Higher heating value

The absorber tail gas contains about 20 mol % hydrogen and has a higher heating value of ca 2420 kj/m (65 Btu/SCF). With increased fuel costs and increased attention to the environment, tail gas is burned for the twofold purpose of generating steam and eliminating organic and carbon monoxide emissions. 

Higher heating value (OD basis) to convert MJ/kg to Btu/lb, multiply by 430.3... 

The moisture content of freshly mined lignitic coals can be as high as 73%, but it is usually 30—65%. The more mature, consoHdated coals have lower moisture contents and thus a higher heating value. Figure 2 shows moisture and ash contents, as well as net heating values for lignitic coals from the world s principal deposits (19). 

The fuel properties of wood can be summarized by ultimate and proximate analyses and deterrnination of heating value. The analytical procedures are the same as those for coal, but with some modifications. Analytical results generally vary about as much within a species as they do between species, except that softwood species generally have a higher carbon content and higher heating values than hardwood species because of the presence of more lignin and resinous materials in softwood species (see Fuels from waste). 

The proximate analysis of charcoal is 20-25% volatile matter, 70—75% fixed carbon, and 5% ash. Charcoal briquets have lower heating values than charcoal lumps, because of additives in the briquets. The higher heating value of lump charcoal is - 28 kJ/kg (12,000 Btu/lb). The higher heating value of briquets is 23 to 25 kj/kg ( -- 9,900-10,800 Btu/lb). 

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. 

FIG. 27-13 Available heats for some typical fuels. The fuels are identified by their gross (or higher) heating values. All available heat figures are based upon complete combustion and fuel and air initial temperature of 288 K (60 F). To convert from MJ/Nm to Btii/ft, multiply by 26.84. To convert from MJ/dm to Btii/gal, multiply by. 1588. 

Lower Heating Value. The lower heating value of the gas is one in whieh the H2O in the produets has not eondensed. The lower heating value is equal to the higher heating value minus the latent heat of the eondensed water vapor. 

When liquefied, propane has a Btu content of 91,044 per gallon (higher heating value). At ordinai y temperatures, propane is relatively unreactive with other chemicals such as acids, alkalis, or oxidizers. 

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... 

Figure 6. Higher heating value of C02- and H20-free equilibrium mixtures as a function of starting composition at 50 atm and 700°K...

The higher heating value is plotted on the composition coordinate in Figure 6. These curves are for 50 atm and 700 °K. The contours of constant heating value increase uniformly in the direction of pure methane. These contours, of course, are very similar to the contours of CH4 concentration which are plotted in Figure 7 for the same conditions, 50 atm and 700°K. 

Figure 10 depicts the effect of temperature on higher heating value and on CH4, H2, and CO concentrations for four different starting compositions. The four starting compositions are ... 

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