Selection of Air Compressor for Underground Air Supply Equipment
2024-03-18
The pit at a certain site is powered by wind energy, with a centralized air supply from a ground air compressor station. With the discovery of a new copper vein in the deep part of the pit at this site in 2013, the original centralized air supply system of the ground air compressor station can no longer meet the underground production of the new copper vein, such as pioneering, digging, deep drilling and concrete pouring. Meanwhile, the original air supply system has problems such as aging equipment, high energy consumption, high operation cost and low safety performance. Therefore, it is necessary to choose suitable air supply equipment and air supply system for underground production. Learn about Selection of Air Compressor.
1. Background of air compressor selection
1.1 Status of old air compressor
The two air compressors currently used in the air compressor station at the entrance of the pit ( table 1 ) are reciprocating air compressors, with serious aging and high failure rates, which are low-efficiency and high-energy-consumption equipment, and the measured exhaust efficiency in 2013 was only 38 per cent to 51.68 per cent ( table 2 ), which is far less than the 85 per cent standard provided for in the national standard. In recent years, the output pressure of the equipment can only be up to 6.5kg/cm2, which is difficult to guarantee the wind demand of underground rock drilling and rock loading equipment, and it has seriously affected the normal work of the mining company underground.
| Table 1 Parameters Related to the Two Air Compressors Currently Used at the Site | ||||||
| Specification | Number of Units | Factory Time | Motor Power(KW) | Theoretical Air Volume(m³/min) | Actual Annual Power(KWh) | Maintenance Cost(Ten Million CNY) |
| 1-100/8 | 1 | 1961 | 480 | 100 | 115.2 | 30 |
| 1-103/8 | 1 | 1971 | 475 | 103 | 111.6 | 54 |
| Total | 2 | 955 | 203 | 226.8 | 84 | |
| Table 2 Efficiency Parameters of the Two Air Compressors Currently Used at the Site | |||||
| Specification | Theoretical Volumetric Flow Rate (m³/min) | Actual Volumetric Flow Rate (m³/min) | Actual Volumetric Flow Rate (m³/min) | Standard Exhaust Efficiency (%) | Wind Speed (m/s) |
| 1-100/8 | >0.85qe | 47.3 | >85 | 47.3 | 16.38 |
| 1-103/8 | >0.85qe | 59.3 | >85 | 57.46 | 7.87 |
| Note: qe is the rated flow rate of air compressor | |||||
1.2 Extension of deep mining
With the commencement of the fourth phase of the prospecting project at the site, the existing air compressors can no longer meet the production needs. 190 and 240 sections were under construction concurrently from January to June 2014. 4 rock drills were working at the same time during the construction of the two workings in the 190 section, requiring an air volume of 13.2m³/min; 8 rock drills were working at the same time during the construction of the 240 section, requiring an air volume of 26.4m³/min; the total air volume was 39.6m³/min. The shaft in the middle section of 140 started to be dug down from July to December 2014, and 14 rock drills worked simultaneously with an air demand of 46.2m³/min.
The total duct length from the compressor station to gate 150 in the middle of 240 is about 2300m (see Figure 1).
2. Factors to consider when selecting an air compressor
In the well arrangement of air compressors you need to consider the impact of the environment, i.e., dust, humidity, corrosion and other factors are applicable to the PLC control system of the air compressor used on the ground. In the underground, if the equipment is affected by dust and high humidity and other harsh environments, it will accelerate the corrosion of electronic components, shorten the life of the equipment, and at the same time, lead to the failure of the air compressor action, and increase the failure rate. This mine belongs to the acidic environment, if the water-cooled compressor is used, it is not only inconvenient but also corrosive. Therefore, in the selection of equipment, we need to pay attention to the following aspects:
(1) Adopt air-cooled air compressor.
(2) Due to the influence of the lowering of the shaft, heat dissipation, space arrangement and other issues, the air volume of a single air compressor is not greater than 30m³ / min as far as possible.
(3) The air inlet filtration adopts oil bath filter, which can improve the filtering effect of dust.
(4) It has the function of anti-voltage fluctuation.
(5) Adopt simple mechanical, instrumentation and electronic control system, which is used in engineering construction, improving the service life of control system components and avoiding frequent equipment failure.
(6) Strengthen the oil, gas, water separation effect of the air compressor, which can minimize the water in the lubricating oil and avoid the phenomenon of emulsification of lubricating oil, and improve the effect of lubricating oil use and service life.
3. Analysis on the technical performance of piston air compressor and screw air compressor
3.1 Piston air compressor
3.1.1 Advantages of piston air compressor
(1) Regardless of the flow rate, it can reach the required pressure.
(2) High thermal efficiency.
(3) The exhaust pressure is almost constant when the air volume is adjusted.
3.1.2 Disadvantages of piston air compressors: Selection of Air Compressor
(1) The air compressor is large in size and heavy in weight, and the exhaust volume of the single air compressor is less than 500m³/min.
(2) Complex structure, many wearing components (piston ring, valve plate, valve, piston, packing components, springs, etc.), unbalanced inertia force (torque), installation complexity, the need to install the foundation, vibration.
(3) Discontinuous gas delivery, gas pressure with pulse.
(4) Low working efficiency.
3.1.3 Efficiency and energy saving of piston compressors
After running for a period of time, the compression efficiency of the piston air compressor gradually decreases, while the energy consumption gradually increases, mainly because:
(1) The high exhaust temperature of the piston air compressor leads to a reduction in compression efficiency. Only in the case of isothermal compression can power be saved.
(2) The piston ring of piston compressor has poor sealing effect, resulting in large internal leakage.
(3)Piston air compressor has many friction parts and large mechanical loss, resulting in rapid performance decline.
(4)Piston air compressor has many friction parts, resulting in high operating resistance.
(5)Piston compressor has dead volume.
3.2 Screw air compressors
3.2.1 Advantages of screw compressors
(1)The air compressor is small in size, light in weight, simple in structure, and has fewer wearing parts.
(2)No pulse of exhaust, small vibration, simple installation, no need to install foundation, it can realize high speed, good continuity of gas transmission and small pressure pulsation.
(3) PM VSD Screw air compressor has the function of capacity adjustment control, which can maintain high efficiency in a wide range of working conditions. According to the air consumption in the system, the screw air compressor can utilize the capacity adjustment device to automatically adjust the air intake ( the capacity adjustment range is from 0 to 100%), so as to achieve the purpose of producing the required amount of air with any amount of air, thus saving the energy consumption, moreover, when the user uses the air compressor again, it will be started automatically.
(4) The motor of the screw air compressor can be adjusted in speed so that the air volume can be changed. The pressure signal can control the rotational speed of the motor by continuously and accurately measuring the operating pressure of the unit (pressure sensor). Screw air compressors have a controlled air volume flow range of 0 to 100% and an energy consumption range of 15% to 100%. Compared with the piston compressor, the efficiency is improved by more than 25% to 30%, and the energy saving ratio is more than 25%.
3.2.2 Disadvantages of screw air compressors
(1) The surface of the moving parts is curved, which requires high-performance equipment processing.
(2) The gap between the moving parts is sealed, it is difficult to achieve high pressure (general single-stage compression can only reach 1.5MPa).
3.2.3 Efficiency and energy saving of screw air compressors
(1) The rotor cross-section is asymmetric, tooth shape and linear, by optimizing the design can reduce the area of the triangle, improve the compressor’s compression efficiency.
(2) The teeth composition of the screw rotor will no longer have a point, straight line and pendulum line, they use arc, ellipse, parabola and other curves, so that the rotor teeth from the “line” sealing improved to “band” sealing, The sealing effect is improved, which is conducive to the formation of lubricant film and reduction of tooth wear.
(3) The small difference between the teeth of the screw rotor can reduce the reflux loss, improving the thermal efficiency by 10% to 12% and saving 25% of electricity.
(4) The compound shape line is streamlined, which can reduce the hydrodynamic loss.
3.3 Comparison of piston air compressor and screw air compressor
Compared with piston compressor, screw compressor has the following advantages: fewer parts and wearing parts, long maintenance cycle, light weight, reliable operation, simple and compact structure, easy operation, easy to realize automation, obvious energy saving effect, small fluctuation of gas delivery pressure, high efficiency, good power balance and so on.
4. Selection of location and type of air compressor
(1) The existing environment in Sector 190 does not provide the safe distance and ventilation conditions for the installation of air compressors, which is a major limitation. If the compressor is installed in section 190, it will not be able to supply air to the operation site in section 240. According to the existing construction sites, the number of equipment and air consumption, installing air compressors in section 240 can supply air to all construction sites in section 240 and section 190 at the same time. Therefore, two twin-screw compressors were selected for parallel air supply at the pump house in section 240 (see figure 2).
(2) The main technical parameters of the twin-screw compressor: volume flow rate of 30.0m³/ min, exhaust pressure of 0.8MPa, the main motor power / voltage of 180kW / 6kV, exhaust temperature for the ambient temperature of +8 ℃, the exhaust outlet oil content (mass fraction) ≤ 3 × 10-6, the noise ≤ (78 ± 3) dB, the equipment dimensions (L × W × H) for 4000mm × 1300mm × 1500mm.
5. Conclusion
In view of the problems of centralized air supply in ground air compressor stations and the influence of underground working conditions on air compressors, our company decided to use screw air compressors for underground air supply by comparing the technical performances of piston air compressors and screw air compressors, which resulted in the improvement of air supply efficiency, obvious energy-saving effect, easy operation, reliable operation and long maintenance cycle, meeting the needs of underground production and air supply.