CARBOFOSSILS - solid combustible minerals; a product of transformation
of plants. The basic components: carbonic organic substance, mineral admixtures
and moisture. They occur as usual in the form of sedimentary rock layers; are
subdivided into lignite, black coal and anthracite. Carbofossils are used mainly
in power engineering, for producing of metallurgical coke and in the chemical
industry. The basic technical characteristics: ash value, moisture and sulfur
content, yield of volatile substances. The global reserves are about 3700 billion
t. Kuzbass is the main base of Russia’s solid fuel.
Technical analysis of coals All kinds of solid combustible minerals
combine two components: organic substance and mineral component, which were earlier
considered as ballast but now more often as a source of a valuable mineral, in
particular - of rare and dispersed elements. To estimate capabilities and modes
of processing combustible minerals they apply technical analysis allowing one
to determine trends of using them as a power and chemical raw material. Technical
analysis is considered as definition of parameters stipulated by coal quality
specifications. The technical analysis usually combines methods intended
for defining in carbons and combustible slates of ash value, content of moisture,
sulfur and phosphorus, yield of volatile substances, combustion heat, caking capacity
and some other characteristics of quality and technological properties. Complete
technical analysis shall be carried out not always; frequently it is enough to
carry out a reduced technical analysis consisting of defining the moisture and
ash value, and yield of volatile substances.  Moisture
Due to the fact that molecules of water can be bound up with the carbon surface
by various nature forces (absorption on the surface and in pores, hydrating of
macromolecule polar groups, making part of the crystalline hydrate structure of
the mineral portion) at different ways of educing moisture from coal, there are
obtained differing sizes of its dehydrated mass and, accordingly, differing values
of moisture. Mass of coal with moisture content, with which it is shipped
to the consumer is to be referred to as the working weight of coal; and the moisture,
which is educed therefrom during drying of the sample to a constant weight at
105°Ñ , is to be referred to as total moisture of the coal working mass.
The moisture content in a combustible mineral is characterized by its humidity.
This value is to be expressed by the ratio of weight educed at temperature of
dehydration (eliminating moisture) versus the sample mass being analyzed. The
moisture is to be designated by letter W (Wasser). Moisture of coal shall
reduce the useful weight during transportation, a great volume of heat is used
for its evaporation when burning fuel; besides damp coal gets frozen in winter.
The common moisture content varies depending on the carbonization extent
of the mineral in the following line. Peat > Lignite > Anthracite
> Black coal  Ash
content Carbofossils contain a significant amount (2-50%) of
mineral substances, which after burning form ash. The ash residue is formed after
calcinating coal in a muffle kiln open firepot at the temperature of 850 ± 25
° C. 95-97% of the ash consist of the Al, Fe, Ca, Mg, Na, Si, K oxides. The remaining
are the P, Mn, Ba, Ti, Sb compounds of both rare and dispersed elements.
The ash content is to be designated by letter À d (Asche) and expressed in the
% mass. The cumulative moisture content is referred to as ballast. The content
of mineral substances proper is designated by letter Ì . It is determined with
the help of physical and physicochemical methods (for example, microscopic, fluoroscopic,
radioisotope). Volatile substances Volatile substances
are vaporous and gaseous products educed during decomposition of a solid combustible
mineral organic substance at heating under standard conditions. The volatile substances
yield is to be designated by symbol V (volat.), the analytical sample yield -
Va, dry substance - Vd, dry and ash-free substance - Vdaf.
This characteristic is important for estimating the thermal stability of structures
making the coal organic mass. The volatile substances yield during calcinating
served as a basis for one of carbon classifications per grades. Heat
of combustion Heat of combustion is a basic power parameter of
coal. It is determined experimentally by burning a carbon batch in a bomb calorimeter
or by computation using the element analysis data. They distinguish maximum
heat of combustion (Qs) as the amount of heat educed during complete
combustion of a coal mass unit in a bomb calorimeter in oxygen medium, and the
lowest specific heat of the combustion (Qi) as the maximum heat of
combustion minus heat of evaporation of water educed and formed of coal during
combustion. The maximum heat of combustion shall be frequently determined for
the ash-free condition of coal (Qsaf) and the lowest – for
the working condition (QQir). D.I. Mendeleev has suggested
a formula for computing the maximum heat of combustion on the element analysis
data (kcal/kg): Qsaf=81°Ñ+300Í-26(Î-S) where
Ñ , Í , Î , S – a mass share of elements in the SCM (solid combustible mineral
substance), %. The maximum heat of combustion of the basic solid fuels:
Peat |
5500-5700 kcal/kg | 23-24 Mjoule/kg
| Lignite |
6100-7700 kcal/kg | 26-32 Mjoule/kg |
Black coal |
7700-8800 kcal/kg | 32-37 Mjoule/kg
| Anthracite |
8000-8500 kcal/kg | 34-36 Mjoule/kg
| Caking capacity One of the
most important (if not paramount) direction of using the black coal is its processing
into a metallurgical coke – a solid product of high-temperature (> 900°C) decomposition
of coal without air access, which has certain properties. Not all coals are capable
of baking, i.e. transforming during heating without the air access into a plastic
condition with a subsequent generation of the bound non-volatile residue. If this
baked residue meets the requirements set to the metallurgical coke, they refer
to the coking ability of coal. Thus, the coking ability is a caking capacity but
the first notion is narrower. Coals of the G, Zh, K and OS grades can bake but
the metallurgical coke can be produced only of the K grade coals, which are closer
to them by its properties. SCM element analysis
As was already mentioned the organic weight of all SCM kinds consists of Ñ , Í
, Î , S and N. Their cumulative amount exceeds 99 % mass taking into account an
organic substance of any coal and peat. Carbon and hydrogen content
Carbon and hydrogen are to be determined per yield of ÑÎ2 and Í2Î
when burning a coal batch in a current of oxygen. These oxides are trapped in
absorption vessels filled with solutions of KOH and Í2SO4
accordingly. These latter are weighed prior to and after burning of the batch,
and the C and H content of a sample is computed by the mass difference usually
in the % mass. It should be noted that in the process the results can be distorted
due to absorption of water and carbonic gas of non-organic origin and generated
owing to thermal decomposition of mineral components. Nitrogen
content Content of nitrogen in coals is insignificant usually
not exceeding 1%, occasionally amounting to 3-4%. Sulfur content
As a whole, sulfur is more widespread in coals. Its content is from percent fractions
up to 10-12%. They distinguish sulphate (SSO4), pyrite (Sp)
and organic sulfur (So), their cumulative content is referred to as
the total sulfur (St). The content of sulfur established per the element
analysis data, is an important characteristic, which determines special requirements
for processing and usage of the raw material remarkable for its high concentration.
The volatile sulfur-bearing products educed such as Í2S and SO2,
are extremely hazardous when getting in the environment, and during designing
production one should take into account their high corrosivity. 
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