April 9-12, 2006
APPA 2006Engineering & Operations Technical Conference
Sacramento, California
Reduction of Rainwater Intrusion Into Deerhaven Unit 2 Coal Pile Reclaim System
John B. (Jack) Miller – Black & VeatchAli McDaniel – Gainesville Regional Utilities
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Overview
Describe the Process That Lead to the Decision to Install the Cover
Review the
Design Development
Design Features
Construction Process
Examine the Initial Measurements of Its Effectiveness
Gainesville Regional Utilities (GRU) Recently Installed a Rain Shield Over the Coal Reclaim for Their
Deerhaven Unit 2. This Presentation Will:
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About the Authors
Ali McDanielMaterial Science Engineer – GRU’s Project and Construction Manager for This Project
Jack MillerMechanical Engineer – Black & Veatch’s Project Manager for the Feasibility Study and Detailed Design
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About GRU
GRU Is a Municipally-Owned Utility Serving the City of Gainesville, Florida for 100 Years
Gainesville Is Located in North Central Florida
GRU Serves 87,000 Retail and Wholesale Customers
Owns and Operates Two Power Plants, John R. Kelly and Deerhaven Generating Stations
Installed Capacity of 611 MW to Serve a Peak Demand of 450 MW
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About Deerhaven Unit 2
Deerhaven Unit 2 Is a 235 MW Pulverized Coal-Fired Steam-Electric Generating Unit
Commissioned in 1982
Burns Low Sulfur East Kentucky Compliance Coal
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Aerial View of Deerhaven Generating Station Looking North Northeast
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Problem Definition
Rain!!
Wet Coal
O&M Impacts Plugging in the Reclaim, Conveying Storage and Milling Systems
Negative Impact to Thermal Efficiency
Can Cause Significant Unit Derates and Relatively Expensive Replacement Power
In 2003, Wet Coal Effects Directly Resulted in the Need for 12,879 MWh of Replacement Energy
Annually 58 inches max.48 inches avg.34 inches min.
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Overview of Coal Handling System
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Highlights ofCoal Handling Operations
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Highlights of Coal Handling Operations
Coal Is Delivered by Unit Trains Carrying About 11,000 Tons
Unloaded From Track Hopper at 3,000 TPH
Conveyed to Dual Discharge Fixed Boom Stacker
Can Build 1,800 Ton Conical Coal Pile on North and South Sides
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View of Stockout Tower Looking West
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Highlights of Coal Handling Operations
Reclaim System Operates at 500 TPH (2" x 0" Coal at 15% Moisture)
Four Below-Grade Hoppers: Three on the South (Active Reclaim)
One on the North (Emergency Reclaim)
Hoppers Feed a Common 30-Inch Belt Conveyor
Conveys Coal to the Six Storage Bunkers Via a Crusher Tower
Bunkers Hold 18 Hours of Fuel at Typical Burn Rate
Coal Is Fed to Burners Through B&W MPS 75N, DVS Rotating Classifier Pulverizers
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Graphic Display – Stockout and Reclaim System
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Coal Pile Management Equipment
Excess Coal Is Moved From Stockout Pile to Long-Term Storage Using Dozers and Front-End Loaders
Takes Three Machines Three Days to Move and Spread 11,000 Tons
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Analysis and Developmentof Solution
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Analysis and Development of Solution
Wet Coal Effects Had Been Manageable Until Coal Fines Content Increased
In Late '90s, Began Using Lower Sulfur East Kentucky Coal
Sizing Changed From Nominal 2" x 0" to ¾" x 0"
Fines Increased Considerably
More Conducive to Plugging When Wet
More Conducive to Excessive Ratholing Above the Reclaim Hopper
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Ratholing at the Center Reclaim Hopper
Ratholing Provides Direct Path for Rainfall and Runoff to Enter the Reclaim Hopper and Flow Directly Onto Reclaim Belt Primary Source of Entrained Water in the Coal and Attendant Problems
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GRU Study
Correlation Between Rainfall and Need for Replacement Energy Due to Unit Derates
Short-Term Rain Events of Greater Than 2 Inches Cause Derates on a Proportional Basis More Rain, More Replacement Energy Needed
Results for 2003
Months inWhich Derates
Occurred in 2003
20-Year Average Rainfall Recorded
at Deerhaven (Inches)
Actual RainfallRecorded at Deerhaven in 2003 (Inches)
Duration ofDerate (hrs)
Replacement Energy
Necessitated byDerate (MWh)
February 3.1 7.2 29 1,366
March 4.5 10.9 74 4,592
May 2.5 1.9 43 2,365
June 6.9 10.1 55 4,132
July 6.1 4.0 5 425
Totals 23.1 34.1 207 12,879
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B&V Study
Potential Solutions
Improve Pile Management Practices Reduce Fines Stratification
Modify Reclaim Equipment Water Collecting Gates
Install Alternate Reclaim Above Grade, Dewatering Dozer Trap
Install Cover Over Active Reclaim Intercept Rainfall – GRU’s Preferred Alternative – Estimated Cost $1.5 Million
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GRU Economic Analysis
Focused on Cost of Replacement Energy Resulting From Unit Derates
Recognized That 2003 Experience (12,879 MWh) Was Based on Above Average Rainfall
Conservatively Assumed Average Annual Derate of 40 MW for 120 Hours
Correlates to 4,800 MWh of Replacement Energy
Based on Fuel Forecast (Natural Gas and Coal) – Avoidance of Replacement Energy Yielded and IRR of 13.4% Satisfied GRU Threshold
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Design
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Functional Design Criteria
Sized to Prevent Rainfall From Impinging on Active Reclaim Area
High Enough to Accommodate 1,800 Ton Conical Pile
Maximize Area of Coverage Within Space Between Stockout Tower and Perimeter Drainage Swale
Support System Cannot Impede Movement of Coal by Mobile Pile Management Equipment
Support Structure Should Be Resistant to Contact by Mobile Equipment
Must Accommodate Night Time Pile Management Operations
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Other Design Criteria
Design Life: 30 Years
Environment: Subtropical Climate Hot Summers; Mild Winters
Temperature and Humidity: 70 F and 90% – Design115 F and 100% – Extreme
Max10 F – Extreme Min
Rainfall: 10-Year Return Period, 24-Hour Event 0.30 Inches Per Hour, 7.2 Inches Total
Wind Speed: Per the Florida Building Code (FBC)
Seismic: Aa = .05; Av = .05, Soil Profile S-3
Grade: 189 msl
Lighting: 5 Footcandles of Illumination, Ability to Control Lighting Level
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Design
Foundation System
16 – 48 Inch x 55 Foot Drilled Piers
Reinforced Concrete Pier Cap Two Piers Per Cap
2' x 3' Reinforced Concrete Grade Beams
Cover Support Structure
Concrete Columns
Precast Concrete Beams
Top of Support Is 25 Feet Above Grade
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Cover Support Structure – Concrete Columns and Beams
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Cover and Its Structural Framework
Initial Concept Was a Geodesic Dome
Finally Selected a Rectangular Plan Arrangement to Maximize Coverage Within Allotted Area
Arched North to South Clear Span of 175 Feet
160 in Length East to West and 91 Feet Above Grade at High Point of Arch
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Cover and Its Structural Framework
Trusses:
Fully Triangulated Space Truss
Truss Depth Is 8 Feet
7 Trusses With 25 Foot Spacing
Fabricated From 8 Inch Wide Flange Aluminum Struts
Lateral Stability Provided by 4 Inch Aluminum Tubing
Framework Is Bolted Together
Skin: 0.050 Inch Thick Aluminum Skin Is Bolted to Frame
Lighting:
Interior: 24 HPS Fixtures Attached to Inside of Cover Framework
Exterior: 8 HPS Fixtures Attached to Support Structure
Each Switch Controls Six Fixtures Provides Adjustability
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Construction
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Construction
Contracting Approach
Engineering – Black & Veatch (Owner’s Engineer)
Cover Supply (Detailed Design, Furnish and Erect) – Conservatek
General Construction – Yates Construction
Construction Management – GRU
Overall Schedule
Design, Fabrication and Delivery of Cover – 60 days
Erection of Cover – 60 days
General Construction
Original Schedule Was 4 Months
Actual Schedule Was 8 Months
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ConstructionSite Preparation
For Foundation and Support Structure Construction – Removed 50% of Coal From Active Pile
For Erection of Cover Framework and Skin – Rebuild Minimum Coal Base of 12 Feet to Function as Construction Platform
Coal Base Filled the 175' x 160' Covered Area Plus 30 to 50 Foot Margin on the East West and South Sides
Foundations and Concrete Support Structures
Six Week Delay in Mobilizing Drilled Pier Contractor
Encountered Unforeseen Subsurface Obstructions Causing Damage to Caisson
Installed 16-48 Inch Diameter Drilled Piers
Tied Pairs of Piers Together With Reinforced Concrete Pier Cap
Tied Outboard Pier Caps Together With 2 Foot by 3 Foot Grade Beams
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Drilled Pier Caisson
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Drilled Pier Installation Equipment
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Damaged Drilled Pier Caisson
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Pier Cap Form Work
Foundations and Concrete Support Structures
Poured in Place Concrete Columns Were Constructed on the Pier Caps
Precast Support Beams Were Placed on Top of the Columns
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Concrete Support Structure – Lifting of Precast Beam
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Concrete Support Structure – Positioning of Precast Beam
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Concrete Support Structure – Setting of Precast Beam
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Completed Concrete Support Structure
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Erection of Cover and Supporting Structural Framework
Unique Design of Cover Necessitated Custom Designed Lifting Towers
Framed Two Bays at a Time Lift and Proceed. Once Peak Was Reached, Sheeting to the Mid-Point of the Cover Was Accomplished
The Process Was Conducted Two Bays at a Time in That Manner Until Complete
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Erection Towers and Partially Completed Trusses
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Positioning Erection Towers – Partially Completed Trusses
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North Side of Trusses Resting on Concrete Support – Skin Partially Installed
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Skin Installation About 2/3 Complete – Repositioning South Towers
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Skin About 2/3 Complete – Opening for Stockout Chute Almost Complete
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View of Erection Towers on South Side and Underside of Trusses
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Close-Up View of Erection Towers on South Side
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South Side of Cover Being Raised Onto Concrete Supports
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Completing Setting of Cover on Concrete Supports
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Completed Cover Looking Northwest
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Completed Cover Looking Northeast
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Completed Cover Looking North From Tripper Gallery
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Cost of Cover
Preliminary Estimate Was $1,500,000 – Plus or Minus 30%
As Bid Costs Totaled $1,718,543
Final Cost Was $1,890,573
Subsurface Difficulties
Additional Dewatering Requirements for Foundation Work
Extended Schedule
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Initial Measurement of Results
Rainfall During First 5 Months of Operation Was 60% Above Average
No Wet Coal-Related Derates or Replacement Energy Requirements During That Time!
Estimated Savings Potentially Accruing From Avoided Replacement Energy Could Have Been $660,000
April 9-12, 2006
APPA 2006Engineering & Operations Technical Conference
Sacramento, California
Questions?