Cajun Converter, Don’t Ya Know
A system developed by ORMAT Technologies in Nevada uses waste heat from turbines driving compressors to generate electricity at a natural gas plant in the Bayou State
By Jeremy Alford
When the winter months start cutting into the humidity of south Louisiana, manly conversations around water coolers and copy machines often turn to redfish and speckled trout. Lower temperatures force the fish into shallow marshes, spurring tall tales from eager anglers. Not surprisingly, it was the topic of conversation during a recent December visit to Enterprise Products’ Neptune natural gas processing plant in Centerville. It’s a sleepy rural community nestled in the heart of St. Mary Parish, a sportsman’s paradise about 100 miles southwest of New Orleans.
With zeal, a control systems specialists told me the "specks" were finally biting. A few more tips followed here and there, but the dialogue quickly turned more technical. For those who work at the Neptune plant, there is something even more exciting to talk about than fishing these days. "You need to put these on," says Bobby Gautreaux, Neptune’s plant operator, handing me a lab coat and hardhat. "This is really amazing stuff you’re going to see. Really impressive."
Gautreaux also handed me a complex diagram of purple and orange lines flowing through a generator, vaporizer, and preheater. Nine cooling fans were depicted atop the equipment to control the ambient temperature of the system I came to view, and voltage readouts running down the left-hand portion of the page told me what was what. Needless to say, the fishing tips were easier to understand – at least initially. But after Neptune’s new find was thoroughly explained, I easily comprehended the pride running through the plant.
In February 2004, engineers at the Neptune plant installed a 4.5-megawatt ORMAT Energy Converter (OEC), which generates electrical power by capturing waste heat produced by a pair of gas turbines used to drive natural gas compressors. Today, the converter – the first of its kind in the U.S. – outputs a significant portion of the plant’s energy needs and even a steady flow of excess power to sell to the local energy company.
Not only has a new revenue stream been created for the company, they have become more self-sustainable, and interruptions in purchased power – from storms or other occurrences – are a thing of the past. The multi-million dollar investment was originally scheduled to pay for itself in six years, but since the OEC was placed in operation, the timeline has decreased to three years due to recent increases in power rates.
Based in Sparks, Nevada, ORMAT Technologies has offered turnkey eco-efficient energy solutions to the pipeline industry since 1965. They used geothermal energy technology as a basis for creating their converter – an engineering marvel that took nearly 40 years to catch on. While it may not be the cure-all for the nation’s energy needs, Neptune and ORMAT officials believe the system makes natural gas more efficient and allows it to continue as a legitimate piece of the overall energy picture. Even as gas prices skyrocket, sending many plants in south Louisiana packing, backers of the converter contend it creates a real, transitional energy source, at least until renewable sources become more prevalent. For Neptune specifically, however, they have found a saving grace for their operations through a converter that uses a source they once wasted.
Using the Rankine Cycle as a basis, the OEC uses n-pentane, a non-freezing, ozone-benign organic working fluid, rather than steam. The thermal energy inside the exhaust heat is transferred to a vaporizer in nonflammable fluid form. The resulting pressurized vapor drives a special turbine coupled to a generator.
It’s a rough-and-tumble system, Arie adds, as many OEC units operating in other countries have been online with few problems for more than 25 years, functioning continuously under the most severe environments. The OEC units can also use a wide variety of other locally available fuels, such as LPG, kerosene, jet fuel, and diesel fuel.
The OEC made a perfect match for Neptune, says Pervaiz Nasir, director of technology for Enterprise, because the cryogenic gas plant uses gas turbines as a prime mover. This process decreases a plant’s ability to use exhaust heat for any real purpose, he says, and as a result, it goes to waste. On paper, it made sense for Neptune to incorporate the OEC, but like many others, they had to be convinced the technology was ready.
"It’s not easy to convince people to buy it," Arie says of the OEC." The main point of the sales pitch has always been the same: for the company to become self-sustainable and find new revenue streams. It was a pitch not lost on Neptune officials. Nasir says a study commissioned at the plant uncovered a potential 84.6 million Btus an hour of surplus waste heat from two turbines not being used.
From the plant’s inception, Nasir says Enterprise was desperate for ways to use this waste heat to generate refrigeration or electricity in a profitable manner. There were two potential areas where the plant could use this heat. The first involved using an absorption process to generate refrigeration for cooling operations. This option had a very low return on the initial investment, Nasir says, and the plant is already air-cooled. Additionally, there is no reliable and economical source of cooling water available in the area. The second, and most tangible, option involved using the heat to generate power.
The OEC also served as a chance for the Neptune plant to be a trendsetter, Nasir says. Similar equipment has been used at geothermal facilities throughout the world for decades, but the system at Neptune is the first where a hot oil system supplies both the plant’s primary function and the heat requirements for the OEC. There were hopes that others would take notice, and Neptune would be ahead of the curve. That strategy may already be paying off. "The Neptune project has broader significance for improving the efficiency of gas processing plants throughout the United States," Nasir says.
An Investment Pays Off
Not surprisingly, officials at the Neptune plant say their phone has been ringing off the hook from other companies interested in the technology. Most recently, Gautreaux says General Electric sent representatives to the Centerville plant to inquire about the system. Nasir estimates that 40 other gas plants in the U.S. could incorporate similar systems. Additionally, if compressor stations in service on individual pipelines are included, another 250 sites could use waste heat for energy production.
The entire converter system is operated through a Windows-based software applicator, which Gautreaux described repeatedly as "very sweet." A simple sway and click of the mouse gets the unit up and running, while the software tracks the progress of the system. One person can run the converter from the comfort of a control room. For the most part, the operation is automatic and unmanned. "We were very skeptical of such a simple setup," Gautreaux says. "But with only one touch of a button, you’re exporting power within 30 minutes."
Another attribute of the system is its environmental impact – or lack thereof. State and federal environmental agencies visited the Neptune plant on several occasions last year to test any byproducts of the process and came away with praise. Gautreaux says, "Any environmental impact you can find is simply hot air coming off the converter. The only indication you have that it’s running is the noise."
Arie says ORMAT strives to combine ecology and economy, and the company offers OEC as proof. And while fishing will remain a major topic of conversation at the south Louisiana plant, it will also be rivaled by ORMAT’s innovative energy-creator for years to come. To put it another way, the Neptune team bought into the technology – hook, line and sinker.
Jeremy Alford is a freelance writer in Baton Rouge, Louisiana
For more information on ORMAT Technologies and its energy systems, visit www.ormat.com