Air compressors are very important equipment for large and medium-sized power plants. With the increasing number of pneumatic equipment in power plants, its reliability is directly related to the safe and stable operation of the unit. The second phase A instrument air compressor of our factory was put into use in 2001. Since the air compressor oil temperature is too high after the operation, it is a common defect. From the beginning of this year, the air compressor output is insufficient, the air pressure is too low, and it appears. In order to ensure the safety of the air compressor, the air compressor was overhauled in the second phase of the instrument.
1 Principle and characteristics of centrifugal air compressor Firstly, the motor drives the impeller of the compressor to rotate. Under the action of centrifugal force, the gas is sucked into the diffuser to form a thin zone. Due to the continuous rotation of the impeller, the gas can be continuously The crucible is removed to maintain the continuous flow of gas in the air compressor. The gas increases the pressure due to the centrifugal action, and leaves the impeller at a large speed. The gas gradually decreases the speed through the diffuser, and the kinetic energy is converted into static pressure energy, which further increases the pressure. If the pressure obtained by an impeller is not enough, the requirements for the outlet pressure can be achieved by connecting the multi-stage impellers in series. The series connection between the stages is achieved by a bend and a reflux.
Since the temperature of the gas increases during the compression process and the gas is compressed at a high temperature, the work power will increase. In order to reduce the compression work, the centrifugal compressor with higher pressure uses a built-in cooler during the compression process. That is, the gas exiting from an intermediate stage does not directly enter the next stage, but is cooled by the volute and the outlet pipe to the intercooler, and the cooled low-temperature gas is then compressed into the lower stage through the suction chamber.
2 Analysis of the causes of faults during operation and measures taken during overhaul 2.1 Air compressor oil temperature and gas temperature high The second phase centrifugal air compressor of our plant has high oil temperature and high secondary exhaust temperature in summer, since the air compressor has been put into operation, summer Oil temperature and temperature are often high during operation to reach alarm and trip values. The second-stage air compressor cooling water pipeline is at the end of the second-stage closed water system. The water temperature is high, and the maximum temperature in summer is 38°C, which has a great influence on the oil temperature of the air compressor, but if the temperature is relatively low, Water cooling, the investment cost is large, the scheme is difficult to implement, so only the method of increasing the heat exchange effect of the cooler is used to reduce the oil temperature and temperature.
Due to the high quality of closed water in our factory, there are few impurities in the external cooler, no need to clean, and the built-in cooler has a very high heat exchange area, and the cleaning requirements are relatively high. We used soaking and rinsing methods before last summer. Clean the built-in cooler to reduce the oil temperature and air temperature of the air compressor. Because the impurities have been fouled inside the heat exchange tube, it is difficult to clean thoroughly with ordinary soaking and rinsing methods, so the effect is not obvious. This overhaul will be two. The internal copper tube of the built-in cooler is completely renewed, and the pressure leakage test is performed. The heat exchange effect can be significantly improved, which can completely solve the phenomenon of excessive oil temperature and temperature.
2.2.1A air compressor operation current value is maintained in summer 19A -22A, winter is 25A-28A, spring and autumn is 22A-25A (because air temperature affects air density, so the air compressor current value is different at different times) From this year's point of view, the air compressor current has a certain degree of reduction. In April, the current value is 20A-22A, and the air pressure also drops significantly. The average air pressure from April 7 to 12 is only 0.64-0.65MP (three units). Operation), seriously affecting the safe operation of the unit. The analysis is due to the air venting of the air cooler is not smooth, and the passage is blocked. The treatment of this defect is the same as that of 2.1. By replacing the first and second built-in coolers during overhaul. The internal copper tube is repaired after being tested and tested.
2.2.2 The blade is seriously worn, and the surface is damaged or notched. It also affects the output of the air compressor. In 2007, the air compressor of the A instrument was found to have a broken gap at the blade of the first-stage cylinder impeller (12). At that time, the manufacturer had Repair, but will affect the output of the air compressor. The air compressor impeller increases the pressure and speed of the air through its own curved groove structure and high-speed rotation. The centrifugal air compressor has about 2/3 of the pressure increase generated by the impeller. of. When the impeller of a certain stage is seriously worn, the curve groove structure of the impeller itself is changed, and the ability of the impeller to increase the air pressure and speed is reduced, so that the output is reduced. This time, in addition to the wear at the notch, the blades of the outer ring are abraded. Because the impeller is rotating at a high speed, it must be repaired by a professional department and subjected to a dynamic balance test to determine whether it can be reused. For this overhaul, the impeller is transported to the stage. The air compressor manufacturer carries out repair and upgrade processing, and is loaded back after passing the dynamic balance test.
There are many reasons for the vibration of the air compressor, such as dynamic and static friction, low oil temperature, rotor misalignment, surge, bearing damage, etc. The vibration occurring at the start is mainly caused by the surge of the air compressor. The surge of the centrifugal air compressor is because the air volume delivered by the compressor is reduced to a certain extent, the pressure generated by the air compressor is insufficient to maintain a stable conveying airflow, and the reverse flow generated by the airflow inside the air compressor is in the air compressor. Caused by turbulence or eddy currents. In order to prevent the occurrence of surge, the system sets the minimum load point throttling limit TL, and starts to open the bypass valve when the current reaches the TL value when the air compressor is running, and discharges part of the gas that is not needed by the system to the atmosphere. Therefore, the reason for the surge at the start-time air compressor is that the TL value is set too small, causing the air compressor to operate in the surge region after starting. The measure is to adjust the TL value to an appropriate size (this air compressor is about 21A). Can be completely solved. The analysis believes that the air compressor has not been able to load the phenomenon. At that time, the thermal control personnel adjusted the throttling limit to 17A, which is lower than the surge point 21A. After starting, the pressure reaches the surge point, and the bypass valve cannot be opened. Surging phenomenon. During the overhaul, the throttle limit of the air compressor was adjusted to 23A, and the phenomenon of surge was eliminated after the air compressor was turned on.
In addition, the serious wear of the air compressor impeller will also increase the phenomenon of air compressor surge. Air compressor impeller When a blade is seriously worn, in addition to the vibration caused by the imbalance of the rotor itself, the air is easily vortexed when passing through the blade, and the local airflow is blocked, resulting in vibration increase and even surge.
2.4 Compressed air water content is too large First-stage air cooler condensate automatic trap failure, condensate drain pipe blockage or air cooler leak, forming water to make the liquid level too high, the water is carried by the air flow when starting, causing compression The air content in the air is too large. This overhaul has cleaned the inside of the trap, and some damaged parts have been repaired. Scientific application of the L2000 general-purpose RF admittance level meter and common fault analysis Wei Fanghe Zhao Jie Zhao Zhanmeng (Henan Coal Chemical Group Hemei Company) The chemical branch company uses the L2000 universal RF admittance level meter to measure the fly ash and pulverized coal level, and analyzes the common problems and faults in the installation process of the level meter and the actual production application process. Handling solutions.
1 Overview The level measurement is an important measurement parameter in each production field. It is one of the five detection parameters of the instrument. The accuracy of the measurement will directly affect the stable operation of the device and equipment. The requirements for measuring instruments in different equipments and different process environments are also different. The current level measuring instruments mainly include static pressure level meter, ultrasonic level meter, capacitive level meter, radar level meter and core. Radioactive level gauge, RF admittance level gauge, etc. Henan Coal Chemical Hebi Coal and Electricity Co., Ltd. 600,000/year methanol project in the power station device bag dust removal system, coal gasification device bag filter and fly ash system using the L2000 universal RF admittance level gauge on the field equipment internal fly ash , pulverized coal, etc. are measured. The instrument is a new type of RF admittance level measuring instrument improved by PRINCO in the United States based on the principle of traditional capacitive level meter.
This paper mainly introduces the working principle and characteristics of the instrument, as well as the precautions and common fault analysis in the actual application process.
2L2000 Universal RF Admittance Level Meter Working Principle and Features 2.1L2000 Universal RF Admittance Level Meter works on the basis of radio frequency (RF) technology. The radio frequency is applied to the probe for continuous analysis of the surrounding environment. Since the dielectric constant and conductivity of all media are different from air, the change in the small capacitance caused by the probe when it contacts the medium is detected and converted by the circuit. Into the switch signal output. Its unique anti-adhesive circuit only reacts to the change of capacitance caused by the change of the level, so it can be eliminated (Continued from page 312). To prevent water from accumulating in the air compressor, the following measures should be taken: 2.4.1 The condensate of the air compressor first and second air coolers is automatically drained to the trench to facilitate inspection of the hydrophobic condition during normal operation.
2.4.2 Before starting or stopping the air compressor, manually open the manual bypass valve of the condensate automatic trap to drain the accumulated water.
2.4.3 Regularly check the hydrophobicity of the automatic hydrophobicity during operation. The amount of condensed water in the air is reduced in winter. When the automatic trap is not hydrophobic, the manual bypass valve is opened every two days to eliminate residual water and prevent dust, rust and other dirt from clogging. Hydrophobic pipe.
The second-stage A instrument air compressor overhaul ended on June 30, and was commissioned on July 1. The specific vibration and air pressure parameters are compared with those before the overhaul. Please see the following table: Table 3-1A Air compressor before and after overhaul Vibration and pressure value time first stage cylinder vibration secondary cylinder vibration outlet pressure before overhaul 0.64MP (three units running) 0.73MP after overhaul (three units running) after the first stage cylinder vibration, two cylinder vibration, both ratio There was a certain degree of decline before the overhaul, and the outlet pressure was significantly improved. There was no surge after the operation, except for the false signal generated by the accumulation of materials.
The important difference between RF admittance technology and capacitor technology is that it uses Null-KoTeTM circuit to solve the problem of hanging materials. In addition, three-end technology is adopted. The connection between the electronic unit and the probe uses a special coaxial three-terminal cable. The center line of the cable is used to transmit the capacitance change from the probe to the electronic unit, while the coaxial shield line transmits a shield voltage (admittance) signal. The purpose of the shield is to eliminate the capacitance between the center line and the ground. The ground wire is another separate wire in the cable. Thus, the cable capacitance does not affect the capacitance signal from the probe, and there is no need to "zero" the electronic unit cable capacitance to obtain an accurate reading.
The shield also prevents output variations caused by changes in capacitance caused by temperature changes in the cable. For the problem of the hanging material on the probe, a new probe structure is adopted, which has five layers of concentric structure: the innermost layer is the central measuring rod, the middle is the COTE-SHELD shielding layer, and the outermost is the grounding mounting thread, which is insulated with insulating material. Separate separately. Since there is no potential difference between the measuring rod and the shielding layer, even if the resistance of the sensing element is small, no current will flow. The electronic instrument measures only the current from the center of the probe to the wall of the tank, so that The measuring end is protected from the influence of the hanging material. Only when the liquid level in the container does rise to contact the center rod, the measured current is formed between the center rod and the ground through the material to be tested. It is a structural image of the L2000 general-purpose radio frequency RF admittance level meter. In addition, due to the large difference in ambient temperature before and after overhaul (two months apart), oil temperature, temperature, current and other parameters have incomparable factors. After overhaul, the temperature of the first stage cylinder is 38.7 °C, and the temperature of the second stage cylinder is 42.3 °C. 42.6 ° C, compared with the air compressor of the B instrument is about 3 ° C -4 ° C; on July 5, all four units are running, and the pressure of the air compressor of the A instrument is between 0.67 and 0.69 MP. It is also higher than the air pressure during the operation of the three units before the overhaul. It can be seen from the above that this overhaul has achieved the expected results.
This overhaul completely solved the situation that the second stage A instrument air compressor could not be put into normal operation, through the repair of the first stage cylinder impeller, the replacement of the built-in cooler, the adjustment of the throttling limit TL and the periodic inspection of the hydrophobicity. And emissions are extremely important for the maintenance of air compressor equipment. In addition, the replacement of some bearings in this overhaul, the calibration of the rotor dynamic balance, the replacement of lubricating oil, tubing and filter elements are also very important.
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