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Chemical Process Safety. Runaway Reactions. Two CSB Videos: Review. Reactive Hazards ( 31 July 2007 ) Runaway: Explosion at T2 Laboratories (19 Dec 2007; video: 22 Sep 2009 ). “167 serious uncontrolled reactions with 108 deaths from 1980 – 2001”. Two CSB Videos: Review. Reactive Hazards:
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Chemical Process Safety Runaway Reactions
Two CSB Videos: Review • Reactive Hazards (31 July 2007) • Runaway: Explosion at T2 Laboratories (19 Dec 2007; video: 22 Sep 2009) “167 serious uncontrolled reactions with 108 deaths from 1980 – 2001”
Two CSB Videos: Review • Reactive Hazards: • What do you remember about the video? • Lessons “learned”
Two CSB Videos: Review • Reactive Hazards: • 1984 Bhopal • CSB formed & established chemical process safety • Synthron: butyl acrylate (solvents: toluene, cyclohexane) • 1500 gal reactor • HE was used to condense solvent vapors & cool exothermic reaction • Batch size increased • HE couldn’t remove enough heat • BP Amoco: HP nylon • Polymerization reactor bypass to 750 gal waste tank • Overfilled waste tank; no PI or vent • Secondary decomposition reaction • MFG Chemical: allyl alcohol vapor release • 30 gal test reactor (3rd test significant heat generation) • Production in 4000 gal reactor (SA/vol ratio: HE inadequate) • 1st Chemical Corporation: mono-nitro toluene (MNT) • 145’ distillation tower; MNT left in reboiler • Leaking steam valve • Heated to 450 oF– decomposition reaction
Two CSB Videos: Review • Reactive Hazards: • What do you remember about the video? • Lessons “learned”
Two CSB Videos: Review • Runaway: Explosion at T2 Laboratories: • What do you remember about the video? • Lessons “learned” Producing a gasoline additive: methylcyclopentadienyl manganese tricarbonyl (MCMT) Reactor
Two CSB Videos: T2 Laboratories Brief overview of process steps • Added to reactor • sodium metal in mineral oil • methylcyclopentadiene dimer • diethylene glycol dimethyl ether (diglyme) • close the vessel • set pressure to 3.45 bar and heating oil temp to 182.2 C • heating melted sodium that reacted with methylcyclopentadiene forming sodium methylcyclopentadiene, hydrogen, and heat • Hydrogen gas was generated • when mix reached 100°C, agitation was shut off • at 150°C hot oil flow stopped • at 180°C cooling was initiated with water admitted to the reactor jacket. • maintain temperature from the exothermic reaction via water evaporation.
Two CSB Videos: T2 Laboratories 175th batch exploded Former Reactor Site
Figure 2. Control room.* * From CSB final report; Sep 2009.
Figure 4. Injury and business locations.* * From CSB final report; Sep 2009.
Figure 5. Portion of the 3-inch-thick reactor.* * From CSB final report; Sep 2009.
Figure 4. Injury and business locations.* * From CSB final report; Sep 2009.
Two CSB Videos: T2 Laboratories CSB Investigation Runaway exothermic reaction • Occurred during the first metalation step of the process • An uncontrollable rise in temperature and resultant pressure lead to the burst of the reactor • Upon bursting, contents ignited in air • Creating an explosion equivalent of 635 kg (1420 lb) of TNT exploding from a single point
Two CSB Videos: T2 Laboratories CSB Investigation Possible causes for the explosion Investigation considered: • cross-contamination of the reactor • contamination of raw materials • wrong concentration of raw materials • local concentration of chemical within the reactor • application of excessive heat • insufficient cooling
“The CSB determined insufficient cooling to be the only credible cause for this incident, which is consistent with witness statements that the process operator reported a cooling problem shortly before the explosion. The T2 cooling water system lacked design redundancy, making it susceptible to single-point failures including • water supply valve failing closed or partially closed. • water drain valve failing open or partially open. • failure of the pneumatic system used to open and close the water valves. • blockage or partial blockage in the water supply piping. • faulty temperature indication. • mineral scale buildup in the cooling system. Interviews with employees indicated that T2 ran cooling system components to failure and did not perform preventive maintenance. * From CSB final report; Sep 2009.
Two CSB Videos: Review • Runaway: Explosion at T2 Laboratories: • What do you remember about the video? • Lessons “learned” • “T2 did not recognize the runaway reaction hazard associated with the MCMT it was producing.” Contributing causes: “The cooling system employed by T2 was susceptible to single point failures due to a lack of design redundancy. The MCMT reactor relief system was incapable of relieving the pressure from a runaway reaction.”
Two CSB Videos: T2 Observations • Scaled up from 1 liter to 9300 liter directly • Batch 42 the recipe was increased by 1/3 (testing?) • Periodically experienced problems with cooling • No “backup” cooling system • Used city water supply (minerals?) • Did not recognize and control reactive hazards • No evidence found by CSB that T2 performed a recommended HAZOP. • There was a need for reactive chemistry testing.
CSB Testing on T2 Recipe CSB testing completed with a VSP2 (Vent Sizing Package 2)Adiabatic Calorimeter (116 ml test cell) diglyme decomposition reaction 1 exotherm * From CSB final report; Sep 2009.
Follow-up Topics • Key Findings of CSB investigation: • Cooling discussion • Overpressure • Runaway reactors • Hazard analysis
A second exothermic reaction occurred • This reaction became uncontrollable around 200°C • The reaction was the uncontrolled decomposition of diglyme (the solvent used) • Probably catalyzed by the presence of sodium. • By the time the rupture disk opened (28.6 bar) • It was too late • If the rupture disk had opened at 6.2 bar, then no explosion would have occurred * From CSB final report; Sep 2009.
Over pressure Wave Profile, 1 Psi=0.07 bar psi 0.017 Bar 0.14 Bar 0.017 Bar 1.7 Bar * From CSB & SACHE module by R. Willey, 2012.
Combustion Behavior – Most Hydrocarbons Smoke and fire are very visible! Slide courtesy of Reed Welker.
Combustion Behavior – Carbon Disulfide No smoke and fire, but heat release rate just as high. Slide courtesy of Reed Welker.
Combustion Behavior – Methane Methane burns mostly within vessel, flame shoots out of vessel.
Combustion Behavior – Dusts Much of the dust burns outside of the chamber.
Definitions - 1 LFL: Lower Flammability Limit Below LFL, mixture will not burn, it is too lean. UFL: Upper Flammability Limit Above UFL, mixture will not burn, it is too rich. Defined only for gas mixtures in air. UNITS:
Definitions - 2 Flash Point: Temperature above which a liquid produces enough vapor to form an ignitable mixture with air. Defined only for liquids at 1 atm. pressure. Auto-Ignition Temperature (AIT): Temperature above which adequate energy is available in the environment to provide an ignition source.
Definitions - 3 Limiting Oxygen Concentration (LOC): Oxygen concentration below which combustion is not possible, with any fuel mixture. Expressed as volume % oxygen. Also called: Minimum Oxygen Concentration Max. Safe Oxygen Conc. Others
Definitions - 4 Explosion: A very sudden release of energy resulting in a shock or pressure wave. Shock, Blast or pressure wave: Pressure wave that causes damage. Deflagration: Reaction wave speed < speed of sound. Detonation: Reaction wave speed > speed of sound. Speed of sound in air: 344 m/s, 1129 ft/s at ambient T, P. Deflagrations are the case with explosions involving flammable materials.
Definitions - 5 • Minimum Ignition Energy (MIE): Smallest energy to initiate combustion. • Higher for dusts & aerosols than for gases • Many HC gases have MIE ~ 0.25 mJ • Auto-oxidation: slow oxidation and evolution of heat can raise T and lead to combustion. i.e. liquids with low volatility. • Adiabatic compression: of a gas generates heat, increases temperature, and can lead to autoignition. • Ignition sources: usually numerous and difficult to eliminate. Objective is to identify and eliminate, but not to solely rely on this step to eliminate combustion risk. (Table 6-5; Crowl)
Typical Values - 1 LFL UFL Methane: 5.3% 15% Propane: 2.2% 9.5% Butane: 1.9% 8.5% Hydrogen: 4.0% 75% See Appendix B Flash Point Temp. (deg C) Methanol: 12.2 Benzene: -11.1 Gasoline: -43
Typical Values - 2 AIT (deg. C) Methane: 632 Methanol: 574 Toluene: 810 LOC (Vol. % Oxygen) Methane: 12% Ethane: 11% Hydrogen: 5% Appendix B Great variability in reported AIT values! Use lowest value. Table 6-2
Flammability Relationships Figure 6-2
Aerosol Flammability Too rich Too lean M. Sam Mannan, Texas A&M, Mary Kay O’Conner Process Safety Center
Minimum Ignition Energies What: Energy required to ignite a flammable mixture. Typical Values: (wide variation expected) Vapors: Dusts: Dependent on test device --> not a reliable design parameter. Static spark that you can feel: about mJ Lightning: about 500 megajoules Or ~ 500,000,000,000 mJ Table 6-4
Experimental Determination - Flashpoint Figure 6-3 Cleveland Open Cup Method. Closed cup produces a better result - reduces drafts across cup.
Experimental Determination - LFL, UFL Run experiment at different fuel compositions with air: 10 Need a criteria to define limit - use 1 psia pressure increase. Other criteria are used - with different results! 8 6 Maximum Explosion Pressure (barg) 4 2 LFL UFL 0 0 2 4 6 8 10 See Figure 6-5 Fuel Concentration in air (vol%) Flammability limits are an empirical artifact of experiment!
Experimental Determination: P versus t TI 10 PI Pmax 8 6 Pressure (bar-abs) (dP/dt)max 4 Ignitor 2 0 0 50 100 150 200 250 Time (ms) Final experimental result:
