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Scotch Marine Boiler Design

Scotch Marine Boiler Design . Goal The purpose of this presentation is to provide project decision-makers with fundamental, and critical, boiler design information. . Two Basic Designs Dominate the Scotch Marine Boiler Market:. Wetback Dryback. Wetback vs. Dryback.

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Scotch Marine Boiler Design

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  1. Scotch Marine Boiler Design

  2. GoalThe purpose of this presentation is to provide project decision-makers with fundamental, and critical, boiler design information.

  3. Two Basic DesignsDominate the Scotch Marine Boiler Market: Wetback Dryback

  4. Wetback vs. Dryback This presentation will show you the differences • Basic construction comparison • Design principles • Technical considerations • Total operating costs comparison

  5. Three-Pass Wetback

  6. Wetback Design Principles • Separate tube sheets between all major temperature changes (between tube passes) • Rear turnaround is totally surrounded by water • No expensive refractory to maintain • Rear doors are either lightweight lift off type or split-hinged • Sealing materials are inexpensive, non-proprietary • Efficient “functional footprint”

  7. Four-Pass Dryback

  8. Dryback Design Principles • Common rear tube sheet between passes • Rear turnaround is a refractory wall • Door refractory is a maintenance item • Rear door is vessel-sized in diameter, extremely heavy, and hinged or davited • Sealing materials are typically proprietary • Large “functional footprint”

  9. Wetback Separate rear tube sheets Separate tube sheets are free to expand and contract at their own rate in response to the 1300 – 1600 F temp. differential between passes. Dryback Common rear tube sheet Common tube sheet experiences extreme thermal stress in response to temp. differentials, increasing the likelihood of leaks. Tube Sheets

  10. Rear Tube Sheets Wetback is Separate Dryback is Common

  11. Wetback Surrounding water absorbs burner heat, improving efficiency by 1 to 3%. Efficiency is sustainable, as turnaround does not deteriorate over time. Dryback Rearrefractory wall reflectsburnerheat, promoting greater exterior radiation losses. Hot flue gases erode refractory baffle resulting in “short circuiting,” and loss of efficiency. Rear Turnaround

  12. Wetback NO expensive refractory to maintain Significant maintenance cost savings over the life of ownership Dryback Refractory must be inspected regularly and replaced periodically Replacement costs are burdensome, involving proprietary sealing kits, special rigging and down time Rear Refractory Replacement

  13. DoorsWetback • Front Doors are typically split-hinged, or davited • Rear Doors are lightweight (< 60#) lift-type

  14. DoorsWetback • Larger models typically feature hinged, or davited rear doors • Split doors maintain efficient “functional footprint”

  15. DoorsDryback Annual inspections are typically more costly for the dryback, requiring proprietary door sealing kits, special tools, and considerable manpower in “muscling” massive, and typically sagging, doors into “bolt-thru” alignment.

  16. DoorsDryback • Large, heavy, single front door offers complicated multi-sectioned design • Additional costs for seal kits and labor can significantly impact annual operating expenses

  17. Sealing KitsWetback Simplified design requires far fewer seals All are non-proprietary, inexpensive, and easy to install

  18. Sealing KitsDryback “Watch Case” design requires numerous proprietary sealing kits for each inspection, and every vessel service

  19. Functional Footprint Dryback Wetback Dryback: Vessel-diameter door means a larger functional footprint, demanding additional floorspace Wetback: Lift-type or split-hinged doors have minimal impact on floorspace requirements

  20. The Wetback Advantage:Summary Wetback Boilers - • Offer far fewer maintenance concerns: - No rear door refractory to repair - No refractory baffling to burn-out - Far less thermal stress on tube sheets, and tube ends • Don’t require proprietary parts • Offer maximum sustainable efficiency: Maintenance-free water backed turnaround provides better heat absorption at the most critical heat transfer point.

  21. Maintenance Costs ComparisonBottom Line We surveyed a few of our service reps who perform repair/maintenance work on boilers and specifically asked them to share dryback expenses. We averaged them together and came up with the following maintenance report;

  22. Based on repairs costs of a 300 HP boiler with a life span of 25 years • Average cost to replace refractory rear door; $6,000 each time • Average cost to replace proprietary door gaskets; $500 each time

  23. The rear door needs to be replaced every 3 years, or 8 times. The gaskets need replaced 2-3 times per year. • Refractory door; $6,000 x 8 times = $48,000 • Door gaskets; $500 x 2 times/year x 25 = $25,000 • Wetback gaskets; $30 x 1/year x 25 years = $750 Total maintenance costs for 25 years $72,250 They could have bought a new boiler and burner!!

  24. Add In Consideration to Sustainable Efficiency Improvement. Don’t You Think Someone Should Know That Before Making an Equipment Decision?Any Questions?

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