Nature of Combustion Products

Some of the important properties which are considered when choosing the ingredients for pyrotechnic formulations are density, hygroscopicity, melting and boiling points and decomposition temperatures, oxygen content of oxidizers, thermal conductivity of fuels and containers, nature of combustion products and toxicity etc. 

Incineration is a rapid, exothermic reaction between a fuel (waste) and oxygen (O2). Incineration produces the same end products and by-products, whether the material burned is municipal solid waste, hazardous waste, or medical waste. This is because of the fact that complex fuel molecules first undergo thermal decompositions upon being preheated by the preceding flame, forming smaller molecules such as methane, acetylene, ethylene, carbon monoxide, hydrogen, and alike, and it is the combustion of these smaller molecules that primarily influence the nature of combustion products and pollutants formed. This aspect of combustion chemistry has significantly helped in the development of detailed kinetic mechanisms of combustion for all types of hydrocarbon fuels. Solid decomposition... 

Air is made up of a mixture of different gases and material from natural processes such as wind erosion, evaporation from the sea, earthquakes, and from human activity in the form of combustion products from processes and vehicles. 

Gas-Fired water heaters are also made more efficient by a variety of designs that increase the recov-ei y efficiency. These can be better flue baffles multiple, smaller-diameter flues submerged combustion chambers and improved combustion chamber geometry. All of these methods increase the heat transfer from the flame and flue gases to the water in the tank. Because natural draft systems rely on the buoyancy of combustion products, there is a limit to the recovery efficiency. If too much heat is removed from the flue gases, the water heater won t vent properly. Another problem, if the flue gases are too cool, is that the water vapor in the combustion products will condense in the venting system. This will lead to corrosion in the chimney and possible safety problems. 

The mechanism of combustion of blackpowder is extremely complex and only an outline can be given here. It will be convenient to consider first the initial chemical reactions in ignition, then the reactions which occur during the main combustion and finally the nature of the products. 

Of the various synthetic processes that are available, two are of most relevance in the present context - precipitation from aqueous solution and melt forming. These methods are used where it is not possible to produce adequate products directly from natural sources. This will be because there is no suitable mineral, due to the chemical nature of the product, of particle size and shape requirements, or to purity considerations. The other principal synthetic method in use for filler production is pyrolysis/combustion. This type of process in which the particles are formed in the gas phase is used where very small particles are required, such as with carbon blacks and some silicas. This type of filler is not widely used in thermoplastics and so these processes are not discussed in any detail here, although some information specific to the production of antimony oxide will be found later. 

Retene is a methyl isopropyl phenanthrene (Fig. 2). As mentioned above, Wakeham [43] was the first to address the natural non-combustion production of retene in relation to lake sediments. The starting material for retene is abietic acid, a diterpenoid found primarily in the resin of coniferous trees. When burned, the abietic acid forms retene. It can also degrade via one of two pathways to retene without combustion (Fig. 5). One pathway is through dehydro abietin and another intermediate to retene. The other proceeds through dehydroabietane, another intermediate to simonellite and finally to retene. These mechanisms can occur in both the atmosphere [44] and in aquatic systems. Therefore, where there is abietic acid, retene can follow. This becomes especially important in areas where there are high densities of conifers, and thus abietic acid. 

One of the important hydrocarbon combustion reaction intermediates is the CH radical. Although CH chemiluminescence (.42 A — X2ir) has been observed in many hydrocarbon flames, the mechanism of CH formation and its reaction kinetics have been difficult to unravel in situ due to the low steady-state concentrations and the complex nature of combustion reactions. This project was undertaken to investigate a means of CH radical production and to study its reactions with various important species so that an overall picture of the oxidation processes, particularly with regard to the mechanism of NO formation, may be better understood. 

Volume of combustion products produced per standard cubic foot of natural gas burned 11.5 std ft3 (11.5 m3 per standard cubic meter)... 

BOILERS—The control of combustion products varies with the fuel combusted and boiler design. For natural gas and fuel oil combustion, the control mechanism for NOx and CO emissions is typically a burner system that... 

Gross heating value of natural gas= 1059Btu/scf of natural gas Combustion products per cubic foot of natural gas burned =11.5 scf/scf natural gas... 

Natural gas and air in proper proportions will ignite and liberate heat. The liberated heat is absorbed primarily by the products of combustion and air. The sudden rise of temperature of the mixture gases also causes a sharp increase in pressure. Under a confined situation, this instantaneous pressure increase can result in an explosion. This is why it is important that everyone involved with the natural gas industry understand the flammability limits and the nature of combustion. 

As is the case with methane, experiments have been performed with ethane for the purpose of separation of gaseous mixtures in analytical procedures. Phillips37 found that ethane was oxidized in a 3.1 per cent mixture with air at 450° C. over palladium asbestos. Mixtures of ethane and methane are difficult to separate by preferential combustion over platinum or palladium but hydrogen may be removed from such mixtures due to its lower reaction temperature.31 The nature of the products obtained from the hydrocarbon oxidation in these experiments was not reported. 

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