Carbon-Free Fuels

Carbon capture occurs upstream of the power plant while creating an intermediate carbon-free fuel from a carbonaceous energy resource such as coal. Capture is combined with fuel preparation and refining, and thus, the energy conversion itself does not involve emission of CO2. In this case, the carbon capture becomes more akin to operations in a refinery or bulk chemical production plant. 

Climate Change and Carbon-Free Fuel Chance... 

State-of-the-art DMFCs have not been considered for use in vehicles, except small vehicles, because of the lower efficiency and power density. In addition, a carbon-free fuel would be preferable for use in FC-powered vehicles. Alternative fuels, oxidation catalysts, reaction medium, electrolyte membranes, and electrode preparation have been evaluated to obtain optimal DLFCs. L-Ascorbic acid (AA), widely known as vitamin C, has been proposed as a novel fuel that does not require the use of an anode catalyst metal. DLFCs that use ethanol and D-glucose as renewable biofuels have been studied and developed using an anion exchange membrane (AEM). Hydrazine fuel cells were reconsidered for use in transportation based on the application of recent PEMFC technology. A novel anode catalyst for NaBILj oxidation is also described. 

Soot. Emitted smoke from clean (ash-free) fuels consists of unoxidized and aggregated particles of soot, sometimes referred to as carbon though it is actually a hydrocarbon. Typically, the particles are of submicrometer size and are initially formed by pyrolysis or partial oxidation of hydrocarbons in very rich but hot regions of hydrocarbon flames conditions that cause smoke will usually also tend to produce unbumed hydrocarbons with thek potential contribution to smog formation. Both maybe objectionable, though for different reasons, at concentrations equivalent to only 0.01—0.1% of the initial fuel. Although thek effect on combustion efficiency would be negligible at these levels, it is nevertheless important to reduce such emissions. 

Products of Combustion For lean mixtures, the products of combustion (POC) of a sulfur-free fuel consist of carbon dioxide, water vapor, nitrogen, oxygen, and possible small amounts of carbon monoxide and unburned hydrocarbon species. Figure 27-12 shows the effect of fuel-air ratio on the flue gas composition resulting from the combustion of natural gas. In the case of solid and liquid fuels, the... 

The process is conducted at 700 °C. It yields semicoke, which is popular as a smokeless domestic fuel. It can at times be used in boiler also to avoid smoke. Yield of coke oven gas is less, of tar high, and of ammonia less. Calorific value of coke oven gas generated is more. The process produces aliphatic natured tar. Following carbonization the coke discharging process is difficult as it swells extensively but does not shrink much upon carbonization. Free carbon in tar (produced from the cracking of hydrocarbons) is less Coke produced is weaker. Volatile matter in the coke produced is more. Hydrogen content in the coke oven gas is less. 

Jansen, D., W. Haije, M. Carbo, V. Feuillade, J.W. Dijkstra, and R. Brink, Advanced membrane reactors for carbon-free fossil fuel conversion, ECN GCEP Project Presentation, GCEP Energy Research Symposium, Stanford, September 2006. 

Many of these plants may be built before CCS is ready and we will need to use our electricity more efficiently to slow the demand for such power plants, while building as many cleaner power plants as possible. Natural gas is far more cleaner for this power than coal. Generating hydrogen with renewables may be needed in order to avoid building coal-fired plants. More electricity from renewable power would reduce the pressure on the natural gas supply and reduce prices. The United States could have essentially carbon-free electricity before 2050 with hydrogen fuel playing a key role. 

Both the production of hydrogen from coal and the production of oil from unconventional resources (oil sands, oil shale, CTL, GTL) result in high C02 emissions and substantially increase the carbon footprint of fuel supply, unless the C02 is captured and stored. While the capture of C02 at a central point source is equally possible for unconventionals and centralised hydrogen production, in the case of hydrogen, a C02-free fuel results, unlike in the case of liquid hydrocarbon fuels. This is all the more important, as around 80% of the WTW C02 emissions result from the fuel use in the vehicles. If CCS were applied to hydrogen production from biomass, a net C02 removal from the atmosphere would even be achievable. 

This new cycle cannot only produce more and extra H2SO4 but also facilitate a flexible to H SO production ratio. In gas plants, from H S splitting is an alternative clean fuel. Environmentally, prodnction based on this H S-splitting cycle is carbon-free. 

Hydrogen can be produced from carbon-free or carbon-neutral energy sources or from fossil fuels with CO capture and storage (sequestration). Thus, the use of hydrogen could eventually eliminate greenhouse gas emissions from the energy sector. 

Thermodynamic calculations presented here are based on Gibbs free energy minimization and were carried out using HSC Chemistry. The equilibrium amount of each species that is formed is normalized on the basis of one mole of n-Ci6, a model compound for diesel fuel, fed to the reactor. Carbon formation is a function of both the S/C ratio and reforming temperature. Figure 17 shows the minimum amount of S/C ratio thermodynamically required for carbon-free SR of n-Ci6 at a given temperature. Carbon-free operation of n-Cig is thermodynamically possible above the curve. Higher temperatures and S/C ratios inhibit carbon formation. 

Transitioning towards a carbon-free energy system is all the more timely as the production of fossil fuels is anticipated to peak in the 21st century owing to the steadily rising production rate and unavoidable resource limitations peak-oil or plateau around 2015-2020, peak-gas around 2030 and peak-coal around 2060 (if exploited with no restriction, which would lead to an unacceptable C02 concentration of 600 ppm in the atmosphere). 

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