Combusting particle, material properties

Other properties of dusts that affect the likelihood of ignition and the severity of combustion include particle size, concentration, oxygen presence, presence of impurities, moisture content, and air turbulence. Small particles ignite easier than large particles. Fine dusts often have high rates of pressure rise during combustion. Similar to flammable gases and vapors, certain concentrations of dusts in air are combustible. Particle size affects the concentration required for combustion. If a concentration is too low, combustion is not likely. The presence of inert material in a dust can reduce its... 

Carbon Black (CB) is a colloidal form of elemental carbon, which usually consists of spherical particles. Size of these molecules is less than few dozen nanometers. Particles create agglomerations with different spatial configuration. Structure and configurations of particles influence properties of carbon black. The genesis of obtaining carbon black is mainly based on incomplete combustion of carbonaceous materials. The main precursors include wood, coal, natural gas and hydrocarbons. The basic production methods for this material include furnace method, lamp method, and now more widely used plasma method. Commercially available carbon black fillers have varying level of structure, particle size, chemical reactivity and pH that lead to different levels of reinforcement. 

Table 5.9 Selected material properties for combusting particle.

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

PCDD/F and other chlorinated hydrocarbons observed as micropollutants in incineration plants are products of incomplete combustion like other products such as carbon monoxide, polycyclic aromatic hydrocarbons (PAH), and soot. The thermodynamically stable oxidation products of any organic material formed by more than 99% are carbon dioxide, water, and HCl. Traces of PCDD/F are formed in the combustion of any organic material in the presence of small amounts of inorganic and organic chlorine present in the fuel municipal waste contains about 0.8% of chlorine. PCDD/F formation has been called the inherent property of fire. Many investigations have shown that PCDD/Fs are not formed in the hot zones of flames of incinerators at about 1000°C, but in the postcombustion zone in a temperature range between 300 and 400°C. Fly ash particles play an important role in that they act as catalysts for the heterogeneous formation of PCDD/Fs on the surface of this matrix. Two different theories have been deduced from laboratory experiments for the formation pathways of PCCD/F ... 

Carbon black Finely divided carbon made by incomplete combustion or decomposition of natural gas or petroleum-based oils in different types of equipment. According to the process and raw material used, it can be furnace (e.g., HAF), thermal (e.g., MT), or channel carbon black (e.g., EPC), each having different characteristics, such as particle size, structure, and morphology. The addition of different types of carbon blacks to rubber compounds results in different processing behavior and vulcanizate properties. 

In a nutshell, the performance of weapons and munitions increases with the use of nanosized particles because of the increased surface area and enhanced heat transfer resulting in reduced ignition delay, burn time, improved mechanical properties and high density-specific impulse. Further, formulations based on micron-sized materials with a wide distribution suffer from defects such as slow energy release, incomplete combustion and inability to support rapid combustion which can be overcome with the use of nanoparticles or nanomaterials [102]. 

The central thesis of the theory of the non-steady combustion of powders and explosives developed by Ya.B. in this article is the assumption of rapid readjustability of the gas phase of combustion compared to thermal changes in the condensed phase, which allows us to consider the gas phase as quasi-steady. This fundamental property of burning condensed materials allows us not only to significantly simplify the solution of the problem by reducing it to an analysis of the non-steady temperature distribution in the surface layer of the condensed material, but also not to carry out a detailed analysis of the complex structure of the combustion zone above the material (the multi-stage character of the chemical transformation, thermal decomposition, and gasification of the dispersed particles of condensed material and other processes). 

Wood powder is a kind of upgraded fuel that is burned in large-scale combustion plants for heat production. However, it is possible to use wood powder for power generation as well. It is a biofuel made of sawdust, shavings and bark. The raw material is crushed, dried and milled to tine particles in order to obtain the best fuel properties. There are many different wood powder qualities dependant on different physical properties such as particle size distribution, particle shape and also moisture content. The powder is usually handled in a closed system from milling to storing in silos to avoid the risk of dust explosions. The raw materials and type of mill used determine the properties of the wood powder (Paulrud et al, 2002). 

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