Coal liquid fuel emissions

Emissions Sampling of Combustion Effluents from a Stationary Diesel Engine That Bums a Coal-Derived Liquid Fuel... 

The major question involving burning characteristics of coal liquids relates to the higher nitrogen content compared to petroleum fuel oils and the potential effect on NO emissions. Since NO emissions are sensitive to burning conditions, however, actual burning tests are required under various conditions to assess the effects. 

The Consolidated Edison test results, as shown in Table VI, indicated complete suitability of SRC-II coal liquids as a high quality boiler fuel. No operational problems were encountered and no deposits were observed. Combustion efficiency was comparable to that for the low-sulfur No. 6 fuel oil, as were the levels of carbon monoxide and hydrocarbon emissions. Modifications to burner equipment required to handle the SRC-II fuel oil are considered to be no more extensive than those required for similar variations in petroleum fuels. Particulate emissions for the SRC-II fuel oil were generally lower than for the No. 6 fuel oil, and were in all cases below the new source performance standards proposed by EPA (0.03 lbs/MM Btu). 

Muzio, L. J. and Arand, J. K., "Combustion and Emission Characteristics of Coal-Derived Liquid Fuels," EPRI Report AP-1878, 1981. 

Coal-derived synthetic liquid fuels are potentially attractive substitutes for imported oils. Coal-derived liquids, however, have a tendency to form excessive amounts of soot and to produce high N0X emission levels during combustion compared to distillate oils (1). Polycyclic organic matter (POM) may also be enhanced along with the soot formation. 

Synthetic liquid fuels derived from coal and shale will differ in some characteristics from conventional fuels derived from petroleum. For example, liquid synfuels are expected to contain significantly higher levels of aromatic hydrocarbons, especially for coal-derived fuels, and higher levels of bound nitrogen. These differences can affect the combustion system accepting such fuels in important ways. In continuous combustors, i.e. gas turbines, the increased aromatics content of coal-derived fuels is expected to promote the formation of soot which, in turn, will increase radiation to the combustor liner, raise liner temperature, and possibly result in shortened service life. Deposit formation and the emission of smoke are other potential effects which are cause for concern. Higher nitrogen levels in synfuels are expected to show up as increased emissions of N0X (NO+NO2) An earlier paper presented results of an experimental study on the effect of aromatics and combustor... 

These coal liquids originally were intended to serve as boiler fuels. The sulfur content may be sufficiently low to qaulify them as replacement for high-sulfur coal, and bring sulfur dioxide emissions within acceptable limits. However, for large boilers, such as major base load power plants, pollution control via coal hydroliquefaction probably is not competitive with stack gas scrubbing (I). 

In other fuel markets, coal liquids can be more competitive. Industrial boilers presently are not amenable to stack gas scrubbing. The same is true of smaller utility plants. In particular, peak load units require a clean, storable liquid fuel as an alternative to natural gas. However, the high viscosity of primary coal liquefaction products is undesirable for many of these applications. Also, their residual sulfur and nitrogen contents may be excessive as emission standards become more stringent. 

Sasol II, with an output of 50,000 barrels per day of products, came on stream in 1980. This was followed in 1983 by Sasol III. These two new plants were designed for zero emissions of liquid wastes. With the addition of these projects, which cost over 7 billion, South Africa had the capacity to provide approximately 40 percent of its liquid fuels and chemicals needs from coal. 

Improvement of the atmosphere continues to be of great concern. The continual search for fossil fuel resources can lead to the exploitation of coal, shale, and secondary and tertiary oil recovery schemes. For instance, the industrialization of China, with its substantial resource of sulfur coals, requires consideration of the effect of sulfur oxide emissions. Indeed, the sulfur problem may be the key in the more rapid development of coal usage worldwide. Furthermore, the fraction of aromatic compounds in liquid fuels derived from such natural sources or synthetically developed is found to be large, so that, in general, such fuels have serious sooting characteristics. 

The combination of high value outputs, scale-effects and flexibility in general, may lead to a very efficient, cost-effective and clean overall system. Cost-effective means that the electricity produced has to compete with electricity from coal. For fair comparison the cost of clean electricity generation must be considered with a similarly low environmental burden. For instance, costs for removal or storage of the emitted carbon dioxide from coal plants have to be included. For electricity this inches an allowable cost price of 0.05 Euro/kWh. This value is the EU strategic goal and seems achievable for large advanced systems [5] where electrical efficiencies between 50 and 60% can be obtained [6]. In the case of the produced liquid fuels, cost-effective means that the cost price must correspond to the cost prices of fossil fuels, which will be used in the future in cars with low or very low emissions. For the liquid fuels FT diesel is taken as example and the cost price would have to be 0.34 Euro/litre (of diesel). 

The large-scale petroleum consumers are exploring ways to supplement the convenient liquid fuel and chemical feedstock aspects of a conventional petroleum resource. Coal could be used in this way since the known reserves of hard coal have an estimated life of more than 200 years. However, extraction of coal is generally more difficult, equipment to consume it directly is more complex, and efficient emission control is more complicated than for petroleum combustion. 

The producers of coal, the most polluting fuel, will say there is no energy shortage - there is coal to last for several hundred years — and liquid fuels, from methanol through gasoline to fuel oil can be made from coal. They, like the oil companies, will argue carbon dioxide is not a problem and sulfur emissions can be reduced. 

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