On-Site Power, Reciprocating Engines

Why Power Producers are Turning to Recips

Issue 4 and Volume 121.

The intermittent nature of renewable generation, low-priced natural gas and advancements in engine technology and flexibility have given reciprocating engines new life as a competitive form of reliable generation.

Reciprocating engines are becoming increasingly popular for utility-scale power projects. 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.

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.

In this issue of Power Engineering, Sargent & Lundy details the benefits of reciprocating internal combustion engine technology, answers several common questions about the technology, and identifies issues you should carefully consider when evaluating reciprocating engines for a range of applications.

Last 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 supplies 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,” Andreas M. Lippert, engineering leader for GE’s Distributed Power business, said last year at POWER-GEN Europe. “Our Sky Global power plant in Texas basically uses no more water than an ordinary household.”

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.

Engine efficiency ratings are now comparable to efficiency ratings for gas turbines. Best of all, reciprocating engines are significantly cheaper based on output.

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 fell to $2.85 per million Btu (MMBtu), on average, in February due to unusually warm weather. But DOE officials predict gas prices will rise to an average of $3.03 per MMBtu in 2017. That’s still low enough to incentivize the continued construction of gas-fired plants in the U.S. In 2018, gas prices are expected to average $3.45 per MMBtu. In 2006, the wellhead price of natural gas in the U.S. averaged $6.42 per MMBtu.

We see tremendous potential for this emerging market, but the lack of adequate natural gas infrastructure is preventing the market from maximizing its potential.

Flexible generation and the benefits of reciprocating engines will be a big topic of discussion at POWER-GEN International 2017 Dec. 5-7 in Las Vegas, Nevada.