Coal carbon

Coal carbonization processes are generally defined according to process operating temperature. Terms are defined in Table 2. 

The combustion of coal may be simply represented as the staged oxidation of coal carbon to carbon dioxide... 

Coal carbonization to produce metallurgical coke involves much the same chemistry as pyrolysis. 

Coumarone—indene or coal-tar resins, as the name denotes, are by-products of the coal carbonization process (coking). Although named after two particular components of these resins, coumarone (1) and indene (2), these resins are actually produced by the cationic polymerization of predominantly aromatic feedstreams. These feedstreams are typically composed of compounds such as indene, styrene, and their alkylated analogues. In actuaUty, there is very tittle coumarone in this type of feedstock. The fractions used for resin synthesis typically boil in the range of 150—250°C and are characterized by gas chromatography. 

Until the end of World War II, coal tar was the main source of these aromatic chemicals. However, the enormously increased demands by the rapidly expanding plastics and synthetic-fiber industries have greatly outstripped the potential supply from coal carbonization. This situation was exacerbated by the cessation of the manufacture in Europe of town gas from coal in the eady 1970s, a process carried out preponderantly in the continuous vertical retorts (CVRs), which has led to production from petroleum. Over 90% of the world production of aromatic chemicals in the 1990s is derived from the petrochemical industry, whereas coal tar is chiefly a source of anticorrosion coatings, wood preservatives, feedstocks for carbon-black manufacture, and binders for road surfacings and electrodes. 

Until 1960—1970, in countries where natural gas was not available, large amounts of coal were carbonized for the production of town gas, as well as a grade of coke which, although unsuitable for metallurgical use, was satisfactory as a domestic fuel in closed stoves. The early cast-iron and siUca horizontal retorts used at gasworks were replaced by continuous vertical retorts. These operated at flue temperatures of 1000—1100°C. The volatile products were rapidly swept from the retort by the introduction of steam at 10—20% by weight of the coal carbonized. 

Until the 1940s light oil obtained from the destmctive distillation of coal was the principal source of benzene. Except for part of the World War 11 period, the quantity of benzene produced by the coal carbonization industry was sufficient to supply the demand even when a large portion of benzene was used for gasoline blending. 

After 1950, benzene in motor fuel was largely replaced by tetraethyllead but the demand for benzene in the chemical industry persisted and soon exceeded the total production by the coal carbonization industry. To meet this growing demand, methods for producing benzene directiy from petroleum sources were developed. 

Sources of Raw Materials. Coal tar results from the pyrolysis of coal (qv) and is obtained chiefly as a by-product in the manufacture of coke for the steel industry (see Coal, carbonization). Products recovered from the fractional distillation of coal tar have been the traditional organic raw material for the dye industry. Among the most important are ben2ene (qv), toluene (qv), xylene naphthalene (qv), anthracene, acenaphthene, pyrene, pyridine (qv), carba2ole, phenol (qv), and cresol (see also Alkylphenols Anthraquinone Xylenes and ethylbenzenes). 

The importance of these concepts can be illustrated by the extent to which the pyrolysis reactions contribute to gas produdion. In a moving-bed gasifier (e.g., producer-gas gasifier), the particle is heated through several distinct thermal zones. At the initial heat-up zone, coal carbonization or devolatilization dominates. In the successively hotter zones, char devolatihzation, char gasification, and fixed carbon... 

Table 1. Production yields from coal carbonization...

The production of coke involves the heating of coal in the absence of air, called the carbonization or destructive distillation of coal. Carbonization, besides its main purpose of production of coke, also results in a coproduct called coke oven gas from which various liquid products such as tar, benzol, naphthalene, phenol, and anthracene are separated. There are two main types of carbonization based on the temperature to which the coal is heated in the absence of air. One type is low-temperature carbonization (LTC) the other is high-temperature carbonisation (HTC). Some features of LTC and HTC are listed in Table 1.28. The LTC Process is mainly carried out to manufacture domestic smokeless fuel. This presentation, however, concentrates on the HTC process by which metallurgical coke is produced. 

Typical Group A materials (e g., cement, baghouse fly ash, pulverized coal, carbon fines) are the best candidates for fluidized dense-phase (Wypych,... 

Stamicarbon [Staatsmijnen carbon] Stamicarbon bv is the licensing subsidiary of the Dutch chemical company DSM. It offers a number of processes, including HPO and HSO. Historically, the process for which the company was best known was a coal carbonization process today, a urea-manufacturing process is probably its most important one. 

Ufer A proces for refining the light oil produced in coal carbonization. The oil is washed with sulfuric acid and a controlled amount of water is then added to the mixture. The complex mixture of reaction products ( resins ) enters the oil phase the dilute sulfuric acid can be used directly for making ammonium sulfate. Invented in Germany in 1924 by A. Ufer operated in Germany and Canada in the 1920s and 1930s. 

Lynch, L.J. Sakurovs, R. Barton, W.A. Webster, D.S. Bacon, N.A. Parks, T. Reactive Inertlnlte and Coal Carbonization -NMR Thermal Analysis Studies NERDDP End of Grant Report, Project No. 662, l5o7 Chapter5. 

Figure 6c is taken from another, as yet unpublished study of coal carbonization during co-processing of bitumen and coal (2) ... 

Numerous tests indicated the factors that influence the results of shotfiring and showed, in particular, that variations in results are caused by changes in the composition of the methane-air mixture (e.g. when gas produced by coal carbonization, which is liable to variations in composition, or natural gas which varies in composition depending on its origin, was used for testing instead of pure methane). This emphasized the need to use a test gas of constant composition. 

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