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The Texas plant, which first fired up in May, can produce 25 megawatts, enough to power all the homes in a medium-size town simultaneously. It isn't yet sending electricity to the local grid; Brown hopes that will happen within the next several months, once the plant completes an extensive series of tests and gets connected with Texas utility company Ercot.
Meanwhile, the company is looking to partner with an energy company on its first full-size plant, which will be capable of producing 12 times as much energy. Net Power's goal is to complete that project by 2022.
The Texas plant cost $150 million to build, and Brown says the price of running it will be on par with that of a conventional power plant--clearly, a critical factor for wide adoption. The goal is to go even further.
"We've got to make it cheaper than polluting systems," Brown says. "Here in the U.S., we tend to think that if we can afford it, then the system works. But that's not good enough. We've got to make it so cheap that China and India will choose it, and developing nations will be able to afford it."
It's an ambitious goal, but a worthwhile one. Electricity generation is the cause of about 40 percent of the world's annual greenhouse gas emissions. The world's total emissions rose in 2018, even as scientists point to the dire need to reverse the trend immediately.
According to Toshiba’s engineers, the solution combined the company’s gas turbine and steam turbine technology. “Regarding gas turbines, Toshiba has technologies for air-cooled nozzles and blades and, also, combustion in the air with a pressure of around 2 MPa [megapascal] and a temperature up to 1,500C. Regarding steam turbines, Toshiba has developed and commercialized USC [ultrasupercritical] steam turbines in [the 1990s], and are now developing advanced USC (A-USC ) steam turbines. Their conditions are around 24 MPa and 600C for USC and around 31 MPa and 700C for A-USC,” it said.
The engineering challenges were hefty. The system’s “inlet pressure is 30 MPa, which is much higher than those of current commercialized gas turbines. And the inlet temperature is 1,150C, which is much higher than those of commercialized [USC] steam turbines and is the same level as those of so-called E-class gas turbines,” the company said.
First, the engineers applied a double-shelled structure for the turbine and combustor—such as is common for USC steam turbines. It also leveraged its A-USC expertise to develop high-temperature materials for the casings and rotors in the sCO2 turbine. Engineering a durable thermal barrier coating (TBC), which they noted plays a crucial role in the sCO2 turbine and combustor’s cooling design (because temperature differences through the TBC in an sCO2 turbine is almost double that of conventional air-cooled gas turbines), posed as significant an engineering challenge. The company also engineered highly efficient cooling technologies, including cooling nozzles and blades, to manage the cycle’s extreme heat flux.
But finessing the technology has proven slower than expected. When Toshiba first announced it would develop the next thermal generation power system in June 2012, the company and partners Shaw Group, Exelon, and NET Power aimed to demonstrate the 25-MWe [mega watt electric; MWth is thermal] Allam cycle natural gas plant by mid-2014, planning a full-scale 250-MW commercial plant by 2017. However, while Toshiba wrapped up a six-month test to validate the combustor in August 2013 at a California facility (using a model that was a fifth of the one installed at NET Power), Toshiba first announced that it would supply the first-of-its-kind turbine in October 2014. The partners didn’t fully assemble and complete high-speed balancing tests for the rotor until August 2016. By October 2016, however, the turbine had been fully assembled and shipped to La Porte.