ANALYSIS AND OPTIMIZATION OF SYSTEMS AVAILABILITY IN SUGAR, PAPER AND FERTILIZER INDUSTRIES

Abstract

The sugar, fertilizer, paper mills etc. are complex, repairable engineering systems comprising of a large number of subsystems interconnected in series/ parallel or both. For efficient working, it is essential that the various subsystems of the plants remain perpetually in upstate. However, in reality the subsystems are subject to random failures. These however, can be inducted back into service after repairs/ replacements. The failures of the subsystems and their components are difficult to predict precisely, as they depend upon the operating conditions and repair policy used. From economic and operational point of view it would be desirable to ensure the maximum possible level of system availability. This thesis is devoted to the analysis and evaluation of overall as well as various subsystem availabilities of the sugar, paper and fertilizer plants. Based on the analysis appropriate maintenance strategies for all the cases have been worked out. Subject matter of the thesis has been presented in different chapters as follows: Chapter I - Introduction and literature survey Chapter 2- Availability analysis of sugar plants Chapter 3- Availability analysis of paper mills Chapter 4- Availability analysis of fertilizer plants Chapter 5- Maintenance scheduling for high availability Chapter 6- Optimum repair/ operational budget Chapter 7- Conclusion and scope for future work. Besides, the thesis also includes a list of available references connected with the present work. Repairable engineering systems are characterized by a large number of interconnected components with their own failure behaviour and repair time distribution. System availability in such cases is a complex function of failure and repair time distributions of the components in the system. Survey of literature reveals that majority of the published work deals with idealized systems with limited applicability. The analysis based on Markov model apply to series, parallel combined series/parallel systems. Several computer simulation models are also available. For the performance analysis of sugar, paper and fertilizer plants, the availability models have been designed by application of Chapman— Kolmogorov equations and the steady state subsystem/system availabilities are obtained by the use of Laplace Transform approach. The system models for the three plants have been based on the actual study conducted in medium sized sugar, paper and fertilizers plants located around Roorkee. The failure time/repair time data as well as the current maintenance practice in the plants were studied. Chapters 2, 3 and 4 present the availability models for three industries. Based on the availability models, the sensitivity analysis for various assumed operating conditions were carried out to assess the relative importance of the various subsystems vis—a— vis their failures, repairs, reliability etc. The analysis also incorporates the effect of common cause failures. Based on these models the best plant operating policies and their preventive maintenance schedules have been worked out and compared with the existing practice. Chapter 6 is devoted to minimizing the maintenance cost allocation to various subsystems so as to achieve optimum repair policy. For this Lagrange's multiplier technique has been employed. The findings of this thesis have been discussed with the management of the three plants with a view to apprise them of the potential benefits that would 9ccruthrough the implementation of the results.