Equilibrium gas composition

The addition of H2O and CO2 to the fuel gas modifies the equilibrium gas composition so that the formation of CH4 is not favored. Carbon deposition can be reduced by increasing the partial pressure of H2O in the gas stream. The measurements (20) on 10 cm x 10 cm cells at 650°C using simulated gasified coal GF-1 (38% H2/56% CO/6% CO2) at 10 atm showed that only a small amount of CH4 is formed. At open circuit, 1.4 vol% CH4 (dry gas basis) was detected, and at fuel utilizations of 50 to 85%, 1.2 to 0.5% CH4 was measured. The experiments with a high CO fuel gas (GF-1) at 10 atmospheres and humidified at 163°C showed no indication of carbon deposition in a subscale MCFC. These studies indicated that CH4 formation and carbon deposition at the anodes in an MCFC operating on coal-derived fuels can be controlled, and under these conditions, the side reactions would have little influence on power plant efficiency. 

The gasification is performed using oxygen and steam (qv), usually at elevated pressures. The steam—oxygen ratio along with reaction temperature and pressure determine the equilibrium gas composition. The reaction rates for these reactions are relatively slow and heats of formation are negative. Catalysts maybe necessary for complete reaction (2,3,24,42,43). 

A physical sense of this limitation is simple. It implies that catalysis "does not shift the equilibrium , i.e. in the presence of a catalyst the equilibrium gas composition is in equilibrium itself. Generally speaking, it does not only hold for catalytic reactions. Limitations on the equilibrium constants of eqns. (72), (73), and (75) suggest that reactions do not "shift the equilibrium of the others since the equilibrium is detailed. 

Figure 5 Equilibrium gas compositions as functions of (a) temperature, (b) total pressure, (c) Nb/(Nb+Ge) mole fraction, and (d) H/(H+CI) mole fraction in the reactant gas. After Wan.9...

The most important factor affecting equilibrium gas composition is temperature. Deviations from equilibrium can be explained by the presence of pyrolysis gas, arising during thermal decomposition, by uneven gas and solid distribution, due to channeling, baking, clinkering or formation of blowholes, or by inadequate rates of reaction. 

To calculate sulfur emissions, an equation for gas-slag chemical equilibrium for sulfur (Equation 2) and a mass balance for sulfur are solved simultaneously. First, the equilibrium gas compositions were calculated for the combustion of coal with air for a range of sulfur concentrations in the coal. This was done using Alcoa s Chemical Equilibrium Computer Program (23). Next, the concentrations of sulfur in the slags for equilibrium with the combustion gases were calculated. Finally, the quantity of additives needed to obtain these compositions were calculated from sulfur mass balances. 

Thermochemical data needed to calculate the equilibrium gas compositions were taken from the Janaf tables (12). The free energy equations for the sulfur vapor polymers—S2, S3. S4, S5, S6, S7, and S8—were derived by Kellogg (13), based on second law correlations of their mass spectrometric data. 

Equilibrium gas compositions, heats of reaction, and adiabatic temperature changes were calculated for each initial reaction temperature. The variables studied were temperature, pressure, feed steam-carbon ratio, and feedstock. 

Equilibrium gas compositions (on a dry basis) for steam reforming of hexane are given as a function of temperature, pressure, and feed steam-carbon ratio in Figure 5. In the range of variables studied, the carbon dioxide content is almost independent of temperature, pressure,... 

Table A-7 Enthalpy of formation values calculated from equilibrium gas compositions.

Figure 5-59. Water vapor dissociation in thermal plasma equilibrium gas composition in hot thermal discharge zone as function of its temperature at atmospheric-pressure conditions (1) O2, (2) O, (3) OH, (4) Hj, (5) HjO, (6) H.

The temperature-pressure dependent equilibrium gas compositions shown represent the actual test gas composition at each test temperature. Generally, the equilibrium gas composition was obtained in the reactor by interaction of the inlet gas species. This was verified by analyses of the reactor exit gas in a gas chromatograph. 

INLET AND EQUILIBRIUM GAS COMPOSITION OF PHASE I CORROSION TESTS ... 

Once the temperature and liquid composition are known for die inflection point, the equilibrium gas composition, y, can be deteimined from the appropriate equilibrium relationship. These calculations can be repeated at other liquid concentrations to est li the entire temperature pit le for the column along with the temperature-ooirected equiUbrium curve as a fiinction of liquM concentration. The required column height can be detetmined by conventional graphical integration. As an alternative to graphic integration, von Stockar and Wilke propose an analytical approach as defined in the next step. 

Figure 17.12 Equilibrium gas composition as a function of O2/CH4 ratio, in which S/C = 0.88 and T — 900 °C. Observed gas composition was plotted as fiUed markers.

The reforming properties were also examined in view of thermodynamic equilibrium calculation. Figure 17.12 shows equilibrium gas composition under the condition of S/C = 0.88 at 900 °C as a function of O2/CH4 ratio. Actual O2/CH4 ratio was estimated to be 0.264 from CH4 input and oxygen permeation flux values shown in Table 17.1. The observed gas composition seems to show a good agreement with thermodynamically calculated values. A small deviation of H2 concentration seems to originate from an accuracy of the Q-mass spectrometer. 

Figure 3.9 Thermodynamic equilibrium gas composition and reformer adiabatic temperature versus air ratio (X) for gasoline reforming [7] feed temperatures were 400°C for air, 200°C for steam and 20°C for the fuel left, S/C = 0 right, S/C = 0.7.

Figure 3.23 Thermodynamic equilibrium gas composition versus reaction temperature and pressure for propane cracking [79].

Figure 4.5 Thermodynamic equilibrium gas composition for methanol steam reforming versus S/C ratio reaction temperature, 280°C pressure, 5 bar [46].

The addition of H2O and CO2 to the fuel gas modifies the equilibrium gas composition so that the formation of CH4 is not favored. Increasing the partial pressure of H2O in the gas stream can... 

Substituting the appropriate values for K and the concentrations yields two roots of -0.0445 and 1.454. The larger root is physically impossible it wants to react more CO and H2O than are initially present. The remaining root of -0.0445 is used to compute the equilibrium gas composition, which is shown in the following table. 

Hence the equilibrium gas composition is independent of the amount of solid (or liquid) present. For real gases, we have to use the general form of Eq. (4.2.56) ... 

Figure 8.1. Equilibrium gas composition for methane oxidation at CH4 O2 = 2, 800 C and (a) 1 atm total pressure (b) 4 atm total pressure.

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