Combustion of char

The amount and physical character of the char from rigid urethane foams is found to be affected by the retardant (20—23) (see Foams Urethane polymers). The presence of a phosphoms-containing flame retardant causes a rigid urethane foam to form a more coherent char, possibly serving as a physical barrier to the combustion process. There is evidence that a substantial fraction of the phosphoms may be retained in the char. Chars from phenohc resins (qv) were shown to be much better barriers to pyrolysate vapors and air when ammonium phosphate was present in the original resin (24). This barrier action may at least partly explain the inhibition of glowing combustion of char by phosphoms compounds. 

Combustion of char or feedstock produces ash, unreacted organic material, which can be melted into liquid slag. Slag can be resolidified to form clinker. 

Combustion of char and gas occurs within the jet to provide the heat necessary for the endothermic devolatilization, gasification, and desulfurization chemical reactions. Extraction steam from the steam turbine is also fed to the gasifier. CO and H2 are the... 

It (1 ) deals with the derivation of relations giving the particle size distribution in the bed, overflow, and carryover streams and their respective weights. This theory will be extended to include the effects of particle growth or shrinkage (Z>1 or Z<1). For typical combustion of char containing sulfur followed by sulfur dioxide absorption by limestone, relations will be derived to determine the extent of sulfur retention. The reaction, carryover, and overflow rates will be evaluated with particular attention to their dependence on Z. 

Table II. Kinetic Data for the Combustion of Chars and Coke...

Earlier work in this laboratory has shown that combustion of chars of low and high-rank coals occurs under regime II conditions ( ), l e under circumstances where pore diffusion as well as chemical reaction exercises marked rate control Hie values of the activation energy for the Millmerran and Wandoan chars 20... 

One of the more innovative pyrolytic gasification processes is an indirectly heated, fluid-hed system (c/. Alpert et al, 1972 Bailie, 1981 Paisley, Feldmann, and Appelbaum, 1984). This system uses two fluid-bed reactors containing sand as a heat transfer medium. Combustion of char formed in the pyrolysis reactor takes place with air within the combustion reactor. The heat released supplies the energy for pyrolysis of the combustible fraction in the pyrolysis reactor. Heat transfer is accomplished by flow of hot sand from the combustion reactor at 950°C to the pyrolysis reactor at 800°C and return of the sand to the combustion reactor (Fig. 9.5). This configuration separates the combustion... 

The pyrolysis products are mixed (block Mixer 1) and divided into two portions to ecd the so-called dense bed. The reactors Dense bed 1, Dense bed 2, and Flame 1 --lame 4 include extended chemical mechanisms describing the combustion of char, tar ind pyrolysis gases... 

The results show that combustion of char has a progressive adverse effect on acceptor activity. Work is now in progress to understand the reasons for this and eventually ameliorate the effect. 

Avedesian MM. Combustion of char in fluidized beds. PhD dissertation University of Cambridge, 1972. 

C and subsequently analysed the extent of aromatisation was investigated as a function of HTT. This technique has been also applied to chars prepared in the presence of inorganic additives, thus assessing the effect of these latter on the development of aromaticity and the relationship between the structure and combustibility of char. The additives chosen were flaming inhibitors, which include both an inhibitor and an enhancer of smouldering combustion. The influence of these additives on cellulose degradation will be discussed more in detail in Section 14.3.5. 

It is generally accepted that j sification consists of more than five chemical processes such as pyrolysis, p>artial oxidation of char, further decompx)sition of tar, secondary reactions, and combustion of char or It is obviously difficult to simulate actual coal gasification precisely by applying reliable scientific analysis of fundamental exp>eriment. Since coal gasification is a very complicated both from experimental and theoretical pxiints of view, its chemical process cannot be completely understood merely by the accumulation of kinetic data. 

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