Dominion’s 585-MW Virginia City Hybrid Energy Center, located in southwestern Virginia, relies on two circulating fluidized bed boilers that burn coal and local waste coal mixed with up to 20% biomass. The project also features one of the industry’s largest air-cooled condenser systems to minimize the plant’s water usage. The $1.8 billion project entered commercial service July 10, on budget and on schedule
Dominion Virginia Power (Dominion) is Dominion Resources Inc.’s electric distribution company in Virginia. Unlike most large utilities, Dominion continues to experience load growth, anticipated to be around 4,000 MW over the next decade. In addition, Dominion has committed to meet the state’s renewable portfolio standard (RPS) of 15% generation from renewable sources by 2025. Dominion’s latest project addresses these two supply requirements with a single plant.
The latest addition to Dominion’s fleet is the $1.8 billion Virginia City Hybrid Energy Center (VCHEC), located in Wise County, Va., about 40 miles north of Bristol, Tenn. This facility burns a combination of coal and coal waste, plus up to 20% biomass (by energy input) each year, equivalent to about 1.08 million tons of wood (as-fired). The facility operating permits require burning a minimum of 10% biomass, provided adequate wood resources are available. Thus, a percentage of VCHEC’s electricity production is considered renewable under the Virginia RPS. A video featuring the power station is available at http://yt.cl.nr/iF4vA6C-Hqs.
Plant Design Recycles Waste
Two Foster Wheeler fuel-flexible circulating fluidized bed (CFB) boilers, designed to burn coal, waste coal, and wood, form the heart of the 585-MW plant. The steam produced by the boilers powers a single 668-MW nameplate steam turbine provided by Toshiba. The low-emissions CFB combustion system is further supplemented by air quality control equipment, which includes a dry scrubber, baghouse particulate filter, selective noncatalytic reduction system, and activated carbon injection system to minimize mercury emissions. Dominion notes that the Prevention of Significant Deterioration and Maximum Achievable Control Technology permits contain some of the most stringent emissions requirements for any coal plant ever in the U.S. SPX Cooling Technologies provided the air-cooled condenser, one of the largest in the nation. Emerson Process Management supplied the distributed control system.
VCHEC will burn coal waste products found in numerous waste coal piles in the region, reducing the environmental impact of water runoff from those piles that often reaches streams and rivers. Removing and burning this coal waste will enable landowners to rectify legacy environmental problems. The CFB’s fuel flexibility allows the plant to burn a wide range of regional waste coals while enjoying the use of this low-cost fuel supply.
The plant also incorporates many water-saving design features not found in the typical coal plant. For example, water recycled from leachate from the solid waste storage facility is used in the dry scrubber and for ash wetting. Water usage at the plant is about one-tenth that of the typical coal plant of similar size. Overall, VCHEC approaches zero wastewater discharge when the plant is operating.
Facility performance also was improved by recycling waste heat from the CFB boiler bed ash system discharge stream to directly preheat the boiler feedwater, improving the overall plant heat rate. This was an innovative engineering design and a first for a Foster Wheeler CFB plant design.
Construction Challenges Overcome
Dominion awarded the engineering, procurement, and construction contract for the new plant to The Shaw Group Inc. in February 2007. Full notice to proceed was issued when the final air permit was approved on June 30, 2008. Site mobilization was under way in January so that construction immediately began on the day the permit was received. Erection of the CFB boilers began in April 2009, and steam turbine erection began the following February. Boiler first fire was completed in November 2011, followed by first synchronization on Mar. 7, 2012. The plant was declared commercial on July 10, 2012.
|1. Unloading biomass. The Virginia City Hybrid Energy Center’s circulating fluidized bed combustion system is capable of burning a variety of fuels. In addition to run-of-mine coal and waste coal, the station can burn up to 20% biomass and wood chips. Here, a truck full of biomass is being unloaded at one of the two truck unloading stations. Courtesy: The Shaw Group Inc.|
The project team overcame a number of significant challenges during construction, particularly with regard to logistics, fuel handling, piping, and equipment deliveries.
Determining Laydown Yard Logistics. The project site is located in a mountainous region of southwestern Virginia with no single area on the plant site large enough for all the material storage. In fact, during construction, Shaw used nine different remote storage and equipment laydown yards. At the peak of construction, the project received more than 900 truck deliveries per month of material and equipment that was off-loaded at one of the designated remote laydown yards.
The project team solved its logistical problems using a two-pronged approach. First, radio frequency identification tags were placed on critical components for tracking, and skilled craft labor was selected to manage each laydown yard. Second, instead of bringing individual components to the job site, extensive modularization away from the power block was used. When completed, large assemblies were then delivered as the schedule required.
Locating Fuel Storage Areas. As with laydown area, finding permanent coal and wood storage areas on a limited plant site was equally challenging. The solution was to use the topography to advantage. Unloading facilities are strategically placed higher in elevation than the storage areas to minimize the civil work. The coal storage area, designed to hold enough coal for 10 days of operation, is at a higher elevation than the plant to simplify material handling. For biomass, dozers push the material against the side of the mountain, which is used as a backstop. Biomass fuel is unloaded by two truck-unloading skids adjacent to the biomass storage pile, also sized for 10 days of operation (Figure 1).
Accelerating Piping Installation. Accelerating the boiler hydrostatic tests one month for logistical reasons slowed the progress of plant piping installation on the remainder of the plant. When an analysis of the schedule found that the rate of piping installation would need to be accelerated to 17,000 linear feet per month—more than twice the initial rate—the project team established a pipe installation recovery plan, reorganized the field engineering and construction teams, and increased the resources assigned to the work. The successful recovery plan pushed piping installation to as high as 21,000 linear feet per month, and the project was soon back on schedule.
Delivering the Generator Stator. The generator stator weighs almost 800,000 pounds, making it the project’s heaviest equipment delivery. The logistics of moving the stator to the project site required crossing more than 176 miles of Tennessee and Virginia roads and securing Department of Transportation permits for the 42 bridges crossed. Each bridge permit required a study to confirm the bridge’s ability to handle the 265-foot-long, 22-foot-wide, 640-ton load (the weight of the stator, trailer, and tow vehicles)—a process that took much longer than expected. The project team resequenced the stator installation so that the delivery schedule did not affect the project’s critical path.
Recovering from Fire Damage. In February 2012, with the project 99% complete and well into the final stages of commissioning, a fire started on the roof of the boiler building in the early hours of a Saturday morning. A damage assessment found that a significant section of the building roof and more than 400 electrical circuits were damaged, requiring replacement. A strong coordinated effort and excellent work by craft labor recovered the projected three-week schedule loss in a single week. According to Shaw’s project manager, Josh Skudlarick, “This could have been a devastating event, but by a strong team effort working together with a positive ‘can-do’ attitude, we achieved a quick recovery.”
Safety Is Everyone’s Business
Safety was the number one priority on the project. Key metrics and forward-looking indicators were developed with the goal of preventing injuries. In addition, all recordable and near-miss incidents had a root cause analysis performed to further mitigate future incidents. Notably, the first 7,673,304 consecutive work hours were completed without a lost-time accident. Overall, the safety results are commendable:
- No fatalities
- Occupational Safety and Health Administration recordable incident rate: 1.68
- Lost-time accident rate: 0.12
More Biomass Plants Coming
In addition to VCHEC, Dominion also owns the 83-MW Pittsylvania Power Station in Hurt, Va., that burns biomass. Dominion Virginia Power also received approval from the Virginia State Corporation Commission in March 2012 to convert three existing coal-fired units to burn biomass. Altavista, Hopewell, and Southampton Power Stations are all single-unit plants rated at about 63 MW on coal, but they will produce about 51 MW when burning biomass. Dominion says the conversions should be completed by the end of 2013.
— Dr. Robert Peltier, PE is POWER’s editor-in-chief.