Coal of Д rank (long-flame coal)
For many millions of years the remains of the plants on Earth are transformed into one or another useful natural resource. Those remains are first of all transformed to peat and then, as the consequence of water pressure, layers of soil, absence of oxygen and increased temperature it is transformed into a brown coal and afterwards - into hard coal.
Hard coal is also subject to metamorphism process, that means - changes. They are connected with the amount of contained moisture, volatile components, carbon that determine how actively the coal will burn. Also vitrinite (lat. - glass) amount is changed. Vitrinite is formed from trunks, stubs, leaves and branches of trees during the transition from peat state into coal state during the constant waterlogging. This is the way the long-flame coal is formed and it has its own chemical contents and properties.
According to statistics, there are almost 49088 millions of tons of hard coal in Russia. The long-flame coal is not less than 50% from total. Mainly such coal can be found in Minusinsk in Khakass republic. The coal has been mined here from the year of 1904 and total coal reserve is 2,7 billion of tons. The most big occurrences are Izykh and Chernogorsky. Kuznetsk basin is also famous, especially Erunakovsky occurrence. Also recently the unique occurrences of long-flame coal that is not deep, has been found in Kostenkovo village in the Kemerovo Region. It is being mined now. In the Russian part of the Donetsk basin there are almost 2 billions of tons of long-flame coal. The amount of long-flame coal in the Far East is approximately 90 millions of tons. This type of coal is also widespread in Tungus, Irkutsk, South-Yakut and other basins. There are vast reserves in Karaganda, especially in Jalin coal strip mine. At this stage long-flame coal is the most perspective rank of coal that has high demand.
The mining of this type of coal is done both in the way of coal strip mines and in internal mines. The way of mining depends on how deep the coal lies.
Long-flame coal is a natural resource of the hard coal class. It consists of high molecular weight and has a certain composition.
The specific heat is 5000-7000 Kcal/kg (5800 in average).
The vitrinite reflectance in long-flame coal begins from 0,4% and ends in 0,79%. Long-flame coal is usually of grey-black color. It has average relative density - 1-1,7 g/cm3. It is rather pory and has well defined layering. There may be the diminishing of poriness level during the transition from long-flame coal to bituminous (fat) coal. This leads to the decrease of elasticity and mechanical durability. Due to the high output of volatile components this type of coal can be easily burned. It burns with a long smoky flame and actually this is why it is named so. It is not caked and its ash is not slagging.
So, how is the long-flame coal burned? It is heated under the temperature and the moisture is vapourized. It comes into the chamber pipe in the form of steam. As the temperature rises, the coal begins to coke 
and gives off coke gas. This gas is mixed with the second-hand air that appears when you open coaling door, burns in it and provides the main heat. What is important is that the gas should burn in the area of secondary combustion of the chamber and not in the combustor, because if the coke gas burns together with coal, the latter will overheat and will give away even more coke gas. This will lead to uncontrolled burning process. This is why the burning of coal and the burning of gas should be performed separately. Once heated to the needed level and given away the coke gas, long-flame coal turns to coke. Being burnt, coke produces enough heat for charring another portion of coal. By controlling the air flow we can control the burning process and the heat output. We should also say that long-flame coal is the best fuel for burning chambers and boilers of any construction. It is easily burnt and does not require forced air supply.
Long-flame coal is classified according to the size of its chunks. So there may be ДКО (range coal), ДР (???), ДПК (??? - the most universal and popular kind of coal), ДОМ (long-flame small-nut) and others. The qualities of those kinds are slightly different (within several percents. For example, ДПК has 24,9% of ash, while ДОМ has 28%.
Long-flame coal is the best kind of fuel because it can be easily burnt and does not require forced air supply. In order to begin the burning process only small amount of wood is required and this allows to save a lot. This means that such coal can be easily used in utility sphere. The long-flame coals with small amount of ash may also be the raw material for liquid fuel or chemical products, as well as to get coke and semi-coke. Also long-flame coals are ideal for production of special carbon sorbents and activated coals that are used in pharmacy. However, the most obvious application for such type of coal is heating. For example, the houses in Kemerovo District are heated with the coal from Kuznetsk Basin. And if you remember that sometimes there are -30 degrees of Celsius in winter, you will clearly see the effectiveness of this type of coal for this task.
Characteristics of rank Д coals
