Duke Energy verifies Cliffside unit 6 air compliance

Share This Story

CHARLOTTE, N.C. - Repeated performance testing at the new 825-megawatt Cliffside Steam Station unit 6 demonstrates Duke Energy delivered on its promise to build one of the cleanest coal units in the nation.

Cliffside unit 6 in Mooresboro, N.C., uses the most effective air emissions controls available. This innovative use of proven technologies enables the unit to be classified as a minor source of hazardous air pollutants (HAPs.)

Testing for a variety of air emissions has shown all are well below permit limits under full load conditions.

Pollutant Unit 6 Performance Permit Limit Pass
Sulfur dioxide 0.02 to 0.04 lb/MMBtu 0.12 lb/MMBtu Yes
Nitrogen oxides 0.04 lb/MMBtu 0.07 lb/MMBtu Yes
Mercury 0.001 to 0.008 lb/GW-hr 0.019 lb/GW-hr Yes
Particulate matter (filterable) 0.002 lb/MMBtu 0.012 lb/MMBtu Yes
Particulate matter (filterable & condensable) 0.004 lb/MMBtu 0.018 lb/MMBtu Yes
Carbon monoxide 0.065 lb/MMBtu 0.12 lb/MMBtu Yes
Volatile organic compounds 0.0001 lb/MMBtu 0.003 lb/MMBtu Yes
Sulfuric acid 0.001 lb/MMBtu 0.005 lb/MMBtu Yes
Lead 0.0000009 lb/MMBtu 0.000022 lb/MMBtu Yes
Hydrogen chloride 0.41 lb/hr 1.83 lb/hr Yes


Future test results may vary, but control equipment will assure compliance well below permit limits.

"During the time the company was going through the air permitting process to build Cliffside unit 6, there was significant debate about whether a new coal unit could achieve this level of emissions reductions. We can close that chapter and put those concerns to rest," said plant manager Rick Roper. "This unit's air permit is one of the most restrictive in the country, and it's performing very well."

State regulators determine what permit limits are required to protect air quality and public health. To be considered a minor source of HAPs, a unit would have to emit less than 10 tons a year of any one HAP or 25 tons a year of all HAPs combined.

Hydrogen chloride (HCl) is the HAP emitted in greatest volume from a coal plant, and Cliffside unit 6 is emitting less than a quarter of its permitted amount. This is equivalent to less than 2.5 tons of HCl emitted annually or greater than a 99.913-percent removal rate.

Cliffside unit 6 removes 99 percent of sulfur dioxide, 90 percent of nitrogen oxides and 90 percent of mercury. The performance of unit 6 shows it is well positioned to demonstrate compliance with the federal mercury rule that will be in effect by April 2015, including the mercury standard of 0.013 lb/GW-hr.

It also handles all coal ash in a dry form and manages it in an engineered, lined landfill.

Cliffside unit 6 received recognition this fall for its innovation. The October issue of POWER Magazine named the plant as a POWER Top Plant for 2013.

It is also a finalist for the "Best Coal Project" in the Projects of the Year Awards sponsored by Power Engineering and Renewable Energy World magazines to be awarded in November.

Cliffside unit 6 began commercial operation last December.

In addition, Duke Energy has built four natural gas combined-cycle plants in North Carolina since 2011, with a fifth expected to begin commercial operation in Wilmington later this year.

This new generation allows the company to retire older, less efficient coal plants, and Duke Energy will have retired seven of its 14 coal plants in North Carolina by the end of this year.

All of the remaining coal plants have installed advanced pollution controls that are highly effective in reducing emissions of sulfur dioxide, nitrogen oxides and HAPs, including mercury and HCl.

Across the country, Duke Energy is planning to retire nearly 6,300 megawatts of coal capacity in the coming years, which represents 25 percent of its coal fleet. By the end of 2013, Duke Energy will have retired more than 3,800 megawatts of this older coal capacity.

About Duke Energy Carolinas

Duke Energy is the largest electric power holding company in the United States with more than $110 billion in total assets. Its regulated utility operations serve approximately 7.2 million electric customers located in six states in the Southeast and Midwest. Its commercial power and international business segments own and operate diverse power generation assets in North America and Latin America, including a growing portfolio of renewable energy assets in the United States.