Moisture of coal

Total moisture of coal Ultimate analysis of coal Ultimate analysis of coke Chlorine in coal and coke Phosphorus in coal and coke Arsenic in coal and coke Analysis of coal ash and coke ash Determination of moisture-holding capacity of hard coal General introduction and methods for reporting results Determination of total moisture of coke Proximate analysis, determination of moisture content of the general analysis test sample... 

ASTM D-1412. Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30°C. 

Air drying removes most of the surface moisture of coal, while a temperature of approximately 107°C (225°F) is needed to remove inherent moisture. At temperatures of approximately 200 to 300°C (392 to 572°F), moisture from the decomposition of organic materials is driven off, but water of hydration requires a considerable amount of energy for expulsion. For example, the water of hydration in clay minerals may require a temperature in excess of 500°C (932°F). However, the issues of decomposition moisture and water of hydration of mineral matter are not usually dealt with in conventional analysis because the temperatures specified in the test methods for moisture determination are well below those needed to remove such moisture. 

There are two kinds of moisture that exist in the coal surface moisture and inherent moisture. Since the CWS is basically a mixture of coal particle and water, the surface moisture of coal does not have too much impact in the GE gasification process. However, a higher surface moisture content means a higher transportation cost. Inherent moisture includes all the moisture that is physically or chemically held within coal. In the CWS preparation step, inherent moisture of the coal plays an important role. With an increase in the inherent moisture, it has been found that the maximum coal concentration possible in a CWS decreases. 

Fourth point Wetting coal, increase the moisture of coal. 

The heating medium temperature at the dryer inlet is 550°C-700°C and 70°C-170°C at the dryer outlet. The initial moisture of coal is usually 10%-15% the final moisture is about 4%-6%. A typical pneumatic dryer setup for coal drying is shown in Figure 51.8. Wet coal from the bin (11) is proportioned by feeder (12) to the lifting tube (5), where it... 

ASTM. 2011a. Standard Test Method for Equilibrium Moisture of Coal at 96 to 97 Percent Relative Humidity and 30°C (ASTM D1412). Annual Book of Standards. American Society for Testing and Materials, West Conshohocken, PA. 

Indeed, at this point a distinction should be made between the natural bed moisture of coal and the as-received moisture of coal. The natural bed moisture of coal is the amount of water that a particular coal will hold when it is fully saturated at ca. 100% relative humidity (i.e., at the conditions approximating those of an undisturbed coal seam). It is also considered to be an indication of the total pore volume of the coal that is accessible to water. On the other hand, the as-received moisture content of coal relates to the amount of water in the coal at the time the coal is received for analysis. This may be somewhat smaller than the natural bed moisture, especially if the coal has been allowed to dry partially. In contrast, excessive amounts of surface moisture on the coal could lead to values for as-received moistures that are in excess of the natural bed moisture. 

Numbers represent % of total moisture of ash-free freshly mined coal. 

A high, moisture content necessitates finer grinding of coal for rapid water release. For such coals, the classifier in the pulverizer is set to return more of the oversize material for further grinding. 

The specific electrical conductivity of dry coals is very low, specific resistance 10 ° - ohm-cm, although it increases with rank. Coal has semiconducting properties. The conductivity tends to increase exponentially with increasing temperatures (4,6). As coals are heated to above ca 600°C the conductivity rises especially rapidly owing to rearrangements in the carbon stmcture, although thermal decomposition contributes somewhat below this temperature. Moisture increases conductivity of coal samples through the water film. 

The moisture in coal consists of inherent moisture, also called eqm-librium moisture, and surface moisture. Free moisture is that moisture lost when coal is air-dried under standard low-temperature conditions. 

The bulk density of broken coal varies according to the specific gravity, size distribution, and moisture content of the coal and the amount of settling when the coal is pded. Following are some useful approximations of the bulk density of various ranks of coal. 

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). 

FIG. 27-20 Effect of moisture in coal on pulverizer capacity. Sufficient drying can be accomplished to restore capacity if air temperatures are high enough. [K = ( F -I- 459.7)/1.8] (Combustion Engineer, Combustion Engineeiing Inc., New York, 1966. )... 

The moisture component of coal and other solid fuels that is not available to bond or freeze to other particles. 

External moisture that is not bonded to a particle of coal or other fuel. External moisture will ice in cold weather and lump fuel together in a solid mass. Where this occurs, thaw sheds may be used to heat the mass before further transport or use. 

The composition of coal is conveyed by representing its proximate and ultimate analysis. The former implies determination of contents of moisture, volatile matter, fixed carbon, and ash, while the latter implies total carbon, hydrogen, oxygen, nitrogen, sulfur and ash. Here, an account will be provided of the constituents of coal, moisture, volatile matter, ash, fixed carbon, and some miscellaneous components. 

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