WAYS TO IMPROVE THE ECONOMIC EFFICIENCY OF MINE DRAINAGE INSTALLATIONS

V. M. VORONCHIKHIN

(Presented by the scientific seminar of the Department of Mining Machines, Mine Transport, and Mining Mechanics)

At the main drainage installations of Kuzbass mines, despite the different average daily inflow of water, pumps of the AYaPZ-300 type with a nominal capacity of 300 m³/hour are, as a rule, installed. In connection with this, at many drainage installations the total operating time of the pumps is 8–12 hours, although, according to mine operating-safety conditions, the pumping of the normal daily inflow of water is to be provided in no more than 20 hours [1].

The overestimated capacity of the pumps, in turn, necessitates the installation of more powerful motors and, consequently, an increase in the charge for installed capacity.

In addition, most of the main-drainage pumps develop excessive head. As is known [2], the number of impellers of a centrifugal pump operating to pump the normal daily inflow is adopted on the basis of ensuring a stable operating regime and creating the necessary capacity.

To ensure a stable operating regime of the pump, the following condition must be satisfied:

\[ H_{\mathrm{g}} \leq (0.9 \div 0.95) H_0, \tag{1} \]

where \(H_{\mathrm{g}}\) is the geodetic height of water delivery;
\(H_0\) is the head developed by the pump at zero capacity (with the gate valve on the discharge pipeline closed).

For centrifugal sectional pumps,

\[ H_0 = H'_0 \cdot i, \tag{2} \]

where \(H'_0\) is the head developed by one impeller at zero capacity;
\(i\) is the number of impellers.

After substituting expression (2) into condition (1), we obtain

\[ H_{\mathrm{g}} \leq (0.9 \div 0.95) H'_0 \cdot i, \]

whence the number of impellers is

\[ i \geq \frac{H_{\mathrm{g}}}{(0.9 \div 0.95) H'_0}. \tag{3} \]

The number of impellers required to create the necessary capacity is

\[ i \geq \frac{H}{H'}, \tag{4} \]

where \(H\) is the pump head at the required capacity; \(H'\) is the same, but for one impeller.

The pump is adopted with the number of impellers determined from expressions (3) and (4) and rounded up to the nearest larger integer.

However, in many drainage installations of Kuzbass mines, pumps have been installed with a number of impellers one, and sometimes two or three, impellers greater than the calculated number. In this case the pump develops a higher capacity and operates for fewer hours pumping water. Therefore some mine workers have formed the opinion that the economy of operation of the drainage installation remains the same or decreases only insignificantly because of the reduction in the pump efficiency. In addition, in the technical literature [3, 4] there are indications of the possibility of regulating the capacity and increasing the efficiency of mine pumps by partially closing the gate valve on the discharge pipeline, but no analysis is given of the change in the specific consumption of electric power per cubic meter of water delivered.

The power on the pump shaft is determined by the formula

\[ N = \frac{Q \cdot H \cdot \gamma}{3600 \cdot 102 \cdot \eta_{\mathrm{n}}}, \ \text{kW}, \tag{5} \]

where \(Q\) is the pump capacity, \(\mathrm{m^3/hour}\);

\(H\) is the pump head, m water column;

\(\gamma\) is the specific weight of water, \(\mathrm{kg/m^3}\);

\(\eta_{\mathrm{n}}\) is the pump efficiency.

Let us denote the quantities that do not depend on the pump operating regime by a certain constant, taking \(\gamma = 1050 \ \mathrm{kg/m^3}\):

\[ c = \frac{\gamma}{3600 \cdot 102} = \frac{1050}{3600 \cdot 102} \simeq 0.003, \]

then

\[ N = 0.003 \frac{Q \cdot H}{\eta_{\mathrm{n}}}, \ \text{kW}. \]

The specific consumption of electric power, without taking into account losses in the motor and cable network, is

\[ \omega_{\mathrm{sp}} = \frac{N}{Q} = 0.003 \frac{Q \cdot H}{\eta_{\mathrm{n}} \cdot Q} = 0.003 \frac{H}{\eta_{\mathrm{n}}}, \ \frac{\mathrm{kW \cdot h}}{\mathrm{m^3}} . \tag{6} \]

As follows from expression (6), the specific consumption of electric power increases when the pump efficiency decreases; therefore the range of possible pump operating regimes is limited by the zone of industrial use, or the working zone of the pump, in which

\[ \eta_{\mathrm{n}} \geq (0.85 \div 0.90)\eta_{\max}. \tag{7} \]

At the same time, however, it is not evident from expression (6) that, with an increase in head, the economy of pump operation decreases, since in some cases, for example when the pump operating regime is shifted from point 1 to point 2 (Fig. 1), an increase in head is accompanied by a decrease in the required power and an increase in the pump efficiency. In addition, the pump operating regime at point 1 lies outside the working zone, while by throttling ...

the gate valve, it is possible to shift the pump operating regime to point 2. How in this case does the specific consumption of electrical energy change?

Partly closing the gate valve increases the pressure created by the pump, while the water delivery head (geodetic head \(H_{\mathrm{g}}\)) remains unchanged. The ratio of the geodetic head to the pressure created by the pump is taken [2] as the efficiency coefficient of the pipeline,

\[ \eta_{\mathrm{tr}}=\frac{H_{\mathrm{g}}}{H}; \tag{8} \]

hence

\[ H=\frac{H_{\mathrm{g}}}{\eta_{\mathrm{tr}}}. \]

Substituting the latter relation into expression (6), we obtain

\[ \omega_{\mathrm{ud}}=0.003\,\frac{H_{\mathrm{g}}}{\eta_{\mathrm{n}}\cdot\eta_{\mathrm{tr}}}= \]

\[ =0.003\,\frac{H_{\mathrm{g}}}{\eta_{\mathrm{ust}}}, \]

where \(\eta_{\mathrm{ust}}=\eta_{\mathrm{n}}\cdot\eta_{\mathrm{tr}}\) is the efficiency of the dewatering installation. As is seen from Fig. 1, the efficiency of the dewatering installation increases with increasing capacity and becomes equal to the pump efficiency for an ideal pipeline, for which

\[ \eta_{\mathrm{tr}}=\frac{H_{\mathrm{g}}}{H}=1. \]

Fig. 1. Change in the pump operating regime depending on pipeline resistance

Consequently, partly closing the gate valve reduces capacity and lowers the economy of pump operation because of the increase in pipeline resistance; therefore this method of regulation is permissible only as a temporary measure—for example, if a motor of lower power has been installed and, until it is replaced, water must be pumped without overloading the motor [2, 5].

At some mines of Kuzbass, on the instruction of “Kuzbassenergo,” in order to save electrical energy, each pump operates simultaneously on two, and sometimes even on three, discharge pipelines [6]. The author of work [6] indicates that “in practice there is indeed some increase in pump capacity, but in this case no attention at all is paid to the pump operating regime, to the zone of economical operation”¹ and that “it was established that not in all cases is operation on two pipelines expedient.” This conclusion is erroneous, since when a pump operates simultaneously on two pipelines the velocity of water movement decreases, the hydraulic resistances of the pipeline decrease in proportion to the square of the change in velocity, and when pipeline resistances decrease, the capacity and efficiency of the dewatering installation increase (Fig. 1). The increase in the specific consumption of electrical energy when a pump operates simul-

¹ Emphasized by V. M. Voronchikhin.

simultaneously on two branches may occur for other reasons, for example, because of increased water leakage through faulty gate valves and check valves of adjacent pumps which, when the pump was operating on one branch, were cut off from it by a serviceable gate valve.

To compare different pump operating modes and to evaluate the economy of operation of the drainage installation, Fig. 2 gives the characteristics of the AYaPZ-300 pump with three and four working impellers, operating into a pipeline with a water-lifting head \(H_{\text{g}} = 150\ \text{m}\). The technical and economic operating indicators of pumps on one and on two branches of pipelines are given in Table 1.

Fig. 2. Characteristics of a drainage installation with an AYaPZ-300 type pump.
1 — characteristic of the pump with four working impellers; 2 — same with three impellers; 3 — characteristic of the network when one branch of the pipeline is put into operation; 4 — same when two branches of the pipeline are put into operation simultaneously; 5 — pump efficiency; 6 — efficiency of the drainage installation with four impellers in the pump; 7 — same with three impellers.

As can be seen from Fig. 2 and Table 1, the pump operates most economically with three working impellers when it is connected simultaneously to two branches of the pipeline (point \(D\)). When a pump having four working impellers operates on one branch of the pipeline closed by a gate valve, the drainage installation has the lowest economy (point \(B\)), although the pump efficiency in this mode is maximal.

The excess consumption of electric power per year, with a water inflow into the mine of \(250\ \text{m}^3/\text{h}\), will amount to \(550{,}000\ \text{kWh}\).

Table 1

Conclusions

1. At mine drainage installations it is necessary to install pumps that meet safety regulations, without substantially overstating their capacity.

2. The number of pump impellers must be minimal and determined from the conditions of stable operation and of creating the necessary head to ensure the required capacity. Installing a pump with excessive head increases the capacity of the drainage installation, but at the same time increases the specific consumption of electric power.

3. Regulating pump capacity by partly closing the gate valve on the discharge pipeline may be used only in installations where a definite water flow rate is required. Throttling the pipeline, even in those cases when the operating mode shifts into a zone of higher pump efficiency values, leads to a reduction in the economy of operation of the drainage installation and, for mine drainage, should certainly not be recommended.

4. The simultaneous operation of a pump that is in satisfactory condition on two pipeline branches with serviceable gate valves and check valves increases the economy of operation of the drainage installation.

References

1. Safety Regulations in Coal and Shale Mines. Gosgortekhizdat, 1964.

2. V. S. Pak and V. G. Geier. Mine Ventilating Drainage Installations. Ugletekhizdat, 1955.

3. V. I. Kiselev. Mining Mechanics. Gosgortekhizdat, 1961.

4. Guidance Materials for Conducting Revisions, Adjustments, and Tests of Mine Drainage Installations. Ugletekhizdat, 1959.

5. A. I. Veselov. Mine Turbomachines. Metallurgizdat, 1952.

6. M. P. Petrov. Analysis of the Operation of Main Drainage Installations at the Mines of the Prokopyevsk-Kiselevsk Deposit. Kemerovo, 1959.