at relatively low concentrations, such as phosgene or hydrogen sulfide. Worst Credible Case - The most severe consequences, considering all scenarios and their outcomes, that is considered plausible or reasonably believable. Vapor - The gaseous phase formed by a material that is liquid at ambient temperature and pressure. 213

APPENDIX WORKED EXAMPLES

APPENDIX WORKED EXAMPLES Sufe Design and Optvation ofpi-oc.ess Vents and Emission Contid $wteins by Center for Chemical Process Safety Copyright 0 2006 John Wiley & Sons, Tnc. APPENDIX G WORKED EXAMPLES This appendix provides