Analysis and treatment of hydraulic failure of grate cooler

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Introduction

A 5000t/d new dry cement clinker production line of a company uses the third generation drive grate cooler, which is divided into three stages to drive grate bed by hydraulic pressure. In the past 7 years since the grate cooler was put into operation, there have been several hydraulic failures. Although each failure was finally dealt with after analysis, it was quite difficult to analyze and find the cause of the failure each time. In order to enable peers to quickly judge and deal with similar failures when they first encounter them, the company’s experience in handling failures is summarized for peers to exchange and discuss.

01 The grate bed is crushed

Since put into operation, the grate bed of the three sections of the grate cooler has been crushed to death, and the failure phenomenon and treatment measures are the same. For the first time, the feedback value of the driving frequency of the two sections of grate bed was found to be less than the set value. After contacting the personnel on site, it was found that after the grate bed was in place, the pump pressure gauge showed 16MPa, 16MPa upward pressure and 14.5MPa downward pressure. The upward pressure was basically in place, and 60mm downward pressure was not in place. Open the inspection door of the shell at the discharge end of the grate cooler, and it is found that the thickness of the discharge end of the two grate beds is 1.2m and the thickness of the feed end is 1.8m. When the operation is normal, the upper and lower pressure of the second grate bed is 10-12MPa and the thickness of the material layer is 450mm. Check that everything else is normal. Start the grate bed under heavy load, and there is no obvious change in the grate bed operation. Analysis shows that the material layer of the two sections of grate bed is too thick, the hydraulic driving load is less than the actual load, and the grate bed cannot operate normally because of overload. Finally, the kiln was stopped, and after the temperature was suitable, the personnel entered the grate cooler to clean the clinkers on the two grate beds (25 grate plates in total) and the 10 grate plates, and then the grate beds were started to operate normally.

Grate bed crushing failure phenomenon: grate bed driving frequency is significantly less than the set value and feedback value basic TDD can’t has grate bed or upward, downward back less than in situ, pump and TDD grate bed has several mpa pressure is higher than normal, the proportional valve opening of 100%, grate bed material thickness is significantly thicker than the normal, overloading startup and replacement of spare pump didn’t effect. The treatment measure is to stop kiln and clean 1/3 ~ 1/2 clinker on grate bed to start grate bed.

02 Grate bed push frequency can’t keep up

2.1 Proportional valve flow is small

The driving frequency (that is, the speed of the grate bed) of the three sections of the grate cooler is all 0 ~ 25 times /min. The oil flow in the oil circuit is adjusted by adjusting the opening of the proportional valve in the system, and then the driving frequency of the cylinder is adjusted. In normal operation, the driving frequency of the third stage cylinder is the highest, which is generally 18 times /min, and the field feedback frequency is the same as the given frequency of the central control. Once in production, the cylinder driving frequency needs to be increased. When the central control given frequency is greater than or equal to 20 times /min, the field feedback frequency is always 20 times /min, that is, the cylinder driving frequency is usually unable to keep up, so it is still the case when replacing the standby pump. After several tests, it is found that when the given frequency of central control is less than 20 times /min, the field feedback frequency is the same as the given frequency of central control, and the proportional valve opening changes proportionally with the driving frequency, and the maximum opening reaches 100%. When the given frequency of central control exceeds 20 times /min, the field feedback frequency is always 20 times /min, and the proportional valve opening is always 100%.

The analysis shows that when the proportional valve opening reaches the maximum of 100%, the system flow has reached the maximum and the field feedback frequency has also reached the maximum, although the given frequency of the central control exceeds 20 times /min, the system flow has reached the maximum. Therefore, when the given frequency is high, the field feedback frequency cannot keep up with the given frequency of the central control.

The above analysis shows that the small flow rate of the proportional valve is the reason why the driving frequency of the cylinder cannot keep up, so the original flow rate of 190L/min proportional valve is replaced with a flow rate of 220L/min proportional valve. After several tests, when the given frequency of central control reached 24 times /min, the field feedback frequency was 23.4 times /min, the proportional valve opening was 88.5%, the system was normal, and the production requirements were met. The failure that the cylinder driving frequency could not keep up was solved.

2.2 Wear of hydraulic pump

In the first section of the grate, the central control of the given frequency occurred 9 times /min, and the field feedback frequency was 6-7 times /min. The grate driving frequency could not keep up with the rate, but it could go up and down and in place. The opening of the proportional valve reached 100%, the hydraulic pump pressure was 6MPa(about 10MPa normal), the switch to the standby pump was normal. Analysis shows that after the pump wear, the oil in the pump leaks, the pump oil supply flow decreases, leading to the decrease in the amount of oil into the hydraulic cylinder, the hydraulic cylinder piston moving speed decreases, that is, the hydraulic cylinder to push the frequency decreases, the frequency decreases and the degree of pump wear.

2.3 Leakage in hydraulic cylinder

Once, the driving frequency of the grate bed in the third section could not keep up, and the driving pressure was close to 10MPa when checked. The replacement of the backup pump was ineffective, and the adjustment of the relief valve was ineffective. The proportional valve was basically fully opened.

The analysis shows that the damage of the piston seal of the hydraulic cylinder makes the working cavity collude with the non-working cavity, and part of the oil flow from the working cavity to the non-working cavity, and the amount of oil in the working cavity decreases, and the moving speed of the piston of the hydraulic cylinder decreases, so that the driving frequency decreases. When the oil flows from the working chamber to the non-working chamber through the very small piston gap under the action of pressure, it makes a “snich” sound, and causes high oil temperature due to friction and heat, and the heat of the hydraulic cylinder and pipeline. Hydraulic cylinder piston seal damage is slight, the oil pressure reduction is not obvious; When the seal is seriously damaged, the oil pressure is significantly reduced; The driving frequency of the grate decreases with the damage degree of the seal, and it may even cause the grate to stop running when the seal is seriously damaged.

2.4 The overflow value of the relief valve is reduced

3 section of the grate bed has a central frequency given 20 times/min, the frequency of feedback 14 times/min, TDD grate bed can promote frequency behind but has TDD and has to reach the designated position, the proportional valve opening of 100%, hydraulic pump pressure of 5 mpa (normal around 10 mpa), switch to the standby pump, change proportional valve, check the pipe and hydraulic cylinder temperature is normal, after finally trying to raise the relief valve pressure is normal. Analysis shows that the relief valve set pressure is reduced, resulting in oil overflow when the oil pressure is higher than the set pressure, the oil into the hydraulic cylinder is reduced, resulting in the hydraulic cylinder push frequency is reduced, the frequency reduction is related to the relief valve pressure reduction degree.

The failure of grate bed driving frequency failing to keep up with many times occurs in grate cooler. In the final analysis, the oil flow that drives the piston of hydraulic cylinder decreases, so that the piston moving speed decreases. When this fault occurs, carefully check the hydraulic pump, relief valve, proportional valve, hydraulic cylinder and pipeline along the oil flow line or replace the spare parts test can find out the cause of the fault, and then eliminate the fault.

03 Conclusions

Hydraulic drive system, the failure reasons are often difficult to find, find out why the failure is easy to handle, so for grate cooler failure occurs, the first thing to close analysis of the faults and anomalies from fault phenomenon and analysis the possible reasons, and then from the aspects of analysis which abnormal hydraulic parts will produce these phenomena, final inspection or replacement after the hydraulic pressure test. In addition, at the same time to analyze the hydraulic parts failure will produce what phenomenon, which is conducive to the quick search of the cause of the fault.

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