Morrow Reinvented: HL-Class Gas Turbine Powers a Coal Plant's Rebirth

The Morrow Repower Project, winner of POWER’s 2024 Reinvention Award, exemplified a strategic coal-to-gas conversion at a brownfield site that masterfully combined cutting-edge advanced technology with a commitment to financial and community stewardship.

A decade ago, Cooperative Energy, an electric cooperative, began to contemplate the future of its fleet. Founded in 1941 as South Mississippi Electric shortly after the passage of the Rural Electrification Act, Cooperative Energy had grown into the sole generation and transmission cooperative in the state, furnished with the integral mission of meeting the power requirements of 11 small distribution cooperatives spanning from the Mississippi Delta to the Gulf Coast. In the more than 80 years since, the Hattiesburg-headquartered co-op has operated under a member-owned not-for-profit model, supplying its more than 448,000 members in 55 of Mississippi’s 82 counties with wholesale rates that cover only the costs of providing power and emergency contingencies, with remaining funds (capital credits) returned to members.  

In 2012, the co-op joined the Midcontinent Independent System Operator (MISO) as one portion of the regional transmission operator’s larger balancing authority, allowing it to leverage low-cost energy purchasing while finding new avenues for its own generation. As with all of Cooperative Energy’s efforts, the measure was firmly embedded in its larger imperative to produce affordable and reliable power consistently. But it also sought to provide overall market transparency as stringent new environmental regulations and technological advancements transformed the market dramatically.

A particular concern rested on the future of the R.D. Morrow Sr. Generating Station, a 400-MW two-unit coal-fired facility Cooperative Energy opened in 1978. While the co-op had begun exploring repowering the landmark plant with natural gas as far back as 2013, given uncertainties about the future of coal power, by 2016, decisive action became critical.

“It really came down to economics,” Mark Smith, Cooperative Energy’s senior vice president of Power Generation, told POWER. “We had an approximately 3% capacity factor on coal. The units could not compete in the MISO market due to the cost of operation, as well as flexibility on the unit during operation.”

Along with the prospect of continuously complying with ever-more stringent environmental rules, the plant grappled with high costs to transport its coal 440 miles to the site. To keep the plant viable over the long term, Cooperative was deeply aware it would need to “spend some big money,” Smith said.

In 2016, Cooperative’s generation planning group began an expansive year-long study to explore its power supply options. “It’s something we do periodically to evaluate our fleet and determine the most cost-effective way to serve our members,” said Trey Cannon, director of Generation Projects with Cooperative Energy. The study suggested a repower project at Morrow was the best way forward.

“There were a number of reasons,” Cannon noted. “We had several assets there that were in good shape and feasible for reuse,” such as the switchyard, the transmission system, circulating water systems, and the powerhouse. “And then maybe most specifically, just the size of the steam turbines themselves were very well suited to power a very large gas turbine that’s very efficient,” he said.

After a Burns & McDonnell study showed that repowering presented potential cost savings of between 25% and 35%, Cooperative moved quickly. In June 2018, the co-op’s board cemented a decision to retire the original two-unit plant and replace it under a five-year ambitious conversion plan with an advanced-class natural gas unit.

The 572-MW Morrow Repower project began commercial operation in March 2023. Powered by a 60-Hz Siemens Energy SGT6-9000HL paired with an existing steam turbine, the unique baseload plant is today a reliability powerhouse controlled and dispatched by MISO.

A Rigorous Technology Selection

As a crucial first step, the co-op set out to explore—with an “open mind”—its large heavy-duty gas turbine options, carefully weighing choices from three major gas turbine manufacturers that were then available. “We would take the performance guarantees from each of the three different gas turbine vendors, and we would run them against current production cost models and determine their economic [potential] based on future gas pricing and future power costs and things of that nature,” Smith noted. Siemens Energy’s SGT6-9000HL routinely ranked high in flexibility attributes, including for start time, ramp rate, and turndown of the unit, as well as in efficiency, Smith said.  

However, the decision to order the technology was not without significant risk. When Cooperative was mulling its options in 2018, Siemens Energy had freshly unveiled the HL-class—its largest, most powerful, and most efficient gas turbine model. While Siemens Energy launched the technology following a conservative approach—including a rigorous, nearly decade-long evolutionary development phase and testing at a full-scale rig near Berlin—Morrow was ultimately slated to become “serial number two” for the 9000HL in the 60-Hz market. But for Siemens Energy, the Morrow repowering project’s legacy is more noteworthy because it is also the world’s first baseload repower project to feature an SGT6-9000HL. 

As Hans Thermann, head of 9000HL Product Portfolio Management for Siemens Energy, told POWER, the HL class was designed “with the energy transition in mind” to support the coal-to-gas shift. While based on Siemens Energy’s legacy of H-, F-, and E-class experience and architecture, the advanced air-cooled gas turbine line incorporates technological advancements like an advanced combustion system to enable higher firing temperatures (above 1,600C), efficient internal cooling features for blades and vanes, and a proven rotor architecture.  

These attributes are integral for the high efficiencies and high ramp rates that coal-to-gas repower projects must achieve to thrive, and bolster reliability and affordability in modern power systems, Thermann said. At Morrow, the effort resulted in “roughly a 50% reduction” in carbon dioxide emissions, he said. 

Thermann noted the machine’s versatility was showcased at Duke Energy’s Lincoln Combustion Turbine Station in North Carolina. That project’s 411-MW SGT6-9000HL, installed in April 2020 at the greenfield simple-cycle gas power plant, represents the company’s first 60-Hz machine. Under an innovative four-year agreement with Duke Energy, Siemens Energy has continued to conduct validation testing at Lincoln while Duke Energy utilizes the facility for peaking power needs. 

 “It is equipped with a lot of additional sensors to validate and test every aspect of the engine,” which has helped spur further improvements of key technologies and furnish projects like Morrow with tested solutions, Thermann said. In August 2022, the Duke Energy project notably received two Guinness World Records for the highest power output of a simple-cycle unit and the highest ramp rate—more than 100 MW/minute. 

Cooperative’s confidence in the technology was cemented during the negotiation stage when Siemens Energy offered a comprehensive long-term service agreement (LTSA) to maintain the peak operating efficiency of the gas turbine and generator throughout the project’s lifecycle. The contract covered parts, repairs, field services, program management, and remote monitoring and diagnostics, which are part of Siemens Energy’s Omniverse Digital Services portfolio.  

Meanwhile, as part of the LTSA, Siemens Energy also hired a dedicated technical field adviser, who worked at the site for a year during the construction phase to address potential technical issues. According to Neal Hackett, Siemens Energy’s Service Programs Portfolio manager, the arrangement was crucial in establishing a collaborative and transparent partnership from the beginning, given the first-of-a-kind nature of some of the components.  

When Cooperative was building the units, for example, Siemens Energy delivered the unit “as an empty bird” without its blades and vanes because testing on those components was still underway at the North Carolina unit using different coatings, airfoils, and configurations. And when the North Carolina facility team encountered a concern, the Morrow team “adjusted on the fly and changed some configurations,” Hackett said. Both Siemens Energy and Cooperative were keen to align to ensure the end product was tightly optimized to fit Morrow’s reliability purpose. Cooperative ultimately extended its contract to keep the technical field adviser on for one year after the project went commercial, Hackett noted. 

A Lean, Employee-Led Success

While the Morrow Repower Project’s technology pioneering is significant, the efficiency with which Cooperative—a financially constrained not-for-profit run by about 450 employees—completed this mammoth undertaking is more profound. Smith told POWER the project’s objectives were met well ahead of the five-year schedule that Cooperative’s board set out in 2018. More remarkably, the project achieved commercial operation significantly under budget—with savings estimated at more than $60 million.

Underlying the project’s stunning success is that Cooperative set out on the project with a hands-on but lean mindset that considered its commitment to its employees and surrounding communities. First, it contracted engineering services firm Burns & McDonnell as the owner’s engineer for the project. But rather than pursuing a conventional engineering, procurement, and construction (EPC) contract, the co-op managed the project in-house alongside Burns & McDonnell.

Burns & McDonnell collaborated with Cooperative Energy to repower the R.D. Morrow, Sr. Generating Station with Siemens 9000HL turbine technology, boosting capacity to 572 MW and completing the project under budget with zero safety incidents.
Cooperative Energy partnered with Burns & McDonnell to repower the R.D. Morrow, Sr. Generating Station, increasing capacity from 204 MW to 572 MW using advanced Siemens 9000HL gas turbine technology. Despite pandemic challenges, the project was completed under budget with zero safety incidents, leveraging local labor and Cooperative Energy’s staff expertise. Courtesy: Burns & McDonnell

Smith explained: “We paid them to provide essential services, but all of the contracts were on our papers. They had no skin in the game like an EPC would. Basically, all the risk was Cooperative Energy’s.” Smith said the project involved at least 57 contracts—35 for equipment procurement and 22 for construction and services. The strategy alone resulted in an estimated $50 million in savings, he said. “And the beauty for us is that we got to control [all parts of the job] from project inception all the way to the end,” he said.

More notable is that the approach relied heavily on Morrow’s staff, which Cooperative had already pared down from 110 to 61 through a “natural attrition” strategy that initially sought to avoid layoffs when the plant’s future was uncertain. Supplemented by Burns & McDonnell staff and contractors, the employees took on extraordinary ownership of the project, executing multiple roles during all phases, including demolition, commissioning, and startup of the new unit.  Smith said operators completed various tasks including the installation of insulation and lagging, and mechanics and technicians performed demolition activities, among other things. 

Project management was also lean, spearheaded by Cannon alongside a single construction manager, a small supply chain department that handled equipment procurement, and a legal department that handled contracts. Cooperative also managed to contract highly rated talent. “We had the cream of the crop out there at that job site,” Smith said, partly owing to the lax labor market.

Over the entire project duration, Cooperative employees collectively invested nearly 300,000 work hours, while at construction peak, 400 workers were onsite at the Morrow Repower Project. Remarkably, crews accomplished commercial operations with an almost perfect safety record—made possible through strict safety protocols and intensive training.

“They just really put their heart and soul into it,” Smith stressed. The payoff was immense. “We have calculated that our employees contributed over $12 million to the project budget in reduction of costs,” he said.

According to Cannon, the project also benefitted from Cooperative’s lengthy and thorough planning process. “By the time we broke ground, over 90% of the final design was complete,” he explained. “We were, I guess, calculated and deliberate about that because we wanted to get it right and not affect our members. This was the biggest project our company had ever taken on by far—it was a big deal.”

Smith underscored that the project also leveraged “a stroke of luck” with its fortuitous timing. While the COVID pandemic imposed severe travel limitations, shipping delays, and supply chain issues—including for Siemens Energy—Cooperative found an extraordinary silver lining, as it benefitted from reduced competition in the construction, labor, and materials markets as regional projects were delayed or halted. “We were really blessed,” Smith remarked. “If we were to do this project today, we’d be looking probably at two and a half times the cost,” he said. 

Smith noted that the payoff will, however, multiply in the years to come. “This project truly transformed our cooperative and positioned us well for the future,” he said. “We’re incredibly proud of what our team accomplished.”

Sonal Patel is a POWER senior editor (@sonalcpatel@POWERmagazine).

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