Fuel overall

In Fig. 6.33a. heat Qftjel is taken into the boiler from fuel. An overall energy balance gives... 

Steam costs vary with the price of fuel. If steam is only generated at low pressure and not used for power generation in steam turbines, then the cost can be estimated from local fuel costs assuming a boiler efficiency of around 75 percent (but can be significantly higher) and distribution losses of perhaps another 10 percent, giving an overall efficiency of around 65 percent. 

With regards to the overall balance of combustion, the chemical structure of the motor or heating fuel, e.g., the number of carbon atoms in tbe chain and the nature of the bonding, does not play a direct role the only important item is the overall composition, that is, the contents of carbon, hydrogen, and — eventually— oxygen in the case of alcohols or ethers added to the fuel. 

Thus the quantitative elemental analysis of the fuel establishes an overall formula, (CH O ) , where the coefficient x, related to the average molecular weight, has no effect on the fuel-air ratio. 

The diesel engine operates, inherently by its concept, at variable fuel-air ratio. One easily sees that it is not possible to attain the stoichiometric ratio because the fuel never diffuses in an ideal manner into the air for an average equivalence ratio of 1.00, the combustion chamber will contain zones that are too rich leading to incomplete combustion accompanied by smoke and soot formation. Finally, at full load, the overall equivalence ratio... 

Around 2000, the regulations should become more severe. In this area, a European limit of benzene of 3% appears very probable certain countries such as Germany are even looking at 1%. In Italy, it was decided towards the end of 1991, to limit benzene to 2.5% for leaded and unleaded fuels in the seven largest cities characterized by having heavy atmospheric pollution concurrently, in these same cities, the overall aromatic contents of gasolines should not exceed 33%. 

These are carbon monoxide, CO, unburned hydrocarbons (HC), and the nitrogen oxides, NO. In the U.S.A., a program called Auto/Oil (Burns et al., 1992), conducted by automotive manufacturers and petroleum companies, examined the effect of overall parameters of fuel composition on evaporative emissions and in the exhaust gases. The variables examined were the aromatics content between 20 and 45%, the olefins content between 5 and 20%, the MTBE content between 0 and 15% and finally the distillation end point between 138 and 182°C (more exactly, the 95% distilled point). 

For each type of component, its relative reactivity in ozone formation was taken into account which makes it possible to characterize by weighting the behavior of the overall motor fuel under the given experimental conditions. The overall reactivity is in fact governed by a limited number of substances ethylene, isobutene, butadiene, toluene, xylenes, formaldehyde, and acetaldehyde. The fuels of most interest for reducing ozone formation are those which contribute towards minimizing emissions of the above substances. 

The products could be classified as a function of various criteria physical properties (in particular, volatility), the way they are created (primary distillation or conversion). Nevertheless, the classification most relevant to this discussion is linked to the end product use LPG, premium gasoline, kerosene and diesel oil, medium and heavy fuels, specialty products like solvents, lubricants, and asphalts. Indeed, the product specifications are generally related to the end use. Traditionally, they have to do with specific properties octane number for premium gasoline, cetane number for diesel oil as well as overall physical properties such as density, distillation curves and viscosity. 

Methanol use would also reduce pubHc exposure to toxic hydrocarbons associated with gasoline and diesel fuel, including ben2ene, 1,3-butadiene, diesel particulates, and polynuclear aromatic hydrocarbons. Although pubHc formaldehyde exposures might increase from methanol use in garages and tunnels, methanol use is expected to reduce overall pubHc exposure to toxic air contaminants. 

One factor contributing to the inefficiency of a fuel ceU is poor performance of the positive electrode. This accounts for overpotentials of 300—400 mV in low temperature fuel ceUs. An electrocatalyst that is capable of oxygen reduction at lower overpotentials would benefit the overall efficiency of the fuel ceU. Despite extensive efforts expended on electrocatalysis studies of oxygen reduction in fuel ceU electrolytes, platinum-based metals are stiU the best electrocatalysts for low temperature fuel ceUs. 

X MW in 1986, of the power produced in the same year. Biomass-fueled electric capacity and generation was 19.2% (4.9 x 10 MW) and 21.2% (23.7 X 10 MWh) respectively, of total nonutiUty capacity and generation. Biomass-fueled capacity experienced a 16% increase in 1986 over 1985, the same as natural gas, but it was not possible to determine the percentage of the total power production that was sold to the electric utiUties and used on-site. Total production should be substantially more than the excess sold to the electric utiUties. Overall, the chemical, paper, and lumber industries accounted for over one-half of the total nonutiUty capacity in 1986, and three states accounted for 45% of total nonutiUty generation, ie, Texas, 26% of total California, 12% of total and Louisiana, 7% of total. There were 2449 nonutiUty producers with operating faciUties in 1986, a 15.8% increase over 1985 75% capacity was intercoimected to electric utiUty systems. 

Combustion characteristics of consequence include the overall mechanism of soHd waste combustion, factors governing rates of waste fuels combustion, temperatures associated with waste oxidation, and pollution-formation mechanisms. 

Fig. 2. Overall schematic of solid fuel combustion (1). Reaction sequence is A, heating and drying B, solid particle pyrolysis C, oxidation and D, post-combustion. In the oxidation sequence, left and center comprise the gas-phase region, tight is the gas—solids region. Noncondensible volatiles include CO, CO2, CH4, NH, H2O condensible volatiles are C-6—C-20 compounds oxidation products are CO2, H2O, O2, N2, NO, gaseous organic compounds are CO, hydrocarbons, and polyaromatic hydrocarbons (PAHs) and particulates are inerts, condensation products, and solid carbon products.

Combustion. Coal combustion, not being in the strictest sense a process for the generation of gaseous synfuels, is nevertheless an important use of coal as a source of gaseous fuels. Coal combustion, an old art and probably the oldest known use of this fossil fuel, is an accumulation of complex chemical and physical phenomena. The complexity of coal itself and the variable process parameters all contribute to the overall process (8,10,47—50) (see also COLffiUSTION SCIENCE AND technology). 

Fuel. Natural gas is used as a primary fuel and source of heat energy throughout the iadustrialized countries for a broad range of residential, commercial, and iadustrial appHcations. The methane and other hydrocarbons react readily with oxygen to release heat by forming carbon dioxide and water through a series of kinetic steps that results ia the overall reaction,... 

Natural gas is attractive as a fuel ia many appHcatioas because of its relatively clean burning characteristics and low air pollution (qv) potential compared to other fossil fuels. Combustion of natural gas iavolves mixing with air or oxygen and igniting the mixture. The overall combustion process does not iavolve particulate combustion or the vaporization of Hquid droplets. With proper burner design and operation, the combustion of natural gas is essentially complete. No unbumed hydrocarbon or carbon monoxide is present ia the products of combustioa. 

The use and effective costs of various energy alternatives are shown in Table 2. Use or internal costs include production, transportation, and distribution. Effective costs take into account the use costs estimated external costs, which include costs associated with damage to the environment caused by utili2ation of various fossil fuels and fuel utili2ation efficiencies, ie, the efficiency of converting fuels into mechanical, electrical, or thermal energy. The effective costs are expressed as /GJ of fossil fuel equivalent (15). The overall equation for the effective cost is... 

---