Carbon-based fuels

Fires, because it is inevitably a product of combustion from any carbon-based fuel. 

In this cycle the reaction of H2 + C02 to give reduced carbon-based fuels such as sugar or oil with oxidation back to H20 and C02 could be useful. It is then precisely the same as the biological cycle. Note that at present mankind and organisms utilise... 

Biomass has some advantageous chemical properties for use in current energy conversion systems. Compared to other carbon-based fuels, it has low ash content and high reactivity. Biomass combustion is a series of chemical reactions by which carbon is oxidized to carbon dioxide, and hydrogen is oxidized to water. Oxygen deficiency leads to incomplete combustion and the formation of many products of incomplete combustion. Excess air cools the system. The air requirements depend on the chemical and physical characteristics of the fuel. The combustion of the biomass relates to the fuel bum rate, the combustion products, the required excess air for complete combustion, and the fire temperatures. 

Although liquid hydrogen, LH2, can be used as a fuel source, much of the recent fuel cell research is focusing on the partial oxidation of methanol, natural gas, ethanol, or gasoline to produce the necessary hydrogen. Catalysts that aid in the partial oxidation of these fuels yields a readily available, rich source of hydrogen. Water is the primary exhaust emission produced by fuel cell powered vehicles. If a carbon-based fuel source is utilized, then a carbon-containing by-product will also be produced. 

The oil, coal, and natural gas we burn for energy are made up mostly of carbon. Our dependence on these fuels has, in recent years, caused economic problems, but even more importantly, it has contributed to the worldwide problem of global warming. Most scientists now believe that the burning of carbon-based fuels has increased the concentration of carbon dioxide in the atmosphere, and that this, in turn, has resulted in rising... 

Non-carbon-based fuels Nuclear energy Use of nuclear fuels for the production of electric energy used by sectors that require a high intensity... 

Hot corrosion may also occur in breeder reactors when the fission products deposit on the stailness steel cladding as complex salts based on Csl and Cs20. This mode of corrosion occurs in boilers and turbines burning high-ash coal or residual fuel oil well as well as heat exchangers, alkali-carbonate-based fuel cells and carbonate storage systems. 

The combustion of a carbon-based fuel (coal, natural gas, or oil) produces a gaseous byproduct called flue gas. First consider the combustion of a paraffin hydrocarbon. 

There are additional problems with fossil fuels. The waste products from burning fossil fuels significantly affect our environment. For example, when a carbon-based fuel is burned, the carbon reacts with oxygen to form carbon dioxide, which is released into the atmosphere. Although much of this carbon dioxide is consumed in various natural processes such as photosynthesis and... 

Many scientists have attributed global warming and the greenhouse effect to increases in carbon dioxide in the atmosphere. Because all combustion-fired glass melters are fired with carbon-based fuels such as natural gas or oil, one of the products of combustion is C02. Obviously, the more one saves fuel, the more one reduces C02 emissions. As discussed previously, oxygen-based combustion can reduce fuel consumption by 5 to 45%. This directly relates to a corresponding C02 reduction of 5 to 45%. 

In the 21st century this pattern of energy usage probably will not change significantly. The main reason is that carbon-based fuels will remain plentiful and low in cost. Examination of the reserve supply of fossil fuels indicates a substantial amount of petroleum still in the ground and accessible. At present consumption rates, and analyzing only proven reserves for fossil fuels, it is anticipated that oil reserves will last for at least another 40 years, supplies of gas another 70 years, and coal supplies 200 years. If likely reserves that have not yet been discovered are included, fossil fuels will be plentiful for decades to come. 

Options for reducing man-made carbon dioxide emissions include improvements in the efficient use of carbon-based fuels. This goal could be achieved by moving to lighter-weight vehicles that consume less fuel and also by switching from gasoline to diesel fuel. With a threefold increase in efficiency, it is estimated that a two and one-half to threefold decrease in the amount of carbon emitted per mile driven would result. 

To make fuels that are storable and transportable, there are two primary chemical transformations to consider. One is the conversion of carbon dioxide to methanol, and the other is splitting water. Methanol could be used in a fuel cell where it is converted to carbon dioxide. This must be converted back to methanol to close the carbon loop. Alternatively, if hydrogen is used as a replacement fuel for carbon-based fuel, a hydrogen fuel cell that utilizes the product of solar or electrical water splitting would be available for transportation. 

An alternative to using a direct H2 fuel supply is to refuel a vehicle with a carbon-based fuel such as methanol, and use an on-board fuel processor to transform it into H2. This process has the disadvantage of generating by-products CO and/or CO2 and N2 or NO (see Box 14.8). Thus, the vehicle is classed as reduced-emission rather than zero-emission. An advantage of using an indirect, rather than direct, H2 supply is that there is no longer a need to provide hydrogen-fuel stations. As a consequence, infrastructure costs are reduced. 

In 1997, at the United Nations Conference on Climate Change, the major industrial nations agreed to expand their research efforts to develop renewable sources of carbon-based fuels. For more than a decade, Brazil has been engaged in a program to replace gasoline with ethanol derived from the root crop manioc (cassava). 

The combustion of all carbon-based fuels releases carbon dioxide, which plays a key temperature-regulating role in the atmosphere. Much of the sunlight that shines on Earth is absorbed by the surface and converted to heat (Figure 6.11). Because atmospheric CO2 absorbs heat, some of the heat reflected back from Earth s surface is trapped by this CO2. 

Figure 1.1 Hydrogen-to-carbon atomic ratio in carbon-based fuels. Oil refers to heavy residues and other petroleum fractions.

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