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Regarding power plant efficiency, he’s not just blowing off steam

Professor Jon Longtin is all about efficiency.

Efficiency, in fact, is Job No. 1 for this Stony Brook University (SBU) mechanical engineering professor, who is knee-deep in a multitude of U.S. Department of Energy Advanced Research Projects Agency-Energy projects.

The busy scientist is a co-investigator on ARPA-E efforts including Innovative Natural-gas Technologies for Efficiency Gain in Reliable and Affordable Thermochemical Electricity-generation (INTEGRATE) and Generators for Small Electrical and Thermal Systems (GENSETS), both led by SBU Mechanical Engineering Professor Sotirios Mamalis.

The INTEGRATE project aims to develop natural gas-fueled, ultra-high-efficiency electrical-generation systems that combine next-generation fuel cells with advanced internal combustion engines. GENSETS, meanwhile, is zeroing in on transformative, natural gas-fueled generators that can address household electrical and hot-water needs while reducing greenhouse gas emissions.

Both projects are right up Longtin’s alley. The University of California at Berkeley-trained PhD wields a unique understanding of heat transfer, thermodynamics, and experimental measurement techniques – critical know-how for the Marmalis-led programs.

But it’s in the ARPA-E project that Longtin leads – the Advanced Research In Dry Cooling, or ARID – where his affinity for efficiency plays out on the center stage.

According to the second law of thermodynamics, one unavoidable byproduct of electricity generation is heat – and for a power plant this means a lot of heat, which must be somehow dispersed, safely, into the surrounding environment.

There are two traditional ways in which this is done. A plant is either situated near a large body of water, into which the heat is dumped, or it has an evaporative cooling tower that uses the heat to vaporize water into the atmosphere.

Both methods raise problems. Adding large quantities of heat to rivers and lakes has consequences for wildlife and surrounding vegetation, while those cooling towers consume large volumes of freshwater, an increasingly valuable commodity.

There’s a third option, and here’s where Longtin’s AERTC-based research factors in. “Dry cooling” involves enormous heat exchangers – the size of football fields, suspended high in the air – that condense steam back into liquid water, which is then returned to the steam cycle.

It works, with one sticky wicket: These heat exchangers run considerably warmer than their water-cooled counterparts, putting a sizeable dent in a power plant’s overall efficiency, which is determined in part by the temperature at which the steam is condensed.  

The lower the temperature at which the steam condenses, the greater the plant efficiency. This is why power plants tend to run better in the winter, notes Longtin, whose ARID mission is to apply his efficient thinking to this particular problem. 

On the innovation of his idea, Longtin notes: “When you burn a fuel like natural gas, you create water vapor. Not liquid water, but water vapor. Our project is designed to condense some of the water vapor from the combustion process into liquid water, collect it, and then spray it in front of fans in the air-cooled heat exchanger.

“From the heat exchanger’s point of view, the outside temperature has now dropped 10 to 15 degrees Fahrenheit,” he adds. “As a result, the efficiency of the power plant increases.”

Three years of work – involving Longtin, two Stony Brook PhD candidates, Brookhaven National Laboratory, the Connecticut-based United Technologies Research Center, Chicago’s Gas Technology Institute and researchers from Texas A&M at Kingsville – has resulted in a small-scale prototype of the vapor-condensing technology, built at the AERTC.

The prototype produces just 100 grams of liquid water per hour, but proves out the technology. A larger version, capable of producing some two kilograms of water per hour, is now under construction at BNL, with three months of field tests slated to follow.

The ultimate goal is a full-sized version that can condense about 30 percent of the water vapor produced by most power plants. Although such a large-scale project will not be actually built for the ARID, the foundation for the key technologies is being set out now.

Working on the project at the AERTC has been “great,” according to Longtin, who notes “tremendous support from management and the university, state-of-the-art laboratory facilities” and a plethora of like-minded researchers ready to talk shop.

Although the ARPA-E funding for the ARID project dries up in February, Longtin sees a flowing future for the vapor-condensing tech, including a possible solution for third-world countries where freshwater is dangerously scarce. 

“The condensed water vapor produces surprisingly clean water,” he notes. “It will have to be treated for pH and contaminants, but I think post-processing, it could certainly be used for gray water, such as flushing toilets, doing laundry, and such. With the proper treatment, it could also potentially be used for potable water.

“Although the ARPA-E ARID project was focused specifically on improving power plant efficiency,” Longtin adds, “the prototypes at the AERTC and BNL will serve as demonstrators for additional application areas and funding opportunities moving forward.”



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