Rock Recycling Revolution

If the heart of the environmental movement is conservation and recycling, recent projects undertaken by Duke Energy and its partners should have green activists thrilled to their core.

The utility provider has used the byproducts of its low-pollution power generating operation to cut down on the amount of resources used to construct their Duke Energy Center in Charlotte, N.C. It’s a 48-floor skyscraper that not only has locally-sourced construction materials but also some construction materials that are the byproducts of the company’s coal-fired power plants. It is the second-tallest building in Charlotte and the city’s largest building in terms of square footage.

The Duke of LEED

The Duke Energy Full Circle Gypsum Recycling project recycles calcium sulfate hydrate, a byproduct of clean coal technology, to make gypsum wall board. The board is then used as construction materials for projects at the company’s own facilities. The project is so well managed that 100 percent of the gypsum used at the Duke Headquarters LEED project originated from the company’s own power plants.

Duke Energy supplies energy for approximately 4 million customers from both traditional and clean coal processes. The calcium sulfate hydrate used to create the wall board is created when scrubbers remove sulfur oxides from the flue gas when coal burns. Pulverized coal is mixed with air and, when burned, it heats a boiler that produces steam which turns a turbine and electricity is generated.

When that coal and air burns, as hot as 3,000 degrees Fahrenheit, sulfur dioxide is released. Sulfur dioxide, or SO², is harmful to the environment and a component of acid rain. The boiler channels the sulfur dioxide and the other flue gases through a system of scrubbers which use sorbent particles, mainly limestone, which removes the sulfur and allows the plant’s smokestacks to release mostly steam.

To make this kind of project go off successfully, the company has had to inspect its own operations closely. Duke has had to look at the byproducts of their own projects to see what materials can be turned into construction materials. They also have had to shepherd their materials from the point where they originated (the coal processing plants, for instance) through the process that turns them into construction materials, on to the end where they are installed in their facilities.

That means covering a lot of bases. First, the project specifications for construction require that all wall board used in the buildings has to be made from recycled gypsum from Duke’s own power plants. Specifically, all of the wall board used in the project comes from the National Gypsum Company and, more specifically, from that company’s Mt. Holly gypsum plant number 029 in Mt. Holly, N.C. All of the pieces of wall board were stamped with the number “029” to ensure that the right boards were used at all times. A further control, Duke Energy got written assurances from the contractors and manufacturers that the chain of custody would be strictly observed.

Management at Mt. Holly sees the partnership as part of a chain of initiatives.

“This is just another chapter to the green/sustainability story at the Mt. Holly plant and we are proud to be a small part of Duke Energy’s efforts to ensure a sustainable future for generations to come,” says National Gypsum’s CEO Tom Nelson. “Through our partnership with Duke Energy, we purchase byproduct gypsum from nearby Duke coal-fired plants and use it to produce wall board. We combine Duke’s byproduct gypsum with paper we produce from recycled materials and the result is a totally green building product.”

National Gypsum Director of Marketing John Mixson says the company worked closely with Duke Energy on the project.

“I personally met with Duke Energy’s sustainability team to discuss the important role gypsum board can play in their LEED certification efforts and to highlight the uniqueness of our partnership,” he says. “We also took the project’s management team on a tour of our Mt. Holly plant to help them understand the significant role National Gypsum and Duke Energy play in creating a valuable recycled building material.”

Full Steam Ahead

The Mt. Holly plant’s exclusive agreement with Duke Energy states that all of the gypsum material coming in the door comes from the utility’s plants only. The plants involved are the Marshall Steam Station, the Cliffside Steam Station, the Belews Creek Steam Station and the Allen Steam Station-all of which are less than 100 miles from the LEED project site. Throughout the entire project, more than 40 percent of all of the materials used came from nearby sources.

Keeping track of where everything came from and where it all went turned out to be a challenge.

“For a project of this size, the most difficult demands often relate to providing the necessary supporting documentation,” says Mixson. “In 2010, National Gypsum launched the Green Product Score to provide a quick and simple way for project teams to quickly access the necessary product-related documentation. In a short amount of time, the GPS has demonstrated its value on thousands of projects nationwide.”

Several million feet of National Gypsum’s drywall (5/8-inch Fire Shield board, purple XP mold resistant board as well as Hi-Impact and Hi-Abuse board) were used throughout the building. Construction crews also used the company’s ProForm ready mix.

The building is a green showcase; one that Mixson says enhances National Gypsum’s relationship with Duke and raises the company’s profile. Lights on the inside of the building adjust to the amount of sunlight on any given day and motion sensors turn them off when no one is around to benefit from them. While the building was under construction, 93 percent of the waste from the project was recycled, right down to the truckloads of stone removed from the site which were used by a nearby quarry for the construction of road beds.

It has its own water treatment plant which can process more than a million and a half gallons of stormwater every year and uses that water to nourish two small parks in the area. One of those gardens is on top of the building itself and contributes to the cooling of the building. By cutting cooling costs, the garden will have paid for its own installation in just 11 years; the garden itself is expected to last about 40 years.

The physical site where the building sits was once home to a gas station that had a leaking storage tank, facilitating the removal and replacement of 75,000 cubic yards of contaminated soil.

The building is festooned with multicolored programmable LED lights that not only use a fraction of the energy of traditional lights but also provide a nightly light show for tens of thousands of Charlotte residents and guests.