Brown coal problems

Aluminium and Precipitator Ash. In some Victorian brown coals significant quantities of acid-soluble aluminium are found. This is believed to be present as aluminium hydroxide which is dispersed throughout the water phase of the coal. During combustion of this coal, the refractory aluminium oxide formed takes the shape of the relics of the plant material present in the coal, thus forming an extremely low density ash (approximately 100 kg/m ). Whilst the collection of these particles by electrostatic precipitation is possible, the problem of reentrainment on rapping has necessitated the use of larger sized units than would otherwise be required. It is therefore important to determine the acid soluble aluminium fraction in the coal to determine if precipitation of fly ash is likely to be a problem. 

A macro- and micropetrographical analysis with a view to before technological problems involved in the briquetting process allows one at the most to judge the briquettability of Rhenish brown coal on the basis of trend data. 

For the gasification process no usable quantitative relations were established between the petrographical coal properties and the gasification behaviour. It is possible without any material problems to convert nearly all the Rhenish brown coal types into gaseous hydrocarbons or synthesis gas. 

Brown coal was already an important energy resource in Europe at the beginning of the 20th century. In spite of the many problems in process technology, the usable reserves of this low value energy fuel (Figure 1) will surely be an indispensable basis of supply for another fifty years. 

On the other hand, low-rank coals are currently used just as fuels near coal mines because such coals (e.g., brown coal and lignite) contain large amounts of water (up to 60% w/w) and dewatering or drying is essential when brown coals are transported and stored to be utilized. Dewatered brown coals unfortunately tend to have high spontaneous combustion tendency as compared to non-dewatered coals, which causes serious problems for transportation and storage (Xian et al., 2010). 

The volatile matter increases from less than 8% in antracite to more than 27 wt% in lignite. In addition, the content of water may vary from less than 5 wt% in antracite to about 60% in German brown coal. Nitrogen (0.5-2%) will be converted into ammonia. The sulphur content may typically vary from 0.5-5 wt%. Sulphur will be converted to COS and H2S. Sulphur will poison downstream synthesis catalysts and must be removed. Chlorine is normally below 1 wt%. Chlorine may cause corrosion problems in downstream equipment. Chlorine will react with ammonia from the nitrogen and deposition of ammonia chloride may foul waste heat boilers and limit their operating temperature [230]. 

The humic acids offered commercially by some manufacturers are not recommended as reference materials. These substances are usually obtained from terrestrial sources such as peat or brown coal. They lack strict quality control, Le., the composition differs from batch to batch. Furthermore, these comp>ounds are poorly characterized, even in terms of elemental composition and ash content. Further information on this problem has been provided by Malcolm and McCarthy (1986). 

In addition to operating at atmospheric pressure, the conventional Winkler gasifier has two other critical drawbacks. First, it uses only coals with high reactivity, such as brown coals or lignites. Second, it achieves relatively low carbon conversion, even with high-reactivity coals, and raises the problem of how to use the char it produces. 

Methane is undesirable in most synthesis gas applications. The HTW demonstration plant was also designed specifically for reactive brown coal. Therefore, carbon conversion was not a problem, and the gasifier was a bubbling fluidized-bed design. 

Coal tar epoxies These are a combination of epoxy resins and selected coal tars. Properties can vary, depending on the coal tar-to-epoxy ratio. The ideal compromise appears to be approximately 50/50. Coal tar epoxies are only available in black or dark brown. They cost less than straight epoxies and generally have better wetting properties, so they can be used on slightly less than perfect surface preparation. There are similar re-coating problems as for the two-pack epoxies. 

Individuals whose jobs expose them to unusually high particulate concentrations are especially susceptible to health problems from the pollutant. For example, men and women who work with the mineral asbestos are very prone to development of a serious and usually fatal condition known as asbestosis, in which fibers of the mineral become embedded in the interstices (the empty spaces within tissue) of the lung. Similar conditions are observed among coal workers who inhale coal dust (pneumoconiosis, or black lung disease) textile workers (byssinosis, or brown lung disease) those who work with clay, brick, silica, glass, and other ceramic materials (silicosis) and workers exposed to high levels of beryllium fumes (berylliosis). 

Not long ago, a committee, composed of Prof P. Bedson, Drs Drummond and Hume, Mr T. Bell, one of H.M. Inspectors of Coal Mines, and others, in considering the problem whether Ihe fumes produced by the combustion of tonite were injurious to health, carried out a series of experiments in coal mines for this purpose. The air at the "intake" was analysed, also the air of the "return," and the smoky air in the vicinity of the shot holes. The cartridge was surroimded by the flame-extinguishing mixture, and packed in a brown paper bag. During the first experiment nineteen shots were fired (= 6.29 lbs. tonite). The "return" air showed only a trace of carbonic oxide gas (CO). At the second experiment thirteen shots were fired (= 4.40 lbs. tonite), and analysis of the air of the "return" showed that CO was present in traces only, whilst the fumes contained only 1.9 to 4.8 parts per 10,000. 

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