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Safety

Safety. Determine conditions where fires and /or explosions can occur. Develop estimates for upper/lower flammability limits in mixtures Utilize inerting to prevent fires/explosions. Combustion/Fire/Explosion. Where Does Reaction Occur?.

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Safety

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  1. Safety • Determine conditions where fires and /or explosions can occur. • Develop estimates for upper/lower flammability limits in mixtures • Utilize inerting to prevent fires/explosions.

  2. Combustion/Fire/Explosion

  3. Where Does Reaction Occur? • In gas phase where ignition source, oxygen and fuel coexist. • Can be autocatalytic under certain conditions. • May not need ignition source if temperature is high enough.

  4. Types of Reactions • Slow Oxidation • Energy can be absorbed by surroundings without increase in temperature. • Fire • Energy released can be dissipated by environment with an increase in temperature to a stable point. • Deflagration/Explosion • Energy released cannot be fully dissipated by environment and temperature continuously increases.

  5. Definitions • Flash Point Temperature • Enough fuel exists in air to create a flammable mixture. Will “burn out”. • Fire Point Temperature • Enough fuel exists in air to create a sustainable flammable mixture. • Flammability Limits • Volume percent ranges of fuel in air where burning occurs.

  6. LFL Lower Flammability Limit • Partial pressure of fuel is too low to keep reaction going • UFL Upper Flammability Limit • Partial pressure of oxygen is too low to keep reaction going

  7. Sources for LFL/UFL • MSDS sheets where data was obtained experimentally. • Mixtures of Fuels • Can be calculated with known LFL/UFL of all components

  8. Calculating LFL/UFL of Mixtures

  9. 20:80 Hexane/Heptane Liquid at 25 oC • Assume Liquid is in equilibrium with air in headspace • Calculate mole fraction of each component using Raoult’s Law or suitable model. • Calculate LFL/UFL of mixture

  10. Temperature Dependence of LFL/UFL

  11. T = 20 oC

  12. Pressure Effects

  13. Flammability Diagrams • Flammability Diagrams • Compression and Ignition

  14. 40% Nitrogen 40% Fuel 20% Oxygen

  15. Original Mixture 40% Nitrogen 40% Fuel 20% Oxygen Dilute with Air

  16. Original Mixture 40% Nitrogen 40% Fuel 20% Oxygen Dilute with Air Air Added Original Fuel

  17. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O 1. Draw Air Line 2. Enter LFL & UFL • Determine z • LOC = zLFL(use data, if available) UFL LFL

  18. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O • Add StoichiometricLine • Get Pure Oxygen LFLand UFL (if available) LOC UFL LFL

  19. Constructing Flammability Diagram Fuel + zO2 CO2 + H2O 7. Construct Curve LOC Flammable Region

  20. Compression of Gases

  21. Acrylic Acid ProcessCompressor Section

  22. Safety (MSDS) data for hexane Physical data Appearance: colourless liquid Melting point: -95 C Boiling point: 69 C Vapour density: 3 (air = 1) Vapour pressure: 132 mm Hg at 20 C Specific gravity: 0.659 Flash point: -10 F Explosion limits: 1.2% - 7.7% Autoignition temperature: 453 F

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