The U. The technology has strong backing from the U. That translates into reduced fuel consumption and emissions, low cooling water consumption, and a compact design that should lower capital cost. However, before they can be used for commercial applications—including for waste heat recovery, concentrating solar power, nuclear, and fossil energy— several technical challenges must be overcome. According to the company, firing of the combustor involves the integrated operation of the full NET Power process.
Successful operation of the MWth combustor will allow NET Power to use several together in commercial facilities, each of which is envisioned to be MWe. The company is banking on passage of 45Q carbon capture tax credit reform in the U. So coal-fired power plants haven't changed much since , when Thomas Edison's company built the first one in London.
Most still burn coal to boil water. The steam drives a turbine to generate electricity. At the turbine's back end, cooling towers condense the steam into water, lest the high-pressure steam there drive the turbine in reverse. Those towers vent much of the energy used to boil the water in the first place. That inefficiency helped drive utilities to natural gas.
Not only is gas cleaner—and, in the United States, cheaper than coal—but because it is a gas to begin with, engineers can take advantage of an explosive expansion as it burns to drive a gas turbine. The heat of the turbine exhaust then boils water to make steam that drives additional turbines. Still, Palmer was focused on coal, the bigger climate problem. He built on work he had done at SAIC on a high-pressure combustor for burning coal in pure oxygen. It was more efficient and smaller, and so it would cost less to build.
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It also produced an exhaust of concentrated CO 2 , thus avoiding the separation costs. Palmer and Brown needed to nudge the efficiency higher. But at the time, he was mostly retired, concentrating on his fishing, lawn bowling, and gardening. Palmer and Brown hired Allam as a consultant.
Inspired by some Russian research from the s, Allam thought he saw a way to radically reinvent the staid steam cycle. Forget about boilers, he thought.
He would drive everything with the CO 2 itself, making an ally out of his enemy. Allam envisioned the CO 2 circulating in a loop, cycling between a gas and what's called a supercritical fluid.
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At high pressure and temperature, supercritical CO 2 expands to fill a container like a gas but flows like a liquid. For decades, engineers have worked on Brayton cycles—thermodynamic loops that take advantage of the properties of supercritical fluids, which could be air or CO 2. Supercritical fluids offer advantages: Because they are fluids, a pump can pressurize them, which takes far less energy than a compressor needs to pressurize a gas.
And because of the fluidlike gas's extra density, it can efficiently gain or shed heat at heat exchangers. In Allam's particular Brayton cycle, CO 2 is compressed to times atmospheric pressure—equivalent to a depth of 3 kilometers in the ocean. After the CO 2 drives a turbine, the gas's pressure drops and it turns into a normal gas again. The CO 2 is then repressurized and returned to the front end of the loop. A tiny amount of excess CO 2 —exactly as much as burning the fuel created—is shunted into a pipeline for disposal.
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The Allam cycle, as it is now called, comes with costs. Giant cryogenic refrigerators must chill air—which is mostly nitrogen—to extract the pure oxygen needed for combustion. Compressing CO 2 into a supercritical state also sucks up energy. But both steps are well-known industrial processes.
That would put it within striking distance of the efficiency of a contemporary combined cycle plant. Another perk is that the Allam cycle generates water as a byproduct of combustion, instead of consuming it voraciously as conventional steam cycles do, which could make plants easier to site in arid parts of the world. At this point, Brown and Palmer were still planning to use coal as their fuel. On the downside, the Allam cycle would be tough to pull off with coal, at least initially, because the coal would first have to be converted to a synthetic gas, which adds cost.
Also, sulfur and mercury in that syngas would have to be filtered out of the exhaust. But on the upside, the engineers saw no reason why the technique wouldn't work with natural gas, which is ready to burn and doesn't have the extra contaminants. Brown and Palmer gave up on winning a clean coal grant from the government.
Instead, they sought private investment for a far bigger prize: revolutionizing energy production with carbon capture. In March , the company broke ground on its pilot plant outside Houston. We'll see soon if it works in reality. There are only a million things that can go wrong. One of those is the new turbine, which needs to work at intense temperatures and pressures.
Some steam turbines reach those extremes, but "no one had ever designed a turbine to do that with CO 2 as the working fluid," says NET Power spokesperson Walker Dimmig. In , NET Power officials inked a deal to have the Japanese conglomerate Toshiba retool one of its high-pressure steam turbines to work with supercritical CO 2 , which required changing the lengths and angles of the turbine blades.
Toshiba also engineered a new combustor to mix and burn small amounts of oxygen and natural gas in the midst of a gust of hot supercritical CO 2 —a problem not unlike trying to keep a fire going while dousing it with a fire extinguisher.
The re-engineered combustor and turbine were tested in and delivered to the demo plant in November Now, they are being integrated with the rest of the facility's components, and the plant is undergoing preliminary testing before ramping up to full power sometime this fall. If it does, Brown says, NET Power will have advantages that could encourage widespread market adoption.
First, the CO 2 emerging from the plant is already pressurized, ready to be injected underground for EOR, unlike CO 2 recovered from natural gas wells—the usual source. Another advantage is the plant's size. Not only are the heat exchangers much smaller and cheaper to build than massive boilers, but so are many of the other components.
Overall, NET Power plants are expected to be just one-quarter the size of an equivalent advanced coal plant with carbon capture, and about half the size of a natural gas combined cycle with carbon capture. That means less concrete and steel and lower capital costs. And providing a steady supply of high-pressure gas for EOR, he adds, will only perpetuate a reliance on fossil fuels.
Ross argues that money would be better spent on encouraging broad deployment of renewable energy sources, such as solar and wind power.