Of rapid combustion

Salzer, F. Application Range of Rapid Combustion Apparatus with Electric-Indication for the Determination of Carbon and Hydrogen. Microchem. J. 10, 27 (1966). 

Oxidation processes arc, as a general rule, greatly accelerated by a rise in temperature the first effect of the application of heat may be merely to initiate a slow oxidation which soon ceases on the removal of the source of heat but a higher temperature may cause so marked an increase m the rate of the chemical action that the heat produced suffices to maintain the temperature, and the oxidation or combustion will proceed unaided. This temperature at which the process of rapid combustion becomes independent of external supplies of heat is termed the ignition temperature of the substance (see p. 106). Phosphorus does not commence rapid combustion until a temperature of 60° C. is attained hydrogen will combine, albeit excessively slowly, with oxygen already at 180° C., but the reaction is not very appreciable below 400° C., and continuous inflammation does not occur until near... 

Optimum conditions for best product quality were found to be 200 °C and 1.5 MPa. The lower tanperatme also provides a stable operation with heat of the reaction being dissipated rapidly through evaporation of acetic acid. Temperature overshoot is undesirable because of possibility of rapid combustion of the solvent and titanium. 

Fig. 6. Schematic ignition diagram for a hydrocarbon+ O2 mixture, with appHcations. Region A, very rapid combustion, eg, a jet engine region B, low temperature ignition, eg, internal combustion engine, safety ha2ards regions C and D, slow oxidation to useful chemicals, eg, 0-heterocycHc compounds in C and alcohols and peroxides in D. Courtesy of Blackwell Scientific PubHcations, Ltd., Oxford (60).

Devolatilization and combustion occur close to the coal inlet tubes. However, because of rapid mixing in the bed the composition of the soflds in the bed may be assumed to be uniform. 

Furnaces for Oil and Natural Gas Firing. Natural gas furnaces are relatively small in size because of the ease of mixing the fuel and the air, hence the relatively rapid combustion of gas. Oil also bums rapidly with a luminous flame. To prevent excessive metal wall temperatures resulting from high radiation rates, oil-fired furnaces are designed slightly larger in size than gas-fired units in order to reduce the heat absorption rates. 

Convection heat transfer is dependent largely on the relative velocity between the warm gas and the drying surface. Interest in pulse combustion heat sources anticipates that high frequency reversals of gas flow direction relative to wet material in dispersed-particle dryers can maintain higher gas velocities around the particles for longer periods than possible ia simple cocurrent dryers. This technique is thus expected to enhance heat- and mass-transfer performance. This is apart from the concept that mechanical stresses iaduced ia material by rapid directional reversals of gas flow promote particle deagglomeration, dispersion, and Hquid stream breakup iato fine droplets. Commercial appHcations are needed to confirm the economic value of pulse combustion for drying. 

Burning a portion of a combustible reactant with a small additive of air or oxygen. Such oxidative pyrolysis of light hydrocarbons to acetylene is done in a special burner, at 0.001 to 0.01 s reaction time, peak at 1,400°C (2,552°F), followed by rapid quenching with oil or water. 

Large Fans These could be used to dilute a vapor cloud below its LFL with ambient air (see, for example, Whiting and Shaffer, Feasi-bihty Study of Hazardous Vapor Amelioration Techniques, Proc. 1978 Nat. Conf. on Control of Hazardous Material Spills, USEPA, Miami Beach, April 1978). But caution must be exercised because the turbulence produced by fans will likely promote rapid combustion and a resulting UVCE unless vapors are diluted below the LFL. Nevertheless, in new plants, strategic placement of air coolers may provide enough air flow to reduce the risk of a UVCE. 

Definition of Dust E losion A dust explosion is the rapid combustion of a dust cloud. In a confined or nearly confined space, the explosion is characterized by relatively rapid development of pressure with a flame propagation and the evolution of large quantities of heat and reaction products. The required oxygen for this combustion is mostly supphed oy the combustion air. The condition necessaiy for a dust explosion is a simultaneous presence of a dust cloud of proper concentration in air that will support combustion and a suitable ignition source. 

A simplified model of PC combustion includes the following sequence of events (I) on entering the furnace, a PC particle is heated rapidly, driving off the volatile components and leaving a char particle (2) the volatile components burn independently of the coal particle and (3) on completion of volatiles combustion, the remaining char particle burns. Whue this simple sequence may be generally correct, PC combustion is an extremely complex process involving many interrelated physical and chemical processes. 

PYROPHORIC SUBSTANCE A material that undergoes such vigorous oxidation or hydrolysis (often with evolution of highly-flammable gases) when exposed to atmospheric oxygen or to water, that it rapidly ignites without an external source of ignition. This is a special case of spontaneous combustion. 

---