Moisture-free coal

Data from Reference 4 results are calculated on a moisture-free coal basis (mf coal). 

Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

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. 

Coal analyses are reported on severalbases, and it is customaiy to select the basis best suited to the application. The as-received basis represents the weight percentage of each constituent in the sample as received in the laboratoiy. The sample itself may be coal as fired, as mined, or as prepared for a particular use. The moisture-free (diy) basis is generally the most useful basis because performance calculations can be easily corrected for the ac tual moisture content at the point of use. The dry, ash-free basis is frequently used to approximate... 

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). 

In absolute terms, the quantities of reactor solids found in various processes do vary considerably. The rate of accumulation is related to several factors, such as coal characteristics, recycle solvent quality and reactor design. However, it can be stated in general terms that liquefaction of low rank coals (sub-bituminous C and lignites) does result in higher rates of accumulation of solids than do similar operations with bituminous coals. For example, during normal operations of the SRC-I pilot plant at Wilsonville, Ala., it has been found that the amount of solids retained varies from about 0.2-0.5 wt.% (moisture-free) for bituminous coals to 1.0-1.9 wt.% (moisture free) for a subbituminous C coal (Wyodak) (72). Exxon also reports much larger accumulations for lignites and subbituminous coals than those found for bituminous coals (73). 

Each of these is reported in the proximate analysis. Coal analyses can be reported on several bases as-received, moisture-free (or dry), and mineral-matter-free (or ash-free). 

Nearly all the coals examined are relatively high in ash. Only two of the samples from the Terrace Ridge area contain less than 20% ash, on a moisture-free basis. Most of the remaining samples from this area range from impure coal to coaly shale. Most of the mineral matter is finely divided (dehydrated) clay, silica, and pyrrhotite. This is an important point since the proximate and ultimate analyses for material that deviates so widely from what is normally considered coal cannot be considered particularly reliable for comparison pur-... 

Equilibrium Results. Table V shows all of the isotherm parameters computed for the sorption of methanol on the acetylated and unaltered coals. These values are on a moisture-free basis. 

Moisture in coal takes three forms (l)free or adherent moisture, essentially surface water (2) physically bound or inherent moisture (thai moisture held by vapor pressure and other physical processes) and (3) chemically bound water (water of hydration or combined" water). The ASTM defines total moisture as a loss in weight in an air atmosphere under rigidly controlled conditions of temperature, time, and air flow. Total moisture represents a measurement of all water not chemically combined. Total moisture is determined by a two-slep procedure, involving air-drying for removal of surface moisture from the gross sample, division and reduction of Ihc gross sample, and determination of residual moisture in the prepared sample. An algebraic calculation is used to obtain the total moisture value. 

If the temperature and pressure are increased, then a vehicle is no longer necessary even with the sub-bituminous coal. A series of experiments was carried out without a vehicle using a hydrogen partial pressure of 205 atm and at temperatures ranging from 370° to 427°C. The zinc chloride/moisture free (MF) coal feed ratio and the reaction time were held constant at 2.5/1 and 60 min, respectively, in these runs. 

Lignite (brown coal) has been classified arbitrarily as coal having a moist, ash-free calorific value below 10,260 Btu/lb. A code number that is a combination of a class number and a group number classifies these coals. The class number represents the total moisture of the coal as mined, and the group number represents the percentage tar yield from dry, ash-free coal (Table 1.9). 

The various forms of moisture in coal are described according to the manner in which they are measured by some prescribed standard method. These forms are (1) inherent moisture, (2) surface or free moisture, (3) total moisture, (4) air-dry loss moisture, (5) residual moisture, (6) as-received moisture, (7) decomposition moisture, and (8) water of hydration of mineral matter. 

Analysis of the coal used in these experiments and of a typical char from the lignite coal produced during a series of runs through the hydrogenator are shown in Table 1. The analyses are on a moisture-free basis and were obtained by the U.S. Bureau of Mines using standard ASTM analytical procedures. 

COAL AND CHAR FEED ANALYSIS % by wt - Moisture Free Basis... 

A sample of coal contains 2.4% water. After drying, the moisture-free residue contains 71.0% carbon. Determine the percent carbon on the wet basis. ... 

The ash content of raw and treated coals is reported on a moisture-free basis and the sulfur content on both a moisture- and ash-free basis. The ash reduction achieved corresponds to the overall change in moisture-free ash content divided by the moisture-free ash content of the raw coal. The reduction in total sulfur content corresponds to the change in total sulfur content divided by the total sulfur content of the raw coal, all on a moisture- and ash-free basis. The apparent reduction in organic sulfur content corresponds to the difference between the sulfur content of the acid-leached raw coal and the final sulfur content of the acid-leached, alkali-treated coal divided by the sulfur content of the acid-leached raw coal, all on a moisture- and ash-free basis. Coal recovery corresponds to the mass ratio of coal recovered during the alkaline treatment step to coal charged, all on a moisture- and ash-free basis. 

Solid analyses (Moisture free) ISGS Std. Coal 1 (moisture free) % Total Sulfur 4.23b 2.69 2.64 2.94 1.95... 

Fluor Engineers and Constructors Inc., under contract with EPRI has completed a rather detailed study (8 ) of the cost of producing power via Texaco gasifiers and advanced design gas turbines and steam turbines. They conclude investment costs (mid-1976 dollars) to be 815 million for a plant gasifying 9600 T/D of moisture-free Illinois coal and producing 1150 megawatts of net power. 

Height from base of major coal seam. Determined by x-ray fluorescence. " Moisture free basis. 

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