Coal percent

Gas Analysis t/v Methane Yield per 100 gm. dmf coal Percent decrease in Methane Yield (con-... 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Gallium is often found as a trace element in diaspore, sphalerite, germanite, bauxite, and coal. Some flue dusts from burning coal have been shown to contain as much 1.5 percent gallium. 

The gas reservoirs located ia very deep waters, ia coal beds, and ia tight sands are now more accessible. Fifteen percent of the U.S. gas supply ia 1992 was derived from tight sand formations and 1.4 x 10 of coal-bed methane was added to the proven reserves (22). In 1992, U.S. proven reserves were placed at 4.67 x 10 ia the lower 48 states, and it was estimated that the identified gas resource ia the United States and Canada exceeds 3.4 X 10. Based on the 1992 rate of natural gas consumption, the United States has between 8 and 10 years of proven reserves and a domestic... 

In 1963 a classification of coals by rank (differing from the ECE scheme) was pubUshed by the International Committee for Coal Petrology (Table 2) (9). This includes a classification of brown coal that correlates a number of important properties including the percent reflectance of vitrinite in the coal. This is a simpler version of that used in German practice, which further subdivides soft brown coals into foHaceous and earthy. Most brown coals belong to the latter group. 

In the Audibert-Amu dilatometer test (91), a thin cylinder of compressed powdered coal contacting a steel piston is heated at a rate not over 5°C/min. The piston movement is used to calculate the percent dilation. 

Use of Surfa.cta.nts, Although the use of steam to improve dewatering is consistently beneficial, the effects of surfactants on residual moisture are highly inconsistent. Additions of anionic, nonionic, or sometimes cationic surfactants of a few hundredths weight percent of the slurry, 0.02—0.5 kg/1 of soHds (50), are as effective as viscosity reduction in removing water from a number of filter cakes, including froth-floated coal, metal sulfide concentrates, and fine iron ores (Table 2). A few studies have used both steam and a surfactant on coal and iron ore and found that the effects are additive, giving twice the moisture reduction of either treatment alone (44—46,49). 

The economics seem to be better for systems where dry powdered fresh hme plus ground recycled hme is injected along with a relatively coarse spray which impinges on and dries out from the reagent, as described by Stouffer et al. [Hs EC Res., 28(1) 20 (1989)]. Witnum et al. [9th Ann. Pitt. Coal Prep. Util. Euv. Control Contractors Conf. (1993)] describes an advanced version of that system that has been further optimized to the point that it is competitive with wet hme-stone scrubbing for >90 percent flue gas desirffurization. 

FIG. 17-69 Design curves for electrostatic precipitators for fly ash. Collection efficiency for various levels of percent sulfur in coal versus a) specific collecting surface, and (h) bus sections per 100,000 ftVmin (4.7 mVs). °C = (°F — 32) X (Ramsdell, Design Criteria for Precipitators for Modern Central Station Power Plants, Amen c m Power Conference, Chicago, III., 1968. )... 

Hot air can be introduced into the machine for drying the coal. Air at 150°C dries coal with 8 percent moisture down to about 1 percent. 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

Fixed carbon, the residue left after the volatile matter is driven off, is calculated by subtrac ting from 100 the percentages of moisture, volatile matter, and ash of the proximate analysis. In addition to carbon, it may contain several tenths of a percent of hydrogen and oxygen, 0.4 to 1.0 percent nitrogen, and about half of the sulfur that was in the coal. 

The sulfur content of U.S. coals varies widely, ranging from a low of 0.2 percent to as much as 7 percent by weight, on a diy Basis. The estimated remaining U.S. coal reserves of all ranks, by sulfur content, are shown in Fig. 27-1. Extensive data on sulfur and sulfur reduc tion potential, including washability, in U.S. coals are given in Sulfur and Ash Reduction Potential and Selected Chemical and Physical Properties of United States Coal (U.S. Dept, of Energy, DOE/PETC, TR-90/7, 1990 TR-91/1 andTR-91/2, 1991). 

The composition of coal ash varies widely. Calculated as oxides, the composition (percent by weight) varies as follows ... 

High-Temperature Coke (1173 to 1423 K or 1652 to 2102°F.) This type is most commonly used in the United States nearly 20 percent of the total bituminous coal consumed is used to make high-temperature coke for metallurgical applications. About 99 percent of this type of coke is made in slot-type recovery ovens. Blast furnaces use about 90 percent of the production, the rest going mainly to foundries and gas plants. 

Peat Peat is partially decomposed plant matter that has accumulated underwater or in a water-saturated environment. It is the precursor of coal but is not classified as coal. Sold under the term peat moss or moss peat, peat is used in the United States mainly for horticultural and agricultural apphcations, but interest is growing in its use as a fuel in certain local areas (e.g.. North Carolina). Peat is used extensively as a fuel primarily in Ireland and the former Soviet Union. Although analyses of peat vary widely, a typical high-grade peat has 90 percent water, 3 percent fixed carbon, 5 percent volatile matter, 1.5 percent ash, and O.IO percent sulfur. The moisture-free heating value is approximately 20.9 MJ/kg (9000 Btu/lb). 

Status of Indirect Liquefaction Technology The only commercial indirect coal liquefaction plants for the production of transportation fuels are operated by SASOL in South Africa. Construction of the original plant was begun in 1950, and operations began in 1955. This plant employs both fixed-bed (Arge) and entrained-bed (Synthol) reactors. Two additional plants were later constructed with start-ups in 1980 and 1983. These latter plants employ dry-ash Lurgi Mark IV coal gasifiers and entrained-bed (Synthol) reactors for synthesis gas conversion. These plants currently produce 45 percent of South Africa s transportation fuel requirements, and, in addition, they produce more than 120 other products from coal. 

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