Subbituminous coal States

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 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). 

Coals covering a range of rank downwards from low-volatile bituminous were examined in solvent-free catalytic hydrogenation over the temperature range 300-400°C and for reaction times up to 60 min. The work discussed here specifically Involved four coals which were obtained form the Penn State Coal Sample Bank. These were a subbituminous coal PSOC-1403, and three hvAb bituminous coals, PSOC-1168, PSOC-1266 and PSOC-1510. 

The 10 lb/hr bench-scale hydrocarbonization facility at ORNL is shown in Figure 1 the equipment flowsheet is presented in Figure 2. With this apparatus, yield data have been generated for the mild hydrocarbonization of Wyodak subbituminous coal. Table I summarizes the proximate and ultimate analyses of this coal. When Wyodak coal is hydrocarbonized at 1040°F under a hydrogen pressure of 300 psi (315 psia total pressure), the yields obtained (expressed as wt % of MAF coal fed) were as follows oil, 20 gas, 21 water, 13 and char, 46. Figure 3 shows the variation of oil yield with temperature at a hydrogen pressure of 300 psi as observed, a gentle maximum occurs at about 1040°F. The steady-state, make gas composition under these conditions is presented in Table II. 

For subbituminous coals> which are generally lower in pyrite than bituminous coals, it was impossible to achieve steady-state runs under SRC-II processing conditions without the addition of pyrite or other catalyst. For Belle Ayr coal (Wyodak-Anderson, WY), the pyritic sulfur content was 0.16% and the total oil yield was 40% at 450 C, 2250 psia H2 and one-hr residence time. 

Bituminous is the most abundant rank of coal. It accounts for about 50% of the coal produced in the United States. Bituminous coal has a carbon content of between 77% and 87% on a dry ash-free basis and a heating value that is much higher than lignite or subbituminous coal. On the basis of volatile matter content, bituminous coals are subdivided into low-volatile bituminous, medium-volatile bituminous, and high-volatile bituminous. Bituminous coal is often referred to as soft coal but this designation is a Layman s term and has httle to do with the hardness of the coal. 

The actual physics and chemistry of coal plasticity are not well understood and most theories conclude that the plastic state is the result of thermal rupture of chemical bonds that are responsible for the orientation of the coal units with respect to one another as well as the degeneration of a variety of physical bonds. However, neither the anthracites nor the lignites and subbituminous coals display well-defined plastic behavior, but subjecting the lower-rank coals to liquefaction temperatures in the presence of hydrogen may often induce some degree of plasticity with the resultant problems. 

Energy, Mines, and Resources Canada. 1977-. Statistical Review of Coal in Canada. Ottawa Energy, Mines and Resources Canada. Annually reviews production, consumption, and export statistics of Canadian metallurgical grade bituminous coal and subbituminous coal used for domestic electricity generation. Includes statistics on coal imported into Canada from the United States and South American export markets. 

Processes and equipment for the gasification of inferior coke and chars from low-temperature carbonization of subbituminous and lignitic coals were developed in Germany (13), where the relatively large yield of low-temperature tar was welcomed as raw material for hydrogenation processes. The market for low-temperature tar in the United States has been too small and the selling price too low to encourage the use of low-temperature chars for gas production. 

The basis for the two ASTM criteria (the fixed-carbon content and the calorific value calculated on a moist, mineral-matter-free basis) are shown in Fig.6.13 for over 300 typical coals of the United States. The classes and groups of Table 6.4 are indicated in Fig. 6.13. For the anthracitic and low- and medium-volatile bituminous coals, the moist, mineral-matter-free calorific value changes very little hence the fixed-carbon criterion is used. Conversely, in the case of the high-volatile bituminous, subbituminous, and lignitic coals, the moist, mineral-matter-free calorific value is used, since the fixed-carbon value is almost the same for aU classifications. 

Coal represents over 90 percent of the U.S proven reserves of fossil fuels, and can serve as a source of synthetic fuel for the petrochemical industry as well as a source of electric power production and process heat generation. About one-third of the world s coal reserves are present in the United States. The recoverable reserves of U.S. coal have been estimated to be 250 billion tons. Eastern U.S. coals are generally bituminous with a heating value of 10,000 to 15,000 Btu/lb. Bituminous coals comprise nearly one-half of the total U.S. coal reserves. The western as well as southwestern U.S. coals are mainly subbituminous (with a heating value of 9000-12,000 Btu/lb) and lignite (with a heating value of 8000-10,000 Btu/lb). 

Bituminous coal accounts for, by far, the largest share of all coal produced in the United States- In 1990, production of all types of coal totaled over 1 billion short tons, of which 943 million tons were subbituminous and bituminous coals (Fig, 17.1). Despite its dean burning characteristics, anthracite accounts for a diminishing share of total coal production. Most anthracite is mined in northeastern Pennsylvania. In 1949, anthracite accounted for 9 percent of total coal production by 1990 its share was reduced to less than one-half of 1 percent- Figure 17.2 presents data on coal consumption in the United States. 

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