On Determining the Area of Rational Application of Auxiliary Ventilation Fans

B. M. Titov

(Presented by Prof., Doctor of Technical Sciences I. A. Balashev)

In the article by Engineer A. M. Fridlyand [1], the question is correctly raised of reducing the number of crosscuts between parallel workings and of clarifying the area of rational application of auxiliary ventilation fans.

Without objecting to the methodology of the techno-economic calculation presented by A. M. Fridlyand as a whole, we nevertheless consider it necessary to clarify the question of determining the cost of the energy expended on ventilating paired workings during their driving.

In the case of ventilating a paired working solely by means of the pressure of the main fan, the difference in static pressures between the main and ventilation crosscuts must be not less than \(10\ \text{kg}/\text{m}^2\) [2, p. 111]. Often this pressure difference is considerably smaller; for example, in the mines of the Southern Kuzbass it is only \(1\text{–}5\ \text{kg}/\text{m}^2\) [2, p. 110]. Artificially increasing the pressure difference between the main and ventilation crosscuts by installing regulating stoppings leads to a significant additional expenditure of energy.

In the mines of the Donbass and in ore mines, owing to the smaller cross-section and number of parallel workings, the difference in static pressures between the main and ventilation crosscuts is considerably greater; but even in this case, for ventilating paired workings solely by means of the pressure of the main fan, it is necessary to use ventilation regulating stoppings, since the maximum difference in static pressures between the main and ventilation crosscuts of the level being worked does not coincide in time with the maximum resistance of the preparatory workings of the new level being driven.

Let us compare the energy consumption for ventilating a preparatory working driven with paired faces by means of the pressure of the main fan with the energy consumption for ventilating the same blind working when using an auxiliary ventilation fan. In both cases we shall take the overall mine air-reserve coefficient to be the same, and the efficiency of the fans equal to the average value over the entire period of driving the working.

The power consumed by the motor of the main fan before the ventilation of the blind working,

\[ N'_1=\frac{H Q_w}{102\eta_1}, \tag{1} \]

where \(H\) is the total pressure of the main fan, \(\mathrm{kg}/\mathrm{m}^2\);

\(Q_w\) is the capacity of the main fan, \(\mathrm{m}^3/\mathrm{s}\);

\(\eta_1\) is the overall efficiency of the main fan installation.

The power consumed by the motor of the main fan when ventilating a blind working is

\[ N''_1=\frac{(H+h_{\mathrm{dop}})(Q_w+Q_1)}{102\eta_1}, \tag{2} \]

where \(h_{\mathrm{dop}}\) is the additional pressure of the main fan expended in overcoming the resistance of the ventilation stoppings, \(\mathrm{kg}/\mathrm{m}^2\);

\(Q_1\) is the quantity of air required for ventilating the drivage, \(\mathrm{m}^3/\mathrm{s}\).

The increase in power consumed by the motor of the main fan is

\[ N_1=N''_1-N'_1=\frac{(H+h_{\mathrm{dop}})Q_1+h_{\mathrm{dop}}Q_w}{102\eta_1}. \tag{3} \]

The power required for ventilating the same working when using a local-ventilation fan is

\[ N_2=\frac{H Q_2}{102\eta_1}+\frac{(h_m+h_v)Q_2}{102\eta_2}, \tag{4} \]

where \(Q_2\) is the quantity of air required for ventilating the working, \(\mathrm{m}^3/\mathrm{s}\);

\(h_m\) is the pressure loss in the ventilation pipeline, \(\mathrm{kg}/\mathrm{m}^2\);

\(h_v\) is the pressure loss in the blind part of the working, \(\mathrm{kg}/\mathrm{m}^2\);

\(\eta_2\) is the overall efficiency of the local-ventilation fan installation.

Thus, with respect to energy consumption, the use of local-ventilation fans is expedient only if the inequality\(^1\)

\[ N_1 t a_{e1} > N_2 t a_{e2}, \tag{5} \]

is satisfied, where \(t\) is the operating time of the fan installation, h;

\(a_{e1}\) is the unit cost of the energy consumed by the motor of the main fan, rubles/kWh;

\(a_{e2}\) is the unit cost of the energy consumed by the motor of the local-ventilation fan, rubles/kWh.

Substituting into formula (5) the values of \(N_1\) and \(N_2\) from formulas (3), (4), and neglecting the very small pressure drop in the blind working, \(h_v\), after a simple transformation we obtain

\[ \frac{H Q_1+h_{\mathrm{dop}}(Q_1+Q_w)}{\eta_1}\,a_{e1} > \left(\frac{H}{\eta_1}+\frac{h_m}{\eta_2}\right)Q_2a_{e2}. \tag{6} \]

If the quantity of air required for ventilating the working by means of the pressure of the main fan is obtained equal

\(^1\) It is assumed that the drive of the local-ventilation fan may be either electric or pneumatic.

with the required capacity of the auxiliary ventilation fan, i.e., \(Q_1 = Q_2 = Q\), formula (6) is simplified:

\[ \frac{(Q + Q_{\sh}) h_{\mathrm{dop}} a_{\mathrm{e}1}}{\eta_1} > \frac{Q h_{t} a_{\mathrm{e}2}}{\eta_2}. \tag{7} \]

The efficiency of the main ventilation fan is determined from the aerodynamic characteristic in accordance with its actual operating regime, or is taken approximately equal to 60–65%. The weighted-average value of the efficiency of an auxiliary ventilation fan may be taken as 50%.

Formulas (6) and (7) help determine the rational distance between crosscuts and select the most economical variant of ventilating a working in the case where, technically, for ventilating a blind working it is possible to use the pressure of either the main ventilation fan or an auxiliary ventilation fan. The area of rational application of auxiliary ventilation fans, determined by formulas (6) and (7), expands when account is taken of the costs of driving and maintaining crosscuts made specially for ventilation purposes when using the pressure of the main fan.

REFERENCES

1. Fridlyand A. M. Reducing the cost of mine construction through the proper choice of the method of ventilating mine workings. Ugol’, No. 6, 1955.
2. Batalin S. A. Ventilation in the Mines of the Kuzbass. Ugletekhizdat, 1951.