Subbituminous coals

Conversion of carbon in the coal to gas is very high. With low rank coal, such as lignite and subbituminous coal, conversion may border on 100%, and for highly volatile A coals, it is on the order of 90—95%. Unconverted carbon appears mainly in the overhead material. Sulfur removal is faciUtated in the process because typically 90% of it appears in the gas as hydrogen sulfide, H2S, and 10% as carbonyl sulfide, COS carbon disulfide, CS2, and/or methyl thiol, CH SH, are not usually formed. 

The TOSCOAL Process. The Oil Shale Corp. (TOSCO) piloted the low temperature carbonization of Wyoming subbituminous coals over a two-year period in its 23 t/d pilot plant at Rocky Falls, Colorado (149). The principal objective was the upgrading of the heating value in order to reduce transportation costs on a heating value basis. Hence, the soHd char product from the process represented 50 wt % of the starting coal but had 80% of its heating value. 

Properties. Results for the operation using subbituminous coal from the Wyodad mine near Gillette, Wyoming, are shown in Table 13. Char yields decreased with increasing temperature, and oil yields increased. The Fischer assay laboratory method closely approximated the yields and product assays that were obtained with the TOSCOAL process. 

Analysis. Analyses of a number of lignitic coals are given in Table 3. Figure 1, a distribution plot of 300 U.S. coals according to ASTM classification by rank, indicates the broad range of fixed carbon values (18). According to the ASTM classification, fixed carbon for both lignite and subbituminous coals has an upper limit of 69%, but in practice this value rarely exceeds 61%. 

North America.. In the United States, lignite deposits are located in the northern Great Plains and in the Gulf states. Subbituminous coal is found along the Rocky Mountains. The western half of North Dakota has about 74% of the nation s resources, Montana 23%, Texas 2%, and Alabama and South Dakota about 0.5% each. The lignite resources to 914 m represent 28% of the total toimage of all coal deposits in the United States. The lower cost and low sulfur content have contributed to rapid growth in production. 

In 1974 a 1000 t/d ammonia plant went into operation near Johaimesburg, South Africa. The lignitic (subbituminous) coal used there contains about 14% ash, 36% volatile matter, and 1% sulfur. The plant has six Koppers-Totzek low pressure, high temperature gasifiers. Refrigerated methanol (—38° C, 3.0 MPa (30 atm)) is used to remove H2S. A 58% CO mixture reacts with steam over an iron catalyst to produce H2. The carbon dioxide is removed with methanol (at —58° C and 5.2 MPa (51 atm)). Ammonia synthesis is carried out at ca 22 MPa (220 atm) (53) (see Ammonia). 

Fig. 11. Coal fields of Alaska where M represents bituminous coal subbituminous coal and lignite and X is an isolated occurrence of coal of unknown...

A more complex reaction model was proposed from the results of a kinetic study of thermal liquefaction of subbituminous coal. Data were obtained over a temperature range of 673 to 743 K (752 to 878°F) at 13.8 MPa (2000 psia) by using two solvents, hydrogenated anthracene oil (HAO), and hydrogenated phenanthrene oil (HPO), at a coal-solvent ratio of 1 15. Results were correlated with the following model ... 

Moor-kohle,/. moor coal (black subbituminous coal), -lauge, /. extract from bog earth or peat, -mergel, m. bog marl, -salz, n, salt from peaty soil, -wasser, n. peat water. Moos, n. moss, -achat, m. moss agate, moosartig, a. moss-like, mossy. 

Self-ignition is particularly a risk with lower-grade subbituminous coals and lignite. To avoid oxidation, coal piles should be turned frequently so that heat can vent, and piles should be packed and shaped to nhninhze surface exposure. 

Low volatile bituminous coal and high volatile anthracite coal Subbituminous coal Lignite Coke and coke breeze Wood Bagasse (dry) 11.000- 14,000 9.000- 11,000 7.000- 8,000 12.000- 13,000 8.000- 9,000 7.000- 9,000... 

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). 

A recent study in these laboratories (75) on calcium carbonate precipitation from Wyodak coal has confirmed the relationship between ion-exchangeable calcium and the appearance of calcium carbonates during liquefaction. These experiments were performed on samples of the subbituminous coal which had been demineralized, to ensure that all carboxylic acid groups were in the acidic form, and subsequently exchanged with varying amounts of calcium ions. 

South America and Western Europe). But the large reserves of near-surface subbituminous coals and lignites are also being looked upon as future sources of synthetic fuel gases and liquid hydrocarbons that would augment production of synthetic crude oils from, e.g., Northern Alberta s oil sands (4). 

Similarly, a subbituminous coal (Wyodak-Anderson) which gave only 60% conversion at 427°C in 2 minutes could be converted to >70% at 460°C with no ill effects (see Figure 17). At 470°C there was an indication that conversion had begun to decline at 2 minutes however, this data is extremely limited. The implications of these results with a western subbituminous coal is that a low sulfur boiler fuel may potentially be produced in a single-stage short contact time process. 

Table III shows that hydrogenated and unhydrogenated SRC recycle solvents were equally effective for the conversion of a western subbituminous coal at low reaction severity. At higher severity but at times shorter than 10 minutes, significantly higher conversions were achieved only with the hydrogenated solvents which could donate more hydrogen.

SOLVENT EFFECTS ON SHORT TIME CONVERSION OF BELLE AYR SUBBITUMINOUS COAL (800°F, 3 min., 1500 psi H2)... 

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

Coal Products Isotopic Distribution by Structural Position. Other workers have also investigated deuterium uptake in coal pro-ducts by structural position. Schweighardt, et al. (26) examined a centrifuged liquid product from a Synthoil run which was heated to 450°C with deuterium gas, Kershaw and Barrass (27) examined the products from the reaction of coal with deuterium gas using SnCl2 as catalyst, and Franz (10) examined the products from the reaction of a subbituminous coal with Tetralin-1,l-d2 at 427°C and 500°C. 

Wondrack, L. Szanto, M., and Wood, W. A., Depolymerization of Water-Soluble Coal Polymer from Subbituminous Coal and Lignite by Lignin Peroxidase. Applied Biochemistry and Biotechnology, 1989. 20-1 pp. 765-780. 

Subbing formulations, gelatin in, 12 444 Subbituminous coal, 6 703 classification by rank, 6 1 lit defined, 6 829... 

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