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INFLUENCE OF DESIGN AND MATERIALS WITH CONSIDERATION TO THE ANNUAL MAINTENANCE WORKS IN RECOVERY BOILERS

Simon Praszkier
Göteborg : Chalmers tekniska högskola, 2011. 104 s. Diploma work - Department of Materials and Manufacturing Technology, Chalmers University of Technology; 48/2011, 2011.
[Examensarbete på avancerad nivå]

During the last decades there has been a strive for recovery boilers with high steam outlet temperature, high pressure and load capacity. One of the reasons for this has been the increased profit from producing and selling green energy as a by-product from the Kraft pulping process. While the boilers performance has increased, the design and materials used have much remained the same as before and thus many modern paper mills have had problems with expensive equipment wastage. The annual maintenance outage is very costly for the mills when all the equipment must be inspected and, if needed, repaired. Each problem requires its specific personnel, time and spare parts which are all important resources. Furthermore security issues may require repairs to be queued and every hour is costly while production is stopped. Thus there is great value in reducing the risk of potential problems already in the design stage of the boiler. This thesis investigates how the choice of design and materials affect the annual maintenance shut down and the associated costs. The study has focused on the temperature distribution inside the superheaters, how it depends on the design and how in turn this affects the superheater corrosion. Apart from reviewing the theory behind this matter, raw steam data was collected from the mills and analyzed. Furthermore three actual cases of superheaters corrosion were investigated to find the cause of the corrosion and possible solutions. The studies revealed that many superheater corrosion problems could have been avoided using better materials and a design that reduces the temperature imbalances obtained with the conventional design. Since the pulp and paper industry focuses on buying the cheapest possible design, the costs of some design related problems were investigated. In the cases of superheater corrosion and superheater ties, these costs were compared to those of a more robust initial design. In these cases, it was found that the costs of repair and production losses caused by inadequate designs were high and that the life cycle cost of the boiler could be lower using designs with higher initial costs. Finally a design case where the maintenance perspective has been somewhat overlooked is described and followed by a suggested model for how the maintenance perspective could be included in new boiler project organizations.

Nyckelord: Recovery boiler, maintenance, corrosion, stainless steel



Publikationen registrerades 2011-03-30. Den ändrades senast 2013-04-04

CPL ID: 138438

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