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APPENDICE 2

Research - Extracts From Cement Industry Survey Review of CBM (Condition Based Maintenance) at Cement Industry

Factors Affecting Cement Plant Reliability • Cement Company and factory personnel should expect that performance expectations and targets would

continuously increase. Society demands, and will continue to demand, ever-higher performance with regard to safety and environmental impact. Society, corporate shareholders and management have the right to expect continuous improvement as learning curve effects on operations and maintenance accrue, and unreliability is designed out of equipment

• The existence of a condition/performance monitoring and improvement program is not sufficient to

deliver a step change in factory and equipment reliability however. There are certain items of equipment in the cement manufacturing process where a single failure would be catastrophic for the operations and profitability of the factory. Examples would be mill drives, major process fans, kiln rollers, tyres and girth gear, among a number of others. When attempting to achieve a step change in equipment reliability it is necessary to focus on the criticality of individual pieces of equipment

• Operating a component to failure, or replacing on a periodic basis, is a decision, which depends on the

failure history and characteristics of the component. Sophisticated techniques such as Weibull, hazard or Criticality Matrix Plotting are available to guide the maintenance-planning engineer in deciding which components should be operated to failure or replaced periodically. These techniques can make a real contribution to raising the standards or maintenance planning and reliability of a cement factory. The techniques require the application of complex mathematics and must be based on sound failure histories from the particular cement factory and the industry generally. There is no practical substitute for sound industry experience, backed up by reliable data in order to apply these techniques

Reliability Techniques & Requisite Data/History • Theories of reliability and maintenance management could be applied to the cement industry, however there is a

key barrier to the introduction of many of the techniques. This is a shortage of accurate data across the industry on component failure and history. Without this failure data, preventive maintenance cannot be optimised, and the introduction of reliability modelling using techniques such as Monte Carlo simulation is impossible

• There are many tools and techniques, which can be applied to realise continuous performance improvement.

Preventive maintenance, reliability modelling and Monte Carlo simulation were mentioned in the preceding section. Condition based maintenance, machine condition monitoring and total productive maintenance could be added to this, if reliability and maintenance are the focus of attention

• Initially a simulation of the current reliability based on failure histories is constructed to form a base line for

comparisons. The effects of management interventions to improve the reliability of the cement factory are then incorporated to generate fresh models. These management interventions would involve changing spares holding, introducing equipment standardisation, changing the balance between repair and replacement of components, and introducing continuous condition monitoring

• "Reliability models are used to conduct what-if scenarios, and determine the most appropriate steps to give the

greatest and most effective improvement in equipment reliability. "These techniques are finding ever-widening application, as the power of modern computers allows the techniques to trickle down from high-powered research into industry. The techniques are reliant on a sound basis of failure history from a factory, combined with expert opinion and experience

• The models generated are then used to conduct what-if scenarios, and determine the most appropriate mix of

steps to give the greatest and most cost effective improvement in equipment reliability. A sound basis is then provided for drafting the long-term maintenance plan for the factory. Major changes in maintenance strategy in terms of spares holding, manpower levels, condition monitoring, repair, replace or retire can be justified, with the overall objective of improving the reliability, maintainability and availability of the cement factory

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• Equipment reliability figures are sometimes quoted. Percentage availability, percentage utilisation, mean

time between failures, length of time to repair in the event of failure. But the figures quoted are usually impressive begging the question whether the figures represent average or best ever performance?

• Modern technology can make a clear contribution to improving the reliability of a cement factory.

Condition monitoring via vibration analyses and thermography, plus continuous condition monitoring, of kiln shells, temperature generally, pressures and vibration, are being increasingly introduced. This can give forewarning of the deterioration of a piece of equipment, allowing remedial adjustment and maintenance to be carried out, before an unscheduled failure of the equipment

• Finally there comes a time when the retirement of a particular piece of equipment, or an entire factory should be

considered. Due to the high capital costs of a new cement factory, retirement is normally driven by market conditions, and, or the progression of cement manufacturing process technology. As considerations switch more to the reliability of operations, retirement due to escalating maintenance costs and deteriorating reliability is more likely in the future

• Studies revealed that all cement companies would benefit from improving the reliability of kiln operations and

extending their mean time between stops (MTBS). Consistent operation and equipment centred maintenance with a proper maintenance strategy are high priorities

Kilns • The range of performance within the kiln process peer groups remained a surprise. When market conditions

demand it is clearly possible to push kilns well beyond their design capacities and outputs • The greatest surprise was in the reliability performance of cement kilns. Many factories continue to struggle

to operate their kilns in campaigns extending beyond 100 hours mean time between stops • Improved equipment reliability is a key issue for cement companies throughout the world. The heart of the

cement manufacturing process is the cement rotary kiln, and the most efficient operation is achieved by long continuous operating campaigns by the kilns. Counting the number of stops best monitors kiln reliability, and calculating the mean time between stops (MTBS). A progressive increase in MTBS means progressive improvement in reliability

• A consideration is the time to repair the kiln, or any other item of equipment, in the event of failure. This

measure represents the maintainability of the equipment. Improved reliability and maintainability via increasing time between stops, and shorter time to repair in the event of stops, inevitably leads to increased availability of the equipment. Availability being the percentage of the planned operating time during which the equipment is actually in service. Higher availability leads to increased annual production and profits for the cement company

Spare Parts • Data on spares stock holdings and consumption also varies widely from factory to factory. There is no close

correlation between spares consumption, numbers employed in maintenance and the reliability of cement kiln performance. This is clearly an area where many cement factories would like to focus their improvement efforts

• Cost of failure in terms of lost output will clearly be reduced if a replacement spare is held on stock, however it

is also clear that spares cannot be held against every possible component failure. Failure histories and expert opinion will be used to determine which spares should be kept permanently available. After taking these factors into account the appropriate level of spares holding will be dependent on the estimated replacement value of the factory, and the risk aversion of the cement company. A spares holding of around 10% of the estimated replacement value of the factory is suggested as an initial guideline. Risk aversion will be dependent on the strategic importance of the output from a particular line or factory to the overall profitability of the cement company. In a sold out market situation it would be prudent to invest in a higher level of spares holding in order to better guarantee the continued supply of the market