Coal briquettes

The current emphasis on the use of coal is the production of added-value products using a variety of processes by which the total coal can be used with very little wastage of the products. Such is the character of the mild gasification process (Chapter 22) and a variety of other clean coal processes (United States Department of Energy, 1993) (Chapter 22), which have brought about renewed interest in briquetting and pelletization of coal. 

The production of briquettes (and/or pellets) from coal is a thermal decomposition process, akin to the carbonization process (Chapter 16). Therefore, at the risk of some repetition but for the sake of completeness, a repeat of the general principles of the carbonization process is warranted here. 

Carbonization is essentially a thermal treatment process for the production of a carbonaceous residue (with the simultaneous removal of distillate) from a variety of organic substances (Wilson and Wells, 1950 McNeil, 1966 Gibson and Gregory, 1971)  

The process may also be referred to as destructive distillation and has been applied to a range of organic materials, but more particularly to naturally occurring materials such as wood, sugar, and vegetable matter. The carbonaceous residue from the thermal decomposition of coal is usually referred to as coke (Chapters 13 and 16) (which is physically dissimilar from charcoal) and has the more familiar honeycomb-type structure. 

The thermal decomposition of coal is a complex sequence of events (Stein, 1981 Solomon et al., 1992) (Chapters 13 and 16) that can be described in terms of several important physicochanical changes, such as the tendency of the coal to soften and flow when heated (Chapters 8 and 9) or the relationship to carbon type in the coal (Solomon, 1981). In fact, some coals become quite fluid at temperatures of the order of 400°C-500°C (750°F-930°F) and there is a considerable variation in the degree of maximum plasticity, the temperature of maximum plasticity, as well as the plasticity temperature range for various coals (Kirov and Stephens, 1967 Mochida et al., 1982 Royce et al., 1991). Indeed, significant changes also occur in the structure of the char during the various stages of devolatilization (Fletcher et al., 1992). 

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Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Charcoal screenings, wet Charcoal, wet Chlorine azide Chlorine dioxide Chloroacetaldehyde Chloroacetone (unstabilized) Chloroacetonitrile Chloroformates, n.o.s. Chloroprene, uninhibited Chlorosulphonic acid Coal briquettes, hot Coke, hot Copper acetylide... 

The most common examples of fluid-solid reactions in which the size of solid changes are the reactions of carbonaceous materials such as coal briquettes, wood, etc. with low ash content to produce heat or heating fuels. For example, with an insufficient amount of air, producer gas is formed by the reactions... 

Cooking constitutes a source of VOCs in the indoor environment Food stuffs and fuels emit ample amounts of VOCs. For example, up to 54 hydrocarbons were identified from a study of 16 fuels/ stoves combinations that are usually used in urban and rural settings in China (Tsai et al., 2003). The worst stove/fuel VOC emitters include metal stoves with a flue/unprocessed coal powder, metal stoves with a flue/washed coal powder, brick stove with a flue/maize residue while the least emitters ofVOCs are traditional gas stove/coal gas fuel, improved brick stove with a flue/maize residue and metal coal stove with a flue/honeycomb coal briquette. Many of the compounds emitted in substantial amounts are reactive unsaturated compounds such as benzene, ethylene, acetylene, and propene. For example, up to 2856 mg of ethylene was emitted by per kg of coal powder in the metal stove. Similarly, the observation of elevated levels of benzene and toluene in a food-court in South China has been rationalized in terms of emission from liquefied petrol gas (LPG) stoves (Tang et al., 2005). Thus, cooking is an important contributor of precursors of photochemical smog. 

Determination of the ash content as an ess.en-tial factor for the assessment of brown coal briquettability. 

In 1858 the first Exter press was built for brown coal. Since then, modifications have been made, mostly to adopt modern drive and design methods as well as to use stronger or otherwise improved materials of construction. However, essentially the same press is still used today to produce most of the world s output of brown coal briquettes. Although the importance of brown coal briquettes is fading quickly, further improvements are still being made and new applications are developed, e.g. for the briquetting of biomass. 

In the following the most important considerations will be discussed and a typical, conventional plant for the production of 60-70 t/h of egg-shaped coal briquettes will be described. 

Punch-and-die press with multiple die sets on an indexed table for making large (e.g. coal) briquettes. (No longer used.)... 

Fig. 8.87 Photograph showing different traditional (coal) briquette shapes that were produced with ram extrusion presses.

Fig. 6.10-15 Some typical coal briquettes (bricks) produced with punch-and-die presses...

Fig. 6.10-16 High-quality pillow-and egg-shaped coal briquettes...

Fig. 6.10-16) hard coal briquettes that were suitable for home heating purposes. 

Although the production of the traditional brown coal briquettes has come to very low levels, the technology, based on the ram extrusion principle, is available, mature, and has been further developed until recently. While many classic manufacturers of... 

To overcome the main problem of conventional coal briquettes, excessive pollution, beginning in about the 1960s, research started in Europe, particularly the UK and in Japan to develop smokeless coal briquettes. As a result of fundamental studies into and evaluations of the briquetting of coal at the British National Coal Board s Coal Research Establishment (NCB/CRE) a book on roll pressing was published in 1976 [B.13b]. 

Uber die Theorien der Braunkohlenbrikettentstehung (On the theories of mechanisms involved in the production of brown coal briquettes). Sitzungsber. Sachs. Akad. Wissenschaften (Leipzig), Vol. 109 (1), Akademie Verlag, Berlin, GDR (1970). 

Fig. 6.10-15 Some typical coal briquettes (bricks) produced with punch-and-die presses Fig. 6.10-16 High-quabty pillow- and egg-shaped coal briquettes Fig. 6.10-17 The operating principle of roller briquetting presses Fig. 6.10-18 The ring roller press" [6.7.3.1] Fig. 6.10-19 Flow diagram of a modem anthracite (hard) coal mixing, drying, conditioning, briquetting, and cooling plant...

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