New U.S. DOE Report on Coal-Fired Carbon Capture

Morgantown, W.Va. — Development of new carbon-capture-ready coal-fired power plants are essential to keeping coal, a proven domestic resource, in the domestic energy mix, according to a report released by the U.S. Department of Energy (DOE). Although recent low natural gas prices have favored natural gas combined cycle (NGCC) for new fossil-fuel-fired power plants, the report asserts that it is reasonable to expect gas prices to rise; in this event, retaining the ability to use coal through systems that are constructed ready to capture carbon dioxide (CO2) will be essential for our nation’s continued economic prosperity.

The new report, Techno-Economic Analysis of CO2 Capture-Ready Coal-Fired Power Plants, provides findings from a study conducted by analysts at DOE’s National Energy Technology Laboratory (NETL). The authors evaluated options for new supercritical pulverized coal plants that capture CO2, as would be required under a new rule proposed in April 2012 by the U.S. Environmental Protection Agency (EPA). The proposed rule, Standards of Performance for Greenhouse Gas Emissions for New Stationary Sources: Electric Utility Generating Units, would restrict CO2 emissions from newly constructed power plants to 1,000 pounds of CO2 per megawatt-hour.

Coal-fired units would be allowed to meet the new standard either by (1) including CO2-capture technology during initial plant construction and controlling CO2 emissions from the start of operations, or (2) constructing the unit to allow for future integration of CO2-capture technology, and then controlling CO2 emissions at a level that would meet the standard, on average, over a 30‑year period. The latter compliance option, which assumes that carbon capture begins after the first 10 years of operations, is the focus of the NETL study.

The analysis showed that the economics of a CO2-capture-ready unit can be competitive with other baseload generation options, such as NGCC or nuclear. Given reasonable assumptions about advances that are likely to occur with CO2-capture technology, along with an additional revenue stream from CO2 sales for enhanced oil recovery, a supercritical CO2-capture-ready unit is competitive with NGCC at natural gas prices as low as $7.75 per million Btu. In addition, the capital cost savings of a CO2-capture-ready unit could be as much as 50–60 percent compared to new nuclear generation, according to several recent cost estimates of actual nuclear projects.

Source: NETL

Plants' Role in CO2 Mitigation Questioned

According to a new University of Minnesota study,  plants may not be able to absorb as much of the increased levels of carbon dioxide in the air as originally thought. The study shows that while plants can absorb and benefit from large amounts of carbon dioxide, they may not get enough of the required nutrients from typical soils to absorb the levels of  CO2 that scientists previously believed possible, which raises questions about their role in mitigating fossil-fuel emissions. The study was published in the current issue of the journal Nature Climate Change. Read more

NREL Produces Ethylene via Photosynthesis

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have demonstrated a better way to use photosynthesis to produce ethylene, a breakthrough that could change the way materials, chemicals, and transportation fuels are made, and help clean the air.

NREL scientists introduced a gene into a cyanobacterium and demonstrated that the organism remained stable through at least four generations, producing ethylene gas that could be easily captured. Research results were published in the journal Energy & Environmental Science.

The organism – Synechocystis sp. PCC 6803 – produced ethylene at a high rate and is still being improved. The laboratory demonstrated rate of 170 milligrams of ethylene per liter per day is greater than the rates reported for the photosynthetic production by microorganisms of ethanol, butanol or other algae biofuels.

The process does not release carbon dioxide into the atmosphere. Conversely, the process recycles carbon dioxide, a greenhouse gas, since the organism utilizes the gas as part of its metabolic cycle.

Ethylene is the most widely produced petrochemical feedstock in the world. But currently it is produced only from fossil fuels, and its production is the industry’s largest emitter of carbon dioxide. Steam cracking of long-chain hydrocarbons from petroleum produces 1.5 to 3 tons of carbon dioxide for every ton of ethylene produced.

The NREL process, by contrast, produces ethylene by using carbon dioxide, which is food for the bacteria. That could mean a savings of six tons of carbon dioxide emissions for every ton of ethylene produced -- the three tons that would be emitted by tapping fossil fuels and another three tons absorbed by the bacteria.

NREL principal investigator, Jianping Yu, says it’s the difference between using old photons and new photons. Ethylene from old photons is the ethylene produced from fossil fuels, derived from photosynthetic organisms that captured the sun’s energy millions of years ago. The NREL process uses new photons that are currently hitting plants, algae and bacteria capable of producing fuels directly.

Ten years ago, a group of Japanese scientists led by Takahira Ogawa at Sojo University was the first to try to produce ethylene via photosynthetic conversion in the cyanobacterium Synechococcus 7942. But by the fourth generation, the bacteria were defunct, producing no ethylene at all, Yu said.

NREL turned to a different cyanobacterium, Synechocystis 6803, which scientists had been researching for a long time, knowing how to change its DNA sequences. They manipulated the sequence to design an ethylene-producing gene to be more stable and more active than the original version.

This process resulted in an organism that uses carbon dioxide and water to produce ethylene, but doesn’t lose its ability to produce ethylene over time. The product ethylene is non-toxic to the producing microorganisms and is not a food source for other organisms that could potentially contaminate an industrial process.

“Our peak productivity is higher than a number of other technologies, including ethanol, butanol, and isoprene,” Yu said. “We overcame problems encountered by past researchers. Our process doesn’t produce toxins such as cyanide and it is more stable than past efforts. And it isn’t going to be a food buffet for other organisms.”

After the culture reaches maximum growth, it’s possible that it could keep producing for months at a time, said Rich Bolin, who is a member of NREL’s partnerships group. The ethylene gas it produces naturally leaves the organism, spurring the organism to keep producing more.

The ethylene would be produced in an enclosed photobioreactor containing seawater enriched with nitrogen and phosphorous. The ethylene gas would rise and be captured from the reactor’s head space. It could then undergo further processing, including a catalytic polymer process to produce fuels and chemicals. The continuous production system improves the energy conversion efficiency and reduces the operational cost.

NREL is initiating discussions with potential industry partners to help move the process to commercial scale. Interested companies include those in the business of producing ethylene or - transportation fuels, as well as firms that build photobioreactors.

“Separations in biotechnology are complicated and costly,” said Jim Brainard, director of NREL’s Biosciences Center. “The nice thing about this system is that it is a gas that just separates from the culture media and rises to the head space. That’s a huge advantage over having to destroy the valuable culture that is taking carbon dioxide and light and water to make your product. It’s much easier than a liquid-liquid separation like in ethanol.”

NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by the Alliance for Sustainable Energy, LLC.

Source: NREL