Coal formation, plant types

Coal is formed from peat and the vascular plant remains that accumulate in peat bogs. Anaerobic conditions are considered mandatory for the accumulation and preservation of peat and the formation of coal. Two major types of coals are known humic coal and sapropelic coal (see Breger, 1963, 1976). The former are formed from peat accumulations rich in humic substances derived predominantly from vascular plant remains. The latter represent coal formed from algal (boghead coal) or spore (cannel coal) accumulations. In many respects, sapropelic coal can be considered to have an aquatic origin similar to that of humin of aquatic sediments which forms from the accumulation of aquatic nonvascular plant debris in clastic sediments. Conversely, kerogen can also have the properties of humic coals (Breger and Brown, 1962) is the source materials to the sediment at the time of deposition are predominantly derived from vascular plants. 

The origin of sulfur in most coals is believed to be sulfate ion, derived fi om seawater. During the earliest stages of coal formation, bacterial decomposition of the coalforming plant deposits occurs. Some of these bacteria reduce sulfate to sulfide. This immediately reacts with iron to form pyrite, the principal inorganic form of sulfur in coals. It is also incorporated into the organic portion of the coal. The amount and form of sulfur in coals depend much more on the coal s depositional environment than on its age or rank. In this sense, it is largely a coal-type parameter, not a rank parameter. 

Throughout the last century or so, many scientists have subscribed to the theory that the coal source material has not formed by the degradation of plant material in situ in a peat swamp environment but rather accumulated from the deposition of transported material in aqueous environments such as lakes, seas, and estuaries (Moore, 1940 Stutzer, 1940 Francis, 1961). Indeed, the concept of transportation of the source material also led to the belief that not one but several processes were responsible for the different types of coal. Thus, there was much thought and discussion which actually led to serious questions about the autochthonous theory of coal formation and also brought discredit on the idea that coals form a prescribed and definite progression from peat to anthracite. 

Smith and Smoot, 1990). This may be due to not only the deposition of a variety of different organic compounds that are believed to be the precursors of coal (Chapter 3) but also the accumulation of different parts of the plant (as well as different plants, e.g., trees, ferns, mosses, etc.) during the formation of the sediment (Murchison, 1991 Puttmann et al., 1991). Each compound type, tissue type, or plant type then progresses through the various maturation stages that eventually lead to coal. 

Coal formations offer another opportunity to store CO2 because it adsorbs strongly on the coal surfaces. Contacting coal surfaces with CO2 via flue gas injection may have application at coal-fired power plants near coal mines and in other areas where suitable coals are accessible. Since CO2 adsorbs more strongly than methane on coal surfaces, there is the potential for increasing methane production from coal bed methane operations. The effectiveness of adsorption processes will depend heavily on the type and permeahility of the coal formations. BP operates an ECBM project in northwestern New Mexico and southwestern Colorado. We are adding a commercial-scale demonstration of C02-nitrogen injection during 2001-2002. 

Coal lithotypes represent the macrostructure of coal and are, in fact, descriptive of the coal. A piece of coal will usually exhibit a definite banded appearance due to the accumulation of different types of plant debris during the formation of the organic sediment (White, 1911 Thiessen, 1931 Muller et al., 1990 ... 

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