الفهرس 
English SummaryOnly 14 pages are availabe for public view
 |  | from | 116 |  |  |
| | | from | 116 | | |
Abstract
Fossil-fuel based power plants have the advantages of high reliability and rapid response to loads fluctuations. Hence, the world depends on fossil fuels to meet more than 85% of the global energy needs. However the burning of these fuel, including coal, oil and gas results in an increase of so called greenhouse gases. These gases act as the glass plans of a greenhouse which allow solar radiations to pass through and heat the surface of the earth but do not allow the heat radiated from the ground to pass through thereby trapping it in the process, eventually resulting in global warming. Among all these gases, carbon dioxide has gained the most attention and is considered to be the primary anthropogenic contributor to climate change. A variety of approaches to mitigate CO2 emissions associated with fossil fuels combustion have been proposed including reducing energy consumption, improving thermal efficiency of fossil-fueled power plants, and use of renewable energy such as wind and solar energy. However these solutions are not applicable at least in the short-to-mid ranges. Another approach allows the world to continue to enjoy the benefits of using fossil fuels while drastically reducing the emissions associated with combustion by preventing CO2 from mixing with atmosphere. It is so called carbon capture and storage (CCS). Carbon capture and storage has been globally gaining popularity as a viable greenhouse gases mitigation strategy throughout the last decade. At a minimum, CCS can be a bridging strategy to provide time for alternatives to be developed. Carbon dioxide capture technologies can be classified into pre-combustion, oxyfuel combustion, and post-combustion. This latter approach has the advantage that it offers “end-of-pipe” solutions that avoid major modifications to the base process. Calcium looping (CaL) is an emerging post-combustion technology to capture carbon dioxide from flue gases of fossil fueled power plants exploiting the reversible gas-solid reaction between the carbon dioxide (CO2) and calcium oxide (CaO) to form calcium carbonate (CaCO3) in a fluidized bed. CaL has shown some potential advantages on both lab and pilot scale in terms of net efficiency (5% net lower energy penalty than the amine scrubbing) and cost of CO2 avoided. In this work, a dynamic model of a bubbling bed carbonator, the key reactor in the capture process, is presented in details. The model incorporate both hydrodynamics and chemical kinetics to provide more reliable predictions. The model has been validated with experimental data obtained at combustion lab, Mansoura University using a fluidized bed carbonator of 10.5 cm inner diameter as well as a mathematical model found in literature. The key parameters have been investigated to check for system sensitivity. Bed temperature has a non-monotonic effect on CO2 capture efficiency. Maximum CO2 capture efficiency was found to occur around a temperature of 675 °C. Capture efficiency increases with decreasing fluidization velocity due to enhanced mass transfer and increased residence time. However this results in lower flow rates of treated gases. These findings almost accord with published data. Although increasing bed particle size reduces the total surface area of solid particles, carbon dioxide capture efficiency was found to be directly proportional to particle size. Larger particles result in smaller bubbles and larger emulsion, which enhances mass transfer between bed phases. This effect is superior to the defect of smaller surface areas. Also, the average CO2 capture efficiency was found to increase with increasing static bed height up to a certain limit. Further increase in bed height doesn’t considerably affect the capture efficiency. The proposed model can be used as a design tool that would enable the optimization and commercialization of calcium looping.