Although these data are specific to the Widnes plant, I have presented it as a historical document because it exemplifies principles general to the cement/sulfuric acid plants.
Widnes Kiln Downtime Analysis
Detailed downtime logs were given in the Chief Engineer’s monthly reports, some of which are to be found in the Catalyst archives (#2009.1). A subset of these, covering the periods 29/7/1968 to 28/12/1969 and 2/12/71 to 30/9/1972, was analysed as follows, aggregated for the two kilns, which were not significantly different.
Extended Stops (hours) in descending order of length:
- 814 hours: Refractories: complete in around 100 hours, and the kiln was kept down due to power restrictions during the 1972 miners’ strike.
- 772 hours: Gas cooling tower
- 596 hours: Refractories, clinker coolers
- 552 hours: Refractories
- 463 hours: Nose refractories
- 387 hours: Nose refractories
- 387 hours: Refractories
- 374 hours: Clinker coolers: complete in around 170 hours, and the kiln was kept down due to 1972 rail strike.
- 312 hours: Refractories repaired, but caused by lack of meal due to rawmill failure.
- 279 hours: Refractories
- 266 hours: Refractories
- 239 hours: Refractories
- 232 hours: Feed pipe broke: refractory repairs followed
- 174 hours: Refractories
- 149 hours: Refractories
Long stops (12-120 hours):
- 84 hours: Catalytic converter
- 72 hours: Converter heat exchanger
- 71 hours: Converter heat exchanger
- 50 hours: Firing pipe
- 48 hours: Feed pipe
- 32 hours: Catalytic converter
- 29 hours: SO3 cooler
- 29 hours: Catalytic converter
- 23:55 hours: Absorbers
- 20:45 hours: Feed Pipe
- 17:30 hours: SO3 cooler
- 15:00 hours: SO3 cooler
- 14:50 hours: Kiln feed elevator
- 14:00 hours: Catalytic converter
- 12:30 hours: Precipitator
- 12:20 hours: Converter heat exchanger
Short stop duration:
| Duration hr | Number |
|---|---|
| 0-¼ | 42 |
| ¼-½ | 34 |
| ½-1 | 59 |
| 1-2 | 48 |
| 2-3 | 45 |
| 3-4 | 36 |
| 4-5 | 13 |
| 5-6 | 12 |
| 6-7 | 5 |
| 7-8 | 4 |
| 8-9 | 2 |
| 9-10 | 5 |
| 10-11 | 1 |
| 11-12 | 2 |
Mean Time Between Stops for the period was 116.4 hours.
| Causes of short stops | Number |
|---|---|
| Cement Plant: | |
| Firing pipe | 46 |
| Kiln feed | 21 |
| Clinker conveyors | 15 |
| Refractories | 8 |
| Clinker coolers | 5 |
| Kiln rollers | 2 |
| Kiln drive | 2 |
| Lack of rawmix | 1 |
| Kiln flush | 1 |
| Acid Plant: | |
| Catalytic converters | 48 |
| Converter heat exchangers | 48 |
| Blowers | 41 |
| SO3 coolers | 37 |
| Ducting | 20 |
| Gas coolers | 6 |
| Acid coolers | 2 |
| Precipitators | 2 |
| Tail gas plant | 2 |
| Absorbers | 1 |
It can be seen that two-thirds of the short stops are caused by the acid plant, and these contribute proportionately to the length and duration of refractory stops, which are the main cause of downtime. As with other Anhydrite Process plants, the coarse rawmix, made in the mistaken belief that it minimized dust loss, contributed to difficult burnability, and consequent further stress on burning zone refractories. Leaving aside these special causes, the runtimes of the kilns were in line with good cement industry practice.