Carbon, burning

Carbon Burn-off (%) DR plot (carbon dioxide at 273 K) Nitrogen displaced by nonane... 

Spent shale zone residual carbon burned... 

The hydrogen contained in coke bums at a higher rate than carbon. Hydrogen-burning rates are four to five times greater than carbon-burning rates. 

The physical state of the fuel for a combustion process dictates the type of system to be used for burning. A fuel may be composed of volatile material, fixed carbon, or both. The volatile material bums as a gas and exhibits a visible flame, whereas the fixed carbon burns without a visible flame in a solid form. If a fuel is in the gaseous state, such as natural gas, it is very reactive and can be fired with a simple burner. 

It is difficult, essentially impossible, to measure AH for this reaction because when carbon burns, the major product is always carbon dioxide, C02. It is possible, however, to calculate AH using thermochemical data for two other reactions that are readily carried out in the laboratory (Example 8.6). 

The business manager is frugal so he asks, Why not burn the coal directly and save the cost ot manufacturing the water gas The mechanical engineer is practical so he asks, How much heat will the boiler receive if I use coal instead of water gas The chemical engineer goes to the laboratory to find the answers by measuring the heat released per mole of carbon burned in reaction (4). The laboratory result shows that reaction (4) releases 94.0 kcal/mole ... 

C22-0070. Tabulate the differences in temperature and composition of a first-generation star at the hydrogen-, helium-, and carbon-burning stages of its evolution. 

C22-0073. Second- and third-generation stars may contain significant amounts of carbon yet carbon burning does not begin until the third stage of their evolution. Explain this. 

The result is a type of onion-like model of the star with an iron-nickel core in the centre. The situation is somewhat different for smaller stars the path branches at the point where carbon burning (12C +12 C) begins. While the heavier stars are not affected by this process, the smaller ones (4-8 solar masses) are completely torn apart by carbon burning. 

In the heavier stars, a stage in which 20Ne is destroyed occurs subsequently to the carbon burning, but before the absorption of oxygen. The a-particles formed are used up by the nuclei already present (also from neon itself) in so-called neon burning. 

These reactions take place in the inner zone of stars heavier than 15 solar masses. Hydrostatic carbon burning is followed by explosive neon burning at temperatures of around 2.5 x 109K. Under these conditions, phosphorus (31P) can be formed, although complex side reactions also occur. In comparison with the formation of... 

Carbon burning Carbon Oxygen, neon, sodium, 8 x 108 1.4... 

In an oxygen-rich atmosphere, carbon burns to produce carbon dioxide, CO2. Both carbon monoxide, CO, and carbon dioxide are produced when carbon is burned in an oxygen-deficient atmosphere. This makes the direct measurement of the enthalpy of formation of CO difficult. CO, however, also burns in oxygen, O2, to produce pure carbon dioxide. Explain how you would experimentally determine the enthalpy of formation of carbon monoxide. 

The rate of oxygen utilization is related to the intrinsic rate of carbon burning by the ratio of CO to CO2 produced in the burning reaction. This relation can be expressed in terms of a constant a that is defined as the moles of coke burned per mole of O2 consumed, and varies between 1 and 2. The relation between the two rates is given by... 

One good method of exploring the effects of variables on kiln performance is to prepare performance maps of appropriate subspaces of the kiln performance space. The most widely used map for this application was a graph of catalyst circulation rate versus carbon burned. Temperature and bum-off constraint curves were used to define the operating region given as shaded areas in Fig. 14. The conditions for the kiln used in Fig. 14 are given in Table IV. 

The amount of carbon burning is given by the amount of oxygen moving across the burning front multiplied by the intrinsic value of a oi = 2(/8 + 1)/(J3 + 2). Thus,... 

D Diffusion coefficient, fF/hr Deo CO diffusion coefficient Dox Oj diffusion coefficient / Rate of flow of oxygen through outer surface of bead, moles/hr /s Rate of carbon burning at bead surface... 

Heat of reaction for combustion of coke to CO, Btu/lb dutff Heat of reaction for combustion of fast coke, Btu/lb AHx [axAHcoj + 2(1 - a,) AHJ/a k Rate constant for carbon burning, ft /(lb mole)(hr)... 

Figure 4.45 TCA curve showing carbon burn for spent FCC catalyst heated at 10°C/min in 0.5% O,.

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