Combustible concentration reduction

Combustible Concentration Reduction The technique of maintaining the concentration of combustible material in a closed space below the lower flammable limit. 

Gombnstible concentration reduction can also be used to prevent deflagrations and detonations in process equipment and piping. The combustible concentration is reduced below the lower flammable limit (LFL) by means of ventilation (air dilution). 

Both CI2 and HCl have been shown to chlorinate hydrocarbons on fly ash particles. Pilot-scale data involving the injection of fly ash from municipal waste combustion (33) show that intermediate oxygen concentrations (4—7%) produce the highest levels of PCDD and PCDF. These data also show significant reductions in PCDD and PCDF emissions with the upstream injection of Ca(OH)2 at about 800°C. 

By recirculating a part of the flue gas to the furnace, the combustion zone turbulence is increased, the temperature is lowered and the oxygen concentration is reduced. All of these factors lead to a reduction of NO, fonnation. 

Since NO is a precursor in NDMA formation and high combustion temperatures (usually from 1500 to 1800 0) yield high reaction rates between oxygen and nitrogen, a decrease in NDMA formation can also be achieved by lowering the flame temperature. Excess air seems to be the most economic way to reduce flame temperature and NO synthesis. In a new type of burner developed on this principle the resulting air had only 0.05 - 0.1 mg NO /m as compared with 14 mg/m in conventional burners. Accordingly, malt dried with such burners contains only 1 to 3 mg/kg NDMA, a 15-30 fold reduction of the NDMA concentration. 

In a review of the course and mechanism of the catalytic decomposition of ammonium perchlorate, the considerable effects of metal oxides in reducing the explosion temperature of the salt are described [1], Solymosi s previous work had shown reductions from 440° to about 270° by dichromium trioxide, to 260° by 10 mol% of cadmium oxide and to 200°C by 0.2% of zinc oxide. The effect of various concentrations of copper chromite , copper oxide, iron oxide and potassium permanganate on the catalysed combustion of the propellant salt was studied [2], Similar studies on the effects of compounds of 11 metals and potassium dichromate in particular, have been reported [3], Presence of calcium carbonate or calcium oxide has a stabilising effect on the salt, either alone or in admixture with polystyrene [4],... 

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