Fig. 1. Relative shutdown time of coke plant owing to failures of different equipment categories, %: I) coke ovens, 18.4; II) coke equipment, 30.7; III) coke dry quenching unit, 20.9; IV) coke sorter, 8.3; V) external reasons, 21.7.
Intensification of cokemaking and an increase in output of the main process units require a high degree of failure-free operation of the processes and main equipment. We analyzed statistical information on operational reliability of coke equipment. The objects of study were coke batteries 7-9 of the Avdeevka Coke Plant with 4l.6 m3 oven chambers, for which high material content, significant dimensions, complexity, high equipment cost combined with severe operating conditions for the personnel are characteristic.
In view of the complex structure of a coke plant, to evaluate reliability we first considered not the individual elements, but categories of equipment. Determination of the percentage of failures for each of them enabled us to analyze the reliability of the plant as a whole and to determine the significance of the categories. After this we evaluated the reliability of the components within the category.
Analysis is based on statistical data accumulated during operation of coke equipment over 7 years (1981-1987). The information was collected at two levels: general plant level - according to daily reports of the dispatching service of the plant and department collection - according to accounting journals of the technical condition of the equipment in the departments. The superfluous information that appeared by the same data in two parallel statistical samples ensured its reliability and continuity.
The losses of coke production were broken down into five categories:
- caused by failures of the coke ovens ("drilling," breakdown of doors, frames, anchoring, rupture of the lining, failure of the heating and suction systems for the volatile coking products);
- owing to failures of the coke equipment (coke pusher, door-lifting and coal-loading machines, coke-transport car and electric locomotive);
- associated with failures of equipment of the coke dry quenching unit (lifter, mechanisms of the equipment of the quenching chamber covers, gas circulation system, etc.);
- owing to failures of the coke sorter (conveyors, grizzlies, loading station);
- owing to shutdowns of the coke batteries caused by external reasons (absence of charge, electrical power, cars under load, etc.).
Fig. 1. Relative shutdown time of coke plant owing to failures of different equipment categories, %: I) coke ovens, 18.4; II) coke equipment, 30.7; III) coke dry quenching unit, 20.9; IV) coke sorter, 8.3; V) external reasons, 21.7.
| Relative | Shutdowns of coke plant by years | ||||||||
| 1981 | 1982 | 1983 | 1984 | 1985 | 1986 | 1987 | |||
| Coke ovens | 162/14 | 116/12 | 142/16 | 198/30 | 126/31 | 139/33 | 120/48 | ||
| Coke equipment | 423/37 | 450/48 | 171/20 | 141/21 | 54/13 | 63/15 | 52/21 | ||
| Coke dry quenching unit | 351/31 | 176/19 | 156/18 | 66/10 | 93/23 | 78/19 | 31/12 | ||
| Coke sorter | 156/13 | 42/4 | 55/6 | 56/8 | 24/6 | 31/7 | 7/3 | ||
| External reasons | 56/5 | 157/17 | 146/40 | 208/31 | 109/27 | 106/26 | 41/16 | ||
| Total | 1148/100 | 941/100 | 870/100 | 669/100 | 406/100 | 417/100 | 251/100 | ||
Ai= 100Ti/T.
Fig. 2. Relative frequency of failures (a) and shutdown time (b) of various categories of coke equipment, %: I) coke pusher, 19 and 18 respectively; II) door-lifting machine, 48 and 66.7; III) coal-loading machine, 33 and 15.3.
Shutdowns associated with breakdowns of coke ovens were reduced by roughly 25$. The most significant reduction was for failures and shutdowns of the coke equipment (more than 8 times), CDQU (11 times) and coke sorter (22 times).
However, the percentage of plant shutdowns because of failures of the coke equipment for the entire considered period is very significant: for example, in 1987 more than 20%.
Thus, the greatest losses in production are associated with failures of the coke equipment. Losses due to failures of the coke sorter are relatively limited, while failures of the other three categories are at roughly the same level. It therefore follows that the reliability of the plant is limited by the reliability of the coke equipment and in developing measures directed toward increasing reliability of the entire complex this equipment category should be accorded primary attention.
We determined shutdowns because of failures of different categories of coke equipment: coke pusher, door-lifting, coal-loading machines. The failures of the coke transport car in the electric locomotive, because of their limited number (1 to 3 per year) were not considered in the calculation. The distribution of number of failures of the coke equipment and its consequences (plant shutdown time) are shown in Fig. 2.
As is evident, the highest percentage pertains to the door-lifting machine. The significant number of failures and the associated losses was caused by the operating conditions of this machine and the personnel servicing it: the immediate vicinity to the coke battery, the harmful effects of the incandescent coke cake, coke dust and thermal radiation from the oven chambers. Imperfect design of the machine, its layout and the positioning of the mechanisms that do not meet the operating requirements or technical servicing requirements also had an effect.
The consequences of failure of the coke pusher- and coal-loading machine in terms of shutdown time of the plant are similar, but in terms of number of failures a significant difference was found: 630 failures of the coal-loading machine versus 366 of the coke pusher. As is apparent, failures of the coke equipment do not' equally affect plant shutdown: each failure of the door-lifting machine or coke pusher has more serious consequences than failure of the coal-loading machine.
Fig. 3. Relative frequency of failures of mechanisms and devices of the door-lifting machine, %: I-IV) movement mechanisms 4.5; withdrawal - approach of the door-lifting device 7.2; turning of the door 2.4; lifting and installing of the door 20; V) metal structure of the machines 2; VI) coke guide 60.3; VII-IX) mechanisms for cleaning of the doors, 2; cleaning of the frames 1; movement of the frame cleaning mechanism 0.6.
Fig. 4. Relative frequency of failures of mechanisms and devices of the coal-loading machine, %: I) machine movement mechanism, 15.6; II) metal structure of the machine, 2; III-V) mechanisms for controlling the gate valves of the coal tower, 19; servicing of the gate valves and telescopes, 21.6; lifting and installing the covers of the charging holes, 41.8.
Thus, the need to increase the reliability of the door-lifting machine above all is obvious.
To determine the weak links in mechanisms of the coke equipment a more detailed analysis was carried out of statistical data, allowing for the fact that a number of mechanisms in coke equipment that are operated in departments 3 and 4 of the Avdeevka Plant were in unserviceable condition during collection of the information and were not in use. These included platform cleaning mechanisms, mechanisms for controlling the anchoring springs, for cleaning the elbows and sumps of the standpipes, for cleaning the mating surfaces and covers of the standpipes, closing the cover of the standpipe and opening the valve of the hydraulic seal, controlling the steam injection valves.
Analysis of the frequency of failures of mechanisms In the door-lifting machine (Fig. 3) showed that they operate with an unequal degree cf reliability. More than half of the failures pertain to the coke guide and the mechanism for moving it, 20% pertained to the mechanism for lifting and installing the door. The unreliable operation of the coke guide can be explained by inadequate stability of the skuttle under severe operating conditions, during which every 12 minutes the skuttle interacts with the coke cake which has a temperature of 1100°C and experiences considerable dynamic loads from emptying of the ovens. The greater frequency of failures in the door—lifting mechanisms is mostly associated with unsatisfactory cleaning of the frames and doors of the oven chambers.
Fig. 5. Relative frequency of failures of mechanisms and devices of the coke pusher, %: I-IV) machine movement mechanism, 6.2; movement of the door-lifting device, 9; turning of the door, 5; lifting and installing of the door, 9.7; V-VII) devices for pushing, 10.8; degraphitization, 19.7; levelling, 21.9; VIII) mechanism for servicing the levelling hole, 10; IX) installation of the bunker of the charge beneath the leveller, 2.4; X, XI) mechanisms for cleaning the door, 2.4 and frame 2.4; XII) metal structures of the machine, 0.5.
Fig. 6. Distribution of number of failures (%) according to reasons: I) violation of rules for operating the machines, 40.4; II) shortcomings of the design, 21.2; III) violation of routine servicing and repair, 16.9; IV) low-quality manufacture of components and part, 3; V) other reasons, 18.5.
For the mechanisms of the coal-loading machine we also obesrved a signifi¬cant divergence of the relative frequency of failures (Fig. 4). The least reli¬able mechanisms were the devices for lifting and installing the covers of the charging holes and the mechanisms of the gate valves and telescopes. They both operate in the zone of an open flame, for which reason their frequency of failures is higher.
The mechanisms of the coke pusher (Fig. 5) are characterized by a more uniform distribution in. terms of frequency failures. Exceptions of the levelling device (21.9$) and the degraphitizing device (19.7% of the failures of the coke pusher). The reason for unreliable operation of these mechanisms should be considered the very severe operating conditions: their working cycle consists of a series of back-and-forth movements that are accomplished directly In the oven chamber.
A necessary stage in analysis of reliability of the mechanisms of coke equipment is determining the reasons for failure. This enables us to understand the nature of the damage and destruction, to disclose the nature of the failures, to eliminate or delay their appearance. The distribution number of failures of different mechanisms according to reasons that cause them is shown in the form of a diagram in Fig. 6. An investigation of the reasons for breakdown showed that they mostly occur because of a violation of the rules for technical operation of the machines, shortcomings of the design,, low quality and organizational level of technical servicing and repair of the equipment.
Violation of rules for technical operation as a reason for failures of coke equipment play a much lesser role in 1986-1987 in comparison with 1981-1985. However, the distribution of relative frequency of failures of mechanisms in coke equipment for the entire considered period hardly changed at all and the mechanisms that were least reliable in comparison with the other mechanisms in 1981-1982 remained so in subsequent years.
Thus, regardless of the qualifications of operating personnel, the quality and regularity of technical servicing and repair, number of mechanisms and devices are characterized by low reliability and therefore require significant reworking.
Analysis also shows that most failures pertain precisely to those mecha¬nisms that participate directly in performance of the main processing operation with respect to servicing of the coke ovens - charging and delivery of coke. They operate under extremely unfavorable conditions. It is therefore important to further increase requirements on their design solution and selection of materials. Selection of operating conditions and development of a proper strategy for scheduling repairs and technical servicing of the mechanisms also merit attention. These requirements have still not been fully considered, which has
made the coke equipment for batteries with 41.6 m3 oven chambers one of the bottlenecks in a coke plant.
CONCLUSIONS
1. The least reliable coke equipment is the door-lifting machine.
2. The mechanisms that limit the overall reliability of the machines: for the coke pusher - levelling and degraphitizing devices; for the coal-loading machine - mechanism of the dampers and telescopes, mechanism for lifting and installing the cover of the charging holes; for the door-lifting machine - coke guide with the movement mechanism, mechanism for lifting and installing the door of the oven chamber.