Ash-free 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%. 

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 final results of the proximate analysis of coal (ASTM D-3172 ASTM D-3173 ASTM D-3174 ASTM D-3175 ASTM D-5142 ISO 562) are usually reported to the first decimal place any subsequent figures have little or no significance. The final report of the analysis should always contain the results on a basis of air-dried coal (i.e., coal in its most stable condition and in which it was analyzed), but for purposes of classification or comparison it is often necessary to convert to another basis, such as dry coal, dry, ash-free coal, or as-received coal. 

Ubhayakar et al. [14] studied rapid devolatilization of pulverized coal in hot combustion gases, varying the input gas temperature between 1525 and 1975°C. They used three particle size distributions for the same type of coal as received, the fraction which remained on a 200 mesh screen and that which passed through the screen. The residence time in the gasifier was 7-70 x 10 s. The tests were conducted at a pressure of 1 atm, heating rates up to 10 °C/s, and volatile product yield up to 68% of the original dry-ash-free coal. 

A variety of parameters are commonly measured on coals, such as elemental composition (C, H, O, N, S), content of ash, moisture, as well as physical properties such as calorific power, hardness, and reflectance. These parameters have a wide range of values, and only some ranges can be indicated. For example, the elemental composition (in ash free coals) is 85-92 % C, 2-3% H, and 7-8% O for anthracite, 70-75% C, 5-6% H, and 15-20% O for bituminous coals, and 55-70% C, 6-7% H, and 25-30% O for lignites. Coal may also contain 1-2% N, and up to 4-5% or even higher of S. The content of ash can also vary from a few percent to 20% or higher. 

The effect of the additive upon yield of hydrogen and methane in the pilot-plant unit is shown in Figure 9. At an average gasification temperature of 914 °C, addition of 5% hydrated lime in the coal feed increased the hydrogen yield approximately 30% from 6.25 to 8.1 scf/lb of moisture-and-ash-free coal feed. A similar increase of 17% was obtained when 5% dolomite was used in the coal feed at 945 °C average gasifica-... 

It is reported that to produce about 5 million cu ft of hydrogen/per hour from coal there are needed about 19,000 kwhr of electrical energy, 302,000 lb per hr of steam, about 900,000 cu ft per hr of fuel gas, and 42 tons per hr of moisture- and ash-free coal. 

Solvent Yield of coal extract (wt% of dry, ash-free coal)... 

The use of solvents at temperatures above their critical temperature can lead to enhanced yields of extracts due to changes in the solvent properties. Even nonspecific solvents, snch as hydrocarbons, can give yields of extracts that are ca. 20% w/w of the dry, ash-free coal (Bartle et al 1975 Whitehead and Williams, 1975 Williams, 1975). 

Wang, J., Sakanishi, K., Saito, I., Takarada, T., Morishita, K. (2005). High-yield hydrogen production hy steam gasification of hypercoal (ash-free coal extract) with potassium carbonate comparison with raw coal. Energy Fuel, 19, 2114—2120. 

The reactor feed includes a moisture- and ash-free coal component designated "C." and a carrier solvent. Feed hydrogen and flush oil are included in the solvent for simplicity. 

The concentrations of the above-defined feed and product components are expressed in terms of dimensionless weight fractions material balance feed and product quantities have been normalized with respect to feed moisture- and ash-free coal i.e.,p =P/C.,c =C /C., and = L /C., where P, etc., are the concentrations by weight of components p, etc., in the product, and C. is the concentration of the maf coal at the reactor inlet. 

Okuyama, N., Komatsu, N., Shigehisa, T., Kaneko, T., and Tsuruya, S. (2004) Hypercoal process to produce the ash-free coal. Fuel Processing Technology, 85 (8-10), 947-967. 

Yasumuro, Motoharu (2004) Development of Hyper Coal (ash-free coal) Production Technology, Report, Enviromnent Technology Development Department of NEDO (New Energy and Industrial Technology Development Organization) MUZA KAWASAKI, 20F, 1310 Omiya-cho, Saiwai-ku, Kawasaki-shi, Kanagawa, 212-8554 Japan. 

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