Built in 1986, the plant that is now known as Coastal Carolina Clean Power (CCCP) was originally a coal-fired cogeneration plant under its first owner, Cogentrics Leasing Corp, which provided steam to Guilford Mills, an adjacent textile manufacturer of automobile interiors, and electricity to Progress Energy, the public utility for central North Carolina. In 2002, Green Power Energy Holdings acquired the plant and, due to escalating Appalachian coal prices, began to fuel the plant with biomass. In 2006, the plant was purchased out of bankruptcy by a New York-based private equity firm. After bringing in Texas-based Topaz Power Group to evaluate the facility, it was concluded in 2007 that the plant could not reliably operate on biomass fuel using equipment intended for coal. Consequently, in April 2007, the plant was mothballed, pending development of conversion plans and financing arrangements.
Topaz and the owners analyzed the economic viability of the plant and determined that, given significant market opportunities, ample nearby fuel supplies and an encouraging environment for renewable energy, they would move forward with the conversion. As such, in August 2007, funds were committed and the project to convert the coal fired power plant into a wood biomass fired power plant by replacing the majority of the fuel delivery, storage, processing metering and combustion systems of the existing Kenansville facility commenced.
CCCP received a certificate of public convenience and necessity from the North Carolina Utilities Commission to convert and operate a New Renewable Energy Facility on June 13, 2008. The facility synchronized with the Progress Energy transmission system on October 22, 2008. CCCP completed testing of the conversion project in June 2009. With the completed conversion, CCCP became the first plant in North Carolina certified to sell renewable energy credits under the North Carolina RPS (renewable portfolio standard) for both biomass electricity and steam.
CCCP received a certificate of public convenience and necessity from the North Carolina Utilities Commission to convert and operate a New Renewable Energy Facility on June 13, 2008. The facility synchronized with the Progress Energy transmission system on October 22, 2008. CCCP completed testing of the conversion project in June 2009. With the completed conversion, CCCP became the first plant in North Carolina certified to sell renewable energy credits under the North Carolina RPS (renewable portfolio standard) for both biomass electricity and steam.
The conversion required significant investment into the facility, including the following improvements and additions:
- Developing a whole new fuel yard
- Building a fuel reclamation system
- Installing new metering bins to feed biomass fuel to biolers
- Redesigning the bottom and sifting ash systems
- Upgrading the over-fire air system on the biolers
- Modifying the baghouse and installing mechanical collectors to improve fly ash capture
- Replacing the plant's control system
- Installing facilities necessry to allow the plant to handle additional waste wood
Substantial alterations were also required on the environmental systems of the plant in order to effectively burn the new fuel and remove incombustible byproducts.
The plant was capable of producing 35 MW when it ran on coal, but because of the lower BTU value of wood, the converted facility was certified to produce up to 32 MW. It is a base load facility, so it doesn’t cycle on and off with peak demand. Rather, it runs wide-open 24/7 at approximately 28 MW to meet both its thermal and energy contractual commitments.
Environmental & Water
As with all thermal generation power plants, CCCP must meet a host of requirements mandated from the state and federal government, primarily the EPA, especially regarding air and water. The facility holds all permits and approvals that are necessary for its current operations and is operated subject to such regulatory requirements.
Water for the plant comes from deep wells, and in order to make steam, it has to have a high level of purity. CCCP uses a demineralizer system to purify its water using ion-exchange resins, which remove contaminants. The resins become depleted after so many gallons of service, and have to be regenerated with sulfuric acid.
Water from the wells is pumped into makeup tanks, and from there will go to the demineralizer system. To generate electricity, a basin of water from the demineralizer system is pumped through a condenser, where the boilers will convert it to steam. As steam moves through the turbine, the pressure drops down in stages until it reaches a cooling tower at the back of the line, converting it back into condensate, which can then be recycled back into the process. A deck of distribution nozzles allows the condensate to fall back down through the cooling tower, where fans create a draft of air that flows through the water to cool it back down for reuse. The system is extremely efficient with approximately 99% of the water that is turned into steam being turned back into condensate, and recirculated into the system.
Water from the makeup tanks also supplies the fire protection system, which loops around the fuel yard and throughout the plant. CCCP has two fire pumps—an electric and a diesel backup in case of power loss. The water systems always stay pressurized, and if the fire hydrants are opened, the system will sense that pressure loss and automatically kick the fire pump on, sending an alarm to the control room.
After exiting the boilers, water goes to a neutralization tank, where it is treated for PH control and monitored for various suspended solids and metals. When the settling process is complete, the clean water is discharged to the river basin.
The system is circulatory; while steam is recycled into water to be steamed again, gases leaving the boilers cool down by heating up air and water about to go into the system. Flue gas from the combustion process is at 1,500° inside the boilers, exiting at about 600° after steam is made. On the back end of the boilers, it passes through an economizer, which cools the flue gas down to about 500° by using it to preheat water before it enters the boiler. The flue gas then passes through an air heater, where it is used to preheat the air for combustion, in the process further cooling the flue gas down to about 325°, which is its exit temperature. The gas then passes through a multi-tone dust collector where a cyclonic swirl separates the larger ash particles from the gas. The flue gas then goes into the baghouse, where it passes through a set of 8 ft. pleated bag filters. As it does, particulate matter from the gas is collected on the outside of the bags. The filtered flue gas can now exit safely into the air.
Periodically, the bags are puffed with high-pressure air to shake off the collected dust and ash, which drops to a hopper. The ash is stored in a silo before being disposed of pursuant to the environmental permit requirements.
Operations
CCCP believes that safety and environmental stewardship are top priorities. In this regard, its employees ensure and document proper compliance with OSHA regulations. This involves a great deal of training for the facility’s OMTs (operations and maintenance technicians).
The plant is operational all day, every day, 365 days a year. Each day is divided into two 12-hour shifts on a seven-day rotation—seven on, seven off. Each OMT is responsible for operations and maintenance, rather than having separate crews for each as in many plants.
Generally, one OMT runs the fuel yard at all times, primarily working from a bulldozer; two OMTs work in the plant, performing various tasks and preventative maintenance, while the fourth OMT runs the control room, which is the nerve center of the operation. The control room OMT monitors all the pressure levels and steam flow and stays in constant communication with everybody.
Fuel is a blend of wood and wood waste. Supply is sourced from about 30 suppliers within a 70-mile radius. Because of the way the bulldozer constantly moves the chips around, green chips are mixed well with dryer chips, ensuring the fuel doesn’t burn too quickly or all at once. The layering effect maintains a consistent fuel moisture content.
Trucks delivering fuel wood check in and the driver, when cleared by the OMT, dumps the truck’s contents all at once on a truck tipper. The bulldozer operator maintains two piles at all times, building one up with new material as the other is gradually depleted feeding the plant. The amount stockpiled can vary according to the time of year, but the goal is to maintain about a three-week supply at all times.
The bulldozer pushes the wood chips into a reclaimer, a chain feed conveyor that leads to a system of belt conveyors carrying the chips, eventually, to two Foster Wheeler boiler units, A and B. Chips first pass through two magnets to separate any metals, and through a disc screen that picks out over sized chips. The over sized chips drop to a pile, and twice a year CCCP brings in a grinder to reduce those chips and place them back in the fuel pile. After the disc screen and magnets, the chips convey to a processed fuel reclaimer, which has three feed points—one to the A boiler, one to unit B, and one in the middle that can feed to either or both, as needed.
CCCP burns just more than 1,000 tons a day. Each boiler burns about 25 tons an hour, fed by a metering bin that holds just under 20 tons, or about 45 minutes worth of fuel. The fuel burns in the boilers, creating steam from the purified and recirculated water. At 950°, the steam turns the turbine on a GE generator at 1,510 PSI, creating electricity. A transformer on the back end of the plant leads to a substation, and then to the public utility grid.
Since declaring commercial operations in 2009, the plant has achieved an availability factor of over 90%. According to CCCP, this availability factor exceeds considerably the industry standard for biomass plants, which is 80%.