Screw Air Compressor in Coal Mining Industry

Screw Air Compressor in Coal Mining Industry is one of the important fixed equipment in the process of mining production, which is mainly used to drive the operation of air-operated rock loaders, rock drills and other equipment and related air tools and generate compressed air. The safe operation of the air compressor has an important impact on the production efficiency of coal mines, so the study of the application of air compressors in the coal mining industry is of great practical significance. At the same time, as an important power in the coal mining industry, the mine compressed air system is also an indispensable and important system in mine production. A unit has 4 sets of air compressors, including 1 set in maintenance, 1 set in use and 2 sets in standby, all of which are screw air compressors  produced by a company, which are discussed below.

1. Working Principle of Screw Air Compressor

1.1 Working principle

The working principle of the screw air compressor is as follows: before the air enters, there will be a filter to filter out the impurities and dust in the atmosphere, and the filtered clean air enters into the compressor mainframe through the air inlet control valve, and starts to be compressed after mixing with the cooling lubricating oil evenly. After compression, the oil-containing gas needs to be discharged, and after the above treatment, the oil and gas fine separator is used for separation treatment, so as to obtain the compressed air with less oil content. When the air is compressed to the standard pressure value, the compressed air is discharged into the cooler by the minimum pressure valve and can be used after cooling.

During the suction phase, the suction port at the intake place of the screw air compressor ensures that the compression chamber draws in enough air. The intake phase is controlled by a control valve which draws in the maximum amount of air as the rotor rotates. At the end of the exhaust, the tooth groove is in vacuum.

During the gas containment and transport phase, a confined space is formed between the tooth peaks of the main and auxiliary rotors and the housing, ensuring that the air is sealed in the tooth grooves and cutting off the air from the outside world. The two rotors then continue to work, with the tooth grooves and crests combining at the suction end to carry the gas to the exhaust end. During the compression and injection phases, the distance between the grooves and the toothed crests at the exhaust end is gradually reduced, causing the pressure in the entire enclosed space to gradually decrease, thus keeping the gas in the grooves in a state of compression at all times.

2. Advantages of screw air compressor in coal mine applications

In coal mine applications, the use of screw air compressors is characterized by the following aspects:

(1)High efficiency, energy saving and stability. Screw air compressor can realize forced gas transmission, that is, when the exhaust pressure changes, the exhaust volume basically does not change, the exhaust pressure decreases by 1MPa or increases by 1MPa, the exhaust volume increases by 0.01m³/min or decreases by 0.01m³/min, and the pressure inside the screw air compressor is not affected by the rotational speed, no matter how the rotational speed changes, the internal pressure is basically a fixed value.

(2) Low carbon and environmental protection. PM VSD screw air compressor chassis adopts soundproof design, light weight, small volume, low noise, small footprint, compact and complete structure of the unit, no need for special foundation design and construction, easy installation. The box-type unit contains motor, electric control, compressor, instrumentation, etc., without the need to purchase additional electric control cabinets and instrumentation cabinets, there is no unbalanced mass force, which can achieve balanced and vibration-free operation, and basically achieve the complete balance of power. A unit of four compression fans are LGS_1O7/8 type, exhaust air volume of 107m³/min, air supply pressure of 0.8MPa, equipped with two 315kw motors, in line with the development of low-carbon and environmental protection concept.

(3) Comprehensive protection function is perfect. The screw air compressor has the corresponding protection functions such as unloading delay stop main motor overload stop, stop when the exhaust temperature is too high, fan motor overload stop, etc. It can stop the operation in time when it reaches the critical value or abnormality, which can protect the machine and equipment on the one hand, and avoid the occurrence of accidents and unnecessary losses on the other hand. In addition, the water-cooled unit is equipped with thermostatic valve, which can realize the automatic control of the discharge temperature, and the air-cooled unit is equipped with independent fan cooling system, which can cool down and control the temperature in time when the temperature is too high.

(4) Automation control system. Take programmable controller (PLC) as the center, realize touch screen industrial human-machine interface and human-machine dialogue, set the whole operation display in Chinese, convenient, intuitive and simple. Automation control system can provide real-time maintenance information of the air compressor, timely reminder of maintenance, but also has a pressure curve printing operation function, to provide the dynamic distribution of compressed air consumption distribution, once anomalies can be alarmed in time, but also facilitates the user to accurately analyze the specific parameters of the compression system.

(5) Low cost and low maintenance. In the case of the same volume flow rate and discharge pressure, the cost of 4L-20/8 piston compressor (purchase cost 14868 yuan + compressor oil 10260 yuan + labor cost 7538 yuan) is more than 3 times of the cost of LGS-l07/8 screw compressor (purchase cost about 3840 yuan + compressor oil 3410 yuan + labor cost about 2175 yuan), so the cost of screw compressor has the advantage. Therefore, the cost of screw air compressor has the advantage. Meanwhile, compared with the maintenance of screw air compressor, piston air compressor has 5 main wearing parts, while screw air compressor has only 3, so the maintenance cost of screw air compressor is lower.

(6) Other advantages. Screw air compressors can be installed close to the point of air consumption to, firstly, reduce pipeline input and pressure loss and, secondly, prevent condensation problems due to temperature drop. Screw air compressors feature continuous suction, exhaust and compression, pulsation-free airflow, high quality and low oil content. Screw air compressor has low impact force, and the noise formed by high frequency compression can be absorbed after adding lubricating oil, which ensures smooth operation, low noise and vibration, and creates a good working environment for employees.

3. Screw air compressor in the coal mining industry application problems

The use of screw air compressors in the coal mine production process undoubtedly has many advantages, but in the operation process will inevitably appear a variety of fault problems, only to face up to these problems, one by one to check the cause of the failure, and find a solution in time in order to really play the value of the screw air compressor in the coal mine industry. Generally speaking, the main cause of screw air compressor failure is the impact of the working environment, the following screw air compressor operation process common failure problems are analyzed.

(1) Shutdown faults caused by motor overload. The main reason is that excessive current causes the power line temperature to be too high, causing the equipment to trip automatically. To solve this fault, all power supply voltages must be checked for abnormalities.

(2) Shutdown failure due to high pressure. The main reason is that the isolation valve is closed and the efficiency of the exhaust system is reduced. To solve this fault, you must check the loading solenoid valve or unloading solenoid valve, check whether it is clean or not, if there is any dust should be cleaned immediately.

(3) The Screw Air Compressor in Coal pressure value cannot be raised. The main reason for this fault is that the air content is too large and the pressure value is set too low during take-off. The specific solution is to reset the pressure value at the time of take-off, and at the same time check whether there is any air leakage phenomenon in the air compressor studio, if found, it needs to be dealt with in time.

(4) There is no abnormality in the power supply, but the light is not on. Generally caused by voltage control failure, to promptly check the power supply controller and the secondary control group whether there is a fuse, if necessary, timely maintenance.

(5) No load faults. The air compressor does not load usually because the air inlet valve does not open. The solution is to disconnect the power supply and check whether the air inlet valve opens, if it can open automatically, then check whether there is any abnormal problem with the control motor.

(6) High-temperature shutdown failure. Generally speaking, there are four main reasons for high-temperature shutdown failure, one is a poor electrical connection, you can check whether the contact of the air compressor motor is intact; the second is the high temperature of the working environment, you can ventilate the process to reduce the ambient temperature; the third is the insufficient circulation of the cooling oil, you can check whether there are impurities in the cooling oil, the quality of whether the standard; the fourth is the effect of the cooling is not good, you can check the cooling system is not a problem.

(7) Overload. Causes of this fault include low voltage, blocked pipes, worn bearings, other mechanical faults, incorrect setting data, etc. The solution is to check the setting data to ensure that it is correct. At the same time, we should do a good job of checking the voltage, bearings, pipelines, etc., and deal with any problems promptly.

(8) Electrical faults, such as mainframe overloads and stalls, occur during start-up. The main cause of this fault is that the start-up time of air end is set shorter than the star angle delay time. The solution is to reset the startup time of air end so that it is longer than (star angle delay + load delay).

(9) Exhaust gas temperature is high. An abnormally high ambient temperature has been generated due to changes in the external environment, resulting in a very high exhaust gas temperature. The corresponding solution is first to check whether the cooling system and cooling fan of the body itself are operating normally. Secondly, make sure that there are no foreign objects blocking the cooler air ducts, and if there are any problems, they need to be unblocked in time and the amount and specifications of the lubricating oil need to be carefully checked. In addition, the air filter needs to be cleaned, too much impurity in the air filter is not conducive to the control of exhaust temperature. Finally, pay attention to the regular inspection of the heat control valve.

(10) Water shortage. Failure caused by damage to the water pressure switch. The solution is to check the water pressure switch regularly, do maintenance work, and replace the water pressure switch in time when it is broken.

4. Routine maintenance and repair of screw air compressor

Coal mine production working environment is relatively difficult, in order to ensure the efficiency and service life of the screw air compressor, in addition to the correct operation in the use of the process, to understand the common failure problems and solutions, but also to do a good job of routine maintenance.

(1) To develop a good habit of regular and careful inspection of equipment, once found abnormal, to take timely measures to solve the problem, to avoid abnormal equipment into operation.

(2) Regularly check the key parts of the screw compressor, such as the filter, sensor, oil separation simplified body, hose, etc., usually once every 3 months.

(3) Master the correct method of cleaning the air compressor, clean it regularly and keep it clean.

(4) Lubricating oil plays a decisive role in maintaining the performance of oil-injected screw compressors, and improper or incorrect use can cause damage to the compressor body. Better quality oils are characterized by good oxidative stability, good foaming, fast separation and some corrosion resistance. Therefore, the use of lubricating oil should be replaced in a timely manner, the new air compressor (SKK09 head) after the first use of 4000h to replace the new oil, the second according to the normal oil change every 8000h to change the oil, the rest of the head after the first use of 500h to replace the new oil, the second 1,000h to change the oil, the third according to the normal oil change every 2,000h to change the oil once.

(5) Pay attention to the replacement of the oil filter, the new machine needs to be replaced after the first use of 500h, and then every 2,000h replacement.

5. Conclusion

In summary, the safe operation of the air compressor has a significant impact on the production efficiency of coal mines, in which the screw air compressor is better in terms of safety, convenience, energy saving and other aspects of performance, and small vibration, high efficiency, low noise, screw air compressor has been used in the coal mining industry has achieved better results, it is worthwhile to promote the use of the coal mining industry. However, at the same time, it is also necessary to take into account the high requirements of the equipment itself and the accuracy of the lubrication system, the high standard of professional skills of the field technicians and maintenance personnel, and continue to study in depth, more comprehensive and detailed mastery of the structure of the air compressor, the principle of operation, parts and components and other related knowledge and technology, to further enhance the value of the application of the screw air compressor in the coal mining industry, in order to meet the need for the modernization of the development of the coal mining industry.