Fuels coal slurries

W. Pietsch, Briquetting of coal with roUer presses. An important technology for the production of coal-based compliance fuel. Proc. 20th Int l Techn. Conf on Coal Utilization Fuel Systems, Clearwater, FL (1995), 87-95 also in S.D. Serkin (ed.) Coal Fines The Unclaimed Fuel , Coal Slurry Technology Assoc., Washington, DC (1995), 91-99. 

Coal Slurry Pipelines. The only operating U.S. coal slurry pipeline is the 439-km Black Mesa Pipeline that has provided the 1500-MW Mohave power plant of Southern California Edison with coal from the Kayenta Mine in northern Arizona since 1970. It is a 457-mm dia system that aimuaHy deHvers - 4.5 x 10 t of coal, the plant s only fuel source, as a 48.5—50% slurry. Remote control of slurry and pipeline operations is achieved with a SCADA computer system. In 1992 coal deHvery cost from mine to power plant was calculated to be 0.010/tkm ( 0.015/t-mi) (28). 

The Szego mill has been used for dry as well as wet grinding of coal, in both water and oil, for the preparation of coal-slurry fuels. To grind coal in water to the standard boiler size (80 per cent < 74 im) takes about 7 MJ/Mg (20 kWh/tonne). For micronized grinding, to a 15 xm median size, 2-3 passes through the mill are required and the specific energy... 

Gandolfi, E. A. J., Papachristodoulou, G. and Trass, O. Powder Technology 40 (1984) 269-282. Preparation of coal slurry fuels with the Szego mill. 

Water Electrolysis. An example of the use of computers in pattern recognition can be given from work on the use of coal slurries to provide alternative anodic reactions in the electrolysis of water, with the aim of producing cheap hydrogen for fuel cells. In the presence of the coal slurries, the evolution of oxygen (the usual anodic reaction in the electrolysis of water) does not occur. Instead, a large number of... 

Slurry explosives consist of oxidizers (NH4N03 and NaN03), fuels (coals, oils, aluminum, other carbonaceous materials), sensitizers (trinitrotoluene, nitrostarch, and smokeless powder), and water mixed with a gelling agent to form a thick, viscous explosive with excellent water-resistant properties. Slurry explosives may be manufactured as cartridged units, or mixed on site. 

In place of dihydrogen, other fuels such as alcohols, hydrocarbon liquids, and even coal slurries have been used methanol appears to be an especially promising fuel. 

Liquid Fuels None Possible None Possible None Possible Only possible for liquid-entrained processes above marked with, but Shell cannot take coal slurry. 

Coal below 0.5 mm in size, classified as fine coal, typically makes up 5-20 percent of the feed to the cleaning plant. It is generally processed by methods such as froth flotation, which depend on surface properties. In froth flotation, the fine coal slurry, to which a small amount of flotation agent (usually fuel oil and a short-chain alcohol, such as methyl isobutyl carbinol) is added, is processed through a flotation cell. In the cell, fine bubbles are generated by using either forced air or suction. 

The use of coal slurries, either coal-oil mixtures (COM) or coal-water mixtures (CWM), has been the subject of considerable research because of the potential to replace fuel oil in boilers. Recent work has shifted in favor of CWM over COM, as the cost savings for the latter were not enough to offset conversion costs. CWM is typically composed of 60-75 percent coal, 24-39 percent water, and 1 percent chemical additives. The advantages of CWM compared with dry pulverized fuel are the ease and safety of handling,... 

Sakkestad, B. A. (Ed.), The Proceedings of the 23rd International Technical Conference on Coal utilization Fuel Systems, Coal Slurry Technology Association, Washington, DC, 1998. 

In addition to coal gasification, the formation of coal slurries is another new use of coal. A slurry is a suspension of fine particles in a liquid. Coal must be pulverized and mixed with water to form a slurry. The resulting slurry can be handled, stored, and burned in ways similar to those used for residual oil, a heavy fuel oil from petroleum accounting for 13% of U.S. petroleum imports. One hope is that coal slurries might replace solid coal and residual oil as fuels for electricity-generating power plants. However, the water needed for slurries might place an unacceptable burden on water resources, especially in the western states. 

Of the four applications for coal slurries given here, coal slurry fuels have the most stringent requirements. Hence, the following discussion of slurry properties is with reference to coal slurry fuels. 

As petroleum-based fuels are being depleted, it is expected that coal-derived fuels such as coal slurry... 

Coal slurry fuels are of interest for the following markets ... 

Unlike coal slurry fuels, which are utilized in a fluid form, coal transported by pipeline is used as a solid after dewatering. As a result, it does not need to be stable when stored in tanks, and it is not so critical that its solid loading be maximized. The following variables are important for a pipeline system ... 

The requirements for coal slurry intended to be used in IGCC are similar to those for pipeline transport, with the added requirement that, as for coal-water fuels, the slurry needs to atomize easily in the reactor. Atomization has been found to be easier (producing smaller-diameter droplets at lower jet pressures) as the size of the coal particles in the slurry increases, because of weaker capillary forces holding the slurry together and decreased interparticle friction. As the capillary forces and interparticle friction are also responsible for increasing the viscosity in coal slurries, it is clear that low-viscosity slurries will atomize more readily than high-viscosity slurries. 

Coal Slurry Combustion and Technology, PETC, 1983 Session VII. Richter, W. Pohl, J. H. Proc. 7th Int. Symp. on Coal Slurry Fuels Preparation and Utilization, PETC, 1985, Paper No. 12, pp. 443-462. 

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