Coal matter

Proton n.m.r. investigations of coals swollen in deuterated pyridine showed that the free induction decay /FID/ consists of Gaussian and Lorentzian components related to two populations of protons which have widely different degrees of rotational mobility (1-5). The Gaussian component of FID has been unanimously ascribed to the macromolecular part of the coal matter that is supposed to have very limited rotational mobility. These publications as well as the ensuing debates (6-9) however, reflected the controversy regarding the nature of the Lorentzian /mobile/ protons in coals. 

The removal of both mineral matter and sulfur species to very low values would provide premium solid fuels and possibly new chemical feedstocks. Several techniques are being explored to achieve these goals. The mineral matter in a physically cleaned coal can be further reduced by the solubilization of the aluminosilicate minerals. This can technically be accomplished with the use of alkaline and then acid treatments. A variety of studies are under way to define the conditions required for effective removal of the mineral matter and establish the amount of sulfur reduction that can be accomplished. Others involve the use of fine grinding to liberate the coal from the mineral matter. Then an agglomerant is used to separate the coal matter from the aqueous phase containing suspended mineral matter. A new approach uses microwave energy to selectively decompose the clays into species that can be solubilized and removed. Still another technique involves treatment with carbon dioxide to reduce the particle size and permit the liberation of the mineral matter. Over the next few years these will be studied further and it is hoped that coal will become available in a form with less of these interesting, but not entirely desirable mineral species. 

The endogenetic cleat is formed during the process of physical changes in the properties of coal during the metamorphic process. Coal matter undergoes density changes and a decrease in its volume— processes are associated with the changes in the internal stress system, compaction and desiccation, and the formation of cleat planes. 

Coals (the plural is deliberately used because coal has no defined, uniform nature or structure) are fossil sources with low hydrogen content. The structure of coals means only the structural models depicting major bonding types and components relating changes with coal rank. Coal is classified, or ranked, as lignite, subbituminous, bituminous, and anthracite. This is also the order of increased aromaticity and decreased volatile matter. The H C ratio of bituminous coal is about 0.8, whereas anthracite has H C ratios as low as 0.2. 

This process may also be referred to as destmctive distillation. It has been appHed to a whole range of organic materials, more particularly to natural products such as wood (qv), sugar (qv), and vegetable matter to produce charcoal (see Fuels frombiomass). However, in the present context, coal usually yields coke, which is physically dissimilar from charcoal and appears with the more familiar honeycomb-type stmcture (27). 

Documented efforts at cokemaking date from 1584 (34), and have seen various adaptations of conventional wood-charring methods to the production of coke including the eventual evolution of the beehive oven, which by the mid-nineteenth century had become the most common vessel for the coking of coal (2). The heat for the process was suppHed by burning the volatile matter released from the coal and, consequently, the carbonization would progress from the top of the bed to the base of the bed and the coke was retrieved from the side of the oven at process completion. 

Drying. In many cases, the high moisture content of young coals dictates significant drying (qv) before use. In some cases, partial removal of mineral matter, especially water-soluble species, is desirable. 

Briquettes bum similarly to bituminous coal, although some tend to disintegrate on combustion. Alow (<6-7%) ash content increases the possibility of disintegration. Normal combustion depletes the combined oxygen and volatile matter in the coal quiddy, effectively changing its composition and combustion behavior, making control of combustion difficult. 

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). 

Similar to oil-fired plants, either low NO burners, SCR, or SNCR can be appHed for NO control at PC-fired plants. Likewise, fabric filter baghouses or electrostatic precipitators can be used to capture flyash (see Airpollution controlmethods). The collection and removal of significant levels of bottom ash, unbumed matter that drops to the bottom of the furnace, is a unique challenge associated with coal-fired faciUties. Once removed, significant levels of both bottom ash and flyash may require transport for landfilling. Some beneficial reuses of this ash have been identified, such as in the manufacture of Pordand cement. 

The monoalkyl derivatives in salt form appear to have low toxicity. The monomethyl sulfate sodium salt has an approximate oral lethal dose greater than 5000 mg/kg of body weight for rats (129). Monododecyl sulfate sodium salt is widely marketed as a detergent and shampoo ingredient (oral LD q 1268 mg/kg for rats) (126). Both dimethyl sulfate and monomethyl sulfate occur in the environment in coal fly-ash and in airborne particulate matter (130). 

Mesophase formation in coal-tar pitch is encouraged by a reduction of the natural quinoline-insoluble matter content, which resembles carbon black but is not optically anisotropic and is characterized by an atomic carbon hydrogen ratio of 4 1. In contrast, the atomic carbon hydrogen ratio of mesophase is about 2 1. 

It is incorrect to refer to bitumen as tar or pitch. Although the word tar is somewhat descriptive of the black bituminous material, it is best to avoid its use in referring to natural materials. More correctly, the name tar is usually appHed to the heavy product remaining after the destmctive distillation of coal (qv) or other organic matter. Pitch is the distillation residue of the various types of tar (see Tar and pitch). 

Canadian and European practice (2—4) and geologists and archaeologists in the United States use bitumen or asphaltic bitumen as a synonym for asphalt, and apply asphalt to the mixture of bitumen and inorganic matter that is used for paving purposes. On the other hand, pitches and tars are derived from the destmctive distillation of coal, cmde oils, and other organic materials. 

Graphite is frequently, although incorrectly, analyzed by the proximate method used for coal in which the volatile material is deterrnined by strongly beating the sample in a covered or luted cmcible. Some oxidation of the graphite always occurs so that the value obtained for volatile matter is high and thus the "fixed carbon" is too low. The method lacks both accuracy and precision. 

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