Pulverised fuel particles

PsychrorneLry sec humidity determination Pugh. F. J, 205,228 PumiM. 1. 209, 228 Pulverised fuel particles 47 ... 

The particles to be removed may range in size from large molecules, measuring a few hundredths of a micrometre, to the coarse dusts arising from the attrition of catalysts or the fly ash from the combustion of pulverised fuels. 

There is a large class of industrially important heterogeneous reactions in which a gas or a liquid is brought into contact with a solid and reacts with the solid transforming it into a product. Among the most important are the reduction of iron oxide to metallic iron in a blast furnace the combustion of coal particles in a pulverised fuel boiler and the incineration of solid wastes. These examples also happen to be some of the most complex chemically. Further simple examples are the roasting of sulphide ores such as zinc blende ... 

Fly ash. Fly ash (also called pulverised fuel ash, PFA) is a by-product of the combustion of coal powder in thermoelectric power plants. It consists of very fine and spherical particles (dimensions from 1 to 100 pm and specific surface area of 300 to 600 m /kg) that are collected from exhaust gases with electrostatic or mechanical filters. Its composition depends on the type of coal it derives from the most common PFA is mainly siliceous. Because of the high temperature at which it is formed, it subsequently undergoes rapid cooling so that its structure is mainly amorphous (glassy) and thus reactive. 

Lightman, P. P. . Street, 1968. Microscopical examination of heat treated pulverised coal particles. Fuel 47 7-28. 

Fuel may constitute only about 1 per cent of the total volume of the solids in the bed and the particle size needs to be reduced to about 10 mm, compared with 100 im in pulverised coal burners. 

Additives may be solid or solutions, or suspensions in a suitable solvent, or liquid. Where solids are employed their particle size is usually of the order of 20 -30 fjtn with direct injection into the combustion space in the vicinity of the burner where pulverised coal or liquid fiiels are employed. For solid fuel combustion on a grate, the additive may be mixed with the fuel prior to combustion or injected in some way to the flame region. Mbdng with the fuel may present difficulties of producing a uniform distribution, particularly for solid fuels. The additive is usually separately applied to avoid these problems. 

Griest, W. H. L. A. Harris, 1985. Microscopic identification of carbonaceous particles in stack ash from pulverised-coal combustion. Fuel. 64 821-826. 

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