Ethane heating value

A natural gas having the volumetric composition of 90% methane, 8% ethane, and 2% nitrogen at 1 atm and 25°C is used as fuel in a power plant. To ensure complete combustion 75% excess air is also supplied at 1 atm and 25°C. Calculate (i) the lower and higher heating values of the fuel at 25°C and (ii) the theoretical maximum temperature in the boiler assuming adiabatic operation and gaseous state for all the products. 

Propane is a more reactive paraffin than ethane and methane. This is due to the presence of two secondary hydrogens that could be easily substituted (Chapter 6). Propane is obtained from natural gas liquids or from refinery gas streams. Liquefied petroleum gas (LPG) is a mixture of propane and butane and is mainly used as a fuel. The heating value of propane is 2,300 Btu/ft. LPG is currently an important feedstock for the production of olefins for petrochemical use. 

A fuel gas is known to con tain methane, ethane, and carbon monoxide. A sample of the gas is charged into an initially evacuated 2.000-liter vessel at 25 C and 2323 mm Hg absolute. The vessel is weighed before and after being charged, and the mass difference is found to be 4.929 g. Next, the higher heating value of the gas is determined in a calorimeter to be 841.9 kj/mol. Calculate the molar composition of the gas. 

Ethane heat flux 23 to 28 kW/m at exit conditions with double values at inlet Propane heat flux 14 to 17 kW/m at exit conditions with double values at inlet Butane or naphtha heat flux 11 to 15 kW/m at exit conditions at inlet the values are twice as large. 

The fuel used for experiments was a typical LPG used by industry, composed of more fhan 98% propane, 0.9% ethane, and 0.8% butane with lower heating value equal to 93.2 MJ/Nm3. 

To obtain favorable reaction rates the product gas must contain some unreacted hydrogen. The synthesis of ethane makes this possible and at the same time meets the objective of a high volumetric heating value. Aromatic liquids are relatively inexpensive to produce since they contain little more hydrogen than coal. Another advantage is that a Btu of liquid is cheaper to transport by pipeline than a Btu of gas. 

Selection of Calorimetry Standard Compositions. The composition criteria for low and high Btu calorimetric standards are less severe than for the GC standard. This is because the calorimeter measures the gross heating value of a fuel gas independently of its composition. Thus, simple binary mixtures of methane/ ethane and methane/nitrogen can be selected to attain any desired... 

Table 2 lists the compositions and heating values of several mixtures which were considered for these standards. Figure 2 illustrates the SRK. dew point vs pressure curves for these mixtures. It can be seen that, while the 812 Btu/SCF gas (mixture B) has a dew point temperature of -144°F, the 1261 Btu/SCF gas (mixture 5) approaches the -5°F dew point region. Thus the mixture represented by curve C , a 75% methane, 25% ethane blend with a heating value of 1185 Btu/SCF was chosen to be as near 1200 Btu/SCF as possible and yet maintain a reasonably low dew point temperature of-26°F/. 

For an industrial gaseous fuel (e.g., natural gas, syngas, producer gas and water gas) containing carbon monoxide, hydrogen, methane, ethane and acetylene, the high and low heating values can be calculated with the following two equations based on the volume or mole fraction of each gas ... 

The fact that both heats of formation and equilibrium pressures of the hydrates of spherical molecules correctly follow from one model must mean that the L-J-D theory gives a good account of the entropy associated with the motions of these solutes in the cavities of a clathrate. That the heat of formation of ethane hydrate is predicted correctly, whereas the theoretical value of its vapor pressure is too low, is a further indication that the latter discrepancy must be ascribed to hindered rotation of the ethane molecules in their cavities. 

Explain why the heat capacities of methane and ethane differ from the values expected for an ideal monatomic gas and from each other. The values are 35.309 J-K " mol 1 for CH4 and 52.63 J-K -mol 1 for C2He. 

From such crude data as are to be found in the literature we can calculate approximate values of the equilibrium constants, and hence of the free energies of dissociation for the various hexaarylethanes. From our quantum-mechanical treatment, on the other hand, we obtain only the heats of dissociation, for which, except in the single case of hexaphenylethane, we have no experimental data. Thus, in order that we may compare our results with those of experiment, we must make the plausible assumption that the entropies of dissociation vary only slightly from ethane to ethane. Then at a given temperature the heats of dissociation run parallel to the free energies and can be used instead of the latter in predicting the relative degrees of dissociation of the different molecules. 

Heats of combustion are very accurately known for hydrocarbons. For methane the value at 25°C is 212.8 kcal mol (890.4 kJ mol ), which leads to a heat of atomization of 398.0 kcal mol (1665 kJ mol ) or a value of for the C—H bond at 25°C of 99.5 kcal mol (416 kJ mol ). This method is fine for molecules like methane in which all the bonds are equivalent, but for more complicated molecules assumptions must be made. Thus for ethane, the heat of atomization at 25°C is 676.1 kcal mol or 2829 kJ mol (Fig. 1.11), and we must decide how much of this energy is due to the C—C bond and how much to the six C—H bonds. Any assumption must be artificial, since there is no way of actually obtaining this information, and indeed the question has no real meaning. If we make the... 

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