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These numbers tell the story of how the addition of Selective Catalytic Reduction (SCR) technology has helped the iconic New Mexico coal-fired power plant reduce emissions, keep the plant running, and continue to be an economic driver for the local Navajo community.

In the past few years, emissions regulations for coal-fired power plants in the United States have been the top priority for operators. Meeting environmental regulations is not the only consideration for factory owners. Increasing the cost of emission reduction technologies in existing factories is balanced with the economics of keeping factories online, and the impact of closing factories on local communities, loss of jobs and taxes.

The Arizona Department of Public Services (APS) considered these circumstances when considering the future of its Four Corners Power Station on land leased from the Navajo Nation, approximately 15 miles west of Farmington, New Mexico. The plant has been in operation for nearly 70 years; the first two units of the plant went online in 1963, and the third unit was completed a year later. Units 4 and 5 started operation in 1969 and 1970, respectively.

A few years ago, after the three old units were shut down and demolished, APS formulated a strategy to reduce the emissions of the remaining two 770 MW coal-fired units to comply with the National Environmental Policy Act (NEPA) clean air standards. It was decided to install selective catalytic reduction (SCR) technology on units 4 and 5, which had previously been retrofitted with SO 2 scrubbers in the mid-1980s.

APS hired California-based multinational engineering company AECOM in 2014 to design and build an abatement system that can remove nitrogen oxides (NOx) and sulfur trioxide (SO3). The project includes the installation of SCR retrofits in units 4 and 5. The traditional AECOM company has completed other projects in the four corners, including retrofitting the flue gas desulfurization system to reduce sulfur dioxide emissions, adding fabric filters to control particulate emissions, and other smaller projects. AECOM's work also includes other studies, including preliminary feasibility studies and estimates for the SCR retrofit in 2000.

The SCR retrofit installation started in August 2015, the new technology of Unit 5 was completed in May 2018, and Unit 4 was completed in July 2018.

The project did more than reduce emissions in the four corners. By allowing the factory to continue to operate, the factory continues to be an economic driver for the Navajo and surrounding communities, providing employment opportunities and taxes to support school and community projects.

“APS’ installation of pollution control devices at the Sijiao Power Plant is part of our continued investment in a clean energy future,” APS’s main fossil project manager Brent Gifford told POWER. "It also supports the factory as a 24/7 power generation resource, helping to maintain reliable and affordable energy for Arizona and the Southwest."

The Four Corners SCR project is not easy. Major players as well as APS and AECOM include Riley Power, a part of regional construction companies Sundt Construction and Babcock Power Inc. Riley is known for manufacturing all types of fossil and waste fuel boiler equipment, including SCR systems.

AECOM told POWER that the company’s role in the project “is to design, purchase, and build all the necessary equipment and materials. AECOM worked with the regional construction company Sundt Construction Inc. to build most of the scope. As a regional company, Sundt Bringing a large number of Navajo labors, responsible for the scope of concrete, structural steel and pipeline installation."

The scope of the project is indicated by numbers. According to AECOM, it includes 6,003 cubic yards of concrete; 7,074 tons of structural steel; 2,665 tons of piping systems; 51,567 feet of pipes; 12,163 feet of cable trays; 135,627 feet of power cords; 363,964 feet of control cables; and 20,268 electrical/instruments terminal. The project includes:

"The installed SCR technology will reduce nitrous oxide emissions by more than 80%," Gifford said. "APS is installing these SCRs to meet regional haze regulations authorized under the Federal Clean Air Act, the [Environmental Protection Agency] Federal Implementation Plan, and the consent order signed on August 17, 2015."

1. The Selective Catalytic Reduction [SCR] unit at the Four Corners Plant is the highest in North America, each unit is 230 feet tall. The plant's Unit 4 and Unit 5 both have two SCR reactors. Courtesy: AECOM

AECOM told the POWER SCR (Figure 1) that it was the highest in North America at 230 feet, and added that “AECOM worked with Sundt Construction and Riley Power to help APS reach an agreement with NEPA to improve emissions from units 4 and 5 in 2018. Decree of July 31st."

AECOM told POWER, “Cultivating and managing close working relationships with Sundt personnel and key customer contacts is critical to the success of the project. A project management office was developed to involve all project stakeholders, including owners, engineers, and construction personnel. The project team quickly became a cohesive working group so that problems can be quickly identified and resolved."

The installation of SCR equipment requires a power outage during the lap work. AECOM and Sundt set up a power outage planning team to develop a detailed plan six months before each power outage, identifying key milestones, work activities and emergency plans. The team developed a scoring matrix and brought in third-party experts to evaluate the work and provide suggestions for improvement. Third-party inspectors include project managers and safety managers, who are directly responsible for similar SCR installation projects in advance.

AECOM stated: “Using the modular construction method of the peripheral manufacturing yard, Sundt can meet the insulation requirements of most pipe parts on the ground, thereby improving safety, cost and schedule. The remote modular assembly method also greatly reduces the work area of ​​the power block. Through detailed scheduling and sequencing, Sundt was able to maintain a consistent flow of materials to the three main construction cranes, thereby improving schedule and project efficiency.

“Due to the compactness of the work site and the need to lift heavy components and modular parts from existing operating equipment, it is necessary to install one of the heavy lifting cranes 888 ringer on a steel platform located at an altitude of 160 feet. This crane is composed of The M18000 on the custom-installed concrete pad and the TG2300 tower crane in two locations on site are supplemented, depending on the construction needs."

The project was completed ahead of schedule and within budget, and has what AECOM calls an "excellent safety record." AECOM pointed out, “This is a large-scale project that has brought many construction and safety challenges, especially because most of the work is carried out at high places, requiring a lot of and specific efforts to prevent falling and falling objects. AECOM and Sundt emphasizes that safety is part of the basic project culture through daily safety measures."

These companies conduct job hazard analysis and task hazard analysis at the beginning of each shift and when workers return from breaks. Safety investigations are conducted daily to identify and quickly correct any potentially unsafe practices. Security audits are completed every day. Another challenge is that most of the construction is carried out in factories operating under constantly changing conditions. The design and manufacture of structural steel, piping systems, and SCR components are designed to maximize modularity and allow installation with minimal disruption to the operating plant.

The success of the Four Corners SCR project is especially known for its impact on the local community. The plant purchases coal from the nearby Navajo Mine, which has more than 350 workers and has been in operation since 1963. According to mine operator Navajo Transitional Energy Co., its coal sales agreement with Four Corners will last until at least 2031.

"The Four Corners Power Plant is the economic engine of the Navajo people and surrounding communities, and has an annual economic impact of approximately $225 million on the Navajo and New Mexico economies," Gifford said. AECOM told POWER that “the continued operation of Units 4 and 5 is expected to provide the region with more than $6 billion in economic value over the next 30 years, of which at least 70% will benefit the Navajo Nation and its citizens.”

AECOM stated that the plant and mine pay more than $100 million in taxes, fees and royalties to the Navajo Nation and state, local and federal entities each year. The company pledged to support the local Navajo community from the very beginning of the project and throughout the project period, supporting a number of initiatives, including many activities aimed at local youth.

AECOM told POWER that the Four Corners SCR project “improved the quality of life of the people in the Navajo Reserve through construction and long-term employment and reduction of pollutants emitted by the factory. In addition, one of the goals of the project is to reduce pollution and haze in the Grand Canyon. Restore the magnificence of this important national treasure." ■

— Darrell Proctor is the associate editor of POWER (@DarrellProctor1, @POWERmagazine).

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