Some Issues in the Design of Main Fan Installations for Kuzbass Mines
Abstract Generated abstract
This paper examines the design and operation of main fan installations in Kuzbass coal mines, where ventilation requirements vary widely as workings move to lower horizons and mine networks become more complex. Using survey data from 1955 to 1957 and comparisons of operating ranges for axial and centrifugal fans, it argues that fan selection, drive choice, and regulation methods must be considered together with expected changes in the ventilation network. The study finds that axial fans, particularly larger K-06 units operated at moderate peripheral speeds, could cover most Kuzbass conditions more efficiently than commonly used alternatives, while stepwise or variable-speed regulation may reduce power costs under changing conditions. It also emphasizes reducing air leakage through improved ventilation structures and rapid blade-turning devices for reversal.
Full Text
Some Issues in the Design of Main Fan Installations for Kuzbass Mines
O. M. Kolyshkin
(Presented by the scientific and technical conference of the Mining Faculty)
The ventilation regimes of Kuzbass mines, according to the results of surveys carried out by the adjustment crew of the Kuzbassugol combine in 1955–1957, are characterized (Fig. 1) by air quantities of 50–200 m³/sec at a depression of 70–300 mm water column.
The operating regimes of the fan installations of Kuzbass mines vary within considerable limits, since with the transition to lower horizons the gas abundance of seams, the overall resistance of the ventilation network, and the ventilation scheme change sharply.
Fig. 1. Ventilation regimes of Kuzbass mines (indicated by points) and zones of economical operation of axial fans of the K-06 series.
It should be noted that the existing ventilation schemes of Kuzbass mines are extremely complex. In developing the first horizon, a forcing-and-exhaust ventilation system is usually used, with one supply fan and 15–20 exhaust fans installed on shafts. It is clear that, with such a number of installations, it is difficult, and sometimes impossible, to regulate their operation. With the partial transition of operations to a lower horizon, some of the shaft fans continue to operate. The ventilation scheme—
becomes more complicated, and the operation of borehole fans in this case is useless, since almost all the depression they create is spent on overcoming the resistance of the boreholes. To improve ventilation, it becomes necessary to replace the borehole fans. In such cases it is not uncommon for the fan installation to be replaced 5–7 years after installation. Such replacement requires large capital expenditures (on the order of 300–500 thousand rubles) and by no means always corrects the ventilation situation.
The choice of fan should be made in close connection with changes in ventilation conditions, the resistance of the ventilation network, and the ventilation scheme being used. Unfortunately, in design, operation, and even in instruction at higher educational institutions, ventilation networks are handled by some departments and fans by others, without the necessary coordination.
Figure 1 presents the field of ventilation conditions for economical operation of the standard series of K-06 axial fans. Solid lines indicate operating conditions at a peripheral speed below 78 m/sec; dashed lines indicate those at 94.5 m/sec. The first digits of the numbers placed at the boundary of the zone of economical operation indicate the diameter of the impeller in meters. The numerator of the fraction following these digits shows the number of revolutions per minute, and the denominator gives the peripheral speed of the fan impeller in m/sec.
It is clear from Fig. 1 that the majority of existing ventilation conditions can be provided by K-06 series axial fans at a peripheral speed of 75–78 m/sec.
The Conference on Fan Engineering, held in June 1953 in Moscow and Stalino, recommended using K-06 axial fans at pressures below 300 mm water column. However, the axial fans being produced cannot provide larger air delivery, since their impeller diameter does not exceed 2.8 m. Therefore Kuzbassgiproshakht was compelled to design for the Koksovaya-1 mine, at air quantities of 79–227 m³/sec and depressions of 175–191 mm water column, a VTs-5 centrifugal fan. Under the above ventilation conditions the VTs-5 fan has an efficiency of 30–40%. A K-06 series fan with an impeller diameter of 3.6 m could provide these same ventilation conditions at an efficiency of 60–70%, or yield, over the period of operation, a reduction in electric-power consumption of 50 million kWh.
In the mines of Kuzbass, axial fans operate mainly at the limiting value of peripheral speed, 94.5 m/sec. However, such a speed is by no means always necessary, since pressures up to 200–250 mm water column can also be provided at a lower speed.
Figure 2 gives the ventilation conditions of Kuzbass mines (shown by points) and the areas of economical operation of series V axial fans; solid lines indicate the zones of economical operation at a peripheral speed below 78 m/sec, and dashed lines those at 94.5 m/sec. It is clear from Fig. 2 that even the far from perfect series V fans provide most of the required ventilation conditions at a peripheral speed below 78 m/sec. At a reduced peripheral speed the reliability of fan operation is substantially increased and the noise level is reduced; therefore, operating conditions at high peripheral speeds should not be selected unless absolutely necessary. These operating conditions should be regarded as a reserve for more difficult ventilation conditions that may arise during mine operation.
When ventilation conditions change substantially, it is advisable to regulate fan operation by means of stu-
stepwise change in the number of shaft revolutions. When selecting a fan for variable operating conditions, we recommend plotting these conditions graphically in dimensionless coordinates.
The stepwise change in the fan shaft speed should be carried out in such a way that the maximum value of the efficiency of the fan installation corresponds to the most severe ventilation condition. When regulating the fan, the power consumed changes substantially; therefore it is necessary to provide for the possibility of replacing the motor during operation. Such replacement will make it possible to obtain higher efficiency values for the fan installation by reducing the charge for installed capacity and by increasing the power factor, “cos phi.” The additional capital expenditures connected with the purchase of motors of different capacities can be reduced if these motors are used at different mines.
Fig. 2. Ventilation conditions of Kuzbass mines (shown by dots) and zones of economical operation of Series V axial fans.
If more flexible regulation is required, going beyond the standard speeds, a gear or V-belt drive should be used. The increase in the size of the foundation in this case will be insignificant, since the reducer and motor installed for the first period of operation will be intended for a considerably lower power than the main motor installed in the subsequent period of operation.
With a fan motor power of more than 500–600 kW and a shaft rotation speed of less than 500 rpm, the use of a controlled electric drive may prove economically advantageous. We have carried out an approximate calculation of electric-power consumption and additional capital costs for a fan installation with a VTs-5 fan and a synchronous motor of 1960 kW, designed by Kuzbassgiproshakht for the Koksovaya-1 mine. The calculation results are given in Table 1.
Electric-power consumption, as can be seen from Table 1, is significantly reduced when a controlled drive is used.
Excess electric-power consumption is also caused by air leakages, which in some cases reach (Mine No. 12 of the Kiselevskugol Trust) 70% of the total quantity of air supplied to the mine. The greatest air leakage occurs through the aboveground buildings of shafts equipped with cage hoists, and ventilation--
Table 1
| Electric-drive options | Fan operation at \(n = 300\) rpm | One-time replacement of motor \(n_1 = 250;\ n_2 = 300\) rpm | Regulated drive: controlled mercury rectifier \(n = 200 \div 260\) rpm | Regulated drive: G–D system \(n = 200 \div 260\) rpm |
|---|---|---|---|---|
| Electricity consumption over the operating period, kWh | 134000 | 101000 | 84000 | 94000 |
| Cost of consumed electricity, rubles | 4150 | 3100 | 2600 | 2900 |
| Charge for installed capacity, rubles | 6200 | 2930 | 2950 | 6200 |
| Total cost of electricity, rubles | 10350 | 6030 | 5550 | 9100 |
| Additional capital expenditures, rubles | 0 | 250 | 450 | 500 |
| Total expenditures, rubles | 10350 | 6280 | 6000 | 9600 |
channels because of the insufficiently tight fit of doors, gates, etc., especially when they freeze in winter.
In our opinion, which coincides with the opinion of many engineering and technical workers at Kuzbass mines engaged in the operation of fan installations and ventilation devices, it is necessary to abandon the design of bulky gates, replacing them with doors located inside the duct and fitting tightly under the action of the pressure created by the fan.
A reduction in air leakage, as well as in the cost of ventilation devices, is possible when reversing the ventilation jet by changing the direction of rotation of the impeller of the axial fan with the simultaneous turning of the blades by \(180^\circ\), or, when using the blade-turning device recommended by TsAGI, by an angle close to \(90^\circ\), without changing the direction of rotation, since in this case the number of gates is halved and the need for bypass ducts disappears. Therefore, design organizations must in the near future create an apparatus that will allow the blades to be turned in 3–4 minutes. The creation of an apparatus that permits the impeller blades to be turned without stopping the fan will make it possible to facilitate starting conditions, which is especially important when using a synchronous motor.
Conclusions
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The choice of fan, drive, and methods of regulation depends on changes in the ventilation network; therefore these questions must be solved as a whole and with account taken of the technical and economic indicators of the operation of the fan installation.
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The principal type of fan for ventilating Kuzbass mines should be considered the axial fan. Axial fans should normally operate with a peripheral speed of 75–78 m/sec, and only when forcing an already installed fan should a limiting speed of 94.5 m/sec be adopted. The plants of Glavuglemash must in the very near future organize the production of axial fans of the K-06 series with impeller diameters up to 3.6 m.
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With significant changes in ventilation conditions, provision must be made for stepwise regulation by changing the number of revolutions of the fan shaft; when the motor power exceeds 600 kW, a variable-speed electric drive should be used.
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To reduce air losses and, consequently, electric power losses, serious attention must be given to reducing the number of dampers by developing a device for rapidly turning the blades of the fan impeller.