Minimum oxygen for combustion

There are several different devices for determination of dust explosion characteristics. All devices include a vessel which may be op>en or closed, an ignition source which may be an electrical spark or electrically heated wire coil and a supply of air for dispersion of the dust. The simplest apparatus is known as the vertical tube apparatus and is shown schematically in Figure 15.4. The sample dust is placed in the dispersion cup. Delivery of dispersion air to the cup is via a solenoid valve. Ignition may be either by electrical spark across electrodes or by heated coil. The vertical tube apparatus is used for the classification test and for determination of minimum dust concentration for explosion, minimum energy for ignition and in a modified form for minimum oxygen for combustion. 

The minimum oxygen for combustion (MCXI ) is used to determine the maximum permissible oxygen concentration when inerting is selected as the means of... 

A flammable dust is suspended in air at a concentration within the flammable limits and with an oxygen concentration above the minimum oxygen for combustion. Sparks generated by a grinding wheel pass through the suspension at high speed, but no fire or explosion results. Explain why. 

PTFE decomposes to TFE with first-order kinedcs and a 347.4-kJ/mol activation energy under vacuum pyrolysis conditions It is extremely flame resistant and does not bum in air Its limiting oxygen index (LOI). the minimum oxygen content of an atmosphere under ambient conditions that sustains combustion, is 96%, which means that it requires almost pure oxygen for combustion... 

It is proposed to protect a section of duct used for pneumatically transporting a food product in powder form in air by adding a stream of carbon dioxide. The air flow rate in the present system is 3m /s and the air carries 2% powder by volume. If the niinimum oxygen for combustion (by replacement of oxygen with carbon dioxide) of the powder is 13% by volume, what is the minimum flow rate of carbon dioxide which must be added to ensure safe operation ... 

Temperature. The temperature for combustion processes must be balanced between the minimum temperature required to combust the original contaminants and any intermediate by-products completely and the maximum temperature at which the ash becomes molten. Typical operating temperatures for thermal processes are incineration (750—1650°C), catalytic incineration (315—550°C), pyrolysis (475—815°C), and wet air oxidation (150—260°C at 10,350 kPa) (15). Pyrolysis is thermal decomposition in the absence of oxygen or with less than the stoichiometric amount of oxygen required. Because exhaust gases from pyrolytic operations are somewhat "dirty" with particulate matter and organics, pyrolysis is not often used for hazardous wastes. 

The autoignition temperature is the minimum temperature for a substance to initiate self-combustion in air in the absence of a spark or flame. The temperature is no lower than and is generahy considerably higher than the temperature corresponding to the upper flammabihty limit. Large differences can occur in reported values determined by different procedures. The lowest reasonable value should be accepted in order to assure safety. Values are also sometimes given in oxygen rather than in air. 

Some stabilizers or inhibitors require a certain oxygen concentration in the tank head space atmosphere in order to function. Where inerting is required, careful control is necessary to maintain this minimum oxygen concentration in inerting gas while still staying below the minimum oxygen concentration required for combustion. 

ASTM-D2863-06a Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index), American Society for Testing and Materials, Philadelphia, 2003. 

ASTM D2863-00 Standard method for measuring the minimum oxygen concentration to support candle-like combustion of plastics (oxygen index). 

ASTM D 2863 Test Method For Measuring The Minimum Oxygen Concentration To Support Candle-Like Combustion Of Plastics (Oxygen Index), ASTM, West Conshohocken, PA 2006. 

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