Brown coal deposition properties

The slagging and fouling tendencies of coals largely differ according to the deposit but also differ within the deposit because of widely varying coal composition. Ash properties are so complex that evaluation of coal performance is extremely difficult. The performance of coals in furnaces are further complicated by the processes which control deposition on heat transfer surfaces in boilers. Based on these complications, we must neither deceive ourselves as to the possibility of reliable estimates nor deny the possibility of making a useful estimate of the performance of brown coal in boilers. 

The rate of the oxidation process is determined by the reactivity of the starting carbon and oxidizer. The greater the reactivity of the substrates the lower the temperature of the process in which uniform formation of the pores in the granules is observed. In the case of carbonaceous materials the cokes of brown coals show the greatest reactivity, and the cokes of hard coals the smallest activity. The cokes of pit coals show an intermediate reactivity. This is connected with the earlier mentioned ordering of the crystallographic structure of carbon, which is of significant importance in the case of modification of carbon deposits contained in the carbon-mineral adsorbents in which the carbonaceous compound may be characterized by a differentiated chemical and physical structure. Thus the surface properties of hydrothermally modified complex adsorbents are defined by the course of three processes ... 

Coal is formed from peat and the vascular plant remains that accumulate in peat bogs. Anaerobic conditions are considered mandatory for the accumulation and preservation of peat and the formation of coal. Two major types of coals are known humic coal and sapropelic coal (see Breger, 1963, 1976). The former are formed from peat accumulations rich in humic substances derived predominantly from vascular plant remains. The latter represent coal formed from algal (boghead coal) or spore (cannel coal) accumulations. In many respects, sapropelic coal can be considered to have an aquatic origin similar to that of humin of aquatic sediments which forms from the accumulation of aquatic nonvascular plant debris in clastic sediments. Conversely, kerogen can also have the properties of humic coals (Breger and Brown, 1962) is the source materials to the sediment at the time of deposition are predominantly derived from vascular plants. 

Since the form of the deposits produced and their adhesive properties are determined by different factors (ash composition, particle size, temperature, state of the surface being cleaned, etc.), the best means of cleaning must be considered separately in each specific case. The ash from different fuels may in fact differ considerably. Whereas the m mum size of the ash from coal-dust furnaces is no greater than 120 n, that from shale furnaces reaches 300 M, while the mean diameter of the ash particles from Pechorsk coal [459] fluctuates between 3.5 and 125 p. On the other hand, the light-brown deposits of aluminosilicates are fine and easily blown away, while the dark Fe304 and Fe203 are very hard and the boiler has to be put out of service in order to remove them [457] the deposits formed in the combustion of fuel oil are also extremely hard to remove. 

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