Establishing Rational Fan Operating Modes for the Forced-Exhaust Ventilation Method in Mines of the Southern Kuzbass
Abstract Generated abstract
This paper examines how to select rational fan operating regimes for the pressure suction method of ventilating coal mines in the Southern Kuzbass, with particular attention to reducing effective pressure, air leakage, and endogenous fire hazards. Using an electrical model of a mine ventilation network, the study compares alternative settings of forcing and exhaust fans and tests the proposed use of additional return airway resistances to create zero pressure zones. The results indicate that such resistances cannot reliably establish zero pressure in all working sections, while a regime in which the forcing fan supplies air to the section with the smallest depression loss gives lower acting pressures in worked areas, improves exhaust fan stability, and reduces leakage risks. The paper also recommends preliminary model testing of fan regimes and periodic depression surveys to monitor pressure conditions in mines.
Full Text
ESTABLISHING RATIONAL OPERATING MODES OF FANS UNDER THE PRESSURE–SUCTION METHOD OF VENTILATING MINES OF THE SOUTHERN KUZBASS
A. M. PRIMYSKII
(Presented by the scientific seminar of the Department of Development of Bedded Deposits, Development of Ore Deposits, Mine Construction, Safety Engineering, and Mine Ventilation)
The pressure–suction method of mine ventilation has recently been finding ever wider application in Kuzbass, especially in the Prokop'evsk–Kiselevsk district, where at present 42% of the mines are ventilated by this method. The considerable spread of the pressure–suction method of ventilation is explained by a number of its advantages in comparison with other methods. One of the principal merits of this method of ventilation is the reduction of the danger of endogenous fires arising as a result of a decrease in the magnitude of the effective pressure and, consequently, in the magnitude of air losses. The effective pressure is understood to mean the difference in air pressures between the surface and the workings of the mine [1]. A reduction in the magnitude of the effective pressure, of course, does not completely eliminate air losses to the surface through cracks and subsidence, but it is entirely possible to regulate the magnitude and distribution of the total air losses under the pressure–suction method by properly selecting the operating modes of the pressure and suction fans with respect to the magnitude of the depressions developed by them.
Rational operating modes of fans should be considered to be those modes under which the best techno-economic indicators of mine ventilation are achieved. The principal such indicators are: 1) the magnitude of air losses, depending on the magnitude of the effective pressure, especially within the limits of the extraction sections; 2) the stability of operation of the suction fans; 3) the expenditure of energy by the fans. The value of the indicators, other conditions being equal, depends on the ratio of the compression of the pressure fan and the depressions of the suction fans.
Under the pressure–suction method of ventilation, the compression of the pressure fan at a certain point decreases to zero and then passes into depression. The effective pressure at this point is equal to zero, and this point will henceforth be called the “zero” point, while the zone adjoining it will be called the zone of “zero” pressure.
To establish rational operating modes for fans, it is sufficient to find the most advantageous location of the “zero” point, which depends on the magnitude of the depressions developed by the forcing and exhaust fans. To establish the most advantageous location of the “zero,” it is necessary to analyze various possible locations of the “zero” point.
It should be noted that at Kuzbassgiproshakht (KGPS), when preparing the ventilation reconstruction design for the Krasnogorskaya mine, an analysis of ventilation systems was carried out as applied to the conditions of this mine. In the same analysis an attempt is made to establish rational operating modes for the fans. The conclusions drawn in the design at first glance appear correct and technically feasible, despite a number of difficulties.
These conclusions, in the part concerning fan operating modes, consist essentially of the following.
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The operating modes of the fans under the forcing-exhaust method of mine ventilation must be established so that the forcing fan supplies air to the most remote, difficult-to-ventilate section, i.e., to the section for which the loss of depression is greatest.
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The compression arising thereby in other sections, and impermissible under the Safety Rules, is recommended to be absorbed by means of additional “windows” resistances installed on the return airways of the sections.
We carried out an experimental study of the forcing-exhaust method of ventilation on an electrical model for calculating mine ventilation networks in the “laboratory of mine ventilation and dust control in mines” of the Institute of Mining, Academy of Sciences of the USSR. Various variants of fan operating modes were analyzed; the possibility of establishing zones of “zero” pressure in all development sections by means of “windows” on the return airways was investigated, as was the possibility of regulating the location of the “zero” pressure zone and other questions.
Fig. 1. Mine ventilation diagram.
On the electrical model the mine ventilation scheme shown in Fig. 1 was assembled. The required air distribution in \(m^3/sec\):
\[ Q_{\mathrm{total}} = 72.8;\quad Q_{b-E} = 10.9;\quad Q_{5-D} = 10.9;\quad Q_{4-Zh} = 9.2;\quad Q_{10-V} = 10.9; \]
\[ Q_{10-G} = 10.9;\quad Q_{13-A} = 12.7;\quad Q_{13-B} = 7.3. \]
On the basis of the initial data, the following fans were selected: No. 1—OV—2.4, \(n = 750\), \(\Theta = 25^\circ\); No. 2—OV—1.8, \(n = 750\), \(\Theta = 25^\circ\); No. 3—OV—1.8, \(n = 75\), \(\Theta = 20^\circ\); No. 4—OV—1.4, \(n = 1000\), \(\Theta = 30^\circ\).
After determining the parameters of the current sources modeling the fans, and assembling the electrical circuit of the ventilation network
(Fig. 2) the parameters of the current sources were measured when they were connected jointly to the network, as well as the distribution of currents and potentials at different points of the network relative to point “a.” The parameters of the current sources and the parameters of the corresponding fans are given in Table 1.
Fig. 2. Electrical diagram of the mine ventilation network.
Fig. 3. Characteristics of the fans and current sources modeling the fans.
Table 1
| Current-source parameters | Current-source parameters | Current-source parameters | Fan parameters | Fan parameters | Fan parameters |
|---|---|---|---|---|---|
| No. of sources | $I$, mA | $V$, V | No. of fans | $Q$, m$^3$/s | $h$, mm water column |
| 1 | 7.67 | 38.2 | 1 | 76.7 | 76.4 |
| 2 | 3.16 | 23 | 2 | 31.6 | 46 |
| 3 | 2.3 | 34.3 | 3 | 23.0 | 68.6 |
| 4 | 2.18 | 37.3 | 4 | 21.8 | 74.6 |
Note. The adopted modeling scales are: $1\ \text{V} = 2\ \text{mm water column}$; $1\ \text{mA} = 10\ \text{m}^3/\text{s}$.
Figure 3 shows the characteristics of the selected fans and the characteristics of the current sources (straight lines) modeling the fans. As is evident from Table 1 and Fig. 3, the modeling of the fans was carried out satisfactorily, and their capacities provide the required quantities of air.
Having switched on all the current sources, we establish the zone of “zero” potential (“zero” pressure) at points V and G, increasing the emf of source No. 1 with the same internal resistance. With a “zero” effective pressure at points V and G, the values of the effective pressures at the other points are as follows (in mm water column): $h_{\text{e.E}}=+33.6$; $h_{\text{e.D}}=-33.4$; $h_{\text{e.Zh}}=+38.8$; $h_{\text{e.A}}=-4.0$; $h_{\text{e.B}}=-1.0$.
To avoid compression in seams D, E, Zh, an additional resistance—a “window,” $R_{\text{window}}=0.029\ k\mu$—was placed in section 3–4.
After the “window” was installed, the operating regimes of the fans when switched on jointly were: No. 1, $Q=86.8\ \text{m}^3/\text{s}$, $h=158.8\ \text{mm water column}$; No. 2, $Q=34.4\ \text{m}^3/\text{s}$, $h=26.0\ \text{mm water column}$; No. 3, $Q=27.6\ \text{m}^3/\text{s}$, $h=36.4\ \text{mm water column}$; No. 4, $Q=24.4\ \text{m}^3/\text{s}$, $h=39.8\ \text{mm water column}$.
The distribution of air and the effective pressures at certain points after installation of the “window” are given in Table 2.
As is evident from Table 2, after introducing additional resistance on section 3–4, compression in seams D, E, and Zh only decreased and appeared in seams V, G, and B. By installing a larger additional resistance it is possible to avoid compression completely in seams D, E, and Zh, but in this case compression in seams B, V, and G will increase. This can be explained as follows. We placed the “window” in the zone of action of the forcing fan, as a result of which its compression increased, while the quantity of supplied air decreased somewhat. The distribution of air between the wings also changed: less air went to the right wing, to fan No. 2, since the resistance of the right wing increased; somewhat more went to the left wing than before the resistance was installed; as a result, the depression of fan No. 2 increased, while the depressions of fans No. 3 and No. 4 decreased. For these reasons there was a reduction of compression on sections of the right wing and an increase in absolute pressure (compression appeared) on sections of the left wing.
Table 2
| Section No. | Quantity of air, m³/sec | Point No. | Acting head, mm water column |
|---|---|---|---|
| 1–2 | 86.6 | E | +13.0 |
| 5–E | 11.9 | D | +12.4 |
| 5–D | 12.0 | Zh | +17.0 |
| 4–Zh | 10.5 | V | −7.4 |
| 10–V | 13.8 | G | −7.2 |
| 10–G | 13.8 | A | +3.0 |
| 13–A | 15.5 | B | +6.2 |
| 13–B | 8.5 |
Thus, with the aid of “windows,” even under laboratory conditions it is impossible to achieve the establishment of zero-pressure zones in all working sections, and, consequently, the conclusions of KGPTs cited above are untenable.
Therefore we recommend setting, for the forcing fan, such an operating regime under which forcing would be carried out up to the section for which the loss of depression has the smallest value. In this case all other sections will be in the depression zone.
For the conditions of the example given above, we analyzed the following variants of operating regimes of the previously selected fans.
I. Forcing extends approximately to point 2 (Fig. 1).
II. Forcing up to the section along seam Zh.
III. The forcing fan develops a compression whose magnitude is intermediate between variants I and II.
For each of the variants the setting angle of the blades of only the forcing fan was changed (variant I—$\theta = 23^\circ$, variant II—$\theta = 26^\circ$, variant III—$\theta = 25^\circ$); for the exhausting fans, the blade setting angle and the number of revolutions of the wheel were not changed. Table 3 gives the parameters of the fans during their joint operation for the three variants of regimes.
The distribution of air and acting heads for the named variants is given in Table 4.
Table 3
| No. of fans | Fan type | I variant $r_i$ | I variant $h$ | I variant $Q$ | II variant $r_i$ | II variant $h$ | II variant $Q$ | III variant $r_i$ | III variant $h$ | III variant $Q$ |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | OV--2,4 | 0,36 | 58 | 73,4 | 0,15 | 86,4 | 78,3 | 0,42 | 74 | 76,3 |
| 2 | OV--1,8 | 0,5 | 53 | 30,4 | 0,4 | 38,6 | 32,6 | 0,42 | 44 | 31,8 |
| 3 | OV--1,8 | 0,61 | 74 | 21,9 | 0,56 | 63,2 | 23,6 | 0,58 | 67,2 | 23,0 |
| 4 | OV--1,4 | 0,55 | 81,2 | 21,0 | 0,52 | 69,0 | 22,0 | 0,53 | 72,8 | 21,5 |
Table 4
| No. of sections | No. of points | I variant $Q$, m³/sec | I variant $h$, mm water col. | II variant $Q$, m³/sec | II variant $h$, mm water col. | III variant $Q$, m³/sec | III variant $h$, mm water col. |
|---|---|---|---|---|---|---|---|
| 1--2 | 2 | 73,6 | +9,4 | 78,2 | +30,6 | 76,3 | +21,6 |
| 3--4 | 3 | 30,5 | −3,0 | 32,6 | +17,0 | 31,8 | +9,0 |
| 4--5 | 4 | 21,2 | −15,4 | 22,7 | +3,0 | 22,0 | −4,4 |
| 5--E | 5 | 10,7 | −19,2 | 11,3 | −1,2 | 11,0 | −8,4 |
| 5--D | E | 10,4 | −21,4 | 11,1 | −0,36 | 10,9 | −10,4 |
| 6--7 | D | 21,2 | −21,4 | 22,7 | −0,36 | 22,0 | −10,6 |
| 7--8 | 6 | 30,5 | −26,0 | 32,6 | −8,8 | 31,8 | −15,4 |
| 4--Zh | 7 | 9,1 | −27,0 | 9,8 | −10,2 | 9,5 | −16,8 |
| 3--9 | Zh | 42,9 | −17,8 | 45,6 | 0 | 44,6 | −6,6 |
| 9--10 | 9 | 21,8 | −40,6 | 23,6 | −24,2 | 23,0 | −30,6 |
| 10--V | 10 | 10,8 | −42,2 | 11,6 | −28,2 | 11,2 | −34,6 |
| 10--G | V | 11,0 | −46,4 | 11,8 | −30,0 | 11,4 | −36,4 |
| 11--12 | G | 21,8 | −47,6 | 23,6 | −30,6 | 23,0 | −36,4 |
| 9--13 | 11 | 20,9 | −50,4 | 21,8 | −35,0 | 21,5 | −41,0 |
| 13--A | 13 | 13,4 | −46,0 | 14,0 | −30,6 | 13,9 | −36,6 |
| 13--B | A | 7,2 | −50,4 | 7,7 | −34,0 | 7,5 | −40,2 |
| 14--15 | B | 20,8 | −48,0 | 21,8 | −32,0 | 21,5 | −38,0 |
| 14 | −55,4 | −41,0 | −46,4 |
Analyzing the indicated variants of the fans’ operating regimes, we come to the conclusion that variant II is the most rational for the following reasons: 1) the lowest magnitude of the acting heads in the working sections is attained (Table 4); 2) as a result of the first, air leakage from the surface in the depression zone is reduced, and consequently the danger of spontaneous combustion is reduced; 3) the influence of suction fans on one another is reduced (their stability is increased) as a result of the reduction in the resistance of the common section on which the suction fans operate jointly [2, 374]; 4) the efficiency of reversing ventilation in the mine by the forcing fan is increased; 5) the total external air losses at the fans are reduced.
It should be noted that when drawing up the plan of mining operations for a mine, it is necessary to coordinate it with the requirements of ventilation, in particular with the need to create zones of “zero” pressures within the working sections. The development of mining operations should be planned
so that a situation is not created in which one or several districts are located close to the air-intake shaft, while others are at a considerable distance. In such a situation, which occurs at some mines of the Kuzbass, when the forcing–exhaust method is used we are compelled to limit the compression of the forcing fan to a value of 20–30 mm, equal to the pressure loss to the nearest district, since with a larger compression zone the district will fall into this zone, which is prohibited by the Safety Regulations. As a result, the forcing fan operates extremely uneconomically, and the effectiveness of the forcing–exhaust method is reduced to zero, since in essence it turns into the exhaust method.
Such a situation exists, for example, at mine No. 5/6 of the “Prokopyevskugol” trust, where two forcing fans develop depressions of 27 and 46 mm water column, whereas the depression of individual exhaust fans exceeds 150–200 mm water column; at the mine named after Vakhrushev of the “Kiselevskugol” trust, one of the two fans develops a depression of 27 mm water column.
For a complete evaluation of the analyzed variants of fan operating regimes it is necessary to make an economic comparison of them.
In the economic analysis of the variants under consideration, we determine the total expenditures for electric power for all fans per year:
\[ \Sigma P = \sum_{i=1}^{i=4} \frac{Q_i h_i}{102 \eta_i}\, 24 \cdot 365 \cdot c,\quad \text{rub./year}, \]
where \(Q_i\) is the fan capacity, \(m^3/\text{sec}\);
\(h_i\) is the fan depression, mm water column;
\(\eta\) is the efficiency of the fan installation;
\(c\) is the cost of 1 kWh under the two-rate tariff, 0.13 rubles.
The calculation results showed that the expenditures for electric power under variant I amount to 232400 rub./year; under variant II—265600 rub./year; under variant III—250000 rub./year, and the variants are almost equivalent.
Control over the preservation of the position of the “zero” points and over the absolute pressure in the districts is proposed to be carried out in the following way.
In the development heading, in order to isolate the worked-out space, it is recommended to install a tight board stopping \(P\) (Fig. 4). In this stopping a depressiometer is installed, which normally should indicate a value close to the calculated magnitude of the effective pressure at the place of its installation. When the effective pressure changes, the depressiometer readings will also change, and in the event of the appearance of compressions in the district, the pressure of the forcing fan must be reduced.
Fig. 4. Ventilation scheme of a shield district.
The location of the “zero” pressure zone can be determined by carrying out a depression survey at the mine and constructing a depression map. It is appropriate to note that in the new Safety Regulations (1958 edition) there is no requirement for obligatory depression surveys at mines. At the same time there is no other method that makes it possible to determine, with an accuracy of up to 1 mm water column, the magnitude and sign of the absolute pressure in the districts. Thus, the existing in
In the Safety Rules, the requirement that compression must not be allowed in goaf areas under the pressure-suction method of ventilation is not supported by a developed method for monitoring the magnitude and sign of the pressure.
Therefore, in our opinion, it is necessary to restore in the Safety Rules the requirement for mandatory periodic depression surveys in mines.
Since in the Prokopyevsk-Kiselevsk district almost all endogenous fires arise as a result of air leaks from the surface (under the suction and pressure-suction methods of ventilation) through cracks and subsidence, in order to reduce these leaks it is recommended to install a stopping \(A\) in the ventilation drift (Fig. 4).
Conclusions
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When using the pressure-suction method of ventilation, it is recommended to select the compression of the pressure fan and the depression of the suction fans so that the acting pressures within the limits of the worked-out sections are minimal.
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The compression of the pressure fan should be selected so that it ensures the movement of air to the section whose depression loss has the smallest value.
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The creation of minimal acting pressures in the sections makes it possible to significantly reduce air losses and the hazard of endogenous fires.
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The larger the compression zone, the higher the stability of operation of the suction fans.
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It is recommended that a preliminary check of the operating regimes of the fans be carried out on an electrical model.
LITERATURE
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Pechuk N. M., Ventilation and the Struggle against Gas in Kuzbass Mines, Ugletekhizdat, 1946.
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Skochinsky A. A., Komarov V. B., Mine Ventilation, Ugletekhizdat, 1959.
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Safety Rules in Coal and Shale Mines, Ugletekhizdat, 1958.
Noted Misprints
| Page | Line | Printed | Should read |
|---|---|---|---|
| 32 | 9 from bottom | ra oty | raboty |
| 65 | 21 from bottom | zastrev nin | zastrevanii |
| 65 | 3 from bottom | $\dfrac{m_c v_{nk}^{2} - v_{vk}^{2})}{2} > A$ | $\dfrac{m_c\left(v_{nk}^{2} - v_{vk}^{2}\right)}{2} > A$ |
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