Posts Tagged coal

Cryogenic Carbon Capture

Posted by on Saturday, 4 December, 2010

Coal plants release a lot of carbon when they burn coal, along with sulfur and other contaminants. The ashes and particles can travel long distances after their release, and can create a breathing hazard, as well as causing other problems such as acid rain and creating a dark layer on ice that melts the ice. One of the main methods of getting rid of this carbon is using a scrubber, but a method known as cryogenic carbon capture provides some advantages.

The idea behind cryogenic carbon capture is that equipment can blast the air leaving the plant with a stream of freezing nitrogen gas. According to Sustainable Energy Solutions, the freezing nitrogen will solidify other contaminants such as sulfur and nitrogen oxides, as well as carbon dioxide and other carbon compounds.

Cryogenic carbon capture has another advantage over traditional filtration methods such as scrubbers. The freezing blast of nitrogen gas cools down the air leaving the plant, making the ventilation system more efficient and allowing the coal plant to burn coal more efficiently. The coal plant will not need to spend as much money on a water based coolant system. Since the air coming out of the plant is cooler, cryogenic carbon capture also reduces the effects of releasing hot air into the nearby environment, which can be harmful.

Cryogenic carbon capture is very effective at removing almost all of the carbon from the air. According to Purdue University, the cooling system reduces the temperature of the air leaving the plant to -135 Celsius, or -211 degrees Fahrenheit. At this temperature all of the carbon dioxide freezes into dry ice and drops out of the air in solid form. Sulfur dioxide, with a -73 Celsius freezing point, and nitrous oxide, with a -88 Celsius freezing point, are even easier to freeze and remove from the air. Carbon dioxide has a much lower freezing point than most airborne pollutants.

The cryogenic filtration system includes several devices which attach to the flue that vents the gas as it comes out of the plant. A Brigham Young University presentation explains how this equipment works. A condensing heat exchanger first removes excess water vapor from the gas. This helps conserve energy because water takes more energy than most compounds to freeze. A compressor compacts the gas and sends it to the heat exchanger, which freezes it. The gas is sent through one separator, uncompressed, and then sent through a second separator, removing the frozen carbon dioxide, or dry ice. The contaminants have different melting points so the machinery can use this property to separate compounds such as sulfur oxides from carbon dioxide.

Carbon Capture With Algae

Posted by on Friday, 23 July, 2010

Algae already have a vital role in the ecosystem since they can produce oxygen from carbon dioxide in the air through photosynthesis. Algae at a power plant provide the flexibility to capture carbon at the source and reduce the carbon emissions before these emissions reach the atmosphere. As with other plant materials, algae can also be dried or converted into methane to store fuel for later usage.

Researchers at Indiana University are using algae to capture carbon emissions from a power plant on the campus. According to the university, the power plant uses coal, and the more expensive natural gas when its budget allows. Using algae reduces the impact of the fossil fuel usage, although completely capturing all of the carbon from a standard coal plant would require more than a hundred acres of algae ponds. Obviously this is not feasible in many locations, although a power plant at a university in a rural location might be able to successfully set up this type of system.

The University of Illinois is also working on demonstration projects to use algae for carbon capture. According to the University of Illinois, the main advantage of algae is their rapid growth, which requires them to absorb carbon much faster than other plants. Trees and bushes can not match an algal reproduction rate that can double the size of a clump of algae in four hours. The flue gas from the coal plant does first have to be scrubbed of pollutants such as sulfur dioxide which can kill algae, and reduced in temperature to a level that the algae can handle.

Projects in Southern California provide a demonstration of carbon sequestration using algae. A joint project from several research institutions in San Diego, including UCSD, SDSU, and associated research labs, are setting up carbon capture projects in the deserts of Imperial Valley. The algae ponds will require a large amount of space, and the coastal region of San Diego is densely populated and most nearby cities have high land values, but some nearby desert areas are nearly empty because of the extreme heat. Some of the desert regions in this area are part of national parks or military facilities, so the approval process for setting up algae ponds may not always move quickly.