Organic Rankine Cycle: The Evolution of Water

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Organic Rankine Cycle ORC system
A 350-kW waste heat recovery system developed by Ormat Technologies.

By Jason Gold, CEO of KGRA Energy

Industry can’t exist without water. Producing anything involves heat. When you’re a manufacturing facility, you’re lucky to be pushing out exhaust heat at less than 400 degrees Fahrenheit.

It costs water to make steel, water to make cement, even water to make solar PV panels and wind turbines. And then it costs water to continue to run things. For example, your average solar parabolic plant sucks up between 760 and 920 gallons for every megawatt hour produced. (Editor’s Note: wind and solar PV use a ton less than other power generation options, though.)

Every manufacturing or industrial power process requires heat to make its product. And, currently, the method most plants rely on to curb their excess heat is steam generation. It sounds great on paper, using the excess heat to convert water to steam, which produces energy that can be fed directly back into the process. But, in reality, steam generation needs a lot more water to work, wasting almost 2,300 gallons of water for every megawatt hour of energy generated (according to the U.S. Geological Survey).

Fresh water is the most essential commodity on earth, and yet, it is a scarce natural resource. According to the National Renewable Energy Lab, thermoelectric power alone accounts for 39% of all water consumption in the U.S., consuming over 200 million gallons per day. And the majority of that water is used to cool our heated power-production equipment.

But what would you say if I told you there has been a water-free technology in existence for more than fifty years that manufacturing facilities can use to cool their systems? And there’s a good chance you haven’t even heard of it, despite its recent popularity.

The water-free technology I’m referring to is the organic Rankine cycle (or “ORC”), which traces its roots to the geothermal power generation sector, where it was first popularized in the late 1960s.  These systems operate on the same basic principle as the traditional steam cycle, with two important differences: ORCs use a contained environmental refrigerant instead of water and ORCs are closed-loop, meaning they don’t need anything coming in or going out to run.

ORC system
A waste heat recovery system developed by TAS Energy.

ORC Process

The ORC process uses its environmental refrigerant to cool all of that exhaust heat running through it. The refrigerant moves through a closed-loop system, turning from liquid to steam and back to liquid again. It produces continuous power, is completely self-sustainable, and has a lifespan of at least 20 years. And despite its long-standing popularity in Europe, with over 100 working installations, the U.S. is only now beginning to realize its benefits.

That’s because, historically, industrial operations haven’t had to worry much about the availability of water or the regulations pertaining to the precious natural resource. But things are taking a turn. Public attention continues to grow around the issue of water scarcity. Its status as a precious resource has changed the mentality of power plant developers as they continue to absorb higher costs and struggle with water permitting authorities to bring projects to fruition.  This translates into higher power costs for all customers – both industrial and consumer alike.

ORC’s Growing Popularity in U.S.

With the change in public mentality, public awareness of ORC is spiking. In particular, industrial and power plant operators have accelerated efforts to work with project developers on ORC-based “waste heat recovery” systems.  Across the nation, more than 25 projects have already been completed by a number of developers, with many more in the pipeline.

These waste heat recovery projects harvest the excess thermal energy that is typically vented into the atmosphere by cooling it and repurposing it for power generation.  By using organic working fluids with low vapor points and high molecular density, ORC has become more attractive than water itself.

Steel mills, power plants, oil fields, cement plants, paper mills, and refineries are just a few examples of large industrial facilities that have both usable waste heat and a large appetite for electricity.  Through the use of ORC-based waste heat recovery, these operations are quickly and easily reducing their demand for the traditional water-cooled steam plants – putting water savings in the millions of gallons per year. And on top of that, the byproduct is clean and green energy that feeds directly back into the plant, pumping out power in the megawatts.

The ORC process is transforming the competitive landscape.  ORC systems can be installed quickly, have a small footprint, low maintenance costs, closed-loop systems and range of temperatures they can siphon heat from.  Plant managers are making ORC their next big priority, to reduce their dependence on water-based cooling processes, reduce their environmental footprint, reduce costs, improve efficiencies and give them a competitive edge.

Jason Gold is the Chief Executive Officer of KGRA Energy, LP, a developer of electricity generation projects that harvest waste heat to create clean, renewable energy.

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