Volatile matter in coal

Based on the idea mentioned above, we should pay attention to the quantity of carbon content in the volatile matter in coal. 

The characteristics of this relationship are found to differ greatly from one another in the conditions of liquefaction and the coals used. Thus, the volatile matter in coal is not particularly useful as a parameter. 

The fixed-carbon value is one of the values used in determining the efficiency of coal-burning equipment. It is a measure of the solid combustible material that remains after the volatile matter in coal has been removed. For this reason, it is also used as an indication of the yield of coke in a coking process. Fixed carbon plus ash essentially represents the yield of coke. Fixed-carbon values, corrected to a dry, mineral-matter-free basis, are used as parameters in the coal classification system (ASTM D-388). 

The content of volatile matter in coal is very important to ignition, combustion, and flame stabilization in a practical flame. Flence, coal devolatilization was extensively studied, and many models were proposed. The rate of devolatilization is described by single-step, two-step, and multiple-step reaction models and a functional group decomposition model. In the single-step model, the rate of decomposition is a first-order reaction, and is proportional to the content of volatiles, v, in coals30... 

In another series of experiments Friedel and coworkers268"270) studied the distribution of gaseous products from the laser irradiation of coals of various ranks and particle sizes in various atmospheres. In vacuum experiments the total gas yield varied inversely with coal rank, showing a four-fold increase between anthracite and lignite. The product gas composition as a function of volatile matter in coal is shown in Fig. 20. Yields of acetylene and hydrogen generally increased between anthracite... 

Fig. 20. Distribution of H2, CO, C02, CH4 and C2H2 in the products of laser irradiation of coal as a function of volatile matter in coal. (Redrawn from Karn, F. S., Friedel, R. A., Sharkey, Jr., A. G. Carbon 5, 25 (1967), by permission of the publishers, Pergamon Press Ltd.)...

Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. The volatile matter obtained during the pyrolysis of coal consists mainly of combustible gases such as hydrogen, carbon monoxide, methane plus other hydrocarbons, tar as well as incombustible gases such as carbon dioxide and steam. 

Correlations between hydrogen impurities and volatile matter in coal used by EC during 2008-2009 years... 

Fig. 8.47 (a-c) Correlations between hydrogen (a), oxygen (b) and carbon (c) emissions normalized to ambient nitrogen emission and volatile matter in coal... 

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. 

The pure carbon that occurs in coal is fixed carbon, and the higher the content, the greater the calorific value of the coal. Total carbon implies the fixed carbon plus the carbon present in the volatile matters (in CO, C02, CH4, and hydrocarbons). The total carbon content is thus always higher than the fixed carbon in any coal. A high total carbon-bearing coal will be characterized by a high calorific value. 

As volatile matter in the coal increases to as much as 40% of the coal (dry and ash-free basis), increasing amounts of oils and tars are released. However, for coals of higher volatile content, the quantity of oils and tars decreases and is relatively low in the sub-bituminous coals and in lignite. 

Previous investigations (14, 15) have shown that R° increases as the fixed carbon content increases and decreases as the volatile matter content increases. The relation of R to volatile matter for coals included here is similar to that reported by other investigators (14, 15) a progressive increase in R is accompanied by a corresponding decrease in volatile matter content, as shown in Figure 1. 

ASTM D-3175. Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke. 

ISO 540. Determination of the Fusibility of Ash High-Temperature Tube Method. ISO 562. Determination of Volatile Matter in Hard Coal and Coke. 

Badzioch and Hawksley [9] carried out experiments on the pyrolysis of 11 British coals of various ranks in a laminar flow reactor. They studied pyrolysis at temperatures up to 1000°C, heating coal particles to decomposition in 30-110 ms at a rate between 25000 and 50000°C/s. The volatile product yield in rapid heating was 1.3-1.8 times higher than that found from the difference between the proximate volatile matter of coal and that of char. 

The pyrolytic gasification of biomass has been interpreted to involve the decomposition of carbohydrates by depolymerization and dehydration followed by steam-carbon and steam-carbon fragment reactions. So the chemistries of coal and biomass gasification are quite similar in terms of the steam-carbon chemistry and are essentially identical after a certain point is reached in the gasification process. Note, however, that biomass is much more reactive than most coals. Biomass contains more volatile matter than coal, and the pyrolytic chars from biomass are more reactive than pyrolytic coal chars. 

A 10-in. diameter continuous fluidized-bed reactor system is being operated to produce nonagglomerating coal from high volatile bituminous coal by mild surface oxidation. Minimum pretreatment is defined by acceptability of the coal as a feed to the hydro gasifier. This corresponds to 24-26% volatile matter in the pretreated coal. The following operating variables, in the order of importance, contribute to satisfactory pretreatment—reaction temperature of 725°-750°F., oxygen reacted coal feed ratio of 1.0 1.5 std. cu. ft./lb.9 and a coal residence time of 1-2 hours. 

Coals were selected to encompass a range of rank and volatile matter. Bituminous coals ranged from hvCb to lvb one subbituminous coal was also studied. Their proximate analyses are given in Table I. 

V = volatile matter in feed coal char (including moisture), grams/ gram feed coal char... 

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