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24 December 2009

Fly Ash as a CO2 adsorbent

by Dian Shofinita on 28/05/09 at 6:42 pm | 2 Comments | Print article | Email article
Coal Power Station

Coal Power Station

One of the fossil fuels commonly used today is coal. Coal is the energy source of the most easily taken from nature. However, the generation of energy with coal caused considerable waste, including fly ash. Fly ash is one of the residues of coal combustion. Components contained in fly ash varies depending on the source of coal burned, but all fly ash containing SiO2 and CaO. If not further processed, fly ash can cause negative impacts on the environment. Fly ash can contaminate the ground water that contains impurities such as arsenic, barium, berillium, boron, cadmium, komium, thallium, selenium, molybdenum and mercury.

Utilization of coal is also another negative impact of carbon dioxide emissions. CO2 gas is, furthermore, will have an impact of the greenhouse effect. Therefore, the use of coal as an energy source, needed a method to capture CO2 from the combustion of coal and store it in an insulating material. This technology is known as Carbon Capture and Storage (CCS). Many of CO2 capture methods that are being developed currently, among which are adsorption, absorption, use of membranes, cryogenic process, and utilization of microbes.

One method is to capture CO2 adsorption method using calcium oxide, magnesium oxide, zinc oxide, and copper oxide. Sorbent the most commonly used in industry is the CaO (calcium oxide) contained in nature in the form of CaCO3. To get CaO from limestone, limestone must first be activated, namely by heating limestone to kalsinasi temperature range, which generally ranges from 800-950 degrees Celsius. This process clearly requires akitivasi energy in large numbers, and release CO2 into the environment when activated. This process will remove fear more CO2 into the environment compared with the amount of CO2 captured. Therefore, needed an alternative sorbent that does not require prior activation.
Fly Ash

Fly Ash

Fly ash from coal combustion is one example of the sorbent can be used. Fly ash generated from burning coal contain CaO that can be directly utilized for mengadsorp CO2 without the need activating again, so that the energy requirements for kalsinasi process can be avoided. In addition, fly ash of coal combustion is available in large numbers and continue to produced, so that the fly ash that has been used not need dikarbonasikan back, but can be immediately discarded. Fly ash used in the capture of CO2 has a high calcium content that will directly react with water. Results of fly ash hydration process is the formation of Ca (OH) 2 and the reactive phase of CHS to CO2. The next reaction is:

CaCO3 + H2O" onmouseover="this.style.backgroundColor='#ebeff9'" onmouseout="this.style.backgroundColor='#fff'">CO2 + Ca (OH) 2 -> CaCO3 + H2O
CaCO3 + SiO2 + mH2O" onmouseover="this.style.backgroundColor='#ebeff9'" onmouseout="this.style.backgroundColor='#fff'">CaO.nSiO2.mH2O (CSH) + CO2 -> CaCO3 + SiO2 + mH2O

In addition to reducing CO2 emissions resulting from energy generation process with coal, this method can also take advantage of other coal production side, the fly ash. The existence of appropriate technologies such further expected to help meet the needs of environmentally friendly energy.

John A. Nugraha and Aditya Tanuwijaya, captured CO2 with Fly Ash modified, 2009.

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