Coal liquid fuel combustion efficiencies

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). 

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. 

Coal is a raw material for many chemical syntheses as weU as fuel. Coal is dried to increase its calorific value and simplify loading, unloading, transport, and to improve boiler combustion efficiency. It is also dried for processes like briquetting, coking, gasification, carbonization, and liquid fuel synthesis. Coke oven efficiency can increase 30%-50% in preheating and 10%-15% in drying. 

However, the overall thermal efficiency of these processes is relatively low, on the order of 50%. Thus, total carbon dioxide emissions for a coal-to-liquid plant, including carbon dioxide from the conversion process and from combustion of the liquid fuel, are roughly twice that of diesel fuel produced from petroleum. 

Combustion of oil produces CO, a contributor to global wanning, and while oil combustion is more efficient than combustion of coal, it is less efficient than natural gas. Oil is unique as a liquid fuel and thus is used predominantly in the transportation sector, making reduction of emissions more challenging. Oil extraction can be damaging to the environment, and more frequently, offshore sources are being... 

Most dryers, especially those that directly contact hot combustion gases with the wet solids, operate best with liquid or gaseous fuels. With escalating prices of fuel oils and natural gas, dryers will increasingly use coal when possible. Direct-fired rotary dryers are the easiest to adapt to this source of fuel. Another trend is the development of more efficient drying systems for the use of nontraditional dryers. Better thermal economy is obtained with fluid-bed, spray, and flash dryers, but the rotary is currently more economical for very-high-tonnage operation of products with low unit value. 

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