Combustion gas-solid

Recently, studies from outside the Soviet Union have started to appear in the literature. In the US, Holt and Kingman17 reported the synthesis of transition metal nitrides not from gas-solid combustion reactions, but by using sodium azide as a solid source of nitrogen, according to the scheme ... 

Detailed experimental studies on these gas-solid combustion reactions reveal the dependence of combustion and propagation characteristics, like front propagation velocity, combustion temperature and degree of conversion, on operating parameters like nitrogen pressure, particle size and morphology of the reactant metal and dilution of the gas and solid phases. From these studies the optimum synthesis conditions for a variety of nitrides are determined and information about the mechanisms of several gas-solid combustion reactions is obtained. With the aid of combustion theory, the apparent values of activation energy for several nitridation reactions are calculated from measured combustion characteristics. 

The second type, called gas-solid combustion synthesis, involves at least one gaseous reagent in the main combustion reaction ... 

Covering the side surfaces of the sample limits filtration to one dimension, which simplifies the experimental and theoretical study of gas-solid combustion... 

LINEAR STABILITY OF A PLANAR REVERSE COMBUSTION FRONT PROPAGATING THROUGH A POROUS MEDIUM GAS-SOLID COMBUSTION MODEL... 

In gas-solid extractions the sample is passed through a container packed with a solid adsorbent. One example of the application of gas-solid extraction is in the analysis of organic compounds for carbon and hydrogen. The sample is combusted in a flowing stream of O2, and the gaseous combustion products are passed through a series of solid-phase adsorbents that remove the CO2 and 1T20. 

Fig. 2. Overall schematic of solid fuel combustion (1). Reaction sequence is A, heating and drying B, solid particle pyrolysis C, oxidation and D, post-combustion. In the oxidation sequence, left and center comprise the gas-phase region, tight is the gas—solids region. Noncondensible volatiles include CO, CO2, CH4, NH, H2O condensible volatiles are C-6—C-20 compounds oxidation products are CO2, H2O, O2, N2, NO, gaseous organic compounds are CO, hydrocarbons, and polyaromatic hydrocarbons (PAHs) and particulates are inerts, condensation products, and solid carbon products.

Fluidized-Bed Combustion The principles of gas-solid fluidization and their application to the chemical process industry are treated in Sec tion 17. Their general application to combustion is reviewed briefly here, and their more specific application to fluidized-bed boilers is discussed later in this section. 

All combustion equipment (oil, gas, solid fuel) requires primary air to support combustion and secondary air to permit adequate velocities in flue ways, etc. These requirements are governed by the minimum air/fuel ratio and operating flue-way parameters. There are also published recommended minimum requirements that are generally in excess of these. 

Williams (W2) has recently modified the analysis of Hart and McClure by considering in more detail the effect of diffusional processes on the gas-phase reaction zone. The results of his study show that the diffusional processes tend to stabilize the gas-phase combustion process, indicating that the postulated solid-phase reactions are probably the underlying cause of the instability. 

Peclet number, 352 trickle operation, 92-93 gas phase, 94 liquid phase, 103 Penetration theory, 340 Polymers, 38-40 n-Propane, 178 Propellants, solid combustion, 4-50 flameless, 45... 

The rates of gas—solid reactions are surface area dependent, so finely divided metals, coal etc. may be prone to oxidation leading to spontaneous combustion. 

The rates of gas-solid reactions are surface area dependent, so finely- vided metals, coal etc. may be prone to oxidation leading to spontaneous combustion. A combustible dust will burn much more rapidly than the bulk sold, and if dispersed in air cause a dust explosion (refer to Table 6.2). 

Increasing the surface area of a combustible solid enhances the ease of ignition. Hence dust burns more rapidly than the corresponding bulk solid combustion of dust layers can result in rapid flame spread by train firing . Solid particles less than about 10 pm in diameter settle slowly in air and comprise float dust (see p. 51 for settling velocities). Such particles behave, in some ways, similarly to gas and, if the solid is combustible, a flammable dust-air mixture can form within certain limits. Larger particles also take part, since there is a distribution of particle sizes, and ignition can result in a dust explosion. 

Gas-solid where the solid may take part in the reaction or act as a catalyst. The reduction of iron ores in blast furnaces and the combustion of solid fuels are examples where the solid is a reactant. 

Chemical Reaction. Chemical reaction of particulate material generates stresses within the particle that can lead to fracture. In the case of gas-solid reactions, the particle degradation is also desired because it accelerates the reaction by extending the reactive surface. A relevant commercial example is the particle degradation of solid fuels in combustion processes. This latter topic has been studied by Massimilla and coworkers extensively. The reader is referred for further details to a review given by Chirone et al. (1991). 

The flaming results extend to = 4 in Figures 2.3 and 2.4, at which point gas phase combustion appears to cease. However, combustion must continue since the heat of combustion remains nonzero. This is due to oxidation of the remaining solid fuel. If we consider wood, it would be the oxidation of the surface char composed primarily of carbon. From Example 2.3, we obtain the heat of combustion for carbon (going to CO2) as 32.8 kJ/g carbon. From Figure 2.4, we see a significant production of carbon monoxide at < > 4, and therefore it is understandable that Figure 2.3 yields a lower... 

Heterogeneous combustion, 7 449-454 Heterogeneous copolymerization of acrylonitrile, 11 203—204 with VDC, 25 698-699 Heterogeneous enzyme systems, 10 255-256 Heterogeneous gas-solid catalytic reactions, 21 340-341 Heterogeneous Ideal Adsorbed Solution Theory (HIAST), gas separation under, 1 628, 629... 

Recirculation of combustion products can be obtained by several means (1) by inserting solid obstacles in the stream, as in ramjet technology (bluff-body stabilization) (2) by directing part of the flow or one of the flow constituents, usually air, opposed or normal to the main stream, as in gas turbine combustion chambers (aerodynamic stabilization), or (3) by using a step in the wall enclosure (step stabilization), as in the so-called dump combustors. These modes of stabilization are depicted in Fig. 4.52. Complete reviews of flame stabilization of premixed turbulent gases appear in Refs. [66, 67],... 

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