Doctor of technical sciences, professor Hakimjanov T.E.,
Candidate of technical sciences, associate professor
Abdugalieva G.Yu.
the
method of reduction of gas release from longwall open area into breakage face
Open area is the main source of methane emission. The reduction of
intensity of methane emission from the open area will ensure the reduction of
mining combine stoppages due to the exceeding of maximum permissible methane
concentration, will ensure the increase of coal mining machinery productivity
due to the increase of combine’s supply rate, will reduce the cost of the coal
and increase the load on the longwall.
The
modern technology of underground coal mining uses various methods of reduction
of methane emissions from the open area. One of the rational technical solution
is the removal of highly concentrated methane and air mixture from the open
area with the methods of degassing, i.e. by means of drilling of degassing
wells in the places of the highest concentration (to the unloading zones of
soil and roof pallets) from underground mines or from the surface. The
experience shows that drilling of degassing wells from the operating
excavations to the open area of longwall ahead of the line of the breakage face
is not effective, since their life time is short due to frequent cutting of
wells under the action of abutment pressure ahead of the line of the breakage
face.
Coal pallet
drilling of degassing wells (in soil or roof) from the excavations supported
behind the longwall into the unloaded zones ensures quite effective degassing
(up to 30-40%) of open area. However this method is suitable only for
direct-flow ventilation charts and requires thorough sealing of well head to
the depth of 8-10 m, which is difficult to implement in narrow conditions of
excavations supported behind the breakage face.
There
are methods of degassing of the open area, which are implemented by means of
pumping out of gas and air mixture through the pipes installed in the open
area. These methods require the production of expensive and labor-intensive
operations for well drilling and pipeline installation as well as for digging
and bridging of special excavations. Much volume of fresh air is pumped into
the pipelines and wells; this leads to reduction of gas mixture concentration
down to explosive level and efficiency reduction of the methods.
The most popular
degassing of open area at Karaganda coal basin is by means of drilling of wells
from the surface. The efficiency of this method reaches 70% at the
concentration of the extracted methane up to 90%. However mismatch of location
and structure of vertical wells from the surface and certain mining and
geological conditions reduces the efficiency of their operation. Quite often
there are cases of crippling of wells or stop of methane release at some
distance from the breakage face. In the period when degassing well is in front
of the breakage face, it is under the abutment pressure. To much extent the
efficiency of degassing well depends on the extent to which the particularities
of worked rock mass movement and geomechanical processes that take place in the
worked strata at various mining and geological conditions are taken into
account at its installation.
To
reduce the gas emission of the longwall and to increase the productivity of
coal mining equipment, to increase the load on the breakage face, to improve
the labor conditions and to enhance the safety of operations by means of
conservation of methane and other harmful gases in the open area, the method of
gas emission control from the open area is suggested that is based on the fact
that air and mechanical foam is charged along the whole length of the longwall
along the movement toward the depth of the breakage face [1]. Air and
mechanical foam fills the cavities moisturizing the surface of coal and rock
remnants and forms films in the structure and in empty area, isolates the open
area and thus prevents the spread of the drainage gas mixture.
At the
system of development with long pillars with complete failure of roof and with
the application of mechanized complex with self-advancing support, the tank
with foam-producing liquid is placed at the ventilation heading of the
excavation site, for instance 3% water solution of foam former (PÎ-1). Compressed air needed for
producing of pressure of liquid and foam formation is supplied from the main
pipe of compressed air.
Compressed
air and foam forming liquid are supplied along the whole length of longwall and
foam pillars via flexible pipelines or hoses suspended to the upper part of
support near the open area so that not to hinder free movement of support
section. Foam pillars are installed by means of hanging at the mechanized
support in equal intervals (5-10 m) along the length of the breakage face.
Nozzles of foam pillars are directed between the support sections or in
specially established holes in the support to the open area. Foam pillars are
switched on when the combiner has unloaded another line of coal simultaneously
with the self-advancing support. The foam fills cavities formed in the open
area, moisturizes coal and rock remnants and isolates the open area from the
part of longwall near the breakage face.
Foam is
filled until complete filling of all cavities behind the support. The time of
filling depends on characteristics of foam (its durability, repetition factor)
and breakage face (thickness of strata, hade etc). Along with the foam
charging, technological operations for coal excavation are carried out:
movement of support, cleanup of longwall, movement of conveyor, unloading of
the next line of coal by combiner. Then the cycle is repeated.
The
advantages of this method over analogous ones are no need in maintenance of
excavations and packs in open area, if this is not required by the system of
development and ventilation chart; simplicity and low labor-intensity of
operations and activities; low cost of the applied foam forming solution;
opportunity to use it at various systems of mining and mechanization; no
preparatory operations; no need to stop coal mining from the longwall to carry
out operations related to the isolation of the open area; there is an
opportunity to automate the processes.
It is
worthy to note the wide range of conditions under which the use of the
described method is possible. Along with its application in various systems of
mining, it implies large amount of options of mechanization of second working.
Mining and geological conditions of strata occurrence such as thickness and
hade also affect the speed of advancing of the breakage face and therefore the
parameters of foam charging. These parameters can be varied to much extent by
means of changing the durability and repetition factor of the foam (i.e. by
changing the applied foam formation or its concentration), as well as the
intensity of foam supply. In such way, this method can be used in wide range of
mining and geological conditions.
The
method can make use of various foam pillars, foam generators, foam forming
liquids and solutions produced by the manufacture and used in the economy.
An
example of foam generating plants for production of large amount of foam of
high repetition factor in water, used in this method, can be the foam
generating plant PGU with the capacity of up to 100 m3/min of foam
developed by UNIL VGSCh. The foam of high repetition factor (400-600) is formed
at joint passage through the foam pillar of foam forming solution and air. With
the use of foam generator PGU, it is possible to fill with foam top-down the
vertical and inclined working, the drift can be filled with foam from one point
at accompanying ventilation to the length of 400 m. As a foam former the
composition PO-1 is used that contains 8 parties by weight of steamed kerosene
contacts, 3,5 parties by weight of 28% glue solution and 1 party by weight of
crude alcohol.
The
suggested method is rational for use in mines and ore mines, the atmosphere of
which contains poisonous explosive and radioactive admixtures, mainly in
methane category and super-category mines. This method of gas emission control
from the open area into the longwall will ensure the enhancement of mining
safety in the longwall and the load on the breakage face due to the reduction
of downtime of mining equipment due to the exceeding of norms of gas content in
the longwall.
Literature
1 Hakimjanov T.E.
Gas emission into the breakage faces of coal mines. – Alma-Ata: Nauka, 1986. –
144 p.