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Title:Flash calcination of limestone in a bench-scale sorbent activation process (SAP) unit
Author(s):Sugiyono, Ivan
Advisor(s):Rood, Mark J.; Rostam-Abadi, Massoud
Contributor(s):Rood, Mark J.
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Sorbent Activation Process
flue gas desulfurization
mercury capture
flash calcination
high surface area
calcium-based sorbent
Abstract:Coal-fired power plants produce 40 % of the total electricity in the United States. The flue gas generated from burning coal contains air pollutants including sulfur oxides (SOx), hydrochloric acid (HCl) and elemental and ionic mercury (Hgo and Hg2+). A process option to remove these pollutants from the flue gas is by injection of sorbents downstream of a boiler and up-stream of a particulate control device. Activated carbon (AC) is a suitable sorbent to capture vapor-phase mercury and calcium-based sorbents such as quicklime (CaO) and hydrated lime (Ca(OH)2) are suitable sorbents to capture SOx and HCl. This research addresses producing quicklime by a novel process to remove SOx and HCl from flue gas streams. Quicklime is commercially prepared by thermal decomposition of limestone (CaCO3) in a rotary kiln. The surface area of commercial quicklime, a key parameter of reactivity, is typically < 2 m2/g. Therefore, increasing the surface area of quicklime in a cost-effective process would enhance its effectiveness as a sorbent for control of combustion-generated air pollutants. Illinois State Geological Survey (ISGS), a division of the Prairie Research Institute at the University of Illinois at Urbana Champaign (UIUC), and Electric Power Research Institute (EPRI), Palo Alto, CA, have developed a patent-pending Sorbent Activation Process (SAP) technology for on-site production and direct injection of quicklime into flue gas generated by coal fired power plants (US Patent Application 20,110,223,088). This process is an extension of a similar patented process for on-site production of activated carbon (AC) to remove vapor-phase mercury emissions in the flue gas (US Patents 6, 451, 094 and 6,558,454). SAP utilizes an entrained-flow reactor in which sorbent (AC or quicklime) particles are subjected to a < 5 second residence time during their production. On-site production of quicklime could help lower the production cost of quicklime sorbent for dry sorbent injection (DSI) applications. In this research, a bench-scale SAP unit (2 kg/hr limestone feed rate) was used to prepare quicklime from two limestone samples. The impacts of particle size, surface morphologies of limestone, and operating parameters of SAP including temperature profile, and residence time on the product quicklime were investigated. SAP experiments were designed to provide engineering data and guidelines for operating a pilot-scale (20 kg/hr limestone feed rate) and designing a fullscale SAP units (135 kg/hr limestone feed rate) currently being tested at a coal-fired power plant in the United States. Additionally, kinetic information about calcination of the two limestone samples was obtained from the analysis of non-isothermal decomposition measured by thermogravimetric analysis (TGA) method. Furthermore, the kinetic information was used to predict limestone calcination in SAP. Lime sorbents prepared in SAP contained between 20 and 80 wt % calcium oxide (balance calcium carbonate) and had surface areas ranging between 5 and 12 m2/g depending on operation conditions employed. Non-isothermal TGA experiments were analyzed by several data analysis approaches including Coats-Redfern, Criado linearization and DTG-curve fitting method using DTG-SIM software to obtain the kinetic parameters (activation energy, frequency factor, and reaction order) for thermal decomposition (calcination) of the two limestone samples. The values of the kinetic parameters were in good agreement with those previously reported in the literature. The kinetic models predicted the experimental TGA calcination in N2 with less than 10% deviation. However, only the Coats-Redfern-based kinetic model predicted the TGA calcinations in CO2 data with less than 10 % deviation. The kinetic parameters were used to predict limestone conversions in an ideal flash calciner and in SAP. Ideal flash calciner assumed isothermal condition throughout the reactor while the later one used the actual temperature profiles in SAP to predict limestone conversion at different CO2 partial pressures. The impact of mass and heat transfer limitation, lime sintering phenomenon, and particle size distribution of limestone/lime were not included in the model. The experimental limestone conversions were higher than those predicted by the models. Based on the results from SAP experiments and model predictions, it was concluded that the actual temperature of limestone particle was likely much higher than the gas temperature measured in SAP. Future work should include: 1) installation of additional thermocouples to continuously monitor both axial and radial temperature profiles in the SAP, 2) an understanding of the flow pattern and hydrodynamic inside the SAP to better estimate gas-gas and gas-solid mixing, 3) testing several size-graded limestone samples to evaluate the impact of particle size on limestone calcination, 4) calibrating the propane and combustion air flow rates to obtain more accurate readings, 5) quantify the extent of particle deposition in SAP, 6) measure gas phase concentrations of CO, CO2, O2, NOx, and hydrocarbons (HCs), and verify those measured values, and 7) incorporate mass and heat transports effects in the model to better predict calcination performance of limestone in bench-, pilot-, and full-scale SAPs.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Ivan Sugiyono
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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