Analytical W a
There are four types of humidity:
External (superficial),
Capillary,
Colloidal,
Crystal hydrate.
Humidity of the working fuel mass, %:
W ° = W ext + W cap + W coll + W hydr.
External– moisture that is retained on the surface of fuel particles. It reaches the surface of the pieces from groundwater and precipitation. Depends on the wettability of the surface. It increases with decreasing particle size, amounting to W ext = 3-5%.
Capillary– moisture contained in capillaries (thin channels and cavities of pieces). This is the main component of the moisture content of solid fuels, decreasing with increasing geological age. At the same time, due to a decrease in particle porosity (capillary volume), capillary humidity decreases. For peat W cap = 35%, for coal - W cap< 10%.
Colloidal– moisture, which in the form of tiny colloidal particles (10 - 10 m) is adsorbed by the organic mass of the fuel. Depends on the chemical structure and composition of the fuel. With increasing geological age (with increasing degree of carbonization), colloidal moisture decreases, since the fuel loses its ability to retain colloidal particles due to their aging.
Crystal hydrate– moisture included in the crystalline structure of the fuel and associated with its mineral part. It includes:
Silicates Al 2 O 3 ×2SiO 2 ×2H 2 O; Fe 2 O 3 ×2SiO 2 ×H 2 O,
Sulfates CaSO 4 × 2H 2 O; MgSO 4 × 2H 2 O.
Features of hydrated moisture:
a) very low content (< 0,1%);
b) does not depend on storage conditions;
c) increases with increasing ash content of the fuel;
d) when dried up to 110º C, it is stored in the fuel;
e) is excluded only at t > 600° C as a result of the destruction of crystalline hydrates.
The moisture content of solid fuel is estimated by the loss in mass of the sample (1 ± 0.1 g) kept for 30-60 minutes in a drying cabinet at 102 - 105 ° C.
Negative influence of fuel moisture on the operation of a steam boiler:
2. ignites poorly and burns slowly;
3. combustion efficiency decreases;
4. heat consumption for drying increases;
5. the flowability of particles is reduced;
6. freezing of pieces in stacks occurs;
7. The dust preparation systems are subject to corrosion.
Ash content of fuel is a characteristic that determines the content of mineral impurities in fuel.
Mineral impurities are inorganic (non-flammable) compounds contained in fuel for combustion:
1. Clay (aluminosilicates) Al 2 O 3 × 2SiO 2 × 2H 2 O;
2. Silica 2SiO 2 (main part of sand);
3. Sulfates CaSO 4, MgSO 4, FeSO 4;
4. Carbonates CaCO 3, MgCO 3, FeCO 3;
5. Iron oxides FeO, Fe 2 O 3, Fe 3 O 4;
6. Sulfides FeS 2, CaS 2.
Based on their origin, mineral impurities are divided into:
Primary – contained in the original plants from which fuel was formed;
Secondary - got into the fuel from the outside (through cracks in layers with soil water);
Tertiary - got into the fuel during production, transportation, storage.
With an increase in the geological age of the fuel and an increase in the likelihood of dilution of organic matter with mineral impurities, the ash content of the fuel increases.
Approximate ash composition:
SiO 2 = 30 – 60%; Al 2 O 3 = 10 – 40%; Fe 2 O 3 = 5 – 20%;
CaO = 5 – 20%; K 2 O + Na 2 O + P 2 O 5 = 1 – 5%.
The non-combustible residues formed in the furnace are divided into slag and ash.
Temperature characteristics of ash determined experimentally gradual heating of the ash sample, formed in the form of a triangular pyramid. When heated in an electric furnace, the temperatures corresponding to three degrees of deformation of the sample are recorded.
t 1 – temperature of the beginning of deformation (melting of the top) at 1000 - 1200º C,
t 2 – softening temperature (1100 - 1400º C),
t 3 – temperature of the liquid-melting state, corresponding to the beginning of spreading over the surface at 1200 - 1500º C,
t 0 is the temperature of the true liquid state, at which there is a normal flow of molten slag along the vertical wall (t 0 = t 3 + 50 - 150º C).
t 3< 1350º C – легкоплавкая зола,
If t 3 = 1350 -1450º C – ash of medium fusibility,
t 3 > 1450º C – refractory ash.
In furnaces with liquid slag removal, in the case of reduced boiler load, even a short decrease in temperature in the lower part of the flame t< t 3 может привести к застыванию шлака и ухудшению его удаления. При этом целесообразно сжигание углей, имеющих длинные шлаки.
Temperature characteristics t 1, t 2, t 3 need to be known:
To select the correct combustion mode so that the ash particles are in solid form and do not stick to the festoon and superheater pipes).
Selecting a slag removal system (removal of slag from the furnace in solid or liquid form).
Negative influence of fuel ash content on the operation of a steam boiler:
1. fuel consumption increases;
2. combustion efficiency decreases;
3. heating surfaces become dirty, which impairs heat transfer and increases heat loss with flue gases;
4. pipes of heating surfaces wear out due to ash particles;
5. the load on the equipment of slag and ash removal systems increases.
ASH content (a. ash content; n. Aschegehalt, Aschehaltigkeit; f. teneur en cendres; i. contentido de cenizas) - the ratio of the mass of non-combustible residue (Ash) obtained after burning the combustible part of the fuel to the mass of the original fuel. It is designated by the symbol A (Latin) and is expressed as a percentage. For practical purposes, the ash content value determined from the analytical sample (Aa) is usually converted to the cyxoe Ad or operating Ar state of the fuel. For all types solid fuels ash content is one of the main standardized indicators of characterization and assessment of their quality, used in the development technical specifications, consumer standards, conditions and when counting inventories. An increase in ash content reduces the thermal effect of fuel combustion, increases the cost (as ballast) of their transportation, and negatively affects the technology of processing processes and the quality of the resulting products (, etc.).
Ash-forming components, chemically associated with the organic matter of coals or dispersed dispersed in it (internal ash), as well as those formed due to inorganic inclusions contained in coals and clogging (during mining) host rocks (external ash), have different volatility during thermal processing and undergo unequal changes. Therefore, the conditions for determining ash content and chemical composition ash is standardized. The ash content of coals due to internal ash (the so-called mother ash) usually ranges from 1-15%, but with a finely dispersed distribution of inorganic material it reaches tens of percent with a gradual transition of coals into carbonaceous rocks (with Ad 60%). During conventional coal enrichment, this ash is not removed. Ash content due to external ash depends on the internal structure of coal seams and their technology; the overwhelming majority of mineral impurities forming external ash can be removed with.
Ash content is standardized by state standards. The highest permissible limit of ash content of raw coals, screenings, pieces, middling products and enrichment sludge is established for pulverized combustion conditions (Ad 45%, Ekibastuz coals - 53%). For layer combustion, coals with Ad no more than 37.5% are used, for coking - unenriched caking coals and enrichment concentrates with Ad up to 10.6% (from coal deposits of the Caucasus - up to 13.8%). The maximum ash content of coals for coking sent for enrichment for various basins is 25-36%. The ash content of oil shale varies widely (Ad 48-72%). For conditions of consumption of oil shale, ash content is not standardized; The main indicator of quality is the specific heat of combustion, the value of which is reflected in the ash content. The ash content of peat depends on the geological conditions of its formation and is different for different types and types of peat. Based on ash content, low-ash (less than 5%), medium-ash (5-10%) and high-ash (more than 10%) peats are distinguished.
The ash content of coals and oil shale is determined by ashing a sample of the test fuel in a muffle furnace and calcining the ash residue at a temperature of 800-830°C, for accelerated ashing of oil shale - at a temperature of 850-875°C (GOST 11022-75). The ash content of coals is also determined by the X-ray method - according to the parameters of ionizing radiation after interaction with coal (GOST 11055-78).
Introduction to the work
Relevance of the topic. Maintaining economically feasible relationships between the quality indicators of common coal and the requirements of consumers for them is one of the key technical tasks of modern mechanized coal mining. Among the main quality indicators that have a significant impact on production costs and the competitiveness of coal products is the ash content of mined coal. rock mass. An increase in the ash content of common coal leads to an increase in the costs of enrichment and transportation of the rock mass.
The main direction in overcoming differences in the content of coal mined and shipped to consumers is to improve the methods of their enrichment using mechanical rock sampling or processing plants.
The problem of improving the quality of mined coal and lowering production costs is relevant for the mines of JSC Vorkutaugol, mining seams in difficult mining and geological conditions, characterized by large depths mining operations, the presence of zones with false and unstable ditches, significant areas with an ore-falling main roof, small-scale injunctive and plicative faults.
Almost all Vorkuta mines, including promising ones (Vorkutinskaya, Zapolyarnaya, Severnaya and Komsomolskaya), operate according to temporary technological schemes with the joint transportation of coal and rock from the clonal fields of the second and third stages. consumed by promising mines, according to statistical data, is 37-48%, which is 2.5-3.0 times higher than the red-layer ash content of the developed seams and 1.7-2.3 times higher than the ash content of coal products shipped to consumers.
The costs of enriching 1 ton of rock mass in the conditions of Vorkuta reach 30 thousand rubles in 1997 prices. The costs of underground transport due to clogging of coal increase by 40-48%.
The significant ash content of mined coal is one of the main reasons for the increase in production costs and the decrease in the competitiveness of the mines of Vorkutaugol OJSC in the coal product market.
Purpose of the work. Rationale technological schemes coal mines, ensuring a reduction in the ash content of the rock mass discharged from the mine.
Research objectives:
Study of basic natural factors and conditions
predetermining clogging of mined coals during development
reserves of the bottom part of the trough at the Vorkutskog mines
deposits;
study of the influence of technological schemes and parameters of mining areas on coal quality indicators;
analysis of known methods for reducing the ash content of coal at longwall faces and the technological network of mines and assessment of the feasibility of their use in the conditions of the mines OA ("Vorkutaugol";
development of recommendations and proposals for technical improvement of standard technological modules and links in the underground complex of coal mines, "ensuring reduction: averaging of the ash content of the rock mass discharged from the mine.
The main idea of the work. The parameters of the technological scheme of coal mines must be determined taking into account the regularity: the formation of ash content of the rock mass in the working face of various parts of the underground transport network.
Research methods. When conducting the research, a comprehensive research method was used, including; analysis and synthesis of data on the influence of mining-geological and mining-technical factors on coal quality indicators; mine research of the dynamics of cargo flows at various stages and formation; mathematical modeling of mining engineering
situations. Data from mining studies of random processes were processed using methods of mathematical statistics and probability theory. Protected provisions:
1. By improving the actually existing
technological schemes, the ash content of the rock mass produced at
surface of the promising mines of Vorkutaugol OJSC, may
be reduced by 25-30%, including: due to increased
efficiency of roof management in longwalls by 10-12%; due to
modernization of underground transport networks of mines by 15-18%.
[the lower limits of the reduction in ash content of the rock mass are determined
oleal participation of formations in production and formation ash content,
average statistical values for the Moschny formations,
Roynoy and Fourth are respectively 13-14%, 12-18% and
0-22%.
2. Fundamental requirement during development
measures to improve the quality of mined coal should
read the refusal to cut false roof rocks with clearing
combines. The task of maintaining a false roof is necessary
eat based on technical and organizational measures,
key to leaving temporary protective coal packs at the roof
of the developed formation with the subsequent collapse of these packs on
important conveyor after they have performed their functions.
3. On the operating horizons of mines, characterized by
the ability to quickly change previously accepted
spatial planning solutions for preparation and
formation processing, a significant reduction in the ash content of the extracted
can be achieved by modernizing transport
of these mines on the basis of temporary and stationary storage
bins providing selective portion separation of coal
rocks coming from longwalls, tunneling faces and places of repair and restoration work.
The reliability of scientific statements, conclusions and recommendations is ensured by a large volume of mine research conducted for a wide range of mining
geological and mining conditions; satisfactory convergence of actual and predicted indicators of the ash content of the rock mass in various parts of the mine's transport network by approbation of the main research results under production conditions.
The scientific novelty of the work lies in the following:
The nature and degree of influence of geological and technical factors on the lower limits of reducing the ash content of the rock mass in various parts of the mine's technological scheme have been established.
A physical model of the process of formation of subsequent controlled spalling of a safety coal pack on the longwall conveyor, left by the depot for preventing rock collapses of the “false” roof in the excavation area, is proposed. layer.
Practical significance of the work:
The principles of the layout of UNDERGROUND networks are formulated
transport based on temporary and stationary bunkers!
ensuring a reduction in the ash content of the rock mass;
an effective modification of the underground transport scheme of the Severnaya mine was proposed and justified in order to adapt it to selective portioned separate transportation of coal and rock;
the advantage of technological schemes has been proven for cleaning work with retention or self-collapse of the false roof compared to those used in mines OJSC"Vorkutaugol using the technology of joint excavation of false roof rocks by a combine miner;
The average numerical values of the increment in the ash content of the rock mass were established in various parts of the technological scheme of the mine, differentiated by sources of supply.
Implementation of research results. Designed by
conducting research and practical recommendations
used in the modernization of technological schemes of the mines of JSC "Vorkutaugol", as well as as a methodological basis for
modeling of underground cargo flows in conditions of prepared horizons. The established dependencies are widely used in the educational process in the training of erm specialists.
Approbation of work. The main results of the research were presented and received a positive assessment at technical events at Vorkutaugol OJSC, at the annual conferences of young scientists “Russian Mineral Resources and Their Development”)
