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Carbon Dioxide Sequestration
With the upswing in fossil fuel consumption and the resulting carbon dioxide pollution and the rampant deforestation removing natural carbon dioxide filters, there comes a need for a solution for the CO2 problem. Replanting forests is one possible solution, but it would take far too long for enough forest growth to make a dent in the CO2 percentages.
Removing carbon dioxide from the atmosphere by locking it away in sealed, pressurized chambers kept hundreds of feet beneath sea level is one possible solution. Another is imparting carbon dioxide into the soil and allowing microbes to process the CO2 into naturally occurring substrate materials. Still another approach is to react the CO2 with another material to make it inert. Dissolving the CO2 in water and pumping it into porous lava deposits is already being tested. The acidic CO2-saturated water then reacts with minerals in the rock to make limestone.
The most promising method to date is one developed at Ohio University that flows carbon dioxide over membranes seeded with algae to produce a biomass fuel source. A carbon capture device like this could be a capable photo-bioreactor that uses photosynthesis to grow algae just like a plant would take carbon dioxide up and, through the energy of the sun, convert it into oxygen. But how exactly does this possible savior work?
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How a Carbon Capture Service Plant Works
A large scale plant based on the prototype built at Ohio University would work by passing carbon dioxide rich smoke over acres of blue green algae covered screens. The screens would be held vertically and seeded with algae that thrives in the similar environment of the hot springs of Yellowstone National Park. The algae would then use the CO2 and water from the power plant to reproduce, excreting oxygen and water vapor as it’s only by products. The only real challenge is getting sunlight to every inch of the screens. This is solved by using curved mirrors to collect the light and then filtering it down through optical fibers aimed at the entire grid. Not only does this process sequester and then transform the carbon dioxide, but the algae also absorb components of acid rain, such as nitrogen oxide and sulfur oxide, making coal plants far less detrimental to the environment.
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Potential Costs and Savings
So what does a system like this cost? The initial build of a system like this could add anywhere from 25 to 91 percent to the cost of a new coal power plant. Retrofitting an old plant may run anywhere from 45 to 120 percent. This process will also take some of the energy generated by the power plant, some estimates put this power cost at up to 15 percent of the total produced energy. This would mean higher rates for consumers UNLESS the resulting biomass from the algae screens is converted into fuel. This process could actually lower the cost of fuel.
If we compare this type of plant with a buried pressurized sequestration unit with current estimates liberally set at $100 per ton (averaging .6 tons per Megawatt hour of generated power), then a 3000 MW plant would incur costs of $180,000 a day whereas a comparable algae unit would cost $68,500 per day (based on ten years of operation, the longer the plant runs the lower the cost per day would be), almost 2/3 less.
While limiting the use of fossil fuels by harvesting solar energy, wind power, and even geothermal heat promises to reduce our dependence on fossil fuels, still over 86.4% of them are used for energy, producing over 21.3 billion of carbon dioxide emissions per year. With that much CO2 released into the atmosphere every year, the cost of a carbon capture service plant shouldn’t even be a factor.
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Where are these Plants Feasible?
It is estimated that one acre of land can support an algae-based sequestration station that can handle one 3000MW coal power plant. With all of the empty industrial buildings in major metropolitan areas (think cities like Detroit) there is ample chance to rehabilitate these existing structures to incorporate a biofuel station for use near a new power plant.
Other possible areas are in the biggest growing regions of the country like Wyoming, Utah, and Texas. These states are growing at over a 2% a year clip and will be needing extra power stations to provide for the new population. The open areas on the outskirts of new developments are prime locations for a dual coal/biofuel energy plant.
Microbial carbon dioxide sequestration might be feasible if the costs can be brought down into a more comfortable range (say $25 a ton like one Chinese company has claimed), but until then the use of the method developed at Ohio University may be the best option for new build and retrofit fossil fuel power stations.
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Image courtesy of Whizzer