A company's 5000t/d new dry process cement clinker production line uses a third-generation push grate cooler, which is divided into three stages of hydraulic drive grate bed. In the past 7 years of production, the grate cooler has experienced multiple hydraulic failures. Although each failure was analyzed and eventually resolved, it was quite difficult to analyze and find the cause of each failure. In order to enable colleagues to quickly identify and handle similar faults for the first time, we have summarized the experience of handling faults that have occurred in the company for colleagues to exchange and discuss.
01 Grille bed crushed to death
Since its commissioning, the three-stage grate bed of the grate cooler has experienced grate bed compression failure, and the fault symptoms and treatment measures are the same. For the first time, the central control operation found that the feedback value of the pushing frequency of the two-stage grate bed was less than the set value; Contacted on-site personnel and found that the pump pressure gauge displayed 16MPa after the grate bed was in place, with an upward pressure of 16MPa and a downward pressure of 14.5MPa. The upward pressure was basically in place, but the downward pressure could not return to place by 60mm; Opening the inspection door of the discharge end shell of the grate cooler, it was found that the thickness of the discharge end of the two-stage grate bed was 1.2m, and the thickness of the feed end was 1.8m. When operating normally, the upward and downward pressure of the two-stage grate bed is 10-12 MPa, and the thickness of the material layer is 450mm. All other checks were normal. When the heavy load start function of the grate bed was activated, there was no significant change in the operation of the grate bed. Analysis showed that the material layer of the two-stage grate bed was too thick, and the hydraulic drive load was less than the actual load. The grate bed was overloaded and pressed to death, making it unable to operate normally. Finally, stop the kiln and wait for the temperature to be suitable before personnel enter the grate cooler to clean the clinker on 2 sections of grate beds (25 rows of grate plates in total) and 10 rows of grate plates, and then start the grate beds to operate normally.
Fault phenomenon of the grate bed being crushed: The feedback value of the grate bed pushing frequency is significantly lower than the set value, and the grate bed can hardly move up and down or can move up and down, but cannot return to its original position. The up and down pressure of the pump and grate bed is several megapascals higher than normal, the proportional valve opening reaches 100%, and the material thickness of the grate bed is significantly thicker than normal. Heavy load start-up and replacement of standby pumps have no effect. The solution is to stop the kiln and clean 1/3 to 1/2 of the clinker on the grate bed before starting the grate bed.
02 The pushing frequency of the grate bed cannot keep up
2.1 Proportional valve flow rate is too small
The driving frequency of the oil cylinder for the three-stage grate bed of the grate cooler (i.e. grate bed speed) is 0-25 times/min. The oil flow rate in the oil circuit is adjusted by adjusting the opening of the proportional valve in the system, thereby adjusting the oil cylinder driving frequency. During normal operation, the 3-stage oil cylinder has the highest pushing frequency, usually 18 times/min, and the on-site feedback frequency is the same as the given frequency of the central control. During production, there was a need to increase the frequency of the oil cylinder pushing. When the central control set a frequency of ≥ 20 times/min, the on-site feedback frequency remained at 20 times/min, which means that the usual frequency of the oil cylinder pushing could not keep up. Even after replacing the backup pump, the same situation still persisted. After several experiments, it was found that when the central control set frequency is less than 20 times/min, the on-site feedback frequency is the same as the central control set frequency, and the proportional valve opening changes proportionally with the pushing frequency, with a maximum opening of 100%; When the given frequency of the central control exceeds 20 times/min, the on-site feedback frequency remains at 20 times/min, and the proportional valve opening remains at 100%.
Analysis suggests that when the proportional valve opening reaches a maximum of 100%, the system flow rate has reached its maximum and the on-site feedback frequency has also reached its maximum. Although the central control set frequency exceeds 20 times/min, the system flow rate has already reached its maximum. Therefore, when the set frequency is high, the on-site feedback frequency cannot keep up with the central control set frequency.
The above analysis shows that the reason why the hydraulic cylinder cannot keep up with the pushing frequency is due to the small flow rate of the proportional valve. Therefore, the original proportional valve with a flow rate of 190L/min was replaced with a proportional valve with a flow rate of 220L/min. After several experiments, when the central control set frequency reached 24 times/min, the on-site feedback frequency was 23.4 times/min, the proportional valve opening was 88.5%, and the system was normal, meeting production requirements. The fault of the oil cylinder pushing frequency not keeping up was resolved.
2.2 Wear and tear of hydraulic pump
The first section of the grate bed once experienced a central control given frequency of 9 times/min, and on-site feedback frequency of 6-7 times/min. The grate bed pushing frequency could not keep up, but it could move up and down and the up and down directions could be in place. The proportional valve opening reached 100%, and the hydraulic pump pressure was 6MPa (normally around 10MPa). Switching to the backup pump was normal, and it was determined to be a pump problem. After replacing the new pump, it returned to normal. Analysis suggests that after the pump wears out, the oil inside the pump leaks and the oil supply flow rate decreases, resulting in a decrease in the amount of oil entering the hydraulic cylinder and a decrease in the speed of the hydraulic cylinder piston movement, that is, a decrease in the frequency of the hydraulic cylinder pushing. The amount of frequency reduction is related to the degree of pump wear.
2.3 Hydraulic cylinder leakage
Once, the pushing frequency of the three-stage grate bed couldn't keep up, and the pushing pressure was checked to be close to 10MPa. Replacing the spare pump was ineffective, adjusting the overflow valve was ineffective, and the proportional valve was basically fully opened. However, there was a "hissing" sound in the hydraulic cylinder on one side of the three-stage grate bed, and the cylinder body and oil pipeline were hot and hot. It was analyzed that the hydraulic cylinder was leaking. After replacing the hydraulic cylinder, it was normal.
Analysis suggests that the damaged seal of the hydraulic cylinder piston leads to collusion between the working chamber and the non working chamber, causing some oil to flow from the working chamber to the non working chamber. This reduces the amount of oil in the working chamber, slows down the movement speed of the hydraulic cylinder piston, and lowers the pushing frequency; When the oil flows from the working chamber to the non working chamber through the extremely small piston gap under pressure, it makes a "hissing" sound and causes high oil temperature, hydraulic cylinder and pipeline heating due to friction heating. When the seal of the hydraulic cylinder piston is slightly damaged, the decrease in oil pressure is not significant; When the seal is severely damaged, the oil pressure decreases significantly; The pushing frequency of the grate bed decreases to varying degrees with the degree of seal damage, and when the seal is severely damaged, it may even cause the grate bed to stop running.
2.4 Decrease in overflow value of overflow valve
The central control set a frequency of 20 times/min for the three-stage grate bed, and the on-site feedback frequency was 14 times/min. The pushing frequency of the grate bed could not keep up, but it could move up and down and the up and down directions could be in place. The proportional valve opening reached 100%, and the hydraulic pump pressure was 5MPa (normally around 10MPa). Switching to the backup pump and replacing the proportional valve still remained the same. The temperature of the pipeline and hydraulic cylinder was checked and found to be normal. Finally, an attempt was made to increase the pressure of the overflow valve and it returned to normal. Analysis suggests that a decrease in the set pressure of the relief valve causes oil to overflow when the oil pressure is higher than the set pressure, resulting in a reduction in the amount of oil entering the hydraulic cylinder and subsequently causing a decrease in the frequency of hydraulic cylinder propulsion. The amount of frequency reduction is related to the degree of pressure reduction of the relief valve.
The failure of the grate cooler to keep up with the frequency of grate bed pushing multiple times is ultimately due to a decrease in the oil flow rate that drives the hydraulic cylinder piston, resulting in a decrease in piston movement speed. When this fault occurs, carefully inspect or replace the hydraulic pump, relief valve, proportional valve, hydraulic cylinder, and pipeline along the oil flow line to identify the cause of the fault and eliminate it.
03 Conclusion
When a hydraulic drive system malfunctions, it is often difficult to identify the cause. Once the cause is found, the fault is easier to handle. Therefore, when a grate cooler malfunctions, it is necessary to carefully analyze the fault and abnormal phenomena, analyze the possible causes from the fault and phenomena, and then start by analyzing which hydraulic components are abnormal and causing these phenomena. Finally, check or replace the hydraulic components and conduct tests. In addition, it is necessary to analyze the phenomena that may occur when hydraulic components fail, which is beneficial for quickly identifying the cause of the malfunction.
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