Combustion stoichiometric

Cp a = specific heat of air at constant pressure AT jj = temperature rise for stoichiometric combustion D = surface average particle diameter Pa = air density Pf = fuel density

equivalence ratio B = mass transfer number... 

The exhaust gases from a gas turbine contain substantial amounts of excess air, since the main combustion process has to be diluted to reduce the combustion temperature to well below that which could be obtained in stoichiometric combustion, because of the metallurgical limits on the gas turbine operating temperature. This excess air enables supplementary firing of the exhaust to take place and higher steam temperatures may then be obtained in the HRSG. 

In the conventional gas turbine plant, a hydrocarbon fuel (e.g. methane CH4) is burnt, usually with excess air, i.e. more air than is required for stoichiometric combustion. 

In the second chemical reaction to be considered, insufficient oxygen is supplied to the fuel for stoichiometric combustion (50%), but steam is also supplied (Fig. 8.5c). Now the chemical reactions involved in the partial combustion are ... 

We next consider a number of plants in which the combustion process is modified by changing the oxidation of the fuel. Table 8. ID and Figs. 8.18-8.20. The first group (Dl, D2 and D3) are plants with PO—insufficient air is supplied to the PO reactor, less than that required to produee stoichiometric combustion. The second group (D4, D5 and D6) are plants where air is replaced as the oxidant by pure oxygen whieh is assumed to be available from an air separation plant. 

A simple PO plant (DI). Fig. 8.18, after Newby et al. 112], shows a simple PO plant, of the type listed as Dl in Table 8.ID. In this plant insufficient air is supplied to the PO reactor, less than that required for producing stoichiometric combustion. After expansion in the PO turbine the fuel gas is fed to the main turbine combustor where additional air is also supplied for complete combustion. 

H = visible flame height S = 2.3 X = flame speed = wind speed d = cloud depth g = gravitational acceleration po = fuel-air mixture density pj = density of air r = stoichiometric air-fuel mass ratio a = expansion ratio for stoichiometric combustion under constant pressure (typically 8 for hydrocarbons)... 

Calculate w from the actual mixture composition , the stoichiometric mixture composition <()s, and the expansion ratio for stoichiometric combustion a ... 

Carbon monoxide is usually sampled as the second parameter in conjunction with carbon dioxide or oxygen. In theory, as the optimum is usually to have near-stoichiometric combustion without CO breakthrough it is the most reliable gas to sample. A problem is that although small quantities of CO usually indicate the need for additional air, they can also be caused by flame chilling and careful interpretation of results is needed. 

The flue gas is diluted with air at a ratio that is known as F, i.e. VIVo, where V = actual flue gas volume and Vo = the stoichiometric combustion volume. 

To obtain hygienic combustion, it is essential to adjust the equivalence ratio 0 to an ideal value. This value characterises the ratio of the fuel quantity needed for a stoichiometric combustion to the fuel quantity supplied. In most of the common gas appliances, the air supply slightly exceeds the amount of air needed for complete stoichiometric combustion. The exact value for the surplus of air - often referred to as lambda (X) - depends on the configuration of the burner system in question. 

Another approach is to estimate the fuel concentration at point S by extending the line from point R though the intersection of the minimum oxygen concentration (M) and the stoichiometric combustion line. The analytical result is... 

If a detailed flammability diagram is lacking, then the ISOC is estimated. One approach is to use the intersection of the LFL with the stoichiometric combustion line. A line is drawn... 

Figure 7-8 Estimating a target nitrogen concentration at point S for placing a vessel into service. Point M is the intersection of the LFL line with the stoichiometric combustion line.

A useful application of this result is shown in Figure AC-5. Suppose that we wish to find the oxygen concentration at the point where the LFL intersects the stoichiometric line shown. The oxygen concentration in question is shown as point X in Figure AC-5. The stoichiometric combustion equation is represented by... 

Based on stoichiometric combustion in air. b Based on water and fuel in the gaseous state. 

The amount of explosion overpressure is determined by the flame speed of the explosion. Flame speed is a function of the turbulence created within the vapor cloud that is released and the level of fuel mixture within the combustible limits. Maximum flame velocities in test conditions are usually obtained in mixtures that contain slightly more fuel than is required for stoichiometric combustion. Turbulence is created by the confinement and congestion within the particular area. Modem open air explosion theories suggest that all onshore hydrocarbon process plants have enough congestion and confinement to produce vapor cloud explosions. Certainly confinement and congestion are available on most offshore production platforms to some degree. 

Stoichiometric combustion air requirement, 72 322t Stoichiometric concentration, 27 840 Stoichiometric organic synthesis, metal carbonyls in, 76 72 Stoichiometric parameters, in reactor technology, 27 337-338 Stoichiometric ratios, epoxy/curing agent, 70 418-420... 

Natural gas engines can use lean-burn or stoichiometric combustion. Lean-burn combustion is similar to that which occurs in diesel engines, while stoichiometric combustion is more similar to the combustion in a gasoline engine. 

FIGURE 9.23 Adiabatic flame temperature for stoichiometric combustion of methane in mixtures of oxygen with nitrogen and oxygen with carbon dioxide, computed using NASA s Chemical Equilibrium Analysis (CEA) program [52]. 

The general equation, above, is no longer accurate above an x of 1. Beyond x = [n - (p/2)] = 1 (when p = 0), where water is a product, the heat of reaction is determined by the phase of the product water. At still higher values, the excess oxygen oxidizes the hydrogen to produce water. Finally, at stoichiometric combustion, all carbon and hydrogen are converted to carbon dioxide and water. 

Figure 3. Composition distribution of the aerosol produced by near stoichiometric combustion ((f> = 0.96) and swirl number of 4.3. Oxides were determined as elements using FIXE carbon was inferred from absorption measurements.

Similar plots of the data from higher temperature, nearly stoichiometric combustion. Figure 6, show substantially different trends. The refractory species, i.e., A1, Si, and Ca,show little variation with particle size. Comparison with Figure 5 suggests that this results from vaporization of small amounts of these species. The apparent decrease in the fine particle iron is caused by dilution with other major ash constitutents. Both sulfur and zinc concentrations increase as size decreases in spite of the larger amount of the other species in the fines. 

Capacities of 10-200 MBtu/hr can be accommodated in heaters with single radiant chambers, and three to four chambers with a common convection section are feasible. Stoichiometric combustion air requirements of typical fuels are tabulated ... 

However, in this paper Ya.B. went further and considered the chemical kinetics. He determined the limit of intensification of diffusion combustion, which is related to the finite chemical reaction rate and the cooling of the reaction zone, for an excessive increase of the supply of fuel and oxidizer. If the temperature in the reaction zone decreases in comparison with the maximum possible value by an amount approximately equal to the characteristic temperature interval (calculated from the activation energy of the reaction), then the diffusion flame is extinguished. The maximum intensity of diffusion combustion, as Ya.B. showed, corresponds to the combustion intensity in a laminar flame of a premixed stoichiometric combustible mixture. 

A major advantage of oil is its high energy density (calorific value -around 42-43 MJ/kg), easier transportation and consumption. The ratio of hydrogen atoms to carbon atom is typically around 2 1. That s why a complete combustion of oil emits less CO2 than a complete combustion of coal per unit of energy (73 75 gC02/MJ at stoichiometric combustion). 

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