2 Goal The purpose of this presentation is to provide project decision-makers with fundamental, and critical, boiler design information.
3 Two Basic Designs Dominate the Scotch Marine Boiler Market: WetbackDryback
4 Wetback vs. Dryback Basic construction comparison Design principles This presentation will show you the differencesBasic construction comparisonDesign principlesTechnical considerationsTotal operating costs comparison
6 Wetback Design Principles Separate tube sheets between all major temperature changes (between tube passes)Rear turnaround is totally surrounded by waterNo expensive refractory to maintainRear doors are either lightweight lift off type or split-hingedSealing materials are inexpensive, non-proprietaryEfficient “functional footprint”
8 Dryback Design Principles Common rear tube sheet between passesRear turnaround is a refractory wallDoor refractory is a maintenance itemRear door is vessel-sized in diameter, extremely heavy, and hinged or davitedSealing materials are typically proprietaryLarge “functional footprint”
9 Separate rear tube sheets WetbackSeparate rear tube sheetsSeparate tube sheets are free to expand and contract at their own rate in response to the 1300 – 1600 F temp. differential between passes.DrybackCommon rear tube sheetCommon tube sheet experiences extreme thermal stress in response to temp. differentials, increasing the likelihood of leaks.
10 Rear Tube SheetsWetback is SeparateDryback is Common
11 Rear Turnaround Wetback Surrounding water absorbs burner heat, improving efficiency by 1 to 3%.Efficiency is sustainable, as turnaround does not deteriorate over time.DrybackRear refractory wall reflects burner heat, promoting greater exterior radiation losses.Hot flue gases erode refractory baffle resulting in “short circuiting,” and loss of efficiency.
12 Rear Turnaround Wetback Better Heat Transfer at the Turnaround Means Reduced Maintenance Concerns for the Tube Ends
13 Rear Turnaround Dryback Higher Turnaround Temperatures -Up to 300F Higher- Mean a Tougher (and Often Shorter) Life for Tube Ends
14 Rear Refractory Replacement WetbackNO expensive refractory to maintainSignificant maintenance cost savings over the life of ownershipDrybackRefractory must be inspected regularly and replaced periodicallyReplacement costs are burdensome, involving proprietary sealing kits, special rigging and down time
15 Doors Wetback Front Doors are typically split-hinged, or davited Rear Doors are lightweight (< 60#) lift-type
16 Doors WetbackLarger models typically feature hinged, or davited rear doorsSplit doors maintain efficient “functional footprint”
17 Doors DrybackAnnual 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.
18 Doors DrybackLarge, heavy, single front door offers complicated multi-sectioned designAdditional costs for seal kits and labor can significantly impact annual operating expenses
19 Sealing Kits Wetback Simplified design requires far fewer seals All are non-proprietary, inexpensive, and easy to install
20 Sealing Kits Dryback“Watch Case” design requires numerous proprietary sealing kits for each inspection, and every vessel service
21 Functional Footprint Dryback Wetback Dryback: Vessel-diameter door means a larger functional footprint, demanding additional floorspaceWetback: Lift-type or split-hinged doors have minimal impact on floorspace requirements
22 Maintenance Cost Comparison The True Cost of Dryback Ownership Annual InspectionIn some cases (Ohio units, for example) dryback requires proprietary tubes, adding as much as a 50% premium to tube replacement costsLarger (increased vessel pressure drop) proprietary motors can add as much as a 350% premium to motor replacement costsProprietary sealing kits and more labor to open & close the boiler amount to a 100% premium over costs for a comparable wetbackDryback utilizes proprietary brick throat tile. Specialty labor adds a 25 – 40% premium to replacement costs.Wetback instead uses a one-piece casting.No refractory costs for a wetback vs. at least $5,000 per repair for a comparable dryback boilerRear Door RefractoryThroat TileTube ReplacementBlower Motor
23 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 endsDon’t require proprietary partsOffer maximum sustainable efficiency: Maintenance-free water backed turnaround provides better heat absorption at the most critical heat transfer point.
24 Maintenance Costs Comparison Bottom 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;
25 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 timeAverage cost to replace proprietary door gaskets; $500 each time
26 They could have bought a new boiler and burner!! 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 = $48,000Door gaskets; $500 x 2 times/year x 25 = $25,000Wetback gaskets; $30 x 1/year x 25 years = $750Total maintenance costs for 25 years $72,250They could have bought a new boiler and burner!!
27 Add In Consideration to Sustainable Efficiency Improvement Add In Consideration to Sustainable Efficiency Improvement. Don’t You Think Someone Should Know That Before Making an Equipment Decision? Any Questions?
28 After all, isn’t that the name of the game? Bottom Line: Wetback boilers deliver substantial maintenance and fuel cost savings over the life of equipment ownership, with minimal equipment downtime.Any Questions?After all, isn’t that the name of the game?