Combustion Inhibition

Jaffe and C.E. Carraher, ACS Polymeric Materials Science and Engineering, 1998, 78, 96. 

Flynn and L.A. Wall, Journal of Polymer Science Part B Polymer Letters, 1966, 4, 5, 323. 

Zasko and J. Zasko, Journal of Thermal Analysis and Calorimetry, 1980, 

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Bolinder, ., and Schmid, H. (1986) Manufacture of propulsive powder and combustion inhibiting substances. Fr. Demande 2,576,014 Chan. Abstr., (1987) 106,104794k. 

Rosser, W. A. Wise, H. Miller, J. Mechanism of combustion inhibition by compounds containing halogen, Seventh Symposium (International) on Combustion, London, U.K. Butterworth, 1959, 175-182. 

The highest SEAs are associated with halogen-containing polymers (rigid and flexible PVC, PMMA/PVC alloy) apparently because of combustion inhibition by chlorine (see equations 1-3 and Fig. 22). 

On exposure to flame, there is a kind of microexplosions and injection of lire extinguishing liquid (water) occurring in the combustion zone. In this case, combustion inhibition is likely due to the absorption of a significant heat amount characterized by the high heat capacity and high water evaporation heat. A possible factor in reducing the flame-spread rate is also water displacement of the combustion reaction components from the reaction zone. 

The combustion of methane can be used as a model for the combustion inhibition mechanism in the gaseous phase. This is a radical chain reaction proceeding in a series of step reactions as follows [4] ... 

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

J. W. Hastie and D. W. BonneU, Molecular Chemist of Inhibited Combustion Systems, Feport NBSIF 80-2169, Nad. Buieau of Standards, Washington, D.C., 1980. 

Formation of emissions from fluidised-bed combustion is considerably different from that associated with grate-fired systems. Flyash generation is a design parameter, and typically >90% of all soHds are removed from the system as flyash. SO2 and HCl are controlled by reactions with calcium in the bed, where the lime-stone fed to the bed first calcines to CaO and CO2, and then the lime reacts with sulfur dioxide and oxygen, or with hydrogen chloride, to form calcium sulfate and calcium chloride, respectively. SO2 and HCl capture rates of 70—90% are readily achieved with fluidi2ed beds. The limestone in the bed plus the very low combustion temperatures inhibit conversion of fuel N to NO. ... 

Detergent Additives. Diesel engine deposits ate most troublesome in the fuel dehvery system, ie, the fuel pump and both fuel side and combustion side of the injectors. Small clearances and high pressures mean that even small amounts of deposits have the potential to cause maldistribution and poor atomization in the combustion chamber. The same types of additives used in gasoline ate used in diesel fuel. Low molecular weight amines can also provide some corrosion inhibition as well as some color stabilization. Whereas detergents have been shown to be effective in certain tests, the benefit in widespread use is not fully agreed upon (77). 

Most dry-chemical fire-extinguishing materials also function by inhibiting combustion rather than by cooling or by reducing oxygen concentration. The usual dry-chemical material is a bicarbonate, but some phosphates, eg, ammonium, provide a coating that makes the material suitable for use on fires involving soHd combustibles such as mbber tires, wood, and paper. 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

Flame Retardants. Because PVC contains nearly half its weight of chlorine, it is inherently flame-retardant. Not only is chlorine not a fuel, but it acts chemically to inhibit the fast oxidation in the gas phase in a flame. When PVC is diluted with combustible materials, the compound combustibiHty is also increased. Por example, plastici2ed PVC with > 30% plastici2er may require a flame retardant such as antimony oxide, a phosphate-type plastici2er, or chlorinated or brominated hydrocarbons (145,146). 

Sulfur oxides resulting from fuel sulfur combustion often inhibit catalyst performance in Regions II, III, and a portion of Region IV (see Fig. 7) depending on the precious metals employed in the catalyst and on the air/fuel ratio. Monolithic catalysts generally recover performance when lower sulfur gasoline is used so the inhibition is temporary. Pd is more susceptible than Rh or Pt. The last is the most resistant. Pd-containing catalysts located in hotter exhaust stream locations, ie, close to the exhaust manifold, function with Httie sulfur inhibition (72—74). 

Types of combustibles, e.g. resulting in surface fires for which inerting or an inhibiting agent may be best, or deep-seated combustion requiring a cooling agent, e.g. water. 

The rotational operation of a CFB leads to a vortex motion in the freeboard which tends to inhibit particle loss by elutriation. Because of the relatively compact nature of the CFB and the operating flexibility provided by the rotational motion, the CFB has been proposed for a variety of applications including coal combustion, flue gas desulfurization, gas combustion, coal liquefaction and food drying. 

Carbon dioxide and certain halon compounds have a specialized application for fires in electrical equipment where a non-conducting medium is important. All are toxic to a degree, and operate either by smothering the fire or by a chemical reaction which inhibits combustion. Gas extinguishers must not be used in a confined space because of the toxic risk or the risk of asphyxiation. 

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