CHAPTER 6 – CONCLUSION
6.2 CONCLUSION
The original equipment manufacturer (Babcock and Wilcox) determined a scheduled maintenance service interval of 5 000 hours. The main components in the mill that influenced and determined this interval were the stationary throat slots and mill wear plates. These components were now proven to be improved with the introduction of new technologies:
• Rotating throat assemblies: Original stationary throat slots (5 000 hrs service life) improved by RTA installations (60 000 hrs service life).
• Triton wear plates: OEM wear plates (5 000 hrs service life) improved by Triton material (15 000 hrs service life).
In view of the successes gained with the introduction of the new technologies, there is an opportunity for less maintenance required. If a very conservative approach is taken, the mill services of 5 000 can easily be extended to 8 000 hours without risk to the mill. The mill auxiliary plant’s capability to run for an additional 3 000 hrs between services however has to be tested before this approach can be taken. The carbon seals on the PA fan for instance are prone to failure and a design out maintenance strategy will need to be adopted to eliminate this bottle neck out. In hind side, the introduction of new technologies in this dissertation is nothing else than design out maintenance; evaluating and then eliminating bottle necks in the maintenance process to achieve better performance results. The
advantage of this approach is that there is a cost saving added with maintenance and plant performance enhancement.
The airbags and classifier cone modification were introduced to improve the mill’s reliability and availability. The added benefit is life cycle cost saving with the new technologies. The high chrome mill grinding media was introduced for the purpose of extending mill grinding media life. This material change proved to be successful and with longer material life, the service intervals for ball changes and/or ads are extended. This has the benefit of being able to coordinate service intervals and ball change/add intervals. Refer back to section 4.2.1 where a 5 000 hour mill service will be done after 3 910 hrs due to the wear ion the mill balls. This modification poses a big opportunity for future maintenance cost savings due to a smaller required mill maintenance crew as the amount of required services will be less.
The author would like to suggest future work in this field where a condition based maintenance strategy needs to be investigated. The plant reliability, plant availability and then the cost of maintenance must be compared between a used base and predictive maintenance strategies. The most interesting thing will be to determine the optimum crew size to support a condition based mill approach as the inspection pillar in this approach will need to be extremely reliable for predictions, planning and scheduling of maintenance activities.
The technologies implemented was purposefully first tested for hardware performance and then only evaluated from a financial point of view. This approach assists the financial evaluation of a technology as tangible results can be used as inputs. An investment committee can then easily take a decision for the implementation of a project or not. This approach can only be taken if good references of the proposed technology are sourced from industry. Because of plant differences and various different coal qualities being pulverised in industry, imperial testing is still necessary to determine the actual impact of the technology in the applicable plant.
Due to the technologies introduced, the plant’s maintenance budget will benefit, as savings on maintenance cost will be realised. The NPV for each modification is a saving over time for the power utility. The saving on maintenance cost due to a possible smaller crew for plant maintenance was not part of the scope of this thesis. If a condition based maintenance strategy, as is being suggested, is evaluated, it will be the focus of this research undertaken.
be trended to be able to compare the maintenance results achievable by comparing a time based to a condition based maintenance strategy.
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APPENDIX A – KRIEL PERFORMANCE
TESTS
A1
Coal analysis:
For comparison purposes the following conclusions were made:
• Total moisture on Test 4 (T4) for mill 1C cannot be correct; as the mill outlet temp. during the test was ± 90°C, showing that a grab coal sample is not very accurate. • Hardgrove Index for all the tests is more or less the same and can be assumed to be
constant at 59 for all tests.
• The Calorific Value was only taken as a matter of interest.
• The ash content of tests 2, 4 & 5 differ by less than a percentage point. The differences on the other tests are as follow: T1 = 28%, T3 = 10.6% & T6 = 11.1%. The ash content will influence wear rates more than mill performance and can be assumed to constant for all tests.
•
In conclusion the coal can be assumed as a constant for comparison purposes. No major deviations were noted.