Higher heating value calculation

Figure 27-11 gives the theoretical air requirements for a variety of combustible materials on the basis of fuel higher heating value (HHV). If only the fuel lower heating value is known, the HHVean be calculated from Eq. (27-6). If the ultimate analysis is known, Eq. (27-7) can be used to determine HHV. 

The calculation of the turbine firing temperature (Ttit) is based firstly on the fuel injected into the turbine and the fuel s lower heating value (LHV). The lower heating value of the gas is one in which the Fl20 in the products has not condensed. The lower heating value is equal to the higher heating value minus the latent heat of the condensed water vapor. 

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. 

With H 0(( ) as a product, the higher heating value (HHV) of the fuel is calculated as... 

The higher heating value of R1 —> R3 was calculated based on RDF composition when assuming that only biowaste was degradated and the reduction rate was 60%. 

Boiler Thermal Efficiency Traditionally, boiler thermal efficiency is calculated pour/pm, where in is the LHV (lower heating value) of the fuel. A rule of thumb for economizers is that boiler efficiency increases by 1 percent for every 22°C (40°F) drop in temperature of the dry flue gas. These two statements do not reveal the considerable quantity of additional heat, available to be recovered through condensation of the water vapor in the flue gas, which is lost to atmosphere with hot flue gas. Based on fuel HHV (higher heating value), the total latent heat loss can be substantial an additional 9.6 percent (natural gas), 8.0 percent (propane), 6.5 percent (heating ou). 

Demirbas, A. 1998. Enel properties and calculation of higher heating values of vegetable oils. Enel 77 1117-1120. 

Table 6.12 shows the proximate analysis data and higher heating values (HHV) of samples. The HHV (MJ/kg) of the moss and alga samples as a function of fixed carbon (FC), wt.% can be calculated from ... 

These equations can be used to calculate the gross heating value or higher heating value of fuel whereby water formed during combustion is condensed and combustion gases are cooled to the initial fuel-air temperature. 

Figure 1 shows the calculated cost of hydrogen as a function of the electrolyzer plant cost, in dollars per KW (calculated from the higher heating value of the hydrogen produced — i.e., 10.7 SCFH 1 KW) of output and the overall system efficiency (ratio of KW output to the electrical power input), for an electric power cost of... 

Association (United States) calculates efficiencies based on the lower heating value (LHV) for gas fuels and the higher heating value for oil fuels. It is general practice to report gas-engine performance in terms of British thermal units per horsepower-hour (LHV) and oil-engine... 

To calculate a lower heating value of a fuel from a higher heating value or vice versa, you must determine the moles of water produced when one mole of the fuel is burned. If this quantity is designated n, then... 

The higher heating values of the components are calculated from the given heats of combustion (which are the negatives of the lower heating values) as follows ... 

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. 

TABLE 3.8 Comparison of the Measured and Calculated Higher Heating Values of Biomass, Coal, and Peat ... 

Material Measured higher heating value (MJ/dry kg) Calculated higher heating value (MJ/dry kg) Error (%)... 

The conditions for combustion are atmospheric pressure, 20°C, and product water in the liquid state. The higher heating value per unit volume is calculated from the density (20°C74°C) and the higher heating value per unit mass. 

The fuel consumption rate is a direct measure of cooking power, provided all the gas is subsequently burned in the burner section. The heating value of most biomass with 5-10% moisture (Denver dry) is -18 kj/g, The stove typically produces 20-25% charcoal after the volatiles have been burned. The charcoal typically has a higher heating value of -24 kJ/g. In the tables the power level is calculated from these values. A gasification rate of 10 g/m gives 2.5 kW, coit )arabIe to the large burner on modem gas or electric stoves. 

Calculate the standard higher heating value from the lower heating value or the reverse. 

Tables of enthalpies of formation, combustion, and reaction are available in the literature (particularly thermodynamics texts/reference books) for a wide variety of compounds. It is important to note that these are valueless unless the stoichiometric equation and the states of the reactants and products are included. However, enthalpy of reaction is not always employed in engineering reaction/combustion calculations. The two other terms that have been used are the gross (or higher) heating value and the net (or lower) heating value. These are discussed in the next problem.

If the table of higher heating values for simple organic compounds in Perry (4) is used as the true values then the calculated values from the above formula fit a straight line of slope 1.04 with an intercept of - 1502 J/g and a correlation coefficient of 0.99. 

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