NALCO to set up a carbon sequestration unit in its power plant in Angul; The National Academy of Engineering of US considers carbon sequestration as one of the 14 engineering grand challenges awaiting solutions in the 21st century

Following is an excerpt from a report in Orissadiary.

National Aluminium Company Limited (NALCO), the Navratna PSU, under Ministry of Mines, Govt. of India, has become the first PSU in India by implementing a pilot-cum-demonstration project on Carbon Sequestration in its Captive Power Plant at Angul.

… Nalco has earmarked an area of 0.18 acre for the project to adopt an advanced and innovative technology by engaging the firm M/s Indo-Can Technology Solutions (ICTS), a pioneer in the area of bio-technology solutions, for providing technical consultancy and rendering necessary services to guide Nalco for successful completion of the project within 18 months.

Carbon sequestration is a method for managing and storing of carbon dioxide (CO2) or other forms of Carbon that would otherwise be released into the atmosphere by burning carbon-based fuels. It is a relatively new idea brought about by the worldwide concern that high concentrations of atmospheric CO2 contribute to global warming.

Since Orissa is having huge coal reserves, a large number of Thermal Power Plants and Industries having large power requirements are coming up in the State and this trend will continue to grow in future. These power plants emit huge quantity of CO2 to the atmosphere. In the recent Copenhagen summit India has volunteered to cut down the rate of emission of Green House Gases (GHG) by 20% by 2020.

A battery of system would be introduced into the flue gas stream to clean the flue gas to suit cultivation of algae.

Algae, a kind of microorganism, is the most efficient photosynthetic and CO2 sequestering organism on earth and its productivity potential can be increased by supplementing with high concentrations of CO2, a characteristic not matched by plants, thus making algae more productive than any other crop. Micro-algae could achieve growth rate that is ten times more than that of other land plants. Faster growth implies more photosynthesis and hence higher CO2 consumption. India being in the temperate climate zone is best suited for algae cultivation.

The algae so produced can be used for production of bio-fuel, Poultry & Cattle feed, Aquaculture Feed, pharmaceutical products and a kind of organic fuel having high calorific value. By successfully implementing this project NALCO can pursue to avail the benefit of Carbon Credits under Clean Development Mechanism in two ways (i) through the process of Carbon capturing from flue gas and (ii) also through Bio-Energy and bio product generation.

Carbon Sequestration is a very important research area in Engineering and is in the list of 14 grand challenges awaiting solutions in the 21st century compiled by the US National Academy of Engineering (NAE) Committee on Engineering’s Grand Challenges. See http://www.engineeringchallenges.org/cms/8996/9077.aspx for details. I hope one of the research institutions in Odisha partner with NALCO and others having thermal power plants in Odisha to pursue research in this area.

Following is a big excerpt from the NAE site.

What is carbon sequestration?

Carbon sequestration is capturing the carbon dioxide produced by burning fossil fuels and storing it safely away from the atmosphere.

How do you capture CO2?

Methods already exist for key parts of the sequestration process. A chemical system for capturing carbon dioxide is already used at some facilities for commercial purposes, such as beverage carbonation and dry ice manufacture. The same approach could be adapted for coal-burning electric power plants, where smokestacks could be replaced with absorption towers. One tower would contain chemicals that isolate carbon dioxide from the other gases (nitrogen and water vapor) that escape into the air and absorb it. A second tower would separate the carbon dioxide from the absorbing chemicals, allowing them to be returned to the first tower for reuse.

A variation to this approach would alter the combustion process at the outset, burning coal in pure oxygen rather than ordinary air. That would make separating the carbon dioxide from the exhaust much easier, as it would be mixed only with water vapor, and not with nitrogen. It’s relatively simple to condense the water vapor, leaving pure carbon dioxide gas that can be piped away for storage.

In this case, though, a different separation problem emerges — the initial need for pure oxygen, which is created by separating it from nitrogen and other trace gases in the air. If that process can be made economical, it would be feasible to retrofit existing power plants with a pure oxygen combustion system, simplifying and reducing the cost of carbon dioxide capture.

Advanced methods for generating power from coal might also provide opportunities for capturing carbon dioxide. In coal-gasification units, an emerging technology, coal is burned to produce a synthetic gas, typically containing hydrogen and carbon monoxide. Adding steam, along with a catalyst, to the synthetic gas converts the carbon monoxide into additional hydrogen and carbon dioxide that can be filtered out of the system. The hydrogen can be used in a gas turbine (similar to a jet engine) to produce electric power.

How do you store CO2?

Several underground possibilities have been investigated. Logical places include old gas and oil fields. Storage in depleted oil fields, for example, offers an important economic advantage — the carbon dioxide interacts with the remaining oil to make it easier to remove. Some fields already make use of carbon dioxide to enhance the recovery of hard-to-get oil. Injecting carbon dioxide dislodges oil trapped in the pores of underground rock, and carbon dioxide’s presence reduces the friction impeding the flow of oil through the rock to wells.

Depleted oil and gas fields do not, however, have the capacity to store the amounts of carbon dioxide that eventually will need to be sequestered. By some estimates, the world will need reservoirs capable of containing a trillion tons of carbon dioxide by the end of the century. That amount could possibly be accommodated by sedimentary rock formations with pores containing salty water (brine).

The best sedimentary brine formations would be those more than 800 meters deep — far below sources of drinking water, and at a depth where high pressure will maintain the carbon dioxide in a high-density state.

Sedimentary rocks that contain brine are abundantly available, but the concern remains whether they will be secure enough to store carbon dioxide for centuries or millennia. Faults or fissures in overlying rock might allow carbon dioxide to slowly escape, so it will be an engineering challenge to choose, design, and monitor such storage sites carefully. 

Concerns about leaks suggest to some experts that the best strategy might be literally deep-sixing carbon dioxide, by injecting it into sediments beneath the ocean floor. High pressure from above would keep the carbon dioxide in the sediments and out of the ocean itself. It might cost more to implement than other methods, but it would be free from worries about leaks. And in the case of some coastal sites of carbon dioxide production, ocean sequestration might be a more attractive strategy than transporting it to far-off sedimentary basins.

It is also possible that engineers will be able to develop new techniques for sequestering carbon dioxide that are based upon natural processes. For example, when atmospheric concentrations of carbon dioxide increased in geologic times to a certain unknown threshold, it went into the ocean and combined with positively charged calcium ions to form calcium carbonate – limestone. Similarly, engineers might devise ways of pumping carbon dioxide into the ocean in ways that would lock it eternally into rock.

It may well be that multiple strategies and storage locations will be needed to solve this problem, but the prospect for success appears high. “Scientific and economic challenges still exist,” writes Harvard geoscientist Daniel Schrag, “but none are serious enough to suggest that carbon capture and storage will not work at the scale required to offset trillions of tons of carbon dioxide emissions over the next century.” [Schrag, p. 812]

 

References

Herzog, H., and D. Golomb.  2004.  Carbon Capture and Storage from Fossil Fuel Use.  Encyclopedia of Energy, ed. C.J. Cleveland.  Vol. 1.  Elsevier Science: .

Lal, R.  2004.  Carbon Sequestration, Terrestrial.  Encyclopedia of Energy, Vol. 1 (Elsevier Inc.).

Schrag, D.P.,  et al.  2007.  Preparing to Capture Carbon,” Science 315, p. 812. DOI: 10.1126/science.1137632.

Socolow, R.H.  2005.  Can We Bury Global Warming?  Scientific American (July 2005), pp. 49-55.

Zenz House, K. et al.  2006.   Permanent carbon dioxide storage in deep-sea sediments,” Proc. Natl. Acad. Sci. USA 103 (15 August 2006), pp. 12291-12295.

 

March 22nd, 2011


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