Cogeneration

The Evolution of Reciprocating Engines

In southern Minnesota, where wind turbines and ethanol plants are commonplace, two communities have turned to reciprocating engine technology to meet their future power generation needs.

By Russell Ray, Chief Editor

The Fairmont Energy Station is a 25-MW project equipped with four Cat G16CM34 generator sets. The plant was commissioned in 2014.

Photo courtesy: Caterpillar Inc.

In southern Minnesota, where wind turbines and ethanol plants are commonplace, two communities have turned to reciprocating engine technology to meet their future power generation needs.

The Fairmont Energy Station, a 25-MW project completed in 2014, and the Owatonna Energy Station, a 38-MW project now under construction, feature highly flexible, quick-starting, low-maintenance reciprocating engines suited for today’s market, which places a premium on rapid-cycling capabilities.

Minnesota is home to about 100 wind power projects and ranks No. 7 in net wind power production in the U.S. That means Minnesota power producers must have reliable backup power to fill the sudden gaps created by growing supplies of intermittent wind power. The $30 million Fairmont plant is well suited for the job, capable of reaching full capacity in just eight minutes. That’s significantly faster than power plants using the latest gas turbine technology.

“We required a more flexible and fast responding power source that could make up the difference,” said Peter Reinarts, manager of Generation and Operation at Southern Minnesota Municipal Power Agency (SMMPA), which owns the Fairmont and Owatonna plants.

SMMPA either purchases or operates more than 100 MW of wind power capacity. The four 16-cylinder gas-fired engines provided by Caterpillar for the Fairmont project work in sync with the association’s portfolio of wind power. “The generator sets can be promptly put on or offline to fill in the holes of the current wind generation,” Reinarts said. “These two assets aren’t at odds with each other, but instead work in a dynamic tandem.”

The intermittent nature of renewable generation, low-priced natural gas and advancements in engine technology and flexibility have given reciprocating engines new life in the U.S. as a competitive form of reliable generation. Reciprocating engines are becoming increasingly popular for utility-scale power projects.

Sky Global One, a 51-MW gas-fired plant about 70 miles west of Houston in the Rock Island community of Colorado County, began commercial operation in April 2016. The plant features six 8.6 MW Jenbacher J920 FleXtra gas engines from GE. Photo courtesy: GE

Gas engine power plants have several advantages over plants equipped with gas turbines. Perhaps the biggest advantage is flexibility.

Gas-engine power plants with multiple modular units are better at scaling their output across a wide range of incremental load without sacrificing efficiency. For example, 12 generator sets capable of generating up to 10 MW each can deliver output ranging from just a few MW to more than 100 MW in just minutes. By keeping a few units online, the other units can be deployed individually to offset sudden losses of wind power and bring balance to the grid.

“These new generator sets start quickly, like a car engine,” said Bruce Erickson, vice president of Ziegler Power Systems, which supplied the four Cat G16CM34 generator sets for the Fairmont project. “If the grid needs extra power 10 minutes from now – these generator sets can easily adjust to that need.”

In addition to speed and flexibility, gas-fired reciprocating engines can operate at part load – 25 percent or lower – without sacrificing fuel efficiency. Also, reciprocating engines have much lower maintenance costs versus the cost to maintain a sophisticated gas turbine. What’s more, the output of a modern-day reciprocating engine now exceeds 20 MW, up from 10 MW a decade ago. This has led to the development of more engine-based power plants exceeding a capacity of 200 MW worldwide.

Earlier this year, Sky Global One, a 51-MW gas-fired plant about 70 miles west of Houston in the Rock Island community of Colorado County, began commercial operation. The plant features six 8.6 MW Jenbacher J920 FleXtra gas engines from GE and will supply power to the 18,000 members of the San Bernard Electric Cooperative.

The plant can go from zero to full power in just five minutes, a useful feature in a state that leads the nation in wind power production. In addition to providing power on short notice, the power plant – and others like it – uses very little water.

“Reciprocating engines use no water as part of their cycle,” said Andreas M. Lippert, engineering leader for GE’s Distributed Power business. “Our Sky Global power plant in Texas basically uses no more water than an ordinary household.”

The J920 Flextra, a two-stage turbocharged engine, has a maximum output of 10.4 MW and can achieve electrical efficiencies of 49.1 percent at 50 hertz. The 60 hertz version has a capacity of 9.35 MW and can achieve electrical efficiencies of 49.9 percent. The two-stage turbocharging means the J920 can achieve a fuel efficiency rating of more than 90 percent when used in a combined heat and power (CHP) plant that produces hot water, GE said.

GE recently received an order for two 9.5 MW J920 FleXtra gas engines in Italy. The two units will be used in a district heating repowering project in Rome. Once the project is completed, the new 19-MW power plant will provide power to about 50,000 residential customers in Rome.

“This project showcases the advantages of our J920 FleXtra gas engine technology,” Lippert said, “as more European utilities and municipalities modernize their CHP plants with more efficient, reliable and flexible gas engines to meet increasingly stringent environmental regulations and support the growth of renewable energy on the grid.”

Construction of the plant is expected to begin in 2016 and finish in 2017. In addition, GE has also received orders for several cogeneration projects in Germany.

The Rubart Station, a 110-MW gas-fired power plant featuring 12 Caterpillar G20CM34 generator sets in southwest Kansas, is another example of how reciprocating engines are meeting demands for highly flexible generation systems that can accommodate the fluctuations of renewable power. The plant is capable of reaching full power in less than nine minutes and can generate a wide range of output.

“The facility can produce 10 MW, 110 MW or anything in between without losing efficiency, and that’s an enormous advantage for us,” said Kyle Nelson, senior vice president and chief operating officer at Mid-Kansas Electric Co., the plant’s owner.

Kansas has more than 3,800 MW of installed wind power capacity and is leading the nation in new wind power projects. In the second quarter, Kansas led the nation in new construction announcements at 778 MW, according a report issued last month by the American Wind Energy Association (AWEA). Nationwide, more than 18,000 MW of wind power capacity are under construction or in some advanced stage of development, according to AWEA.

Luckily, the Rubart Station is permitted to double its capacity. The site was built with enough space to add 12 more engines, if more capacity is needed. Rubart is the largest gas-fired power plant ever built by Caterpillar.

Aggreko is a leading provider of temporary power worldwide. The company uses reciprocating engines to provide power for special events, emergencies, and extended projects.

Photo courtesy: Aggreko

Aggreko is a leading provider of temporary power worldwide. The company uses reciprocating engines to provide power for special events, emergencies, and extended projects. It provides comprehensive power generation services, including the engineering, installation and operation of temporary power systems with wide ranging capacities.

Frank Pizzileo, business development manager at Aggreko, said reciprocating engine technology and the market for reciprocating engines are vastly different than a decade ago. Emissions are 16 times lower, engine efficiencies range from 38 to 50 percent, maintenance is simpler, and the price of natural gas is a lot cheaper.

“The technology has come a long way. It’s primarily driven by the need to reduce emissions,” Pizzileo said. “They’re much more tolerant to load swings. You don’t see as much of a derate for higher ambient temperatures and altitudes that you would see in a turbine.”

Financially, a small to mid-size power plant equipped with high-output reciprocating engines can effectively compete against a gas-turbine plant of the same size, Pizzileo said. “For the right application, I bet the project IRR utilizing recips would look pretty good or better.”

Engine efficiency ratings are now comparable to efficiency ratings for gas turbines, he said. Best of all, reciprocating engines are significantly cheaper.

“A 1-megawatt turbine would cost three times as much as a recip engine of the same size,” Pizzileo said. “For us, it is certainly the product of choice for what we bring to the market.”

Power producers are turning to reciprocating engines for a variety of reasons, from providing backup power for intermittent renewable resources on short notice to reducing nitrogen oxide (NOx) emissions for compliance with new federal emission limits.

They have been deemed to be an efficient solution for commercial and industrial CHP systems and grid operators struggling to balance supply and demand.

But the biggest factor behind the increasing use of reciprocating engines for CHP applications is the prospect for low natural gas prices. According to the Department of Energy, natural gas prices are expected to rise over the next two years but will remain low enough to incentivize the continued construction of gas-fired plants in the U.S. Natural gas prices are expected to average $2.36 per million Btu (MMBtu) in 2016 and $2.95 per MMBtu in 2017. In 2006, the wellhead price of natural gas in the U.S. averaged $6.42 per MMBtu.

“It’s a different dynamic,” Pizzileo said.

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