Waste-to-Energy Plant Icon Goes Up in Blaze
April 30, 2024
This article originally appeared in the Nov/Dec 2002 issue of DEMOLITION.
Background and Plan
The Nashville Thermal Transfer Corporation (NTTC) has operated a waste-to-energy plant in the southeasterly sector of the Central Business District of downtown Nashville for almost 30 years. The NTTC facility produces and distributes chilled water and/or steam to 39 downtown commercial and government buildings — including those of the Metropolitan Government of Nashville and Davidson County (Metro), the state of Tennessee and others, including the NFL’s Tennessee Titans, and for the purposes of heating and cooling.
The plant has been in operation since 1974, with expansions in 1976 and 1984. Through the spring of 2002, the NTTC facility had the capacity to convert 1,050 tons per day of waste to energy, producing 250,000 pounds of steam per hour using three waste boiler/incinerators, two natural gas-fired backup boilers, four chillers to produce chilled water for district cooling, and a turbine-generator to produce electricity for in-house use and for sale to the Tennessee Valley Authority (TVA).
Metro estimates its annual municipal solid waste generation at 730,000 tons, with about one-third of this material going to the NTTC facility.
Ironically, as part of his announced Solid Waste Master Plan in 2001, Mayor Bill Purcell slated the NTTC facility for closure within three to five years, replacing it with a new Energy Generating Facility (EGF) utilizing natural gas and electricity rather than municipal solid waste as its fuel sources. This decision was made in the context of promoting more recycling, taking advantage of less expensive waste disposal alternatives and freeing the NTTC site for downtown redevelopment.
The mayor’s decision was based in part on the results of a study begun in July 2000 to evaluate the solid waste management alternatives for Nashville’s metropolitan aera. The study, conducted by Gershman, Brickner & Bratton Inc. (GBB) of Fairfax, Virginia, found the District Energy System (DES) in sound shape and providing a valuable service to its customers; however, from an economic standpoint, the system could not continue to be fueled by solid waste. In light of this, Metro decision to transition away from waste-to-energy-provided steam and chilled water, to see alternatives for the replacement of the EGF and the continuation of the service it currently provides, and to allow for adding new DES customers.
On April 19, 2001, the NTTC Board of Directors approved an Interim Business Plan that included a closing date for NTTC of Sept. 30, 2003, but keeping all steam and chilled water customers on the system. Metro issued a request for proposals, seeking private companies to take over the operation, maintenance and management of its downtown DES, including the design and construction of a new steam and chilled water generating facility to replace NTTC’s currently operating waste-to-energy plant. Constellation Energy Source Inc. (CES), headquartered in Baltimore, was ultimately contracted as Metro’s energy services partner.
The new Energy Generation Plant, with a fixed construction cost totaling approximately $45 million, will be housed in a new 40,000-square-foot, two-story building. The steam production facility subsystem will consist of four 65,000 pounds-per-hour (PPH) boilers to produce 260,000 PPH of 150 PSIG steam for delivery to the DES distribution system. The eight-unit chilled water production subsystem will provide an installed capacity of 20,800 tons of 42 degrees Fahrenheit chilled water for delivery to the DES distribution system.
The Fire
On May 23, 2002, at approximately 8:45 p.m., a three-alarm fire broke out within the waste tipping floor at NTTC, causing more than 100 firemen to respond to the blaze that could be seen for miles of the downtown area. However, for Metro, the fire the night of May 23 became the “line in the sand” for the rapid transition of the entire NTTC system from solid waste-derived energy to more conventional fossil fuels. Fortunately for NTTC’s energy customers, the fire was contained to the solid waste receiving and handling side of the facility and all of the boilers, chillers and primary electrical supply equipment were on the other side of the large vertical reinforced concrete and block wall between the two portions of the plant.
Within about 36 hours of the Fire Department giving the NTTC staff and Metro consultants/contractors the all-clear to attempt to restart the plant’s energy supplies using the natural gas boilers at the plant, NTTC was back on line. Within two weeks, two additional natural package gas boilers, previously ordered by NTTC for added reliability, were installed to provide additional capacity.
The fire damage to the south side of the NTTC facility where the waste was received and handled was extensive. The 15,000-square-foot drive-through receiving building where the trash trucks entered and discharged waste materials was totally destroyed. The fire was so intense on the west side of the tipping floor that several of the 100-foot-long, 4-foot-deep steel beams that supported the roof were left sagging an estimated 1 foot below horizontal and laterally twisted shearing some of their large tie-in support bolts. Three of the 30-foot-high concrete building panels (each weighing about seven tons) that were part of the building sidewalls and structurally wrapped the top of the crane bay adjacent to the roof were loosened and fell during the fire. One of these high panels fell about 60 feet and crushed the unoccupied night watchman’s portable trailer located below the tipping area’s west wall.
Due to quick action, the Nashville Fire Department contained the fire to the tipping area, but hundreds of tons of very wet and unburned trash were left on the tipping floor and over 5,000 tons in the 10,000 cubic-yard waste storage pit. The waste pit was previously serviced by three overhead cranes and provided about five days of fuel supply for the plant’s combustion needs. As a result of the fire, this waste was wet, smoldering in areas and continuing to decay as each hour passed.
The Demolition
Immediately after the fire was under control and the area deemed safe for access, the loadout of wet and charred waste ensued. This was the most fire-damaged material and needed to be immediately removed to allow access to the building and the larger waste pile in the NTTC pit.
As a result of the fire, Metro used its emergency procurement powers and contacted several major demolition contractors in the greater Nashville area. After reviewing the equipment availability and costs, hourly labor rate structures, suggested plans for safety assurance during the demolition and waste excavation/removal process, as well as addressing concerns about methane generation within the waste pile and potential for spontaneous fires within the smoldering waste, Metro stimulated the working relationship and cooperation of two of the larger demolition firms in Nashville to address the immediate needs of the multiphased demolition project.
GBB has served as Metro’s project administrator for the fire-damaged demolition and removal of the estimated 10,000 cubic yards (over 5,000 tons) of waste stockpiled in the storage pit. Metro contracted with Environmental Abatement Inc. (EAI) of Hendersonville as the prime contractor, and Levy Wrecking Company of Nashville was their main subcontractor on the removal of the tipping hall building and extensive vertical concrete building panels damaged during the fire.
Levy removed the 15,000-square-foot steel tipping building in about three weeks from mobilization. Both an 80-ton and 90-ton crane were used in the process. Since the building’s damage was worst on the west side, this area was removed first. Due to the buckling and falling of several of the high concrete building shell panels during the intense heat of the fire, it was decided that all of the upper concrete panels should be removed for safety purposes.
In total, Levy removed approximately 58 large concrete panels, the majority weighing approximately 14,000-16,000 lbs. each. When initial attempts to use the cabled lift-lugs originally used to install the panels failed, it was decided to subcontract the core drilling of four new 3-inch-diameter holds in the top of each 4-inch-thick panel. Once Levy completed the removal of the overhead concrete panels on the west and south sides of the pit area, EAI was able to begin waste removal from the west side of the pit.
The demolition and removal of the total tipping floor building and the west side panels took Levy four weeks. Once the east side of the building was removed, it took Levy another week to remove the final dozen or so large concrete panels. This included the use of a large 300-ton crane with a 210-foot working radius to safely extend from the front edge of the tipping floor to the south, to the far northeast and northwest sides of the crane bay structure.
EAI initially used three excavators located on the concrete tipping floor to remove pit waste, loading out into roll-off containers and trailers. Initially, the two main excavators with grabble buckets were able to reach out into the pit and pick out the garbage. However, as waste was removed, the top of the waste pile got lower into the 35-foot-deep pit. At times, two excavators were actually working from on top of the waste within the storage pit area, unloading onto the tipping floor.
To reach the bottom of the pit, an extended boom with a 0.85-cubic-yard bucket was placed on one CAT excavator and used to drag material from the bottom of the pit up the waste’s angled working face until one of the main excavators could grab and pull the material out of the pit.
The unknown nature of the waste stream caused Metro and the two demolition contractors to proceed with caution and err on the side of safety at all times. During the demolition process, the levels of methane in the pit from the decaying waste and the actual amount of water in the pit from the large amount poured on the waste to gain control of the fire were concerns. EAI subcontracted to K.S. Ware for the hourly monitoring of gas levels, as well as providing a certified industrial hygienist (CIH) at the site.
The original time estimate for removing the garbage from the pit was three weeks, and this time frame was met. Limited smoldering and corner fires were initially encountered at the site, but these did not persist once the top of the pile was removed. Fortunately, the garbage removal process did not encounter any unusually high methane levels that would have slowed the demolition process.
The EAI crew started mobilization and removal of the burned waste remnants on Friday, May 28, and the final major loadout of waste in trailers from the pit was completed on Saturday, July 6. EAI worked on minor punch list items and site cleanup through the following week.
In all, over 7,000 tons of waste was removed from the tipping floor and pit. The demolition of the tipping building generated over 85 tons of scrap metal that were recycled. Specifically, 27 loads of carbon steel weighing 84 tons and approximately one ton of aluminum scrap were recycled. The 30-foot-high concrete panels that were crane-lifted from the building weighed over 300 tons and were crushed up at the site by the excavation buckets and sent to a Class 1 Inert Landfill. The tear-off and replacement of the metal-decked roof over the crane bays resulted in the additional salvage/recycling of over 38,000 pounds of scrap metal.
The Reality of Change
While the NTTC facility provided almost 30 years of service to downtown Nashville buildings, its days were numbered, and change was in the works. However, the fire of May 23 tested the ability of Metro and NTTC staff, Metro consultants, and hired contractors to work together efficiently and effectively to meet the continued demands of the downtown DES customers, most with no alternative internal backup of their own. The waste burned on May 23 was the last at NTTC, as the three overhead cranes used to load the waste were destroyed beyond repair. The two package boilers added to the NTTC will be used in concert with the original natural gas units for the next two years until the new Metro plant being built by CES is completed. The new Energy Generating Facility is starting construction now and is planned to be operational in spring 2004.
Once the Energy Generating Facility is completed, Metro will issue a demolition and salvage request for proposal for the largest and remaining portion of the NTTC facility. Thereafter, only the stories of this solid waste industry icon will remain.