Mineralization of Coal Combustion Flue Gas Carbon Dioxide

SequesTech(TM) ((TM) -Proprietary process, patent held by University of Wyoming US patent approved: 20090280046);Increasing anthropogenic CO2 levels in the atmosphere are raising concerns over climate change and global warming. Flue gas emissions from industrial processes, particularly from coal-fired power plants, are a major source for the release of anthropogenic CO2 into the atmosphere. Concurrently these processes also generate significant quantities of solid residues (ash particles) as a by-product. Multiple CO2 capture and storage (CCS) processes are required to address the anthropogenic CO 2 problem. However, a method which can directly capture and mineralize CO2 at a point source, under actual field conditions, has advantages and could help offset the cost associated with the conventional CCS technologies.;Objectives of this research were to develop a pilot scale fluidized-bed process and test the effects of moisture content of flue gas on accelerated mineral carbonation process of fly ash particles. A pilot scale fluidized-bed process was designed and tested at one of the largest (Jim Bridger) coal-fired power plants (2120 MW) in the USA by reacting flue gas with fly ash particles. The pilot scale process consisted of a moisture reducing drum (MRD) (0.9 m phi x 1.8 m), a heater/humidifier (0.9 m phi x 1.8 m), and a fluidized bed reactor (FBR) (0.9-1.2 m phi x 3.7 m). Flue gas was withdrawn from the stack and was fed to the MRD at about 0.094 m³/s. The MRD and the heater/humidifier pretreat flue gas before it enters the FBR. The MRD captures droplets of water entrained in the flue gas to protect the blower placed between the MRD and the heater/humidifier. The heater/humidifier enables control of flue gas moisture and temperature. Approximately 100-640 kg of fresh fly ash was collected from the electrostatic precipitator through ash hopper and placed in the FBR. Fly ash particles were fluidized by the flow of flue gas through a distributor plate in the FBR. Pilot scale studies were all conducted at 200 SCFM and at a controlled pressure (115.1 kPa) under various flue gas moisture contents (2-16 mol%). The flue gas moisture was controlled by controlling the temperature (25-60° C) of the humidifier water. Experiments were conducted up to120 minutes by reacting the flue gas with fly ash in the FBR. The flue gas CO2, SO2 and NO x concentrations were monitored before and during the experiments by an industrial grade gas analyzer. Fly ash samples were collected from a sample port over 0-120 minutes. Control and treated fly ash samples were analyzed for total inorganic carbon (C), sulfur (S), and mercury (Hg). From C, S, and Hg concentrations, percent calcium carbonate (CaCO3), percent sulfate (SO42-), and percent HgCO3 were calculated, respectively.;Results suggested that among different temperature conditions, 60° C (~16 mol% moisture) showed highest mineralization of flue gas CO2 and SO2. The average percent CaCO3 and average percent SO42- in the 60° C fly ash samples increased from 1.25 to 3.67% and from 0.33 to 2.36%, respectively. The percent HgCO 3 in the fly ash samples increased from 0.02 to 0.36% after reacting with flue gas during an experiment on July 28, 2010 when the flue gas temperature ranged between 25 and 58° C (corresponding to ∼4-14 mol% moisture).;These pilot scale studies suggest that an appreciable amount of flue gas CO2 and significant amounts of SO2 and Hg can be directly captured (without separation) and mineralized by the fly ash particles. The proposed accelerated mineral carbonation process is economical with minimum carbon footprint and can be retrofitted to existing and/or new coal fired power plants as a post-combustion unit. Used in conjunction with capture and geologic sequestration, the accelerated mineral carbonation process has the potential to reduce overall cost associated with CO2 separation/compression/transportation/pore space/brine water treatment. It could also help protect sensitive amines and carbon filters used in flue gas CO2 capture and separation processes and extend their life.