Researchers at MIT have shown the benefits of a new approach toward eliminating carbon-dioxide (CO2) emissions at coal-burning power plants.
Their system, called pressurized oxy-fuel combustion, provides a way of separating all of the carbon-dioxide emissions produced by the burning of coal, in the form of a concentrated, pressurized liquid stream. This allows for carbon dioxide sequestration: the liquid CO2 stream can be injected into geological formations deep enough to prevent their escape into the atmosphere.
Finding a practical way to sequester carbon emissions is considered critical to the mitigation of climate change while continuing to use fossil fuels, which currently account for more than 80 percent of energy production in the United States and more than 90 percent worldwide. CO2 emissions from fossil fuels are projected to rise by more than 50 percent worldwide by 2030.
It might seem paradoxical to reduce the carbon footprint of a coal plant by making its emissions into a more concentrated stream of carbon dioxide. But Ahmed Ghoniem, the Ronald C. Crane (1972) Professor of Mechanical Engineering and leader of the MIT team analyzing this new technology, explains: "this is the first step. Before you sequester, you have to concentrate and pressurize" the greenhouse gases. "You have to redesign the power plant so that it produces a pure stream of pressurized liquid carbon dioxide, to make it sequestration ready."
There are various approaches to carbon capture and sequestration being developed and tested, and the oxy-fuel combustion system "is one of the technologies that should be looked at," says Barbara Freese, lead author of a report on coal power by the environmental group Union of Concerned Scientists. Ghoniem says that of the approaches to oxy-fuel combustion, he and his MIT colleagues are the only academic team examining a pressurized combustion system for carbon dioxide capture.
A paper describing the approach appeared in August in the journal Energy. The Italian energy company ENEL, the sponsor of the research, plans to build a pilot plant in Italy using the technology in the next few years.
Ghoniem explains that any system for separating and concentrating the carbon dioxide from a power plant reduces the efficiency of the plant by about a third. That means that it takes more fuel to provide the same amount of electricity. Therefore, finding ways to minimize that loss of efficiency is key to making carbon-sequestration systems commercially viable.
Reducing the penalty
There will always be some energy penalty to such capture-enabled systems, because it requires some energy to separate gases that are mixed together, such as separating carbon dioxide from the combustion gases emerging from an air-based combustion chamber or oxygen from air for oxy-fuel combustion. As an analogy, "mixing salt and pepper is very easy, but separating them takes energy," he says. "Nobody in their right mind will jump into this and do it unless we can reduce the energy penalty and the extra cost, and only if it is mandated to reduce CO2 emissions" he says. And that's what the new process is designed to do.
Other groups have been looking into oxy-fuel combustion, in which pure oxygen is fed into the combustion chamber to produce a cleaner and more concentrated emissions stream (a mixture of oxygen and CO2 replaces ordinary air for combustion, which is nearly 79 percent nitrogen and 21 percent oxygen, thus eliminating more than three-quarters of the resulting flue gases). The focus of their studies is a system that adds one more element, putting the whole combustion chamber under pressure, which results in a more concentrated, pressurized emissions output.
Ghoniem says even though this process uses more energy at the beginning of the combustion cycle because of the need to separate oxygen from air and pressurize it, the increased efficiency of the power cycle raises the net output of the plant and reduces the compression work needed to deliver CO2 at the requisite state for sequestration, as compared to the unpressurized carbon-capture systems; in other words, the overall energy penalty is reduced. "You have to deliver carbon dioxide at high pressure for sequestration," he points out. The system simply introduces some pressurization earlier in the process, so the output stream requires less compression at the end of the process while extracting more energy from the combustion gases.The pressurization of the combustion system also reduces the size of the components and hence the plant, which could "reduce the footprint of needed real estate, and potentially the price of components," he says. It is expected to lead to an overall improvement of about 3 percent in net efficiency compared to an unpressurized system, and with further research and development this can probably be improved to about a 10 to 15 percent net gain from the current values, he says.
Ghoniem concedes that much more research is still needed for CCS technology. The three areas that need study most, he says, are systems' integration to determine the operating conditions at which the different components work together for highest efficiency; component-level research to optimize of the design of individual parts of the new system, especially the combustion chamber; and process analysis to examine the details of the physics and chemistry involved. His group has been concentrating on detailed computer simulations of the process to aid in the design of better systems.
Other team members include graduate students James Hong and G. Chaudhry, Prof John Brisson, Randall Field from MITEI and Marco Gazzino from ENEL.
Jen Hirsch | EurekAlert!
Multiregional brain on a chip
16.01.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences
Researchers develop environmentally friendly soy air filter
16.01.2017 | Washington State University
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction