Combustion stoichiometric requirements

Air Supply. Oxygen in excess of stoichiometric requirements for complete combustion is needed because incineration processes are not 100% efficient and excess air is needed to absorb a portion of the combustion heat to control the operating temperature. In general, units that have higher degrees of turbulence such as Hquid injection incinerators require less excess air (20 to 60%) while units with less mixing such as hearth incinerators require... 

In processes involving the combustion of fuels, either pure oxygen or air is supplied in amounts greater than the stoichiometric requirements for complete combustion. The terms "theoretical air or theoretical oxygen are thus frequently encountered in combustion problems. The molar composition of dry air at atmospheric conditions [from International Critical Tables, Volume 1, p. 393 (1926)] ... 

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... 

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 ... 

Pure hydrogen gas at room pressure and temperature is adiabatically combusted with air. The combustion takes place with an amount of air that is 30% in excess of what is stoichiometrically required. Calculate the adiabatic flame temperature of the process, the work lost, and the thermo-dynamic efficiency of the process. Assume air to consist of a mixture of 79 mol% of N2 and 21 mol% of 02. 

Although the prediction of N0X emissions under lean and stoichiometric combustion with the extended Zeldovich mechanism is adequate for certain applications, predictive methods for fuels containing bound nitrogen and for rich combustion conditions require substantial improvement. However, the early studies of Fenimore (13, 14) demonstrated the potential importance of HCN and NH type species in fuel-nitrogen interactions. To illustrate the critical importance of the coupling of nitrogenous species reactions in rich combustion, predictions of NO emissions from rich iso-octane combustion in a jet-stirred combustor are shown in Table III. C2 hydrocarbon fragmentation and oxidation creates... 

Although gas turbine combustion systems operate with overall air/fuel ratios which are quite fuel-lean, perhaps three times stoichiometric, stabilization of the combustion process requires that a portion of the combustor, the primary zone, operate stoichiometric or fuel-rich. Under fuel-lean conditions, fuel-bound nitrogen can be converted directly to N0X. Under fuel-rich conditions, fuel-bound nitrogen can be converted to HCN and NH3 in addition to N0X. Of course, in either case, the most desirable product of converted fuel nitrogen would be molecular nitrogen,... 

TABLE 11.2 Stoichiometric Combustion Air Requirements for Pure Liquid Alcohols, MTBE, ETBE, TAME, Isooctane, and Gasoline"... 

Methane is mixed with air at 20% excess over the stoichiometric requirement and undergoes combustion in a burner operating at 2 bar. The inlet gases are at 4 °C and the effluent stream is at 1000 °C. Determine the amount of heat assuming complete oxidation of methane to carbon dioxide and water. For simplicity, assume the heat capacities of the species to be constant and equal to the values given below (in J/mol) ... 

For stoichiometric combustion we need 2 mol of oxygen. The actual amount of oxygen is 20% above the stoichiometric requirement, or, 2 + (o.l)(2) = 2.2 mol. Assuming air to be 2i% oxygen and 79% nitrogen, the inlet stream contains nitrogen in the amount (79/21) times the amount of oxygen ... 

The off-gas generated by the pyrolysis reaction contains combustibles this gas is burned in the SCC, which is sized for sufficient residence time to destmct organics in the off-gas. A carefully controlled quantity of air is also introduced into the SCC, but in this case, excess air, 50-100% of the off-gas stoichiometric requirement, is maintained for complete combustion, in the past, gas cleaiting devices such as bag houses or electrostatic precipitators... 

Stoichiometry is the composition of the air-fuel mixture required to obtain complete combustion. The stoichiometric ratio, r, is the quotient of the respective masses, and m, of air and fuel arranged in the stoichiometric conditions ... 

In a general manner, diesel engines, jet engines, and domestic or industrial burners operate with lean mixtures and their performance is relatively insensitive to the equivalence ratio. On the other hand, gasoline engines require a fuel-air ratio close to the stoichiometric. Indeed, a too-rich mixture leads to an excessive exhaust pollution from CO emissions and unburned hydrocarbons whereas a too-lean mixture produces unstable combustion (reduced driveability and misfiring). 

Where T)is flame temperature in K MC is moisture content of the waste, expressed on a total weight basis SR is defined as stoichiometric ratio or moles O2 avadable/moles O2 required for complete oxidation of the carbon, hydrogen, and sulfur in the fuel, ie, 1/SR = equivalence ratio and is temperature of the combustion air, expressed in K. In Fnglish units, this equation is as follows ... 

Temperature. The temperature for combustion processes must be balanced between the minimum temperature required to combust the original contaminants and any intermediate by-products completely and the maximum temperature at which the ash becomes molten. Typical operating temperatures for thermal processes are incineration (750—1650°C), catalytic incineration (315—550°C), pyrolysis (475—815°C), and wet air oxidation (150—260°C at 10,350 kPa) (15). Pyrolysis is thermal decomposition in the absence of oxygen or with less than the stoichiometric amount of oxygen required. Because exhaust gases from pyrolytic operations are somewhat "dirty" with particulate matter and organics, pyrolysis is not often used for hazardous wastes. 

Stoichiometric Concentration (Used by permission of Frank T. Bodurtha, Inc., New London, New Hampshire). In a combustion reaction in air, the stoichiometric concentration, Cjt, of any reac tant is the concentration theoretically required for complete conversion by reacting completely with oxygen. For example, for the combustion of propane in air ... 

Theoretical Oxygen and Air for Combustion The amount of oxidant (oxygen or air) just sufficient to burn the carbon, hydrogen, and sulfur in a fuel to carbon dioxide, water vapor, and sulfur dioxide is the theoretical or stoichiometric oxygen or air requirement. The chemical equation for complete combustion of a fuel is... 

Theoretical air quantity The stoichiometric quantity of air required for complete combustion of a given quantity of a specific fuel. 

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. 

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. 

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