High carbon values

G. HIGH CARBON VALUES FOR MICRO METHOD, CONRADSON, AND RAMSBOTTOM CARBON NUMBER DETERMINATIONS... 

A high carbon value for gasoline, jet fuel or 2 fuel oil is a good indication that the fuel has been contaminated with residual fuel oil. Heavy streams such as VGO, coker gas oil, and 6 fuel oil can contaminate gasoline, jet fuel and diesel fuel. These streams tend to form carbon residue when pyrolyzed and can be identified as fuel contaminants through carbon residue testing. 

Any of the medium heat-value gases that consist of carbon monoxide and hydrogen (often called synthesis gas) can be converted to high heat-value gas by methanation (22), a low temperature catalytic process that combines carbon monoxide and hydrogen to form methane and water. 

As in most of the high heat-value processes, the raw gas is in the medium heat-value gas range and can be employed direcdy in that form. Removing the carbon dioxide raises the heating value, but not enough to render the product worthwhile as a high heat-value gas without methanation. 

Since the effluent from a softening unit is usually supersaturated with calcium carbonate at the usually high pH values, it is necessary to reduce the pH to a value that allows the solution to be exactiy saturated for the calcium-ion and carbonate-ion concentrations present. The relationship is... 

Gokes derived from resids or blends of resids with other petroleum feedstocks give high GTE values and are utilized as fillers for aluminum anodes and certain specialty carbon and graphite products. The remaining properties differ depending on the final appHcation. Alow ash content is required for... 

Electrical conductivity is of interest in corrosion processes in cell formation (see Section 2.2.4.2), in stray currents, and in electrochemical protection methods. Conductivity is increased by dissolved salts even though they do not take part in the corrosion process. Similarly, the corrosion rate of carbon steels in brine, which is influenced by oxygen content according to Eq. (2-9), is not affected by the salt concentration [4]. Nevertheless, dissolved salts have a strong indirect influence on many local corrosion processes. For instance, chloride ions that accumulate at local anodes can stimulate dissolution of iron and prevent the formation of a film. Alkali ions are usually regarded as completely harmless, but as counterions to OH ions in cathodic regions, they result in very high pH values and aid formation of films (see Section 2.2.4.2 and Chapter 4). 

Fig. B.4 (after Davidson and Keeley [5]) shows values of A plotted against thermal efficiency for a high carbon fuel (coal) and a lower carbon fuel (natural gas). It illustrates that one obvious route towards a desired low production of this greenhouse gas is to seek high thermal efficiency (another is to use lower carbon fuel).

Very hard waters are usually not very aggressive provided that they are supersaturated with calcium carbonate. Underground waters with a low pH value and high carbon dioxide content are, however, aggressive unless corrective treatment is applied. 

The preceeding discussion was confined mostly to the carbon deposition curves as a function of temperature, pressure, and initial composition. Also of interest, especially for methane synthesis, is the composition and heating value of the equilibrium gas mixture. It is desirable to produce a gas with a high heating value which implies a high concentration of CH4 and low concentrations of the other species. Of particular interest are the concentrations of H2 and CO since these are generally the valuable raw materials. Also, by custom it is desirable to maintain a CO concentration of less than 0.1%. The calculated heating values are reported as is customary in the gas industry on the basis of one cubic foot at 30 in. Hg and 15.6°C (60°F) when saturated with water vapor (II). Furthermore, calculations are made and reported for a C02- and H20-free gas since these components may be removed from the mixture after the final chemical reaction. Concentrations of CH4, CO, and H2 are also reported on a C02 and H20-free basis. 

The pure carbon that occurs in coal is fixed carbon, and the higher the content, the greater the calorific value of the coal. Total carbon implies the fixed carbon plus the carbon present in the volatile matters (in CO, C02, CH4, and hydrocarbons). The total carbon content is thus always higher than the fixed carbon in any coal. A high total carbon-bearing coal will be characterized by a high calorific value. 

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