Review of an Adequate Chemical Dust Suppressant Used for Prevention of Dust Explosions in Food Industry

Mary Kay O Connor PROCESS SAFETY CENTER Review of an Adequate Chemical Dust Suppressant Used for Prevention of Dust Explosions in Food Industry Oct-27-2009 Diana Castellanos

OUTLINE Introduction Types of suppressants Solids Gaseous Main characteristics that enhance suppressant effectiveness Overview of Dust Explosion Research at the Mary Kay O Connor Process Safety Center (MKOPSC) Future work 2

DUST EXPLOSIONS 281 incidents, 119 fatalities, and 718 injuries from 1980-2005 An average of 10 dust explosion incidents per year An average of nearly 5 fatalities and 29 injuries per year Injuries or fatalities occurred in 71 percent of the incidents STATISTICS Types of Dust Involved in incidents Coal 8% Plastic 14% Inorganic 4% Metal 20% Other 7% Food 23% Wood 24% [1] Source: U.S. Chemical Safety and Hazard Investigation Board (CSB) 3

DUST EXPLOSIONS 281 incidents, 119 fatalities, and 718 injuries from 1980-2005 An average of 10 dust explosion incidents per year An average of nearly 5 fatalities and 29 injuries per year Injuries or fatalities occurred in 71 percent of the incidents STATISTICS Types of Industries Involved in Dust Incidents Equipment Manufact'g. 7% Fabricated Metal Products 7% Electric Services 8% Rubber & Plastic Products 8% Furniture & Fixtures 4% Other 7% Primary Metal Industries 8% Food Products 24% Lumber/ Wood Products 15% Chemical Manufact'g. 12% [1] Source: U.S. Chemical Safety and Hazard Investigation Board (CSB) 4

WHY DOES IT HAPPEN? Employers and workers are not aware of or underestimated the dust related hazards. No effective safety measure to prevent accidents: Interlocking systems, prevention of mechanical and electric sparks and hot surfaces, good housekeeping in the workrooms [2] There are no adequate suppressant agents for powder explosions in the food industry [2] Bartknecht, W. (1989). Dust Explosions. Course, Prevention, Protection. Germany, Springer Verlag Berlin Heidelberg 5

DUST EXPLOSION PROCESS Mixing Oxidant Dust Explosion pentagon Confinement Fuel Domino effect in dust explosions Primary explosion send a shockwave through the plant Ignition source Suppression methods are based on elimination of al least one of these five elements Dust when dispersed in air may produce a secondary explosion 6

SUPPRESSION WITH SOLID COMPOUNDS ADVANTAGES DISADVANTAGES Keeps the combustible dust concentration below the dust flammability range. x Requires great quantity usage in order to be effective in the supression process. Absorbs high quantities of heat released from explosibe reaction. [3] x Introduces contamination to the product. Suppressant effectiveness is measured by comparing MEC [3] Eckhoff, R. (1997). Dust Explosions in the Process Industries. Great Britain. St Edmundsbury Press Ltd. 8

SUPPRESSION WITH GASEOUS COMPOUNDS ADVANTAGES DISADVANTAGES Reduces oxygen content in the atmosphere. Thus combustion reaction is stoped and the flame cannot propagate. Low product contamination. x x Some supressants requires great quantity usage, therefore they are not cost effective. Introduces asphixiation hazards. LOC for combustion depends on the type of dust and inert gas used [4] [4] CEP www.aiche.org/cep (Letters - August 2009) 9

SUPPRESSANT EFFECTIVENESS Composition High specific heat Higher decomposition rate Small particle size Compatibility with dust product. Low product contamination System will absorb high quantities of heat released from explosive reaction [5] Decomposition rate of inert particle higher that fuel decomposition rate would extinct the flame [6] Smaller inert particle size dissipate faster heat radiation and heat convection [6] Large surface area High surface area available for combustion reaction enhance suppressant decomposition and heat absorption [5] Eckhoff, R. (1997). Dust Explosions in the Process Industries. Great Britain St Edmundsbury Press Ltd. [6] Chatrathi, K. and J. Going (2000). Dust deflagration extinction, Amer Inst Chemical Engineers. 11

BINARY GASEOUS-SOLID SOLID SUPPRESSANT There is a needed to identify the effectiveness of binary gas-solid suppressants which comprises advantages and disadvantages from each compound. 12

EXPLOSION EQUIPMENT MKOPSC 14

EXPLOSION EQUIPMENT MKOPSC Data acquisition system Sensor system (Piezoelectric PT) Dispersion system Ignition system Non-spherical stainless steel vessel Capacity: 26 L. MAWP:1000 psi. Tmax 500 0 F. Vacuum system 15

OPERATION MODE TYPICAL DUST EXPLOSION CURVE 16 t1: Duration of combustion Pex: Explosion overpressure dp/dt: Rate of pressure rise with time Pd: Expansion pressure Typical overpressure versus time during a dust explosion. Adapted from: Proust (2006) 16

PROPERTIES MEASURED BY 26L VESSEL Property Definition ASTM Test Method Application P max Maximum explosion overpressure generated in the test chamber ASTM E 1226 Used to design enclosures and predict the severity of the consequence. (dp/dt) max K St MEC LOC Maximum rate of pressure rise Dust deflagration index Minimum explosible concentration Limiting oxygen concentration ASTM E 1226 ASTM E 1226 ASTM E 1515 ASTM standard under development Predicts the violence of an explosion. Used to calculate K St. Measures the relative explosion severity compared to other dusts. Measures the minimum amount of dust, dispersed in air, required to spread an explosion. Determines the least amount of oxygen required for explosion propagation through the dust cloud. Shelley, S. Update Preventing dust explosions. March 2008 CEP 17

PROPERTIES MEASURED BY 26L VESSEL 18 Deflagration Index (Kst): is a volume normalized rate of pressure rise and is expressed by the cubic law: It relates the maximum rate of pressure rise to the volume of the vessel in which the explosion occurs. (ASTM E 1226) Combustible dusts are classified by their Kst values in increasing order of explosion violence as follows: Kst =0 Group St0: non-explosive 0<Kst =<200 Group St1: weak 200<Kst=< 300 Group St2: strong Kst > 300 Group St3: very strong Increasing Explosibility 18

FUTURE WORK Further analysis of MEC in binary suppressant options should be performed to reveal optimum concentration ratios that reduce explosion violence. Research will also focused on dust products in food industry in order to design a systematic approach that can be used to prevent dust explosions. 20

21 AKNOWLEDGEMENT - Dr. Mannan - Dr. Dedy - Victor Carreto - Dr. Passman - Dow Chemical Company - All member of MKOPSC 21

THANKS QUESTIONS??