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Master's portal of DonNTU
One of the most important measures for creation and maintenance of the normal conditions providing all the necessary prerequisites for satisfying miners’ health and their vital activity in mines is high quality ventilation; that is providing necessary quantity of air to the working places.
Exploitation of mines is connected with the necessity of the mine workings of different length and cross. For aeration of these workings up to the junctions with the other canals of the ventilation in mine special plants and equipment required.
As a rule the ventilation of the blind pits of not very large length (up to 500 m) under not very extensive gas and heat isolation is not difficult. If the length of the blind pit is more then 500m, so providing the required quantity of air in this workings under the present state of equipment arises serious problems.
Poor ventilation and connected with it health conditions cause the reasonable decrease of labor productivity of miners, as well as slackening speed of driving the workings. As a consequence, tardy preparations of the necessary slope workings, prolongation of the mine building period and time for preparation of the new levels.
At present, the problem of the blind pits ventilation is of great importance not only in Ukraine, but abroad.
The task of the project is to analyze the blind pit ventilation means, to calculate the aeration, to prove this or that ventilation method applied, to work out the steps providing the ventilation of the long blind pits.
The blind pits can be ventilated due to the mine depression or with the help of local ventilation fans (LVF). In some cases instead of fans ejectors are used. The aeration of the blind part of åðó working due to the mine depression, according the Safety Rules, has to be done with the help of ventilation pipes or partitions of length no more than 60m. Because of it, for the ventilation of longer workings LVFs are used.
The three ways of the blind pit ventilation are known (with the help of ventilation pipes and LVFs). They are force, suction and combined method.
By the forced method (pic. 1) a fan (1) is installed in the working with fresh current before the blind pit (2) mouth. To avoid possible air recirculation through the flexible pipeline, the distance taken between the mouth and the fan is no less than 10m. And air feeding by the fan- no more than 70% from its losses in the place of installation of the LVF. The distance taken from the end of the ventilation pipes to the face of the working is no more than 8 (12) m.
By the suction ventilation (pic. 2) a fan (1) is installed on the fresh current after the pit mouth, in the course of aeration current. Fresh air is supplied to the face over the working, but it is sucked by the pipeline (2). Because of it, in the preface part of the working the content of gas und dust occurs more than by the force ventilation method.
Combined method is used in cases, when the two named methods can not provide air to the blind pit.
Estimating the ventilation methods from the point of work safety, ability of providing the necessary atmosphere conditions in the long workings, where the main difficulties are connected with the necessity of keeping normal heat conditions, one should give preference to the force ventilation method, that lets to provide more comfortable work conditions in the preface area. In none gas mines by the works on not very large depth for quick ventilation after explosures, it is advisable to use the combined ventilation.
With the aim of clarifying the ventilation methods and layouts of the airways to the faces, as well as the factors having the influence on the ventilation state and reliability of the local ventilation systems as a whole, the blind pits of the following mines were investigated: “1/3 Novogrodovskaya” (the 4th ventilation drift of the coal-bed L1 of the slope ¹2); the 2nd northern ventilation drift of the coal-seam L1 of the slope ¹2; assembling entry 17 of the southern lava of the coal seam L1 of the slope ¹1), “Rossia”(the 1st southern ventilation drift of the northern slope II of the coal bed step L1; the 2nd southern ventilation drift of the southern slope II of the coal seam L1) and Ukraine”(Slope ¹1 of the coal bed K8 the III step).
Having conducted the analysis, it was stated that the blind pits are ventilated by force ventilation method with the help of LVF of type ÂÌ-6 and ÂÌÝÓ-10 and flexible pipeline 0,8m in diameter.
Unsatisfying aeration state of the blind pits often causes people’s injury and death in these workings as well as in the nearest parts of the mine.
So, in the mine “Ukraine”, in the blind pit 1100m long, where the ventilation was conducted by the Local Ventilation Fan, the aeration pipes were 620m long only and the rest of the working wasn’t ventilated. The samples of the atmosphere in the mine have shown, the quantity of oxygen was 2, 8%. It caused the man’s death.
Poor ventilation in the blind pits is a reason for keeping unsatisfying heat conditions. In most cases the ineffective fans with low efficiency are used for aeration in workings (ÂÌ-6, ÂÌÖ-8 and others). Feeding of the fans is usually high, but discharge of air in the working doesn’t always provide the standard given in the Safety Rules. To control the air inflow to the blind pits the special gear has been worked out.
On the basis of the conducted research concerning the aeration of the blind pits, it has been stated that aerodynamic strength of the pipelines is 1,5-2 times more than standard, and air penetration is 2-3 times more than standard.
The calculation of air expense according to methane (carbon dioxide) isolation can be made as follows.
Extracting the mineral in the blind pits by coal-plough machine, perforator or by boring the coal-seam, as well as driving the shaft according the formula
where Qf.a – air expense, to be provided to the preface area of the blind pit, m3/min; If.a – methane isolation at the preface area, m3/min; C – permissible (according to the Safety Rules) methane concentration in the outgoing airflow out of the working, %; Co – methane concentration in the airflow incoming the blind pit, %.
By the explosive extraction of the mineral in the blind pits it can be defined according the formula
where S-area of the cross section of the working on light, m2; 1f.pl- distance between the ventilation pipeline and the face, m2; Kv.d- vortical diffusion factor; If.a max – maximum methane isolation in the preface area after explosion of coal, m3/min; Cmax- the highest permissible methane concentration in the preface area after explosion of coal, %.
Calculation of air expense for ventilation of the blind pits for gases, occurring after explosion
where Vg-volume of gases after explosion, l; T- time of ventilation after explosion, min; S- average area of cross section in light by variable cross, m2; 1n-length of the blind part of working, m2; Kwf - factor of water filling of the blind pit; Kl.pl-factor of air losses in ventilation pipelines.
Calculation of air expense for quantity of people
where Np.f.a.-the highest number of people, working in the preface area of the blind pit, people.
Air expense for minimal speed in the working
where Vn min – minimal permissible air speed in the blind pit, m/s.
Air expense for minimal speed in the preface area up to the temperature
where Vf.min-minimal permissible air speed in the preface area up to the temperature, m/s.
While applying the combined flexible pipeline the factor of the air losses can be defined by the formula
where Kl.pl1- the factor of air losses for the last part of the pipeline without polyethylene hose; Kl.pl2- the factor of air losses for the part of pipeline with polyethylene hose.
Aerodynamic resistance of the flexible combined ventilation pipeline can be defined by the formula
where rpl.r - specific aerodynamic resistance of the flexible ventilation pipeline without air losses, kµ/m; n1 and n2-number of 90° and 45° turns; 1pl1- length of the last part of the pipeline without polyethylene hose, m; dpl1- diameter of the last part of the pipeline without polyethylene hose, m; rpl.ê-aerodynamic resistance 1m of the pipeline with the polyethylene hose; 1pl2- length of the part of the pipeline with polyethylene hose,m; dpl2- diameter of the part of the pipeline with polyethylene hose, m.
Fan feeding, which works for the flexible or rigid pipeline
Fan pressure that works for the flexible ventilation pipeline or for the combined pipeline
Air expense at the face will make
Air expense on the place of the LVF has to be equal
During the research it is planned to display the peculiarities of the long blind workings ventilation, to work out the steps aiming to improve the ventilation, as well as to establish the possible patterns.
At present the work for magister degree is being developed. After December 2009 the further information one can receive from the teacher.
 Picture - 1. The force ventilation of the blind pits (10 frames, 5 repetitions, 41,8 Êb) |  Picture - 2. Suction ventilation of the blind pits. (10 frames, 5 repetitions, 43,8 Êb) |
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